Research and Application Progress of Aerogel Materials in the Field of Batteries and Supercapacitors

Abstract

Aerogels, characterized by their exceptional porosity, vast specific surface areas, minimal density, and unparalleled thermal insulation capabilities, have become a focal point of attention in the energy sector over the past decade, particularly in the realms of batteries and supercapacitors. This comprehensive review delves into aerogels and their preparation methods, while reviewing their recent applications in batteries and supercapacitors. It delves deeply into the research and development progress, as well as the application advancements of aerogel materials in separators, electrolytes, and electrodes. Furthermore, this article highlights that the research on aerogels still faces some challenges, such as steep costs, sophisticated production steps, and relatively weak overall mechanical strength. Therefore, in the future, it is necessary to further strengthen the fundamental research and technological innovation of aerogel materials, and promote their industrialization process and wide application in the field of energy storage, particularly in the areas of batteries and supercapacitors.

1. Introduction

Aerogels embody lightweight solid materials composed of nanoparticles or nanowires that aggregate to form a nano-scale framework and nanoporous network structure, with the pores filled with a gaseous dispersed medium [1,2,3]. In 1931, Kistler [4] successfully synthesized SiO₂ aerogel by drying SiO₂ wet gel under supercritical conditions. Aerogels are among the lowest-density solids in the world, with densities as low as 1 kg/m³, which exhibit an extremely high porosity, which can reach 80% to 99.8% [5]. This means that a significant portion of the aerogel’s volume consists of pores. These pores act as barriers to heat conduction, effectively inhibiting the transfer of heat. Consequently, aerogels possess extremely low thermal conductivity, with a room-temperature vacuum thermal conductivity of 0.001 W/m·K, making them one of the most efficient thermal insulation materials [6,7]. Additionally, aerogels have a tremendous specific surface area, reaching up to 2000 m²/g, which provides abundant surface reaction and adsorption sites [8,9,10,11].

Aerogels, categorized based on their composition, preparation methods, and microstructure, come in various types. (1) By composition, these include inorganic aerogels, organic aerogels, and composite aerogels, etc. Inorganic aerogels are composed primarily of inorganic substances. Common inorganic aerogel materials include silica aerogels [12], alumina aerogels [13], carbon aerogels [14], graphene aerogels [15], and Mxene aerogels [16]. Inorganic aerogels are generally manufactured utilizing sol–gel methods or supercritical drying and are characterized by low density, high specific surface area, and excellent thermal insulation properties. They find widespread applications in thermal insulation materials, adsorbents, catalysts, and other fields. Organic aerogels are prepared primarily from organic substances and can be further divided into synthetic organic aerogels [17] and biomass-derived aerogels [18]. Organic aerogels exhibit good flexibility, plasticity, and processability, making them suitable for applications in flexible electronics, catalyst supports, acoustic materials, and other areas. Hybrid aerogels are composites consisting of two or more single-component aerogels or aerogel matrices reinforced with fibers, whiskers, nanotubes, etc. [19]. (2) By microstructure, aerogels can be classified into microporous aerogels, mesoporous aerogels, and mixed porous aerogels. Microporous aerogels have pore sizes smaller than 2 nm. Mesoporous aerogels have pore sizes ranging from 2 nm to 50 nm. Mixed porous aerogels possess both micropores and mesopores. Aerogels can also be classified based on other characteristics such as density, mechanical properties, and optical properties. The diverse classification methods reflect the different physical and chemical properties of various aerogel types, each suited for distinct application areas.

Aerogels, as a type of nano-scale porous solid novel material, enjoy numerous varieties of applications in fields including thermal insulation, energy storage, biomedicine, pollutant removal, aerospace, sound absorption, and many others [20,21,22], as shown in Figure 1. Firstly, as one of the best thermal insulation materials, aerogels possess an extremely low thermal conductivity, effectively hindering heat conduction, convection, and radiation. This renders aerogels widely applicable in aerospace, energy-efficient building construction, and chemical industries. For instance, aerogels can be combined with ordinary glass to create highly efficient thermal insulation composites, enhancing energy-saving and insulation effects in the building sector. Additionally, aerogels can be used as the covering layer of solar collectors, enhancing the utilization of solar energy. Secondly, aerogels demonstrate immense potential in energy storage devices. In particular, conductive polymer aerogels, with their three-dimensional interconnected structures, offer large specific surface areas, providing superior conductive pathways for charge transport. This material is suitable for electrodes in supercapacitors, lithium-ion batteries, and other energy storage devices, boasting high conductivity and large surface areas, thereby enhancing device performance. Thirdly, aerogels hold promising applications in biomedicine. Organic and carbon aerogels, due to their biocompatibility and biodegradability, can be utilized in the production of diagnostic agents, artificial tissues, organs, and organ components. Furthermore, aerogels can be employed in drug controlled-release systems, whereby special degradation properties can be achieved through controlled preparation conditions. These aerogels degrade after a stable existence in the biological environment as needed, with non-toxic degradation products. Fourthly, aerogels play a crucial role in environmental protection. Their exceptional adsorption capabilities make them excellent materials for addressing ecological disasters. For example, aerogels can adsorb harmful gasses and organic compounds from the air, purifying the atmosphere. They also have potential applications in wastewater treatment. Fifthly, aerogels find extensive use in aerospace. They can be utilized in the creation of Mars exploration spacesuits, providing effective thermal protection for astronauts. Additionally, aerogels can be incorporated into bulletproof materials, enhancing the safety of military equipment. Beyond these fields, aerogels are also significant in electronics, optics, and acoustics. In electronics, aerogels can be used to produce dielectric materials with low dielectric constants, addressing issues like crosstalk, interconnection delays, and increased power loss within circuits. In optics, aerogels are suitable for high-transparency optical components and devices. In acoustics, aerogels serve as acoustic delay or high-temperature sound insulation materials. In summary, aerogels, with their superior properties, exhibit broad application prospects across various fields. As technology advances and costs decrease, the application areas of aerogels will continue to expand and deepen.

Alternatively, energy storage solutions hold paramount importance in modern energy systems, where they not only reconcile energy supply and demand disparities but also elevate energy usage efficiency and catalyze the expansion of renewable energy technologies [23]. As the worldwide appetite for clean energy intensifies, the exploration and deployment of energy storage technologies have emerged as a central area of concentration and interest. In the field of energy storage, aerogels also play an important role. Firstly, aerogels exhibit highly efficient energy conversion capabilities attributed to their outstanding physical and chemical characteristics, including extensive porosity, reduced mass, low heat conductivity, and significant surface area. These characteristics make aerogels ideal materials for energy conversion processes. In fields such as photothermal conversion and electrothermal conversion, aerogels can significantly enhance energy conversion efficiency and reduce energy losses. Furthermore, aerogels enhance energy storage capacity by providing ample space for energy storage through their porous structures. Regarding the accumulation of thermal energy and the electrochemical storage of energy, aerogels significantly improve energy storage density and cycle stability and extend the lifespan of energy storage devices. Beyond their direct applications in energy conversion and storage, aerogels can also be composited with other materials to impart additional functional properties to the composites. These advanced functionalities offer limitless possibilities for the widespread application of aerogels in the energy sector. The mechanisms underlying aerogels’ role in energy conversion and storage are primarily manifested in four aspects: (1) Photothermal Conversion Mechanism: Aerogels, with their porous structures and high specific surface areas, can efficiently absorb sunlight and convert it into thermal energy. (2) Electrothermal Conversion Mechanism: In electrothermal conversion, aerogels serve as electrode materials or electrolyte carriers, facilitating the process where electrical energy is converted into thermal energy through electron or ion transport. The porous characteristics of aerogels contribute to the rapid transport of electrons or ions, thereby enhancing electrothermal conversion efficiency. (3) Thermal Energy Storage Mechanism: Aerogels’ low thermal conductivity effectively prevents heat loss, enabling them to store thermal energy. In phase change energy storage, aerogels act as support matrices for phase change materials, preventing leakage during phase transitions and enhancing energy storage density. When thermal energy needs to be released, the porous structure of aerogels facilitates uniform heat distribution and rapid release. (4) Electrochemical Energy Storage Mechanism: In electrochemical energy storage systems like lithium-ion batteries, aerogels serve as carriers for anode/cathode materials or electrolytes. Their porous structures contribute to rapid lithium-ion insertion and extraction, thereby improving battery energy density and cycle life. Additionally, aerogels can function as catalyst supports, enhancing electrochemical reaction rates and efficiencies within batteries. In conclusion, the significance of aerogels in energy conversion and storage lies in their efficient, stable performance, and multifunctionality. Their unique mechanisms render aerogels highly promising and valuable for extensive research and application in the energy field.

