Improving cycling performance and high rate capability of LiNi0.5Mn0.3Co0.2O2 cathode materials by sol-gel combustion synthesis

Abstract

The layered LiNi_0.5Mn_0.2Co_0.2O₂ (NMC532) material displays capacity loss and poor rate performance even though it is a widely used cathode in commercial Li-ion batteries (LIBs). In this work, the structural and electrochemical performance of the NMC532 cathode were optimized using the fuel-to-oxidizer ratio assisted sol-gel combustion synthesis (SCS). It was shown that the fuel-to-oxidizer ratio markedly influenced the exothermicity of the combustion reaction which affected the crystal structure, morphology, and electrochemical performance of the final NCM532 materials. The fuel lean (FL) composition produced NMC532 cathode materials with the biggest crystallite and particle sizes, less cation mixing degree and better layered structure compared with the fuel stoichiometric (FS) and fuel rich (FR) compositions. The FL cell presented an initial discharge capacity of 180 mAh g⁻¹ and the highest capacity retention of 92.2 % when it was cycled at 0.1 C between 2.5 and 4.4 V. Also, the FL cell displayed exceptional rate capability with the average capacities reaching 180, 178, 175, and 173 mAh/g at current densities of 1 C, 3 C, 5 C, and 10 C, respectively between 3.0 and 4.6 V. The EIS tests and dQ/dV plots showed that the FL cell both had the least impedance and polarization. The superior electrochemical performance of the FL material was ascribed to its optimized structural properties. Furthermore, the electrochemical results also show the influence of voltage window and current density on the performance of the NMC532 cathode materials.