The development of aqueous zinc metal batteries (AZMBs) is significantly impeded by the poor cycle stability of Zn anodes due to the uncontrolled dendrite growth and low Coulombic efficiency (CE). Herein, for the first time, SeO 2 additives are introduced into ZnSO 4 electrolyte to enhance the stability of the Zn anode. According to the experimental results, the protective ZnSe layer is initially in-situ formed on the Zn surface prior to the Zn plating, which acts as a shield for inhibiting the parasitic reactions and dendrite formation. Moreover, this additive strategy yields the unique characteristic of self-healing for recovering the cracks in the consequence of huge volume change, ensuring the durability of ZnSe layer. Consequently, Zn|Zn symmetric cell using SeO 2 additive delivers an enhanced cumulative plated capacity of 2.1 Ah cm −2 under practical test conditions, which far exceeds the previously reported works. Meanwhile, the average CE of 99.6% for 250 cycles is also demonstrated in Zn|Cu half cells with the presence of the SeO 2 additive. In addition, the positive effect of the SeO 2 additive is further illustrated in the Zn-MnO 2 full cells with a limited Zn.

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The solid electrolyte interphase (SEI)-forming additives strategy is of great significance for improving the cycle stability of zinc (Zn) anodes. Although various additives have been reported, the relationship between their molecular structures and SEI chemistries is poorly understood. Herein, a molecular design principle for sulfonamide-containing additives that endow Zn anodes with a robust SEI layer is proposed. The incorporation of the benzene ring and amino group (−NH 2 ) leads to high adsorption energy, low lowest unoccupied molecular orbital lowest unoccupied molecular orbital (LUMO), and a small highest occupied molecular orbital-LUMO (HOMO-LUMO) gap, facilitating the reduction process of sulfanilamide (SA) additives. Coupled with SA/ZnSO 4 electrolytes, Zn|Zn symmetric cells deliver an ultralong cycle life of 4800 h (200 days) at 2 mA cm −2 and 2 mAh cm −2 . Additionally, a high cumulative plated capacity (CPC) of 6000 mAh cm −2 and 2700 mAh cm −2 is also achieved at a capacity per cycle of 10 mAh cm −2 and 30 mAh cm −2 , respectively. More importantly, the versatility of SA additives is also demonstrated in Zn-V 2 O 5 , Zn-I 2 , and Zn-MnO 2 full cells at a low N/P ratio (the theoretical capacity ratio between the negative and positive electrode) of 5.3, 8.3, and 4.5, respectively. This molecular structure strategy provides a promising path to develop effective SEI-forming additives.

A novel strategy is proposed to construct a compact-nanobox (CNB) structure composed of irregular nanograins (average diameter ≈ 10 nm), aiming to confine the electrode-electrolyte contact area and enhance initial Coulombic efficiency (ICE) of transition metal oxide (TMO) anodes. To demonstrate the validity of this attempt, CoO-CNB is taken as an example which is synthesized via a carbothermic reduction method. Benefiting from the compact configuration, electrolyte can only contact the outer surface of the nanobox, keeping the inner CoO nanograins untouched. Therefore, the solid electrolyte interphase (SEI) formation is reduced. Furthermore, the internal cavity leaves enough room for volume variation upon lithiation and delithiation, resulting in superior mechanical stability of the CNB structure and less generation of fresh SEI. Consequently, the SEI remains stable and spatially confined without degradation, and hence, the CoO-CNB electrode delivers an enhanced ICE of 82.2%, which is among the highest values reported for TMO-based anodes in lithium-ion batteries. In addition, the CoO-CNB electrode also demonstrates excellent cyclability with a reversible capacity of 811.6 mA h g (90.4% capacity retention after 100 cycles). These findings open up a new way to design high-ICE electrodes and boost the practical application of TMO anodes.