Natural Mineral Materials for Enhanced Performance in Aqueous Zinc-Ion Batteries

Abstract

Aqueous zinc-ion batteries (AZIBs) have emerged as promising candidates for large-scale energy storage due to their inherent safety, cost-effectiveness, and environmental compatibility. However, challenges such as zinc -dendrite growth, hydrogen evolution reactions, and cathode dissolution hinder their practical application. To tackle these issues, a wide range of investigative approaches have been conducted to improve the performance of AZIBs. Recently, much attention has been paid to the application of natural mineral materials in AZIBs, since these low-cost minerals align well with the high sensitivity of battery costs in large-scale energy storage. This review systematically explores the application of natural mineral materials to address these issues across battery components, including protective layers on anodes and cathodes, functional films of separators, additives in electrolytes, etc. A multitude of minerals, such as halloysite, montmorillonite, attapulgite, diatomite, and dickite, are highlighted for their unique structural and physicochemical properties, including hierarchical porosity, ion-selective channels, and surface charge regulation. Finally, prospects for future research are discussed to construct AZIBs with a combination of excellent performance and cost efficiency and to bridge laboratory innovations with commercial viability.

1. Introduction

Depleting fossil fuel resources will no longer be sufficient to meet the ever-increasing energy demands and have caused numerous irreversible environmental issues. Electrochemical energy storage (EES) has garnered growing interest due to its high efficiency, modularity, ease of maintenance, relatively low environmental pollution, and minimal infrastructure dependency [1]. Moreover, with the rising demand for electrochemical energy storage devices, there is an increasing need for high-performance batteries with cost-effective, safe, and environmentally friendly features [2]. Although traditional lithium-ion batteries (LIBs) offer benefits such as high energy density, long cycle life, and low self-discharge rate, and have achieved successful commercialization in areas like 3C batteries and power batteries, the flammability of the electrolyte during reactions poses significant safety risks. Additionally, the relatively limited reserves of lithium resources, coupled with the rapid development of new energy vehicles and large-scale energy storage stations, have led to a growing trend of lithium resource shortages [3]. Aqueous zinc-ion batteries (AZIBs) using zinc metal as the anode have attracted considerable attention in recent years due to their high theoretical gravimetric and volumetric capacity of 820 mAh g⁻¹ and 5851 mAh mL⁻¹. The moderate redox potential of zinc metal (−0.762 V vs. SHE) makes it suitable for aqueous electrolytes, offering enhanced safety and environmental friendliness [4]. Furthermore, the relatively abundant reserves of zinc resources along with the ability to assemble water-based batteries in ambient air significantly reduce overall costs, aligning well with the low-cost requirements of large-scale energy storage batteries [5,6]. However, the use of zinc as an anode in aqueous zinc-ion batteries still faces several challenges, such as dendrite formation, hydrogen evolution reactions, and zinc anode corrosion, which result in lower practical energy density and shorter cycle life. Additionally, although many cathode materials for aqueous zinc-ion batteries exhibit high theoretical specific capacities, issues such as insufficient conductivity, high carrier adsorption energy, and the gradual dissolution of transition metal ions during cycling severely impact electrode reaction kinetics and lead to rapid capacity decay. Therefore, there is an urgent need to further advance fundamental research and technological development in the field of aqueous zinc-ion batteries.

To address the critical challenges of anode dendrite growth, hydrogen evolution corrosion, and cathode material degradation in aqueous zinc-ion batteries, researchers have conducted systematic efforts across multiple dimensions, including electrode material design, electrolyte optimization, interface engineering, and separator modification, achieving significant progress. However, most modification strategies involve complex synthesis processes or expensive functional materials, leading to a substantial increase in battery system costs, which contradicts the core requirement of economic feasibility for large-scale energy storage applications. In this context, natural mineral materials have demonstrated unique application potential. Natural minerals, as essential resources on Earth, possess diverse structures and a wide range of physical and chemical properties, such as unique nanostructures, excellent mechanical properties, large specific surface areas, and special surface charges, making them widely applicable in catalysis, medicine, energy storage, and other fields [7,8]. Compared to other inorganic materials, natural minerals are not only abundant, cost-effective, and environmentally compatible but also exhibit strong surface adsorption, high ion exchange capacity, rich pore structures, and tunable properties, enabling their extensive use in lithium-ion batteries [9,10,11,12] and other energy storage systems [13,14,15].

In recent years, the application of natural mineral materials in AZIBs has garnered increasing attention, yet current research in this area lacks systematic reviews, resulting in insufficient clarity and comprehensiveness in understanding their rapid advancements. Consequently, this review analyzes the main challenges faced by AZIBs and their underlying causes and introduces the representative natural minerals that have successfully utilized to build advanced AZIBs. The mineral-related progress in AZIBs is summarized according to the four main components of the batteries—namely, anodes, cathodes, separators, and electrolytes. Moreover, prospects for promising research directions are proposed to further expand and deepen the potential application of low-price mineral materials in the development of improved AZIBs. Overall, we hope that the aims of this review can serve as a research roadmap for the developing field of combining natural minerals and AZIBs.

2. Zinc Anode Materials

Zinc dendrite growth represents one of the most critical challenges in aqueous zinc-ion battery technology, significantly compromising battery performance, safety, and cycle life. While zinc dendrite formation is a well-documented issue in traditional alkaline aqueous electrolytes, its occurrence remains inevitable even in mildly acidic electrolytes, albeit with some degree of suppression. During battery charging, zinc ions are reduced from the electrolyte and deposited onto the zinc anode. Ideally, this deposition process should proceed uniformly; however, in practice, factors such as low electrolyte concentration, inhomogeneous zinc ion distribution, uneven current density, and electrode surface roughness often lead to non-uniform zinc deposition. This localized deposition results in the accumulation of zinc ions at specific sites on the anode surface, forming microscopic protrusions. As shown in the Figure 1, due to the tip-enhanced electric field effect, these protrusions attract additional Zn²⁺, leading to increased local overpotential and preferential deposition at the same sites. As the charging process continues, these protrusions grow into zinc dendrites [16]. In the absence of mitigation strategies, dendrite growth can progress unimpeded, reaching substantial dimensions until mechanical failure occurs, causing dendrite fracture and detachment from the electrode, resulting in the formation of “dead zinc.” The detached dendrites disperse into the electrolyte, where they react to form byproducts, increasing impedance and reducing Coulombic efficiency, thereby creating a detrimental feedback loop. More critically, uncontrolled dendrite growth may penetrate the battery separator, reaching the cathode and inducing internal short circuits, which can lead to thermal runaway and potential fire hazards [17].

In addition to Zn dendrite formation, another major challenge for the anode in zinc-ion batteries (ZIBs) is the occurrence of side reactions caused by the interaction between water and oxygen in the electrolyte with the Zn anode. Due to the high polarity of water and the relatively low metal activity of hydrogen compared to zinc, parasitic reactions such as corrosion and the hydrogen evolution reaction (HER) are inevitably triggered on the zinc metal surface [18,19]. Corrosion on the zinc surface is primarily localized, driven by the uneven distribution of electrolyte concentration and charge density [20]. While replacing alkaline electrolytes with mildly acidic electrolytes has mitigated the tendency for dendrite growth, the HER remains unavoidable in widely used weakly acidic electrolyte environments (e.g., zinc sulfate). This reaction leads to localized pH increases, which in turn promote the formation of byproducts [21], such as Zn(OH)₂ and Zn₄(OH)₆SO₄·xH₂O in ZnSO₄ electrolytes [22,23]. These byproducts exhibit poor Zn²⁺ conductivity, passivate the zinc metal surface, and hinder Zn²⁺ transport. The typical reaction equations for these parasitic processes are as follows:

$$Zn\left(s\right)+H_{2}O\left(l\right)\to Z{n}^{2+}\left(aq\right)+H_2\left(g\right)+2O{H}^{-}\left(aq\right)$$

(1)

$$Z{n}^{2+}\left(aq\right)+2O{H}^{-}\left(aq\right)\to Zn(OH{)}_2\left(s\right)$$

(2)

$$4Z{n}^{2+}\left(aq\right)+S{O}_4^{2-}\left(aq\right)+6O{H}^{-}\left(aq\right)\to Z{n}_4\left(OH{)}_6{SO}_4\right(s)$$

(3)

Indeed, a mutually reinforcing relationship exists between dendrite growth and interfacial side reactions. The formation of zinc dendrites exposes fresh surfaces to the electrolyte, which are inherently rough, exhibit non-uniform charge distribution, and possess a large surface area. These characteristics not only exacerbate non-uniform deposition but also accelerate interfacial side reactions [24]. Therefore, controlling Zn plating to minimize or prevent dendrite formation is crucial. One effective strategy is surface modification of the zinc anode. Surface modification not only prevents direct contact between the electrode and electrolyte but also promotes uniform distribution of surface charges and ions, thereby reducing interfacial side reactions and homogenizing initial nucleation. Conductive metals such as Au [25], Ag [26], Cu [27], and In [28] are excellent candidates for surface modification. On one hand, these highly conductive metals can regulate and balance the local electric field intensity on the anode surface. On the other hand, they serve as corrosion-resistant protective layers, lower the nucleation overpotential of Zn²⁺, guide uniform ion deposition, and enhance the anode’s corrosion resistance.

