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Article

Electrochemically Inert Li2MnO3: The Key to Improving the Cycling Stability of Li-Rich Manganese Oxide Used in Lithium-Ion Batteries

by
Lian-Bang Wang
,
He-Shan Hu
,
Wei Lin
,
Qing-Hong Xu
,
Jia-Dong Gong
,
Wen-Kui Chai
and
Chao-Qi Shen
*
State Key Laboratory Breeding Base of Green Chemistry-Synthesis Technology, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
*
Author to whom correspondence should be addressed.
Materials 2021, 14(16), 4751; https://doi.org/10.3390/ma14164751
Submission received: 7 July 2021 / Revised: 19 August 2021 / Accepted: 21 August 2021 / Published: 23 August 2021
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Versions Notes

Abstract

:
Lithium-rich manganese oxide is a promising candidate for the next-generation cathode material of lithium-ion batteries because of its low cost and high specific capacity. Herein, a series of xLi2MnO3·(1 − x)LiMnO2 nanocomposites were designed via an ingenious one-step dynamic hydrothermal route. A high concentration of alkaline solution, intense hydrothermal conditions, and stirring were used to obtain nanoparticles with a large surface area and uniform dispersity. The experimental results demonstrate that 0.072Li2MnO3·0.928LiMnO2 nanoparticles exhibit a desirable electrochemical performance and deliver a high capacity of 196.4 mAh g−1 at 0.1 C. This capacity was maintained at 190.5 mAh g−1 with a retention rate of 97.0% by the 50th cycle, which demonstrates the excellent cycling stability. Furthermore, XRD characterization of the cycled electrode indicates that the Li2MnO3 phase of the composite is inert, even under a high potential (4.8 V), which is in contrast with most previous reports of lithium-rich materials. The inertness of Li2MnO3 is attributed to its high crystallinity and few structural defects, which make it difficult to activate. Hence, the final products demonstrate a favorable electrochemical performance with appropriate proportions of two phases in the composite, as high contents of inert Li2MnO3 lower the capacity, while a sufficient structural stability cannot be achieved with low contents. The findings indicate that controlling the composition through a dynamic hydrothermal route is an effective strategy for developing a Mn-based cathode material for lithium-ion batteries.

1. Introduction

Since rechargeable lithium-ion batteries were first applied to electronic products in the 1990s, their development has been continual [1]. After three decades, Li-ion batteries have evolved and become an essential component of well-established energy storage strategies, with excellent efficiency in terms of energy and power densities, life span, and design flexibility [2,3]. Meanwhile, the storage demand from clean energy technologies requires Li-ion batteries, given their merits of low cost, high safety, and environmental compatibility [4]. Compared with new generation anode materials, such as silicon–carbon composites with a specific capacity of 700–2000 mAh g−1, improvement in the capacity of cathode materials is somewhat lagging [5,6]. As the bottleneck of capacity and energy density, cathode materials are believed to be the main factor when further optimizing the electrochemical performance and addressing other issues of Li-ion batteries [5,7].
Currently, the most widely used cathode materials are ternary NMC and LiFePO4, while Li-rich manganese-based materials have attracted considerable attention due to their low cost and high specific capacity. Generally, this type of cathode material, noted as xLi2MnO3·(1 − x)LiTMO2 (transition metal (TM) = Ni, Co, and Mn, etc.), exhibits a superior specific capacity (>250 mAh g−1) and high operation voltage to realize an excellent energy density; thus, xLi2MnO3·(1 − x)LiTMO2 is assumed to be a promising cathode material for the next generation of lithium-ion batteries [8]. However, the large price fluctuation of cobalt and nickel in recent years, as well as their negative impact on the environment, have driven researchers to design Li-rich manganese oxide without Ni and Co, using xLi2MnO3·(1 − x)LiMnO2 as a substitute [9,10]. The preparation routes of xLi2MnO3·(1 − x)LiMnO2 include solid-state calcination [11], sol–gel synthesis [12], pyrolysis reduction [13], and hydrothermal/solvothermal reaction [14]. The specific capacity of xLi2MnO3·(1 − x)LiMnO2 has been significantly improved in comparison with common lithium manganese oxides (LiMn2O4, LiMnO2), but its capacity degradation during cycling is relatively severe [15].
The structure of the xLi2MnO3 (1 − x)LiMnO2 composite is believed to be a mixture of the Li2MnO3 and LiMnO2 crystal domains [16,17], while the hypothesis of a solid-state solution has also been presented in some studies [18,19]. In the composite, the crystal structure of Li2MnO3 is combined with monoclinic C2/m, but LiMnO2 can display diverse structures, such as monoclinic or orthorhombic structures, when using different synthetic methods. In most publications, Li2MnO3 was activated in the initial cycles and provided an extra capacity, similarly to xLi2MnO3·(1 − x)LiTMO2 mentioned above. During the activation process, the conjoint removal of Li+ and O forms an active “MnO2-like” phase, and anionic and cationic vacancies are generated simultaneously to cause lattice densification [20,21]. Irreversible O2 extraction (Li2MnO3 → LixMnO2 + (2 − x)Li+ + 1/2O2 + (2 − x)e−), occupation of the Li+ site by the transition metal, and phase transformation to spinel or rock salt induce a decline in capacity [22,23,24]. While recent research has demonstrated that Li2MnO3 is activated to generate oxygen anion On− (n < 2), redox of the oxygen anion during cycling could contribute considerably to increasing its capacity [25]. In order to improve the stability of the material and to mitigate the reduction in capacity due to structure evolution, elemental doping and surface modification with oxides are widely applied [26]. However, applying additional optimization treatment procedures generally goes against attempts to develop cost-effective and time-saving methods for the production of cathode materials [27].
In this work, a xLi2MnO3·(1 − x)LiMnO2 composite was prepared via a one-step dynamic hydrothermal synthetic route; interestingly, the contained Li2MnO3 was not activated even when cycled under 2–4.8V for 15 cycles. The x-values of 0.045, 0.072, and 0.114 in xLi2MnO3·(1 − x)LiMnO2 were characterized by ICP–OES, and the sample containing 0.072 Li2MnO3 manifested the best electrochemical performance. The inertness of Li2MnO3 is ascribed to its high crystallinity with few defects, as its presence effectively improved the electrochemical cycling capability of xLi2MnO3·(1 − x)LiMnO2 due to its structural stability. The mechanism still requires further investigation, however, this research provides a novel method to synthesize xLi2MnO3·(1 − x)LiMnO2 cathode material with a low cost and a stable cycling capability for application in lithium-ion batteries.

