Fig. 1: The gradient porosity design for NCM cathodes.

The cross-sections of the pristine NCM (P-NCM) and the gradient-porous-structured NCM (GP-NCM) before electrochemical cycling are shown as the “Before cycling” areas. There are more voids between the primary particles in GP-NCM compared with P-NCM, in which the primary particles are tightly packed. After cycling, GP-NCM is resistant to intergranular fracture (represented by the bottom right corner region in GP-NCM), whereas severe microcracks occur in P-NCM (represented by the bottom right corner region in P-NCM), exposing internal fresh surfaces to various surface-related degradations. The chemo-mechanical stability of GP-NCM is crucial to its stable cycle performance.