Consequently, in this paper, we have primarily focused on outlining the commonly used synthesis methods for aerogels, encompassing five key approaches, the sol–gel method, templating method, self-assembly, electrospinning, and 3D printing, as shown in Figure 1. Building upon this foundation, we have further elaborated on the progress made in the application of aerogels in batteries and supercapacitors. For instance, aerogels have been applied in separators, solid electrolytes, and electrodes, exhibiting functionalities such as thermal insulation and protection, the suppression of sulfur shuttling, the inhibition of lithium dendrite growth, enhancement in thermal stability, and providing rapid ion transport pathways. This review enhances our understanding of the distinctive characteristics of aerogel materials and their tailored applications within the realm of energy storage, providing strong support for the research and application of energy storage technologies.

2. Preparation Methods of Aerogels

There are various methods to obtain aerogel materials, including the sol–gel method, templating method, self-assembly, electrospinning, and 3D printing. The choice of the appropriate preparation method is typically based on factors such as the nature of the raw materials, the desired aerogel structure, and the intended application scenario.

2.1. Sol–Gel Method

The sol–gel technique represents a pivotal methodology for the fabrication process of porous inorganic or organic polymeric materials under relatively mild conditions [24]. As a type of wet chemistry, it holds a prominent position in chemical synthesis and finds extensive applications in the field of functional composite material fabrication. The chemical process begins with the dispersion of alkoxide-based precursors in a solvent, followed by a hydrolysis reaction under certain conditions to form active monomers. These monomers then undergo polymerization, catalyzed by either an acid or base, to initially form a sol. This sol further ages into a gel with a network-like spatial structure, which is then subjected to drying or heat treatment to obtain the desired porous material [25,26]. The sol–gel method boasts several unique advantages: Firstly, the gel precursors are initially dispersed in the solvent to form a homogeneous phase, facilitating molecular-level uniformity. Secondly, doping at the molecular level is readily achievable since the sol process takes place in a solution. Lastly, compared to solid-state reactions, the diffusion of components within the sol–gel system occurs at the nano-scale, enabling relatively mild reaction conditions.

Zhou et al. [25] prepared a unique high-surface-area porous material, MXene/SiO₂ hybrid aerogel, through a combination of the sol–gel method. The as-prepared samples exhibit a three-dimensionally interconnected and integrated network architecture where SiO₂ is crosslinked with two-dimensional MXene. The MXene/SiO₂ hybrid aerogel exhibited outstanding electrochemical performance, including a high discharge capacity of 823 mAh g⁻¹ after 200 cycles at 0.5 C. Parale et al. [26] utilized a sol–gel method to prepare NiCo₂S₄ nanoporous aerogels using two-dimensional g-C₃N₄ nanosheets as carriers, designing a 3D macroporous aerogel, as shown in Figure 2. The method both incorporated NiCo₂S₄ and organized the two-dimensional g-C₃N₄ into a three-dimensional network resembling a sandwich. The composite aerogel electrode 3D NiCo₂S₄/g-C₃N₄ (3%) showed a high value of 1083 F·g⁻¹ at 5 mA·cm⁻², with 87.03% cycling stability retained.

The sol–gel technique belongs to the realm of wet chemistry methodologies and is relatively easy to scale up for continuous production. However, the sol–gel method still faces several challenges: Firstly, metal alkoxides are commonly used as precursors, which are relatively expensive, and the raw materials often contain a significant amount of organic molecules or functional groups that are harmful to humans. Secondly, the preparation process is time-consuming, often requiring several days to a week to complete, from the sol–gel formation to solvent exchange and drying. Furthermore, due to the abundance of micropores in the gel material, conventional drying processes tend to damage the porous structure of the gel, leading to the pore collapse and destruction of the original gel structure. Therefore, the gel material has stringent requirements for drying equipment conditions, and expensive equipment including supercritical drying or freeze-drying is typically used [27].

2.2. Template Method

The template method involves using substances with ordered nanostructures, easily controlled shapes, and low costs as templates. The precursors of the target material are deposited into the templates through physical or chemical methods, and then the templates are removed to obtain the desired nanocomposites with specific micro-morphologies and chemical compositions [28,29,30,31]. Based on the composition and characteristics, this technology can be segmented into soft templates and hard templates. Soft templates typically refer to microscopic structures formed by surfactant molecules aggregated according to certain rules, such as vesicles, micelles, and microemulsions. Hard templates, on the other hand, mainly refer to rigid templates, including polymeric polymers, porous silicon, and carbon. The template method is an important approach for synthesizing nanocomposites, allowing the design of template structures and sizes according to the performance and structural requirements of the desired materials, thereby meeting actual needs.

Du et al. [30] utilized SiO₂-NH₂ particles as templates to prevent the π–π stacking, thereby creating N-doped rGO aerogels, as shown in Figure 3. These resulting rGO aerogels, featuring a three-dimensional hierarchical structure, possess a high surface area (481.8 m²/g). The as-prepared samples exhibit outstanding performance, achieving a capacitance value of up to 350 F/g and maintaining a remarkable capacity maintenance of 88% even after undergoing 10,000 cycles, indicating a prolonged service life. Chang et al. [31] successfully prepared graphene oxide composite phenolic resin carbon aerogel (GO/PFCA) with a layered structure using the template method. The optimized PFCA-7.5/8 exhibited a high electrochemical performance of 138.33 F g⁻¹ at 5 mV s⁻¹.

2.3. Self-Assembly

In recent years, with the rise in nanotechnology research, self-assembly techniques have gradually become a research hotspot in the surface chemistry field, finding widespread applications in the manufacture of functional nanomaterials for energy, environmental, optical device, information transmission, biomedical, and other fields [32,33,34]. This method relates to the technique whereby basic units spontaneously connect and form polymers with specific arrangement sequences and stable structures through a large number of weak interactions, such as electrostatic attraction, coordination bonds, hydrogen bonds, and so forth. However, self-assembly also has drawbacks such as a long duration and insufficient process control stability.

