Distinctive interphasial properties and high structural reversibility endowed by B-/CN- electrolyte additive and its superior electrochemical performance for graphite/LiCoO2 pouch cells

The exploration of high energy density batteries requires cathodes with a high specific capacity and high voltage. LiCoO2 (LCO), a prospective cathode material for lithium-ion batteries (LIBs), displays a decent capacity but without a compatible electrolyte to withstand its high voltage. To create an enduring cathode electrolyte interphase (CEI), a novel electrolyte additive, 2-cyanophenylboronic acid (CBB), which possesses both cyano (CN-) and boronic acid (B-) functional group, is firstly put forward to be applied in LCO/Li cells as well as graphite/LCO pouch cell. Data from experimental and theoretical research both reveal that CBB preferentially decomposes on LCO surface, constructing a thin, robust and homogeneous CEI film rich in B-F/B-O species with fast kinetics and low impedance, suppressing the LCO surface transformation upon cycling due to the alleviated Co dissolution. CBB additive can enhance the structural reversibility (in-situ X-ray diffraction), decrease the electrolyte decomposition and eliminate the HF formation, constructing a much smoother surface than base electrolyte. LCO/Li cells with 1% CBB deliver more excellent capacity retention (96%) and a much superior rate capability (145 mAh/g, 5C) than that of base electrolyte (67%, 115 mAh/g). Intriguingly, graphite/LCO pouch batteries containing 1% CBB for 300 cycles deliver more outstanding capacity retention of 80% than that of base electrolyte (2%). This work reveals that CBB can function as an efficient electrolyte additive for high voltage LCO cathode, of which its distinctive CEI modification on the LCO surface provides valuable perspectives for its commercial application towards high energy density LIBs.