Preparation and characterization of gel electrolyte with bacterial cellulose coated with alternating layers of chitosan and alginate for electric double-layer capacitors

Abstract

A novel gel electrolyte has been prepared using bacterial cellulose (BC) coated with chitosan (CTS) and alginate (Alg) layers, which contain 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4). The gel electrolyte was optimized for use in solvent-free solid-stage electric double-layer capacitors (EDLCs). The inoculated BC was oxidized and coated with alternating layers of CTS and Alg via ionic crosslinking to produce the gel electrolytes. The CTS content of the obtained gel electrolytes linearly increased with an increase in the number of CTS and Alg layers on the BC fibers. The results imply that the CTS and Alg layers successfully bound onto each BC fiber, which was consistent with Fourier transform infrared spectroscopy measurements. Based on a structural analysis, the fabricated gel electrolytes had a nanofibrous structure with a fiber diameter range of approximately 78.6–99.0 nm, a high thermal stability, and a significantly improved tensile strength compared to gel electrolytes of only CTS or Alg. In addition, EDLCs have been fabricated using the new gel electrolyte with activated carbon as the active material. The electrochemical performance of the EDLCs was determined via charge–discharge testing and alternating current impedance measurements. The EDLCs cell with a gel electrolyte of BC coated with 15 layers of CTS and Alg containing EMImBF4 showed a high discharge capacitance, implying that the high affinity of this gel electrolyte for the activated carbon electrode leads to reduced electrode/electrolyte interfacial resistance, which shows the potential of this approach compared with liquid-phase EMImBF4 to obtain high-performance, safety-oriented EDLCs.