An Ultrathin Solid Electrolyte for High‐Energy Lithium Metal Batteries

Abstract Solid‐state electrolytes (SSEs) are key to unlocking the potential of lithium metal batteries (LMBs), but their high thickness (>100 µm) due to poor mechanical properties limits energy density improvements. Herein, an ultrathin (≈5 µm) polymer SSE with a high Young's modulus (10.6 GPa), made from a polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) matrix and an ethylene diamine tetraacetic acid (EDTA) additive is proposed. By virtue of the electron‐donating property, EDTA induces the conformation transformation of PVDF‐HFP, enhancing the mechanical strength by a fine‐grain strengthening mechanism. In addition, PVDF‐HFP with cis‐conformation shortens the pathway for Li⁺, promotes the Li⁺ dissociation and immobilizes the anions of lithium salt, thus increasing the ionic conductivity (2.47 × 10⁻⁴ S cm⁻¹) and transfer number (0.59) of the electrolyte. Moreover, the electrolyte also possesses a wide voltage window (4.7 V) and good heat/flame resistance. The half cells and full cells with the electrolytes show good cycling and rate performance. Notably, a pouch cell based on the electrolyte exhibits impressive energy densities of 516 Wh kg⁻¹ and 1520 Wh L⁻¹ (excluding packages), showing great potential for practical use in LMBs.