Nonflammable Solid‐State Polymer Electrolyte for High‐Safety and Ultra‐Stable Lithium‐Ion Batteries.

High safety and stability in batteries are crucial factors for the large‐scale application of lithium‐ion technology. In this work, flame‐retardant aluminum diethylphosphonite (ADP) is coated by urea‐formaldehyde (UF) shell to conquer the side reactions caused by ADP during cycling process. And then the core@shell structured ADP@UF is combined with poly(ethylene oxide) (PEO), high thermal stability can be realized. When exposed to high temperatures, ADP@UF generates N⋅ and P⋅ radicals to eliminate the combustion the H⋅ and OH⋅ radical, to inhibit fire. By controlling the percentage of flame retardant added, PEO‐ADP@UF has totally achieved the effect of inflaming retarding, realizing stable electrochemical properties at the same time. The −NH2 in UF forms hydrogen bonds with PEO, and acts as a Lewis base to promote the dissociation of lithium salts to increase the lithium‐ion mobility number. Compared to PEO, battery with PEO‐ADP@UF has outstanding cycling performance (103 mAh g−1 at 1 C, 2.5–4.2 V) and long service life (800 cycles). [ABSTRACT FROM AUTHOR]