Built-in positive charge-mediated in-situ polymerized electrolyte for high-voltage lithium metal batteries

To address low room-temperature ionic conductivity and poor interfacial stability of solid-state lithium metal battery (SLMB) electrolytes, Al 3+ substituted sepiolite (Sep(Al)) acts as a versatile initiator to induce the cell-confined ring-opening polymerization of 1,3-dioxolane (DOL), which affords a built-in positive charge (IPC) solid electrolyte (IPC SE). Al 3+ modification enhances Sep(Al)'s surface charge density and Lewis acidity, raises DOL polymerization conversion to 93.6% and forms a uniform polymer network. Al 3+ /Mg 2+ in Sep(Al) competitively coordinate with TFSI − , optimize Li + solvation and salt dissociation, and endow IPC SE with a Li + transference number of 0.71 and a 5.3 V electrochemical window. Density functional theory and molecular dynamics simulations confirm that PDOL–Al 3+ complexes reduce the electrolyte's HOMO energy level. With Al 3+ /Mg 2+ synergistic coordination, reduced free DOL, and network confinement, IPC SE's oxidative and interfacial stability improves. Electrochemical tests show that Li||Li symmetric cells with IPC SE cycle over 1800 h (0.1 mA cm −2 critical current density). Li||NCM811 coin cells retain 62.7% capacity after 1000 cycles at 0.2C; pouch cells retain 82.5% after 100 cycles at 0.1C (coulombic efficiency >98%). This “multifunctional initiator” strategy integrates positive charge regulation with in-situ polymerization, optimizes polymerization efficiency and interfacial stability, breaks polyether-based electrolyte bottlenecks, and provides a facile, scalable method for high-performance SLMBs.