Hydrogel Electrolytes for Quasi-Solid Zinc-Based Batteries

Abstract

On account of high energy density depending on the utilized zinc metal anode of high theoretical capacity and its excellent security due to aqueous electrolytes that usually be locked in polymer hosts referred to as hydrogels, quasi-solid zinc-based batteries have been subjected to more and more interest from researchers. The good water retention and electrolyte load capacity of the hydrogel, contributing to the acquirement of high ionic conductivity and durability of the as-obtained quasi-solid electrolyte, play a significant role on the performance of the devices. Moreover, the chemistry of hydrogels can be tuned to endow quasi-solid electrolytes with additional functions in terms of application scenarios of solid-state batteries. Herein, the frontier disciplines of hydrogel electrolytes for Zn-based batteries were reviewed. The cross-linking process of the polymer networks for hydrogel materials with different functions, such as stretchability, compressibility, and self-healing, were also discussed to analyze the properties of the polymer electrolyte. Based on the merits of the functionalized hydrogel, the further application of hydrogel electrolytes in Zn-based batteries is the focus of this paper. The electrochemical performance and mechanical property of Zn-based batteries with functionalized hydrogel electrolytes under extreme conditions were presented to evaluate the crucial role of the polymer hydrogel electrolyte. Finally, the challenges of hydrogel electrolytes for currently developed Zn-based batteries are highlighted with the hope to boost their commercial application in energy conversion devices.

Keywords: electrolytes; hydrogel; self-healing; stretchability; zinc-based batteries.

Figure 1

Hydrogel in a wide range of applications.

Figure 2

(A) Illustration of ZIBs. (B) Cycle performance of the self-healing ZIBs at original state and after multiple rounds of cutting/self-healing. (C) Photographs of the two self-healing ZIBs in series powering an LED array before cutting (light on), after cutting (light off), and after self-healing (light on again). Reprinted with permission from Huang et al. (2019). Copyright (2019) John Wiley and Sons. (D) Schematic diagram and characterization of PAM-based electrolyte. (E) Eight yarn batteries were connected in a series to power a 1 m long electroluminescent panel, a long LED belt, and electroluminescent pane under different bending conditions. Reprinted with permission from Li et al. (2018a). Copyright (2018) American Chemical Society.

Figure 3

(A) Comparisons of the adhesion force and bending demonstration of PAM-battery and AF-battery at −20°C. (B) Application demonstration of the AF-battery at subzero temperatures. Reprinted with permission from Mo et al. (2019). Copyright (2019) Royal Society of Chemistry.

Figure 4

(A) Galvanostatic discharge-charge cycling curves at a current density of 5 mA cm⁻². Reprinted with permission from Ma et al. (2018a). Copyright (2018) American Chemical Society. (B) Synthesis of the PANa hydrogel electrolyte. Reprinted with permission from Huang et al. (2018a). Copyright (2018) John Wiley and Sons. (C) Photographs of the self-healing aqueous battery powering a clock before cutting (left), after cutting (middle), and after self-healing (right). Reprinted with permission from Huang et al. (2018b). Copyright (2018) John Wiley and Sons.