Zinc–air batteries are compelling portable-power alternatives to hazard-prone Li-ion technologies because they deliver higher practical specific energies (&gt;400 Whkg–1) in safe, low-cost forms. However, conventional packed-powder Zn anodes undergo dendritic growth during extended cycling, limiting their effectiveness for applications that require rechargeable batteries, while the ad hoc structures of both the Zn anode and air cathode hinders pulse-power function. To overcome the Zn dendrite problem and to increase the discharge capacity of Zn-based batteries, we express the zinc anode in a 3-dimensional (3D) “sponge” architecture that incorporates three critical design factors: (i) an inner core of electronically conductive Zn that is retained throughout battery charge/discharge; (ii) amplification of electrified interfaces to distribute current uniformly throughout the electrode structure, and thus eliminate dendrite-forming high current densities; and (iii) confined void volume elements within the electrode interior that expedite saturation/dehydration of zincate to ZnO. By adopting this 3D design, we can discharge Zn-air cells to &gt;90% Zn utilization (728 mA h gZn–1) in a primary Zn-air cell, while also demonstrating extensive charge-discharge cycling when pairing the Zn sponge anode with NiOx or AgOx cathodes. En route to rechargeable Zn-air batteries, we redesign the air cathode to express the electrochemical functionality inherent to fuel cells, electrolyzers, and electrochemical capacitors. Air cathodes based on ultraporous carbon nanofoam paper functionalized with nanoscale MnOx coatings deliver high-rate O2-reduction (ORR) activity (fuel-cell function) and an O2-independent capacitive-delivery mechanism (electrochemical-capacitor function; F cm–2 over 10s of seconds). As a final step towards a rechargeable Zn-air battery, we present practical recharge-enabling O2-evolution catalysts (electrolyzer function; OER) that will be incorporated within our dual-function air cathode, such that the resulting “trifunctional” cathode architecture expresses three functionalities: ORR, OER, and pulse power.

Surmounting the roadblocks to rechargeable zinc–air batteries by 3D architectural redesign of the air-breathing cathode and Zn anode

251st National Meeting (2016)

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