From trash to treasure: Silicon waste finds new use in Li-ion batteries

Li-ion batteries (LIBs) are widely used in various mobile electronics. Concerns of global warming and climate change have recently boosted the demand for LIBs in electric vehicles and solar photovoltaic output smoothing. Si has been studied as an active material with a high theoretical capacity of 3578 mAh/g, which is around ten times higher than that of graphite (372 mAh/g).

Now, a team of researchers at Osaka University has used flake-shaped Si nanopowder wrapped by ultrathin graphite sheets (GSs) to fabricate LIB electrodes with high areal capacity and current density.

Generally treated as industrial waste, Si swarf is generated at a rate of 100,000 tons per year globally from Si ingots that are produced from silica through processes at 1000~1800°C. Water-based coolants and fixed abrasive grain wire saws are paving the way to the use of Si swarf as an anode active material with a high capacity at a reduced cost.

Nano carbon materials have been applied to Si electrodes to improve electrical conductivity and cyclability. Many strategies for dealing with large volume change of Si electrodes at relatively high costs have been demonstrated. However, the Si electrodes do not combine all the requirements for high electrode performance, namely reduced cost, environmental friendliness of materials and processes, and circular economy.

“In this study, Si/graphite sheet composites from Si swarf and expanded graphite are used as the active material with reduced cost and thermal budget (Fig. 1). Si nanopowder is dispersed and wrapped between GSs fabricated from expanded graphite (Fig. 2),” explains first author Jaeyoung Choi. “GS bridges are formed across cracks and suppress cracking and peeling-off of Si. Agglomerated GSs wrap Si/GS composites, and work as stable frameworks that secure electrolyte paths and buffer spaces for Si volume change.”

The Si/GS composite structure and the delithiation limitation improve the cyclability up to 901 cycles at 1200 mAh/g. The areal delithiation capacity and current density of the Si/GS electrodes linearly increase to 4 mAh/cm² and 5 mA/cm², respectively, with the mass loading for more than 75 cycles (Fig. 3), while thick electrodes with C-coated Si fabricated in C₂H₄ are not competitive.

“Si anode batteries with high capacity and high current density have the potential to be used in electric vehicles. This potential, combined with increasing generation of Si swarf as industrial waste, will allow our work to contribute to reduced greenhouse gas emissions and the achievement of SDGs,” says corresponding author Taketoshi Matsumoto.

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The article, “Si swarf wrapped by graphite sheets for Li-ion battery electrodes with improved overvoltage and cyclability,” was published in Journal of The Electrochemical Society at DOI: https://doi.org/10.1149/1945-7111/abdd7e

About Osaka University

Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan’s leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan’s most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.

Website: https://resou.osaka-u.ac.jp/en