High-Voltage Aqueous Zinc Batteries Achieved by Tri-functional Metallic Bipolar Electrodes

Aqueous rechargeable zinc batteries are very attractive for energy storage applications due to their low cost and high safety. However, low operating voltages limit their further development. For the first time, this work proposes a unique approach to increase the voltages of aqueous zinc batteries by using tri-functional metallic bipolar electrode with good electrochemical activity and ultrahigh electronic conductivity, which not only participates in redox reactions, but also functions as an electrical highway for charge transport. Furthermore, bipolar electrode can replace expensive ion selective membrane to separate electrolytes with different pH; thus, redox couples with higher potential in acid condition and Zn/Zn(OH)42- couple with lower potential in alkaline condition can be employed together, leading to high voltages of aqueous zinc batteries. Herein, two types of metallic bipolar electrodes of Cu and Ag are utilized based on three kinds of aqueous zinc batteries: Zn-MnO2, Zn-I-2,I- and Zn-Br-2. The voltage of aqueous Zn-MnO2 battery is raised to 1.84 V by employing one Cu bipolar electrode, which shows no capacity attenuation after 3500 cycles. Moreover, the other Ag bipolar electrode can be adopted to successfully construct Zn-I-2 and Zn-Br-2 batteries exhibiting much higher voltages of 2.44 and 2.67 V, which also show no obvious capacity degradation for 1000 and 800 cycles, representing decent cycle stability. Since bipolar electrode can be applied in a large family of aqueous batteries, this work offers an elaborate high-voltage concept based on tri-functional metallic bipolar electrode as a model system to open a door to explore high-voltage aqueous batteries.

Automated summary

This study proposes a unique approach to increase the voltages of aqueous zinc batteries by using a tri-functional metallic bipolar electrode. The bipolar electrode not only participates in redox reactions but also functions as an electrical highway for charge transport. It can also replace expensive ion selective membrane to separate electrolytes with different pH, leading to high voltages of aqueous zinc batteries.