Puzzle-like molecular assembly of non-flammable solid-state polymer electrolytes for safe and high-voltage lithium metal batteries

Developing safe and high-voltage solid-state polymer electrolytes for high-specific-energy lithium metal batteries holds great promise. However, low ionic conductivity, limited Li⁺ transference number, narrow voltage window, and high flammability greatly hinder their practical applications. Herein, we propose a puzzle-like molecular assembly strategy to construct a solid-state polymer electrolyte via in situ polymerization. The triallyl phosphate and 2,2,3,3,4,4,4-heptafluorobutyl methacrylate segments are spliced into the vinyl ethylene carbonate matrix to enhance anion affinity and promote lithium salt dissociation, resulting in a high ionic conductivity of 0.432 mS cm^-1 and a Li⁺ transference number of 0.70 at 25 °C. Meanwhile, the polymer electrolyte exhibits a high oxidation voltage of 5.15 V, enabled by its intrinsic high-voltage tolerance and the formation of a robust inorganic-rich interphase. As a result, the Li||LiNi_0.6Co_0.2Mn_0.2O₂ cell maintains stable performance for 300 cycles and reliably cycles even with an application-oriented mass loading of 15.8 mg cm^-2. The 2.6-Ah Li||LiNi_0.8Co_0.1Mn_0.1O₂ pouch cell reaches a high specific energy of 349 Wh kg^-1. Furthermore, the developed polymer electrolyte displays superior nonflammability and the Li||LiFePO₄ cell exhibits stable cycling for over 120 cycles at 100 °C. Both accelerating rate calorimetry and nail penetration tests verify the high safety of the pouch cells using the designed polymer electrolyte, showing the potential for practical applications.