Next-Generation Rechargeable Zn Batteries for Electric Vertical Takeoff and Landing (eVTOL) Aircraft

The U.S. military is becoming increasingly electrified with applications ranging from handheld electronics, ordnance systems, electric ground and aerial vehicles, and large-scale energy storage systems for base microgrids.  The energy density, cost, and safety of Li-ion batteries are insufficient to meet the requirements for many of these applications.  Additionally, Li-ion batteries are a manufacturing security risk due to low natural reserves of critical components in the U.S.  Rechargeable zinc-air batteries have the potential to double the energy density at half the cost compared to Li-ion batteries.  Moreover, zinc-air batteries can be manufactured using abundant, low-cost, and non-toxic materials.  Safety issues with zinc-air batteries are eliminated by using a non-flammable aqueous electrolyte.  However, rechargeable zinc-air batteries developed to date have poor charge-discharge cycle life, low packaged energy density, and low roundtrip electrical efficiencies.  During the Phase I project, Lynntech in collaboration with Georgia Tech demonstrated feasibility of rechargeable zinc-air batteries with greatly improved cycle life, energy density, and electrical efficiency.  This was accomplished utilizing a novel zinc electrode structure to suppress dendrite formation and corrosion side reactions, a near-neutral pH electrolyte to further improve cycle stability, and a bifunctional air cathode to improve round trip electrical efficiencies.  This approach also increased zin utilization rates leading to high packaged energy and power density.  After demonstrating performance with small lab-scale batteries, Lynntech then demonstrated the improved zinc-air battery was scalable to large area 170 cm2 cells with no loss in performance.  During the Phase II project, Lynntech and Georgia Tech will scale up the production of cell materials and increase the mass loading and capacities of the zinc electrodes.  The structure of the air cathode will be further optimized to improve the overall electrical efficiency of the zinc-air battery.  Improved components will then be used to fabricate and test a breadboard 250 Wh zinc-air battery system.  The energy density, power density, and cycle life of the breadboard zinc-air system will be determined.  Results from the Phase II effort will then be used to design a preliminary full-scale zinc air system based on 5 kWh modules with a target energy density of 400 Wh/kg and a cost of