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Abstract Understanding defect evolution and structural transformations constitutes a prominent research frontier for ultimately controlling the electrochemical properties of advanced battery materials. Herein, for the first time, we utilize in situ high-energy Kr ion irradiation with transmission electron microscopy to monitor how defects and microstructures evolve in Na- and Li-layered cathodes with 3d transition metals. Our experimental and theoretical analyses reveal that Li-layered cathodes are more resistant to radiation-induced structural transformations, such as amorphization than Na-layered cathodes. The underlying mechanism is the facile formation of Li-transition metal antisite defects in Li-layered cathodes. The quantitative mathematical analysis of the dynamic bright-field imaging shows that defect clusters preferentially align along the Na/Li ion diffusion channels ( a-b planes), which is likely governed by the formation of dislocation loops. Our study provides critical insights into designing battery materials for extreme irradiation environments and understanding fundamental defect dynamics in layered oxides. 

Layered cathode materials (LCMs), because of their high energy density and relatively stable performance, represent an important class of cathode materials for alkali metal ion ( e.g. , Li + and Na + ) batteries. Chemomechanical behaviors of LCMs, which affect battery performance dramatically, have drawn extensive attention in recent years. Most chemomechanical processes have some common chemical and structural origins that are at the center of materials chemistry, for example, defects and local bonding environments in the solid state. In this review, we first discuss the chemomechanical breakdown of LCMs by introducing their categories and negative effects on the battery performance. We then systematically analyze factors that govern the initiation and propagation of chemomechanical breakdown and summarize their formation mechanisms. Strategies that can enhance the chemomechanical properties of LCMs or reduce the destructive effects of chemomechanical breakdown are then discussed. Finally, light is shed on the new state-of-the-art techniques that have been applied to study chemomechanical breakdown. This review virtually includes most aspects of the chemomechanical behaviors of LCMs and provides some insights into the important chemical motifs that determine the chemomechanical properties. Therefore, we believe that advanced design protocols of LCMs can be developed to effectively address the chemomechanical breakdown issue of LCMs. 

While Li ion batteries are intended to be operated within a mild temperature window, their structural and chemical complexity could lead to unanticipated local electrochemical events that could cause extreme temperature spikes, which, in turn, could trigger more undesired and sophisticated reactions in the system. Visualizing and understanding the response of battery electrode materials to thermal abuse conditions could potentially offer a knowledge basis for the prevention and mitigation of the safety hazards. Here we show a comprehensive investigation of thermally driven chemomechanical interplay in a Li 0.5 Ni 0.6 Mn 0.2 Co 0.2 O 2 (charged NMC622) cathode material. We report that, at the early stage of the thermal abuse, oxygen release and internal Li migration occur concurrently, and are accompanied by mechanical disintegration at the mesoscale. At the later stage, Li protrusions are observed on the secondary particle surface due to the limited lithium solubility in non-layered lattices. The extraction of both oxygen and lithium from the host material at elevated temperature could influence the chemistry and safety at the cell level via rearrangement of the electron and ion diffusion pathways, reduction of the coulombic efficiency, and/or causing an internal short circuit that could provoke a thermal runaway. 

Benefiting from abundant resource reserves and considerable theoretical capacity, sodium (Na) metal is a strong anode candidate for low‐cost, large‐scale energy storage applications. However, extensive volume change and mossy/dendritic growth during Na electrodeposition have impeded the practical application of Na metal batteries. Herein, a self‐sodiophilic carbon host, lignin‐derived carbon nanofiber (LCNF), is reported to accommodate Na metal through an infiltration method. Na metal is completely encapsulated in the 3D space of the LCNF host, where the strong interaction between LCNF and Na metal is mediated by the self‐sodiophilic sites. The resulting LCNF@Na electrode delivers good cycling stability with a low voltage hysteresis and a dendrite‐free morphology in commercial carbonate‐based electrolytes. When interfaced with O3‐NaNi_0.33Mn_0.33Fe_0.33O₂and P2‐Na_0.7Ni_0.33Mn_0.55Fe_0.1Ti_0.02O₂cathodes in full cell Na metal batteries, the LCNF@Na electrode enables high capacity retentions, long cycle life, and good rate capability. Even in a “lean” Na anode environment, the full cells can still deliver good electrochemical performance. The overall stable battery performance, based on a self‐sodiophilic, biomass‐derived carbon host, illuminates a promising path towards enabling low‐cost Na metal batteries.