Research: Deformation and Fracture in Li-ion Battery Electrodes
Developing batteries with extended life will significantly enhance the performance of future of electric vehicles. A range of phenomena limit battery life, from electrolyte decomposition; solid-electrolyte interphase layer build-up on active electrode surfaces; decomposition of the binder; corrosion in current collectors; and metallic Li plating.
In prior work, the CRL developed in-situ experimental techniques and computational methods to measure and model stress and damage evolution in electrode materials during lithium insertion.
For the next phase of the GM/Brown CRL, we plan to understand how the large volume changes in high capacity electrode materials during the lithiation and delithiation leads to the severe mechanical and chemical degradation. Improving the mechanical integrity of composite electrodes is critical to ensure the long-term cycle stability for BEV (battery electric vehicle) applications. In this endeavor, the main focus is to characterize the irreversible swelling and deformation of Si and Si alloy film electrodes and composite electrodes. In addition, the effect of the prelithiation methods (thermal evaporation vs. electrochemical plating), Li dosage, voltage window, binder, electrode porosity, and the ratio of Si to other active materials (e.g., graphite) on the stress evolution and irreversible swelling/deformation can be investigated and correlated with the mechanical integrity of the electrode and cycle performance.
In addition, we plan to address voltage hysteresis seen most clearly at low rates of cell operation. Hysteresis is a critical problem for high capacity electrodes, particularly Li-Si, which leads to energy loss (low energy efficiency) and makes it difficult to control the state-of-charge and manage power in electrified vehicles. GM has created simple models on hysteresis and compared their behavior experimental results. Open questions include the effect of self-discharge and stress on hysteresis. The research activities at Brown can be focused on understanding and reducing hysteresis in lithiated silicon and silicon alloy electrodes.