Designing boron-based single-ion gel polymer electrolytes for lithium batteries by photopolymerization

Abstract

Single-ion lithium conducting polymer electrolytes based on delocalized borate groups have been designed and synthesized by rapid UV-photopolymerisation. For this purpose, three different functional lithium boron sp3 anionic monomers, containing fluorinated, ethoxy, or a blend of both functionalities have been synthesized. These monomers were photopolymerized in the presence of a PEG-di-acrylate crosslinker and tetraglyme as plasticizer. By this method, gel polymer electrolytes (SIPEs) endowed with lithium single-ion conduction were prepared. 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 showed 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 were investigated as solid electrolytes in lithium metal symmetrical cells showing good performance (<0.85 V at ±0.2 mA·cm-2 for 175 h).