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 LiCoO

2

cathode and reveal that misfit strain plays a dominant role in the surface layer exfoliation process. We illustrate that highly strained LiCoO

2

surface can initiate massive surface cracks

leading to the LiCoO

2

surface layer broken and exfoliation. Mechanical cracking coupled with chemical etching aggravates the surface layer degradation

leading to a weathering-like degradation on LiCoO

2

surface. Our work reveals that interfacial degradation of electrode materials is a complex physicochemical process.

Impact Statement

Interfacial 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 LiCoO

2

surface degradation is a complex physicochemical process.