The Refuelable Zinc-air Battery: Alternative Techniques for Zinc and Electrolyte Regeneration

Abstract

An investigation was conducted into alternative techniques for zinc and electrolyte regeneration and reuse in the refuelable zinc/air battery that was developed by LLNL and previously tested on a moving electric bus using cut wire. Mossy zinc was electrodeposited onto a bipolar array of inclined Ni plates with an energy consumption of 1.8 kWh/kg. Using a H 2depolarized anode, zinc was deposited at 0.6 V (0.8 kA/m 2 ); the open circuit voltage was 0.45 V. Three types of fuel pellets were tested and compared with results for 0.75 mm cut wire: spheres produced in a spouted bed (UCB); coarse powder produced by gas-atomization (Noranda); and irregular pellets produced by chopping 1-mm plates of compacted zinc fines (Eagle-Picher, Inc.). All three types transported within the cell. The coarse powder fed continuously from hopper to cell, as did the compacted pellets (< 0.83 mm). Large particles (> 0.83 mm; Eagle-Picher and UCB) failed to feed from hopper into cell, being held up in the 2.5 mm wide channel connecting hopper to cell. Increasing channel width to ~3.5 mm should allow all three types to be used.Energy losses were determined for shorting of cells during refueling. The shorting currents between adjacent hoppers through zinc particle bridges were determined using both coarse powder and chopped compressed zinc plates. A physical model was developed allowing scaling our results for electrode polarization and bed resistance Shorting was found to consume < 0.02% of the capacity of the cell and to dissipate ~0.2 W/cell of heat. Corrosion rates were determined for cut wire in contact with current collector materials and battery-produced ZnO-saturated electrolyte. The rates were 1.7% of cell capacity per month at ambient temperatures; and 0.08% of capacity for 12 hours at 57 °C.The total energy conversion efficiency for zinc recovery using the hydrogen was estimated at 34% (natural gas to battery terminals)--comparable to fuel cells. Producing zinc shot was quoted at 1.5-3 ¢/lb above base price (52¢/lb, ASM) for super purity ingot.Both the spouted-bed and the Eagle-Picher processes might conceivably be configured for fleet operation in user-owned and operated equipment located a the fleet's home base. This would eliminate the need for green-field industrial plants and fuels distribution systems. Scaleup of the spouted bed process and detailed examination of the Eagle-Picher process are recommended.

Rechargeable Zn-air batteries: Progress in electrolyte development and cell configuration advancement

“…Cooper et al also demonstrated that the size of Zn particles should be limited to below~0.85 mm to insure continuous feed [93]. The refilling time for a typical application is about 10e20 min, which is relatively long compared with gasoline refilling.…”

Materials science aspects of zinc–air batteries: a review

“…Zn particles produced by different methods have been tested, including cut wire chunks, compacted electrodeposited dendrites, Zn spheroids reconstructed electrochemically in a spouted bed reactor (see, e.g., Fig. 11); zinc pellets are preferred to compacted dendrites owing to their better fluid dynamic behavior [93,[99][100][101][102]. The spent Zn particles, along with the KOH electrolyte, are replaced hydraulically by pumping from an external tank.…”

Zinc regeneration in rechargeable zinc-air fuel cells—A review

“…The main obstacles can be briefly summarized as follows: (i) poor recharge-ability, (ii) low utilization of the anode, (ii) sluggish kinetics of the cathode, (iii) longevity challenge. Compared with the Zn-air battery, the Zn-air fuel cell (ZAFC) offers several benefits, such as higher specific energy density, more attractive costs, better environmental compatibility and faster onsite refueling which requires only a standard electrical supply [1][2][3][4]16,19,20]. It also has the potential of achieving the performance of the state-of-art H2-air fuel cells used as energy converters [1].…”

“…It was well realized in the 1960s that such batteries could have a high potential and wide applications if a low-cost zinc anode was available. Then the use of hydrophobic Teflon film made the high-energy Zn-air button cell come to being, which has since become a dominant power source for hearing aids [5,19,20]. Recently, technologies based on mechanical recharging have demonstrated significant progress [16,19,20], which led to practical availability of Zn-air systems with power from 170 to 350 Wh/kg.…”

“…Then the use of hydrophobic Teflon film made the high-energy Zn-air button cell come to being, which has since become a dominant power source for hearing aids [5,19,20]. Recently, technologies based on mechanical recharging have demonstrated significant progress [16,19,20], which led to practical availability of Zn-air systems with power from 170 to 350 Wh/kg. With further consistent development, power levels of 500 to 600 Wh/kg can be expected in the near future [16].…”