Superior lithium ion conduction of polymer electrolyte with comb-like structure via solvent-free copolymerization for bipolar all-solid-state lithium battery

Abstract

Here, novel solid polymer electrolytes were synthesized by solvent-free “thiol-ene” copolymerization with different chain lengths. It was demonstrated that the optimal polymer electrolyte exhibited excellent thermal stability up to 331 °C, considerable ionic conductivity of 5.05 × 10⁻⁵ S cm⁻¹ at ambient temperature, a wide electrochemical window (0–5.05 V) and good compatibility with a lithium metal electrode. In addition, a solid-state monopolar LiFePO₄//Li battery with an integrated cathode and electrolyte was assembled and delivered a maximum capacity of 167.39 mA h g⁻¹, which is close to the theoretical capacity of the LiFePO₄ cathode. Moreover, the discharge capacity remained at 122.17 mA h g⁻¹ after 200 cycles at 60 °C, which represents a capacity retention of 75%. Remarkably, the monopolar cell could cycle well at room temperature, with a stabilized discharge capacity of 100 mA h g⁻¹ at 0.1C in the 60^th cycle. In particular, taking advantage of the non-fluidity of solid electrolytes, a bipolar cell with a high voltage of 6.07 V was also assembled, which was extremely beneficial for improving the volumetric energy density and decreasing the cost, as well as enhancing the reliability of cell packs. The bipolar cell delivered an initial specific capacity of 136.3 mA h g⁻¹ with a retention of 76% after 40 cycles. Furthermore, the bipolar cell can work well under conditions of bending, cutting and even penetration by a nail. Consequently, this work provides an advanced strategy for the facile synthesis of polymer electrolytes, as well as the fabrication of bipolar cells with high voltages, which favors improvements in energy density.