Cellulose based ionic conductive hydrogel as electrolyte of zinc-ion batteries

Abstract

Hydrogels are known for their enhanced flexibility, easily tailorable properties, and safety, making them a prime candidate for flexible wearable electronics energy storage systems. For these applications, mechanical strength and microstructure play a critical role in determining the performance of the hydrogels, hence increasing the demand for further development and research in tougher, more elastic, and high ion transport system hydrogels. In this study, cellulose based hydrogels with unique unidirectional channels and excellent compressibility were investigated. These hydrogels were employed as hosts for both zinc sulfate 〖(ZnSO〗_4) and zinc acetate (Zn(CH_3 COO)_2) electrolytes individually, with varying concentrations investigated to optimize their performance as electrolytes and separators within zinc ion batteries. The project aims to optimize the fabrication process, explore the influence of various electrolyte types and concentrations on ionic conductivity, and lastly evaluate the electrochemical performance of the resulting hydrogels when employed in zinc-ion coin cell batteries. In this project, a hydrogel with hierarchical porosity was successfully fabricated via chemical crosslinking and unidirectional freezing of a prepared slurry. The hydrogel is composed of cellulose nanofibers (CNF) bound by a laminar porous polyvinyl alcohol (PVA) wall. Characterization methods used include scanning electron microscopy (SEM), impedance testing, compression testing and cycling tests within zinc-ion battery cells. The obtained results indicated better electrochemical performance for the ZnSO_4 hydrogel compared to Zn(CH_3 COO)_2 hydrogel. When employed in a zinc ion coin cell battery, the fabricated cellulose-based hydrogel electrolyte containing 3 M ZnSO_4 ions, delivered a specific capacity of 121.5 mAh/g at 5 A/g.