Methodology. An attributional life cycle assessment is conducted to quantify and compare conventional and circular LIB supply chains for the production of battery cathode materials. This analysis complies with the International Organization for Standardization (ISO) 14040 standards but omits conversion to environmental impact indicators and external review ), normalizing by the mass of the individual element of interest within the output product (e.g., Li in Li2CO3) and then normalizing again by the mass of that element in the functional unit for this life cycle assessment (defined in the next section). For elements where more than one pathway of production exists in the GREET model (i.e., Ni and Li), the overall environmental impacts are calculated by averaging pathways weighted by their respective share of global production (45% Li production from brine and 55% from ore, and 60% Ni production from mixed hydroxide precipitate and 40% from Class Defining functional units. Functional units standardize comparisons of the resource consumption and emissions in life cycle assessments. In this study, two functional units are considered in this assessment to normalize environmental impacts between conventional and circular supply chains: the battery-grade material required to make one kg of stoichiometric lithium nickel cobalt aluminum oxide (LiNi0.80Co0.15Al0.05O2, NCA-eq) and lithium cobalt oxide (LiCoO2, LCO-eq) cathode material. Mass was selected as the primary normalizing factor because any energy-based functional unit (e.g., per kWh) could vary based on battery manufacturing and cycling characteristics. The NCA chemistry was selected because reports suggest future cathodes may utilize less Co compared to NMC batteries in EVs, and NCA comprised the second-largest category of EV battery chemistries in 2016, following NMC batteries . LCO is a representative chemistry used in handheld rechargeable devices (e.g., cellphones and laptops) which are currently available to recycle in larger quantities than EV LIBs. The environmental impacts of other LIBrelevant materials (Cu and Mn) in conventional supply chains can be found in Table .