Potential improvements of the life cycle environmental impacts of a Li/S battery cell

Övrigt konferensbidrag, 2018

The lithium sulfur (Li/S) battery is a promising battery chemistry for two reasons: it requires no scarce metals apart from the lithium itself and it brings the promise of high specific energy density at the cell level. However, the environmental impacts of this battery type remain largely unstudied. In this study, we conducted a life cycle assessment (LCA) of the production of an Li/S cell to calculate these impacts. The anode consists of a lithium foil and the cathode consists of a carbon/sulfur composite. The electrolyte is a mixture of dioxalane, dimethoxyethane, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate. The current collector for the cathode is an aluminium foil and a tri-layer membrane of polypropylene and polyethylene acts as separator. The functional unit of the study is 1 kWh specific energy storage. Three key environmental impacts were considered: energy use, climate change and lithium requirement. In our baseline scenario, we consider the pilot-scale production of a battery with a specific energy of 300 kWh/kg, having the mesoporous material CMK-3 as carbon material in the carbon/sulfur cathode, and using coal power and natural gas heat as energy sources. This scenario results in an energy use of 580 kWh/kWhstored and a climate change impact of 230 kg CO2eq/kWhstored. The main contributor to energy use is the LiTFSI production and the main contributor to climate change is electricity use during cell production. We then model a number of possible improvements sequentially: (1) reduction of cell production electricity requirement due to production at industrial-scale, (2) sourcing of electricity and heat from renewable instead of fossil sources (i.e. solar power and biogas heat), (3) improvement of the specific energy of the Li/S cell to 500 kWh/kg and (4) a shift of the carbon material in the cathode to carbon black (without considering changes in performance). By implementing all these four improvements, energy use and climate change impact can be reduced by an impressive 54 and 93%, respectively. In particular, the improvements related to industrial-scale production and sourcing of renewable energy are considerable, whereas the shift of carbon material is of minor importance. For climate change, the best-case result of 17 kg CO2eq/kWhstored is similar to the best-case results reported in the scientific literature for lithium-ion batteries (LIBs). Regarding lithium requirement, the lithium metal requirement of Li/S batteries and LIBs are also of similar magnitude (0.33-0.55 kg/kWhstored and 0.2 kg/kWhstored, respectively). Using different allocation approaches did not alter the main conclusions of the study.