2.4. Electrospinning

With the advancement in nanotechnology, electrospinning has rapidly emerged as a convenient and effective novel processing technique for producing nano-polymer fiber aerogels. During the electrospinning process, a polymer fluid is electrostatically atomized and ejected into a fine stream, where the solvent evaporates during the ejection, ultimately solidifying into a nonwoven-like fiber that further crosslinks to form an aerogel [35,36]. Zhang et al. [37] successfully prepared a modified polyacrylonitrile/silica aerogel separator utilizing electrospinning techniques. The hydrolysis of cyano groups and the in-situ growth of silica particles enhanced the chemical stability of the polyacrylonitrile nonwoven material. The half-cell with the as-prepared separator exhibited high-rate capacity (85.15 mA h g⁻¹ at 5 C), and maintained a remarkable capacity maintenance of 96.9% after 1000 cycles at 5 C. Electrospinning technology enables the direct and facile production of desired polymer nanofibers in a one-step process, highlighting the necessity for further development of this technology. However, the current electrospinning technology is still immature and faces numerous limitations. For instance, while nanofibers can be manufactured through electrospinning, achieving well-separated nanofibers remains challenging. Additionally, the fibers produced by electrospinning often exhibit low crystallinity and poor strength. Furthermore, there is room for improvement in electrospinning setups regarding voltage, nozzle design, and alignment collectors. Addressing these shortcomings is crucial for enhancing the capabilities and application prospects of electrospinning technology.

2.5. Three-Dimensional Printing

Three-dimensional aerogels refer to aerogel materials fabricated using 3D printing technology. This material combines the low density, high porosity, and excellent thermal insulation properties of aerogels with the precision and customization capabilities of 3D printing [38,39,40,41,42,43]. Through 3D printing, the precise manipulation of aerogel structure is achievable, enabling highly customized designs. This makes it possible to manufacture functional components or structures that meet specific requirements, such as complex insulation materials, filters, or lightweight structural components. Moreover, aerogels inherently possess very high porosity and large surface areas, and 3D printing can further optimize the pore structure by precisely controlling pore size, distribution, and connectivity to meet various application needs. The flexibility of 3D printing technology also allows for the integration of different materials or material combinations into aerogels, achieving multifunctionality such as altering thermal conductivity, electrical conductivity, or mechanical properties. Yuan et al. [41] prepared a GO/PAA gel using polyamic acid (PAA) salt as a crosslinking agent, which could serve as printing ink for direct ink writing (DIW)-based 3D printing. The numerous hydrogen bonds between PAA and GO promote the formation of a crosslinking network, ensuring that the GO/PAA exhibits a high modulus and moldability even at low GO concentrations (25 mg mL⁻¹). The GO/PAA provides rapid electron and ion transport. This supercapacitor exhibits exceptional areal capacitance (59.1 mF cm⁻²).

Liu et al. [43] introduced a multilevel heterogeneous interface engineering design approach to enhance polarization loss and improve electromagnetic energy dissipation properties. They constructed a graphene aerogel with a grid-stacked structure as the conductive skeleton using a 3D printing strategy. Through a solvothermal reaction, nano-needle-like and nano-flake-like structures of the metal oxide NiCoO₂ were grown in situ on graphene’s surface, as shown in Figure 4. The study found that the growth of NiCoO₂ metal oxide generated a large number of heterogeneous interface regions, enhancing the polarization loss capability of the material.

Although 3D aerogel technology brings numerous advantages in material design and manufacturing, challenges such as printing speed, material selection, precise control of the printing process, and post-processing steps need to be considered.

3. The Application of Aerogels in Batteries and Supercapacitors

3.1. Used as Separators

A separator is an essential element in the construction of batteries and capacitors. Despite not participating in electrochemical reactions, it plays a pivotal role throughout the entire operation process [44]. However, the commonly employed commercial polyolefin separators are plagued by certain inherent limitations, notably their inferior heat resistance capabilities, flammability, and insufficient wettability, limiting the application [45]. Aerogel separators, on the other hand, feature a porous structure with a multitude of micropores and mesopores, exhibiting properties like porosity, a lightweight nature, and high specific surface area. As separators, they can serve essential functions including isolation, thermal insulation, electrolyte conduction, improved puncture resistance, and thermal stability, thereby playing a crucial supporting role in enhancing battery performance and safety [46,47,48,49].

3.1.1. Heat Insulation Protection

Thermal runaway is the primary cause of safety accidents in power batteries [44]. At high energy densities, factors such as battery lot consistency, the thermal stability of materials, the compatibility between battery components, and the high flammability of electrolytes can all lead to battery fires or explosions. Aerogels, with their unique nanoporous structure, exhibit outstanding thermal insulation properties. In energy storage devices, effective thermal management is crucial for preventing overheating, improving safety, and extending service life. As thermal barrier materials, aerogels can effectively isolate and slow down heat transfer within the battery, ensuring the stable operation of the energy storage system. Feng et al. [46] obtained a composite (SAC) separator by combining silica aerogel with polypropylene (PP), exhibiting a 30% higher area retention rate compared to PP after undergoing heating at 160 °C for 30 min.

To address the issue of traditional separators being susceptible to high temperatures, Kim et al. [47] proposed a novel separator with a dual-layer functionality. This new composite separator was fabricated by coating porous polyethylene with thermally imidized polyimide aerogel (PIA). Compared to commercial PE separators, the newly proposed separator displays minimal or negligible thermal contraction, while commercial PEs suffer from high thermal shrinkage rates and struggle to maintain their structure at temperatures of 140 °C. After heat treatment, the as-prepared sample remains virtually unchanged. This demonstrates that the composite separator averts battery detonations and safeguards against overcharging. Liu et al. [48] successfully prepared a flexible aramid nanofiber through a simple and mild strategy. This ANF aerogel separator boasts high porosity (86.5% ± 6.1%). This as-prepared separator exhibits excellent fire resistance and thermal stability, with a T5% (temperature at 5% weight loss) of 504 °C. When used in batteries operating at 90 °C, the sample enables very stable charge–discharge cycles, retaining a coulombic efficiency of 99.6% over 200 cycles at 3 C.

Due to their superior heat resistance (exceeding 300 °C), robust chemical stability, and remarkable mechanical prowess, polyimide separators are regarded as the cutting-edge separators of the future generation. Deng et al. [49] prepared a novel PI aerogel (PIA) separator with uniform porosity, high-temperature resistance, and superior electrochemical performance, as shown in Figure 5. The remarkable porosity (78.35%) and electrolyte absorption (321.66%) of the PIA separator contribute to low internal resistance and excellent electrochemical performance in LIBs, which retain a high specific capacity of 118 mAh g⁻¹ after 1000 cycles at a current density of 1 C. The PIA separator was employed in LiFePO₄|Li metal batteries, demonstrating exceptional long-term cycling performance, stable C rate capability, and high-temperature stability. Additionally, the PIA separator supports stable cycling of lithium metal anodes with an areal capacity of 1 mAh cm⁻² and effectively inhibits dendrite growth. The PI fiber separator obtained through chemical crosslinking, instead of traditional thermal imidization, further enhances its high-temperature resistance, with a thermal decomposition temperature of 500 °C, significantly higher than that of the PI fiber separator (326 °C). The PIA separator can effectively improve the thermal safety of batteries, exhibiting a 30% higher thermal runaway temperature compared to Celgard 2400 separators (Jiangxi Xiancai Nanofiber Technology Co., Ltd., Nanchang, China).

