Zincate-Blocking-Functionalized Polysulfone Separators for Secondary Zn-MnO₂ Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Alkaline zinc-manganese dioxide (Zn-MnO2) batteries offer safe, low-cost grid storage potential due to aqueous electrolytes and available materials.
• High-capacity Cu/Bi-stabilized birnessite cathodes necessitate selective separators to prevent zincate (Zn(OH)4^2-) crossover, which degrades electrode performance.
• Dissolved zinc species migrating from the anode to the cathode is a critical failure mechanism in Zn-MnO2 battery systems.

Purpose of the Study:

• To synthesize and evaluate N-butylimidazolium-functionalized polysulfone (NBI-PSU) based separators for selective ion transport.
• To assess the ability of NBI-PSU separators to block zincate ions while allowing hydroxide ion passage.
• To investigate the impact of these novel separators on the cycling performance of high depth-of-discharge Zn/(Cu/Bi-MnO2) batteries.

Main Methods:

• Synthesis of N-butylimidazolium-functionalized polysulfone (NBI-PSU) based membranes.
• Zincate and hydroxide diffusion tests to quantify ion transport selectivity and crossover rates.
• Cycling performance evaluation of Zn/(Cu/Bi-MnO2) batteries incorporating NBI-PSU separators compared to commercial separators.

Main Results:

• NBI-PSU separators demonstrated significantly improved zincate-blocking capabilities compared to commercial Cellophane and Celgard separators.
• The synthesized separators maintained comparable hydroxide ion crossover rates to commercial benchmarks.
• Batteries utilizing NBI-PSU separators exhibited extended cycle life, increasing from 21 to 79 cycles in control cells.

Conclusions:

• N-butylimidazolium-functionalized polysulfone separators are effective in preventing detrimental zincate transport in alkaline Zn-MnO2 batteries.
• These selective separators enhance the cycling stability and longevity of Zn-MnO2 batteries for grid storage.
• The developed NBI-PSU membranes represent a promising advancement for improving the practical application of aqueous zinc-based energy storage systems.