Surface Facet Dependent Cycling Stability of Layered Cathodes

High chemical and mechanical stability of cathode surface are the prerequisites enabling high-performance rechargeable battery. Surface facet is among the surface properties that dictate surface stability and cycling performance, while its underlying mechanism remains elusive. Herein, it is reported that surface stability is closely related to the surface facet for a variety of layered cathodes. The investigation shows that surface structure of P2 layered cathode undergoes sequential transformation upon cycling, which results in severe surface degradation. This study finds that the surface facets perpendicular to the (002) planes experience severe cracking and corrosion, while other surface facets are much more stable. The surface stability difference mainly comes from a geometric effect on strain release, which determines the mechanical stability of surface. Chemically, transition metal condensation forms a passivation layer to effectively prevent the inward propagation of surface degradation. Therefore, the surface facets oblique to the layered-planes are intrinsically more resistant to mechanical cracking and chemical corrosion, which is further verified as a common effect in several O3-type layered cathodes. This work not only deepens the understanding of the mechanism how surface facet affects surface stability, but also validates surface facet regulation can be a promising strategy for optimizing battery materials.