Achieving High Energy Density through Increasing the Output Voltage: A Highly Reversible 5.3 V Battery

The energy density of current Li-ion batteries is limited by the low capacity of intercalation cathode, which leaves relatively little room to further improve because the specific capacities of these cathodes approach the theoretical levels. Increasing the cell output voltage is a possible direction to largely increase the energy density of the batteries. Extensive research has been devoted to exploring >5.0 V cells, but only limited advances have been achieved because of the narrow electrochemical stability window of the electrolytes (<5.0 V). Herein, we report a 5.5 V electrolyte (1 M LiPF6 in fluoroethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and hydrofluoroether [FEC/FDEC/HFE] with a Li difluoro(oxalate) borate [LiDFOB] additive) that enables 5.3 V LiCoMnO4 cathodes to provide an energy density of 720 Wh kg(-1) for 1,000 cycles and 5.2 V graphite parallel to LiCoMnO4 full cells to provide an energy density of 480 Wh kg(-1) for 100 cycles. The 5.5 V electrolytes provide a large step toward developing high-energy Li batteries.