Room-temperature free-radical polymerized electrolyte design towards 650 Wh kg−1 solid-state lithium batteries

The quasi-solid-state gel electrolytes (QSEs) fabricated through free-radical in situ polymerization show great promise for energy-dense solid-state lithium batteries, paving the way for next-generation electric vehicles and the low-altitude economy. However, the high-voltage-resistant QSEs were obtained under strict conditions within batteries, causing highly non-uniform electrolyte and poor compatibility with electrodes. Here we propose a universal C=C bond activation strategy by introducing activators with high maximum molecular surface electrostatic potential (ESP max ) to improve the condensed local softness of C=C bonds in a series of acrylate-based monomers. The activated C=C bonds result in decreased polymerization reaction energy barrier, and thus realize room-temperature free-radical polymerized QSE (RT-QSE). The RT-QSE effectively suppresses harmful interfacial reactions, maintains electrode structure stability and improves electrolyte uniformity, enabling high-areal-capacity cathodes. As a result, the 4 mAh cm −2 cathode remains 95.1% capacity after 100 cycles. Moreover, the 9.53 Ah pouch battery with an areal capacity cathode >10 mAh cm −2 shows a record high energy density of 656.6 Wh kg –1 . This work establishes a general design criterion for selecting activators and monomers to achieve uniform and compatible RT-QSEs for energy-dense solid-state lithium batteries.