Fluorinated polymer coated cyanoethyl-chitin nanofiber composite separators for high performance lithium ion batteries

Abstract

Natural polymer nanofiber-based separators with excellent thermal stability, mechanical strength, and electrolyte wettability have shown great potentials for advanced lithium ion batteries. However, there are two crucial issues to block their practical applications, including high moisture absorption and interfacial instability toward electrodes. Here, a surface coating strategy to overcome these disadvantages and promote natural polymer nanofiber-based separator performance is demonstrated. A hydrophobic polymer, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), is adopted to coating on the surface of cyanoethyl-chitin nanofiber (CCN) separators. The as-fabricated CCN/PVDF-HFP composite separators not only exhibit much lower moisture absorption and higher interfacial instability but also retain high mechanical strength and ionic conductivity in comparison to CCN separators. The LiFePO4/Li cells using CCN/PVDF-HFP separators exhibit much better electrochemical cycle performance and enhanced capacity retention than that using CCN separators.