Synergistic effects of Zr doping and Li2ZrO3/WO3 co-coating on the physicochemical and electrochemical properties of cobalt-free LiNi0.8Mn0.2O2

Abstract

Particle fragmentation and thermal stability during repeated delithiation and lithiation are key issues that affect nickel-rich cobalt-free LiNixMn1-xO2. In this study, the physicochemical and electrochemical characteristics of LiNi0.8Mn0.2O2 (NM) cathode materials were improved by Zr doping and Li2ZrO3/WO3 co-coatings. During solid-phase sintering, ZrO2 reacts with residual lithium on the surface of NM materials to form the lithium-ion conductor Li2ZrO3, while Zr4+ occupies transition metal sites in the material lattice. The reversible capacity of NM modified by 1 mol% ZrO2 and 1 mol% WO3 was 179.5 mAh/g (10.16 % loss) after 200 cycles at 1C (200 mAh/g), while the discharge capacity of pristine NM was 138.0 mAh/g (21.15 % loss). Moreover, the Li+ diffusion coefficient of the co-modified material increased from 4.429 × 10−13 cm2/s to 1.772 × 10−12 cm2/s. According to density functional theory calculations, Zr ion doping enhances the electrical conductivity of NM materials and the binding energy of molecular oxygen. By comparing the structure and morphology of the two samples after cycling, it was demonstrated that elemental co-modification effectively stabilises the crystal structure, reduces electrolyte erosion and improves the electrochemical performance of the material. Thus, this study details a method for improving the structure and thermal stability of cobalt-free nickel-rich cathode materials.