New strategy for Mg-air battery voltage-efficiency synergy by engineering protective film with cation vacancies on Mg anode surface

Although the Mg-air battery with high theoretical energy density is desirable for the energy supply of marine engineering equipment, its applications remain limited due to the low actual discharge voltage and inferior Mg anode utilization rate. In addition to the microstructure of Mg alloy anodes, the properties of discharge product films are of great importance to the discharge performance. Herein, the discharge behaviors of Mg-Y-Zn alloys are first studied mainly from the perspective of film properties. Through contrastive analysis, it is found that the sufficient Y³⁺ produced during the discharge process can substitute Mg²⁺ in Mg(OH)₂ to introduce effective cation vacancies. The Mg-Y-Zn anode with profuse cation vacancies in the product film shows a synergy of potential and efficiency, and this can be attributed to an increase in the migration pathway for Mg²⁺, reducing the diffusion over-potential caused by the protective product film. This study is expected to provide a new strategy from the perspective of cation vacancy design of discharge film for developing high-performance Mg-air batteries.