Ion-Selective and Chemical-Protective Interphase for Highly Durable Zinc Metal Anode

The development of sustainable energy sources such as wind, solar, and hydropower has been vigorously studied to overcome global energy crisis and climate change. However, they suffer from uncertainty and instability in power generation since they significantly depend on external environmental factors. As a result, additional energy storage systems are required to manage excess electricity efficiently and transfer energy timely. Rechargeable batteries that enable facile conversion and storage of energy produced, thus, have been extensively investigated as a rational solution for renewable energy sources. Among various candidates, aqueous zinc ion batteries (ZIBs) are studied as the most attractive system owing to the beneficial properties including insensitive manufacturing condition, low material cost, nonflammability, and environmental benignity. However, the practical application of ZIBs is under challenge due to dendritic growth and low electrochemical reversibility of Zn anode. Like other metals, Zn tends to form a dendritic architecture during plating/stripping processes due to inhomogeneous charge distribution. Furthermore, Zn dendrites with large surface area facilitate detrimental side reactions to induce insulating byproducts, corrosion, and hydrogen evolution reaction (HER) in mild acidic electrolytes. The detrimental side reactions incur local environmental change to accelerate dendritic growth and result in low Coulombic efficiency and subsequent capacity fading.<br/>Several strategies reportedly enhance the electrochemical reversibility of Zn anode. In particular, introducing an artificial protective layer is an attractive method because it can be fabricated by a simple coating process and exhibits tunable electrochemical and mechanical properties according to its layer components. Additionally, an artificial protective layer can achieve homogeneous Zn²⁺ transfer through the interphase matrix and prevents direct contact between the aqueous electrolyte and the electrode surface, thereby increasing the lifespan of batteries. However, numerous artificial protective layers are designed with a thick structure to alleviate infinite volume expansion of Zn during the repetitive charge/discharge cycles, while these thick electrochemically inert layers negatively affect to the overall energy density. Also, studies on ion behavior inside the protective interphase still remain in the early stage, while it is required to develop advanced anode materials.<br/>Herein, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-graft-maleic anhydride (SEBS-MA) is introduced as an artificial protective layer for the Zn anode through a simple spin-coating process. The 180 nm-thick SEBS-MA can withstand the volume change of Zn during repetitive charge-discharge processes due to its high stretchability and mechanical robustness. In the SEBS-MA layer, maleic anhydride groups attract Zn²⁺ dissolved in the electrolyte and form a cation transporting channel, leading to a smooth electrode surface without dendritic metal growth. Moreover, this SEBS-MA layer exhibits an ion-selective property, such that only Zn²⁺ can pass through the layer, whereas water molecules and SO₄^2- anions are highly restricted. The ion-selective layer could effectively suppresses HER and the formation of detrimental species. Consequently, based on the synergetic effects between the electrode surface stabilization and the uniform ion distribution, the SEBS-MA-coated Zn (Zn@SEBS-MA) symmetric cell demonstrates ultralong cycle life (&gt;3,200 h) at a high current density of 3 mA cm^-2 and an areal capacity of 1 mAh cm^-2. The beneficial effect of SEBS-MA was further investigated using Zn@SEBS-MA|MnO2 full cells and could realize durable cycle retention 80% after 2,500 cycles. This work provides a facile fabrication process and accessible analysis methods to rationalize the development of high-performance ZIBs.