2. Materials and Methods

The samples were prepared via a one-step dynamic hydrothermal method. MnO2, Mn(CH3COO)2·4H2O, LiOH·H2O, and NaOH were purchased from Aladdin (Shanghai, China). The preparation procedure is described briefly, as follows: 0.04 mol MnO2, 0.04 mol Mn(CH3COO)2·4H2O, 0.24 mol LiOH·H2O, 0.36 mol NaOH, and 200 mL deionized water were mixed in a 1000 mL dynamic autoclave with a stirrer (stirring rate of 150 rpm). The hydrothermal treatment was carried out at 200 °C for 5 h, with the temperature being increased at a rate of 2 °C min−1. Following the reaction, the autoclave was left to cool down to room temperature under ambient conditions. The sample was collected by centrifugation and was washed with deionized water several times, then dried at 80 °C overnight. The final product was marked as LMO-1. LMO-2 and LMO-3 were obtained with the same reagent concentrations, while the volume of solutions were set to 400 and 600 mL of H2O, respectively. Furthermore, with the purpose of controlling the atmosphere in the reaction system, the gas in the autoclave was sufficiently purged by compressed air before the hydrothermal process. For use in comparisons, pure o-LiMnO2 (marked as LMO-P) was synthesized using ethylene diamine tetraacetic acid disodium salt (EDTA-2Na) according to a previous report [28].
The crystal structures were evaluated by powder X-ray diffraction (XRD; X’Pert Pro, PANalytical, Almelo, The Netherlands) with Cu Kα radiation over the range of 2θ = 10–80°. The morphologies of the samples were investigated using scanning electron microscopy (SEM; Nova NanoSEM 450, FEI company, Hillsboro, OR, USA) and transmission electron microscopy (TEM; Tecnai G2F30 S-Twin operated at 300 kV, FEI company, Hillsboro, OR, USA). The size distribution of the samples was analyzed using a particle dimension laser analyzer in dry mode (LS230, Beckman Coulter, Brea, CA, USA). The chemical valence state of the Mn element was confirmed by XPS (Thermo Scientific K-Alpha, Thermo Fisher Scientific, Waltham, MA, USA). The elemental ratio of the samples was analyzed by inductively coupled plasma optical emission spectrometry (ICP–OES, Agilent 720ES, Agilent Technologies, Santa Clara, CA, USA).
The contents of Mn3+ and Mn4+ from the various samples were obtained via chemical titration according to previous works [29,30]. The final results were the mean values of the triplicate experiments. Chrome blue black R, sulfuric acid, sodium oxalate benchmark solution, EDTA, ammonia–ammonium chloride buffer solution, and ammonium sulfate solution were used in the titration.
The electrochemical performance of the samples was measured using the 2032-type coin cell. A slurry composed of 10 wt.% binder (polyvinylidene fluoride (PVDF)), 10 wt.% conductive additive (Super P Li carbon black), and 80 wt.% active material in N-methyl-2-pyrrolidone (NMP) was cast onto aluminum foil. The electrodes were approximately 100 μm thick and the loading mass of the active material was approximately 1.5 mg cm−2. The half-cells were assembled in an argon-filled glovebox employing pure lithium foil as anodes and Celgard 2400 membranes as separators. The electrolyte was composed of a solution of LiPF6 (1 M) in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (1:1:1 by volume). The coin cells were galvanostatically cycled on a CT2001A (LAND Electronic Co., Wuhan, China) multi-channel battery test system at room temperature. A cyclic voltammetry (CV) test was conducted on an Ivium electrochemical workstation (Ivium-n-Stat, IVIUM Technologies, Eindhoven, Netherlands) at a scan rate of 0.1 mV s−1 between 2.0 and 4.8 V. The electrochemical impedance spectra (EIS) were collected by the Ivium workstation (Ivium-n-Stat, IVIUM Technologies, Eindhoven, Netherlands) within the frequency range of 0.01 Hz–100 kHz with an amplitude of 10 mV.

