Different mechanical and electrochemical behavior between the two major Ni-rich cathode materials in Li-Ion batteries

Abstract

Ni-rich cathode is a new family of lithium storage materials with high reversible capacity and low cost. To compare the fundamental differences between the two major technical routes, long-term cycling performance and mechanical behavior between monocrystalline and polycrystalline NCM811 particles are investigated in standard pouch cells against commercial graphite anode. After 600 deep charge discharge cycles, the cell using monocrystalline NCM811 cathode shows relatively higher capacity retention of 88.9% compared to that of the polycrystalline counterpart. During the charge, monocrystalline NCM811 cathode shows higher swelling force due to smaller volume change to offset the volume expansion of the graphite anode. By contrast, the larger volume change of the polycrystalline cathode easily induces mechanical fracture of the secondary particle. The volume change and the resulted mechanical failure for the polycrystalline NCM811 cathode can be alleviated by decreasing the charge voltage limit of the cell, but at an expense of its energy density.