Collapse of LiNi1–x–yCoxMnyO2 Lattice at Deep Charge Irrespective of Nickel Content in Lithium-Ion Batteries

Abstract

Volume variation and the associated mechanical fracture of elec-trode materials upon Li extraction/insertion are a main cause limit-ing lifetime performance of lithium-ion batteries. For LiNi1-x-yCoxMnyO2 (NCM) cathodes, abrupt anisotropic collapse of the layered lattice structure at deep charge is generally considered char-acteristic to high Ni content and can be effectively suppressed by elemental substitution. Herein, we demonstrate the lattice collapse is a universal phenomenon almost entirely dependent on Li utilization, and not Ni content, of NCM cathodes upon delithiation. With Li removal reaching 80 mol%, very similar c-axis lattice shrinkage of around 5% occurs concurrently for NCMs synthesized in-house regardless of nickel content (90, 70, 50, or 33 mol%); meanwhile, the a-axis lattice contracts for high-Ni NCM, but it expands for low-Ni NCM. We further reveal Co-Mn co-substitution in NCM barely, if at all, affects key structural aspects governing the lattice distortion upon delithiation. Our results highlight the importance of evaluating true implications of compositional tuning on high-Ni layered oxide cathode materials to maximize their charge-storage capacities for next-generation high-energy-density Li-ion batteries.