A nano fiber–gel composite electrolyte with high Li+ transference number for application in quasi-solid batteries

As their Li+ transference number (tLi+), ionic conductivity, and safety are all high, polymer electrolytes play a vital role in overcoming uncontrollable lithium dendrites and low energy density in Li metal batteries (LMBs). We therefore synthesized a three-dimensional (3D) semi-interpenetrating network-based single-ion-conducting fiber–gel composite polymer electrolyte (FGCPE) via an electrospinning, initiation, and in situ polymerization method. The FGCPE provides high ionic conductivity (1.36 ​mS ​cm−1), high tLi+ (0.92), and a high electrochemical stability window (up to 4.84 ​V). More importantly, the aromatic heterocyclic structure of the biphenyl in the nanofiber membrane promotes the carbonization of the system (the limiting oxygen index value of the nanofiber membrane reaches 41%), giving it certain flame-retardant properties and solving the source-material safety issue. Due to the in situ method, the observable physical interface between electrodes and electrolytes is virtually eliminated, yielding a compact whole that facilitates rapid kinetic reactions in the cell. More excitingly, the LFP/FGCPE/Li cell displays outstanding cycling stability, with a capacity retention of 91.6% for 500 cycles even at 10C. We also test the FGCPE in high-voltage NMC532/FGCPE/Li cells and pouch cells. This newly designed FGCPE exhibits superior potential and feasibility for promoting the development of LMBs with high energy density and safety.