3.1.2. Inhibition of Shuttle Effect

The shuttle phenomenon of soluble intermediate lithium polysulfides can cause the loss in active materials and slow down the redox reaction rate, thereby adversely affecting the cycle stability and rate performance of lithium-sulfur batteries. Therefore, inhibiting the shuttle effect in lithium-sulfur batteries is of great importance [50,51]. In recent years, scientists have discovered that the use of aerogel separators can effectively suppress the shuttle effect [52,53,54,55]. Meng et al. [52] modified polypropylene with Ti₃C₂T_x aerogels to address the shuttle effect issue in lithium-sulfur batteries. The unique structure can prevent the restacking of 2D Ti₃C₂T_x, thereby exposing more surfaces. Due to the high conductivity of the Ti₃C₂T_x surface, it also enhances the reaction kinetics. The Ti₃C₂T_x separator both inhibits the shuttle effect and accelerates the redox kinetics of polysulfides. The Li-S battery, equipped with an aerogel-modified separator, showcases an impressive initial discharge capacity of 1487 mAh g⁻¹ at 0.1 C, and demonstrates exceptional cycling endurance with a minimal capacity fade of just 0.037% over more than 1500 cycles at 1 C. Zhu et al. [53] successfully obtained nitrogen-doped carbon aerogels (NHCAs) with coral-like structures and ultra-high specific surface areas. The preparation process is illustrated in Figure 6. The introduction of NHCA serves a dual purpose: it effectively hinders the polysulfide shuttle effect and concurrently constructs a low-impedance conductive pathway between the cathode and separator. To maximize the inhibition of polysulfide shuttle effects, Tan et al. [54] proposed a dual capture strategy to confine sulfur species within the cathode chamber. They applied manganese dioxide (MnO₂)-modified graphene aerogels (MG) to modify commercial Celgard separators (MG@Sep) and prepared I/N co-doped graphene aerogels (ING) as cathode sulfur carriers. The ING/S cathode proficiently confines sulfur species owing to the augmented polar surface of ING, whereas the MG@Sep separator functions pivotally in capturing polysulfides and mitigating the shuttle effect, thereby enhancing battery performance.

To concurrently hinder the shuttling phenomenon of lithium polysulfides and expedite the sulfur reduction reaction process, Liu et al. [55] proposed the concept of a multifunctional separator and designed a composite separator to boost the capacity retention, cycling stability, and electrochemical reactivity of lithium-sulfur batteries. Attributed to the combined benefits of zinc sulfide and rGO aerogel, the lithium-sulfur battery featuring a zinc sulfide-rGO aerogel/polypropylene separator displays an impressive initial capacity of over 800 mAh g⁻¹ and outstanding cycle stability, experiencing minimal decay of just 0.1% per cycle over 500 cycles at a 1 C rate. Remarkably, even at a high sulfur loading of 3.1 mg cm⁻², the battery sustains a robust initial specific capacity of 590 mAh g⁻¹ and retains 92.5% of its capacity after 200 cycles at a 0.5 C rate.

3.1.3. Suppressing Lithium Dendrites

Aerogel separators occupy a pivotal position in mitigating the growth of lithium dendrites within lithium-ion batteries, thereby enhancing their overall safety and performance [56,57,58]. The lithium metal electrode is prone to the formation of dendritic structures made up of metallic lithium during charging and discharging due to uneven deposition or uneven ion transport in the electrolyte. These lithium dendrites can penetrate the separator, leading to safety concerns and issues with battery cycle life. Aerogel separators effectively modulate the flow rate and uniform distribution of the electrolyte, thereby enhancing the ionic diffusion efficiency within the battery system. Ding et al. [56] developed a polyimide aerogel (PIA) featuring a meticulous nitrogen (N) functionalization, serving as an innovative separator for lithium metal batteries. The adoption of PIA separators significantly boosts the rate capability of lithium metal batteries (LMBs) in comparison to conventional polypropylene (PP) separators. In Li||Cu half-cell setups, the PIA separators demonstrate improved repeatability in the lithium deposition and stripping processes throughout multiple charge–discharge cycles (RCE), achieving a steady average coulombic efficiency (CE) of 91% over the course of 80 cycles. This distinctive blend of chemical design and hierarchical porosity enables the separator to modulate the interfacial lithium nucleation dynamics, enhancing battery performance. Sheng et al. [57] reported a novel self-supporting aramid nanofiber aerogel film, as shown in Figure 7. This innovative separator promotes the even distribution of lithium deposition and effectively prevents undesirable side reactions between the liquid electrolyte and Li metal during the charge–discharge process. Moreover, the surface-enhanced partial dealloying phenomenon facilitates the electron capture and reduction of Li⁺ ions into Li metal. Yin et al. [58] prepared a three-dimensional CNT/Ti₃C₂T_x aerogel to modify commercial lithium-sulfur battery separators. This uniquely designed highly porous 3D aerogel structure prevents the restacking of its layers, exposing more active sites of Ti₃C₂T_x. Lithium-sulfur batteries assembled with CNT/Ti₃C₂T_x aerogel-modified separators exhibit excellent discharge capacity, long cycle life, and outstanding rate performance. Consequently, lithium-sulfur batteries using CNT/Ti₃C₂T_x aerogel-modified separators demonstrate high-rate capacity, reaching 1043.2 mAh g⁻¹ at a 2 C rate, and exceptional cycle life with over 800 cycles at 0.5 C.

As a critical component of batteries, the application of aerogel separators has significantly improved battery performance and safety. They hold significant potential and research value in enhancing battery safety, cycle life, and performance stability. The literature summary in

Table 1. A summary of discharge capacities of aerogel-based separators in the referenced works.

Separator Material	Capacity	Cycle	Rate	Ref.
ANFs	102 mA h/g	600	5 C	[48]
PIA	118 mA h/g	1000	1 C	[49]
Ti3C2Tx Aerogel	423 mA h/g	1500	1 C	[52]
MG@Sep	902 mA h/g	200	0.2 C	[54]
Graphene Aerogel/Polypropylene	590 mA h/g	200	0.5 C	[55]
PIA	86.1 mA h/g	200	1 C	[56]
CNT/Ti3C2Tx	582.8 mA h/g	800	0.5 C	[58]

comprehensively details the utilization of aerogels as separator materials for batteries. This table offers a concise snapshot of pivotal studies, emphasizing the specific aerogel materials that have been utilized, their impact on discharge capacity, and their cycling stability.

Aerogels hold broad prospects and potential in separator applications, yet they also confront numerous challenges, particularly in terms of film-forming properties and mechanical strength. While their high porosity enhances thermal insulation, it simultaneously compromises their film-forming capability and mechanical strength. In separator applications, it is imperative that aerogel separators possess adequate flexibility and tensile strength to withstand the mechanical stresses during battery charging and discharging. Therefore, improving the film-forming properties and mechanical strength of aerogels is another critical issue to address. With the continuous advancement in preparation technologies and deepening research, it is believed that the performance of aerogels in separator applications will continue to enhance, further expanding their fields of application.

