Impact of the Range of Voltage Change on the Electrode/Electrolyte Interface of Layered Rock-Salt Positive Electrode Materials

The influence of the operating voltage range on the high-voltage charge/discharge characteristics of layered rock-salt positive electrode materials was investigated. The discharge capacity retention of LiNi 1/3 Co 1/3 Mn 1/3 O 2 significantly improved as the discharge cutoff voltage ( V dc ) increased. The polarization due to an increase in charge transfer resistance ( R ct ) was substantially increased by charge-discharge cycling of LiNi 1/3 Co 1/3 Mn 1/3 O 2 with lower V dc . In contrast, the increases in polarization and R ct were significantly suppressed when cycling with higher V dc . The increase in R ct is caused by increased activation energy ( E a ) of Li-ion transfer reaction at the electrode/electrolyte interface. An electrochemically inert Ni-O structure, which increases E a and R ct , was observed at the surface of the LiNi 1/3 Co 1/3 Mn 1/3 O 2 cycled with 2.5–4.6 V. The formation of the Ni-O structure was suppressed at the surface during cycling with 4.2–4.6 V. It was also confirmed that the observed dependence of the capacity retention, polarization, and R ct on the operating voltage range is basically common to LiCoO 2 and LiNi 0.81 Co 0.15 Al 0.04 O 2 . The electrode/electrolyte interface with low Li-ion transfer resistance is stably retained when the charge/discharge voltage is limited to the high-voltage region only.