LiF modified stable flexible PVDF-garnet hybrid electrolyte for high performance all-solid-state Li–S batteries

Polymer-based solid electrolytes are very promising for high energy density solid-state Li–S batteries owing to their flexibility and higher safety. However, poor room temperature Li-ion conductivity of polymer-based solid electrolyte is the biggest challenge for their practical utilization. Here, a flexible composite polymer-ceramic electrolyte (CPE) comprising of PVDF and garnet-type Li_6.5La_2.5Ba_0.5ZrTaO₁₂ for room temperature all-solid-state-Li-S battery (ASLSB) is demonstrated. The PVDF-garnet CPE exhibits a high Li-ionic conductivity of 0.34 mS cm⁻¹ at 20 °C. PVDF-garnet-based CPEs are not electrochemically stable and undergoes severe dehydro-fluorination upon galvanostatic cycling with Li electrode. For the first time, PVDF-garnet-based CPEs are modified with LiF additive, evidenced by steady galvanostatic cycling at 0.2 mA cm⁻² for more than 800 h. The effect of LiF addition on the stability of PVDF-based CPEs is explained by XPS studies and electrochemical measurements. ASLSB fabricated with the modified CPE displays a high specific capacity of 936 mA h g⁻¹ with 0.1C rate at 20 °C, along with very good stable performances over 80 continuous cycles. The ASLSB also shows very good rate capability and high Coulombic efficicency. The performance of CPE vindicates the potential applications towards room-temperature operating all-solid-state-Li-S batteries.