Preparation and application of PAM-based composite hydrogel electrolyte in Zn−MnO2 battery

Abstract

With the advantages of being cheap, safe, and environmentally friendly, aqueous Zn-ion batteries (AZIBs) show promise in large-scale energy storage and smart wearables. Moreover, with the expansion of the field of flexible electronics, the huge demand potential of wearable smart electronic devices is increasingly being underscored, which proposes higher requirements for the structural and electrochemical stability of energy storage devices and device safety in physical deformation processes. Aqueous electrolyte-based AZIBs are prone to interface separation during bending, which affects battery stability and makes it difficult to realize further practical applications in flexible electronics. Unlike aqueous electrolytes, hydrogel electrolytes are flexible and foldable, assuring the structural and performance stability of flexible energy storage devices under the action of external impacts. Particularly, polyacrylamide (PAM)-based hydrogels are the preferred materials for preparing hydrogel electrolytes due to their better ionic conductivity, strain, and stability. Herein, montmorillonite–PAM hydrogel (MMT–PAM) electrolytes with a three-dimensional network structure were produced by a two-step process using two-dimensional layered montmorillonite and acrylamide monomer. The addition of montmorillonite provides adsorption sites for the in situ polymerization of acrylamide monomer to enhance the mechanical properties of the hydrogel and facilitates the rapid transport of Zn2+ through the abundant negative charge on the MMT surface, increasing its ionic conductivity (34 mS∙cm−1 at room temperature is much higher than that of the PAM hydrogel electrolyte (17 mS∙cm−1)) to obtain MMT–PAM hydrogel electrolytes with better electrochemical properties. The MMT–PAM hydrogel electrolyte-based Zn–MnO2 batteries –demonstrated a specific capacity of 289 mA·h∙g−1 at a current density of 0.2 A∙g−1 and could be stably cycled for 2000 cycles, whereas the PAM hydrogel electrolyte-based Zn–MnO2 batteries only cycled for hundreds of cycles at the same current density before short-circuiting, thus demonstrating the long battery cycle life of the MMT–PAM hydrogel electrolyte-based Zn–MnO2 batteries. The MMT–PAM-based batteries maintained a high specific capacity even at a high current density of 4 A∙g−1. Furthermore, flexible batteries based on MMT–PAM hydrogel electrolytes could still work properly under different external impacts, such as cutting and piercing. The prepared flexible batteries were folded and immersed in aqueous solution to provide stable voltage and remarkable water resistance, demonstrating their possible application in flexible electronics. Therefore, this work sheds light on the possibility of further application of hydrogel electrolytes in aqueous Zn–MnO2 batteries and the further development of flexible energy storage devices based on hydrogel electrolytes.

Keywords

• zn–mno2 battery
• hydrogel electrolyte
• montmorillonite
• cycle stability
• mechanical strength
• flexible batteries