As the world warms up, it's becoming increasingly obvious that we can't just keep belching all our carbon dioxide out into the atmosphere. Scientists are searching for ways to pluck it out of the air and stash it underground, store it in concrete, turn it into carbon nanofibers or even make fuel out of it. Now researchers at MIT have found another way to reuse this unwanted element – build lithium-carbon dioxide batteries.
Carbon dioxide may sound versatile given that list of possible uses, but the problem is that converting it into different forms often requires high voltages and plenty of energy. That can cancel out the benefits of removing it from the atmosphere in the first place.
So the MIT team set out to see if CO2 could be captured and used in a battery. Because CO2 isn't very reactive, previous attempts at lithium-carbon dioxide batteries have needed to use metal catalysts, but the researchers here found a way to do so using a carbon electrode instead.
First, the carbon dioxide is preactivated by incorporating it into an amine solution. This watery solution is then combined with another liquid electrolyte, and used in the battery with a carbon cathode and a lithium anode.
"What we've shown for the first time is that this technique activates the carbon dioxide for more facile electrochemistry," says Betar Gallant, an author of the study. "These two chemistries — aqueous amines and nonaqueous battery electrolytes — are not normally used together, but we found that their combination imparts new and interesting behaviors that can increase the discharge voltage and allow for sustained conversion of carbon dioxide."
Not only does the battery provide power on a level comparable to existing lithium-gas batteries, but as it discharges it converts the carbon dioxide in the electrolyte into a solid mineral carbonate form. That's a much more efficient way to convert CO2 from a gas to a solid than most other techniques, and that solid form can then be used for other purposes – including making the carbon cathode for future batteries.
The current version is a proof-of-concept however, and the researchers say that commercial lithium-carbon dioxide batteries are still years away. In the meantime, several other problems need to be sorted out, such as rechargeability – for now, the battery can only run for about 10 cycles.
In future, the team says the system could also be adapted into a continuous-operation version. That means that rather than using up the preloaded supply of CO2, a steady stream of the stuff could be funneled through the system, converting the gas into a usable solid form and generating power in the process.
The research was published in the journal Joule.
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