Beyond Lithium Ion: The Lithium/Sulfur Cell
Professor Elton Cairns
Lawrence Berkeley National Lab
Current lithium ion cells are reaching their maximum energy storage capability (~200 Wh/kg) and are still not able to provide a safe, low-cost battery of sufficient energy storage capability for electric vehicles of more than 100-mile range. A new generation of battery with a specific energy of at least 400 Wh/kg, low cost (<$200/kWh), good safety, and low environmental impact is urgently needed. The next generation of rechargeable cells must have a theoretical specific energy well above 1000 Wh/kg (as compared to ~550 Wh/kg for Li-ion cells). The Li/S cell is probably the most attractive candidate for the next cell beyond the Lithium Ion cell. It has a theoretical specific energy of 2600 Wh/kg, and an estimated practical specific energy of about 600 Wh/kg.
The commercial development of the Li/S cell has been prevented by the short cycle life of the sulfur electrode caused by the rapid capacity loss. This capacity loss is attributed to: 1) the solubility of lithium polysulfides in the (organic solvent) electrolyte, 2) possible loss of contact between the (non-conductive) sulfur and the current collector, 3) the large volume change of the sulfur as it is charged and discharged (76%). Various approaches have been taken to solve these problems, with some success. A selection of attempts to improve the performance and cycle life of the Li/S cell will be reviewed and discussed, along with recent results from our laboratory.
A New Class of Aqueous Insertion Reaction Electrodes With Rapid Kinetics And Long Cycle Life
Prof. Robert A. Huggins
Department of Materials Science and Engineering
One of the major problems related to the integration of renewable energy sources with the large scale electric distribution grid has to do with the high frequency of short-term transients. The amelioration of this problem requires energy storage systems that can operate at very high rates, and with a high efficiency over a very large number of cycles.
The structural features that lead to the exceptional performance of a new group of insertion reaction electrode materials in aqueous electrolyte electrochemical systems for this purpose will be described.
Experiments have already demonstrated the outstanding properties of some members of this family. In one case, over 40,000 full cycles have already been achieved at a very high (17C) rate, with a coulomb efficiency of 99.8%. In another, over 5,000 full cycles at an 8.3 C rate have shown no measurable decrease in capacity.
Talk title coming soon…