Practical Aqueous Calcium-Ion Battery Full-Cells for Future Stationary Storage

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Growing demand for renewable energy necessitates advanced stationary storage solutions.
• Aqueous calcium-ion batteries offer a low-cost, safe, and high volumetric capacity alternative for energy storage.

Purpose of the Study:

• To demonstrate a high-performance, cost-effective aqueous calcium-ion battery for stationary energy storage.
• To investigate the electrochemical performance and storage mechanism of a novel polyaniline anode and potassium copper hexacyanoferrate cathode.

Main Methods:

• Fabrication of an aqueous calcium-ion battery using in situ polymerized polyaniline anode and potassium copper hexacyanoferrate cathode.
• Electrochemical characterization including charge-discharge cycling, rate capability tests, and long-term cycling stability.
• Investigation of the calcium-ion storage mechanism using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy.

Main Results:

• The battery achieved a specific energy of 70 Wh kg^-1 at 250 W kg^-1 and maintained 53 Wh kg^-1 at 950 W kg^-1.
• Demonstrated high Coulombic efficiency (∼96%) and 95% capacity retention over 200 cycles at 0.8 A g^-1.
• Identified NO₃^- doping/dedoping at the anode and Ca-ion intercalation/deintercalation at the cathode as charge-discharge mechanisms.

Conclusions:

• The developed aqueous calcium-ion battery exhibits excellent electrochemical performance, including high energy density, good rate capability, and long cycle life.
• The findings highlight the potential of this battery system for cost-effective and safe grid-scale energy storage applications.
• Advanced spectroscopic techniques provided insights into the calcium-ion storage mechanism, crucial for further battery development.