Electrochemical performance and thermal stability of Li1.18Co0.15Ni0.15Mn0.52O2 surface coated with the ionic conductor Li3VO4

Abstract

Li_1.18Co_0.15Ni_0.15Mn_0.52O₂ cathode material was prepared by the sol–gel method. The material was coated with the ionic conductor Li₃VO₄via direct reaction with NH₄VO₃ at 350 °C. The Li₃VO₄ coated material had a higher ordered hexagonal layered structure, and less Li⁺/Ni²⁺ cation mixing. The surface of the coated material was composed of Li₃VO₄ polycrystals, which were impregnated into the bulk of the active material. The surface coating protected the material from contact with CO₂ in the air, thus inhibiting the formation of an Li₂CO₃ layer. Electrochemical studies showed that the Li₃VO₄ surface coating improved the activation of Mn⁴⁺ ions, resulting in a high discharge capacity. It also prohibited the growth of a solid electrolyte interface film, and facilitated the charge transfer reactions at the electrode/electrolyte interface, thus improving the rate capability and cycle stability of the material. DSC analysis of the fully charged electrode showed that the temperature of the exothermic peak increased from 205.2 °C to 232.8 °C, and that the amount of heat that was released was reduced from 807.5 J g⁻¹ to 551.0 J g⁻¹, highlighting the improved thermal stability of the material after coating with Li₃VO₄ .