These batteries don’t contain cobalt, unlike lithium-ion batteries, and the research team are looking at metal-free batteries in part to better control the domestic supply chain since cobalt and lithium are outsourced. This safer chemistry would also prevent battery fires.
“There would be no battery fires anymore because it's water-based,” said Dr Jodie Lutkenhaus, chemical engineering professor. “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.”
Lutkenhaus said aqueous batteries consist of a cathode, electrolyte and an anode. The cathodes and anodes are polymers that can store energy, and the electrolyte is water mixed with organic salts. The electrolyte is key to ion conduction and 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,” Lutkenhaus explained. “I believe that there is a 1,000% difference in energy storage capacity, depending on the electrolyte choice because of swelling effects.”
According to the team’s research, which was published in Nature Materials, redox-active, non-conjugated radical polymers (electrodes) are promising candidates for metal-free aqueous batteries because of the polymers’ high discharge voltage and fast redox kinetics. The reaction is complex and difficult to resolve because of the simultaneous transfer of electrons, ions and water molecules.
“We’ve been able to demonstrate the nature of the redox reaction by examining aqueous electrolytes of varying chao-/kosmotropic character using electrochemical quartz crystal microbalance with dissipation monitoring at a range of timescales,” a spokesperson for the team explained.
The research group’s work was complemented with computational simulation and analysis. The simulations gave insights into the microscopic molecular-scale picture of the structure and dynamics.
“Theory and experiment often work closely together to understand these materials. One of the new things that we do computationally is that we actually charge up the electrode to multiple states of charge and see how the surroundings respond to this charging,” said chemistry assistant professor Dr. Daniel Tabor.
Researchers macroscopically observed if the battery cathode was working better in the presence of certain kinds of salts through measuring exactly how much water and salt is going into the battery as it is operating.
“We did that to explain what has been observed experimentally,” Tabor said. “Now, we would like to expand our simulations to future systems. We needed to have our theory confirmed of what are the forces that are driving that kind of injection of water and solvent.
“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,” added Tabor.
The project is being funded by the US Department of Energy and the National Science Foundation through the Texas A&M Engineering Experiment Station.