3.2. As Solid-State Electrolytes

Solid-state electrolytes are substances that can conduct ions in a solid form. They are typically composed of inorganics, polymers, or their composites, featuring a three-dimensional network structure filled with tiny pores and channels. These pores and channels provide pathways for ion transport, enabling aerogel solid-state electrolytes to achieve efficient ion conduction in the solid state. The absence of flammable liquid electrolytes significantly reduces safety risks associated with batteries, such as leakage, combustion, and explosions. Currently, solid-state electrolytes have emerged as core materials for high-performance electrochemical storage devices and batteries, with wide applications in energy, electrical engineering, sensors, and other fields [59,60,61,62,63,64,65]. Su et al. [59] designed a three-dimensional carboxymethyl cellulose lithium aerogel, serving as a highly conductive supporting scaffold for poly(ethylene oxide) (PEO)-lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-succinonitrile (SN) electrolytes. The modified electrolyte demonstrates an impressively low melting point of 30.43 °C, accompanied by a robust tensile strength of 3.85 MPa, along with several advanced properties that have been significantly improved. Da et al. [60] prepared a low-density, self-supporting, double-layered aramid nanofiber (ANF) aerogel with dual crosslinking degrees through a novel carbon dioxide-assisted induced self-assembly method, as shown in Figure 8. The functionalized ANFs regulate ion channels, enabling dendrite-free and uniform lithium deposition, which leads to stable long-cycle performance (1400 h) in symmetric cells. As a result, the Li|PAL|LiFePO₄ (LFP) battery demonstrates remarkable durability with over 700 cycles at 1 C while maintaining an exceptionally high coulombic efficiency of greater than 99.8%, underscoring its superior long-term cycle stability. To enhance low-temperature stability, Wang et al. [61] utilized an aerogel-reinforced skeleton to develop a novel hydrogel electrolyte. The hydrogel electrolyte displays exceptional antifreeze properties with an ionic conductivity of 1.35 S m⁻¹ at −25 °C. Employing CoNi LDH@CC and AC@CC electrodes as the cathode and anode, respectively, the SC-PANa/BC/KOH device provides a high specific capacity of 128.17 F g⁻¹ at 25 °C, retaining 78.83 F g⁻¹ at −25 °C.

The addition of inorganic fillers can provide more ion transport channels for electrolytes, improve thermal conductivity, enhance chemical and thermal stability, and further boost battery safety. Zhou et al. [62] prepared a graphene oxide aerogel/polyethylene oxide (GSPE) composite solid-state electrolyte. The GSPE demonstrates remarkable uniformity during the process of lithium deposition, a characteristic that effectively prevents battery short circuits caused by lithium dendrites, significantly enhancing the long-term stable operation capability of the battery. GSPE displays a high lithium-ion conductivity of up to 4.12 × 10⁴ S cm⁻¹ at 50 °C. Vareda et al. [63] synthesized a sodium perchlorate-doped silica-polyvinyl alcohol (PVA) composite aerogel as a novel electrolyte with potential applications in batteries. When the PVA concentration is 15% (w/w silica precursor), the sodium conductivity significantly increases to (1.1 ± 0.3) × 10⁻⁵ S cm⁻¹. Liu et al. [64] successfully crafted a hybrid solid electrolyte (SSP) composed of a succinonitrile electrolyte-infused silica aerogel and polyacrylonitrile, utilizing a straightforward and efficient method. The porous structure of silica aerogel (SAG) infiltrated with a highly conductive succinonitrile electrolyte (SNE) constructs a new fast lithium-ion transport channel within SSP, enabling rapid lithium-ion migration and a large number of freely mobile lithium ions. The NCM811/SSP/Li battery demonstrates a discharge capacity of up to 200.5 mAh g⁻¹ at 0.1 C and excellent rate performance with 80.8 mAh g⁻¹ at 5 C. Li et al. [65] prepared a nano-silica aerogel-modified quasi-solid polymer electrolyte (QPE) via rheologically modulated UV-initiated polymerization. The Lewis acid sites on the SiO₂ aerogel interact with ether oxygen (EO) groups and anions in lithium salts, reducing polymer crystallinity and increasing the number of free Li⁺, thereby enhancing ionic conductivity. The as-prepared electrolyte not only inhibits lithium dendrite growth but also contributes to improved electrochemical cycling stability.

As markets for electric vehicles, wearable devices, and other products continue to expand, the demand for batteries with high energy density, long-lasting cycle life, and exceptional safety performance is increasing. Aerogel solid-state electrolytes are expected to play a pivotal role in these areas, driving rapid development of related industries. However, a key challenge lies in the interfacial compatibility. Excessive interfacial resistance or poor contact can lead to decreased battery performance or even failure. Thus, there is a need for in-depth research on the interaction mechanisms between aerogel solid-state electrolytes and electrode materials, as well as the development of effective interface modification techniques to improve compatibility. Despite the enhanced safety of solid-state batteries compared to liquid batteries, aerogel solid-state electrolytes may still face stability issues during long-term use. Therefore, it is crucial to strengthen research and evaluation efforts on the stability of aerogel solid-state electrolytes.

3.3. As Electrodes

Aerogels possess extremely high porosity and specific surface area, enabling them to provide numerous active sites for electrochemical reactions. As the electrodes, this enhances the energy density and power density of energy storage devices. Furthermore, the high specific surface area increases the contact area between the electrolyte and electrode materials, facilitating rapid ion and electron transport [66].

3.3.1. As the Anode

To address the issue of reduced energy density caused by the excessive mass of metal support structures, Guo et al. [67] synthesized a lithium-philic graphene aerogel composed of rGO and silver nanowires (rGO-AgNW), which was used in the anode preparation process, as illustrated in Figure 9. The aerogel effectively mitigates the concentration of local current and retards the development of lithium dendrites, while the lithium-philic silver nanowires serve as platforms for achieving the uniform deposition of lithium. The rGO-AgNW/Li battery exhibits stable cycling for approximately 2000 h at a current density of 1 mA cm⁻². Equipped with a LiFePO₄ cathode, the fully assembled battery exhibits remarkable cycling endurance and high-rate capabilities. The utilization of the ultra-light rGO-AgNW aerogel as a supportive matrix for lithium metal anodes substantially boosts the energy density of these anodes.

With the emergence of more and more new materials in energy storage, scientists have increasingly paid attention to the sustainability, recyclability, and reusability of raw materials and products [68,69,70]. Pham et al. [71] created a carbon aerogel known as C-MFCA, employing microfibrillated cellulose derived from agricultural waste as the starting material. This process involved crosslinking and carbonization techniques. The final carbon-based product demonstrated remarkable electrochemical properties, featuring an initial specific charge capacity of 348.6 mAh per gram, while retaining a stable performance close to 257.5 mAh per gram even after enduring more than 100 charge–discharge cycles. Liao et al. [72] successfully crafted Co₃O₄ particles coated with nitrogen-doped carbon aerogel (denoted as Co₃O₄@NCA). By incorporating a conductive carbon aerogel matrix and designing a porous nano-micro-hierarchical architecture, the material was endowed with exceptional properties such as a vast specific surface area, superior electrical conductivity, ample pore channels, and a multitude of active sites. These attributes conspicuously boosted its ability to store lithium, resulting in significantly enhanced lithium storage capacity. Ma et al. [73] innovated a robust lithium anode by partially infiltrating molten lithium into a three-dimensional, porous graphene aerogel framework. This distinctive electrode architecture profoundly enhanced the processes of lithium plating and stripping, accomplishing a series of benefits such as decreased localized current density, suppressed dendrite formation, mitigated volume changes, and heightened lithium utilization efficiency. As a result, they were able to demonstrate outstanding cycling stability across 400 cycles (equivalent to 800 h) in symmetric cell configurations, with an exceptionally high cyclic capacity of 15 mAh·cm⁻² maintained even at a current density of 15 mA·cm⁻². Wang et al. [74] successfully crafted graphene aerogel-enveloped Co₃O₄ open microstructures (designated as Co₃O₄ microcages@GA) via straightforward etching and hydrothermal procedures, as shown in Figure 10. When evaluated as an anode material for lithium-ion batteries (LIBs), this composite demonstrated remarkable durability, maintaining a reversible capacity of 1439 mAh/g even after 200 cycles at a current density of 1 A/g. This exceptional electrochemical performance is attributed primarily to the substantial enhancement in conductivity achieved by the integration of graphene aerogel into the material.

