Understanding Colloidal and Surface Phenomena to Manufacture Energy-Dense Lithium-Ion and Solid-State Battery Cathodes

Lithium-ion batteries (LIB) are a technology that have been commercialized since 1991 for portable electronics. Research and development have dramatically reduced the cost of LIBs over the past ten years such that it is becoming more feasible that electric vehicles utilizing LIBs can compete with vehicles using the internal combustion engine. To continue to reduce the cost of LIBs, novel cathode processing strategies must be pursued and the impact of these strategies on the cathode’s microstructure and performance must be well-understood. Moving beyond LIBs, solid-state lithium metal batteries (SSLMBs) are a safer, more energy-dense alternative due to non-flammable, thin solid electrolytes. However, the widespread commercialization of SSLMBs is bottlenecked by the development of a cathode and electrolyte pairing that are scalable, electrochemically stable, and retain good contact throughout cycling.

This dissertation is focused on LIB processing strategies that limit or eliminate the use of N-methyl-2-pyrollidone (NMP), the toxic, expensive solvent used in cathode slurry processing. By implementing a novel suite of rheological testing protocols, this dissertation demonstrates that less NMP is required when a cathode slurry is heated throughout the mixing, storage, and coating stages. Eliminating NMP by replacing it with water is an even more promising possibility, though cathode materials are reactive in water. The surfaces of five commercialized cathode materials were investigated after water exposure and the leaching of the materials’ comprising elements was measured. The most promising of the materials examined from an energy density perspective, LiNi_0.8Co_0.15Al_0.05O₂ (NCA), was found to be entirely unsuitable with water. The cause of this incompatibility was identified and was solved with the addition of an inexpensive additive: polyacrylic acid.

Finally, a UV-curable solid polymer electrolyte was paired with nickel-rich varieties of LiNi_xMn_yCo_1-x-yO₂ (NMC, x ≥ 0.6). The sources of failure in a SSLMB containing polymer electrolyte were deconvoluted and suggest that polyethylene oxide-derived polymer electrolytes are stable with high-voltage cathode materials. By understanding the impact of processing conditions on cathode material interfaces, the cost of LIBs for electric vehicles will continue to drop and SSLMBs may reach commercialization more quickly.