Salting-Out Effect Realizing High-Strength and Dendrite-Inhibiting Cellulose Hydrogel Electrolyte for Durable Aqueous Zinc-Ion Batteries

Abstract

Aqueous zinc-ion batteries are limited by poor Zn stripping/ plating reversibility. Not only can hydrogel electrolytes address this issue, but also they are suitable for constructing flexible batteries. However, there exists a contradiction between the mechanical strength and the ionic conductivity for hydrogel electrolytes. Herein, high-concentration kosmotropic ions are introduced into the cellulose hydrogel electrolyte to take advantage of the salting-out effect. This can significantly improve both the mechanical strength and ionic conductivity. Additionally, the obtained cellulose hydrogel electrolyte (denoted as Con-CMC) has strong adhesion, a wide electrochemical stability window, and good water retaining ability. The Con-CMC is also found to accelerate the desolvation process, improve Zn deposition kinetics, promote Zn deposition along the (002) plane, and suppress parasitic reactions. Accordingly, the Zn/Zn cell with Con-CMC demonstrates dendrite-free behavior with prolonged lifespan and can endure extremely large areal capacity of 25 mAh cm −2 . The Con-CMC also enables a large average Coulombic efficiency of 99.54% over 500 cycles for the Zn/Cu cell. Furthermore, the assembled pouch-type Zn/polyaniline full battery provides great rate capability, superior cyclability (even with limited Zn anode excess), a slow self-discharge rate, and outstanding affordability to external forces. Overall, this work extends our knowledge of the rational design of hydrogel electrolytes.

Hydrogel-stabilized zinc ion batteries: progress and outlook

“…Quan et al introduced high concentrations of co-osmophilic ions into cellulose hydrogel electrolytes to leverage their salting out effect. 53 This significantly improved the mechanical strength and ionic conductivity of the resulting cellulose hydrogel electrolyte, denoted as Con-CMC. Con-CMC exhibited strong adhesion, a wide electrochemical stabilization window, and good water retention.…”

A Review of the Synthesis of Biopolymer Hydrogel Electrolytes for Improved Electrode–Electrolyte Interfaces in Zinc-Ion Batteries

“…Incorporating the principles of the Hofmeister effect (Figure 2), high-concentration kosmotropic ions were introduced into a cellulose hydrogel, exploiting the salting-out effect [53]. Carboxymethyl cellulose (CMC) was selected for its negatively charged framework, good solubility in water, and abundant oxygen-containing functional groups [53]. The hydrogel was produced by adding acetic acid to the CMC solution to facilitate gelation, followed by four freeze-thaw cycles, and drying at room temperature [53].…”

“…Hydrogel electrolytes with reduced free water content and quasi-solid-state properties can suppress water splitting side reactions, zinc dendrite growth, electrode dissolution, and water leakage [50,51]. Moreover, hydrogel electrolytes enhance the stability of electrodeelectrolyte interfaces through (i) the adhesion effect of hydrogel polar groups [50,52], (ii) close contact achievable with electrode active materials due to the mechanical elasticity of hydrogel electrolytes [53,54], and (iii) controlled Zn 2+ deposition through the interaction between Zn 2+ and hydrogel functional groups fixed in the hydrogel 3D network with evenly distributed ion transfer channels [55]. Hydrogels, with their hydrophilic polymer 3D network matrix, can hold aqueous electrolytes [56].…”

GO‐enhanced Gel Polymer Electrolyte for Aqueous Zinc‐Ion Batteries

“…Nevertheless, the problems of dendrite growth and leakage of liquid electrolyte restrict the wide application of AZIBs. [18][19][20] Recently, GPEs have emerged as a promising solution to address the aforementioned challenges of AZIBs, owing to their ability to prevent leakage, exhibit flame retardancy, and possess favorable mechanical properties. [21,22] In order to enhance the performance of GPEs, researchers have conducted investigations into the utilization of physical or chemical modification to ameliorate both the mechanical and electrochemical properties.…”

“…Consequently, they are widely regarded as the most viable option for large‐scale energy storage. Nevertheless, the problems of dendrite growth and leakage of liquid electrolyte restrict the wide application of AZIBs [18–20] …”