Ultrathin Surface Modification By Atomic Layer Deposition on High Voltage Cathode LiNi0.5Mn1.5O4 for Lithium Ion Batteries

Atomic layer deposition (ALD) has been employed to modify the surface of high voltage cathode LiNi_0.5Mn_1.5O₄ by coating ultrathin Al₂O₃ layer on the electrodes. The ultrathin layer of Al₂O₃ can suppress the undesirable reactions during cycling, while maintaining the electron and ion conductivity of the electrode. The ALD Al₂O₃ coated LiNi_0.5Mn_1.5O₄ showed remarkable improvement over bare LiNi_0.5Mn_1.5O₄. After 200 cycles, the ALD Al₂O₃ coated LiNi_0.5Mn_1.5O₄ showed 91% capacity retention when the bare LiNi_0.5Mn_1.5O₄ can only maintain 75% in the same testing condition. In addition, the ALD coated LiNi_0.5Mn_1.5O₄ maintained 63% capacity retention after as long as 900 cycles. At an elevated temperature of 55 ºC, the ALD Al₂O₃ coated LiNi_0.5Mn_1.5O₄ still delivered 116 mAh/g at the 100^th cycle, in comparison, the capacity for bare LiNi_0.5Mn_1.5O₄ decreased to 98 mAh/g. According to the results from charge/discharge test and AC impedance test, the improvement is ascribed to the reduced overpotental and Li ion surface diffusion impedance. The promising results demonstrate the potential of developing high energy and long life lithium ion batteries with highly scalable LiNi_0.5Mn_1.5O₄ preparation and broadly applicable ALD process.