Monday, February 26, 2024

Researchers find major storage capacity in metal-free aqueous batteries

Metal-free aqueous batteries can potentially address the projected shortages of strategic metals and safety issues found in lithium-ion batteries.

Researchers at Texas A&M University in the U.S. have been exploring metal-free, water-based battery electrodes and have discovered that the difference in energy storage capacity is as much as 1,000%.

These batteries are different from lithium-ion batteries that contain cobalt. The team at the university has been researching metal-free batteries stems from having better control over the domestic supply chain since cobalt and lithium are outsourced.

According to researchers, aqueous batteries consist of a cathode, an electrolyte, and an anode, like a regular battery. But in this water-based battery, the anodes and cathodes are polymers that can store energy, and the electrolyte is water mixed with organic salts. The electrolyte transfers the ions back and forth between the cathode and the anode, and the electrolyte is also key to energy storage through its interactions with the electrode.

“If an electrode swells too much during cycling, then it can’t conduct electrons very well, and you lose all the performance,” Chemical engineering professor Dr. Jodie Lutkenhaus said. “I believe there is a 1,000% difference in energy storage capacity, depending on the electrolyte choice because of swelling effects.”

According to their paper, the electrodes – redox-active, non-conjugated radical polymers – are promising candidates for metal-free aqueous batteries because of the polymers’ high discharge voltage and fast redox kinetics. However, little is known regarding the energy storage mechanism of these polymers in an aqueous environment. The reaction itself is complex and difficult to resolve because of the simultaneous transfer of electrons, ions, and water molecules.

Researchers suggest that metal-free batteries might be able to mitigate potential shortages of metals such as cobalt and lithium. It would also prevent battery fires.

“There would be no battery fires anymore because it’s water-based,” Lutkenhaus said. “In the future, if materials shortages are projected, the price of lithium-ion batteries will go way up. If we have this alternative battery, we can turn to this chemistry, where the supply is much more stable because we can manufacture them here in the United States, and materials to make them are here.”

The research team also conducted computational simulation and analysis, which gave insights into the microscopic molecular-scale picture of the structure and dynamics. They observed if the battery cathode was working better in the presence of certain kinds of salts by measuring exactly how much water and salt was going into the battery as it was operating.

“With this new energy storage technology, this is a push forward to lithium-free batteries. We have a better molecular level picture of what makes some battery electrodes work better than others, and this gives us strong evidence of where to go forward in materials design,” Tabor said.

Journal reference:

  1. Ting Ma, Cheng-Han Li, Ratul Mitra Thakur, Daniel P. Tabor and Jodie L. Lutkenhaus. The role of the electrolyte in non-conjugated radical polymers for metal-free aqueous energy storage electrodes. Nature Materials, 2023; DOI: 10.1038/s41563-023-01518-z