2022 Fiscal Year Research-status Report
Early-Stage Sustainability Assessment of Carbon-Nanotubes-Enabled Renewable Energy Technologies using Ex-Ante LCA and Sound Material-Cycle Index
| Project/Area Number |
20K20023
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| Research Institution | Waseda University |
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Principal Investigator |
ティア ヘンイ 早稲田大学, 理工学術院, 次席研究員(研究院講師) (70822485)
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| Project Period (FY) |
2020-04-01 – 2024-03-31
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| Keywords | LCA / lithium sulfur battery / thin film Si solar cell / resource sustainability / social LCA |
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| Outline of Annual Research Achievements |
We proceeded this project in two directions. The results were presented in the Ecobalance International Conference in December 2022.
(1) Lithium-sulfur (Li-S) battery. We investigated a carbon nanotubes (CNT)-based Li-S battery architecture, which can replace cobalt and other critical materials. We used a process-based LCA to evaluate the environmental performance, with a functional unit of 1 kWh Li-S cells normalized from a 100-kWh battery pack. We identified the hotspots in the manufacturing process and proposed three scenarios for technology improvements. These scenarios resulted in reductions of 16 (current collector), 4 (lithium anode), and 8 (DME solution) kg-CO2e per kWh, respectively. The study showed the Li-S technology reduce the environmental impact of batteries significantly.
(2) Thin-film Si solar cell. We explored the environmental implications of closing the silicon loop and upcycling solar cells in Japan. The goal is to reduce end-of-life solar panel waste and produce cleaner solar panels with less silicon domestically. Using three scenarios: business-as-usual, recycling (conventional Si wafer), and upcycling (proposed thin Si film), we found that upcycling could help Japan meet its 2050 net-zero carbon target, but the 2030 carbon reduction target may not be met due to the disproportionate amount of silicon needed for PV production and domestically available recycled silicon. The study also highlights the ripple effects of using thin-film PV, including easier transportation and installation.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
1. Lithium-sulfur batteries. (a) We received updated experiment data. We tested the lithium sulfide DME solution in a higher concentration to reduce the DME requirement. We found that 1/3 DME reduction was possible. We tested the efficiency of drying CNT solution with vacuum filtration before thermal drying. Adding this "filtration", that required much less energy, could greatly reduce the environmental impact of electrode production. We highlighted this significant original finding. (b) We received feedback from expert in conference discussion. Particularly, on how to model the process energy for industrial scale. We updated the model including a hypothetical solvent recovery and waste gas treatments using the latest information. We were able to show a more robust result for the prospective LCA.
(2) Thin-film Si solar cell. (a) We reviewed the solar panel waste estimations from international studies. We were able to confirm the waste "silicon" in most developed countries, that can potentially use as secondary resources with upcycling thin film technologies. (b）We applieda prospective material flow analysis of solar panel wastes in Japan, we estimated that there is a potential to upcycle silicon and achieve close-loop by the mid-century.
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| Strategy for Future Research Activity |
Finally, we are working on the framework for "resource sustainability" evaluation. Previously, we have shown the clear environmental benefits of CNT-enabled solar cells and Li-S batteries. However, only carbon reduction without the considerations of national interest and social value may not enough to comprehensively support a novel and bold government policy.
We want to argue that, the technologies of upcycle domestic solar panel waste, or utilize industrial-by-product sulfur as battery materials can reduce the reliance of imported materials, which may associated with high social costs (like human rights violation) or supply chain risk (due to international politics); examples would be cobalt from Congo, silicon from Xinjiang, China.
We are developing the framework based on the social-LCA and resource criticality methodologies to capture the above social value. We want to tailor an approach that is suitable for Japanese context; and complete the comprehensive three-pillars assessment for people, prosperity and planet.
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