Researchers at Osaka University use silicon chips/graphite flake composite materials to make lithium-ion battery electrodes to achieve high performance, cost reduction and environmental protection

Image: Electrode made of silicon chips/graphite flake composite material see more 

Lithium-ion batteries (LIB) are widely used in various mobile electronic products. Concerns about global warming and climate change have recently promoted the demand for lithium-ion batteries for electric vehicles and solar photovoltaic output smoothing. Si as an active material has been studied to have a high theoretical capacity of 3578 mAh/g, which is about 10 times higher than graphite (372 mAh/g).

Now, a team of researchers at Osaka University uses flake silicon nanopowder wrapped in ultra-thin graphite flakes (GSs) to make LIB electrodes with high area capacity and current density.

Silicon dust, which is usually treated as industrial waste, is produced globally at a rate of 100,000 tons per year. Among them, silicon ingots are produced from silicon dioxide through a process at 1000~1800°C. Water-based coolants and fixed abrasive wire saws are paving the way for the use of silicon shavings as an anode active material with high capacity and low cost.

Nano-carbon materials have been applied to silicon electrodes to improve conductivity and cycling. Many strategies have been proven to deal with large volume changes of Si electrodes at relatively high cost. However, Si electrodes do not combine all the requirements for high electrode performance, that is, cost reduction, environmental friendliness of materials and processes, and circular economy.

"In this study, Si/graphite flake composites from Si scraps and expanded graphite were used as active materials, reducing costs and thermal budgets (Figure 1). Si nano-powders were dispersed and wrapped in expanded graphite GS (Figure 2)),” the first author Jaeyoung Choi explained. "The GS bridge spans the formation of cracks and inhibits the cracking and peeling of Si. The agglomerated GS wraps the Si/GS composite material and acts as a stable frame to ensure the electrolyte path and buffer space for the volume change of Si."

The Si/GS composite structure and delithiation limit increase the cycle performance to 901 cycles at 1200 mAh/g. The area delithiation capacity and current density of the Si/GS electrode increase linearly to 4 mAh/cm2 and 5 mA/cm2, respectively, and the mass load exceeds 75 cycles (Figure 3), while the thick electrode with C coating is made in C2H4 Si is not competitive.

"Silicon anode batteries with high capacity and high current density have the potential to be used in electric vehicles. This potential, coupled with the increase in silicon chips generated as industrial waste, will enable our work to help reduce greenhouse gas emissions and achieve SDGs," said corresponding author Taketoshi Matsumoto.

The article "Silicon chips with improved overvoltage and recyclability for lithium-ion battery electrodes wrapped in graphite sheets" was published in DOI's Journal of the Electrochemical Society: https://doi.org/10.1149/1945-7111 /abdd7e

Founded in 1931, Osaka University is one of the seven imperial universities in Japan. It is now one of Japan's leading comprehensive universities with a wide range of subjects. This advantage is combined with the unique innovation drive that runs through the entire scientific process, from basic research to the creation of applied technologies that have a positive economic impact. Its commitment to innovation has been recognized by Japan and around the world, and was named the most innovative university in Japan in 2015 (Reuters Top 100), and was named the most innovative university in the world in 2017 One of the institutions (Innovation University and Nature Index Innovation 2017). Now, Osaka University is playing its role as a national university corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to the innovation of human well-being, the sustainable development of society, and the transformation of society .

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

Journal of the Electrochemical Society

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Copyright © 2021 American Association for the Advancement of Science (AAAS)