Another approach involves the interfacial layer, which acts as a barrier with a smooth surface to facilitate uniform Zn²⁺ deposition. Materials used for interfacial layers often possess unique structures, such as porous, network, or layered architectures, which can construct diverse zinc ion migration channels and accelerate ion transport. The fabrication of such interfacial layers is relatively straightforward, with the doctor blade coating method being one of the most common ex situ coating techniques due to its simplicity, low cost, and compatibility with a wide range of materials. Zhou et al. [29] developed a novel hydrophobic multi-channel Sc₂O₃-coated zinc anode using the doctor blade coating method and proposed a hierarchical adsorption effect in this modified anode. Density functional theory (DFT) simulations and experimental results demonstrated that the Sc₂O₃ coating reduced the adsorption energy of H₂O molecules compared to bare zinc, effectively preventing direct contact between the zinc electrode and H₂O in the electrolyte and suppressing interfacial side reactions. The Sc₂O₃-coated zinc anode exhibited stable operation for over 100 cycles without short-circuiting, showing low voltage hysteresis and a 1.2% improvement in coulombic efficiency. When paired with popular manganese-based and vanadium-based cathodes, it demonstrated promising application potential. Li et al. [30] introduced an HfO₂ coating to guide uniform Zn²⁺ deposition. This coating not only prevented direct contact between the zinc anode and electrolyte, protecting it from corrosion, but also reduced side reactions and inhibited zinc dendrite growth. In Zn//Zn symmetric cells, the HfO₂-coated zinc anode exhibited a lower voltage hysteresis (48 mV) compared to the bare zinc anode (63 mV) at a current density of 0.4 mA cm⁻². Furthermore, the HfO₂-coated anode demonstrated excellent cycling performance in Zn//MnO₂ full cells, retaining a discharge capacity of 78.3 mAh g⁻¹ after 500 cycles at 1.0 A g⁻¹, whereas the bare Zn//MnO₂ full cell delivered only 37.9 mAh g⁻¹ under the same conditions. Cui’s research group [31] applied a polyamide (PA) coating to the surface of the zinc anode. The PA layer effectively bonded with Zn²⁺, forming a diffusion layer on the anode surface that increased the nucleation overpotential of Zn, reduced the critical nucleation radius, and refined the crystal size of deposited zinc. Additionally, the PA layer restricted two-dimensional mass transport on the electrode surface, inhibiting the migration of Zn²⁺ to protrusions and significantly increasing the number of nucleation sites. These dual mechanisms synergistically promoted uniform zinc deposition. Moreover, the PA layer simultaneously suppressed the permeation of O₂ and H₂O. As a result, the coated zinc anode remained smooth after 1000 cycles, while the bare zinc anode was covered with dendrites after only 450 cycles. Furthermore, batteries assembled with the PA-coated Zn foil exhibited an 88% capacity retention after 1000 cycles at a high rate of 2C.

The protective layer provides a physical barrier that prevents direct contact between the zinc anode and the electrolyte, effectively suppressing hydrogen evolution side reactions. However, specific physical properties are required for the coating to function optimally. To ensure that zinc deposition occurs on the original zinc surface rather than on the coating surface, the protective layer should exhibit poor electrical conductivity while maintaining high-speed channels for Zn²⁺ transport. This design enables the regulation of ion flux and promotes uniform zinc deposition, thereby enhancing the overall performance and stability of the zinc anode.

In aqueous battery systems, the influence of the hydrophilicity or hydrophobicity of protective layers on battery performance has not yet been fully elucidated. However, due to the unique role of water molecules in the electrolyte, the relationship between hydrophilicity/hydrophobicity and battery performance is highly complex. Firstly, good hydrophilicity facilitates rapid wetting of the electrode by the electrolyte, thereby reducing wetting time, improving the capacity utilization of the electrode, and lowering the charge transfer resistance at the electrolyte-electrode interface as well as the impedance of the electrolyte itself. This enhances the diffusion of Zn²⁺ to the electrode surface and promotes its uniform distribution [32,33]. Additionally, studies have shown that the presence of a small amount of water molecules in the electrode material can significantly alleviate the diffusion barrier of Zn²⁺ at the interface [34]. Moreover, in aqueous systems, Zn²⁺ typically coordinates with six surrounding water molecules to form hexaaqua zinc ions ([Zn(H₂O)₆]²⁺), which reduces the strong electrostatic repulsion between zinc ions and the electrode material [35]. Despite these advantages of hydrophilic protective layers in aqueous battery systems, the dissolution of active materials and the decomposition of water molecules during charge-discharge processes can lead to side reactions between the electrode and water molecules, triggering dendrite growth [36]. Therefore, higher hydrophilicity of the protective layer does not necessarily translate to superior electrochemical performance. To date, there is no comprehensive report on the impact of the hydrophilicity or hydrophobicity of protective layers on battery performance in aqueous battery systems.

Natural minerals, as vital resources on Earth, possess stable physical and chemical properties, nanoscale structures and morphologies, and high-aspect-ratio layered units, which can provide a large contact area with zinc anodes and facilitate high-speed channels for Zn²⁺ transport. Additionally, using natural clay as a coating can homogenize the anode surface, resulting in lower charge transfer resistance and uniform Zn²⁺ flux across the Zn surface. Natural clay materials have been extensively explored in the field of lithium-ion batteries, serving as single-ion conductors [37], inorganic fillers in polymer electrolytes [38], and modifiers for separator coatings [39]. To date, numerous natural clay materials have also been investigated for use as low-cost and environmentally friendly anode-electrolyte protective layers in aqueous zinc-ion batteries. Below, we discuss the progress of clay minerals in improving zinc anode performance, categorized by their one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) structures.

Halloysite and palygorskite are two typical one-dimensional (1D) structured clay minerals that have been applied in AZIBs and demonstrated excellent performance. Halloysite is a clay mineral with a natural nanotube structure, composed of alternating layers of silicon-oxygen tetrahedra and aluminum-oxygen octahedra, with the chemical formula Al₂Si₂O₅(OH)₄·nH₂O, where nH₂O represents the water molecules present between the layers. Under the influence of interlayer water, halloysite spontaneously curls into a nanotube morphology, with inner and outer diameters ranging from 10–30 nm and 30–50 nm, respectively (Figure 2a). The nanotube structure of halloysite provides natural channels for zinc ion transport, enabling its use as a filler to achieve higher ionic conductivity in composite systems [40]. Fan et al. [41] addressed the issues of dendrite growth and severe corrosion by coating natural halloysite nanotubes (HNTs) onto Zn foil (HNTs@Zn) to enhance Zn reversibility (as shown in Figure 2b). The negative surface charge of HNTs enables uniform charge distribution on the Zn surface, suppressing dendrite growth beneath the artificial layer. As a result, the HNTs@Zn electrode demonstrated low voltage hysteresis (16 mV) and long cycle life (over 2000 h at 0.2 mA cm⁻²) in symmetric cell tests. Furthermore, full cells with V₂O₅ as the cathode exhibited high reversibility, maintaining a capacity retention rate as high as 82.0% after 3000 cycles at 5 A g⁻¹ (Figure 2d). When observed at high rates, the HNTs@Zn electrode displayed a porous structure, which facilitates electrolyte penetration. To further investigate the effect of HNTs on the wettability of the Zn anode surface, contact angle measurements were conducted using a 1 M Zn(SO₃CF₃)₂ aqueous solution (Figure 2c). A 5 μL electrolyte droplet on the HNTs@Zn surface showed a contact angle of 65.4°, lower than that of bare Zn (82.5°). The smaller contact angle indicates better surface wettability, reflecting a more uniform anode surface and improved ion transport capability, which promotes uniform Zn²⁺ distribution across the anode surface (Figure 2c). Additionally, the positive charge inside the HNT tubes selectively adsorbs SO₃CF₃⁻, reducing the likelihood of byproduct formation. Xu et al. [42] formed a dense HNT coating on the Zn anode surface through time-saving and easily operable electrophoretic deposition. The HNTs-Zn exhibited good dispersibility and a relatively smooth surface, aligning parallel to the Zn surface under an electric field to form a densely packed structure. The hydrophilicity was evaluated by measuring the dynamic contact angle at 25°C, comparing bare Zn and HNTs-Zn. After 1 min, the contact angle of bare Zn was approximately 99.6°, remaining at 54.6° after 15 min, indicating limited hydrophilicity. In contrast, the initial contact angle of HNTs-Zn was about 69.8° after 1 min, smaller than that of bare Zn, and decreased to 0° after 15 min, demonstrating the characteristic uniform pore distribution of HNTs and optimized Zn²⁺ transport. Consequently, the HNTs-Zn anode exhibited lower resistance compared to bare Zn, and the HNTs-Zn//MnO₂ battery showed superior capacity retention, with a discharge capacity improvement to 79% after 400 cycles at 3C. Moreover, no significant byproducts were observed on the HNTs-Zn anode (Figure 2g,h). Attapulgite (ATP) is a hydrated magnesium aluminum silicate clay with a chain-like layered structure, composed of two continuous tetrahedral layers of silicon-oxygen and one discontinuous octahedral layer of magnesium-oxygen or aluminum-oxygen, forming numerous nanochannels [43]. Owing to its unique nanostructure, abundant porosity, low cost, and environmental friendliness, ATP materials have been widely utilized in applications such as adsorbents [44] and lithium-ion batteries [45]. Leveraging its large surface area and numerous adsorption sites, Sun et al. [46] developed an artificial Zn²⁺ buffer layer via doctor-blading to achieve dendrite-free zinc anodes. The attapulgite nanorods exhibit a high surface area of 203.8 m² g⁻¹ and a pore width of 1.18 nm, which facilitate the shortened transport pathways for Zn²⁺ and promote the uniform distribution of Zn²⁺ (Figure 2e). Additionally, the attapulgite nanorods possess high cation exchange capacity and hydroxyl (−OH) groups, which effectively modulate the electric field strength distribution to induce uniform Zn stripping/plating. Based on these unique properties, the attapulgite nanorod layer, serving as an artificial solid electrolyte interface, enhances Zn²⁺ exchange to improve transport efficiency and guides uniform Zn deposition, resulting in a low nucleation overpotential. Contact angle measurements in a 2 M ZnSO₄ aqueous solution revealed the hydrophilicity of the Zn electrode. The ATP-Zn electrode exhibited a contact angle of 37.0° after 1 s, significantly lower than that of bare Zn (89.0°), indicating improved electrolyte wettability and further enhancing Zn²⁺ transport kinetics. In a 2 M Zn(SO₄)₂ + 0.1 M MnSO₄ aqueous electrolyte, the ATP-Zn symmetric cell demonstrated excellent cycling stability, operating for over 1600 h (4000 cycles) at 0.25 mA cm⁻² and 0.05 mAh cm⁻². Moreover, the ATP-Zn symmetric cell exhibited a lower overpotential (40 mV) compared to bare Zn (50 mV), which remained stable during subsequent cycles. In full-cell configurations, the ATP-Zn//MnO₂ battery showed smaller peak potential differences between oxidation and reduction peaks compared to the Zn//MnO₂ battery, indicating improved Zn²⁺ diffusion into the Zn anode interlayer. Furthermore, the ATP-Zn//MnO₂ battery exhibited higher peak current densities, reflecting enhanced electrochemical reactivity. Additionally, Figure 2f demonstrates the excellent electrochemical performance of the full cell.

