In the pursuit of next-generation high energy density lithium-ion batteries, practically incorporating silicon into the negative electrode without sacrificing cycle life, continues to headline many energy storage research and development programs including the DOE-EERE-VTO Next Generation Anodes project. Silicon has the ability to store approximately ten times the number of lithium-ions than the current standard negative electrode material, graphite, and would transform the battery market if successfully implemented into lithium-ion batteries. However, the electrochemical performance of silicon-containing electrodes continues to be afflicted by the continual SEI growth during electrochemical cycling. The development of high-performance silicon-containing electrodes is an important focus area for the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory.

The scalability of the electrode fabrication process is almost as important as its electrochemical performance; here, we note a potential safety concern during the silicon-electrode slurry preparation process. Recent work has shown that significant quantities of gasses are generated when silicon particles are mixed in an aqueous medium using binders such as partially-lithiated polyacrylic acid (Li-PAA).¹^,² Because hydrogen is the main gas generated, the uncontrolled chemical reactions and the resulting pressure buildup could pose a hazard for large industrial-scale processes. In order to better understand the chemical reactions we have developed a method to quantify the volume of gasses generated using the Archimedes principle. We show that the gas volumes are affected by various factors, which include the pH of the electrode slurry and characteristics of the silicon powders. Negligible gas generation is observed in electrode slurries containing the n-methyl-2-pyrrolidone (NMP) solvent, which could be considered as an alternative to the water-based processes presently under consideration. Other electrode preparation factors, such as the silicon powder type, solvents used for slurry dispersion, pH, binders, etc., and the concomitant effects on electrode electrochemical performance will also be discussed during the presentation.

Support from David Howell, Brian Cunningham, and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies is gratefully acknowledged. This work was performed under the auspices of the US Department of Energy, Office of Vehicle Technologies, Hybrid and Electric Systems, under Contract No. DE-AC02-06CH11357

1. Zhang, Y. Liu, B. Key, S. E. Trask, Z. Yang, W. Lu, “Silicon Nanoparticles: Stability in Aqueous Slurries and the Optimization of the Oxide Layer Thickness for Optimal Electrochemical Performance”, ACS Appl. Mater. & Interfaces (2017), p. 32727.
2. A. Hays, G. M Veith, B. Key, J. Li, Y. Sheng, D. L Wood III, “Considerations in Electrode Preparation of Si-Based Slurries for Commercial Li-Ion Batteries”, 232^nd ECS Meeting, Abstract MA2017-02 395 National Harbor, MD (October 2017).