Outstanding performances of graphite||NMC622 pouch cells enabled by a non-inert diluent

Abstract

Although high salt concentration electrolyte (HCE) can construct effective LiF-rich interphase film and solve the interphasial instability issue of graphite anode, its high cost, high viscosity and poor wettability with electrode materials limit its large-scale application. Generally, localized high concentration electrolyte (LHCE) is obtained by introducing an electrochemically inert diluent into HCE to avoid the above-mentioned problems while maintaining the high interphasial stability of HCE with graphite anode. Unlike traditional inert diluents, 1, 1, 2, 2-tetrafluoroethyl-2, 2, 3, 3-tetrafluropropyl ether (TTE) with electrochemical activity is introduced into propylene carbonate (PC)-based HCE to obtain LHCE-2 (1 M LiPF6, PC:DMC:TTE = 1:1:6.1) herein. Experimental and theoretical simulation results show that TTE participates in the oxidation decomposition and film-forming reaction at the NCM622 cathode surface, conducting a cathode electrolyte interphase (CEI) rich in organic fluorides with excellent electron insulation ability, high structural stability and low interphasial impedance. Thanks to the outstanding interphasial properties induced by LHCE-2, the graphite||NMC622 pouch cell reaches a capacity retention of 80% after 500 cycles at 1 C under room temperature. While at sub-zero temperatures, the capacity released by the cell with LHCE-2 electrolyte is significantly higher than that of HCE and conventional EC-based electrolytes. Meanwhile, the LHCE-2 electrolyte inherits the advantages of TTE flame-resistant, thus improving the safety of the battery.