Mechanics of Diffusion-Induced Fractures in Lithium-ion Battery Materials
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Mechanics of Diffusion-Induced Fractures in Lithium-ion Battery Materials Cheng-Kai ChiuHuang, Michael A. Stamps, and Hsiao-Ying Shadow Huang* Department of Mechanical and Aerospace Engineering North Carolina State University R3002, EB3, 911 Oval Drive, Raleigh, NC 27695 ABSTRACT Our study is motivated by the need for development and deployment of reliable and efficient energy storage devices, such as lithium-ion batteries. However, the rate-capacity loss is the key obstacle faced by current lithium-ion battery technology, hindering many potential large-scale engineering applications, such as future transportation modalities, grid stabilization and storage systems for renewable energy. During electrochemical processes, diffusion-induced stress is an important factor causing electrode material capacity loss and failure. In this study, we present models that are capable for describing diffusion mechanisms and stress formation in LiFePO4 nanoparticles, a lithium-ion battery cathode material which promises an alternative, with the potential for reduced cost and improved safety. To evaluate mechanics of diffusion-induced fractures, a plate-like model is adopted with anisotropic materials properties and volume misfits during the phase transformation are considered. Stress distribution at phase boundaries and fracture mechanics information (energy release rates and stress intensity factors) are provided to further understand the stress development due to lithium-ion diffusion during discharging. This study contributes to the fundamental understanding of kinetics of materials in lithium-ion batteries, and results from our stress analysis provides better electrode materials design rules for future lithium-ion batteries. INTRODUCTION Lithium ion batteries have become a widely known commodity for satisfying the world’s mobile energy storage needs. Applications for these high power batteries include anything from laptop computers and mp3 players to orbiting satellites and electric tools. The advantages of Liion over other types or rechargeable batteries such as Nickel-Cadmium and Metal Hydride types lie in their superior energy-to-weight ratio, quicker recharge times, and increased cycle life. In addition, as the world becomes more concerned about rising oil prices and CO2 emissions, the need to increase hybrid or electric vehicle production and performance (along with other high power applications) has fueled research to improve Li-ion battery performance and even discover new battery materials. Since the conception of Lithium-Iron-Phosphate (LiFePO4) as a possible cathode for today’s Li-ion batteries [1], this material with olivine structure has been a focal point for such experimentation and discussion in the Li-ion battery realm. LiFePO4 boast several attractive qualities including a relatively high theoretical capacity of 170 mAh/g, great structure stability, long cycle life, impressive safety attributes and environmentally benign qualities. It’s also widely available across the world at a relatively inexpensive price. But
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