Flame retardant lithium ion battery based on a flexible solid-state polymer electrolyte membrane

The safety issue of a portable battery has increasingly become paramount importance because of intimate contact of wearable devices with the human body. In this study, a flame retardant, thermally stable polymer electrolyte membrane (PEM) has been fabricated consisting of crosslinkable polyurethane precursor, viz., polyethylene glycol-bis-carbamate dimethacrylate (PEGBCDMA), cyclic ethylene carbonate (EC) as a solid plasticizer, and LiTFSI salt. This PEM is solvent-free, transparent, bendable, and twistable, which makes it an ideal candidate for a flexible all-solid-state lithium ion battery. Moreover, the above PEM exhibits high ionic conductivity at the superionic level of 10^-3 S/cm and electrochemical stability in a large operating window of -0.5 V to 4.5 V. The PEM shows over 80% of specific capacity retention up to 250 cycles tested in the LiFePO₄/PEM/graphite full cells, which have met most of the requirements of all-solid-state lithium ion battery for portable devices