Author ORCID Identifier
Year of Publication
Doctor of Philosophy (PhD)
Chemical and Materials Engineering
Dr. Yang-Tse Cheng
Rechargeable lithium-ion batteries (LIBs) are widely used to provide energy and power in portable electronics, electric vehicles, and energy storage systems. The LIB market has grown dramatically as they have a combination of high energy density, high power density, proven reliability, and long cycle life. The manufacturing process is one of the key factors as it strongly affects the cost and performance of LIBs.
This dissertation is focused firstly on the development of a conventional slurry-based electrode manufacturing process. Slurry making is a critical step that affects the subsequent steps in battery manufacturing. In this work, we have investigated the effects of the two main industry-used mixing sequences on the rheological behavior of the slurry, and the relation of the slurry rheology to structural, mechanical, and electrochemical performance of LiNi0.33Mn0.33Co0.33O2 (NMC) electrodes. We show that (1) mixing carbon black (CB) with polyvinylidene fluoride (PVDF) solution before adding NMC can facilitate the formation of a gel-like slurry and form porous clusters of CB and PVDF; (2) dry powder mixing of CB and NMC can facilitate the binding of the CB to the NMC surfaces, reducing the amount of CB in the PVDF and resulting in a liquid-like slurry; (3) after drying of the liquid-like slurry, a dense CB/PVDF layer can form on the NMC surfaces, which can provide high binding strength but may block ionic transport and weaken the electronic connection, reducing the C-rate capability.
Secondly, the effects of the molecular weight of the polyvinylidene fluoride (PVDF) binder on the electrochemical performance and mechanical integrity of the NMC electrodes made by a dry-powder-coating process were investigated. The microstructure, binding strength, and electrochemical behavior of the electrodes made with two types of PVDF polymers were compared. We show that a thin PVDF layer can form on the NMC particle surface after heating the PVDF to above its melting point. The microstructure and porosity of the PVDF layer depend strongly on the molecular weight of the PVDFs. With increasing molecular weight, the PVDF layer becomes more porous, improving the high-rate capacity without decreasing binding strength and long-term cycling performance of the electrodes.
Thirdly, the influence of using low toxic dimethyl sulfoxide (DMSO) as a solvent on the manufacturing of NMC electrodes was investigated. By using viscosity and electrochemical measurements, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), we show that the toxic N-Methyl-2-pyrrolidone (NMP) solvent may be replaced by DMSO without altering the conventional LIB manufacturing process.
Fourthly, the influence of using DMSO as a solvent on the manufacturing of Ni-rich electrodes was investigated. By using rheological and electrochemical measurements, peel tests, SEM, and XPS, we show that LiNi0.8Co0.1Mn0.1O2 (NMC 811) slurries made using the DMSO solvent can have similar shear thinning behavior, viscosity, and wettability as those made using the conventional toxic solvent. The peel strength and electrochemical behavior of the electrodes made using the two solvents are also similar.
Digital Object Identifier (DOI)
This work was partially supported by Ford Motor Company University Research Project “Using Mixing Science to Improve Battery Quality” in 2017 and the National Science Foundation Award 1355438 “Powering the Kentucky Bioeconomy for a Sustainable Future.” in 2017.
Wang, Ming, "Improving Manufacturing Processes for Making Lithium Ion Battery Electrodes" (2022). Theses and Dissertations--Chemical and Materials Engineering. 139.
Available for download on Sunday, May 19, 2024