3. Results and Discussion

The high crystallinity and phase composition of the hydrothermally synthesized xLi2MnO3·(1 − x)LiMnO2 samples were distinctly confirmed by XRD measurement (Figure 1a). The diffraction peaks of LiMnO2 can be indexed to the α-NaFeO2-type layered structure with a space group of R3m. Meanwhile, the intensity of the peaks at 18.7° and 44.7° can be ascribed to Li2MnO3 with the C/2m space group, declining gradually as the oxygen in the autoclave decreased, which was more obvious in the enlarged interval between 42° and 48° (Figure 1b). This trend can be attributed to residual oxygen in the reaction system inevitably producing Li2MnO3, and the chemical reaction can be formulated as follows:
Mn(II) + MnO2 + 4Li+ + 6OH− + 1/2O2 → 2Li2MnO3 + 3H2O
The ICP–OES results in Table 1 present the molar ratio of Li and Mn with the calculation of the Mn valance. The x-values in LMO-1, LMO-2, and LMO-3 are 0.114, 0.072, and 0.045, respectively. Meanwhile, in LMO-P, the content of Li2MnO3 is only 0.9%, which can be regarded as pure LiMnO2. The ratio of the two phases from the different samples is displayed in Figure 1c. In addition, the Mn valence state (Mn3+ and Mn4+) in each sample was tested using the chemical titration method, and the results are shown in Table 2. According to the chemical titration results, the composition of the xLi2MnO3·(1 − x)LiMnO2 samples is in accordance with the ICP–OES characterization.
Figure 2 presents the XPS spectra of four samples, where the chemical state of Mn 2p can be clarified as the combination of Mn4+ (2p3/2 643.4 eV) and Mn3+ (2p3/2 641.7 eV) [31,32]. The Mn4+ content decreased with the decline of oxygen in the reaction system, as reflected by the less Li2MnO3 in the final product. The area of fitted XPS curves indicates that Mn3+ is the majority species, while the Mn in LMO-P sample can be regarded as Mn3+ entirely, a conclusion that is consistent with the XRD and ICP results.
The SEM images of four products are presented in Figure 3a–d, all of which show similar morphologies with a particle size ranging from 30 to 150 nm. The size distribution was further examined using a laser particle size analyzer (Figure 3f–i), in which the mean sizes of 81.4, 82.3, 80.9, and 82.1 nm were determined for LMO-1, LMO-2, LMO-3, and LMO-P, respectively. The particle size of the synthesized products is smaller than reported before [11,12]. The use of an alkaline solution with stirring established an appropriate reaction environment for generating nanoparticles with a large surface area and to prevent agglomeration. Hence, the contact area between the active material and electrolyte was enlarged, which produced a shorter diffusion path for Li+ to minimize polarization during charging–discharging [33].
The HRTEM image of LMO-2 in Figure 3e exhibits lattice fringes with an interplanar space of 0.25 nm, assigned to the (011) crystal plane of orthorhombic LiMnO2, and lattice fringes with 0.47 nm of the (001) crystal plane from Li2MnO3, which confirm the good crystallinity of the product and the co-existence of the two phases. The lattice fringe spacings of LiMnO2 (011) and Li2MnO3 (001) were also calculated based on the XRD pattern of LMO-2. According to the Bragg equation, 2dsinθ = nλ (n = 1), the peak at 2θ = 18.7° with a lattice fringe spacing of 4.74Å corresponds to Li2MnO3 (001), while that at 2θ = 35.6° of 2.52Å is LiMnO2 (011), in accordance with HRTEM.
Figure 4 displays the cyclic voltammograms (CVs) of the various samples in the potential interval from 2.0 to 4.8 V at a scan rate of 0.1 mV s−1. The intense oxidation peak at 3.5–4.1 V observed in the first cycle is interpreted as an irreversible de-lithiation from the octahedral sites of LiMnO2 upon charging [31,34]. Generally, the products with Li2MnO3 presented another oxidation peak around 4.7 V due to the activation of Li2MnO3 with Li+ extraction and anion oxidation [34,35]. However, this behavior cannot be distinguished in our research, which demonstrates that the Li2MnO3 generated via our route is electrochemically inert, even under a high potential. Furthermore, the redox peaks around 3.0 V are ascribed to Mn3+/Mn3.5+ in Li2Mn2O4 transformed from initial LiMnO2 for all of the samples [36]. In the first charging step, this can be explained by the de-lithiation of Li+ from octahedral sites and the subsequent migration of Mn3+ from the original octahedral sites to neighboring vacant octahedral sites. When Li+ intercalates into the de-lithiated matrix in the discharge step, it cannot re-insert into the original octahedral sites, but instead forms tetragonal Li2Mn2O4 [37,38]. Two peaks characteristic of cubic spinel LiMn2O4 could be detected at 3.95 and 4.10 V for LMO-2, LMO-3, and LMO-P (Figure 4b–d) [39,40]. While for LMO-1 (Figure 4a), these two peaks are merged, this phenomenon should be ascribed to the higher content of inert Li2MnO3 influencing the lithium ion de-intercalation process in spinel LiMn2O4 [41].
The charge/discharge profiles of the first cycle are displayed in Figure 5a. The initial charge and discharge plateaus at 3.6 and 3.0 V are characteristic of o-LiMnO2, akin to previous reports and in agreement with the results observed by CV [28]. The discharging capacity and coulombic efficiency of the initial cycle is 90.3 mAh g−1 (62.2%), 100.3 mAh g−1 (66.4%), 111.2 mAh g−1 (70.4%), and 126.4 mAh g−1 (72.4%) for LMO-1, LMO-2, LMO-3, and LMO-P, respectively. The capacity of each sample is directly proportional to the content of LiMnO2, and the coulombic efficiency of the initial cycle declined with the increase in the Li2MnO3 phase. Such a phenomenon is ascribed to the existence of Li2MnO3, hindering the de-intercalation of lithium-ion and impeding the phase transformation from LiMnO2 to Li2Mn2O4, thus resulting in a low coulombic efficiency. However, once the LiMnO2 is entirely transformed to Li2Mn2O4, the existence of Li2MnO3 was beneficial for preventing structural distortion and improving cycling stability. Furthermore, no obvious peak was present in the related dQ/dV curves in the high potential range of 4.5–4.8 V (Figure 5b). As previously reported, the electrochemical activity of Li2MnO3 is induced by structural defects, and with more stacking faults, Li2MnO3 is more easily activated to offer extra capacity, and even the activation the voltage plateau was not obvious [42,43]. However, this is inconsistent with our experimental results, where the highest capacity decreased with the increase in Li2MnO3 content; thus, the contribution of Li2MnO3 activation to increasing capacity could be excluded, and the inertness of Li2MnO3 was confirmed.
Plots of the cycling performance of the synthesized materials at 0.1 C (1 C = 300 mA g−1) at ranges of 2.0–4.5 and 2.0–4.8 V are shown in Figure 6a,b. Under both conditions, the capacity gradually increased in the initial cycles, which can be attributed to the increasing content of Li2Mn2O4 upon o-LiMnO2 transformation [44]. In comparison, the samples cycled with 2.0–4.8 V presented a higher capacity, which is usually explained by the activation of Li2MnO3 at a high potential to offer extra capacity. Nevertheless, the inertness of Li2MnO3 in our research implies that more sufficient de-intercalation of Li+ at a high potential is responsible for the increase in capacity. This could also explain why the highest capacity decreases with an increase in Li2MnO3 content.
The speed of the phase transformation from o-LiMnO2 to Li2Mn2O4 is related to the content of Li2MnO3 in the composite [13]. It is clear that LMO-P reached the highest capacity of 206.1 mAh g−1 in six cycles with a potential range of 2.0–4.8 V, while the capacity of the 50th cycle was only 161.5 mAh g−1 with a retention rate of 78.4%. In comparison, LMO-1, LMO-2, and LMO-3 achieved higher capacities of 189.4, 196.4, and 197.6 mAh g−1 in the 33rd, 19th, and 17th cycles, respectively, and the retention rates of the corresponding samples were 97.3%, 97.0%, and 89.5%, respectively. The cycling performance at a rate of 1 C after activation at 0.1 C for 15 cycles is displayed in Figure 6c. The results show that the capacity retention of LMO-P degraded to 60.3%, while LMO-1, LMO-2, and LMO-3 maintained 95.4%, 89.1%, and 73.3%, respectively. The higher charging–discharging rate demands faster Li+ de-intercalation and, thus, the structure of a cathode material must be well stabilized, and the existence of Li2MnO3 effectively improved this factor. The different cycling capability demonstrates that the existence of inert Li2MnO3 improved the structural stability of the material with deep de-lithiation. Meanwhile, the ratio of Li2MnO3 in the composite should be optimized to balance the capacity property and the cycling stability, thus achieving the best electrochemical performance; from this point of view, LMO-2 with 7.2% Li2MnO3 is the most appropriate choice.
In fact, the capacity degradation associated with LiMnO2 is due to Mn dissolution and irreversible layer-to-spinel transformation stemming from Jahn–Teller distortion [40,45]. The introduction of a Li2MnO3 phase could increase the mean valence of Mn to suppress the disproportionate reaction of Mn3+; more importantly, the layered structure is compatible with LiMnO2 and the stable layered complex structure can effectively delay irreversible transformation to spinel LiMn2O4 [13,46].
The charging–discharging curves of different materials in the 50th cycle are shown in Figure 7, in which the voltage hysteresis can be detected. As mentioned earlier, the structure of LiMnO2 is transformed and collapses during cycling, and the diffusion path of the lithium-ion then changes to cause voltage hysteresis. In comparison, the existence of Li2MnO3 relieves voltage hysteresis under either high or low voltage for the redox reaction of Mn3.5+/4+ and Mn3+/3.5+, which illustrates that Li2MnO3 suppresses further structural distortion of the material.
In order to identify the structural evolution of the composite, ex situ XRD measurements were taken for the discharged LMO-2 cathode disk after 15 cycles, as shown in Figure 8. The o-LiMnO2 phase remarkably vanished, whereas newly formed phases of cubic LiMn2O4 and tetragonal Li2Mn2O4 could be detected. Moreover, the existence of a Li2MnO3 phase can be confirmed, which means that Li2MnO3 did not participate in the electrochemical reaction. The amount of cubic LiMn2O4 illustrates that inert Li2MnO3 is not capable of thoroughly suppressing phase transformation, while structure distortion and collapse are prevented, resulting in an improved cycling stability.
The electrochemical impedance spectra (EIS) of the samples before and after cycling are shown in Figure 9. The semicircle of a high frequency is ascribed to the surface film resistance (Rf) formed by the decomposition of the electrolyte, while the semicircle of a high- to medium-frequency represents the charge–transfer resistance (Rct) of the electrochemical process, and the line in the low-frequency range indicates a diffusion-controlled process in the solid electrode [47,48]. The fitted values of the simulated circuit displayed in Table 3 demonstrate a decrease in Rct after cycling, which is attributed to the better electronic and ionic conductivity of the transformed LiMn2O4 phase with a three-dimensional spinel structure [49]. Furthermore, both before and after cycling, the values of Rct were higher for the sample with more Li2MnO3; this phenomenon implies the inferior conductivity of Li2MnO3 and that Li2MnO3 does not change the state even after being cycled under a high potential. On the contrary, Rs corresponds to the resistance of the cell, which consists of electrolyte resistance and circuit ohmic resistance. It is supposed that after cycling, the battery is aged, and the electrolyte is partially decomposed to generate impurity, thereby obstructing ion transfer to increase the value of Rs, as shown in Table 3 [50]. Meanwhile, the formation of an SEI film on the electrode surface blocking the transfer of Li+ results in the emergence of Rf compared to the EIS before cycling, which is more obvious in the enlarged EIS image after cycling (Figure 9c).
Compared with the electrochemical properties of the xLi2MnO3·(1 − x)LiMnO2 cathode materials generated using various methods (Table 4), the superiority of those prepared using the dynamic hydrothermal route designed here is remarkable. Our synthetic procedure saves time, and the formation of the 0.072Li2MnO3·0.928LiMnO2 nanocomposite leads to an optimum performance. The specific discharging capacity and cycling stability of the product are much better than the previously reported results, except for 0.23Li2MnO3·0.77LiMnO2 produced via the solid-state method. However, in this composite, Li2MnO3 is activated after 20 cycles and does not show stability under extended cycling [11]. Modification strategies, including element doping and carbon composition, can also be implemented on the xLi2MnO3·(1 − x)LiMnO2 material to further improve the cycling stability and capacity, which will form the scope of future work.