Two-dimensional (2D) layered clays represent another characteristic architecture in natural clays, such as montmorillonite (MMT) and dickite. MMT is a naturally layered silicate mineral belonging to the smectite group, with each MMT aluminosilicate layer (0.96 nm thick) typically consisting of two Si-O tetrahedral layers and a central Al-O octahedral layer. The ordered 2D layered structure, combined with a negatively charged network, enables MMT to facilitate the unimpeded transport of cations such as Li⁺, Na⁺, K⁺, Ca²⁺, and Zn²⁺. The abundant Si-O and H-O sites on the aluminosilicate layer surface ensure excellent electrolyte affinity (Figure 3a). Notably, the pore structure of MMT governs the mass transfer process during electrochemical reactions. MMT exhibits a hierarchical pore structure, where micropores (pore size < 2 nm) are primarily formed between the layers of montmorillonite, while mesopores and macropores exist between the stacked montmorillonite blocks. These microporous channels serve as atomic interlayer ion transport pathways, providing higher ionic conductivity and zinc ion migration numbers [47,48]. Due to its excellent divalent cation conductivity, MMT has been widely adopted in AZIBs as an artificial solid electrolyte interphase (SEI) membrane to enhance electrochemical performance.

Yan et al. [49] designed a dense and smooth montmorillonite-coated zinc foil (MMT-Zn), which provides fast channels for Zn²⁺ migration, achieving a high Zn²⁺ transference number (t⁺ ≤ 0.82). This design alleviates zinc corrosion and passivation issues while effectively suppressing zinc dendrite formation (Figure 3b). Contact angle tests revealed that the electrolyte droplet on MMT-Zn had a contact angle of 132°, compared to 35° on bare Zn, indicating that MMT-Zn can isolate most water from the Zn foil. Consequently, the dense MMT interlayer can store a large number of zinc ions and reduce water contact with zinc, effectively inhibiting side reactions such as hydrogen evolution and corrosion. Electrochemical results demonstrated that the MMT-Zn symmetric cell exhibited stable low overpotential (50 mV) and long cycle life (1000 cycles) at 1 mA cm⁻² and 0.25 mAh cm⁻², and an overpotential of 100 mV at ultra-high current and capacity (10 mA cm⁻²/45 mAh cm⁻², over 1000 h, 77% depth of discharge). Interestingly, the authors applied the MMT interlayer to the MnO₂ cathode, suppressing the dissolution and diffusion of discharge products into the electrolyte, thereby maintaining capacity stability. As a result, MMT synergistically improved the performance of both electrodes, enabling the MMT-Zn//MMT-MnO₂ full cell to achieve ultra-long cycle life and high capacity (1100 cycles, 191.5 mAh g⁻¹ at 2C) (Figure 3c). Additionally, researchers can modify MMT using surfactants, molecular intercalation, and ion exchange to further enhance its performance in AZIBs. Wang et al. [50] developed a novel coating through the integration of cetyltrimethylammonium bromide (CTAB)-pillared organo-montmorillonite with ZnSO₄/MnSO₄ solutions, yielding zinc oxide-modified montmorillonite (ZnOMMT). This composite material was strategically applied to both the zinc anode and MnO₂ cathode in rechargeable zinc-ion batteries, demonstrating enhanced interfacial stability and electrochemical performance through synergistic coordination between the lamellar montmorillonite structure and zinc-ion transport pathways. The strong pillar effect of CTAB cations constructed robust nanoscale interlayer tunnels in ZnOMMT, facilitating better Zn²⁺ diffusion (t⁺ = 0.66). Electrochemical results showed that the ZnOMMT@Zn symmetric cell achieved a long lifespan of 1100 h at 1 mA cm⁻² and 1 mAh cm⁻², while the full cell exhibited high capacity (267 mAh g⁻¹ after 300 cycles at 0.5 A g⁻¹ and 205 mAh g⁻¹ after 700 cycles at 1.0 A g⁻¹). Hong et al. [51] used intercalated montmorillonite (Zn-Mont) as an artificial solid electrolyte interphase to regulate Zn²⁺ migration and deposition behavior on the zinc anode surface. The Zn-Mont coating, with its low Zn²⁺ migration energy barrier and selective Zn²⁺ channels, ensured uniform Zn²⁺ flow and fast kinetics, preventing ion accumulation at the anode interface and suppressing Zn dendrite growth. Additionally, the Zn-Mont layer prevented direct contact between Zn metal and the bulk electrolyte, mitigating water- or oxygen-induced side reactions, achieving high reversibility (Coulombic efficiency > 99.6%), long-term stability (over 1000 cycles), and ultra-low polarization (overpotential ≈ 28 mV). When paired with an MnO₂ cathode, the Zn@Zn-Mont//MnO₂ full cell exhibited excellent cycling stability, retaining 85.4% capacity after 1000 cycles at 2C. Liu et al. [52] addressed issues related to clay minerals as SEI membranes by intercalating MMT with urea (UMMT), which contains polar functional groups (−C=O and −NH₂). The urea integration not only formed a dense and robust montmorillonite coating through strong charge interactions with Zn²⁺, enhancing Zn²⁺ diffusion and increasing Zn²⁺ concentration on the deposition surface, but also formed strong hydrogen bonds with MMT layers, improving mechanical properties. Furthermore, the UMMT coating acted as a desolvation layer, mitigating side reactions caused by active water. As a result, the UMMT coating enabled more stable Zn plating/stripping compared to the MMT layer. Electrochemically, the UMMT@Zn electrode outperformed bare Zn and MMT@Zn electrodes in symmetric cells, exhibiting ultra-low polarization (65 mV at 6 mA cm⁻²) and an ultra-long lifespan (over 1300 h). The superiority of UMMT was further demonstrated in the UMMT@Zn//V₂O₅ full cell, which achieved a high capacity of 254 mAh g⁻¹ after 4000 cycles at 10 A g⁻¹.

Dickite, a member of the kaolinite group of clay minerals, shares the general chemical formula Al₂Si₂O₅(OH)₄ and exhibits a 1:1 layered structure. Its basic unit consists of alternating SiO₄ tetrahedral sheets and AlO₆ octahedral sheets, connected by hydrogen bonds, which allow polar organic small molecules to intercalate into the interlayer space and expand the interlayer distance of dickite [53]. Under oxidizing agents (e.g., potassium chlorate), urea intercalated in dickite decomposes, releasing gases that cause the dickite layers to expand, forming a porous structure with pore sizes ranging from 0.3 to 1.2 μm [54]. Compared to untreated dickite, the expanded dickite exhibits significantly increased surface area, pore volume, and surface charge, making it a promising surface coating material for Zn anodes. Its structural and charge properties facilitate efficient Zn²⁺ transport. Li et al. [55] utilized urea to expand dickite, obtaining a coating material (DCU) for the surface of Zn anodes. The expanded dickite layers carry negative charges at their edges, attracting Zn²⁺ and repelling SO₄²⁻, which imparts selective permeability to Zn²⁺ and enhances the Zn²⁺ transference number (t⁺ = 0.89). The attraction of Zn²⁺ by the expanded dickite layers creates a “Zn²⁺ reservoir,” promoting Zn²⁺ enrichment. Under the influence of an electric field, “fast lanes” for Zn²⁺ transport form at the edges of the expanded dickite layers (Figure 3d), thereby enhancing ionic conductivity (13.54 mS cm⁻¹). The expanded dickite coating exhibits strong hydrophobicity; contact angle tests (Figure 3e) showed that the dickite-coated Zn anode had a contact angle of 76.44°, indicating better hydrophilicity compared to bare Zn (69.2°). After applying the expanded dickite coating, the contact angle increased to 94.97°, demonstrating that the DCU coating forms a barrier between the substrate and aqueous electrolyte, preventing direct contact between water and the Zn anode, mitigating hydrogen evolution reactions and electrode corrosion, and suppressing byproduct formation. Additionally, the K⁺ present in the expanded dickite preferentially adsorbs at the tips of Zn dendrites, reducing further Zn²⁺ deposition on the dendrite surface and inhibiting dendrite growth. Full cells assembled with DCU-Zn anodes exhibited stable cycling for 3000 cycles at a current density of 3 A g⁻¹, demonstrating excellent cycling performance (Figure 3f). In a follow-up study, the same team successfully exfoliated 1:1 layered dickite into ultrathin dickite nanosheets (DE) with thicknesses below 5 nm using an ultrasound-assisted solvothermal method, achieving a yield exceeding 40%. These ultrathin dickite nanosheets were then mixed with sodium alginate (SA) and coated onto Zn foil (DE-Zn) [56]. The ultrathin dickite nanosheets were uniformly dispersed in the SA matrix, forming a polygonal network structure that provided fast ion transport channels, contributing to a high ion transference number (t⁺ = 0.90) and ionic conductivity (21.13 mS cm⁻¹). Symmetric cells assembled with DE-Zn anodes exhibited a polarization voltage of 40 mV at 0.5 mA cm⁻² and stable operation for up to 5500 h, maintaining stability even at 10 mA cm⁻². The DE-Zn//MnO₂ full cell retained a high discharge specific capacity (144 mAh g⁻¹) after 750 cycles at 0.15 mA g⁻¹, showcasing outstanding electrochemical performance.

