Addressing the Voltage and Energy Fading of Al-Air Batteries to Enable Seasonal/Annual Energy Storage
Authors: Xu Cheng , Liu Xu , Passerini Stefano 
Published: February 2024

The European Commission's Strategic Energy Technology Plan (SET Plan-2018) aims to slow down anthropogenic global warming by 2030 and is seen as a crucial intermediate step to guarantee net-zero greenhouse gas emissions by 2050. Its achievement requires a significant increase in renewable energy. Various technologies have been proposed to solve this issue, including power-to-X options, i.e., converting renewable electricity into a storable form (e.g., hydrogen), and secondary-battery-based power-to-power options.1 Nonetheless, seasonal and even annual energy storage in a low-cost manner is still a challenge. In this context, employing the earth-abundant, low-cost, and easy to transport and store Al metal as the energy carrier may offer some valuable options, e.g., the combination of Al production via inert-electrode smelting (power to metal) and Al conversion to electricity via Al-air batteries (AABs, metal to power).2 However, voltage decay during discharge severely decreases the practical energy density of AABs, especially, upon long-term operation.3,4
,5

Herein, the electrochemical behavior of AMA in KOH aqueous solutions containing various concentrations of dissolved aluminum, predominantly present as , is compared to investigate the impact of . It is observed that an increasing polarization of AMAs occurs even before any precipitate is generated on their surface. Further experimental and computational results reveal that the accumulation of greatly reduces the OH- concentration and, in turn, negatively affects the reaction kinetics. Therefore, the voltage decay issue of AABs is caused by the accumulation of in the electrolyte rather than Al(OH)3 on AMAs. Subsequently, it is demonstrated that seeded precipitation of in the electrolytes to Al(OH)3 precipitate with releasing OH- via utilizing its lower solubility at 20 °C than at 50 °C allows effective recovery of the potential of AMAs and the voltage of AABs. At last, prototype AABs are assembled and tested to evaluate the feasibility of voltage recovery via the proposed seeded precipitation process.

References

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(5) Liu, S.; Ban, J.; Shi, H.; Wu, Z.; Shao, G. Near Solution-Level Conductivity of Polyvinyl Alcohol Based Electrolyte and the Application for Fully Compliant Al-Air Battery. Chem. Eng. J.
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