A New All-Solid-State Hyperbranched Star Polymer Electrolyte for Lithium Ion Batteries: Synthesis and Electrochemical Properties

A new hyperbranched multi-arm star polymer with hyperbranched polystyrene (HBPS) as core and polymethyl methacrylate-block-poly(ethylene glycol) methyl ether methacrylate(PMMA- b -PPEGMA) as arms was firstly synthesized by atom transfer radical polymerization. The obtained hyperbranched multi-arm star polymer (HBPS-(PMMA- b -PPEGMA) x ) exhibited good thermal stability with a thermal decomposition temperature of 372   °C. The transparent, free-standing, flexible polymer electrolyte film of the blending of HBPS-(PMMA- b -PPEGMA) x and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) was successfully fabricated by a solution casting method. The ionic conductivity of the hyperbranched star polymer electrolyte with a molar ratio of [EO]/[Li] of 30 could reach 8.3   ×   10 −5   S   cm −1 at 30   °C (with the content of PPEGMA of 83.7%), and 2.0   ×   10 −4   S   cm −1 at 80   °C (with the content of PPEGMA of 51.6%). The effect of the concentration of lithium salts on ionic conductivity was also investigated. The obtained all-solid-state polymer electrolyte possessed a wide electrochemical stability window of 4.7   V ( vs. Li + /Li), and a lithium-ion transference number ( t Li + ) up to 0.31. The interfacial impedance of the fabricated Li│polymer electrolyte│Li symmetric cell based on hyperbranched star multi-arm polymer electrolyte exhibited good interfacial compatibility between all-solid-state polymer electrolyte and electrodes. The excellent properties of the hyperbranched star polymer electrolyte made it attractive as solid-state polymer electrolyte for lithium-ion batteries.