Conventional lithium-ion batteries are nearing their practical energy limit of about 300 Wh kg-1, while liquid electrolytes raise leakage and fire risks. Lithium (Li) metal anodes offer a high theoretical capacity of 3,860 mAh g-1 and low potential, and lithium-rich manganese-based oxide (LRMO) cathodes can exceed 250 mAh g-1, making Li-LRMO solid-state batteries attractive. In situ polymerized quasi-solid-state gel electrolytes (QSEs) are promising, but they usually require thermal initiation above 60 °C with azobisisobutyronitrile (AIBN) as initiator. This can cause instant polymerization, heat and gas buildup, uneven solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers, and electrode degradation. Based on these challenges, further research is needed to develop mild, uniform and electrode-compatible in situ polymerization for energy-dense solid-state batteries.
In a study published (DOI: 10.1016/j.esci.2026.100626) online on 20 July 2026 in eScience, researchers at Nankai University and the Haihe Laboratory of Sustainable Chemical Transformations in Tianjin, China, developed a room-temperature free-radical polymerization route for QSEs. The team used high-ESPmax (maximum molecular surface electrostatic potential) activators to activate acrylate monomers and enable uniform gelation inside batteries. Their Li-LRMO pouch cell with a high-areal-capacity cathode delivered 656.6 Wh kg-1, demonstrating a practical path toward energy-dense solid-state lithium batteries and a general design rule for activators and monomers.
The team selected pentaerythritol tetraacrylate (PETEA) as an acrylate monomer, AIBN as the initiator and tris(pentafluorophenyl)borane (TPFPB) as a high-ESPmax activator. TPFPB coordinates with the carbonyl (C=O) group, redistributing electron density away from the carbon-carbon double (C=C) bond and increasing its condensed local softness. Boron-11 nuclear magnetic resonance (11B NMR) showed a shift from -0.07 to 0.66 ppm, and density functional theory (DFT) calculations showed the initiation barrier dropped from 0.46 eV to 0.11 eV. This enabled room-temperature polymerization in both bottles and coin cells. The RT-QSE formed uniform, lithium fluoride (LiF)-rich SEI and CEI layers, supported stable Li plating/stripping for more than 1,200 h at 0.5 mA cm-2 and 1.0 mAh cm-2. Atomic force microscopy (AFM) showed a higher Derjaguin-Muller-Toporov (DMT) modulus for the RT-QSE-derived SEI than for the high-temperature QSE (HT-QSE). The RT-QSE also maintained a more stable LRMO lattice without voids or vacancies, while the HT-QSE showed disordered surfaces and uneven interphases. A 4 mAh cm-2 LRMO cathode retained 95.1% capacity after 100 cycles. Ultrasonic scanning showed better electrolyte infiltration. The 9.53 Ah pouch cell, with a cathode exceeding 10 mAh cm-2, delivered 656.6 Wh kg-1 and 94.4% initial Coulombic efficiency (ICE).
The authors indicated the advance addresses a long-standing trade-off in free-radical in situ polymerized electrolytes: high temperature speeds gelation but damages interfaces, while room temperature is mild but often cannot start initiation effectively. They said "the high-ESPmax activator strategy turns sluggish acrylate monomers into reactive coordination compounds, allowing uniform gelation inside thick electrodes." According to them, the design is not limited to one monomer or activator, offering a practical route to scale up quasi-solid-state Li-LRMO pouch cells. They added that the approach could make solid-state battery manufacturing more uniform and compatible.
The RT-QSE platform could accelerate practical solid-state lithium batteries for electric vehicles, low-altitude aircraft and grid storage, where safety and energy density are critical. Because it builds on acrylate chemistry and can be tuned through activator ESPmax, the approach may fit scalable pouch-cell manufacturing. The authors said low-temperature performance of thick LRMO cathodes still needs improvement through cathode modification and plasticizer engineering. If these issues are addressed, the strategy could help move solid-state batteries from laboratory coin cells and Ah-level pouch cells to practical applicable batteries with more uniform interfaces and longer cycle life. It also offers a general design rule for selecting activators and monomers.