Gel-combustion synthesis of Li1.2Mn0.4Co0.4O2 composites with a high capacity and superior rate capability for lithium-ion batteries

Abstract

Owing to the merits of high capacity and low cost, Li-rich layered composite cathode materials have received extensive attention. Nevertheless, such materials always suffer from a poor rate capability, which seriously hinders their widespread practical applications. In this work, Li_1.2Mn_0.4Co_0.4O₂ composites were fabricated by a gel-combustion method, in which lithium carbonates formed by an in situ burning reaction were homogeneously mixed with metal oxides, leading to excellent electrochemical properties. The sintering temperature and time were optimized to 900 °C and 15 h. The samples prepared at optimum conditions exhibited a high discharge capacity and excellent rate capability. At a current density of 20 mA g⁻¹, the specific discharge capacity was 310.5 mA h g⁻¹ for the first cycle and the capacity retention was 75.8% after 30 cycles. When the current densities increase by 10 times to reach 200 mA g⁻¹, the initial discharge capacity is still as high as 241.4 mA h g⁻¹, superior to that of 203 mA h g⁻¹ at the same current density reported previously by the oxalate-precursor method. Even when the current densities increase by 20 times, the capacity remained as high as 203.7 mA h g⁻¹, and the capacity retention was 79.4% over 30 cycles. The high discharge capacity and improved rate capability of the optimized sample were beneficial with a perfect layered structure with c/a >5.0, appropriate particle size of about 450 nm, high lithium ion diffusion coefficient around 1.42 × 10⁻¹³ cm² s⁻¹, and the presence of a maximum content of Mn³⁺ (11.6%), as determined by XPS. The preparation method reported herein may provide hints for obtaining various advanced Li-rich layered composite materials for use in high-performance energy storage and conversion devices.