Battery Material Characterization Using On-Chip Electrochemical Platforms

One dimensional nanomaterials offer unique physical phenomena and improved physical properties, which have the potential to benefit diverse societal applications. Harnessing these benefits require developing both material synthesis processes as well as characterization methods to better understand their performance. To overcome the challenge of nanomaterial characterization at the single particle level, this dissertation employed a unique on-chip platform and dielectrophoretic nano assembly techniques to isolate single nanomaterials for further study and investigation. This facilitated characterization of battery relevant materials at the individual level for their responses to mechanical action and electrochemical reaction. Silicon-Germanium (SiGe) and manganese dioxide (MnO2) nanowires were chosen as representative battery electrode materials to be tested for their nanomechanical behavior. Although being ceramic materials, structural defects were revealed to cause plastic deformation and recovery in these materials at the nanoscopic size regimes as opposed to the brittle behavior observed in their macroscopic counterparts. In case of SiGe, a high surface defect density and nanotwin boundaries caused plastic deformation and recovery through dislocation movement and annihilation, respectively. On the other hand, MnO2 crystal structure is a mixture of heteroscopically sized grains, which get activated under external load and go through reversible phase transformation. These findings were courtesy of AFM based three-point bending test methodology, which also revealed loading rate dependent ductile to brittle transition and discussed loading orientation with reference to the crystal. The MnO2 crystal is made of network of MnO6 octahedra and has rectangular tunnels suitable for ionic conduction. This material was investigated for insertion of Li and Mg ions, two candidates for the battery electrochemistry. Li insertion shows reversible intercalation below 1.0 Li per Mn limit, over which it initiates conversion reaction. On the other hand, Mg ion readily converts the host material irreversibly to an alloy phase at 0.5 Mg per Mn. These conclusions were made from electron microscope imaging and spectroscopy. Moreover, this method addresses the challenge of limited radial diffusion associated with in-situ TEM electrochemistry set-ups and allows for radial ionic diffusion in electrode materials thereby, mimicking their real-life operation.