4. Conclusions

A series of xLi2MnO3·(1 − x)LiMnO2 nanocomposites were prepared via a one-step dynamic hydrothermal method. A high concentration of alkaline solution, intense hydrothermal conditions, and stirring were used to produce nanoparticles that possess a large surface area and uniform dispersity. The composite characterized by a good crystallinity was found to be composed of orthorhombic LiMnO2 and monoclinic Li2MnO3. The proportion of the two phases in the composite can be effectively controlled by the amount of oxygen in the autoclave, which, in turn, influences the electrochemical performance.
In contrast with most previously reported lithium-rich materials, the Li2MnO3 in this composite is completely inert, even when cycled at 2.0–4.8 V, and the typical activation reactions that contribute to extra capacity were not observed. This is ascribed to the high crystallinity and few faults in Li2MnO3; as an inert phase, Li2MnO3 effectively suppresses the structural distortion and collapse of the composite during cycling, which results in an improved cycling stability.
The composite with a 0.072Li2MnO3·0.928LiMnO2 composition exhibited the best electrochemical performance and delivered a high capacity of 196.4 mAh g−1 at 0.1 C under 2–4.8 V. The capacity was maintained at 190.5 mAh g−1 with a retention rate of 97.0% by the 50th cycle, which demonstrates an excellent cycling stability. This research describes a novel route to synthesize xLi2MnO3·(1 − x)LiMnO2 cathode materials with a low cost and a stable cycling capability, for use in lithium-ion batteries.

