High voltage electrochemical performance of ultrahigh-Ni cathode via in situ constructed nano-LiF and CNT composite cathode electrolyte interphase layer

Ultrahigh-nickel LiNi x Co y Mn 1-x-y O 2 cathode material (Ni content ≥ 0.9) is of great significance for the development of high energy density of lithium-ion batteries. However, its high surface activity leads to more surface residual lithium formation and deterioration of electrochemical performance, especially at high voltage. Here we add NH 4 F and nitrogen-doped carbon nanotubes (CNT) during the dimethyl carbonate (DMC) washing process, and constructed in situ the nano-LiF and CNT composite cathode electrolyte interphase (CEI) layer while removing part of residual lithium, effectively optimizing the surface environment of LiNi 0.9 Co 0.05 Mn 0.05 O 2 . The modified LiNi 0.9 Co 0.05 Mn 0.05 O 2 has a capacity retention rate of 61.3 % after 200 cycles between 2.8 and 4.5 V at 1C, significantly higher than the 46.7 % of the unwashed sample, and a specific discharge capacity of 146.9 mAh g −1 at 5C, compared to 127.5 mAh g −1 for the unwashed sample. Benefit from the alleviation of polarization and the increase of Li + diffusion coefficient, the stable CEI layer provides effective protection for LiNi 0.9 Co 0.05 Mn 0.05 O 2 under 4.5 V, alleviating surface side reactions. In this paper, a simple and effective strategy is developed to optimize the surface of Ni-rich cathode material, which provides a new insight for the treatment of surface residual lithium.