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ABSTRACT Current Li‐ion battery technology relies on Li⁺insertion/extraction coupled with electron gaining/loss at both cathodes and anodes. Although extensive efforts have been devoted to studying the structure change of cathode materials with Li⁺extraction/insertion, changes in the magnetic properties arising from the accompanying redox processes have been largely overlooked. Here, we systematically investigate both the structure evolution and magnetic‐property changes during the delithiation of the representative layered oxide LiCoO₂, by combining the operando synchrotron‐based x‐ray diffraction with dedicated magnetic measurements. We construct a magnetic phase diagram as a function of Li contentxin Li_xCoO₂, which closely mirrors the corresponding structure evolution diagram. The results reveal a series of complicated magnetic transitions upon Li extraction: paramagnetic → antiferromagnetic → paramagnetic → diamagnetic → paramagnetic. Moreover, the variation in the effective magnetic moment of Co⁴⁺is strongly correlated with local structural changes within the CoO₆octahedra, indicating that the Co⁴⁺spin‐state fluctuation may play an important role in the structure evolution and electrochemical performance. These findings help close a critical gap in understanding structure‐magnetism coupling during the electrochemical cycling and may inspire the design of new layered oxide cathodes from a spin‐electronics perspective. 

Abstract One of the most challenging aspects of developing high-energy lithium-based batteries is the structural and (electro)chemical stability of Ni-rich active cathode materials at thermally-abused and prolonged cell cycling conditions. Here, we report in situ physicochemical characterizations to improve the fundamental understanding of the degradation mechanism of charged polycrystalline Ni-rich cathodes at elevated temperatures (e.g., ≥ 40 °C). Using multiple microscopy, scattering, thermal, and electrochemical probes, we decouple the major contributors for the thermal instability from intertwined factors. Our research work demonstrates that the grain microstructures play an essential role in the thermal stability of polycrystalline lithium-based positive battery electrodes. We also show that the oxygen release, a crucial process during battery thermal runaway, can be regulated by engineering grain arrangements. Furthermore, the grain arrangements can also modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered oxide cathode materials. 

Metal nanoparticles of multi-principal element alloys (MPEA) with a single crystalline phase have been synthesized by flash heating/cooling of nanosized metals encapsulated in micelle vesicles dispersed in an oil phase (e.g., cyclohexane). Flash heating is realized by selective absorption of a microwave pulse in metals to rapidly heat metals into uniform melts. The oil phase barely absorbs microwave and maintains the low temperature, which can rapidly quench the high-temperature metal melts to enable the flash cooling process. The precursor ions of four metals, including Au, Pt, Pd, and Cu, can be simultaneously reduced by hydrazine in the aqueous solution encapsulated in the micelle vesicles. The resulting metals efficiently absorb microwave energy to locally reach a temperature high enough to melt themselves into a uniform mixture. The duration of microwave pulse is crucial to ensure the reduced metals mix uniformly, while the temperature of oil phase is still low to rapidly quench the metals and freeze the single-phase crystalline lattices in alloy nanoparticles. The microwave-enabled flash heating/cooling provides a new method to synthesize single-phase MPEA nanoparticles of many metal combinations when the appropriate water-in-oil micelle systems and the appropriate reduction reactions of metal precursors are available.