An Ultrathin Solid Electrolyte for High-Energy Lithium Metal Batteries

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.