Nanomechanical Properties of Electrodeposited Li and Fabrication of 3D Architected Cathodes for Li-Based Batteries

Abstract

Advancements in the active materials of Li-based batteries provide a promising route to significantly improve electrochemical performance. Li metal has a 10x increase in gravimetric capacity compared to conventional graphite anodes and can be utilized with a solid electrolyte. However, current solid-state Li metal anode batteries cannot reliably cycle large amounts of Li due to chemical and mechanical degradation at the solid electrolyte / Li interface. One key factor in the failure of solid electrolytes is the dearth of mechanical data on Li at the relevant length scales and microstructures to solid-state batteries. The initial stages of Li formation at the solid electrolyte / Li interface also require further exploration to help improve the performance of solid-state Li batteries. In the first part of the thesis, we will discuss the methods used to investigate Li electrodeposited in-situ in a scanning electron microscope (SEM) chamber from a thin film solid-state battery. We probed the formation of this Li and found preferential growth at the domain boundaries of the surface of the cell, corroborated by electrochemical simulations. Cryogenic electron microscopy was determined to be the optimal method for examining the microstructure of Li and was utilized to reveal the single crystalline microstructure of Li pillars. Uniaxial compression experiments were performed on single crystalline Li pillars that grew from these batteries. We found that Li pillars with diameters of 360-759 nm first deformed elastically, then yielded and flowed plastically, with an average yield stress of 16.0 ± 6.82 MPa, 24x stronger than bulk polycrystalline Li. The mechanical results are discussed in the framework of dislocation starvation and nucleation, in addition to thermally activated deformation processes. Next generation battery systems may also utilize 3D electrodes to allow for both high energy (large mass loading) and power densities (small diffusion lengths). The last section of the thesis investigates the fabrication of 3D architected LiCoO2 structures and their performance as Li-ion battery cathodes. Using a novel hydrogel photoresin with relevant salt contents, the structures were fabricated using digital light processing and calcination. The electrochemical performance of the architected cathodes was examined and the electrodes exhibited a relatively high areal capacity up to ∼8 mAh/cm2 and a capacity retention of 82% after 100 cycles.