New water-based battery could help reduce dependence on lithium for energy storage

Critical components of lithium-ion batteries such as lithium and cobalt are largely imported into the U.S. exposing the entire segment to significant risk if in case of geopolitical tensions escalate. Researchers at Texas A&M University are one of the many groups supported by the U.S. Department of Energy and National Science Foundation that are looking for alternatives to lithium-ion batteries.

Metal-free, water-based batteries

Jodie Lutkenhaus and Daniel Tabor, professor and assistant professor of chemical engineering, at the university have been researching water-based batteries for a few years now. According to the researchers, the batteries consist of a cathode, anode, and an electrolyte, like regular batteries.

The difference, however, is that the electrodes are made of polymers, instead of metals and the electrolyte used is water mixed with organic salts. In such a setup, the battery does not catch fire and water-based electrolyte becomes key in conducting ions and storage of energy. During its interactions with the electrodes, the latter can swell up leading to a loss of performance.

The researchers have found that redox-active, non-conjugated radical polymers are therefore the ideal materials for making these electrodes since they have a high discharge voltage. Depending on the material used, the difference in energy storage capacity can be as high as 1,000 percent.

“We 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,” the researchers write in the paper published in Nature Materials. However, the reaction between the polymer and the electrolyte is difficult to resolve since there are many simultaneous transfers of electrons, ions, and water molecules.

The research group has relied on computational simulation and analysis for their findings and obtained insights about structures and dynamics at a microscopic molecular scale, a press release said.

In some of the experiments conducted, the researchers were also able to macroscopically observe whether the cathode worked better in conjunction with certain salts in the electrolyte by measuring salt and water concentrations.

The researchers plan to carry out further simulations in the future to better understand the theory behind the workings of the battery, which can then be used to design better materials to make them.

Abstract

Metal-free aqueous batteries can potentially address the projected shortages of strategic metals and safety issues found in lithium-ion batteries. More specifically, 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. Here we demonstrate the nature of the redox reaction for poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) by examining aqueous electrolytes of varying chao-/kosmotropic character using electrochemical quartz crystal microbalance with dissipation monitoring at a range of timescales. Surprisingly, the capacity can vary by as much as 1,000% depending on the electrolyte, in which certain ions enable better kinetics, higher capacity and higher cycling.