In contrast to two-dimensional clays, three-dimensional clay minerals possess hierarchically porous architectures that confer superior specific surface areas and enhanced adsorption capacities. Diatomite, a representative 3D layered clay, is a biogenic siliceous sedimentary rock primarily composed of SiO₂, with minor constituents including Fe₂O₃, Al₂O₃, CaO, MgO, and organic matter, exhibiting exceptional chemical stability. Retaining the structural characteristics of diatom frustules, this silicate mineral exhibits a unique hierarchical porous network, endowing it with remarkable adsorption capabilities and high surface area [57]. Wang et al. [58] employed an in situ tape-casting technique to deposit a diatomite (DL) coating on zinc anodes. The porous framework of diatomite enhanced Zn²⁺ deposition uniformity, suppressed dendrite propagation, and maintained ordered anode morphology post-cycling. Furthermore, the DL coating physically isolated metallic zinc from electrolyte contact, effectively mitigating parasitic reactions. Electrochemical evaluations demonstrated that symmetric cells with DL-coated anodes achieved stable cycling for 200 h at 10 mA cm⁻², while DL-Zn//Mn₃O₄ full cells exhibited significantly improved cycling stability and rate capability, retaining 120 mAh g⁻¹ after 400 cycles at 5 C with 80% capacity retention.

Table 1. Summary of the electrochemical performances of aqueous zinc-ion batteries modified by natural minerals.

Type	Anode	Cathode	Separator	Electrolyte	Zn//Zn Symmetric Battery Performance	Full Battery Performance	Ref
Attapulgite (1D)	ATP-Zn	MnO2	GF	2 M ZnSO4 + 0.1 M MnSO4	1600 h at 0.25 mA cm−2 for 0.05 mAh cm−2	210 mAh g−1 after 300 cycles at 1 C	[46]
Mullite (1D)	Zn	AC@I2	/	Zn-ML	140 h at 0.5 mA cm−2 for 0.1 mAh cm−2	127.4 mAh g−1 after 3000 cycles at 0.5 A g−1	[59]
Palygorskite (1D)	Zn	α-MnO2	GF	HCCE	/	212 mAh g−1 after 1000 cycles at 0.5 A g−1	[60]
Sepiolite (1D)	Zn	AC@I2	GF	PCS	2000 h at 1 mA cm−2 for 1 mAh cm−2	82.95% retention after 10,000 cycles at 5 A g−1	[61]
Sepiolite	Zn	VCS	GF	2 M ZnSO4	/	92.7% retention after 1000 cycles at 10 A g−1	[62]
HNTs (1D)	Zn	MoS2	GF	3 M Zn (CF3SO3)2	/	74% retention after 800 cycles at 0.2 A g−1	[63]
HNTs	Zn	MnO2	HNT-GF	2 M ZnSO4 + 0.1 M MnSO4	3000 h at 1 mA cm−2 for 1 mAh cm−2	93.4% retention after 1000 cycles at 2 A g−1	[64]
HNTs	CFC−Zn	HCC-V3S4	GF/D	2 M ZnSO4	/	95% retention after 200 cycles at 0.5 A g−1	[65]
HNTs	HNTs@Zn	V2O5	GF	1 M Zn (CF3SO3)2	2000 h at 0.2 mA cm−2 for 0.2 mAh cm−2	82% retention after 3000 cycles at 5 A g−1	[41]
HNTs	Zn	HNTs-PPy	GF	2 M ZnSO4	/	87.4% retention after 500 cycles at 0.5 A g−1	[66]
HNTs	HNTs-Zn	MnO2	GF	2 M ZnSO4	650 h at 0.5 mA cm−2 for 0.5 mAh cm−2	79% retention after 400 cycles at 3 C	[42]
HNTs	Carbon cloth and CNF	MnO2	hydrogel	M-HNTs/PAM	1200 h at 4.4 mA cm−2 for 1.1 mAh cm−2	92.7% retention after 1000 cycles at 10 C	[67]
Bentonite (2D)	Zn	NVO	GF	WiSCE	1000 h at 1 mA cm−2 for 1 mAh cm−2	88.29% retention after 5000 cycles at 3 A g−1	[68]
Kaolin (2D)	Zn	NH4V4O10	KL-Zn	KL-Zn	2200 h at 0.2 mA cm−2 for 0.1 mAh cm−2	241.6 mAh g−1 after 500 cycles at 1 A g−1	[69]
Kaolin	Zn	K-CEI-α-MnO2	AGM	1.8 M ZnSO4 + 0.2 M MnSO4	/	85% retention after 200 cycles at 0.05 A g−1	[70]
Montmorillonite (2D)	MMT-Zn	MMT-MnO2	GF	2 M ZnSO4 + 0.1 M MnSO4	1000 h at 10 mA cm−2 for 45 mAh cm−2	191.5 mAh g−1 after 1100 cycles at 2 C	[49]
Montmorillonite	ZnOMMT-Zn	ZnOMMT-MnO2	GF	2 M ZnSO4 + 0.2 M MnSO4	1100 h at 1 mA cm−2 for 1 mAh cm−2	205 mAh g−1 after 700 cycles at 1 A g−1	[50]
Montmorillonite	UMMT-Zn	V2O5	/	2 M ZnSO4	1300 h at 6 mA cm−2 for 3 mAh cm−2	254 mAh g−1 after 4000 cycles at 10 A g−1	[52]
Montmorillonite	Zn-Mont	MnO2	/	2 M ZnSO4 + 0.1 M MnSO4	900 h at 1 mA cm−2 for 0.5 mAh cm−2	85.4% retention after 1000 cycles at 2 C	[51]
Montmorillonite	Cu@Zn	α-MnO2	/	Pro-Pr3+ -ZnMT	/	92.2% retention after 800 cycles at 0.8 mA cm−2	[71]
Montmorillonite	Zn	MnOOH	/	WIME	1800 h at 0.5 mA cm−2 for 0.25 mAh cm−2	/	[72]
Dickite (2D)	DE-Zn	MnO2	GF	2 M ZnSO4+ 0.1 M MnSO4	5500 h at 0.5 mA cm−2 for 0.1 mAh cm−2	144 mAh g−1 after 750 cycles at 0.15 A g−1	[56]
Dickite	DCU-Zn	MnO2	GF	2 M ZnSO4+ 0.1 M MnSO4	1000 h at 0.5 mA cm−2	144 mAh g−1 after 3000 cycles at 3 A g−1	[55]
Dickite	Zn	LiMn2O4	DUC	2 M ZnSO4 +1 M Li2SO4	/	/	[73]
Diatomite (3D)	DL-Zn	Mn3O4	GF	2 M ZnSO4+ 0.1 M MnSO4	200 h at 10 mA cm−2 for 2 mAh cm−2	80% retention after 400 cycles at 5 C	[58]

illustrates the applications of various minerals in different components (anode, cathode, separator, and electrolyte) of zinc-ion batteries.

In summary, the growth of zinc dendrites and electrolyte-induced side reactions are critical challenges that significantly impact the performance and lifespan of AZIBs. To address these issues, researchers have developed various natural mineral coatings. One-dimensional (1D) minerals, leveraging their nanotube structures and high specific surface areas, effectively enhance the electrochemical stability and surface wettability of zinc anodes. Two-dimensional (2D) minerals, with their layered structures and charge characteristics, provide fast transport channels for zinc ions while suppressing dendrite growth. Three-dimensional (3D) minerals utilize their porous structures to improve the uniformity of zinc ion deposition and reduce direct contact between solvent molecules and zinc anode. These coating materials could not only extend the cycling life of batteries but also enhance rate performance and capacity retention, offering a promising pathway for optimizing the performance of aqueous zinc-ion batteries.

3. Separators

The separator is a critical component of secondary batteries, serving as an electron-insulating barrier between the cathode and anode to prevent direct electron conduction while allowing for selective ion transport through its porous structure. Additionally, the separator stores the required amount of electrolyte to facilitate ion migration during electrochemical reactions [74]. In AZIBs, glass fiber (GF) separators are commonly used due to their excellent chemical stability, compatibility with electrolytes, and superior ionic conductivity [75]. However, the disordered pore structure and rough surface of GF often lead to uneven charge distribution, promoting dendrite growth. Furthermore, the low mechanical strength and brittle nature of GF make it susceptible to dendrite penetration, further degrading the battery’s electrochemical performance [76,77]. The considerable thickness of GF (up to 600 µm) also occupies excessive space in the battery, reducing volumetric energy density, increasing ion transport distance and raising internal resistance, resulting in poor CV curves [78]. To address these limitations, researchers have developed various modification strategies for GF separators. For instance, functional supramolecules with zincophilic groups can be grafted onto GF separators to ensure uniform Zn²⁺ distribution, reducing Zn²⁺ accumulation and dendrite formation on the electrode surface. Sun et al. [78] reported a Janus separator by growing vertical graphene on one side of the GF separator. The derived 3D graphene scaffold provides a large surface area and porous structure, reducing local current density on the Zn anode side and ensuring uniform Zn plating/stripping with high reversibility. The Janus separator achieves uniform electric field distribution and lower local current density at the anode/electrolyte interface, leveraging zincophilic characteristics to establish uniform Zn²⁺ flux, enhancing rate and cycling performance (93% capacity retention after 5000 cycles at 5 A g⁻¹) and enabling the V₂O₅//Zn full cell to achieve an outstanding energy density of 182 Wh kg⁻¹. Su et al. [79] sprayed MXene nanosheets onto one side of the GF separator to create an MXene-GF separator. MXene nanosheets, with their abundant surface polar functional groups, exceptional ionic conductivity, and excellent electrolyte wettability, effectively homogenize local current distribution and accelerate Zn²⁺ migration. However, these advanced materials may be costly and less practical for large-scale applications. Therefore, there is an urgent need to develop cost-effective, reliable, and high-performance separator materials. Recently, bio-renewable materials such as cotton and cellulose have been explored as low-cost and high-performance separators. For example, cotton-derived cellulose exhibits excellent mechanical strength, superior insulation properties, and outstanding hydrophilicity. Wong’s team [77] prepared a cellulose separator by collecting cellulose fibers from cotton through a simple filtration method. The cellulose separator not only demonstrates excellent tensile strength (29.2 MPa) and elastic modulus (4.16 GPa) but also features uniform and dense nanopores with abundant hydroxyl groups. It promotes ion migration and electrolyte penetration, reduces the desolvation activation energy of hydrated Zn²⁺, lowers Zn nucleation overpotential, and ensures uniform Zn²⁺ flux. These properties effectively suppress Zn dendrites and adverse side reactions, significantly improving Zn stripping/plating reversibility. Zn//Zn symmetric cells equipped with this separator remain stable at a cumulative plating capacity of 1000 mAh cm⁻² and can withstand an ultra-high areal capacity of 20 mAh cm⁻². The assembled Zn//MnO₂ batteries also exhibit significantly improved rate and cycling performance compared to those using other separators. Beyond cotton, cellulose can be extracted from various biomass sources [80]. For instance, separators made from algae-derived cellulose nanofibrils feature a dense, flat surface and uniform mesopores (~20 nm). The mesoporous structure facilitates uniform Zn²⁺ distribution, eliminating the “tip effect” and stabilizing Zn deposition, thereby enhancing electrochemical stability. Zn//Zn symmetric cells equipped with these novel separators demonstrate over 2000 h of cycling stability at 2 mA cm⁻² with a low hysteresis voltage of 29 mV. Even at a high current density of 30 mA cm⁻², they achieve a high cumulative deposition capacity exceeding 3200 mAh cm⁻² at a cycling capacity of 15 mAh cm⁻².

