An intrinsic polymer electrolyte via in situ cross-linked for solid lithium-based batteries with high performance

Since the introduction of poly(ethylene oxide) (PEO)-based polymer electrolytes more than 50 years, few other real polymer electrolytes with commercial application have emerged. Due to the low ion conductivity at room temperature, the PEO-based electrolytes cannot meet the application requirements. Most of the polymer electrolytes reported in recent years are in fact colloidal/composite electrolytes with plasticizers and fillers, not genuine electrolytes. Herein, we designed and synthesized a cross-linked polymer with a three-dimensional (3D) mesh structure which can dissolve the Li bis(trifluoromethylsulfonyl)imide (LiTFSI) salt better than PEO due to its unique 3D structure and rich oxygen-containing chain segments, thus forming an intrinsic polymer electrolyte (IPE) with ionic conductivity of 0.49 mS cm^-1 at room temperature. And it can hinder the migration of large anions (e.g. TFSI^-) in the electrolyte and increase the energy barrier to their migration, achieving Li⁺ migration numbers (t_Li+) of up to 0.85. At the same time, IPE has good compatibility with lithium metal cathode and LiFePO₄ (LFP) cathode, with stable cycles of more than 2,000 and 700 h in Li//Li symmetric batteries at 0.2 and 0.5 mAh cm^-2 current densities, respectively. In addition, the Li/IPE/LFP batteries show the capacity retention >90% after 300 cycles at 0.5 C current density. This polymer electrolyte will be a pragmatic way to achieve commercializing all-solid-state, lithium-based batteries.