Life cycle assessment of a novel hybrid energy storage system: Environmental hotspots and sustainability options based on experimental insights

This article reports on the life cycle assessment (LCA) of a novel hybrid energy storage system (HESS) for stationary use. The system combines a vanadium redox flow battery (VRFB) with a supercapacitor, simultaneously delivering high energy and high power. The LCA aimed to identify environmental hotspots in the HESS lifecycle and to provide recommendations for an environmentally-sustainable technology deployment. New life cycle inventory (LCI) datasets for the supercapacitor and DC-DC converters were created based on manufacturer data. A focus was laid on vanadium pentoxide (V2O5), the active component in the VRFB's electrolyte with significant environmental impacts. Existing LCI datasets for primary and secondary V2O5 production were evaluated regarding their quality and applicability. Additionally, a new laboratory scale process for recycling of waste vanadium electrolyte was developed and served as input for the LCA. The recycled electrolyte, which can be directly used in VRFBs, had a global warming potential (GWP) of 0.91 kg CO2-eq/kg at a vanadium concentration of 1.6 mol/l. The LCA of the HESS lifecycle for a real use case showed a GWP ranging from 0.10 to 0.53 kg CO2- eq/kWh, depending on scenario. V2O5 and the electricity losses during dis−/charging were identified as main environmental hotspots. The overall impacts of the system could be significantly reduced, if using recycled instead of primary vanadium electrolyte and renewable instead of conventional electricity sources for charging. The findings of this study underscore the importance of sustainable V2O5 sourcing and a circular economy for vanadium electrolyte to support the environmentally-sustainable market deployment of the HESS.