Author Contributions

Conceptualization, L.-B.W. and C.-Q.S.; funding acquisition, L.-B.W. and C.-Q.S.; investigation, H.-S.H., Q.-H.X. and W.L.; methodology, H.-S.H., J.-D.G. and W.-K.C.; writing—original draft preparation, H.-S.H. and C.-Q.S.; writing—review and editing, C.-Q.S.; project administration, L.-B.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (grant number 22075251), the Key Research and Development Program of Science and Technology Department of Zhejiang Province (grant number 2021C01176), and the Preferential Foundation of Zhejiang Province Postdoctoral Research Project (grant number ZJ2019075).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Ozawa, K. Lithium-Ion Rechargeable Batteries with LiCoO2 and Carbon Electrodes—The LiCoO2/C System. Solid State Ion. 1994, 69, 212–221. [Google Scholar] [CrossRef]
  2. Goodenough, J.B.; Park, K.S. The Li-ion rechargeable battery: A perspective. J. Am. Chem. Soc. 2013, 135, 1167–1176. [Google Scholar] [CrossRef]
  3. Armand, M.; Tarascon, J.M. Building better batteries. Nature 2008, 451, 652–657. [Google Scholar] [CrossRef]
  4. Whittingham, M.S. History, Evolution, and Future Status of Energy Storage. Proc. IEEE 2012, 100, 1518–1534. [Google Scholar] [CrossRef]
  5. Zuo, W.H.; Luo, M.Z.; Liu, X.S.; Wu, J.; Liu, H.D.; Li, J.; Winter, M.; Fu, R.Q.; Yang, W.L.; Yang, Y. Li-rich cathodes for rechargeable Li-based batteries: Reaction mechanisms and advanced characterization techniques. Energy Environ. Sci. 2020, 13, 4450–4497. [Google Scholar] [CrossRef]
  6. Su, X.; Wu, Q.L.; Li, J.C.; Xiao, X.C.; Lott, A.; Lu, W.Q.; Sheldon, B.W.; Wu, J. Silicon-Based Nanomaterials for Lithium-Ion Batteries: A Review. Adv. Energy Mater. 2014, 4, 1–23. [Google Scholar] [CrossRef]
  7. Li, W.; Song, B.; Manthiram, A. High-voltage positive electrode materials for lithium-ion batteries. Chem. Soc. Rev. 2017, 46, 3006–3059. [Google Scholar] [CrossRef] [PubMed]
  8. Chen, J.; Zou, G.Q.; Deng, W.T.; Huang, Z.D.; Gao, X.; Liu, C.; Yin, S.Y.; Liu, H.Q.; Deng, X.L.; Tian, Y.; et al. Pseudo-Bonding and Electric-Field Harmony for Li-Rich Mn-Based Oxide Cathode. Adv. Funct. Mater. 2020, 30, 2004302. [Google Scholar] [CrossRef]
  9. Sun, Y.K.; Chen, Z.; Noh, H.J.; Lee, D.J.; Jung, H.G.; Ren, Y.; Wang, S.; Yoon, C.S.; Myung, S.T.; Amine, K. Nanostructured high-energy cathode materials for advanced lithium batteries. Nat. Mater. 2012, 11, 942–947. [Google Scholar] [CrossRef] [PubMed]
  10. He, P.; Yu, H.; Li, D.; Zhou, H. Layered lithium transition metal oxide cathodes towards high energy lithium-ion batteries. J. Mater. Chem. 2012, 22, 3680–3695. [Google Scholar] [CrossRef]
  11. Li, X.L.; Liu, D.J.; Zhang, D.W.; Chen, X.Y.; Tian, X.L. One-step synthesis and electrochemical behavior of LiMnO2 and its composite from MnO2 in the presence of glucose. J. Phys. Chem. Solids 2009, 70, 936–940. [Google Scholar] [CrossRef]
  12. Saroha, R.; Gupta, A.; Panwar, A.K. Electrochemical performances of Li-rich layered-layered Li2MnO3-LiMnO2 solid solutions as cathode material for lithium-ion batteries. J. Alloys Compd. 2017, 696, 580–589. [Google Scholar] [CrossRef]
  13. Yang, F.; Zhang, Q.; Hu, X.; Peng, T. Synthesis of layered xLi2MnO3·(1−x)LiMnO2 nanoplates and its electrochemical performance as Li-rich cathode materials for Li-ion battery. Electrochim. Acta 2015, 165, 182–190. [Google Scholar] [CrossRef]
  14. Huang, X.; Zhang, Q.; Chang, H.; Gan, J.; Yue, H.; Yang, Y. Hydrothermal Synthesis of Nanosized LiMnO2–Li2MnO3 Compounds and Their Electrochemical Performances. J. Electrochem. Soc. 2009, 156, A162–A168. [Google Scholar] [CrossRef]
  15. Zheng, J.; Myeong, S.; Cho, W.; Yan, P.; Xiao, J.; Wang, C.; Cho, J.; Zhang, J.G. Li- and Mn-Rich Cathode Materials: Challenges to Commercialization. Adv. Energy Mater. 2016, 7, 1601284. [Google Scholar] [CrossRef]
  16. Yu, X.; Lyu, Y.; Gu, L.; Wu, H.; Bak, S.-M.; Zhou, Y.; Amine, K.; Ehrlich, S.N.; Li, H.; Nam, K.-W.; et al. Understanding the Rate Capability of High-Energy-Density Li-Rich Layered Li1.2Ni0.15Co0.1Mn0.55O2 Cathode Materials. Adv. Energy Mater. 2014, 4, 1300950. [Google Scholar] [CrossRef]
  17. Hy, S.; Felix, F.; Rick, J.; Su, W.N.; Hwang, B.J. Direct in situ observation of Li2O evolution on Li-rich high-capacity cathode material, Li[NixLi1−2x/3Mn2−x/3]O2 (0≤x≤0.5). J. Am. Chem. Soc. 2014, 136, 999–1007. [Google Scholar] [CrossRef]
  18. Koga, H.; Croguennec, L.; Mannessiez, P.; Menetrier, M.; Weill, F.; Bourgeois, L.; Duttine, M.; Suard, E.; Delmas, C. Li1.20Mn0.54Co0.13Ni0.13O2 with Different Particle Sizes as Attractive Positive Electrode Materials for Lithium-Ion Batteries: Insights into Their Structure. J. Phys. Chem. C 2012, 116, 13497–13506. [Google Scholar] [CrossRef]
  19. Jarvis, K.A.; Deng, Z.Q.; Allard, L.F.; Manthiram, A.; Ferreira, P.J. Atomic Structure of a Lithium-Rich Layered Oxide Material for Lithium-Ion Batteries: Evidence of a Solid Solution. Chem. Mater. 2011, 23, 3614–3621. [Google Scholar] [CrossRef]