Mineral-based materials have flourished in the separator field due to their low cost and environmentally friendly characteristics. Halloysite, with its hollow tubular multi-layered wall structure and unique surface electronegativity, was utilized by Liu et al. [64] to fabricate a composite separator (HNT-GF) by coating HNTs onto one side of a GF separator via a simple dip-coating method. As an inorganic mineral, HNTs not only enhance the mechanical strength and thermal stability of the separator but also provide a guiding effect through their nanotube structure to homogenize interfacial Zn²⁺ flux. Additionally, the positively charged Al−OH inner surface and negatively charged Si−O−Si outer surface impart ion-sieving functionality to the separator. Specifically, SO₄²⁻ are trapped within the nanotubes to restrict their transport, thereby improving desolvation kinetics and suppressing SO₄²⁻-related passivation reactions. Simultaneously, Zn²⁺ are uniformly deposited on the outer surface and efficiently migrate under electric field driving, increasing the Zn²⁺ transference number (t⁺ = 0.71). Symmetric cells using the HNT-GF separator exhibit a long lifespan of 3000 h at 1.0 mA cm⁻² and 1.0 mAh cm⁻². The excellent electrochemical performance is further demonstrated by an outstanding average coulombic efficiency of 99.7% over 950 cycles. After 1000 cycles, Zn//MnO₂ full cells with the HNT-GF separator retain 93.4% capacity (Figure 4).

Porosity, defined as the percentage of internal pore volume relative to the total separator volume, is closely related to liquid absorption rates. Pore size significantly impacts ion transport in electrolytes and mechanical strength. On the one hand, larger pores allow for freer and less restricted ion diffusion, improving ion transport efficiency. However, excessively large pores can drastically reduce mechanical strength, failing to block zinc dendrite penetration and leading to short circuits. On the other hand, smaller pores may inhibit dendrite penetration to some extent but could also increase ion transport resistance and reduce diffusion efficiency. Furthermore, excessively high porosity accelerates the self-discharge process in zinc-ion batteries, degrading voltage consistency and cycling stability [74]. Expanded dickite, with its porous structure, can serve as a coating material for non-woven fabrics, enabling the development of novel composite separators with large pores, well-developed channels, and high porosity to enhance battery performance. Liu et al. [73] successfully prepared a new composite separator by coating a porous expanded dickite slurry onto an ethylene-propylene side-by-side non-woven fabric using polyacrylic acid emulsion as a binder. The pore structure of the composite separator can be adjusted by varying the expanded dickite content. As the expanded dickite content increases, the separator’s breathability, porosity, electrolyte adsorption rate, and ionic conductivity gradually improve. At a high expanded dickite content of 90 wt%, the discharge specific capacity reaches 132.7 mAh g⁻¹.

4. Cathode Materials

Manganese-based oxides, vanadium-based oxides, and Prussian blue analogs, as cathode materials for AZIBs, exhibit poor electronic conductivity, resulting in high charge transfer resistance. The electrochemical behavior of these inorganic materials primarily relies on redox reactions involving changes in metal oxidation states and the associated charge compensation through structural adjustments and counterion interactions [81]. Manganese-based oxides, due to their high electrochemical activity, low cost, natural abundance, and multivalent states (Mn²⁺/Mn³⁺/Mn⁴⁺), have been widely employed in energy storage systems [82,83]. Among various manganese oxides, MnO₂, Mn₂O₃, Mn₃O₄, MnO, and Zn₂MnO₄ have been investigated as cathodes for AZIBs [35,84,85,86]. MnO₂, in particular, demonstrates structural versatility through diverse connectivity patterns of MnO₆ octahedral units, forming polymorphs with chain-, tunnel-, or layered-type architectures. These tunnel (e.g., α-, β-, γ-MnO₂) or layered (δ-MnO₂) configurations enable reversible Zn²⁺ intercalation/deintercalation through their open frameworks. The Zn²⁺ intercalation mechanism of manganese-based oxides (taking γ-MnO₂ as an example) can be represented by the following equation:

$$Z{n}^{2+}+2e^{-}+2\alpha -Mn{O}_2\to Zn{Mn}_2{O}_4$$

(4)

Vanadium oxides typically exhibit multiple oxidation states (+5, +4, +3) in oxide forms, with their coordination polyhedra transitioning among tetrahedral, trigonal bipyramidal, square pyramidal, and distorted octahedral geometries as the valence state changes. This structural adaptability grants vanadium oxides rich structural chemistry and diverse crystalline arrangements [87]. The primary crystal structures of vanadium-based oxides—layered and tunnel-type frameworks—significantly influence the number of electrochemically active sites for Zn²⁺ insertion and overall performance [88]. Among these, V₂O₅ represents the most studied vanadium oxide, characterized by its unique layered structure composed of distorted VO₆ octahedra. These octahedra share edges to form corrugated layers, which can alternatively be interpreted as interconnected VO₅ square pyramids sharing basal corners. The weak interlayer van der Waals interactions and large interlamellar spacing facilitate Zn²⁺ intercalation [89].

However, these oxide-based materials exhibit inherent limitations. In manganese-based systems, manganese undergoes disproportionation reactions during prolonged electrochemical cycling. The Mn³⁺ species generated during discharge partially dissolve into the aqueous electrolyte as Mn²⁺ instead of fully reverting to higher oxidation states upon charging. This irreversible dissolution induces structural collapse of the cathode, leading to rapid capacity decay, poor cycling reversibility, and inferior rate capability. Vanadium-based oxides face analogous challenges, where vanadium ion dissolution during cycling causes progressive capacity fading. Furthermore, dissolved ions may deposit on zinc anodes, forming passivation layers that degrade overall energy density. Heteroatom doping has emerged as an effective strategy to enhance cathode stability. For instance, Sr²⁺ and Na⁺ co-doping in vanadium oxides improves aqueous electrolyte compatibility [90]. During cycling, Sr²⁺ migrate from the vanadium oxide lattice to the cathode surface, forming a Sr-rich cathode-electrolyte interphase (CEI) layer composed primarily of SrCO₃. Concurrently, Na⁺ remain within the oxide framework, stabilizing the layered structure post-Sr²⁺ leaching. This SrCO₃-dominated CEI layer effectively suppresses vanadium dissolution, achieving 92% capacity retention over 1000 cycles. A similar approach has been applied to manganese oxides through Ca²⁺ doping [91]. Ca²⁺-intercalated MnO₂ releases Ca²⁺ during cycling, which react with SO₄²⁻ at the cathode surface to form a CaSO₄·2H₂O-based CEI layer. This dual-functional interface exhibits low interfacial resistance while inhibiting cathode dissolution, enabling stable operation at 5C rates with 88% capacity retention after 500 cycles.

Minerals, with their diverse crystalline structures and compositional properties, have found extensive applications in cathode engineering for aqueous zinc-ion batteries. As previously mentioned, MMT has been employed as a protective coating on cathodes. Its ordered two-dimensional layered structure, combined with a negatively charged network, enables efficient Mn²⁺ adsorption to suppress MnO₂ dissolution [49,50]. Kaolinite, a phyllosilicate clay mineral with the chemical formula Al₄[Si₄O₁₀](OH)₈, features a TO-type structure where tetrahedral silica sheets (T) are covalently bonded to octahedral gibbsite-like aluminum hydroxide layers (O), stacked along the c-axis (Figure 5a). The inherent negative charge of kaolinite arises from unbalanced chemical bonds at crystal edges, exposing hydroxyl groups on its surface that can adsorb metal cations from solutions—a property widely exploited in wastewater treatment as a cation adsorbent [92]. Recent advancements have leveraged kaolinite to enhance AZIB performance. During prolonged cycling, MnO₂ cathodes gradually degrade through irreversible transformation into thick Zn-birnessite nanosheets, causing severe capacity fade. Liu et al. [70] addressed this issue by developing an artificial kaolinite-based cathode-electrolyte interphase (K-CEI) to regulate Mn²⁺ deposition during charging. The K-CEI layer functions as a Mn²⁺ scavenger, effectively inhibiting cathode dissolution through hydroxyl-mediated interactions. During discharge, dissolved Mn²⁺ from MnO₂ are captured by the K-CEI. In subsequent charging cycles, a portion of these Mn²⁺ remains confined near the K-CEI, reducing the quantity available for Zn-birnessite formation and preserving cathode structural integrity (Figure 5b). This mechanism enables the K-CEI-modified cell to deliver a reversible capacity of 380.89 mAh g⁻¹ at 50 mA g⁻¹ for 1000 cycles (over 1994 h) with negligible capacity loss at 125 mA g⁻¹. When applied to Zn//ξ-MnO₂ batteries with high mass loading (12 mg cm⁻²), the K-CEI system achieves an energy density of 126 Wh kg⁻¹ after 100 cycles with coulombic efficiency exceeding 99.15%, vastly outperforming unmodified counterparts (23 Wh kg⁻¹). Furthermore, the universal applicability of K-CEI has been validated across various MnO₂ polymorphs (α-, β-, γ-phase), demonstrating consistent performance enhancement in rechargeable Zn//MnO₂ systems (Figure 5c,d,e,f).

