The Effect of Silicon Nanoparticle Size on Cycle and Calendar Life

Lithium-ion batteries are now ubiquitous in modern electronics, electric vehicles, and many other applications. As the battery industry continues to push for better, longer lasting batteries, many have turned to using a different anode material that would provide higher-energy density and require less frequent charges. While graphite is the tried-and-true anode material for lithium-ion batteries, a silicon anode battery could provide up to ten times higher theoretical energy density than graphite. However, there are a lot of challenges standing in the way between silicon anode batteries and commercialization—the large volume expansion of silicon (around 200-300% expansion, compared to graphite at 10%) and the unstable solid-electrolyte-interface (SEI) of silicon results in anodes that mechanically degrade and calendar age faster than their graphite counterparts. Previous research has demonstrated that plasma-enhanced chemical vapor deposition (PECVD) silicon nanoparticles with a hydrophilic coating such as polyethylene oxide (PEO) results in silicon anodes with good cycle life 1, 2, 3, 4. In this system, smaller particle sizes typically yielded better cyclability than larger particle sizes, which is contrary to conventional wisdom that more surface area is detrimental as it allows for more SEI formation and side reactions. However, since silicon anodes experience large volume changes during cycling, the surface area might not be the dominant contribution to capacity fade. Larger silicon particles result in larger total expansions of the electrode, which causes more mechanical damage like cracks to form, exposing fresh surface area to electrolyte and SEI formation. This research investigates the performances of PEO-coated PECVD Si electrodes with nanoparticles ranging from 3 to 27 nm in diameter. We measure the cycle life at a rate of 0.333C, as well as the calendar lifetimes of each electrode. We characterize each electrode with SEM imaging, tortuosity measurements, and electrochemical impedance spectroscopy to understand the differences in microstructure that contribute to capacity fade and impedance rise. References: 1 G. M. Carroll, M. C. Schulze, T. R. Martin, G. F. Pach, J. E. Coyle, G. Teeter and N. R. Neale, "SiO2 Is Wasted Space in Single-Nanometer-Scale Silicon Nanoparticle-Based Composite Anodes for Li-Ion Electrochemical Energy Storage," ACS Applied Energy Materials, vol. 3, no. 11, pp. 10993-11001, 2020. 2 S. Jiang, B. Hu, R. Sahore, H. Liu, G. F. Pach, G. M. Carroll, L. Zhang, B. Zhao, N. R. Neale and Z. Zhang, "Tailoring the Surface of Silicon Nanoparticles for Enhanced Chemical and Electrochemical Stability for Li-Ion Batteries," ACS Applied Energy Materials, vol. 2, no. 9, pp. 6176-6183, 2019. 3 M. C. Schulze, G. M. Carroll, T. R. Martin, K. Sanchez-Rivera, F. Urias and N. R. Neale, "Hydrophobic versus Hydrophilic Interfacial Coatings on Silicon Nanoparticles Teach Us How to Design the Solid Electrolyte Interphase in Silicon-Based Li-Ion Battery Anodes," ACS Applied Energy Materials, vol. 4, no. 2, pp. 1628-1636, 2021. 4 M. C. Schulze, F. Urias, N. S. Dutta, Z. Huey, J. E. Coyle, G. Teeter, R. Doeren, B. J. Tremolet de Villers, S. Han, N. R. Neale, and G. M. Carroll, "Control of nanoparticle dispersion, SEI composition, and electrode morphology enables long cycle life in high silicon content nanoparticle-based composite anodes for lithium-ion batteries," J. Mater. Chem. A, vol. 11, pp. 5257–5266, 2023.