This project explores the potential of composite silicon anodes for multifunctional lithium ion (Li-ion) based devices. Li-ion batteries are widely used for high power and energy density applications, such as electric vehicles, cell phones, laptop computers, and unmanned aerial vehicles. Silicon anodes promise even higher electrochemical energy densities, but their use is complicated by the high volumetric expansion that silicon undergoes when fully lithiated. Furthermore, open-circuit voltage in Li-ion cells with silicon anodes is highly sensitive to mechanical stress. This project will harness these effects to create novel multifunctional structures capable of integrated energy storage, mechanical actuation, and inertial, vibration, and chemical sensing. The fundamental capabilities and trade-offs of this new and novel class of devices will be characterized through modeling, design optimization, and experimental testing. Project outcomes will have broad impacts on a variety of technologies, including medical microrobots, wearable electronic devices, and electric vehicles. A diverse research team of graduate and undergraduate students will work together on fundamental research tasks, as well as in translational engineering workshops to learn skills crucial to converting fundamental research into commercial products and systems.
This project seeks a fundamental understanding of the coupled electrochemical and mechanical dynamics of lithiated Si composite structures, through theoretical, experimental, and device design research. Fundamental equations of electrochemistry and mechanics will be combined to predict the displacement and force provided by these active structures. The governing partial differential equations will be simplified via supportable engineering assumptions, linearization, and model order reduction, to produce numerically efficient models providing an insightful understanding of the underlying physics and chemistry. These models will be used in turn to design the chemistry, morphology, and mesoscale structure of composite anodes, including the Si, binder, and conductive additives, to explore the Pareto frontier between electrical and mechanical power. For the first time, the large volume change associated with lithiation of Si composites will be harnessed to create actuated structures that move in a desired fashion when charged and discharged. Also for the first time, the Larché-Cahn potential will be used to make batteries that self-sense their stress state. Starting from novel, first principle models and a notional mesostructure, the full governing equations will be simplified to efficiently and accurately predict output voltage based on applied loads and electrical current input. Chemical composition, morphology, and structure will be varied to study the tradeoff between energy storage and sensitivity to applied loads. The new actuating and self-sensing energy storage structures will be paired with standard cathodes and electrolytes, and tested for electrical, mechanical, and sensor performance. The results of the project will be encapsulated in first-principles models, which will be experimentally validated against measurements of voltage, current, displacement, and applied load.
|Effective start/end date||7/15/17 → 6/30/21|
- National Science Foundation: $567,353.00