Advanced Materials for Energy Conversion and Storage
Simpson, Zachary Ian. “Advanced Materials for Energy Conversion and Storage”, Boston College, 2013. http://hdl.handle.net/2345/3042.
In this work, we present our findings regarding the low-temperature, solid-state conversion of Cu₂S nanowires to Cu₂S/Cu₅FeS₄ rod-in-tube structures, Cu₂S/ZnS segmented nanowires, and a full conversion of Cu₂S nanowires to ZnS nanowires. These conversion reactions occur at temperatures as low as 105 degrees Celsius, a much lower temperature than those required for reported solid-state reactions. The key feature of the Cu₂S nanowires that enables such low conversion temperatures is the high ionic diffusivity of the Cu⁺ within a stable S sublattice. The second portion of this work will focus on the oxide-stabilization and utilization of TiSi₂ nanonets as a lithium-ion battery anode. This nanostructure, first synthesized in our lab, was previously demonstrated to possess a lithium storage capacity when cycled against a metallic Li electrode. However, with subsequent lithiation and delithiation cycles, the TiSi₂ nanonet structure was found to be unstable. By allowing a thin oxide layer to form on the surface of the nanonet, we were able to improve the capacity retention of the nanonets in a lithium-ion half-cell; 89.8% of the capacity of the oxide-coated TiSi₂ was retained after 300 cycles compared to 62.3% of the capacity of as-synthesized TiSi₂ nanonets after 300 cycles. The layered structure of C49 TiSi₂ exhibited in the nanonets allows for a specific capacity greater than 700 mAh g(-1), and the high electrical conductivity of the material in conjunction with the layered structure confer the ability to cycle the anode at rates of up to 6C, i.e., 10 minute charge and discharge cycles, while still maintaining more than 75% of the capacity at 1C, i.e., 1 hour charge and discharge cycles.