In Situ-Polymerized High-Entropy-Driven Solid Polymer Electrolyte for Safer Solid-State Lithium Metal Batteries

The most promising way to achieve scaled-up solid-state battery production is to use the in situ polymerization process, which inherits excellent interfacial contact and is compatible with existing battery manufacturing processes. However, the resulting solid polymer electrolytes suffer from poor oxidation stability and, thus, cannot match mainstream high-voltage cathodes. Herein, in situ-polymerized high-entropy-driven solid polymer electrolytes based on five cyclic ether structured monomers are designed for safer high-voltage solid-state lithium metal batteries. The constructed disordered alkyl chain with weakened solvation ability can effectively improve the voltage tolerance to 5.2 V and accelerate the segment motion of polymer chains, which induces the formation of an anion-derived LiBr-rich organic-inorganic hybrid passivation layer, achieving long-term cycling stability over 1000 h and deep cycling under 6.45 mA cm^-2. The cells paired with polyanionic compounds or high-voltage layered oxides demonstrate excellent rate performance when charging to 100% state of charge in 7.5 min and long-term cycling stability for more than 700 cycles. A 287.13 W h kg^-1 solid-state lithium metal pouch cell was fabricated with a capacity retention of 98.67% for 100 cycles, which provides an innovative strategy to realize large-scale application of safer solid-state batteries.