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||LiNi0.6Co0.2Mn0.2O2 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||LiNi0.8Co0.1Mn0.1O2 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. Low conductivity and poor thermal safety limit solid polymer electrolytes for lithium metal batteries. Here, authors present a puzzle-like molecular design that enhances salt dissociation and stability, enabling safe, high-voltage batteries with improved cycling performance.