Dielectric polymer based electrolytes for high-performance all-solid-state lithium metal batteries

Solid polymer electrolytes (SPEs) are urgently required for achieving practical all-solid-state lithium metal batteries (ASSLMBs) but remain plagued by low ionic conductivity. Herein, we propose a strategy of salt polarization to fabricate a highly ion-conductive SPE by employing a high-dielectric polymer that can interact strongly with lithium salts. Such a polymer with large dipole moments can guide lithium cations (Li⁺) to be arranged along the chain, forming a continuous pathway for Li⁺ hopping within the SPE. The as-fabricated SPE, poly(vinylidene difluoride) (PVDF)-LiN(SO₂F)₂ (LiFSI), has an extraordinarily high dielectric constant (up to 10⁸) and ultrahigh ionic conductivity (0.77 × 10⁻³ S cm⁻¹). Based on the PVDF–LiFSI SPE, the assembled Li metal symmetrical cell shows excellent Li plating/stripping reversibility at 0.1 mA cm⁻², 0.1 mAh cm⁻² over 1500 h; the ASS LiFePO₄ batteries deliver long-term cycling stability at 1 C over 350 cycles (2.74 mg cm⁻²) and an ultralong cycling lifespan of over 2600 h (100 cycles) with high loading (11.5 mg cm⁻²) at 28 °C. First-principles calculations further reveal the ion-dipole interactions-controlled conduction of Li⁺ in PVDF–LiFSI SPE along the PVDF chain. This work highlights the critical role of dielectric permittivity in SPE, and provides a promising path towards high-energy, long-cycling lifespan ASSLMBs.