Selective and uniform Li-ion boosting polymer electrolytes for dendrite-less quasi-solid-state batteries

Solid-state Li-metal batteries (LMBs) are attracting extensive attention owing to their exceptionally high energy density. Solid electrolytes play a vital role in the practical application of LMBs due to their nonflammable nature and interfacial stability with Li metal, but they ordinarily have a low ionic conductivity and dimensional stability. Here, a selective Li⁺ conductive solid-state electrolyte (SLCSE) that comprises a highly conductive yet mechanically robust, anion-immobilized (CMA) polymer matrix synthesized by soft-rigid coupled ether-abundant epoxy monomers and branched polyamine, is reported. Rationally incorporated rigid benzene-ring constituents in the CMA matrix not only enhance mechanical strength but also boost Li⁺ transportation by suppressing crystallinity. The semi-interpenetrating network of the CMA matrix and polyvinylidene fluoride-co-hexafluoropropylene displays synergistic Li⁺ acceleration behavior by promoting the dissociation and diffusion of Li⁺ while immobilizing anions, which is elucidated via molecular dynamics simulations. The SLCSE exhibits a high ionic conductivity (3.4 mS cm⁻¹) with a high Li⁺ transference number (0.77), and SLCSE-based LMBs (Li/SLCSE/LiCoO₂ cell) show a high discharge capacity of 146 mAh g⁻¹ (0.2 C) and 126 mAh g⁻¹ (3 C). Furthermore, they show exceptional long cycle stability (90% capacity retention after 500 cycles at 0.5 C), representing remarkable Li dendrite suppression capability.