Improving cyclability and power of batteries with ‘stable’ nanomaterials
This project provides fundamental understanding on the stability of nanomaterials for application in the design of next generation lithium ion cathode technologies. While nanomaterials can exhibit improved electrochemical performance in cathode applications, inherently high interfacial areas cause unconventional instability, high surface reactivity (and solubility), and significant modifications in phenomena such as grain growth, sintering, and solid-state phase transformations. Thermodynamically, these can be attributed to an increased contribution of interfacial enthalpies to the total free energy of the system. However, despite valuable insights from computational efforts, there is still a dearth of understanding on the relationship of interfacial and bulk thermodynamics and cathode degradation mechanisms in lithium-based cathodes, particularly at the nanoscale. Here we use thermochemistry (calorimetry) as a tool to measure interface energies in representative classes of lithium based nanomaterials: the layered a-NaFeO2 structured LiNiO2, LiCoO2, and the LiMn2O4 spinel; and use the data to develop conceptual models to thermodynamically control representative cathode-degradation phenomena, namely the cycling-induced sintering and grain growth, dissolution and solid state phase transitions.
Understanding correlation between thermodynamics and mechanical behavior
Because properties of nanocrystalline materials are strongly dependent on the interfacial features, this project aims to design low energy grain boundaries to improve mechanical behavior. In particular, we are looking at oxide nanoceramics and have demonstrated a strong dependence of nanomechanics on interfacial chemistry and energetics.
The images show transparent Zirconia with grain sizes at the nanoscale and the hardness measurements demonstrating size strengthening effects.
Sponsored by: Army Research Office Grants W911NF1810361 and W911NF1710026
Controlling sintering and grain growth at nanometer grain sizes
These new properties have inspired a variety of new applications in several fields, ranging from nanosensors to cathode materials for fuel cells and lithium batteries. As well, the possibility is opened for the development of new materials in response to the current energy problems such as the U.S. increasing demand for energy, dependence on foreign oils, and climate change. However, the optimization of nanoceramic processing is still a challenge, and understanding the fundamental concepts requires further research. Within this project, Prof. Castro focuses on the larger volume fraction of interfaces present in nanoceramics to improve processing control. His groups uses ultra-sensitive calorimetric techniques to quantify interfacial energies and use the data to predict and control properties.