An interdisciplinary team of scientists has worked out a way to make electric vehicles that are not only carbon neutral, but carbon negative, capable of actually reducing the amount of atmospheric carbon dioxide as they operate.
They have done so by demonstrating how the graphite electrodes used in the lithium-ion batteries that power electric automobiles can be replaced with carbon material recovered from the atmosphere.
The recipe for converting carbon dioxide gas into batteries is described in the paper titled “Carbon Nanotubes Produced from Ambient Carbon Dioxide for Environmentally Sustainable Lithium-Ion and Sodium-Ion Battery Anodes” published in Wednesday’s issue of the journal ACS Central Science.
“Our climate change solution is two fold: To transform the greenhouse gas carbon dioxide into valuable products and to provide greenhouse gas emission-free alternatives to today’s industrial and transportation fossil fuel processes,” Stuart Licht, professor of chemistry at the George Washington University, said. “In addition to better batteries, other applications for the carbon nanotubes include carbon composites for strong, lightweight construction materials; sports equipment; and car, truck and airplane bodies.”
The unusual pairing of carbon dioxide conversion and advanced battery technology is the result of a collaboration between Dr. Licht and the laboratory of Assistant Professor of Mechanical Engineering Cary Pint at Vanderbilt University.
The team adapted the Licht lab’s solar thermal electrochemical process (STEP) that produces carbon nanotubes from carbon dioxide by incorporating them into both lithium-ion batteries like those used in electric vehicles and electronic devices and low-cost sodium-ion batteries under development for large-scale applications, such as the electric grid.
In lithium-ion batteries, the nanotubes replace the carbon anode used in commercial batteries. The team demonstrated that the carbon nanotubes gave a small boost to the performance, which was amplified when the battery was charged quickly. In sodium-ion batteries, the researchers found that small defects in the carbon, which can be tuned by STEP, can unlock stable storage performance that is more than three and a half times above that of sodium-ion batteries with graphite electrodes. Most importantly, both carbon-nanotube batteries were exposed to about two and a half months of continuous charging and discharging and showed no sign of fatigue.
“This trailblazing research has achieved yet another amazing milestone with the incorporation of the carbon nanotubes produced by Stuart Licht’s STEP reduction of carbon dioxide process into batteries for electric vehicles and large scale storage,” said Michael King, chair of GW’s Department of Chemistry. “We are thrilled by this translation of basic research into potentially useful consumer products while mitigating atmospheric carbon dioxide buildup. This is a win-win for everyone.”
The researchers estimate that with a battery cost of $325 per kWh (the average cost of lithium-ion batteries reported by the Department of Energy in 2013), a kilogram of carbon dioxide has a value of about $18 as a battery material – six times more than when it is converted to methanol – a number that only increases when moving from large batteries used in electric vehicles to the smaller batteries used in electronics. And unlike methanol, combining batteries with solar cells provides renewable power with zero greenhouse emissions, which is needed to end the current carbon cycle that threatens future global sustainability.
“This approach not only produces better batteries but it also establishes a value for carbon dioxide recovered from the atmosphere that is associated with the end-user battery cost unlike most efforts to reuse CO2 that are aimed at low-valued fuels, like methanol, that cannot justify the cost required to produce them,” Dr. Cary Pint (Vanderbilt University) said.
Coauthors of the paper with Drs. Licht and Pint include Anna Douglas, graduate student in the interdisciplinary materials science program at Vanderbilt; Rachel Carter, graduate student in mechanical engineering at Vanderbilt; Jiawen Ren, postdoctoral associate in chemistry at GW; and Matthew Lefler, graduate student in chemistry at GW.