Environmental assessment of silicon kerf recycling and its benefits for applications in solar cells and Li-ion batteries

Abstract

Silicon and its usage in photovoltaics and advanced Li-ion traction batteries is a key material for the decarbonisation of the energy and mobility sector. To achieve sustainable silicon-based products, an efficient raw material processing is required. However, the production of silicon and its purification is energy- and resource intensive. Further, during the production of photovoltaic cells, about 40% of the silicon used is lost as sawdust, the so-called silicon kerf, which is often not recycled to a high quality. Compared to primary production, silicon recycling requires less electrical energy and no fossil reductants. However, an environmental assessment of the GHG reduction potential of silicon kerf recycling in comparison to primary production of silicon is limited in literature.In this paper, we will provide a comprehensive environmental assessment of silicon kerf recycling located in Sichuan and Xinjiang in China and Germany, since China is the biggest producer of silicon worldwide. For the assessment of the recycling, a detailed process-specific material and energy flow balance based on industry and literature data is used. The results are evaluated with relation to the primary production of metallurgical silicon and a sensitivity analysis of used electricity mix and transport distance is performed. Results show that recycled metallurgical silicon from silicon kerf creates up to 77% lower GHG emissions compared to conventional primary silicon. Further, environmental hotspots are identified and discussed. Based on the findings, recommendations for target-oriented process engineering are given to further reduce the material-related GHG impacts of silicon based products. Finally, the impact of the results is reflected on the market potential of innovative products like photovoltaics and Li-ion batteries.