Biomass materials possess significant potential for utilization in energy storage systems, stemming from their abundant availability, cost-effectiveness, and eco-friendliness. To alleviate the volume effect of silicon and improve its conductivity, Li et al. [75] devised a straightforward, economical, and eco-friendly method to synthesize a conductive, copper ion-reinforced sodium alginate (SA) aerogel-supported, free-standing silicon anode (Si@CNTs/Alg-Cu-II) tailored for lithium-ion batteries (LIBs). In this irregular layered porous aerogel, silicon particles were bound by the macromolecular chains and dynamic hydrogen bonds of SA and subsequently confined within the porous aerogel to release volumetric stress. Considering the entire mass of the Si@CNTs/Alg-Cu-II composite, which incorporates 25.62% silicon, this innovative structure demonstrated a remarkable capacity of 835.6 mAh/g following 100 cycles of operation at a current density of 0.1 A/g. MoS₂ semiconductor materials used for energy storage can provide higher electron transmission efficiency and better ion channels [76,77]. Wu et al. [78] implanted MoS₂-Mo₂C heterostructures into porous carbon aerogel to prepare MoS₂-Mo₂C@C aerogel with a heterostructure. When the prepared aerogel was used as an anode for LIBs, it achieved good long-term cycling stability and superior rate performance. A notable specific capacity of 598.1 mAh g⁻¹ was achieved at 2.0 A g⁻¹. The remarkable electrochemical performance of the anode can be credited to the synergistic effects of its porous architecture, vast surface area, and abundant defects within its heterostructure, all of which contribute significantly to enhancing its overall performance. In lithium-ion batteries (LIBs), cobalt oxide is considered an ideal anode material owing to its abundant resources, high specific capacity, and low cost. However, its volume expansion during charge–discharge cycles and low conductivity hinder its development. Wen et al. [79] encapsulated Co₃O₄ microcubes within graphene aerogel (GA) using a metal–organic framework (MOF) as an initial template, resulting in the formation of Co₃O₄ microcubes@GA composites. GA, which functions as a three-dimensional conductive scaffold and mechanical support, enhances the conductivity and structural robustness of the composites. After 200 cycles at 1 A g⁻¹, the Co₃O₄ microcubes@GA exhibited a discharge specific capacity of 1234.9 mAh g⁻¹ (coulombic efficiency, CE = 98.97%).

Lithium-ion hybrid capacitors (LIHCs) boast the technological advantages of high energy density, high power density, and rapid charge–discharge capabilities. Cao et al. [80] crafted a self-standing FeS@C/carbonized bacterial cellulose aerogel (FeS@C/CBC) anode specifically for LIHCs. This was achieved by initially growing MIL-88-NH₂ on a bacterial cellulose (BC) base, which was subsequently subjected to simultaneous carbonization and sulfurization processes. The resulting FeS@C/CBC anode inherits the distinctive three-dimensional, porous, and self-supporting structure of CBC. Notably, after enduring 1000 cycles at a current density of 1 A g⁻¹, this self-supporting anode demonstrated a remarkable reversible capacity of up to 669 mAh g⁻¹.

Sodium metal stands out as a promising anode material for sodium-ion batteries (SIBs), owing to its impressive theoretical capacity and wide availability. Nevertheless, its practical utilization, particularly under high current densities, is hindered by its inherent challenge of cycling instability stemming from the inevitable volumetric fluctuations that occur during cycling, which restricts its rate performance. Tian et al. [81] fabricated three distinct types of heterobimetallic selenides that were encapsulated within graphene aerogel (GA), serving as anode materials for sodium-ion batteries (SIBs). The composite material of bimetallic selenides and graphene aerogel (GA), with its unique structural characteristics such as porous octahedrons, cubes, or spheres, significantly shortens the migration paths of sodium ions (Na⁺) and accelerates the diffusion process of sodium ions and electrons. In its application as an advanced anode material for sodium-ion batteries (SIBs), the MoSe₂-Cu_1.82Se@GA composite with a porous octahedral structure has demonstrated remarkable capacity performance, achieving up to 444.8 mAh g⁻¹ after 1000 cycles at a high current density of 1 A g⁻¹. Tian et al. [82] crafted a composite material, GA@PMC, which combines graphene aerogel (GA) reinforcement with phosphorus-doped mesoporous carbon (PMC) to serve as a host for sodium storage-active nanoparticles. When deployed in conventional sodium storage devices, including sodium-ion batteries (SIBs), sodium-ion hybrid capacitors, and sodium-ion-based dual-ion batteries, the FeSe₂/GA@PMC electrode consistently demonstrated outstanding electrochemical performance. Notably, the optimized FeSe₂/GA@PMC-2 electrode retained a remarkable specific capacity of 345.1 mAh g⁻¹ even after enduring 1000 cycles at a high current density of 5 A g⁻¹ within a sodium-ion half-cell configuration. Wang et al. [83] employed direct ink writing-based 3D printing techniques to create a V₂CT_x/rGO-CNT microgrid aerogel, specifically designed to optimize the sodium plating and stripping processes in sodium metal anodes, resulting in the development of a Na@V₂CT_x/rGO-CNT anode. This intricate, hierarchical, and porous 3D structure not only ensures the stability of the electrode throughout numerous sodium plating and stripping cycles but also boasts a vast surface area that effectively reduces current density. It further provides ample active sites for sodium metal nucleation and enhances the kinetics of sodium-ion and electron transport. The study’s outcomes demonstrate the exceptional cycling durability of the V₂CT_x/rGO-CNT electrode, which sustains over 3000 h of operation (under a current density of 2 mA cm⁻² and a capacity of 10 mAh cm⁻²) with an impressive average coulombic efficiency of 99.54%. Yang et al. [84] utilized cutting-edge 3D printing techniques to fabricate a three-dimensional (3D) nitrogen-doped graphene aerogel (3DP-NGA) microlattice framework, serving as a host to facilitate uniform sodium nucleation and deposition. The nitrogen doping enhances the sodium affinity of the sites, efficiently preventing the proliferation of sodium dendrites. The resulting 3DP-NGA/3DP-NVP@C–rGO full battery demonstrated a remarkable capacity of 85.3 mAh g⁻¹ following 1000 cycles at a current density of 100 mA g⁻¹. Pan et al. [85] fabricated a 3D-printed microlattice aerogel comprising 50% Ti₃C₂T_x/rGO, which was infused with sodium-attracting Ti₃C₂T_x nanosheets. This unique structure provides an abundance of nucleation points for sodium metal, fostering uniform deposition. By effectively suppressing dendrite growth, this specially crafted design significantly boosts the cycling stability of sodium metal. The full battery, featuring a 3D-printed Na@Ti₃C₂T_x/rGO anode and a complementary 3D-printed Na₃V₂(PO₄)₃@C-rGO (NVP@C-rGO) cathode, exhibited an impressive capacity of 85.3 mAh g⁻¹ following 500 cycles at a current density of 100 mA g⁻¹.

