SBIR-STTR Award

The objective is to increase the capacity and safety of the lithium/ lialcl4.6so2/carbon rechargeable cell by altering the electrolyte and the positive electrode, and by improving the methods currently employed for making the electrolyte. Aluminum is removed as discharge proceeds, since one of the products is an insoluble complex between the aluminum, reduced so2, and the carbon surface. The dilemma is that adding more aluminum as lialcl4, while it might improve the capacity, would also raise the electrolye freezing point to an unacceptable high level. We propose to change the composition of the electrolyte such that the low freezing point is maintained, yet adding solutes which are likely to increase the capacity. In addition, insoluble materials which could be instrumental in increasing the capacity by encouraging the formation of complexes similar to the one which forms on the ketjenblack now used in these cells will be added to the carbon positive electrode. We expect improvements in safety through the addition to the electrolyte of materials which would improve the morphology of the plated lithium

During phase i, we built lithium/so2 rechargeable cells in which lithium salts were made more soluble without organic cosolvents by using additional highly soluble non-lithium salts. Since cells ran below 3 volts, the discharge product was likely dithionite, as it is in organic electrolyte primary cells. Phase ii objective: to develop this system by identifying the best electrolyte, positive electrode, and separator compositions for the best performance and resistance to overcharge. Description of effort: six tasks starting with the cycling of wound aa prototypes, leading to the testing of d size cells, evaluating performance, safety, and shelf life.

Anticipated Results:
if the project is successful, we will have established how to construct cells which maintain the state of the art advantages of li/lialcl4*xso2/c rechargeables, but with capacities commensurate with the amount of active materials present.