Liberating Lithium Ions from Polymer Matrix via Harnessing Ion‐Dipole Interaction Toward Stable Solid‐State Lithium Metal Batteries

Abstract

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≡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≡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|LiFePO4 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).