The Role of Mechanical Stress and Deformation in Lithium Metal Battery Design

Abstract

To meet increasing energy density demand of consumer electronics, electric vehicles and grid-scale storage, lithium metal has been proposed to be the anode choice for the next generation of lithium ion battery due to its high theoretical capacity and low electrochemical potential. However, the dendrite growth during the lithium deposition process has been the most critical issue that prevents the commercialization of lithium metal battery because it can not only cause capacity loss but also lead to internal short circuit and safety hazard. At the same time, SEI growth would also lead to active material loss and impedance failure. In this dissertation, first, the failure mechanisms of lithium metal battery were studied in details with in-situ experiments. The results showed that dendrite growth was highly coupled with SEI formation, and at large current density, the sharp tips of lithium dendrites would penetrate separator and eventually lead to short circuit. Second, electrochemical models were developed to simulate the concurrent evolution of dendrite morphology and SEI layer, and suggested that uniform SEI layer and smaller SEI resistivity would be beneficial to form stable lithium surface morphology during deposition. Third, linear stability analysis was conducted for suppressing lithium dendrite with thin film to show that the mechanical blocking strategy would only be effective if the thin film thickness and modulus meet a critical design criterion. Fourth, a new lithium dendrite suppression strategy using piezoelectric feedback mechanism was proposed, and a proof of concept design was implemented and tested with experiments. The results showed that using a piezoelectric separator can effectively suppress lithium dendrite growth and prevent short circuit during the cycling of lithium metal battery. In the last part, a novel battery pack design consisting of many micro batteries carried by an inert fluid was proposed to achieve higher energy and power density comparing to conventional battery pack design, and provide unique capabilities such as battery scaling with vehicle life, superfast refilling, heat dissipation and ongoing battery recycling.