Study on the Construction and Properties of Bacterial Cellulose-Based Cathode for Flexible Zn-Ion Batteries

Flexible Zn-ion batteries (ZIBs) have been considered as desirable candidate of flexible energy storages due to its high safety, low cost and high energy density. However, there is a challenge that ZIBs can possess both high electrochemistry properties and good mechanical stability. Among them, the lack of suitable substrate material has long been the major obstacles against the development of flexible electrode for ZIBs. In this work, we prepared the bacterial cellulose/polyaniline/carbon nanotubes (BC/PANI/CNTs) flexible electrode through a simple in-situ polymerization with subsequent vacuum filtration. Typically, the BC suspension and aniline monomer were dissolved into HCl solution. After the ammonium persulfate dispersed in another HCl aqueous solution, the obtained solution was subsequently added dropwise into the above mixture in an ice bath. Then, the acid treated CNTs was added to achieve the whole dispersion. The resulted film was collected by vacuum filtration and the BC/PANI/CNTs flexible electrode was finally obtained by further dried in an oven. Benefiting from the BC substrate, the BC/PANI/CNTs flexible electrode possesses a 3D porous structure, which can provide the rapid diffusion channel of electrolyte ion and improve the contact between the active material and electrolyte ion. Moreover, the BC substrate endow the BC/PANI/CNTs electrode with high flexibility and large mass loading of active materials. The scanning electron microscopy (SEM) image of the BC/PANI/CNTs electrode shows that the PANI is uniformly anchored on the surface of BC nanofiber, and the CNTs is dispersed in the porous network and connected with BC/PANI nanofibers. Furthermore, the X-ray diffraction (XRD), Raman spectra, Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirm the structure of the BC/PANI/CNTs. The BC/PANI/CNTs, tested as a flexible cathode for ZIBs, achieve both good electrochemical performance, such as mass loading of 7.3 mg/cm(2), gravimetric capacity of 157 mAh/g, areal capacity of 1.148 mAh/cm(2), and excellent mechanical flexibility, which can be bended, twisted and rolled. To further explore the application value of this flexible electrode in electronic equipment, the quasi-solid-state ZIBs was prepared with the BC/PANI/CNTs as cathode, the Zn/carbon cloth (CC) as anode, and the ZnSO4/polyvinyl alcohol (PVA) as gel electrolyte, respectively. The assembled quasi-solid-state ZIBs deliver a specific capacity of 109 mAh/g, and over 90% of the initial capacity is retained after 200 charge/discharge cycles at a low current density of 0.5 mA/cm(2). The low-cost BC/PANI/CNTs flexible electrode has excellent performance and mechanical property, providing a feasible scheme for the scalable application of ZIBs.

Automated summary

In this study, a flexible BC/PANI/CNTs electrode was prepared through in-situ polymerization and vacuum filtration, utilizing bacterial cellulose as a substrate to provide a 3D porous structure, enabling rapid diffusion of electrolyte ions and improved contact between active material and electrolyte ions. The electrode exhibits good electrochemical performance and mechanical flexibility.