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

Abstract

Non-woven based battery separators have been developed rapidly in recent years due to their unique advantages in process, cost and performance. In this study, a novel double-crosslinked three-dimensional network coating was constructed by hyperbranched polyethyleneimine (PEI), Polydimethylsiloxane diglycidyl ether (PDMSDGE) and poly(vinylidene fluoride-co-hexafluoropropylene) PVDF-HFP. Then the caoting used to modify tissue paper, which composed of packed cellulose fibers is typical nonwoven with excellent hydrophilic properties required for lithium separators. As we expected, the composite separator shows unique advantages in terms of porosity, electrolyte absorption, mechanical properties and thermal stability. At the same time, the nucleophilic hyperbranched PEI in the coating makes the composite separator in a lithium-rich state in lithium ion battery, so the separator has a certain electric pumping capacity by electrokinetic surface conduction and electroosmosis. As a result, the electrochemical performance and battery performance are excellent too. In addition, we compared the performance of the double-crosslinked coating with two systems of single-crosslinked coating, PEI/PDMSDGE and PEI/PVDF-HFP. The results showed the excellent performance of the composite separator with double-crosslinked coating in terms of mechanical properties retention (95.05%) after electrolyte infiltration and discharge capacity retention (86.89%) after 200 cycles, which given by the stable molecular structure of the three-dimensional double-crosslinked network.