Misfit strain-induced mechanical cracking aggravating surface degradation of LiCoO₂

Cycling-induced cathode interfacial degradations are usually attributed to chemical process, while the physical effect is overlooked to a large extent. Herein, we investigate the failure mechanism of LiCoO2 cathode and reveal that misfit strain plays a dominant role in the surface layer exfoliation process. We illustrate that highly strained LiCoO2 surface can initiate massive surface cracks, leading to the LiCoO2 surface layer broken and exfoliation. Mechanical cracking coupled with chemical etching aggravates the surface layer degradation, leading to a weathering-like degradation on LiCoO2 surface. Our work reveals that interfacial degradation of electrode materials is a complex physicochemical process.Impact StatementInterfacial degradations are usually believed as chemical effect dominated failure. Herein, we show that the overlooked physical effect, misfit strain, in fact plays a critical role in the surface degradation process and stress that LiCoO2 surface degradation is a complex physicochemical process.