A zinc battery with ultra-flat discharge plateau through phase transition mechanism

Rechargeable aqueous zinc batteries have attracted enormous attention due to the distinctively economic and environmental advantages. However, the present zinc batteries delivered sloping voltage profiles based on the dominant mechanism of Zn ion intercalation. Typically, a Zn–V₂O₅ battery exhibits a discharge slope of ~4.3 V/(Ah g⁻¹) and a slope of ~1.5 V/(Ah g⁻¹) is observed for MnO₂ cathodes. Furthermore, the rate capacity based on intercalation is limited. Here we report a highly flat voltage profile for a reversible alkaline zinc battery with α-Bi₂O₃ as the cathode. Different from the conventional zinc batteries, zinc-α-Bi₂O₃ batteries possess a first-order phase transition process that is the responsible cause of their outstanding performance, such as an ultra-flat output voltage [slope: ~0.1 V/(Ah g⁻¹)], a high discharge capacity of 323 mAh g⁻¹ at 0.1 A g⁻¹ and excellent rate capacity with a 155 mAh g⁻¹ capacity even at 20A g⁻¹ (61C). In addition, a high areal energy density of 1.5 mWh cm⁻² is achieved at power density of 4.4 mW cm⁻². Moreover, the quasi-solid-state Zn-α-Bi₂O₃ battery is also fabricated using a sodium polyacrylate (PANa) as the hydrogel electrolyte, exhibiting promising application as power source for flexible devices.