Prospective Life Cycle Assessment of Two Supercapacitor Architectures

Supercapacitors have numerous applications in which high power, long cycle life, and rapid recharging are required. However, the environmental assessment of supercapacitors has been limited despite their potential to decouple anthropogenic activities from environmental impacts. The present work assesses the environmental performance of two supercapacitor architectures at a future point in time when technology maturity has been realized by conducting an ex-ante prospective life cycle assessment. The supercapacitors investigated involve either an aqueous electrolyte, i.e., sulfuric acid (1.5 M H2SO4), or an ionic liquid, i.e., 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (MPPyFSI). To perform this prospective assessment, life cycle inventories were built and scaled up to emulate the optimized industrial production conditions. In the process, new inventories for specialty chemicals (i.e., MPPyFSI and its precursors) were devised and disclosed as part of this LCA. Three functional units were considered for the environmental comparison between the two supercapacitors. The functional units considered are specific capacitance with respect to the supply voltage (1 F supplied at 3.5 V), time-restricted power output (1 W supplied for 1 min), and sustained energy delivery for a fixed duration (1 W h supplied in 1 min). The selection of the functional unit is crucial and should be based on the intended application of the supercapacitor, as guided by the IEC 62391-1 standard. Life cycle impact assessment results revealed the improved environmental performance of MPPyFSI over H2SO4 supercapacitors for all functional units adopted in this work. Around 60-80% lower carbon emissions and energy demand are observed for the ionic liquid-based supercapacitor. In conclusion, the supercapacitor's vital role in achieving energy transition goals motivates further environmental assessment using the life cycle assessment methodology. Furthermore, to ensure consistency, comparability, and reproducibility of future research, the functional unit should be harmonized following the footsteps of those in the field of batteries and photovoltaics.