Over the past few years, divalent magnesium-ion batteries (MIBs) have gained notable interest in energy storage, in addition to the well-established monovalent metal ion batteries. Nevertheless, the quest for suitable anode materials poses a formidable obstacle that must be overcome. Liu et al. [86] devised an innovative approach to fabricate a bimetallic Bi-Sn micro/nanosphere composite, CNC-CA@Bi-Sn, seamlessly embedded within a carbon aerogel matrix. This composite was derived from cellulose nanocrystals through a straightforward ion-induced gelation process followed by in situ thermal reduction. The CNC-CA@Bi-Sn electrode demonstrated remarkable electrochemical properties (187 mAh g⁻¹ even after 500 cycles at a higher current density of 1000 mA g⁻¹). This underscores its exceptional rate capability and extended cycling stability. The outstanding performance can be credited to its distinctive features: a three-dimensional nanoporous structure, a biphasic microstructure rich in phase boundaries, and the complementary effects of the biphasic matrix and carbon buffer matrix, which efficiently accommodate significant volume changes during magnesium-ion insertion and extraction, drastically reduce diffusion pathways, and enhance Mg²⁺ diffusion kinetics. Cheng et al. [87] prepared a unique hybrid of nearly monodisperse bismuth nanospheres (4–9 nm in diameter) uniformly anchored in an interconnected carbon aerogel (CNC-CA@Bi-NS) matrix derived from cellulose nanocrystals (CNCs) through ion-induced gelation and in situ thermal reduction, serving as an anode for MIBs. The nitrogen-doped porous matrix serves a dual function: it operates as a superior electrical conduit for efficient electron transport, and simultaneously offers ample room and an extensive surface area to accommodate and allow for electrolyte penetration, thereby accelerating charge transfer processes. Notably, the CNC-CA@Bi-NS electrode displayed an outstanding reversible specific capacity of 346 mAh/g, which corresponds to an impressive 90% of its theoretical capacity, even after undergoing 100 cycles at 0.5 C.

Furthermore, zinc-ion batteries that operate in a divalent aqueous environment have attracted considerable interest because of their affordability and enhanced safety features. However, the adverse effects of zinc dendrites and side reactions significantly hinder their commercialization. Utilizing 3D host materials is a solution to these issues. Chen et al. [88] introduced polyvinyl alcohol (PVA) and MXene to form a hierarchical porous aerogel material to create a unique MPA framework for zinc metal anodes. These advantages encompass the establishment of a uniform electric field distribution, the provision of pathways for the directional transmission of Zn²⁺ ions, and the availability of ample zinc deposition space thanks to the high specific surface area. These factors collectively ensure consistent and highly stable zinc plating/stripping processes. During cycling, the fluorine-based functional groups on the MXene surface react with the electrolyte to form a ZnF₂ solid electrolyte interphase (SEI), effectively safeguarding the composite anode. Finally, a Zn@MPA||NVO full battery was constructed, featuring Zn@MPA as the anode and NaV₃O₈·1.5H₂O as the cathode. This battery achieved an impressive initial capacity of 154.2 mA h cm⁻² after 800 cycles, maintaining a capacity retention rate of 93.86% at 5 A g⁻¹. Such three-dimensional, highly conductive, and zincophilic electrodes offer an ideal host for uniform zinc deposition, effectively inhibiting the zinc dendrites.

3.3.2. As the Cathode

As a novel type of a secondary battery, sulfur batteries have garnered significant attention, because of their outstanding qualities including a high energy capacity, affordable pricing, and eco-friendliness, and low toxicity. However, issues like poor conductivity and the shuttle effect have hindered the widespread application of lithium-sulfur batteries [89,90,91]. To achieve uniform distribution of sublimed sulfur within the cathode, Chen et al. [92] successfully prepared rGO@S aerogels, where the sublimed sulfur was uniformly impregnated. As the cathode, these rGO@S aerogels delivered a specific capacity exceeding 1200 mA h g⁻¹ at 0.5 C, accompanied by high cycle stability, evidenced by a mere 1.5% decay in discharge specific capacity from the 60th to 90th cycle at 0.5 C. Hu et al. [93] designed and synthesized a highly conductive freestanding cathode for lithium-sulfur batteries, featuring a unique structure where sulfur was deposited on graphene. This freestanding cathode exhibited exceptional conductivity, enabling rapid ion/electron transport and effective polysulfide immobilization, thereby enhancing lithium storage performance. The inherently poor conductivity of transition metal oxides limits their catalytic performance, which in turn restricts sulfur utilization and rate capability in Li-S batteries. To boost the electrochemical performance of Li-S batteries, Lin et al. [94] loaded VO₂ nanoparticles onto nitrogen-doped bacterial cellulose aerogel (N-CBC) to obtain a novel sulfur host for use in lithium-sulfur (Li-S) batteries. The sulfur cathode based on the H-VO₂@N-CBC scaffold demonstrated remarkable cycle stability by retaining a capacity of 758 mAh g⁻¹ after 300 cycles at a rate of 1 C. Shan et al. [95] developed an independent, ultra-lightweight cathode with outstanding electrochemical performance by growing nickel–cobalt layered double hydroxide (NiCo-LDH) nanosheets on the surface of ultra-light nickel microwire aerogels (NMWAs). The integrated thin-film cathode sulfur host (NMWAs@NiCo-LDH/S) exhibited remarkable performance in terms of both rate capability and cycle stability. This cathode demonstrated a superior reversible capacity of 805.8 mAh g⁻¹ at a high rate of 5.0 C. Remarkably, even after enduring 700 cycles under the stringent condition of a 5.0 C high current density, it was able to maintain a reversible capacity of 647.1 mAh g⁻¹.

Secondary zinc batteries exhibit significant advantages of high energy density, environmental friendliness, and safety. However, they still suffer from drawbacks, including capacity fading, zinc dendrites, zinc electrode deformation, self-discharge, limited energy density enhancement, and technical challenges. In addition to the problems caused by the anode metal zinc, the cathode materials also have important effects for the performance. Li et al. [96] described a scalable approach for synthesizing MnO₂ aerogel (A-MnO₂) composed of ultra-thin nanosheets that are abundant in defects, specifically designed for zinc-ion batteries. This aerogel structure, made from ultra-thin nanosheets, enhances the availability of electrochemically active sites and reduces the distance ions must diffuse. Consequently, A-MnO₂ exhibits significantly enhanced electrochemical kinetics, leading to superior electrochemical performance compared to the defect-free MnO₂ nanorod control sample. Xiang et al. [97] successfully prepared a novel composite aerogel (ZVOH@rGO) through a facile one-step process, which was employed as the cathode. Benefiting from the combined advantages of ion doping, controlled morphology, and the distinctive aerogel architecture, the electrode demonstrates ultra-fast charge–discharge performance and exceptional cycling durability. After 9800 ultra-long cycles at a current density of 12 A g⁻¹, its capacity retention rate remains as high as 75.6%, demonstrating exceptional durability. Xing et al. [98] prepared nitrogen-doped carbon aerogels (N-CNAGs) with a hierarchical structure, as shown in Figure 11. The unique hierarchical pore structure of N-CNAG significantly enhances the efficient transport and permeation of electrolyte ions. The zinc-ion hybrid supercapacitor composed of a zinc anode and an N-CNAG cathode achieves a remarkable high specific capacitance of 706 F g⁻¹ under a current test of 1 A g⁻¹. More importantly, when the current density increases from 1 A g⁻¹ to 5 A g⁻¹, it still maintains an excellent rate capability of 50%. This outstanding performance is primarily attributed to the dual advantages of N-CNAG’s hierarchical pore structure and high active nitrogen content. Yao et al. [99] accomplished the synthesis of an innovative three-dimensional carbon nanotube/reduced graphene oxide (P-CNT/rGO) aerogel. When employed as the cathode material in zinc hybrid capacitors (ZHCs), this aerogel demonstrated a remarkable enhancement in its capacitance, achieving 213.4 F/g at 0.5 A/g. Furthermore, the P-CNT/rGO aerogel boasted exceptional rate capability, maintaining 45.5% of its capacitance even at an extremely high current density of 100 A/g compared to 0.1 A/g, thereby substantially improving both its specific capacitance and ion transport capabilities.

