Dicationic tetraalkylammonium-based polymeric ionic liquid with star and four-arm topologies as advanced solid-state electrolyte for lithium metal battery

Abstract

Dicationic four-arm polymeric ionic liquid based on poly(N,N,N-trimethyl-N-((2-(dimethylamino)ethyl methacrylate)-7-propyl)-ammonium bis(trifluoromethanesulfonyl) imide) is prepared via atom transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate and anion functionalization. A solid-state electrolyte comprising polymeric ionic liquid matrix, ionic liquid plasticizer and LiTFSI is subsequently developed. The solid-state electrolyte with star topology possesses high thermal stability up to 407 °C. The low Tg and crystallinity endow the electrolyte with more amorphous structure and higher mobility of polymer segments. The ion conductivity of electrolyte based on four-arm polymer achieves 0.114 mS cm−1 at 30 °C, which is 42.5 times that of the linear counterpart. The electrochemical stability window and Li+ transference number reach 4.9 V and 0.40, respectively. In combination with the superior interfacial characteristics between this four-armed electrolyte and lithium electrode, the assembled lithium metal cell delivers high discharge capacity of 165 mAh g−1 at 0.1C with 94% capacity retention over 100 cycles. The growth of lithium dendrites is effectively inhibited. It also presents a discharge capacity of 149 mAh g−1 at 0.5C, the capacity retention of which is 70% after 500 cycles. This design of dicationic scaffold with star topology provides a new orientation for developing high performance polymer electrolyte for practical applications.