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).