Life cycle assessment of lithium-sulfur batteries with carbon nanotube hosts: Insights from lab experiments

Abstract

Lithium‑sulfur (Li-S) batteries are candidates for next-generation batteries. It can be produced sustainably using sulfur instead of controversial cathode minerals like cobalt. However, Li-S batteries must improve their energy density and cycle life at their current state of development. Hosting the sulfur on carbon nanotubes (CNT) is a potential solution. This study investigated the environmental performance of a CNT-based Li-S battery based on original experiment data. The CNT in the batteries functioned as binders, conductive fillers, and current collectors, reducing auxiliary materials and simplifying manufacturing processes. We conducted a cradle-to-gate life cycle assessment (LCA) to clarify the environmental performance. We showed that the global warming potential (GWP) of the Li-S battery pack in a conventional battery structure was 105 kg CO2e/kWh. By partially substituting current collectors, increasing lithium anode efficiency, and reducing solvent usage, we could achieve 87, 82, and 78 kg CO2e, respectively. The lowest GWP of Li-S battery was 20 % lower when compared to a graphite‑nickel manganese cobalt oxides (NMC) battery. In addition, the other environmental indicators, including human toxicity, ecotoxicity, and acidification, were 26 % to 79 % lower, showing no major environmental burden shift. One exception was the mineral resource depletion, which was 2 % higher because lithium metal, instead of synthetic graphite, was used as a high-capacity anode pair. This study also found that modifying the cathode production process by using a less energy-intensive filtration before evaporating the remaining solvent could significantly reduce the energy required, thus mitigating the previously identified environmental hotspot. Our finding highlighted that a prospective LCA collaborating with battery experimentalists could lead to novel discoveries for environmentally sustainable battery production. Overall, we showed that Li-S batteries are environmentally preferred at the production stage, as supported by advanced experiments. Further research into improving the cycle life of Li-S batteries is crucial when considering the use stage to reduce the environmental impact per functional unit of energy delivered over the battery lifetime.