Design and characterization of micro-nano cellulose fibers composite separators for sodium-ion batteries

Abstract

Cellulose fibers characterized by low cost, well chemical stability and environmental friendliness, are a significant direction for sodium-ion batteries separator materials. However, the cellulose film is dense due to the hydrogen bonding between hydroxyl groups, corresponding to the low porosity, ionic conductivity and poor wettability to the electrolyte of sodium-ion batteries, which seriously limits application performance. A strategy to regulate the microstructure of cellulose films using micro-nano cellulose fiber composites is proposed in this thesis. Micro-cellulose fibers are extracted from cattail rods and nano-cellulose fibers are obtained from ordinary qualitative filter paper, respectively. Cellulose-based composite separators are synthesized by a conventional screening method and the influence of composite ratios on the separator behaviors is explored. The composite separator with micro-nano fibers mass ratio of 2:1 has a better overall performance, including porosity of 88.3 % and ionic conductivity of 0.63 × 10⁻³ S cm⁻¹. The assembled Na₃V₂(PO₄)₃/Na half-cells deliver high cycle capacity retention rate of 97.0 % at 1 C after 500 cycles, rate capacity retention rate of 85.5 % at 10 C, as well as a small potential polarization and fine interface stability. These results provide alternative approach for the design of high-performance and low-cost cellulose-based separators for sodium-ion batteries.