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Singlecrystal 23/17/2023 ![]() To solve the deficiencies caused by different reasons, creative strategies are necessary to improve structural stability in NCM particles 15. Another issue was recently raised that uneven stresses, observed in cycles driven at high voltage, induced intragranular cracks in polycrystalline, which exacerbated structural collapse and capacity loss in Ni-rich NCM 12, 13, 14. ![]() Therefore doping strategies would consequently decrease specific capacity. Although some traditional methods doping and coating strategies have been reported to inhibit cation mixing and suppress interfacial reactions, the excessive coating layer (>20 nm) and unregulated doping strategy may hinder the migration of Li +, resulting in poor rate capability 10, 11. In addition, the dissolution, migration, and segregation of TMs on the surface further deteriorate battery performance 7, 8, 9. During delithiation, the layered oxide material may transform into a spinel-type phase and then to a completely disordered rock salt-type structure, which is believed to inhibit the diffusion of lithium ions. It is commonly accepted that these transitions from layered to spinel or rock-salt phases, and migration/segregation of transition metals (TMs) induce structural reconstruction that facilitates capacity fade 4, 5, 6. However, the increased voltage cutoffs also aggravate material decomposition and impede the battery performance 1, 2, 3. Specific capacity improvement has been reported in high Ni content lithium nickel cobalt manganese oxide (NCM) electrodes for lithium-ion batteries (LIBs) charged at high voltage. Our modified process effectively regulates the performance fade issue of single-crystal cathode and provides new insights for improved design of high-capacity battery materials. We also discover that surface chemistry can significantly enhance the cyclic performance. We directly observe a close correlation between surface chemistry and phase distribution from homogeneity to heterogeneity, which induces heterogeneous internal strain within the particle and the resulting structural/performance degradation during cycling. Here, we investigate the correlation of the surface structure, internal strain, and capacity deterioration by using operando X-ray spectroscopy imaging and nano-tomography. Understanding how the surface structural changes determine the performance degradation over cycling is crucial, but remains elusive. However, after being cycled at high voltages, these single-crystal materials exhibit severe structural instability and capacity fade. Single-crystal cathode materials for lithium-ion batteries have attracted increasing interest in providing greater capacity retention than their polycrystalline counterparts.
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