All-fluorinated electrolyte for non-flammable batteries with ultra-high specific capacity at 4.7 V

By increasing the charge voltage, Li metal batteries (LMBs) with LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes could release a specific energy of >500 Wh kg-1. However, high-nickel cathodes working at ultra-high voltages accelerate degradations in the bulk and at the surface, thus significantly degrading cycle life and decreasing the specific capacity. Here, we rationally design an all-fluorinated electrolyte with addictive tri(2,2,2-trifluoroethyl) borate (TFEB), which based on 3, 3, 3-fluoroethylmethylcarbonate (FEMC) and fluoroethylene carbonate (FEC), which could cycle with high stability for high nickel cathode (LiNi0.8Co0.1Mn0.1O2 ) with a ultra-high cut-off voltage ( 4.7 V) in Li metal batteries, while maintaining the fire-extinguishing properties. Chemical Electronic Theory and Density Functional Theory indicate the rebuilding mechanism of the combination between FEC, PF6- and TFEB tends to decrease the FEC•(-H) production for inhibiting transition metal dissolution and the gas production. Therefore, the all-fluorinated electrolyte (LiPF6-FEC/FEMC/TFEB) promotes to form LiF-rich solid electrolyte interphase (SEI) and F-/B-rich cathode electrolyte interphase (CEI), preserving high compatibility interface at the anode and cathode interfaces. Remarkably, the NMC811||Li cell has significant performance by using limited Li and high-loading cathode, which the specific capacity is over 230 mA h g−1 with high CE (Coulombic efficiency), keeping over 99.7% after 100 cycles, advancing all-fluorinated electrolyte applicable in ultra-high voltage and energy-density batteries.