Abstract
High-energy density lithium-rich layered oxides are among the most promising candidates for next-generation energy storage. Unfortunately, these materials suffer from severe electrochemical degradation that includes capacity loss and voltage decay during long-term cycling. Present research efforts are primarily focused on understanding voltage decay phenomena while origins for capacity degradation have been largely ignored. Here, we thoroughly investigate causes for electrochemical performance decline with an emphasis on capacity loss in the lithium-rich layered oxides, as well as reaction pathways and kinetics. Advanced synchrotron-based X-ray two-dimensional and three-dimensional imaging techniques are combined with spectroscopic and scattering techniques to spatially visualize the reactivity at multiple length-scales on lithium- and manganese-rich layered oxides. These methods provide direct evidence for inhomogeneous manganese reactivity and ionic nickel rearrangement. Coupling deactivated manganese with nickel migration provides sluggish reaction kinetics and induces serious structural instability in the material. Our findings provide new insights and further understanding of electrochemical degradation, which serve to facilitate cathode material design improvements.
Highlights
High-energy density lithium-rich layered oxides are among the most promising candidates for next-generation energy storage
These new insights into the distinct behaviors of LR-NCM transition metals elucidate the origins of capacity degradation, voltage decay, and facilitate the development of high-capacity cathode designs
Researchers primarily focus on voltage decay phenomena, which is correlated to thermodynamic changes caused by phase transformation[18]
Summary
High-energy density lithium-rich layered oxides are among the most promising candidates for next-generation energy storage These materials suffer from severe electrochemical degradation that includes capacity loss and voltage decay during long-term cycling. Lithium- and manganese-rich (LMR) oxides are promising candidates due to their noteworthy energy density that exceeds 900 Wh Kg−1 (vs Li metal)[1,2] These materials suffer from serious electrochemical degradation, including voltage decay and capacity loss, which restricts real-world implementation[3,4]. We directly capture spatial structure evolutions in high-capacity Li1.2Ni0.13Co0.13Mn0.54O2 (LR-NCM) cathodes during long-term cycling using advanced synchrotron-based Xray imaging techniques and X-ray absorption near edge structures (XANES) These techniques highlight the different behaviors of various transition metals (nickel and manganese) in the secondary particle level, revealing deactivated and correlated anisotropic reactivity for manganese and ionic rearrangement for nickel. These new insights into the distinct behaviors of LR-NCM transition metals elucidate the origins of capacity degradation, voltage decay, and facilitate the development of high-capacity cathode designs
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