High-performance composite electrolytes for solid-state lithium metal batteries: Enhancing ionic conductivity and interfacial compatibility through polyvinylpyrrolidone blending and inorganic filler incorporation

One of the significant challenges in advancing safe and high-energy-density solid-state lithium metal batteries is achieving high ionic conductivities and ensuring good interfacial compatibility between the solid electrolyte and the electrodes. To address these challenges, the study proposes a composite electrolyte that is made through a solution casting method, utilizing polyvinylidene fluoride hexafluorophosphate (PVDF-HFP) and polyvinylpyrrolidone (PVP) in conjunction with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and mid-entropy inorganic filler Li 1.5 Sn 1.0 Al 0.5 Zr 0.5 (PO 4 ) 3 . The polymer blend with an optimized ceramic filler exhibits an exceptional room-temperature ionic conductivity 1.48 × 10 −4 S cm −1 , a significantly high Li-ion transference number of 0.74, and shows electrochemical stability up to 4.58 V. The symmetric Li||Li cell fabricated with the composite electrolyte exhibits uniform Li + deposition/stripping for over >500 h at 2 mA cm −2 . Further, a full cell with LiFePO 4 cathode and lithium anode is fabricated and shows excellent electrochemical performance with 78% capacity retention after 1000 cycles at 2C. The findings from this study advance the development of practical inorganic polymer electrolytes for fast-charging lithium batteries. • Li 1.5 Sn 1.0 Al 0.5 Zr 0.5 (PO 4 ) 3 with P(VDF-HFP)/PVP-LiTFSI composite electrolyte films were fabricated via the solution casting method. • Electrolyte membrane with 15 % inorganic filler exhibited an exceptional RT conductivity of 1.48 × 10 −4 S cm −1 . • The electrolyte shows stable Li stripping/plating for 500 h at 2 mA cm −2 with a nearly constant polarization of 0.15 V. • Li.||LiFePO 4 cell retain capacity >78 % after 1000 cycles at 2C.