Urea and PVP assisted modified hydrothermal synthesis of spherical LiNi0.4Co0.2Mn0.4O2 cathode materials for battery application

Spherical LiNi0.4Co0.2Mn0.4O2 powders are synthesized via the modified hydrothermal method with the presence of urea and polyvinyl pyrrolidone (PVP). For comparison, LiNi0.4Co0.2Mn0.4O2 powders are also synthesized via the normal hydrothermal method without urea and PVP. In the normal hydrothermal process, incomplete compound formation with extra Li2MnO3 phase is observed. Whereas, phase-pure LiNi0.4Co0.2Mn0.4O2 powders with the well-ordered layered structure are obtained via the modified hydrothermal process. The modified hydrothermal process considerably reduces the cation disorder of Li+/Ni2+ and yields spherical-shaped particles. The LiNi0.4Co0.2Mn0.4O2 powders synthesized via the modified hydrothermal process delivers a high discharge capacity of 159 mAh/g at 0.1 C with the capacity retention of 94% at 0.3 C after 100 cycles. On contrary, the powder synthesized via the normal hydrothermal process delivers a low specific capacity of 126 mAh/g at 0.1 C with capacity retention of only 74% at 0.3 C after 100 cycles. Based on the results of electrochemical impedance and galvanostatic intermittent titration, the charge transfer resistance and charge diffusion coefficient of the sample synthesized via the modified hydrothermal process are found to be 16 ohm and 7.5 × 10−12 cm2/s, respectively. The present study reveals the feasibility to prepare phase-pure LiNi0.4Co0.2Mn0.4O2 cathode with a promising high-rate performance by adding PVP and urea during the hydrothermal synthesis process.