Stress and Deformation caused by Insertion in Li Ion Batteries

Harvard University, Cambridge MA

Investigators

Abstract

Lithium-ion batteries are the batteries of choice for diverse applications, especially for those sensitive to size and weight, such as portable electronics and electric cars. At the heart of a Lithium-ion battery is a challenging problem that couples electrochemistry and mechanics. Each electrode in a Lithium-ion battery is a host for Lithium, absorbing or exuding Lithium when the battery is charged and discharged. Repeated lithiation and delithiation induce cyclic deformation and possibly fracture, a mechanism known to cause the capacity of the battery to fade. Lithiation-induced deformation and fracture is a bottleneck in developing batteries of high capacity. This project will develop theory and conduct experiments to study effects of anisotropic insertion, particle size and changing rate. Furthermore, the project will formulate a theory of coupled mass transport and deformation in inelastic hosts, and use the theory to study co-evolution of stress, Lithium concentration, and surface morphology, a phenomenon reported in recent literature. Given the role of batteries to the society undergoing a profound transformation in its attitude toward environment and resources, the integration of mechanics and electrochemistry is timely. The PIs have already begun to integrate electrochemistry into a course in mechanics, and posted course materials online. The educational impact of this project is already evident from the enthusiasm of the graduate students in the PIs' groups. Their imagination is captured by this unique opportunity to bring the discipline of mechanics to the heart of a technology that will transform society.