Performance Study of Cellulose Acetate/Aramid Fiber Separator for Lithium Batteries

Cellulose separators have garnered widespread attention due to their excellent thermal stability, high liquid absorption rate, and high porosity. However, pure cellulose separators also face drawbacks such as poor mechanical properties and inadequate flame retardancy. To further enhance the performance of cellulose separators, a sandwich-structured composite separator composed of Cellulose Acetate （CA）and aramid fiber （AF）was fabricated using a hierarchical electrospinning process. The influence of different layered structures on the separator performance was investigated. The results indicate that a higher concentration of the spinning solution is conducive to obtaining fibers with desirable morphological structures. Higher spinning voltage yields finer fibers with narrower diameter distribution, yet excessive voltage may compromise process stability, leading to defective fiber morphology. Owing to the excellent liquid absorption capacity of CA, the separators prepared via the electrospinning process all exhibit high saturated electrolyte uptake rates, ranging from 299% to 423.6%. The incorporation of AF significantly enhanced the mechanical properties and flame retardancy of the separators. In terms of electrochemical performance, the separators with a bilayer AF structure exhibited higher ionic conductivity (2.436 mS cm⁻¹) and lower interfacial impedance (570 Ω) compared to those with a single layer of AF, attributed to the presence of polar aramid groups. Moreover, compared with polypropylene (PP) separators (4.4 V), the CA/AF composite separators demonstrate a broader electrochemical stability window (approximately 4.8 V). Regarding battery performance, the CA separator is relatively fragile and unable to withstand long-term charge-discharge testing. However, the other two composite separators exhibit superior cycling and rate performance compared to the PP (polypropylene) separator. Among them, the strong adsorption of lithium ions by aramid molecules endows the bilayer AF separator with a higher discharge capacity.