Active Material Investigations in Lithium- and Sodium-Ion Batteries

Abstract

This thesis focuses on both methods to evaluate and produce new lithium- and sodium-ion battery active materials, as well as studying the use of new active materials. It focuses on the development and use of single-layer pouch cells, all-dry synthesis of mid-nickel positive electrode materials for lithium-ion batteries, and the development and use of lead-containing negative electrode materials for sodium-ion batteries. The first part of the thesis develops a method to make single-layer pouch cells and shows the benefits of this form factor. First, a comparison between single-layer pouch cells, coin cells, and stacked pouch cells is made, showing that when single-layer pouch cells are made without a negative electrode overhang, they give the best possible electrochemical performance. Finally, single-layer pouch cells are used in a case study comparing LFP and NMC full cells. The second part of the thesis develops an all-dry synthesis technique to make NMC640 in a water- and waste-free process. The all-dry synthesis consists of mixing transition metals and metal oxides with a lithium source and an optional tungsten coating in an auto grinder before calcination. The best all-dry synthesized materials with 0.3 mol% tungsten coating perform as well or better than a commercial NMC640 material in electrochemical half cell evaluations. The remaining parts of the thesis introduce lead as a promising sodium-ion negative electrode material. First, in half cell testing, it is found that lead negative electrodes with high active material loadings can cycle with no capacity loss when their electrodes contain single-walled carbon nanotubes and the electrolyte solvent is monoglyme. However, due to the large volume change of lead during sodiation, the lead particles break down into smaller particles and cause overall restructuring of the electrode. This repeated volume change also causes irreversible capacity loss in full cells. An initial attempt is made to make lead-carbon composite active materials that can mitigate the effects of the volume change. Overall, this thesis provides insights into new active materials, new methods to test them, and new production processes for them to produce lower cost and longer lifetime batteries.