The Na₃V₂(PO₄)₃ (NVP) material has emerged as the cathode material of choice for sodium-ion batteries, attributed to its remarkable thermal stability and extended cycling durability. Sıdıka Yıldırım Gültekin et al. [100] synthesized carbon-coated Na₃V₂(PO₄)₃ (NVP/C) and Na₃V₂(PO₄)₃ (GA-NVP/C) composite aerogel. The research delved into the influence of graphene aerogel additives on the electrochemical characteristics and efficiency of the cathode material. After 250 cycles, GA-NVP/C exhibited higher stability compared to NVP/C. Zhang et al. [101] incorporated MXene-rGO aerogel into cathode materials, leading to a substantial boost in conductivity. The harmonious combination of the highly conductive MXene-rGO and the highly reactive N3.5MTP sites imparted remarkable performance to N3.5MTP@MXene−rGO. Furthermore, N3.5MTP@MXene-rGO showcased exceptional power density and a discharge capacity of 189 mAh g⁻¹, surpassing the majority of cathode materials currently available.

The literature summary in

Table 2. The performance of some aerogel electrodes in the referenced works.

Aerogel as Electrode Material	Capacity	Cycle	Rate	Ref.
Co3O4@NCA-1	600.2 mA h/g	200	0.1 A/g	[69]
Co3O4 microcages@GA	1439 mA h/g	200	1 A/g	[71]
Si@CNTs	835.6 mA h/g	100	0.1 A/g	[72]
MoS2-Mo2C@C	375.1 mA h/g	3000	10 m A/g	[73]
FeS@C/CBC	669 mA h/g	1000	1 m A/g	[74]
Co3O4@GA	1234.9 mA h/g	200	1 A/g	[75]
MoSe2-Cu1.82Se@GA	444.8 mA h/g	1000	1 A/g	[76]
FeSe2/GA@PMC-2	345.1 mA h/g	1000	5 A/g	[77]
3DP-NGA	85.3 mA h/g	1000	0.1 A/g	[79]
Ti3C2Tx/rGO	85.3 mA h/g	500	0.1 A/g	[80]
CNC-CA@Bi-Sn	187 mA h/g	500	1 A/g	[81]
CNC-CA@Bi-NS	346 mA h/g	100	0.5 A/g	[82]
NMWAs@NiCo-LDH/S	647.1 mA h/g	700	5 A/g	[90]
MXene-rGO	154.98 mA h/g	5000	2 A/g	[97]

comprehensively details the utilization of aerogels as electrode materials for batteries and capacitors. This table offers a concise snapshot of pivotal studies, emphasizing the specific aerogel materials that have been utilized, their impact on discharge capacity, and their cycling stability.

In summary, aerogel electrodes possess outstanding electrochemical characteristics, marked by their high specific capacitance capabilities and unparalleled cycling stability. These advantages stem from their unique porous structure, which facilitates electrolyte penetration and rapid ion transport. As electric vehicles, wearable technology, smart grids, and other sectors undergo rapid advancements, there is a growing need for high-performance electrode materials, underscoring the promising prospects of aerogel electrodes. By integrating functional elements like conductive polymers and metal nanoparticles, or carbon nanotubes, into aerogels, additional functional properties like conductivity, catalytic activity, or antibacterial performance can be imparted to the electrodes. This multifunctional design further expands the application scope of aerogel electrodes. Nevertheless, the stability and durability of aerogel electrodes remain concerns. Under harsh conditions like high temperatures, high humidity, or strong electric fields, the microstructure of aerogels may undergo changes, impacting their electrochemical performance. Consequently, it is essential to intensify research and evaluation efforts on the stability and durability of aerogel electrodes to ensure their consistent performance under various conditions.

4. Conclusions

With their distinctive physical and chemical attributes, aerogels exhibit considerable promise in the realms of batteries and capacitors. Their high porosity, low mass density, and vast specific surface area introduce novel avenues for elevating the performance benchmarks of energy storage systems. Nevertheless, achieving their ubiquitous deployment in these systems necessitates the overcoming of several formidable challenges. Firstly, the insufficient conductivity and electrochemical stability of aerogels limit their direct application as electrode materials. Additionally, the structural stability of aerogels in electrolytes poses a concern, as it may lead to a decline in battery performance or shortened lifespan. Cost and scalability are also key challenges, as the production of high-quality aerogels is often expensive, and current production scales are small, limiting their suitability for large-scale applications. Lastly, environmental impact considerations cannot be overlooked, requiring the production and use of aerogels to minimize environmental impact.

Despite these challenges, the prospects for the application of aerogels in batteries and capacitors remain very promising. Technological advances and innovations offer potential solutions to overcome these obstacles. Progress in materials science and nanotechnology may lead to the development of more advanced aerogel materials with improved conductivity, enhanced structural stability, and increased electrochemical performance. The design of novel aerogels, such as those created through molecular design and nanostructure engineering, can help increase production efficiency, reduce costs, and enable more complex structural designs. Furthermore, the optimization of interface engineering can enhance charge transfer rates, while the use of simulation and computational materials science can accelerate the development and screening of new materials. Interdisciplinary collaboration, involving researchers from materials science, chemistry, physics, and engineering, will be essential to addressing the complex challenges of aerogel applications. Through these efforts, aerogels are expected to play a crucial role in improving battery performance, safety, and longevity, driving energy storage technologies towards greater efficiency and environmental sustainability.

The future development of aerogels will also benefit from the establishment of standardization and regulation. Setting clear performance standards and testing protocols will help facilitate the commercialization and market acceptance of the technology. This involves not only the performance of the materials but also the environmental impact assessment of the production process. As the global demand for sustainable energy solutions continues to grow, the application of aerogels in batteries and capacitors is likely to see broader exploration and implementation. Additionally, policy support and financial investment will play a critical role in driving the development of aerogel technology. Collaboration between government and the private sector can accelerate the transition from laboratory research to commercial products. Education and public outreach are also important, as they can increase public awareness and acceptance of aerogel technology. Ultimately, the successful application of aerogels will depend not only on technological advancements but also on the interplay of market dynamics, policy environments, and societal needs.

In conclusion, the application of aerogels in the fields of batteries and capacitors presents a multifaceted challenge, requiring concerted efforts from materials science, engineering technology, environmental science, and social science. Through ongoing research and innovation, combined with a deep understanding of market and societal needs, aerogels are expected to become a key component of future energy storage technologies, contributing to the realization of cleaner and more efficient energy systems. As technology continues to evolve and applications deepen, aerogels are anticipated to play an increasingly important role in advancing energy storage technology and addressing global energy challenges.