Combinatorial studies of silicon-based alloy negatives for lithium-ion batteries.

摘要

Si-based materials are promising candidates to replace graphite as the negative electrode in Li-ion batteries. Si and Si-based materials are attractive because they can reversibly alloy with large amounts of Li. This leads to batteries with higher energy density when compared to cells made with graphite negative electrodes.; A crucial problem remains to be overcome before Si-based materials can be used in commercial Li-ion cells. Graphite electrodes can withstand up to a thousand or more charge/discharge cycles without losing significant amounts of capacity. The Si-based materials, on the other hand, lose much of their capacity after only a few cycles. This makes them unacceptable for use in rechargeable batteries.; Alloy electrodes that are amorphous tend to have better capacity retention than crystalline materials of similar composition. There are many elements that alloy with Li, so there is a large sample space of possible composite electrode materials that can be tested. A method is needed that can produce libraries with large composition ranges that also contain amorphous material.; Amorphous films can be produced by sputter deposition that would not be amorphous if created by other means such as physical mixing or melt spinning. Sputter deposition also lends itself easily to combinatorial methods. This thesis describes the development of a combinatorial deposition system that can produce ternary films with linear and orthogonal composition variations and large amorphous ranges. Infrastructure to perform combinatorial electrochemical testing has also been developed.; Studies of a-Si and a-Si-based alloys containing Al, Ag, Ge, Sn and Zn have been conducted. Results of combinatorial studies for binary and ternary systems are presented. In-situ XRD studies have been conducted for a-Si and some specific compositions of SiZn. These results are discussed as well as the phases formed during electrochemical cycling of these cells.