Tissue paper‑based composite separator using double-crosslinked polymer electrolyte as coating layer for lithium-ion battery with superior ion transport and cyclic stability

Nonwoven-based separators have unique advantages in meeting the demand of high power lithium-ion batteries (LIBs). However, conventional coating layer is usually found to give separator poor cyclic stability due to electrolyte plasticizing. Therefore, double-crosslinked coating layer was attempted to fabricate on substrate through sequencial reactions between diglycidyl ether terminated polydimethylsiloxane (PDMSDGE), poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and branched polyethyleneimine (PEI). Due to low cost, convenient acess, good hydrophilicity and prominent thermal stability, tissue paper was choosen as a substrate. This designed double-crosslinked composite separator (DN@CS) was observered to have unique advantages in terms of porosity, electrolyte uptake and wettability, ionic conductivity as well as transference number, which finally endowed battery with excellent discharge performance especilly at higher C-rate. As a result of mutual entanglement between two networks, the double-crosslinked separator possessed stronger skeleten, thus giving superior mechanical properties retention (95.05%) after electrolyte infiltration and higher discharge capacity retention (86.89%) even experienced 200 cycles. Moreover, the affinity between branched PEI and Li+ has been discovered to enable uniform Li deposition through electrokinetic effects. Clearly, this designed double-crosslinked network will bring new breakthrough for separator during the development of higher power LIBs.