The research objective of this Grant Opportunity for Academic Liaison with Industry (GOALI) project is to understand and, ultimately, control one of the poorly understood phenomena in electrochemical energy storage, namely the coupled mechanical/chemical degradation in lithium ion batteries. As a result of lithium diffusion, electrodes may fracture which limits the durability and performance of lithium ion batteries. Fracture can also prevent electrodes from achieving their high theoretical capacity. This project focuses on characterization and modeling of stresses in electrodes. In situ techniques will be used to measure the effects of diffusion, surface reactions, and mechanical properties on stresses in electrodes. Ex situ observations will reveal the mechanisms of crack formation and growth. The experimental findings will be used to further advance coupled mechanical/chemical degradation models for lithium ion batteries.
If successful, the results of this research will form the basis for surface engineering approaches to control stresses and mitigate the coupled mechanical/chemical degradation in lithium ion battery electrodes. The results will also help establish materials selection criteria for high capacity and durable lithium ion batteries, as well as enable battery life prediction and health monitoring. The research will directly impact a number of technological areas that depend on energy storage, including automotive, aerospace, electronics, and communication. Participating postdoctorial researchers and students will gain deep knowledge and broad experience in electrochemistry, mechanics of materials, thermal sciences, chemistry, and physics by conducting collaborative research in academic and industrial laboratories. A new course on energy storage will be jointly developed and taught at both the University of Kentucky and General Motors. The research results will be disseminated through publications to advance the state of knowledge in electrochemical energy storage.
This collaborative project between University of Kentucky and General Motors R&D Center has helped unveil several mechanisms responsible for the coupled mechanical and chemical degradation in electrode materials that are critical to the future development of lithium ion batteries. In particular, this improved understanding of the degradation mechanisms has led to the development of new strategies to overcome degradation, such as self-healing based on reversible liquid-to-solid phase transformation and ultra-thin surface coatings (also known as artificial solid-electrolyte interphases), that will enable advanced batteries with greater energy and power density, longer life, and lower cost. Advanced lithium ion battery electrodes experience large volume changes caused by concentration changes within the host particles during charging and discharging. Electrode failure, in the form of fracture or decrepitation, can occur as a result of repeated volume changes. The results obtained from this project showed that, in addition to mechanical properties, the size and shape of electrodes and the charging and discharging conditions (e.g., voltage and current) can strongly affect electrode fracture. A dimensionless parameter, called the electrochemical Biot number, was identified as a controlling parameter for stress and strain energy evolution in electrodes. In particular, the electrochemical Biot number determines the maximum stress and strain energy. As one of the outcomes of the project, tensile stress and strain energy based criteria were proposed for the initiation and propagation of cracks in insertion electrodes. These criteria helped guide the development of new materials and strategies to mitigate coupled mechanical and chemical degradation, such as patented technologies of self-healing and surface modification. Several PhD students on the project have been co-supervised by the PI and co-PI. The students, some of them received summer internships at GM, conducted their thesis research at both General Motors R&D Center and University of Kentucky. After receiving their PhDs, they are continuing their R&D work on electrochemical energy storage in either the auto industry or national labs. A new course on electrochemical energy storage was developed and taught at the University of Kentucky for four semesters to senior undergraduate and first year graduate students across multiple disciplines, including materials engineering, chemical engineering, mechanical engineering, and chemistry. The results obtained from the project have been disseminated in more than 25 journal publications and 3 issued US patents, as well as a number of presentations by the PI, co-PI, and their students at conferences and university seminars.
