Resolving the Localized Stress Evolution: Toward Long-lasting Rechargeable Batteries

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Wind and solar energy are the fastest growing sources of electricity in Canada. The biggest concern with wind and solar energy is that they're intermittent. An energy storage solution is required to buffer the electricity fluctuation. Rechargeable batteries are considered as the most promising and practical solution in near future. The global grid-connected battery energy storage market is 3.8 GW by 2017, which is expected to reach 23.4GW by 2022. In Canada, rechargeable batteries (50 MW) take 81% of the total grid energy storage capacity by 2018. The storage cost per cycle is a determinant index for grid-scale applications. When fully charged/discharged in each cycle, lithium-ion battery cells will typically last only 300-500 cycles, which needs to be remarkably improved in order to reduce the storage cost per cycle. One of the persistent challenges associated with electrode degradation and battery failure is the stress induced by ion intercalation, companied by large volume fluctuation of electrode materials. Many in situ microscopy and spectrometry technologies have been developed and provided valuable insights into the impacts of the stress buildup and release (e.g. the stress-induced structures changes). However, the strength of the localized stress remains poorly understood, which is a knowledge gap in improving the cycle life of rechargeable batteries. Recently we developed an in situ solution to quantitively measure the localized stress on electrodes using microcantilever sensors, free-standing beams with extremely high sensitivity to stress variations. Based on the newly developed stress measurement solution and our experience with in situ microscopes, we propose to investigate the localized stress evolution in thin film electrodes with designed nanostructures and to interpret the stress evolution in the context of the dynamic changes of electrodes in Young's modulus, volume, and chemical composition. Multiple in situ technologies, such as in situ transmission electron microscopy (TEM) and in situ atomic force microscope (AFM), will be utilized to monitor the physical and chemical properties changes along with the stress. The proposed research will provide answers to two critical questions in long-lasting electrodes design: What is the optimal charge/discharge conditions, and what is the most efficient nano-engineering method to minimize the stress generation? These answers will help to reduce the energy storage cost per cycle and accelerate the deployment of renewable energy in Canada. This program covers basic science to applied research to the design and development of integrated systems. As part of the project, we would like to train a graduate student and two to three undergraduate students in the new area across materials science, electrochemistry, nano-engineering, nano-mechanics and energy storage. Two postdoctoral fellows will also gain valuable research experience through the project.