Author ORCID Identifier
https://orcid.org/0000-0003-4355-7864
Date Available
12-17-2027
Year of Publication
2025
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Engineering
Department/School/Program
Chemical Engineering
Faculty
Yang-Tse Cheng
Faculty
J. Zach Hilt
Abstract
Lithium-ion battery electrodes consist of active materials, conductive agents, and binders. Conductive agents are added to improve the electronic conductivity of the electrode materials, while binders are used to ensure mechanical integrity by providing adhesion and cohesion between electrode materials. Commercial lithium-ion battery electrodes are manufactured through a slurry-based wet process, in which an organic solvent is used to dissolve the polymeric binder before mixing it with the active material and the conductive agent. However, the typically used N-Methyl-2-Pyrrolidone (NMP) solvent is hazardous and energy-intensive, as it requires recovery. Thus, the use of the NMP should be avoided to decrease its detrimental effects on health and the environment. A solventless dry process for electrode manufacturing has the potential to reduce the cost and environmental impact of electrode manufacturing. In this dissertation, electrostatic spray deposition (ESD), in which pre-mixed electrode materials are charged using a spray gun and particles are drawn to a current collector, is investigated as a solvent-free dry electrode manufacturing process.
In the first study, I investigated the pre-mixing of powders before ESD. In the mixture, binder and conductive agents form conductive domains, affecting the surface area of the active materials and the conductivity of the electrode. These domains need to be optimized for improved electron transfer between the current collector and active material (long-range conductive pathways) and charge transfer reactions at electrode active surfaces (short-range conductive pathways). This can be achieved by the mixing step in dry manufacturing, as different mixing processes lead to different microstructures. I manufactured electrodes by using two different mixing processes, planetary ball mill mixing and planetary high-speed mixing, before the ESD. Electrodes made by ball mill mixing retained better discharge capacity, which was attributed to the low charge transfer resistance and improved ionic conductivity due to porous conductive pathways formed between and on the active material particles. High-speed mixing, on the other hand, caused dense layers of binder and conductive agent agglomerates, limiting the contact area of the active materials and increasing the resistance.
In the second study, I compared the performance of the positive LiNi0.8Mn0.1Co0.1O2 (NMC811) electrodes manufactured by dry ESD and wet slurry processes. More pressure during calendering was found necessary for the dry-made (dry) electrodes to have the same porosity, leading to more cracks within the NMC particles and better adhesion. At slower discharge rates, below 2 C, the dry electrodes exhibited a higher specific capacity or about the same capability as that of the slurry-made ones. At higher discharge rates, greater than 2 C, both types of electrodes have poor rate performance, though the slurry-made (slurry) electrodes had a slightly higher capacity. Despite more calendering-induced cracks in the dry electrodes, both electrodes had comparable long-term cycling behavior when tested in full cells with graphite-negative electrodes. This study shows the viability of using the dry-powder ESD process for manufacturing thick electrodes with high active material content, meeting the need for high energy demand.
In the third study, I conducted a comprehensive investigation of the effects of the different electrode formulations by altering the ratio of polyvinylidene fluoride (PVDF) binder and carbon black (CB) with NMC811 active material (AM) using a dry coating process. Specifically, I examined four distinct electrode formulations: 96:3:1, 96:2:2, 90:7.5:2.5, and 90:5:5 (AM: PVDF: CB), equivalent to PVDF/CB mass ratios of 1:1 and 3:1. I found that a high PVDF content at PVDF/CB ratio of 3:1 provides high mechanical strength. However, the electrode ionic conductivity decreases due to the insulating PVDF aggregates. The PVDF/CB ratio of 1:1 approaches the optimum ratio for balanced electronic and ionic conductivities, as well as electrode mechanical strength, thereby leading to enhanced electrochemical performance. For electrodes with the PVDF/CB ratio of 1:1, I observed that electrodes with higher AM content (e.g., 96%) showed a comparable C-rate and full-cell cycling performance to that with lower AM content (90%).
In the fourth study, thick (e.g., avg. 4.6 mAh cm-2) graphite electrodes were manufactured using the ESD process to achieve high energy density. I thoroughly examined two electrode formulations with 92:8 (Graphite: PVDF wt%) and 90:2:8 (Graphite: CB: PVDF wt%) to assess their physical properties and electrochemical performance. I used an adhesive PVDF binder layer between the electrode casting and the current collector to improve the adhesion of the graphite electrode film to the copper current collector. The addition of 2% CB in the graphite electrodes significantly reduced electronic resistance by establishing a percolation network of CB, resulting in enhanced electronic conductivity and improved cycling performance. While in electrodes without CB, insulating PVDF binder coverage on graphite active material particles led to increased resistance and irreversible reactions.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2025.631
Recommended Citation
Uzun, Kubra, "MANUFACTURING OF LITHIUM-ION BATTERY POSITIVE AND NEGATIVE ELECTRODES" (2025). Theses and Dissertations--Chemical and Materials Engineering. 181.
https://uknowledge.uky.edu/cme_etds/181
