Designing Boron‐Based Single‐Ion Gel Polymer Electrolytes for Lithium Batteries by Photopolymerization

Single-ion lithium conducting polymer electrolytes based on delocalized borate groups are designed and synthesized by rapid UV-photopolymerization. For this purpose, three different functional lithium boron sp3 anionic monomers, containing fluorinated, ethoxy, or a blend of both functionalities are synthesized. These monomers are photopolymerized in the presence of a poly(ethylene glycol) dimethacrylate crosslinker and tetraglyme as plasticizer. By this method, gel polymer electrolytes endowed with lithium single-ion conduction are prepared (SIGPEs). The impact generated by the different functionalities of the borate groups and the addition of plasticizer on the electrochemical and ion conducting properties of the synthesized polymer electrolytes are analyzed in detail. These polymer electrolytes show high ionic conductivity (1.71 × 10−4 S cm−1 at 25 °C) and high lithium transference number values (up to 0.85). Finally, they are investigated as solid electrolytes in lithium metal symmetrical cells showing good performance (<0.85 V at ±0.2 mA cm−2 for 175 h).