Li2Ni0.2Co1.8O4 having a spinel framework as a zero-strain positive electrode material for lithium-ion batteries

Abstract

Zero-strain insertion materials are ideal electrode materials for lithium-ion batteries because they do not undergo dimensional change during lithium insertion and extraction. Herein, a zero-strain insertion material, Ni-substituted Li₂Co₂O₄ (Li₂Ni_0.2Co_1.8O₄) having a spinel framework, was synthesized and characterized to study the zero-strain mechanism. The change in the lattice dimensions of Li₂Ni_0.2Co_1.8O₄ during lithium extraction was very small (only 0.1%), confirming that Li₂Ni_0.2Co_1.8O₄ is a zero-strain insertion material. It had a flat voltage profile at 3.5 V with a reversible capacity of 100 mA h g⁻¹, which was quite different from the voltage profile of LiCoO₂ having a layered structure. Detailed structural analysis by X-ray absorption spectroscopy revealed that there was no dimensional change because the changes in two crystallographic factors, contraction of the Co–O bond and distortion of the oxygen sublattice, cancelled out. The zero-strain lithium-ion battery combined with Li₂Ni_0.2Co_1.8O₄ and Li[Li_1/3Ti_5/3]O₄ showed good cyclability.