An H2O‐Initiated Crosslinking Strategy for Ultrafine‐Nanoclusters‐Reinforced High‐Toughness Polymer‐In‐Plasticizer Solid Electrolyte

Incorporating plasticizers is an effective way to facilitate conduction of ions in solid polymer electrolytes (SPEs). However, this conductivity enhancement often comes at the cost of reduced mechanical properties, which can make the electrolyte membrane more difficult to process and increase safety hazards. Here, a novel crosslinking strategy, wherein metal-alkoxy-terminated polymers can be crosslinked by precisely controlling the content of H2 O as an initiator, is proposed. As a proof-of-concept, trimethylaluminum (TMA)-functionalized poly(ethylene oxide) (PEO) is used to demonstrate that ultrafine Al-O nanoclusters can serve as nodes to crosslink PEO chains with a wide range of molecular weights from 10 000 to 8 000 000 g mol-1 . The crosslinked polymer network can incorporate a high concentration of plasticizers, with a total weight percentage over 75%, while still maintaining excellent stretchability (4640%) and toughness (3.87 × 104 kJ m-3 ). The resulting electrolyte demonstrates high ionic conductivity (1.41 mS cm-1 ), low interfacial resistance toward Li metal (48.1 Ω cm2 ), and a wide electrochemical window (>4.8 V vs Li+ /Li) at 30 °C. Furthermore, the LiFePO4 /Li battery shows stable cycle performance with a capacity retention of 98.6% (146.3 mAh g-1 ) over 1000 cycles at 1C (1C = 170 mAh g-1 ) at 30 °C.