Artificial Solid Electrolyte Interphase for Suppressing Surface Reactions and Cathode Dissolution in Aqueous Zinc Ion Batteries

Vanadium-based compounds have been widely used as electrode materials in aqueous zinc ion batteries (ZIBs) due to the multiple oxidation states of vanadium and their open framework structure. However, the solubility of vanadium in aqueous electrolytes and the formation of byproducts during the charge/discharge process cause severe capacity fading and limit cycle life. Here, we report an ultrathin HfO₂ film as an artificial solid electrolyte interphase (SEI) that is uniformly and conformally deposited by atomic layer deposition (ALD). The inactive hafnium­(IV) oxide (HfO₂) film not only decreases byproduct (Zn₄SO₄(OH)₆·xH₂O) formation on the surface of Zn₃V₂O₇(OH)₂·2H₂O (ZVO) but also suppresses the ZVO cathode dissolution in the electrolyte. As a result, the obtained HfO₂-coated ZVO cathodes deliver higher capacity and better cycle life (227 mAh g^–1@100 mA g^–1, 90% retention over 100 cycles) compared with pristine ZVO (170 mAh g^–1@100 mA g^–1, 45% retention over 100 cycles). A mechanistic investigation of the role of HfO₂ is presented, along with data showing that our method constitutes a general strategy for other cathodes to enhance their performance in aqueous ZIBs.