Non-flammable liquid polymer-in-salt electrolyte enabling secure and dendrite-free lithium metal battery

• A novel concept of liquid “polymer-in-salt” electrolyte is proposed. • Nonflammable electrolyte with fast Li + mobility is achieved. • A robust organic/inorganic dual layer solid electrolyte interface is constructed. • Excellent electrochemical performance is presented in lithium metal battery. Lithium-metal batterie (LMB) is regarded as one the most promising high energy battery systems, however the safety concern from lithium dendrites and organic liquid electrolytes seriously impedes its widely application. Herein, a non-flammable liquid “polymer-in-salt” composite electrolyte with superior dendrite-suppression capability is well designed and achieved by using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, polyethylene glycol dimethyl ether (PEGDME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE). Non-flammable TTE used here is on one hand to reduce the high viscosity of this “PEGDME polymer in LiTFSI salt” electrolyte (PISE), and thus enhance its wettability; on the other hand, to maintain the merits of highly contented salt. By taking advantage of these localized highly concentrated lithium salts, aggregated ion clusters are generated in this PISE-TTE system, which construct fast ionic transportation channels, and thus accelerates Li + transportation. Furthermore, this PISE-TTE electrolyte system interacts with Li anode forming a robust organic/inorganic dual layer solid electrolyte interphase (SEI) layer. With the assistance of this tough SEI, the optimized PISE 0.7 -TTE 90 exhibits outstanding anti-dendrite growth behavior in Li/Li and Li/Cu cells. Moreover, PISE 0.7 -TTE 90 also delivers an impressive performance in both Li/LiFePO 4 (LFP, a capacity of 150 mAh g −1 at 0.5C after 150 cycles) and Li@Cu/LFP (electrochemically deposited Li on Cu current collector, a capacity of 150 mAh g −1 at 0.5C after 50 cycles) cells.