Surface Structure and High-Voltage Charging/Discharging Performance of Low-Content Zr-Oxide-Coated LiNi_1/3Co_1/3Mn_1/3O₂

The surface structures, high-voltage charging/discharging performances, and Li-ion transfer at the electrode/electrolyte interface of LiNi 1/3 Co 1/3 Mn 1/3 O 2 coated with small amounts of Zr oxide by the sol-gel method were investigated. Island-like ZrO 2 grains as well as grain-free (sea-like) zones were observed on the surfaces of the coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples. The ratio of the area of these sea-like zones to the total surface area of the LiNi 1/3 Co 1/3 Mn 1/3 O 2 sample increased from 44 to 85% when the Zr oxide content was decreased from 1.0 to 0.125 wt%. A compound oxide phase containing Zr, Ni, Co, and Mn was formed uniformly on the sea-like zones; the depth of this phase was approximately 2 nm. The initial discharge capacities of the coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples were equal to that of bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 . Further, the cycling performances of the coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples were significantly higher, as were their discharge capacities and discharge voltages, while their charge-transfer resistances ( R ct ) were lower. It was also found that the coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples had lower activation energies ( E a ) for charge transfer than the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 . Thus, it can be surmised that the area and structure of the sea-like zones determined the R ct and E a values and cycling performances of the coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples.