Surface regulation enables high stability of single-crystal lithium-ion cathodes at high voltage

TLDR

Single‑crystal cathode materials promise higher capacity retention than polycrystalline counterparts, yet they suffer severe structural instability and capacity fade at high voltages, and the role of surface structural changes in this degradation remains unclear. The study aims to investigate how surface structure and internal strain correlate with capacity deterioration in single‑crystal cathodes. Operando X‑ray spectroscopy imaging and nano‑tomography were employed to map surface chemistry, phase distribution, and internal strain during cycling. The results reveal that surface chemistry drives heterogeneous phase distribution and internal strain, leading to performance degradation, but a modified surface‑regulation process mitigates fade and improves cyclic performance, offering new design insights.

Abstract

Abstract Single-crystal cathode materials for lithium-ion batteries have attracted increasing interest in providing greater capacity retention than their polycrystalline counterparts. However, after being cycled at high voltages, these single-crystal materials exhibit severe structural instability and capacity fade. Understanding how the surface structural changes determine the performance degradation over cycling is crucial, but remains elusive. Here, we investigate the correlation of the surface structure, internal strain, and capacity deterioration by using operando X-ray spectroscopy imaging and nano-tomography. 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. We also discover that surface chemistry can significantly enhance the cyclic performance. 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.