Matthew Assembles 3D-Printed NMC Cells in an Argon-Filled GloveBox

Author: Matthew Sullivan | Major: Mechanical Engineering | Semester: Spring 2022

This semester, with support funding from the University of Arkansas Honors College, I was able to conclude my research on 3D-printed high energy cathode materials for lithium-ion batteries (LIBs). This project was sponsored by Dr. Meng in the department of Mechanical Engineering to find a scalable and facile method to improve the electrochemical stability of the promising electrode LiNi_xMn_yCo_1-x-yO₂ (NMC). With the information gained from this project, it has been learned that optimization of electrode surface area through 3D printing improves the cycling stability of this cathode material, allowing for future high energy LIBs to benefit from this cost-effective and scalable approach.

This topic was chosen in the fall of 2019 to assist in an ongoing experiment on NMC. Dr. Meng’s lab generally focuses on nanoscale interface coatings for LIB electrode material through atomic and molecular layer deposition (ALD, MLD). ALD and MLD also benefit from being a highly scalable and manufacturing-friendly process to provide a passivation layer between LIB electrodes and electrolytic solutions. By combining A/MLD with 3D printing was assumed that highly stable NMC cathode materials could be used and brought closer to safe commercialization. In the process, I learned a great deal about 3D printing techniques and theory, as well as what factors lead to the instability of the NMC electrode material. In particular, areal current density appeared to be directly confrontable by the 3D printing method. Areal current density refers to the amount of current applied to the electrode divided by its surface area (mA/cm²). Typically, electrodes are made in a thin, flat sheet. As a result of this, the surface area of the flat electrode is greatly reduced compared to the infinite possibilities of 3D-structured electrodes through 3D printing. By increasing the surface area of the NMC electrode, thereby reducing the areal current density, side reactions would be greatly reduced and the electrode maintained higher stability at low-current testing.

Dr. Meng helped in this project by offering lots of experience and training in designing and conducting experiments. For this process, I needed to learn many skills and become familiar with many battery-specific instruments. Initially, setting up and learning to use the 3D printer was difficult, as many factors of the printing process such as the viscosity of our NMC slurries, printing speeds, and bed temperatures greatly impacted the results of the study. By explaining the effects of these factors, we were able to optimize our printing parameters and design a printed electrode with the best chance of success. After these factors had been finalized, a suitable printing geometry that provided optimal surface area to volume ratios was selected and the electrodes were fabricated. To start, low-current testing for 500 charge cycles was run to determine how stable the printed electrode was compared to a traditional electrode. The same charging parameters were given to each cell, and success would be defined as the printed electrode revealing a more stable profile with higher capacity than the traditional sample.

Fortunately, this testing revealed that the printed samples maintained higher capacity after 500 cycles than the bare sample, suggesting that the printed sample maintained a healthier crystal structure. The difference is suspected to come from the reduction in areal current density in the printed sample compared to the traditional sample. This reduction likely reduced the spontaneity of side reactions between the electrode and electrolyte, maintaining the transition metals and oxygen present in pristine NMC structure.

With this experiment concluded, I was also able to begin a new project focusing on new electrode materials. Rather than focus on 3D printing these electrodes, I have begun work with new coating materials through ALD and MLD. I expect to continue this new project into graduate school, where hopefully my work will be able to improve on the existing framework of A/MLD coatings of alkali metal anodes.