To address the poor conductivity of many cathode materials, compositing active materials with conductive additives (typically carbon-based) has proven effective in enhancing electrical performance while improving material dispersion to expose more active sites. Tong et al. [93] uniformly loaded MnO₂ onto highly conductive carbon nanotubes (CNTs), significantly mitigating MnO₂’s inherent conductivity limitations. Cao et al. [94] synthesized a MnO₂@graphene composite via ball milling, which reduced MnO₂ particle size to create additional electrochemically active surfaces. The graphene sheets concurrently improved electrical conductivity and buffered volume changes during cycling, resulting in enhanced cycling stability. Liu et al. [65] designed a novel composite carbon substrate through electrospinning and calcination, incorporating acid-treated natural halloysite and carbon nanotubes (HCC) as structural and interfacial modifiers. The natural halloysite, with its abundant surface −OH groups, exceptional hydrophilicity, and regular nanotubular morphology, facilitated the hydrothermal synthesis of nanospherical V₃S₄ cathodes (HCC-V₃S₄) anchored on the composite substrate (Figure 5g). Paired with a Zn nanosheet/carbon fiber cloth (CFC) flexible anode prepared by electrodeposition, the assembled flexible ZIB demonstrated superior hydrophilicity (HCC contact angle: 33.07° vs. 111.07° for pristine carbon fiber) and electrochemical performance, achieving an energy density of 155.7 Wh kg⁻¹, a power density of 5000 W kg⁻¹, 95% capacity retention after 200 cycles, and exceptional long-term cyclability. Zhang et al. [62] developed a self-supporting composite cathode (VCS) comprising V₁₀O₂₄·12H₂O, acid-treated natural sepiolite, and CNTs via hydrothermal synthesis and freeze-drying. Sepiolite, a magnesium-rich silicate clay featuring silica tetrahedra and discontinuous magnesium-oxygen octahedra, possesses multichannel structures and surface-enriched silanol groups (Si−OH). The layered V₁₀O₂₄·12H₂O, with structural water molecules, reduced Zn²⁺ effective charge. Acid-treated sepiolite enhanced electrode hydrophilicity while providing mechanical reinforcement for self-supporting properties (Figure 5h). CNT incorporation further improved conductivity, enabling a specific capacity of 191 mAh g⁻¹ at 500 mA g⁻¹ (0.4–1.8 V) with 93.6% retention after 100 cycles. Even at 10 A g⁻¹, the system maintained 115 mAh g⁻¹ after 1000 cycles, demonstrating high-rate capability.

Naturally, direct modification of manganese-based or vanadium-based materials using long-chain organic conductive polymers has also been explored as an effective strategy to enhance their electrochemical performance in aqueous zinc-ion batteries. Polypyrrole (PPy), in particular, has garnered significant attention due to its redox activity and superior electrical conductivity. Guo et al. [95] synthesized PPy-coated α-MnO₂ core-shell nanorods (α-MnO₂@PPy) as cathode materials to enhance cycling performance. Compared to bare MnO₂, which exhibited rapid capacity decay to 70 mAh g⁻¹ after 30 cycles at 100 mA g⁻¹, the modified material demonstrated mitigated capacity degradation, retaining 85 mAh g⁻¹ after 100 cycles. Liu et al. [96] reported a cathode composed of VO₂-5@PPy hollow nanospheres. The interstitial spaces between nanospheres facilitated Zn²⁺ transport and accommodated substantial volume changes during cycling, delivering a specific capacity of 440 mAh g⁻¹ at 0.1 A g⁻¹. Additionally, the system maintained a reversible capacity of 143 mAh g⁻¹ after 860 cycles at 1 A g⁻¹. However, PPy suffers from limitations such as low specific surface area and instability in electrolytes, which can induce parasitic reactions under cycling conditions, compromising battery lifespan and practicality [97]. To address these issues, Xu et al. [66] developed a composite material by integrating HNTs—a silicate mineral with hollow tubular morphology and high surface area—with PPy via in situ polymerization. PPy nanoparticles were uniformly and densely coated on HNT surfaces (~3.8 nm thickness), with siloxane and hydroxyl groups enhancing aqueous dispersion. Surface valence state and band structure analyses revealed electron cloud delocalization from PPy to HNTs, indicating strong interfacial coordination. Compared to pure PPy, the HNTs-PPy composite increased the electrolyte-electrode contact area, improving cycling stability. Zn-ion batteries equipped with HNTs-PPy cathodes achieved 87.4% capacity retention after 500 cycles at 0.5 A g⁻¹. Beyond serving as conductive additives, HNTs’ hollow tubular architecture has been exploited as a structural template for cathode synthesis. Yang et al. [63] utilized natural HNTs as templates to control the morphology of porous tubular MoS₂ via a template-assisted thermal decomposition method using (NH₄)₂MoS₄ as a precursor. MoS₂ adopts a graphite-like layered structure, where molybdenum (Mo) atoms are sandwiched between two sulfur (S) layers in an S-Mo-S configuration. These layers are weakly bonded by van der Waals forces with an interlayer spacing of ~0.65 nm, enabling faster ion diffusion compared to oxide materials. The MoS₂-based cathode exhibited a discharge capacity of 146.2 mAh g⁻¹ at 0.2 A g⁻¹ with 74.0% capacity retention after 800 cycles, along with robust rate capability (115 mAh g⁻¹ at 1 A g⁻¹). This hierarchical design highlights the potential of mineral-templated synthesis for developing high-performance ZIB cathodes.

In general, manganese-based oxides, vanadium-based oxides, and Prussian blue analogs compose the mainstream cathode materials for AZIBs. However, challenges persist, including poor electronic conductivity, high charge transfer resistance, and structural degradation due to manganese/vanadium dissolution during prolonged cycling. To address these limitations, mineral-based protective layers have been extensively employed to enhance interfacial stability. Furthermore, composite material design has proven instrumental in improving cathode conductivity and electrochemical performance. For instance, integrating mineral frameworks with carbon-based matrices effectively enhances charge transport while accommodating volume expansion. Synergistic combinations of conductive polymers and natural minerals further improve conductivity, cycling stability, and structural integrity. Advanced modification strategies—such as heteroatom doping, mineral adsorption, conductive material hybridization, and organic polymer functionalization—significantly enhance the electrochemical performance of manganese/vanadium-based cathodes by suppressing dissolution and improving cyclability. These innovations provide novel pathways for AZIB cathode development, though further optimization of long-term durability and cost-effectiveness remains critical for practical implementation. Future research should prioritize scalable fabrication methods and in-depth mechanistic studies to bridge laboratory-scale achievements with commercial viability.

5. Electrolytes

As a critical component of zinc-ion batteries, the electrolyte establishes the operational environment essential for long-term stability and cycling reproducibility. Aqueous electrolytes have been extensively studied due to their inherent advantages: low cost, high safety, and superior ionic conductivity (typically >20 mS cm⁻¹) derived from water’s high dielectric constant [98]. Numerous zinc salts have been explored for AZIBs, including ZnSO₄, ZnF₂, ZnCl₂, Zn(NO₃)₂, Zn₃(H₂PO₄)₂, Zn(ClO₄)₂, Zn(TFSI)₂, Zn(CF₃SO₃)₂, and Zn(CH₃COO)₂. Among these, ZnSO₄ has emerged as the most widely adopted electrolyte owing to its high aqueous solubility, stable SO₄²⁻ coordination structure, excellent compatibility with metallic zinc, and broad electrochemical stability window [99]. By contrast, Zn(CH₃COO)₂-based electrolytes exhibit reduced H⁺ concentration and elevated pH, which benefits acid-sensitive cathodes such as vanadium oxides [100]. However, their slower ion mobility (Zn²⁺ transference number: 0.38 vs. 0.56 for ZnSO₄) compromises zinc stripping/plating kinetics, limiting their utility in anode-focused studies [101]. ZnF₂ electrolytes have also garnered attention, demonstrating comparable performance to ZnSO₄ while enabling the formation of fluorine-rich SEIs on zinc anodes. These fluorine-rich SEIs effectively suppress parasitic reactions (e.g., hydrogen evolution) on the zinc anode, enhancing cycling stability and reversibility [102].

However, aqueous electrolytes inherently compromise the interfacial stability between zinc anodes and electrolytes, leading to poor anode reversibility accompanied by severe HER and dendritic growth. Additionally, due to the high reactivity of water as a solvent, cathode materials inevitably suffer from issues such as material dissolution and byproduct formation, resulting in significant capacity fading and rapid performance degradation. To address these challenges, electrolyte additives have emerged as a highly effective and widely adopted strategy. In manganese-based batteries, the “disproportionation reaction” caused by proton insertion leads to substantial mass loss in cathode materials. According to the “common ion effect”, adding MnSO₄ to a ZnSO₄ aqueous solution alters the dissolution equilibrium, thereby inhibiting the dissolution of MnO₂. Zinc-ion batteries using this electrolyte exhibit excellent capacity retention, with a capacity decay rate of only 0.007% [5].

