Hybrid solid state electrolytes blending NASICON-type Li1+xAlxTi2–x(PO4)3 with poly(vinylidene fluoride-co-hexafluoropropene) for lithium metal batteries

• Novel hybrid solid state electrolytes (SSEs) were developed for Li-metal batteries. • SSEs consisted of NASICON-type Li 1+x Al x Ti 2‒x (PO 4 ) 3 (LATP) powders and polymers. • LATP powder was synthesized by sol-gel method followed by calcination at 850 °C. • Optimal LATP ratio was determined enabling ionic conductivity: 1.11 × 10 –4 s cm –1 . • Li-metal battery displays excellent cyclic durability during long-duration cycling. Lithium-ion batteries (LIBs) with Li metal as the anode electrode are very promising energy storage systems for high energy/power density applications. However, Li dendrite formation and growth on the Li anode due to non-uniform Li metal deposition is one of the major issues yet to be addressed. In this work, novel hybrid solid state electrolytes (SSEs) were developed through blending poly(vinylidene fluoride-hexafluoro propylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and sodium superionic conductor (NASICON)-type Li 1+ x Al x Ti 2‒ x (PO 4 ) 3 (LATP) powders. The LATP powders were synthesized by the sol-gel technique followed by calcination at 850 °C. The as-prepared LATP particles formed a well-defined crystalline structure with a rhombohedral lattice. The LATP content within the hybrid SSEs plays a crucial role in improving the mechanical durability, ionic conductivity, rate capability, discharge capacity, and cyclic stability. Analyzing various SSE configurations, an optimal ratio of LATP was determined (i.e., 10–15 wt.%) enabling an ultra-high ionic conductivity of ∼1.11 × 10 –4 S cm –1 . Employing the LATP-based SSE developed in this work, the dissolution of iron from the LiFePO 4 cathode was mitigated and a stable solid electrolyte interphase layer was formed resulting in uniform Li metal deposition along with exceptional cyclic durability during long-duration charge/discharge cycling.