Rather than using a power-hungry process to convert carbon dioxide to specialized chemicals using metal catalysts, the lithium carbon dioxide battery could continuously convert carbon dioxide into a solid mineral carbonate as it discharges. This would open up new types of batteries, similar to lithium air cells, especially for operation in the power grid to use a continuous flow of CO2 from existing plants.
The key to the battery is an aqueous electrolyte made of amine, an organic derivative of ammonia, that the carbon dioxide dissolves into, and is then used with lithium and carbon electrodes.
Assistant professor of mechanical engineering Betar Gallant, doctoral student Aliza Khurram, and postdoc Mingfu He looked into whether carbon-dioxide-capture chemistry could be put to use to make carbon-dioxide-loaded electrolytes. By incorporating the gas in a liquid state, they found a way to achieve electrochemical carbon dioxide conversion using only a carbon electrode.
“What we’ve shown for the first time is that this technique activates the carbon dioxide,” said Gallant. “These two chemistries — aqueous amines and nonaqueous battery electrolytes — are not normally used together, but we found that their combination imparts new and interesting behaviours that can increase the discharge voltage and allow for sustained conversion of carbon dioxide.”
They developed a prototype lithium-carbon dioxide battery with voltage and capacity that are competitive with that of state-of-the-art lithium-gas batteries. Moreover, the amine acts as a molecular promoter that is not consumed in the reaction.
The key was developing the right electrolyte system, says Khurram. The amine material they chose is currently used for carbon capture and sequestration (CCS) applications that capture CO2 from the air, but had not previously been applied to batteries.
The prototype has a limited life of 10 charging cycles, and so needs more development. “Lithium-carbon dioxide batteries are years away,” said Gallant, as this research covers just one of several needed advances to make them practical.
The researchers are also investigating the possibility of developing a continuous-operation version of the process, which would use a steady stream of carbon dioxide under pressure with the amine material, rather than a preloaded supply the material, thus allowing it to deliver a steady power output as long as the battery is supplied with carbon dioxide. Ultimately, they hope to make this into an integrated system that will carry out both the capture of carbon dioxide from a power plant’s emissions stream, and its conversion into an electrochemical material that could then be used in batteries. “It’s one way to sequester it as a useful product,” she said.