A single-ion gel polymer electrolyte of PLTB@PVDF-HFP (polymeric lithium tartaric acid borate@poly(vinylidene fluoride-co-hexafluoropropene)) was prepared and its ionic conductivity was optimized via solvent composition tailoring. It was manifested that the ethylene carbonate/dimethyl carbonate (EC/DMC) swollen PLTB@PVDF-HFP exhibited a superior lithium ionic conductivity at room temperature to that of the traditional liquid electrolyte system (1M LiPF6/EC/DMC). The Li4Ti5O12/LiFePO4 cells using the EC/DMC swollen PLTB@PVDF-HFP as polymer electrolyte showed stable charge/discharge voltage profiles with small voltage hysteresis, preferable rate capability and excellent cycle performance at room temperature. These superior performances of EC/DMC swollen PLTB@ PVDF-HFP could endow this class of gel polymer electrolyte a very promising alternative to state of the art liquid electrolyte system.