A family of single-ion lithium conducting polymer electrolytes based on highly delocalized borate groups is reported. The effect of the nature of the substituents on the boron atom on the ionic conductivity of the resultant methacrylic polymers was analyzed. To the best of our knowledge the lithium borate polymers endowed with flexible and electron-withdrawing substituents presents the highest ionic conductivity reported for a lithium single-ion conducting homopolymer (1.65 × 10 À 4 S cm À 1 at 60 °C). This together with its high lithium transference number t Li þ = 0.93 and electrochemical stability window of 4.2 V vs Li 0 /Li + show promise for application in lithium batteries. To illustrate this, a lithium borate monomer was integrated into a single-ion gel polymer electrolyte which showed good performance on lithium symmetrical cells (< 0.85 V at � 0.2 mA cm À 2 for 175 h).

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 sp 3 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).