A breakthrough utilizing an anionic redox reaction (O 2− /O n− ) for charge compensation has led to the development of high‐energy cathode materials in sodium‐ion batteries. However, its reaction results in a large voltage hysteresis due to the structural degradation arising from an oxygen loss. Herein, an interesting P2‐type Mn‐based compound exhibits a distinct two‐phase behavior preserving a high‐potential anionic redox (≈4.2 V vs Na + /Na) even during the subsequent cycling. Through a systematic series of experimental characterizations and theoretical calculations, the anionic redox reaction originating from O 2p‐electron and the reversible unmixing of Na‐rich and Na‐poor phases are confirmed in detail. In light of the combined study, a critical role of the anion‐redox‐induced two‐phase reaction in the positive‐negative point of view is demonstrated, suggesting a rational design principle considering the phase separation and lattice mismatch. Furthermore, these results provide an exciting approach for utilizing the high‐voltage feature in Mn‐based layered cathode materials that are charge‐compensated by an anionic redox reaction.

SnS nanoparticles embedded in N-doped carbon are prepared by using Sn(salen) and exhibited outstanding electrochemical performance for lithium-ion batteries.

Integrated with heat-generating devices, a Li-ion battery (LIB) often operates at 20–40 °C higher than the ordinary working temperature. Although macroscopic investigation of the thermal contribution has shown a significant reduction in the LIB performance, the molecular level structural and chemical origin of battery aging in a mild thermal environment has not been elucidated. On the basis of the combined experiments of the electrochemical measurements, Cs-corrected electron microscopy, and in situ analyses, we herein provide operando structural and chemical insights on how a mild thermal environment affects the overall battery performance using anatase TiO2 as a model intercalation compound. Interestingly, a mild thermal condition induces excess lithium intercalation even at near-ambient temperature (45 °C), which does not occur at the ordinary working temperature. The anomalous intercalation enables excess lithium storage in the first few cycles but exerts severe intracrystal stress, consequently cracking the crystal that leads to battery aging. Importantly, this mild thermal effect is accumulated upon cycling, resulting in irreversible capacity loss even after the thermal condition is removed. Battery aging at a high working temperature is universal in nearly all intercalation compounds, and therefore, it is significant to understand how the thermal condition contributes to battery aging for designing intercalation compounds for advanced battery electrode materials.

Sodium-ion batteries (NIBs) are promising alternatives to lithium-ion batteries for large-scale energy applications such as energy storage systems, owing to the earth-abundance and low cost of sodium resources. Among layered oxide cathode materials for NIBs, O3-type NaCrO 2 has attracted considerable attention owing to its electrochemically active Cr 3+/4+ , which is unlike that of LiCrO 2 , and potential for carbon coating with a high thermal stability. In this study, we propose a new facile and eco-friendly method for applying nitrogen-doped carbon to NaCrO 2 using coffee waste as a carbon source. The synthesized O3-type NaCrO 2 /coffee waste-derived N-doped carbon composite exhibits an outstanding electrochemical performance as an NIB cathode material. The sodium/composite cell achieved a 73.7% capacity retention after 500 charge/discharge cycles and an approximate 50% discharge capacity during 43 s of charge. The results demonstrate the potential use of coffee waste for battery materials with improved electrochemical performances.

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