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

One way to lower the cost of lithium ion batteries using LiNi x Mn y Co z O 2 (NMC) or LiNi 0.80 Co 0.15 Al 0.05 O 2 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 LiNi x Co y Al z O 2 (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 Li 2 CO 3 and Li 5 AlO 4 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 Ni Li 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.