An Environment-Friendly High-Performance Aqueous Mg-Na Hybrid-Ion Battery Using an Organic Polymer Anode

Aqueous Mg ion batteries (AMIBs) show great potential in energy storage for their advantages of high capacity, abundant resource, and environmental friendliness. However, the development of AMIBs is limited due to the scarcity of suitable anode materials. In this study, a new polymer anode material (PNTAQ) with flower-like nanosheet structure is synthesized for aqueous Mg-Na hybrid-ion battery (AMNHIB). PNTAQ possess carbonyl functional groups which can be oxidized and reduced reversibly in aqueous solution containing alkaline metal ions. PNTAQ displays a discharge specific capacity of 245 mAh g⁻¹ at 50 mA g⁻¹ in 1 M MgCl₂ + 0.5 M NaCl electrolyte, which is much higher than that in single 1 M MgCl₂ or 0.5 M NaCl electrolyte. Even cycling at 1000 mA g⁻¹ for 1000 times, the capacity retention can still maintain at 87.2%. A full Mg-Na hybrid-ion cell is assembled by employing β-MnO₂ as cathode and PNTAQ as anode material, it exhibits a specific capacity of 91.6 mAh g⁻¹ at 100 mA g⁻¹. The polymer electrode material well maintains its framework structure during the discharge/charge cycling process of the hybrid-ion battery.