CO2-sourced polycarbonates as solid electrolytes for room temperature operation lithium battery

In the last years, polycarbonates have been identified as alternatives to poly(ethylene oxide) as polymer electrolytes for lithium battery applications. In this work, we show the design of CO2-sourced polycarbonates for its use in a room temperature lithium battery. Novel functional polycarbonates alternating oxo-carbonate moieties and polyethylene oxide segments are synthesized by the facile room temperature (rt) organocatalyzed polyaddition of CO2-sourced bis(?-alkylidene carbonate)s (bis-?CCs) with polyethylene oxide diols. The effect of the polyethylene oxide molar mass on the ionic conductivity and on the thermal properties of the poly(oxo-carbonate)s is investigated. The best candidate shows a low glass temperature of -44°C and a high ionic conductivity of 3.75 * 10-5 S cm-1 at rt when loaded with 30 wt% bis(trifluoromethanesulfonyl)imide salt (LiTFSI) without any solvent. All solid semi-interpenetrated network polymer electrolyte (SIN-SPE) is then fabricated by UV-cross-linking of a mixture containing a specifically designed poly(oxo-carbonate) bearing methacrylate pendants, diethylene glycol diacrylate and the previously described poly(oxo-carbonate) containing LiTFSI. The resulting self-standing membrane exhibits a high oxidation stability up to 5 V (vs Li/Li+), an ionic conductivity of 1.1 * 10-5 S cm-1 at rt (10-4 S cm-1 at 60°C) and promising mechanical properties. Assembled in a half cell configuration with LiFePO4 (LFP) as cathode and lithium as anode, the all-solid cell delivers a discharge capacity of 161 mAh g-1 at 0.1C and 60°C, which is very close to the theoretical capacity of LFP (170 mAh g-1). Also, a stable reversible cycling capacity over 400 cycles with high coulombic efficiency of 99 % is noted at 1C. Similar results are obtained at rt provided that 10 wt% of tetraglyme as plastisizer were added to SIN-SPE.
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