Chemical modification of nanocolumnar semiconductor electrodes for enhanced performance as lithium and sodium-ion battery anode materials
The successful commercialization of lithium-ion batteries is responsible for the ubiquity of personal electronics. The continued development of battery technology, as well as its application to new emerging markets such as electric vehicles, is dependent on developing safer, higher energy density, and cheaper electrode materials and battery chemistries. The focus of this dissertation is on identifying, characterizing and optimizing new materials for lithium- and sodium-ion batteries. Batteries are incredibly complex engineered systems with each electrode composed of conductive additive and polymeric binder in addition to the active material. All of these components must work together for the electrode system to function properly. In this work, glancing angle deposition (GLAD) and reactive ballistic deposition (RBD) are employed to grow thin films of novel materials with reproducible morphology for use as battery electrodes. The use of these thin film electrodes eliminated the need for conductive additives and polymer binders allowing for the active materials themselves to be studied rather than the whole electrode system. Two techniques are employed to modify the chemical properties of the electrode materials grown by RBD and GLAD: Alloying (Si-Ge alloys for Li-ion batteries and Sn-Ge alloys for Na-ion batteries) and partial chalcogenation (partial oxidation of silicon, and partial sulfidation and selenidation of germanium for Li-ion batteries). Both of these techniques are successfully employed to enhance the electrochemical properties of the materials presented in this dissertation.