High-Power, Low-Corrosion Aluminum-Air Battery

Thursday, 5 October 2017: 16:20
National Harbor 8 (Gaylord National Resort and Convention Center)
B. J. Hopkins and D. P. Hart (Massachusetts Institute of Technology)
Aluminum-air (Al-air) batteries are promising candidates for use in electric vehicles due to their high pack-level energy densities and to the abundance, recyclability, lightweight, low cost, and three-electron-redox properties of aluminum. Severe capacity fade during open-circuit conditions, however, has limited Al-air commercialization for over 50 years. Open-circuit capacity fade is caused by corrosion wherein the aluminum anode reacts with water from the aqueous electrolyte. Existing strategies to mitigate open-circuit corrosion, however, generally lead to reduced powers and energy densities. Optimized aqueous systems that use anode alloying and or electrolyte additives achieve high powers (500 mW cm-2) and energy densities (4 kWh kg-Al-1) but suffer from unacceptably high open-circuit corrosion currents (10 mA cm-2). In contrast, gel electrolyte systems yield low powers (91.1 mW cm-2) and energy densities (1.2 kWh kg-Al-1) but achieve no long-term open-circuit corrosion. Here we present a high-power (433 mW cm-2), energy-dense (3.9 kWh kg-Al-1) Al-air battery that experiences no long-term open-circuit corrosion.

Open-circuit corrosion can be stopped with no discernible effect to closed-circuit performance by displacing the aqueous electrolyte with a non-conducting liquid oil. When the battery is in closed-circuit conditions, the aqueous electrolyte can effectively displace the oil due to the natural and designed underwater oleophobic properties of the anode and cathode—the oil beads up and is flushed out by the electrolyte. The figure shows measured anode corrosion via hydrogen collection before and after the electrolyte has been displaced by oil and suggests that long-term open-circuit corrosion is completely stopped. We estimate that an Al-air vehicle battery pack with the proposed corrosion mitigation system could achieve energy densities of 222 Wh-kg-1 (2x that of Li-ion vehicle packs) and 183 Wh-L-1 (comparable to Li-ion vehicle packs) at costs as low as 18 US$-kWh-1 (33x less than Li-ion packs). We anticipate that our findings will further enable the use of aluminum as a critical element for energy storage.