Raw material use in a battery electric car – a thermodynamic rarity assessment

Abstract

The transition to full electromobility must be carefully evaluated, as large amounts of strategic metals will be required, for which there is presently little to no recovery or recycling (e.g. gold, silver, tantalum or cobalt). In this study, we perform a comprehensive metal assessment of two passenger cars (conventional and battery electric models) in terms of mass and thermodynamic rarity. Thermodynamic rarity is based on the property of exergy and is defined as “the amount of exergy resources needed to obtain a mineral commodity from average crustal concentration using the best available technology” (measured in kJ). Thus, the thermodynamic rarity approach assigns a greater exergetic value to scarce (understood as having a relative low average crustal concentration) and difficult-to-extract minerals. Of the 60 metals analyzed, almost 50 metals have been identified within the studied cars, representing 800 (conventional) and 1,200 kg (battery electric), showcasing the fact that a car constitutes a “road mine”. Furthermore, given that the technology behind battery electric cars is in development, three generations of Li-ion batteries were analyzed to study the effect on resource use of a metal changing composition over time. Albeit the battery modules of the three generations present a similar mass content (approximately 70 kgs), the thermodynamic rarity decreases from 275 to 100 Gigajoules, due to the reduced proportion of cobalt, which is by far the most exergetic metal within the battery. Additionally, with the thermodynamic rarity approach, the most exergy intensive parts within a battery electric car have been identified – the high-voltage battery modules, the electric drive, the power module, the charger, the electrical air conditioning compressor and the electromechanical brake servo – providing an indicator facilitating proactive mid- to long-term ecodesign measures and recycling strategies.