  20. Rousse, G.; Tarascon, J.M. Sulfate-Based Polyanionic Compounds for Li-Ion Batteries: Synthesis, Crystal Chemistry, and Electrochemistry Aspects. Chem. Mater. 2013, 26, 394–406. [Google Scholar] [CrossRef]
  21. Yang, J.S.; Li, P.; Zhong, F.P.; Feng, X.M.; Chen, W.H.; Ai, X.P.; Yang, H.X.; Xia, D.G.; Cao, Y.L. Suppressing Voltage Fading of Li-Rich Oxide Cathode via Building a Well-Protected and Partially-Protonated Surface by Polyacrylic Acid Binder for Cycle-Stable Li-Ion Batteries. Adv. Energy Mater. 2020, 10, 1904264. [Google Scholar] [CrossRef]
  22. Gu, M.; Belharouak, I.; Zheng, J.; Wu, H.; Xiao, J.; Genc, A.; Amine, K.; Thevuthasan, S.; Baer, D.R.; Zhang, J.G.; et al. Formation of the spinel phase in the layered composite cathode used in Li-ion batteries. ACS Nano 2013, 7, 760–767. [Google Scholar] [CrossRef]
  23. Lee, W.; Muhammad, S.; Sergey, C.; Lee, H.; Yoon, J.; Kang, Y.M.; Yoon, W.S. Advances in the Cathode Materials for Lithium Rechargeable Batteries. Angew Chem. Int. Ed. Engl. 2020, 59, 2578–2605. [Google Scholar] [CrossRef]
  24. Nayak, P.K.; Erickson, E.M.; Schipper, F.; Penki, T.R.; Munichandraiah, N.; Adelhelm, P.; Sclar, H.; Amalraj, F.; Markovsky, B.; Aurbach, D. Review on Challenges and Recent Advances in the Electrochemical Performance of High Capacity Li- and Mn-Rich Cathode Materials for Li-Ion Batteries. Adv. Energy Mater. 2018, 8, 1702397. [Google Scholar] [CrossRef]
  25. Assat, G.; Tarascon, J.M. Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries. Nat. Energy 2018, 3, 373–386. [Google Scholar] [CrossRef]
  26. Hy, S.; Liu, H.D.; Zhang, M.H.; Qian, D.N.; Hwang, B.J.; Meng, Y.S. Performance and design considerations for lithium excess layered oxide positive electrode materials for lithium ion batteries. Energy Environ. Sci. 2016, 9, 1931–1954. [Google Scholar] [CrossRef]
  27. Li, Q.; Li, G.S.; Fu, C.C.; Luo, D.; Fan, J.M.; Xie, D.J.; Li, L.P. Balancing stability and specific energy in Li-rich cathodes for lithium ion batteries: A case study of a novel Li-Mn-Ni-Co oxide. J. Mater. Chem. A 2015, 3, 10592–10602. [Google Scholar] [CrossRef]
  28. Shen, C.Q.; Xu, H.; Liu, L.; Hu, H.S.; Chen, S.Y.; Su, L.W.; Wang, L.B. EDTA-2Na assisted dynamic hydrothermal synthesis of orthorhombic LiMnO2 for lithium ion battery. J. Alloys Compd. 2020, 830, 154599. [Google Scholar] [CrossRef]
  29. Fang, D.; Xie, J.L.; Hu, H.; Yang, H.; He, F.; Fu, Z.B. Identification of MnOx species and Mn valence states in MnOx/TiO2 catalysts for low temperature SCR. Chem. Eng. J. 2015, 271, 23–30. [Google Scholar] [CrossRef]
  30. Dong, J.Y.; Lu, G.; Yue, J.S.; Cheng, Z.M.; Kang, X.H. Valence modulation in hollow carbon nanosphere/manganese oxide composite for high performance supercapacitor. Appl. Surf. Sci. 2019, 480, 1116–1125. [Google Scholar] [CrossRef]
  31. Li, X.H.; Su, Z.; Wang, Y.B. Electrochemical properties of monoclinic and orthorhombic LiMnO2 synthesized by a one-step hydrothermal method. J. Alloys Compd. 2018, 735, 2182–2189. [Google Scholar] [CrossRef]
  32. Zhang, X.D.; Shi, J.L.; Liang, J.Y.; Yin, Y.X.; Zhang, J.N.; Yu, X.Q.; Guo, Y.G. Suppressing Surface Lattice Oxygen Release of Li-Rich Cathode Materials via Heterostructured Spinel Li4 Mn5O12 Coating. Adv. Mater. 2018, 30, 1801751. [Google Scholar] [CrossRef] [PubMed]
  33. Li, K.Y.; Shua, F.F.; Zhang, J.W.; Chen, K.F.; Xue, D.F.; Guo, X.W.; Komarneni, S. Role of Hydrothermal parameters on phase purity of orthorhombic LiMnO2 for use as cathode in Li ion battery. Ceram. Int. 2015, 41, 6729–6733. [Google Scholar] [CrossRef]
  34. Yang, F.; Zhang, Q.; Hu, X.; Peng, T.; Liu, J. Preparation of Li-rich layered-layered type x Li2MnO3·(1−x)LiMnO2 nanorods and its electrochemical performance as cathode material for Li-ion battery. J. Power Source 2017, 353, 323–332. [Google Scholar] [CrossRef]
  35. Sun, Y.; Zan, L.; Zhang, Y.X. Enhanced electrochemical performances of Li2MnO3 cathode materials via adjusting oxygen vacancies content for lithium-ion batteries. Appl. Surf. Sci. 2019, 483, 270–277. [Google Scholar] [CrossRef]
  36. Tang, S.B.; Lai, M.O.; Lu, L. Electrochemical studies of low-temperature processed nano-crystalline LiMn2O4 thin film cathode at 55 °C. J. Power Source 2007, 164, 372–378. [Google Scholar] [CrossRef]
  37. Croguennec, L.; Deniard, P.; Brec, R.; Biensan, P.; Broussely, M. Electrochemical behavior of orthorhombic LiMnO2: Influence of the grain size and cationic disorder. Solid State Ion. 1996, 89, 127–137. [Google Scholar] [CrossRef]
  38. Thackeray, M.M. Manganese oxides for lithium batteries. Prog. Solid State Chem. 1997, 25, 1–71. [Google Scholar] [CrossRef]
  39. Pang, W.K.; Lee, J.Y.; Wei, Y.S.; Wu, S.H. Preparation and characterization of Cr-doped LiMnO2 cathode materials by Pechini’s method for lithium ion batteries. Mater. Chem. Phys. 2013, 139, 241–246. [Google Scholar] [CrossRef]
