Branded with low cost and a high degree of safety, with an ambitious aim of substituting lithium-ion batteries in many fields, sodium-ion batteries have received fervid attention in recent years after being dormant for decades. Layered materials are a major focus of study owing to the extensive experience already gained in lithium-ion batteries, and the pursuit of a Mn-rich composition is critical to reduce the cost while retaining the performance. This review provides a timely update of the recent progress of Mn-rich layered materials for sodium-ion batteries based on the understandings of the phase forming principles, structure transformation upon cycling and charge compensation mechanisms and discusses potential ambiguities in the pursuit of high-performance materials.

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Pre-extracting Li+ from Li-rich layered oxides by chemical method is considered to be a targeted strategy for improving this class of cathode material. Understanding the structural evolution of the delithiated material is very important because this is directly related to the preparation of electrochemical performance enhanced Li-rich material. Herein, we perform a high temperature reheat treatment on the quantitatively delithiated Li-rich materials with different amounts of surface defect-spinel phase and carefully investigate the structural evolution of these delithiated materials. It is found that the high temperature reheat treatment could cause the decomposition of the unstable surface defect-spinel structure, followed by the rearrangement of transition metal ions to form the thermodynamically stable phases, More importantly, we find that this process has high correlation with the remaining Li-content in the delithiated material. When the amount of extracted Li+ is relatively small (corresponding to the higher remaining Li-content), the surface defect-spinel phase could be dominantly decomposed into the LiMO2 (M = Ni, Co, and Mn) layered phase along with the significant improvement of electrochemical performance, and continuing to decrease remaining Li-content could lead to the emergence of M3O4-type spinel impurity embedding in the final product. However, when the extracted Li+ further achieves a certain amount, after the high temperature heat-treatment the Mn-rich Li2MnO3 phase (C2/m) could be separated from Ni-rich phases (including R m, Fd m, and Fm m), thus resulting in a sharp deterioration of initial capacity and voltage. These findings suggest that reheating the delithiated Li-rich material to high temperature may be a simple and effective way to improve the predelithiation modification method, but first the amount of extracted Li+ should be carefully optimized during the delithiation process.

Multivalent transition metal oxides possess abundant phase and valence states, the transition of which is closely related to a wide range of functionalities that have applications in various areas, such as rechargeable batteries, supercapacitors,

Lithium‐rich and manganese‐based oxide (LRMO) cathode materials are regarded as promising cathode materials for lithium‐ion batteries with anionic redox characteristics and higher specific energy density. However, the complex initial structure and complicated reaction mechanism of LRMO is controversial. Herein, the reaction mechanism and unusual electrochemical phenomena are reconsidered after proposing the concept of structure distribution between Li2MnO3 and LiMO2 structures. The initial structure states show different types of composition characteristics of Li2MnO3 and LiMO2, including “large and isolated distribution” and “uniformly dispersed distribution” characteristics, as summarized by multiple aberration correction scanning transmission electron microscopy observations at the atomic‐scale for cross sectional samples. Based on the density functional theory calculations, X‐ray absorption spectroscopy, and atomic‐scale observations during the different voltage states, the results accordingly suggest that the distribution characteristic is the essential cause of the unusual behavior in LRMO. It governs the reaction behavior, leading to the changes in electronic structure of O2p and TM3d, and the maintenance of layered structure, reversibility of the anionic redox, as well as, the voltage hysteresis. This work constructs the interrelationships of electrochemical behavior—distribution characteristic—reaction mechanism, contributing to the further application of LRMO materials in the electric vehicle market.

Lithium-rich and manganese-based oxides (LRMO) with anionic redox behavior are regarded as the cathode material for the next generation commercial lithium-ion batteries (LIBs) that are most likely to achieve the...

All-solid-state batteries attract significant attention owing to their potential to realize an energy storage system with higher safety and energy density. In this work, a halide electrolyte coating with high lithium-ion conductivity obtained by mechanical coating under n-heptane solvent and annealing at 200 °C of Ni-rich LiNi0.83Co0.14Mn0.03O2 (NCM) for Li6PS5Cl-type all-solid-state batteries is reported. A 10% Li3InCl6-coated NCM material was assembled into a 10% LIC@NCM/Li6PS5Cl/In all-solid-state battery with an initial charge capacity of 201.3 mAh g–1, a discharge specific capacity of 158.7 mAh g–1, and a Coulombic efficiency of 79.06%. After 100 cycles at room temperature at 0.1C current density, the capacity retention was 92% and the capacity retention was 72% after 270 cycles. In comparison, all-solid-state batteries using matched Li6PS5Cl and untreated NCM had a capacity retention rate of 53% after 100 cycles at 0.1C under the same charge/discharge regime and environment. It is indicated that the cycling performance and rate performance of the NCM material significantly improve after the 10% LIC coating. In this paper, X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), high-resolution high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and other tests and analyses confirmed the following: the pregenerated interfacial layer of approximately 2 nm on the surface of NCM after the 10% halide solid electrolyte coating improves the structural stability of the material during charging and discharging, the LIC coating layer slows down the decomposition of LI6PS5Cl during cycling, and the capacity increase at high rates is due to the reduction of the interfacial impedance between the cathode material and LI6PS5Cl solid electrolyte.

Benefiting from the advanced solid-state electrolytes (SSEs), conventional cathodes have been widely applied in all-solid-state lithium batteries (ASSLBs). However, Li-rich Mn-based (LRM) cathodes, which possess enhanced discharge capacities beyond 250 mA h g–1, have not yet been studied in ASSLBs. In this work, the practical application of LRM cathodes in ASSLBs using a high-voltage-stability halide SSE (Li3InCl6, LIC) is reported for the first time. Furthermore, we decipher that the active oxygen released from LRM cathodes at a high operation voltage seriously oxidizes the LIC electrolytes, thus resulting in the large interfacial resistance between cathodes and electrolytes and hindering their industrialized application in ASSLBs. Therefore, surface chemistry engineering of LRM cathodes with an ionic conductive coating material of LiNbO3 (LNO) is employed to stabilize the LRM/LIC interface. Consequently, the LRM-based ASSLBs deliver a high specific capacity of 221 mA h g–1 at 0.1 C and a decent cycle life of 100 cycles. This contribution gives insights into studying the interfacial issues between LRM cathodes and halide electrolytes and sheds light on the application of LRM cathode materials in ASSLBs.