Water-based Batteries Offer Future Alternative to Lithium

Batteries are becoming so important to the financial prosperity of many countries that they are looking at ways to keep the whole supply chain at home. The COVID-19 pandemic showed that the global supply chains that we have relied on for the last few decades were not as robust as we believed. Countries that could get the raw materials that they needed kept them to themselves, while the rest were forced to wait.

As we come out of the worst of the pandemic, some entities have decided to take matters into their own hands and boost domestic supply chains to stop reliance on potential rivals. Now, most developed countries are looking to bring manufacturing and its supply chain back onshore. For batteries, although the intention was there, materials like lithium and cobalt, which are vital to today’s lithium-ion batteries, are only sourced in a few areas in the world. For years, batteries have always been one of the hottest areas of research, but that has been given a further boost by the impetus to remove scarce elements from batteries and build them with abundant elements that are found closer to home. Well funded research institutions around the world are trying to overcome the drawbacks to designs such as sodium-ion and iron air chemistries for batteries.

One of those institutions is Texas A&M University, where the researchers are looking at ways to increase storage capacity in safer metal-free, water-based battery electrodes. The group under chemical engineering professor Dr. Jodie Lutkenhaus and chemistry assistant professor Dr. Daniel Tabor has recently published their findings. 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.

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

In the paper, the authors described how 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. The researchers also demonstrated 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.

Tabor’s research group supported the experimental efforts 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 in this paper is that we actually charge up the electrode to multiple states of charge and see how the surroundings respond to this charging,” Tabor said. She continued, “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."

The project is funded by the U.S. Department of Energy and the National Science Foundation through the Texas A&M Engineering Experiment Station.