  40. Jang, Y.I.; Huang, B.; Wang, H.; Sadoway, D.R.; Chiang, Y.M. Electrochemical Cycling-Induced Spinel Formation in High-Charge-Capacity Orthorhombic LiMnO2. J. Electrochem. Soc. 2019, 146, 3217–3223. [Google Scholar] [CrossRef]
  41. Kim, S.-W.; Pyun, S.-I. Lithium transport through a sol–gel derived LiMn2O4 film electrode: Analyses of potentiostatic current transient and linear sweep voltammogram by Monte Carlo simulation. Electrochim. Acta 2002, 47, 2843–2855. [Google Scholar] [CrossRef]
  42. Francis Amalraj, S.; Markovsky, B.; Sharon, D.; Talianker, M.; Zinigrad, E.; Persky, R.; Haik, O.; Grinblat, J.; Lampert, J.; Schulz-Dobrick, M.; et al. Study of the electrochemical behavior of the “inactive” Li2MnO3. Electrochim. Acta 2012, 78, 32–39. [Google Scholar] [CrossRef]
  43. Boulineau, A.; Croguennec, L.; Delmas, C.; Weill, F. Reinvestigation of Li2MnO3 Structure: Electron Diffraction and High Resolution TEM. Chem. Mater. 2009, 21, 4216–4222. [Google Scholar] [CrossRef]
  44. Uyama, T.; Mukai, K.; Yamada, I. High-pressure synthesis and electrochemical properties of tetragonal LiMnO2. RSC Adv. 2018, 8, 26325–26334. [Google Scholar] [CrossRef] [Green Version]
  45. Shao-Horn, Y.; Hackney, S.A.; Armstrong, A.R.; Bruce, P.G.; Gitzendanner, R.; Johnson, C.S.; Thackeray, M.M. Structural Characterization of Layered LiMnO2 Electrodes by Electron Diffraction and Lattice Imaging. J. Electrochem. Soc. 1999, 146, 2404–2412. [Google Scholar] [CrossRef]
  46. Zhang, Q.; Peng, T.; Zhan, D.; Hu, X. Synthesis and electrochemical property of xLi2MnO3·(1−x)LiMnO2 composite cathode materials derived from partially reduced Li2MnO3. J. Power Source 2014, 250, 40–49. [Google Scholar] [CrossRef]
  47. Song, J.; Li, B.; Chen, Y.; Zuo, Y.; Ning, F.; Shang, H.; Feng, G.; Liu, N.; Shen, C.; Ai, X.; et al. A High-Performance Li-Mn-O Li-rich Cathode Material with Rhombohedral Symmetry via Intralayer Li/Mn Disordering. Adv. Mater. 2020, 32, 2000190. [Google Scholar] [CrossRef]
  48. Zi, Z.Y.; Zhang, Y.T.; Meng, Y.Q.; Gao, G.; Hou, P.Y. Hierarchical Li-rich oxide microspheres assembled from {010} exposed primary grains for high-rate lithium-ion batteries. New J. Chem. 2020, 44, 8486–8493. [Google Scholar] [CrossRef]
  49. Luo, X.D.; Yin, Y.Z.; Yuan, M.; Zeng, W.; Lin, G.; Huang, B.; Li, Y.W.; Xiao, S.H. High performance composites of spinel LiMn2O4/3DG for lithium ion batteries. RSC Adv. 2018, 8, 877–884. [Google Scholar] [CrossRef] [Green Version]
  50. Vetter, J.; Novak, P.; Wagner, M.R.; Veit, C.; Moller, K.C.; Besenhard, J.O.; Winter, M.; Wohlfahrt-Mehrens, M.; Vogler, C.; Hammouche, A. Ageing mechanisms in lithium-ion batteries. J. Power Source 2005, 147, 269–281. [Google Scholar] [CrossRef]
  51. Dang, F.; Hoshino, T.; Oaki, Y.; Hosono, E.; Zhou, H.; Imai, H. Synthesis of Li-Mn-O mesocrystals with controlled crystal phases through topotactic transformation of MnCO3. Nanoscale 2013, 5, 2352–2357. [Google Scholar] [CrossRef] [PubMed]
  52. Liu, Q.; Li, Y.X.; Hu, Z.L.; Mao, D.L.; Chang, C.K.; Huang, F.Q. One-step hydrothermal routine for pure-phased orthorhombic LiMnO2 for Li ion battery application. Electrochim. Acta 2008, 53, 7298–7302. [Google Scholar] [CrossRef]
  53. Zhao, H.Y.; Wang, J.; Wang, G.F.; Liu, S.S.; Tan, M.; Liu, X.Q.; Komarneni, S. Facile synthesis of orthorhombic LiMnO2 nanorods by in-situ carbothermal reduction: Promising cathode material for Li ion batteries. Ceram. Int. 2017, 43, 10585–10589. [Google Scholar] [CrossRef]
  54. Tong, W.M.; Chu, Q.X.; Meng, Y.J.; Wang, X.F.; Yang, B.; Gao, J.J.; Zhao, X.D.; Liu, X.Y. Synthesis of mesoporous orthorhombic LiMnO2 cathode materials via a one-step flux method for high performance lithium-ion batteries. Mater. Res. Express 2018, 5, 065511. [Google Scholar] [CrossRef]
Materials 14 04751 g001 550
Figure 1. The XRD patterns (a,b) and ratio of the two phases (c) of the four synthesized samples.
Figure 1. The XRD patterns (a,b) and ratio of the two phases (c) of the four synthesized samples.
Materials 14 04751 g001
Materials 14 04751 g002 550
Figure 2. The XPS spectra of the various samples (a–d).
Figure 2. The XPS spectra of the various samples (a–d).
Materials 14 04751 g002
Materials 14 04751 g003 550
Figure 3. The SEM images of the various samples (a–d), TEM image of LMO-2 (e), and particle size distribution of the samples (f–i).
Figure 3. The SEM images of the various samples (a–d), TEM image of LMO-2 (e), and particle size distribution of the samples (f–i).
Materials 14 04751 g003
Materials 14 04751 g004 550
Figure 4. Cyclic voltammograms (CVs) of the various samples in the potential range of 2.0–4.8 V (a–d).
Figure 4. Cyclic voltammograms (CVs) of the various samples in the potential range of 2.0–4.8 V (a–d).
Materials 14 04751 g004
Materials 14 04751 g005 550
Figure 5. The charge/discharge profiles of the various samples in the first cycle (a) and the corresponding dQ/dV curves (b).
Figure 5. The charge/discharge profiles of the various samples in the first cycle (a) and the corresponding dQ/dV curves (b).
