Electronic Ionic Polymer Composite-Based Interface via Boosting Zinc Deposition and Transportation for Highly Stable Zn Metal Anodes

Zinc metal with high volumetric and specific capacities (5855 Ah L^-1 and 820 mAh g^-1) is low-priced (0.5 – 1.5 $ lb^-1 of Zn metal vs. 8 – 11 $ lb^-1 of Li metal) and abundant in the earth (79 ppm of Zn metal vs. 17 ppm of Li metal). Typically, even though Zn metal, unlike alkaline metals such as Li and Na, exhibits more inert in aqueous systems, aqueous Zn ion batteries (AZIBs) are thermodynamically unstable in aqueous electrolytes due to the lower reduction potential of Zn (-0.76 V vs. SHE) than H⁺/H₂ (0 V vs. SHE). As shown in the reaction, because E_Zn²⁺ (-0.76 V) is lower than E_H⁺ (0 V), hydrogen evolution reaction (HER) has a higher tendency to occur before the Zn deposition reaction. Since HER can compete with the Zn deposition reaction, the reduction of Zn metal during the cycling is accompanied by water decomposition, resulting in a rise in the electrolyte's hydrogen ion concentration index (pH). When Zn metal is in contact with the electrolyte, the change of local pH can produce electrochemically non-conductive byproducts. The passivation of the surface accelerates the growth of dendrites and hinders Zn²⁺ diffusion. These reactions are interdependent, so for an ideal Zn anode, only reversible oxidation/reduction reactions should occur at the interface.<br/><br/>Therefore, modifying the Zn surface to prevent inappropriate side reactions with electrolytes to inhibit the continued production of by-products is preferred. Introducing 3D structural designs and artificial solid electrolyte interphase (SEI) layers tends to extend the lifespan of AZIBs by forming dense deposition structures. Another strategy involves incorporating materials with strong crystal orientations to control Zn deposition behavior effectively. Gradual Zn deposition in the planar direction can regulate internal stress and prevent charge accumulation. However, under high current densities, increased Zn²⁺ flux disrupts uniform ion transfer during deposition/desorption cycles, leading to internal stress and charge accumulation. These issues can alter the deposition structure and growth pattern of Zn. Furthermore, the complex and costly processes still require significant refinement for practical applications. While numerous studies have addressed the reversibility of Zn anodes from several perspectives, the complex correlation between the electrode and interface and cell performance has yet to be studied. Therefore, substrates with strong orientation relationships should be designed to control the active atoms to alleviate local charge accumulation and enable sufficient ion transfer.<br/><br/>In this work, we proposed a mixed electronic-ionic transport polymer composite (referred to as EIPCs) overlayer to relax internal stress and sufficient ion transfer by facile spin-coating process. The EIPCs-based interface is composed of poly (acrylic acid) (PAA) and graphene oxide (GO) at the electrode-electrolyte interface. The synergy effect of rapid Zn ion diffusion dynamics and electric field regulation effectively mitigated the typical surface Zn deposition and volume fluctuations. The growth of dendrites along the (002) basal plane exhibited lower surface energy and chemical activity, suppressing side reactions. In addition, the water-solved polymer (PAA) forms hydrogen bonds with the functional groups of graphene oxide to build a compact and well-aligned 2D stack. As a result, low interfacial resistance and high (002) preferential orientation further facilitate rapid plating/stripping during the cycle. The Zn@EIPCs with synergistic effect achieved improved anode performance with a long lifespan (&gt;1500 h) and high current density (20 mA cm^-2). We also conducted a full-cell test with different cathodes (Zn_0.25V₂O₅, I₂) to confirm its versatility. The novel EIPCs interface design, dynamically suppressing dendritic formation, can significantly enhance the stability of AZIBs and other aqueous energy storage systems.