High Cycling Rate-Induced Irreversible TMO6 Slabs Glide in Co-Free High-Ni Layered Cathode Materials

Co-free high-Ni layered transition metal oxide is a promising cost-effective cathode material for high-energy Li-ion batteries, but it suffers from undesirable rate performance and rapid capacity decay upon high-rate cycling. The underlying structural changes under fast electrochemical processes remain unclear to date. In this study, atomic scale structural evolutions of Co-free high-Ni layered cathode at different cycling rates are revealed by advanced TEM characterization. It is found that the phase transition after high-rate cycling is much different from that after low-rate cycling. The low-rate cycled sample shows a typical layer-to-rock salt transition. However, O1-type stacking faults are uncovered in the high-rate cycled sample owing to irreversible TMO6 slabs glide, which induces severe lattice distortion and structural dislocations. These findings deepen the understanding of the rate-dependent structural degradation mechanism of Co-free high-Ni layered cathodes, and have significant implications for improving current materials to withstand high-rate applications.