Impact of the Synthesis Conditions on the Performance of LiNi_xCo_yAl_zO₂ with High Ni and Low Co Content

Abstract

One way to lower the cost of lithium ion batteries using LiNixMnyCozO2 (NMC) or LiNi0.80Co0.15Al0.05O2 is to lower the Co content in the positive electrode materials. This work systematically studied the impact of the synthesis conditions on the performance of LiNixCoyAlzO2 (x ≥ 0.8, z ≤ 0.05 and x + y + z = 1) (NCA) with high Ni and low Co content. The impacts of oxygen flow rate, sintering temperature, initial Li/TM ratio and sintering time on the structural and electrochemical properties of NCA were systematically studied. The conditions when impurity phases such as Li2CO3 and Li5AlO4 appear were carefully examined. The impact of residual lithium compounds on the electrochemical performance was also discussed. It was found that the synthesis conditions, which affect the a-axis, c-axis and NiLi content of the NCA samples, have strong impacts on the lithium diffusion at low and high states of charge based on differential capacity vs. voltage (dQ/dV vs. V) measurements at various rates and temperatures. Additionally, the reversible capacity and cycling stability correlated strongly with the intensity of the dQ/dV vs V peak at 3.5 V (discharge) measured with a C/20 rate at 30°C.