Liberating lithium ions from polymer matrix via harnessing ion-dipole interaction toward stable solid-state lithium metal batteries

Although polymer electrolytes have shown great potential in solid-state lithium metal batteries (LMBs), the polymer chain segments anchor the movement of lithium ions (Li${}^{+}$), which induces the low ionic conductivity of the electrolytes and limits their application. Herein, a strategy of harnessing ion-dipole interactions is proposed to liberate lithium ions from polymer chains. The adiponitrile (ADN) molecular dipole with strong bond dipole moment (-C $\equiv$ N, 11.8 × 10${}^{-30}$ C m) is introduced into the polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) polymer matrix, achieving an electrolyte with high ionic conductivity of 5.1 × 10${}^{-4}$ S cm${}^{-1}$ at 30 °C. It is demonstrated that the strong ion-dipole interaction between -C $\equiv$ N and Li${}^{+}$ weakens the ion-dipole interaction of F···…Li${}^{+}$, facilitating Li${}^{+}$ dissociation and liberating Li${}^{+}$ from polymer chains. Moreover, a hybrid and unsaturated solvation structure is formed with the ADN molecular dipole, PVDF-HFP polymer chain, and TFSI${}^{-}$ anion, corresponding to the solvent-separated ion pair (SSIP) solvation structure. Thus, the obtained electrolyte realizes high ionic conductivity and lithium-ion transference number (0.74). Consequently, the assembled lithium symmetric cell delivers stable Li stripping/plating reversibility over 900 h. Additionally, the Li|LiFePO${}_4$ full cells exhibit long-term cycling stability at 0.5 C over 300 cycles with a capacity retention of 96.4% and ultralong cycling of 1000 cycles at a high rate (5 C). (© 2024 Wiley‐VCH GmbH)