Water-Insoluble Side-Chain-Grafted Single Ion Conducting Polymer Electrolyte for Long-Term Stable Lithium Metal Secondary Batteries

Lithium metal is an attracting anode as an alternate of graphite, but the irregular deposition and stripping in the charge and discharge processes using binary electrolyte generate lithium dendrite and dead lithium, resulting in an unexpected safety issue and poor Coulombic efficiency. In this article, lithium 4-aminophenylsulfonyl(trifluoromethylsulfonyl)imide (LiATFSI) is side-chain-grafted to a commercial poly(styrene-co-maleic anhydride) (PSMA) copolymer to get a polyimide based single ion conducting polymer electrolyte, PSMA-g-LiATFSI. The lithiated polymer is water-insoluble because of the abundant nonpolar benzene ring and reduced ion exchange capacity (IEC). The lithium symmetric cell using the blend single ion conducting polymer electrolyte operates stably for more than one month, but the cell using commercial binary electrolyte terminates with a short circuit. And the single ion conducting lithium metal secondary battery delivers a stable discharge capacity of 120 mAh g–1 at 1 C for 1000 cycles with an average Coulombic efficiency of 99.83%, but the dual ion conducting lithium metal secondary battery deteriorates continuously. SEM characterization reveals that the lithium foil using gel single ion conducting polymer electrolyte remains flat with metallic luster, but the lithium foil using commercial dual ion electrolyte grows up with irregular porous protuberances. This work demonstrates that the gel single ion conducting polymer electrolyte can avoid concentration polarization and thus enables uniform lithium stripping and deposition for long-term stable lithium metal secondary batteries.