Cathode-Electrolyte-Interphase Film Formation on a LiNiO2 Surface in Conventional Aqueous Electrolytes: Simple Method to Improve the Electrochemical Performance of LiNiO2 Electrodes for Use in Aqueous Li-Ion Batteries

Passivation films, the so-called solid-electrolyte interphase and cathode-electrolyte interphase (CEI), are considered to be essential for the operation of rechargeable batteries because they have a positive impact on electrochemical performance including cyclability. In the field of aqueous Li-ion batteries (ALIBs) to date, it is generally accepted that these films can only be formed in super-concentrated electrolytes containing fluorine-based organic anions such as N(SO2CF3)(2) and SO3CF3. This study demonstrates for the first time that a CEI film can be created on a LiNiO2 (LNO) electrode in conventional aqueous electrolytes and improve electrochemical performance such as reversible capacities and cyclability. The results reveal that a CEI film, mainly composed of Li2CO3 and LiOH, is formed on the LNO surface in a saturated LiNO3 aqueous electrolyte containing LiOH beginning at the first de-intercalation of Li+ ions, suppressing side reactions between the surface and aqueous electrolyte, and improving the recovery rate of structural changes of LNO during the charge/discharge process. As a result, this study suggests that LNO has great potential for application as a cathode material for high energy density ALIBs.