Design of Phosphate-Based Gel Electrolytes Toward Stabilizing the Lithium Metal Battery Interface

Interface instability between the electrode and electrolyte limits the practical application of lithium metal batteries (LMBs). Gel polymer electrolytes (GPEs) not only improve battery safety, but also mitigate the side reactions on lithium metal anodes (LMAs). However, the stability of the gel electrolyte at the LMB electrode-electrolyte interface and the overall battery safety still require further optimization. In this study, the crosslinked skeleton containing ─P═O groups induces a looser, anion-rich solvation structure, facilitating the establishment of fast ionic conduction pathways and forming a stable lithium-rich electrode-electrolyte interface. Furthermore, the inherent non-flammability of the crosslinked impermeable gel network further enhances electrolyte safety, with no significant safety failures observed even under fast charging and abuse testing. Based on this design, this gel polymer electrolyte (designated PTGPE) exhibits superior ionic conductivity (5.81 mS cm^{- 1}) and lower activation energy (0.014 eV). The corresponding Li|PTGPE|NCM811 coin cell retains 70.2% capacity after 800 cycles at 0.5 C, and the high-energy 5 Ah Li||NCM811 pouch cell delivered a specific energy of 437.32 Wh kg^{- 1} alongside a capacity retention exceeding 90% over 260 cycles. This study provides a design approach for developing lithium metal gel batteries with stable interfaces and high safety.