Improved conductivity and electrochemical properties of LiNi0.5Co0.2Mn0.3O2 materials via yttrium doping

Abstract

A series of LiNi_0.5Co_0.2−xMn_0.3Y_xO₂ (x = 0, 0.01, 0.02, 0.03) materials was synthesized using a co-precipitation method, and the impact of yttrium doping on the crystalline structure, particle morphology, particle size, electronic conductivity and electrochemical performances was investigated. The PXRD refinement, SEM, EDS and XPS results indicate that yttrium ions have been successfully incorporated into the matrix structure of the materials, and that the crystalline structure and particle morphology of the LiNi_0.5Co_0.2Mn_0.3O₂ cathode material is not changed after yttrium doping. Electrochemical test results show that the rate capability, cycling stability and low-temperature performance of the yttrium doped materials are remarkably improved. Especially, the LiNi_0.5Co_0.18Mn_0.3Y_0.02O₂ sample exhibits the best electrochemical performance, delivering a high discharge capacity of 125.6 mA h g⁻¹ at a rate of 10C, with a capacity retention of 83.0% after 150 cycles at a rate of 1C in the voltage range of 3.0–4.5 V. The material also shows a discharge capacity of 148.9 mA h g⁻¹ at −20 °C at a rate of 0.2C, which is 81.0% of the same discharge rate at 25 °C, with a capacity retention of 81.5% after 50 cycles. CV and EIS measurements show that LiNi_0.5Co_0.18Mn_0.3Y_0.02O₂ exhibits lower polarization, lower charge transfer resistance and a larger lithium ion diffusion coefficient than LiNi_0.5Co_0.2Mn_0.3O₂. Additionally, the electronic conductivity of the LiNi_0.5Co_0.18Mn_0.3Y_0.02O₂ sample is 2.69 × 10⁻² S cm⁻¹, which is fourteen times higher than that of LiNi_0.5Co_0.2Mn_0.3O₂. Therefore, both the electronic conductivity and ionic conductivity of LiNi_0.5Co_0.2Mn_0.3O₂ are improved by yttrium doping, which are beneficial to enhancing electrochemical performance.