Electrolyte additives also play critical roles in modulating solid electrolyte interphases, mitigating dendrites, corrosion, and interfacial resistance. For instance, inorganic additives like LiCl [103] provide solvated Li⁺ into the electrolyte. Li⁺ reacts with O²⁻ to form a dense SEI comprising Li₂O and Li₂CO₃, which shields the anode surface and inhibits dendrite propagation. Concurrently, Cl⁻ reduces Zn²⁺ polarization and enhances Zn²⁺ mobility. Xu et al. [104] demonstrated that Na₂SO₄ additives in ZnSO₄ electrolytes homogenize Zn²⁺ deposition, effectively eliminating dendrites. Liu et al. [105] implemented in situ Sn doping via SnCl₂ co-deposition. Theoretical calculations indicated that Sn reduces surface free energy, preferentially depositing at dendritic tips to suppress their growth. These three methods all rely on the coordination of metal cations with O²⁻ to densify the SEI and inhibit dendrite deposition. Unfortunately, the high cost of rare or high-purity metals increases production expenses, while residual metal ions pose environmental risks, conflicting with sustainability principles. Additionally, compatibility issues between inorganic additives and electrode materials may compromise battery performance [106]. Therefore, developing low-cost, eco-friendly additives that enhance long-term stability remains a critical challenge for advancing aqueous zinc-ion batteries.

Recent reports [9] indicate that natural fillers, particularly natural clays, can achieve performance comparable to electrolytes produced through complex methods. This is primarily due to the unique properties of clays, including their stable physical and chemical characteristics, nanoscale structures or morphologies, and rich surface properties, making them highly suitable as electrolyte fillers. Additionally, the environmental friendliness and low cost of clays provide extra advantages, especially considering the future large-scale production of zinc-ion batteries for widespread applications. Zhou et al. [69] utilized the abundant reserves, low cost, layered structure, electronic insulation, and zinc ion conductivity of kaolinite (KL) to prepare a solid-state electrolyte (KL-Zn) (Figure 6a). Experimental results demonstrated that the KL-Zn electrolyte exhibits a wide voltage window of 2.73 V, high ionic conductivity of 5.08 mS cm⁻¹, and a high Zn²⁺ transference number of 0.79. The KL-Zn electrolyte effectively suppresses side reactions and promotes uniform zinc deposition on the metal surface, enabling the symmetric cell to achieve excellent performance with long-term cycling stability of 2200 h at 0.2 mA cm⁻² and 0.1 mAh cm⁻². The Zn//NH₄V₄O₁₀ full cell using KL-Zn as the electrolyte delivered a reversible capacity of 259.2 mAh g⁻¹ after 200 cycles at 0.5 A g⁻¹, with a capacity retention rate of 83%. Combined with theoretical calculations, these results are attributed to the two-dimensional layered structure, large lattice spacing, and low zinc diffusion barrier of KL-Zn, which construct ion channels that not only guide ordered zinc transport and reversible deposition at the anode interface but also inhibit vanadium dissolution and structural distortion at the NH₄V₄O₁₀ cathode interface (Figure 6b). Huang et al. [72] introduced a novel “water-in-montmorillonite” (WiME) solid-state electrolyte. The layered structure of montmorillonite effectively confines water within its interlayers, and a series of tests showed that water activity decreases with increasing MMT content in the electrolyte, indicating strong interactions between water molecules and clay that restrict water mobility. This results in high ionic conductivity of 64.82 mS cm⁻¹ and exceptional self-discharge suppression, retaining 92.7% capacity after 720 h of rest. The WiME architecture facilitates uniform Zn deposition, yielding a smooth zinc anode surface and promoting cycling stability at high current densities. COMSOL 5.6 simulations (Figure 6c) further demonstrated the role of the “clay-confined water” structure in uniform zinc deposition. Compared to traditional ZnSO₄ (ZSO) electrolyte, WiME exhibits a uniform electric field across the anode surface, effectively dispersing Zn²⁺ and preventing their accumulation at tips (Figure 6e). Symmetric cells based on WiME demonstrated excellent long-term cycling stability exceeding 1900 h, and the full Zn//MnOOH cell showed stable cycling for 500 cycles without capacity decay (Figure 6d), highlighting the synergistic effects of suppressed parasitic reactions, uniform zinc deposition, and enhanced interfacial stability achieved by WiME. Tian et al. [68] designed a low-cost, quasi-solid “water-in-swelling clay” electrolyte (WiSCE) to provide a favorable aqueous environment for zinc metal anodes. WiSCE was prepared by mixing a high concentration (50% weight/volume) of swelling clay (bentonite BT, Al₂H₂O₁₂Si₄) with a base electrolyte (2 M ZnSO₄ aqueous solution). Bentonite (BT), with its two silica tetrahedral sheets and one alumina octahedral sheet, exhibits excellent hydration and swelling capabilities [107]. When immersed in an aqueous electrolyte, a large number of water molecules can intercalate into the BT crystal, a phenomenon known as interlayer swelling. By effectively confining water molecules within the interlayers of mineral clays with exceptional swelling capacity, water activity is significantly suppressed (Figure 6f), preventing water-induced parasitic reactions on the zinc metal anode and enabling a highly reversible Zn plating/stripping process. The Zn//NVO full cell based on WiSCE demonstrated outstanding cycling stability at various current densities, with capacity retention rates of 90.47% after 200 cycles at 0.1 A g⁻¹, 96.64% after 2000 cycles at 1 A g⁻¹, and 88.29% after 5000 cycles at 3 A g⁻¹. It also exhibited a long shelf life (>60 days), excellent high-temperature adaptability (50 °C), and superior cycling stability at both low and high charge/discharge rates. Li et al. [59] prepared a zinc-based solid electrolyte (Zn-ML) using mullite as the raw material through zinc ion exchange. Mullite, a chain silicate mineral primarily composed of Al, Si, and O, features ordered Al-O/Si-O polyhedra forming upper (Path 1) and lower (Path 2) tunnel structures, as depicted in Figure 6g,h. The calculated diffusion energy barriers for Path 1 and Path 2 are 0.313 eV and 0.435 eV, respectively, demonstrating superior zinc diffusion kinetics. The Zn-ML electrolyte exhibits low electronic conductivity, low zinc diffusion barriers, and strong polyiodide adsorption capabilities, guiding reversible zinc deposition and inhibiting the dissolution of active iodine and polyiodide shuttling during cycling. Theoretical calculations reveal that the Zn-ML electrolyte features fast zinc diffusion kinetics and strong interactions with polyiodide ions, physically separating the redox reactions of zinc metal to zinc ions and iodine to iodide ions at the anode and cathode sides of the solid electrolyte. This effectively enables uniform zinc deposition and eliminates iodine dissolution and polyiodide shuttling. Electrochemical results show that the Zn-ML electrolyte has a high Zn²⁺ transference number (t⁺ = 0.51), high ionic conductivity (7.8 mS cm⁻¹), and a wide working voltage window (2.7 V), laying a solid foundation for superior electrochemical performance. Symmetric Zn//Zn cells maintained highly reversible low-voltage polarization cycling behavior at 0.5 mA cm⁻² and 0.1 mAh cm⁻², indicating stable anode interface reactions. The Zn//AC@I₂ cell achieved a cycle life exceeding 3000 cycles at 0.5 A g⁻¹ with a capacity retention rate of 85.2% and a rate capacity of 128.6 mAh g⁻¹ at 1 A g⁻¹, demonstrating the Zn-ML solid electrolyte’s effectiveness in suppressing iodine dissolution and polyiodide shuttling.

In aqueous environments, proton (H⁺) migration occurs through a hydrogen bond network, where protons hop from one oxygen atom to another via hydroxyl group rotation and preferential hydrogen bond breaking. This migration mechanism requires a complete and tightly connected proton transfer pathway or hydrogen bond network. However, in water-lean electrolytes, the uneven distribution and lack of correlation among water molecules often result in unsatisfactory proton conduction performance, partly due to the absence of effective regulation mechanisms [108,109]. Liu et al. [71] proposed a montmorillonite-based water-lean quasi-solid electrolyte with a strongly hydrated Pr³⁺ additive, which effectively regulates proton transfer pathways. As illustrated in Figure 7a, the construction principle of the proton conduction network in the water-lean quasi-solid electrolyte is shown. MMT can effectively adsorb water molecules and cations within its layered structure, facilitating the construction of an interlayer proton conduction network compared to non-layered mullite. Pr³⁺, with its higher coordination number and weaker 4f orbital shielding compared to Zn²⁺, can aggregate more water molecules in its solvation structure. Additionally, Pr³⁺ is easily adsorbed on the surface and interlayers of MMT. Therefore, under water-lean conditions, it effectively aggregates water molecules in the Pr³⁺-containing electrolyte, constructing a stable and interconnected proton transfer pathway throughout the electrolyte. This charge carrier conduction mode prevents slow kinetics or other potential side reactions caused by excessive ion/molecule activity. The Pr³⁺ additive not only dominates proton conduction kinetics but also regulates reversible manganese interface deposition, reducing surface potential and enabling more Pr³⁺ to adsorb with solvated water molecules. This abundance of interfacial water molecules constructs connected proton transfer channels, increases the interfacial dielectric constant, and enhances interfacial reaction activity. Electrochemical results demonstrate that the Cu@Zn//α-MnO₂ full cell achieves a high specific capacity of 433 mAh g⁻¹ and excellent stability over 800 cycles. Furthermore, an Ah-level pouch cell based on this electrolyte, with a mass loading of 15.19 mg cm⁻², exhibits a cycle life of 100 cycles.

