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

Abstract

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 LiNi1/3Co1/3Mn1/3O2 significantly improved as the discharge cutoff voltage (Vdc) increased. The polarization due to an increase in charge transfer resistance (Rct) was substantially increased by charge-discharge cycling of LiNi1/3Co1/3Mn1/3O2 with lower Vdc. In contrast, the increases in polarization and Rct were significantly suppressed when cycling with higher Vdc. The increase in Rct is caused by increased activation energy (Ea) of Li-ion transfer reaction at the electrode/electrolyte interface. An electrochemically inert Ni-O structure, which increases Ea and Rct, was observed at the surface of the LiNi1/3Co1/3Mn1/3O2 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 Rct on the operating voltage range is basically common to LiCoO2 and LiNi0.81Co0.15Al0.04O2. 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.