Mechanically Robust Yet Highly Conductive Diblock Copolymer Solid Polymer Electrolyte for Ambient Temperature Battery Applications

In this paper we present a solid polymer electrolyte (SPE) that uniquely combines ionic conductivity and mechanical robustness. This is achieved with a diblock copolymer poly­(benzyl methacrylate)-poly­(ε-caprolactone-r-trimethylene carbonate). The SPE with 16.7 wt % lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) showed the highest ionic conductivity (9.1 × 10^–6 S cm^–1 at 30 °C) and apparent transference number (T₊) of 0.64 ± 0.04. Due to the employment of the benzyl methacrylate hard block, this SPE is mechanically robust with a storage modulus (E′) of 0.2 GPa below 40 °C, similar to polystyrene, thus also making it a suitable material for load-bearing constructions. The cell Li|SPE|LiFePO₄ is able to cycle reliably at 30 °C for over 300 cycles. The promising mechanical properties, desired for compatibility with Li-metal, together with the fact that BCT is a highly reliable electrolyte material makes this SPE an excellent candidate for next-generation all-solid-state batteries.