Although liquid electrolytes offer strong usability, they pose risks of electrolyte leakage in corresponding batteries. Additionally, the demand for advanced flexible power sources in flexible electronics requires electrolytes with high flexibility and integrity [110]. By introducing polymers into aqueous solutions, gel electrolytes with excellent electrochemical performance have been developed. Xu et al. [67] prepared a high-strength, ultra-stable hydrogel electrolyte (M-HNTs/PAM) by crosslinking HNTs modified with 3-(methacryloyloxy)propyltrimethoxysilane (MPS) and polyacrylamide (PAM). M-HNTs served as a crosslinker for PAM, enhancing the interaction between M-HNTs and PAM through radical polymerization (Figure 7b,c). The abundant polar groups, strong covalent bonds, and intermolecular hydrogen bonds in M-HNTs formed a three-dimensional network with PAM, improving ionic conductivity, mechanical properties, flexibility, water absorption, and extensibility (Figure 7d,e). The M-HNTs/PAM hydrogel exhibited a tensile strength of 40 kPa and a tensile strain of 1200%. Flexible Zn//Zn symmetric cells based on the M-HNTs/PAM hydrogel electrolyte demonstrated stable Zn plating/stripping for 1200 h at 4.4 mA cm⁻² and 1.1 mAh cm⁻². Flexible ZIBs using the M-HNTs/PAM hydrogel electrolyte showed excellent cycling stability, with a capacity retention rate of 92.7% after 1000 cycles at 10C. Moreover, these flexible ZIBs could withstand rigorous tests such as bending, folding, hammering, and even puncturing. Li et al. [61] developed an organic-inorganic hybrid hydrogel electrolyte (polyvinyl alcohol/sulfonated cellulose/sepiolite, PCS) to enhance ionic conductivity and reduce side reactions in ZIBs. In this system, hydrogen bonds formed between sulfonic acid groups in the polymer and hydroxyl groups in sepiolite, ensuring strong connections and uniform distribution of components. These hydrogen bonds strengthened the binding between organic and inorganic components, improving the electrolyte’s ionic conductivity and mechanical properties. Additionally, the sulfonic acid groups (-SO₃⁻) in the electrolyte exhibited strong affinity for cations, serving as active centers for regulating Zn²⁺ migration and uniform deposition. The porous structure between the multilayers of sepiolite further optimized ion transport channels, adjusted the desolvation structure of Zn²⁺, and improved reaction kinetics to induce uniform Zn²⁺ deposition (Figure 7f,g). Electrochemical results showed that the PCS hydrogel electrolyte had a significantly lower desolvation activation energy (35.12 kJ mol⁻¹) compared to liquid electrolytes (70.27 kJ mol⁻¹) and PC hydrogel electrolytes without sepiolite (43.39 kJ mol⁻¹). The synergistic effect of organic and inorganic components in the electrolyte effectively suppressed dendrite growth and reduced side reactions. Zn//Zn symmetric cells achieved over 2000 h of cycling at 1 mA cm⁻² and 1 mAh cm⁻². Zn-I₂ batteries using the PCS electrolyte retained 82.9% capacity after 10,000 cycles at 5 A g⁻¹. Gao et al. [60] proposed a novel inorganic high-concentration colloidal electrolyte (HCCE) induced by palygorskite nano-inorganic materials to replace the commonly used liquid electrolytes in aqueous zinc-ion batteries. Palygorskite has an intermediate structure between chain-like and layered structures, featuring a 2:1 layer-chain microstructure with fibrous morphology and channels extending parallel to the fiber length. The fibers vary in size but are primarily 1–2 µm in length and 20–70 nm in diameter. Lattice dislocations and strong Zn²⁺ adsorption reduce the tight hydration sheath around water molecules (Figure 7h). Based on HCCE, the desolvation energy barrier of hydrated Zn²⁺ on the surface was only 32.3 kJ mol⁻¹, nearly 1.7 times lower than that of conventional liquid electrolytes (52.5 kJ mol⁻¹), indicating high electrolyte-electrode kinetics. Thus, HCCE not only achieved ionic conductivity comparable to liquid electrolytes but also exhibited a higher Zn²⁺ transference number (t⁺ = 0.64). HCCE established protective layers on both anode and cathode surfaces, inhibiting Mn dissolution and enabling dendrite-free Zn anodes. The Zn/HCCE/α-MnO₂ battery demonstrated high durability at both high and low current densities, with nearly 100% capacity retention (290 mAh g⁻¹) after 400 cycles at 200 mA g⁻¹ and 89% capacity retention (212 mAh g⁻¹) after 1000 cycles at 500 mA g⁻¹ (Figure 7i). Considering material sustainability and battery performance, colloidal electrolytes may provide a viable alternative to liquid and solid-state electrolytes for zinc-ion batteries. These gel electrolytes demonstrate synergistic improvements in ionic transport, mechanical robustness, and interfacial stability, offering viable alternatives to liquid and solid-state systems for sustainable, high-performance zinc-ion batteries.

To sum up, mineral-based materials have shown clear potential in optimizing electrolyte performance to address these issues. While traditional aqueous electrolytes offer high ionic conductivity, they are prone to triggering side reactions. By introducing mineral-based additives to prepare solid-state electrolytes, interfacial reactions can be regulated, effectively suppressing dendrite growth and reducing cathode dissolution. Solid-state electrolytes, with reduced free water content, significantly mitigate water-induced side reactions and hydrogen evolution. Additionally, mineral materials can be used to construct stable ion transport channels. Gel electrolytes, relying on polymer networks to immobilize water, enhance mechanical strength and interfacial stability, while the incorporation of mineral nanoparticles improves ion transport capabilities. These optimization strategies, combined with the unique properties of mineral materials, contribute to enhancing the cycling life, rate performance, and interfacial stability of AZIBs. Future research should focus on further optimizing the ion transport kinetics and interfacial stability of electrolytes to advance their application in large-scale energy storage systems.

6. Conclusions

AZIBs hold immense potential for next generation rechargeable batteries, especially the ones used in scale energy storage, yet their practical deployment is hindered by challenges such as dendrite growth, cathode dissolution, and electrolyte instability. This review systematically summarizes the pivotal role of natural mineral materials in addressing these limitations across battery components. In anode engineering, mineral coatings (e.g., halloysite, montmorillonite) effectively homogenize Zn²⁺ flux, suppress dendrite formation, and mitigate corrosion through structural regulation and surface charge modulation. For cathode stabilization, mineral-based composites (e.g., kaolinite-modified interfaces, vanadium-sepiolite hybrids) inhibit transition metal dissolution while enhancing conductivity and structural integrity. Separator modifications using mineral frameworks (e.g., halloysite-coated glass fiber, dickite-enhanced membranes) improve mechanical strength, regulate ion transport, and block dendrite penetration. In electrolyte systems, mineral additives (e.g., montmorillonite-confined water, kaolinite-based quasi-solid electrolytes) suppress parasitic reactions, reduce water activity, and enhance ionic conductivity, while mineral-reinforced gel electrolytes demonstrate exceptional flexibility and interfacial stability for wearable applications.

In addition, there is still enormous room to further exploit natural minerals in AZIBs. To propel the field toward commercialization and maximize the potential of natural minerals in AZIBs, several critical research directions need to be prioritized. These directions not only address existing gaps but also align with global sustainability goals and technological advancements.

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Multifunctional Mineral Design: Future studies should focus on engineering minerals with dual or multi-functional properties. For instance, montmorillonite could be chemically modified to simultaneously act as a Zn²⁺-selective membrane and a host to load catalysts for suppressing hydrogen evolution. Integrating redox-active mineral phases (e.g., MnO₂-bearing clays) into cathodes could enhance energy density while stabilizing Mn³⁺/Mn⁴⁺ redox couples. Such multifunctionality would streamline battery architecture and reduce reliance on auxiliary additives, improving cost-effectiveness.

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Scalable and Sustainable Synthesis: To authentically realize the environmental benignity of natural minerals, the extraction and processing must conform to green chemistry principles. Innovations in low-energy mineral purification (e.g., bioleaching, mechanochemical activation) and scalable coating techniques (e.g., roll-to-roll deposition for separators) are desirable. Additionally, leveraging abundant, underutilized minerals could reduce dependency on rare resources. Life cycle assessments should guide the development of closed-loop systems for mineral recycling, minimizing environmental footprints.

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Comprehensive and Deeper Understanding: While remarkable progress has been achieved in leveraging mineral materials for AZIBs, concerted efforts are still required to deepen insights into this field. For instance, numerous studies have relied on binders like PVDF to integrate minerals with battery components, yet the impact of these polymers is underexplored. In addition, the complicated micro-nano architectures of natural minerals warrant deeper analysis of their interaction with active materials, electrolytes, and even side-reaction products. Notably, beyond the benefits from minerals, their potential adverse impacts—such as the clogging of mineral-derived nanopores by side products or electrolyte components—also need to be systematically evaluated. A deeper understanding will clarify mineral functionalities and guide the design of advanced AZIBs.

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Advanced Characterization and Modeling: A deeper understanding of mineral-electrolyte-electrode interactions requires cutting-edge characterization tools. Operando techniques such as synchrotron X-ray tomography and in situ Raman spectroscopy can map dynamic processes like Zn²⁺ transport in halloysite nanotubes or Mn dissolution at kaolinite-modified interfaces. Computational modeling, including density functional theory (DFT) and molecular dynamics (MD), could predict ion migration barriers in mineral frameworks and optimize interfacial charge distribution. These insights will accelerate the rational design of mineral-enhanced systems.

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Synergistic Integration with Emerging Technologies: Combining mineral materials with advanced manufacturing methods could unlock novel architectures. For example, 3D-printed dickite scaffolds might guide spatially controlled Zn deposition, while AI-driven material discovery could identify optimal mineral-polymer hybrids for flexible electrolytes. Hybrid systems integrating mineral-coated anodes with solid-state electrolytes or redox mediators could further enhance energy density and safety.

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Long-Term Stability and Real-World Testing: Rigorous validation under practical conditions is imperative. Testing should include high areal capacity electrodes (>5 mAh cm⁻²), wide temperature ranges (−20°C to 60°C), and prolonged cycling (>10,000 cycles). Accelerated aging protocols and failure mode analysis will clarify degradation mechanisms in mineral-based components. Field trials in grid-scale storage or electric vehicles will provide actionable feedback for iterative improvements.

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Circular Economy Approaches: Developing circular strategies for mineral recovery and reuse is critical. For instance, spent montmorillonite separators could be regenerated via acid washing, while dissolved Mn²⁺ from cathodes might be adsorbed and recycled using mineral adsorbents. Upcycling mineral waste (e.g., mining byproducts) into battery components could further align AZIBs with circular economy principles.

In sum, by bridging the unique advantages of natural minerals with innovative engineering strategies, AZIBs are expected to achieve unprecedented performance, stability, and cost-effectiveness, paving the way for next-generation energy storage systems. Collaborative efforts among material scientists, electrochemists, and industrial partners will be pivotal in translating these advancements from the laboratory to real-world applications.