Materials 14 04751 g005
Materials 14 04751 g006 550
Figure 6. Cycling performance at 0.1 C with the 2.0–4.5 V range (a), 0.1 C with the 2.0–4.8 V range (b), and 1 C with the 2.0–4.8 V range (c).
Figure 6. Cycling performance at 0.1 C with the 2.0–4.5 V range (a), 0.1 C with the 2.0–4.8 V range (b), and 1 C with the 2.0–4.8 V range (c).
Materials 14 04751 g006
Materials 14 04751 g007 550
Figure 7. The charging–discharging curves of various samples in the 50th cycle at potential range of 2.0−4.8 V (a–d).
Figure 7. The charging–discharging curves of various samples in the 50th cycle at potential range of 2.0−4.8 V (a–d).
Materials 14 04751 g007
Materials 14 04751 g008 550
Figure 8. The XRD pattern of the discharged LMO-2 cathode disk after 15 cycles.
Figure 8. The XRD pattern of the discharged LMO-2 cathode disk after 15 cycles.
Materials 14 04751 g008
Materials 14 04751 g009 550
Figure 9. Electrochemical impedance spectra (EIS) of the various samples before (a) and after 15 cycles (b,c).
Figure 9. Electrochemical impedance spectra (EIS) of the various samples before (a) and after 15 cycles (b,c).
Materials 14 04751 g009
Table
Table 1. The experimental results of the Li/Mn atom ratio, e Mn average valance, and corresponding calculated x-values.
Table 1. The experimental results of the Li/Mn atom ratio, e Mn average valance, and corresponding calculated x-values.
SampleLi/Mn expLi/Mn theoreticalMn Valance expx Values in
xLi2MnO3·(1 − x)LiMnO2
o-LiMnO21130
Li2MnO32241
LMO-11.114\3.1140.114
LMO-21.072\3.0720.072
LMO-31.045\3.0450.045
LMO-P1.009\3.0090.009
Table
Table 2. Different manganese valences and their respective content obtained using the chemical titration method, and the composition of xLi2MnO3·(1 − x)LiMnO2.
Table 2. Different manganese valences and their respective content obtained using the chemical titration method, and the composition of xLi2MnO3·(1 − x)LiMnO2.
SampleMn3+Mn4+x-Values in
xLi2MnO3·(1 − x)LiMnO2
LMO-188.8%11.2%0.112
LMO-292.9%7.1%0.071
LMO-395.3%4.7%0.047
LMO-P99.3%0.7%0.007
Table
Table 3. Electrochemical parameters for the alternating current EIS results, calculated using Z-view software.
Table 3. Electrochemical parameters for the alternating current EIS results, calculated using Z-view software.
SamplesAs PreparedAfter Cycling
Rs (Ω)Rct (Ω)Rs (Ω)Rf (Ω)Rct (Ω)
LMO-15.56384.1912.7123.53237.61
LMO-25.88274.018.8024.88134.10
LMO-35.52146.738.9927.5364.07
LMO-P5.38112.428.7529.4130.44
Table
Table 4. Summary of the synthetic conditions and electrochemical properties of the obtained lithium manganese oxide cathode materials prepared using different methods.
Table 4. Summary of the synthetic conditions and electrochemical properties of the obtained lithium manganese oxide cathode materials prepared using different methods.
ProductMethodVoltage
Range		Synthesis
Condition		Current Density
(mA g−1)		Maximum/Selected Cycle
Discharge Capacity (mAh g−1)		Reference
0.23Li2MnO3·0.77LiMnO2Solid state2.0−4.5 V750 °C/20 h20218/218 (30th)[11]
0.61Li2MnO3·0.39LiMnO2Sol–gel2.0−4.8 V600 °C/3 h
900 °C/12 h		10177/167 (30th)[12]
0.44Li2MnO3·0.56LiMnO2Hydrothermal +
solid state +
pyrolysis reduction		2.0−4.8 V200 °C/2 h
450 °C/10 h 500 °C/15 h
340 °C/4 h		30270/200 (30th)[13]
H0.46Li1.54MnO3Hydrothermal2.0−4.8 V180 °C/48 h200208/120 (20th)[14]
LiMnO2−Li2MnO3Hydrothermal2.0−4.5 V200 °C/72 h10192/182 (5th)[51]
o-LiMnO2Hydrothermal2.0−4.5 V160 °C/12 h20173/162 (20th)[52]
m-LiMnO2
Mixed m/o-LiMnO2
o-LiMnO2		Hydrothermal2.0−4.5 V180 °C/4 h
180 °C/8 h
220 °C/8 h		20219.8/94.5 (50th)
198.8/112.5 (50th)
180.0/106.8 (50th)		[31]
o-LiMnO2 nanorodsSolid state2.0−4.25 V750 °C/10 h20178.6/165.3 (40th)[53]
Mesoporous
o-LiMnO2		Solid state2.0−4.4 V600 °C/3 h20191.5/162.6 (50th)[54]
o-LiMnO2Dynamic hydrothermal2.0−4.5 V200 °C/3 h30166/145 (50th)[28]
0.072Li2MnO3·0.928LiMnO2Dynamic hydrothermal2.0−4.8 V200 °C/5 h30198.4/190.5 (50th)This work
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Wang, L.-B.; Hu, H.-S.; Lin, W.; Xu, Q.-H.; Gong, J.-D.; Chai, W.-K.; Shen, C.-Q. Electrochemically Inert Li2MnO3: The Key to Improving the Cycling Stability of Li-Rich Manganese Oxide Used in Lithium-Ion Batteries. Materials 2021, 14, 4751. https://doi.org/10.3390/ma14164751

AMA Style

Wang L-B, Hu H-S, Lin W, Xu Q-H, Gong J-D, Chai W-K, Shen C-Q. Electrochemically Inert Li2MnO3: The Key to Improving the Cycling Stability of Li-Rich Manganese Oxide Used in Lithium-Ion Batteries. Materials. 2021; 14(16):4751. https://doi.org/10.3390/ma14164751

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Wang, Lian-Bang, He-Shan Hu, Wei Lin, Qing-Hong Xu, Jia-Dong Gong, Wen-Kui Chai, and Chao-Qi Shen. 2021. "Electrochemically Inert Li2MnO3: The Key to Improving the Cycling Stability of Li-Rich Manganese Oxide Used in Lithium-Ion Batteries" Materials 14, no. 16: 4751. https://doi.org/10.3390/ma14164751

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