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Solid-state batteries (SSBs) are gaining attention as they promise to provide better safety and a higher energy density than conventional liquid electrolyte batteries. Solid polymer electrolytes (SPEs) are promising candidates due to their flexibility providing better interfacial contact between electrodes and the electrolyte. However, SPEs exhibit very low ionic conductivity at ambient temperatures, which prevents their practical use in batteries. Herein, a simple and effective technique of hot press rolling is demonstrated to improve ionic conductivity and, hence, the performance of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)-based solid polymer electrolyte. Applying hot press rolling to the electrolyte membrane induced structural changes in the grain boundaries, which resulted in a reduction in the crystallinity of the material and, hence, an increase in the amorphous phase of the material, which eased the movement of the lithium ions within the material. This technique also improved the surface of the membrane, making it homogeneous and smoother, which resulted in better interfacial contact between the electrodes and electrolyte. Electrochemical tests were carried out on electrolyte membranes treated with and without hot press rolling to evaluate the effect of the treatment. The hot pressed electrolyte membrane showed significant improvements in its ionic conductivity and transference number. The cycling performance of the LFP/Li batteries using a hot press rolled electrolyte was also evaluated, which gave a specific discharge capacity of 134 mAh/g at 0.1 C. These results demonstrate that hot press rolling can have a significant effect on the electrochemical performance of solid polymer electrolytes. [ABSTRACT FROM AUTHOR]

Solid-state batteries (SSBs) are regarded as favorable future technology as they promise to deliver high energy density and improved safety. However, despite extensive research efforts, the development of SSBs still fall short of expectations mainly because of suitable solid electrolyte which can provide high ionic conductivity as well as good flexibility to enhance interface contact between electrolyte and electrodes. In this work, we have prepared free-standing, flexible composite solid polymer electrolyte (CSPE) membranes by incorporating LLZTO ceramic particles in PVDF-HFP/LiTFSI based solid polymer electrolyte (SPE). Addition of 20 wt% LLZTO has shown to improve the electrochemical properties of the solid electrolyte such as ionic conductivity (8.2 × 10−4 S cm−1 at 60 °C), transference number, electrochemical stability and long-term interface stability with the lithium-metal also showed significant improvement. Furthermore, solid-state LiFePO 4 /SPE/Li and LiFePO 4 /CSPE/Li batteries were fabricated, and charge/discharge cycling was performed, where battery with SPE and CSPE exhibited discharge capacity of 119 mA h g−1 and 131 mA h g−1 respectively at 0.1C rate, 60 °C. [Display omitted] • Composite solid polymer electrolytes (CSPEs) based on LLZTO incorporated in PVDF-HFP/LiTFSI solid polymer electrolyte. • Addition of LLZTO increases the ionic conductivity of the solid electrolyte reaching up to 8.2 × 10−4 S cm−1 at 60 °C. • LiFePO 4 /CSPE/Li battery delivers discharge capacity of 131 mAh.g−1 at 0.1C, 60 °C. • Enhanced interface stability between solid electrolyte and lithium metal anode is achieved by incorporating LLZTO. [ABSTRACT FROM AUTHOR]