UC San Diego

Alloy-type anodes are promising next-generation electrodes for Li-ion batteries because of their high specific capacity, but the severe volume expansion causes fast capacity decay. Here, two methods were explored to improve alloy-type anodes. First, a thermodynamically driven grain boundary engineering was proposed as a potential strategy. SnSb with Bi addition fabricated through ball milling and annealing was selected as a model system. The Bi-doped SnSb demonstrated improved cycling performance with < 1% porosity. Transmission electron microscopy shows grain boundaries Bi segregation, and thermodynamic modeling further indicates the stabilization of a nanoscale liquid-like interfacial phase. In situ X-ray microscopy shows the crack suppression effect for the Bi-doped sample, suggesting a potential grain boundary sliding as a stress relief mechanism. Second, cryogenic milling was demonstrated as a novel method to engineer alloy-type anodes. This process can suppress cold welding, exfoliate bulk graphite into multilayer graphene, and evenly disperse them between the grains to form nanostructured electrodes. Based on the cross-section electron microscopy and X-ray microscopy, the dispersed graphene between the nanosized grains can effectively alleviate the volume expansion upon lithiation. Compared to the traditional ball milling methods under room temperature, the cryomilled SnSb-C composite anode showed improved cycling stability and rate capability. For ceramic processing methods, electric field assisted sintering process can have a lower sintering temperature and faster sintering time compared to conventional sintering. For the second part of the thesis, nonthermal electric field effects on ZnO polycrystalline specimen was investigated. In undoped ZnO, electric field can induce defect polarization and subsequently alter the grain boundary structure. We also demonstrated the possibility of creating and controlling graded microstructure via electric fields. In Bi2O3-doped ZnO, electric field can drive the migration of Bi-rich secondary liquid phase. In summary, the first part of the dissertation introduces grain boundary engineering and cryogenic milling as two novel approaches to improve alloy-type battery electrodes. The second part of the dissertation investigated electric field effects on ceramic microstructure evolution. The feasibility of tailoring ceramic microstructure with electric field was demonstrated.