Weakened Solvation Structure Electrolytes Enable High-Voltage Graphite||LiCoO2 Batteries

In traditional electrolytes, due to the difference of donor number, the cyclic ethylene carbonate (EC) is usually used as the carrier of Li+, while the linear carbonate is used as the cosolvent. However, the poor desolvation ability of EC also leads to poor rate performance. Herein, we reversed the roles of carbonates, where the linear ethyl methyl carbonate (EMC) served as the Li+ carrier and the cyclic 3,3,3-trifluoropropylene carbonate (TFPC) acted as the cosolvent. This strategy helped significantly decrease the solvation effect while meeting the need for good solid electrolyte interphase (SEI) growth. Fluorobenzene (FB) was also introduced due to its low viscosity and high electrochemical stability. This electrolyte with a weakly solvated structure greatly improved the rate performance of electrodes. Moreover, the fluorine-rich interface introduced by the design effectively inhibited the dissolution of Co4+ in the high-voltage LiCoO2 (LCO) cathode. The LCO delivered a specific capacity of 177 mAh g–1 and a good cycle life with a high cutoff voltage of 4.6 V. A commercial high-voltage graphite||LCO pouch cell using this electrolyte showed a good capacity retention of 99.1% over 100 cycles and a high energy density of 285 Wh kg–1 at 0.3 C (counted by the mass of the whole battery) when charged to 4.5 V.