A hybrid solid electrolyte for solid-state sodium ion batteries with good cycle performance

A ceramic in polymer hybrid solid electrolyte (HSE) based on a poly vinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymer comprising Na₃Zr₂Si₂PO₁₂(NASICON) ceramic particles was prepared by a simple solution casting method followed by activation in a liquid electrolyte. The prepared HSE exhibits good flexibility, high ionic conductivity of 2.25 × 10^-3S cm^-1at room temperature (RT), and good interface stability. The carbon coated sodium vanadium phosphate (Na₃V₂(PO₄)₃/C) cathode was synthesized by the sol-gel method and assembled into batteries with different electrolytes. The batteries based on HSE exhibit better electrochemical performance than that of NASICON ceramic solid electrolytes, which delivers a reversible capacity of 98 mAh · g^-1at 0.2 C and exhibits good capacity retention of 85% after 175 cycles at 0.5 C. Not only does the HSE inherit great flexibility, but also exhibits good interfacial contact with electrodes. The schematic diagram of Na-ion conductivity in ceramic, polymer and HSE was illustrated to demonstrate the sodium ion transport mechanism. The HSE with high ionic conductivity and good flexibility for interfacial contact with electrodes shall provide a designing strategy for different solid-state batteries.