Mar 21, 2011
There is a lot of talk about storage being the next breakthrough in energy. My fellow undergrad alumni and now PhD candidate Betar Gallant believes the Electrochemical Energy Lab (http://web.mit.edu/eel/) may have two unique solutions. Under Professor Yang Shao-Horn of Mechanical Engineering and Materials Science and Engineering, the lab is furthering the efficiency of lithium air batteries. They are also working to develop high-power and high-energy-density carbon nanotube electrodes using a layer-by-layer assembly process in collaboration with MIT Professor Paula Hammond of Chemical Engineering.
Many believe that lithium air batteries could be the successor to current lithium ion batteries, and while there has been great progress, major obstacles still remain. The lab’s main priority is to find and test catalysts that can increase the round-trip efficiencies of lithium air batteries, which are determined by the gap between the discharging and charging voltages. Through design of a Au-Pt catalyst, the team, led by Graduate Student Yi-Chun Lu, recently successfully increased the efficiency to 73% (the record so far), but efficiencies greater than 90% are necessary for commercial viability. The lab is currently focusing on fundamental characterization of catalysts to identify the best candidates and on using this knowledge to design new catalysts that can enable high efficiency and good cycle ability, all at reasonably low cost. Meanwhile, Li-air batteries currently have short cycle lives, largely related to repeated dissolution and re-deposition of lithium at the lithium anode, which roughens and degrades the metal surface. This degradation is a major obstacle for the technology that remains to be addressed.
There is a performance gap between commercially available electrochemical capacitors and existing batteries; the former have high power density, while the latter have high energy density. Betar and her colleague Dr. Seung Woo Lee believe the sweet spot will be found in between these two and that layer-by-layer technology could be the solution.
Layer-by-layer is a process that utilizes the attraction between positively and negatively charged “building blocks” – in this case, carbon nanotubes — to create self-assembled thin film electrodes with highly tunable properties. The result is a porous, ultrathin material that can bond to a wide range of surfaces – think everything from smart cards to computer circuits – and has a high energy density compared to conventional electrochemical capacitors owing to the special properties of the charged surfaces. As micro devices like Kindles and Ipads become slimmer, they need powerful thin film batteries, and layer-by-layer could be the technology used to power these types of electronics in the future.
Looking to the Future
Five years ago, MIT President Susan Hockfield announced the MIT Energy initiative, which would utilize the resources from all five schools to develop ways to meet future energy demands. Energy storage is the next stage in tackling our current problems, and the research being done by students such as Betar and the Electrochemical Energy Lab will allow MIT to keep its pledge to be a leader in shaping the future of energy.