The refinement step dominates environmental impacts of circular and conventional supply chains. Combining material extraction, transport, and refinement steps yields a cradle-to-gate comparison of the most differentiated steps of conventional and circular LIB supply chains for producing battery-grade cathode materials (Fig. ). Here the environmental impacts of the LIB refinement step in California are analyzed for a hypothetical scenario employing the same circular multi-step refinement technologies as Redwood Materials (i.e., RC+Me+Hy) in Nevada, but using California (CISO) electricity to produce battery-grade cathode materials. A circular supply chain in California for NCA EV and LCO smartphone batteries lowers energy and greenhouse gas emissions by at least 47.3% and water consumption by over 37.6%. In the case of recycling NCA EV batteries in California, the entire cradle-to-gate greenhouse gas emissions of the circular supply chain are lower than the transport emissions of mined concentrate in conventional supply chains (Fig. , Table ). Circular production of LCO-grade materials leads to higher environmental impacts than that of NCA-grade materials based on the mixed-stream feedstock composition processed by Redwood Materials. Overall, upstream steps (extraction and transport) contribute marginally to the total environmental impacts of both circular supply chains, accounting for ≤4.9% CO2-eq emission, ≤8.2% energy consumption, and ≤0.24% water consumption. Accordingly, the refinement process dominates the environmental impacts of the circular supply chain. In contrast, upstream steps in the conventional supply chain play a larger role (still smaller than refinement) in cradle-to-gate environmental impacts, contributing between 7.8-31.0% to the environmental metrics considered (Table ). Environmental impacts of refinement are analyzed based on electricity generated from balancing grid authority CISO and upstream supply chain steps (extraction and transport) are based on data from GREET and transport models developed in the preceding section and depicted in Fig. . Specific environmental impacts of each step are detailed in Tables S5-S7. recycling facility. Practical LIB feedstock and refinement pathways are analyzed from recycling company (Redwood Materials) and modeling is employed to examine the environmental impacts of upstream material extraction and transport steps. The analysis reveals that refining end-of-life LIBs into battery-grade cathode materials exhibits lower environmental impacts than conventional refinement of mined materials, mixed salts products are more beneficial for circular refinement, and the source of input electricity is the principal factor governing circular refinement environmental impacts. Upstream circular supply chain steps contribute marginally to overall environmental impacts, and the refinement step comprises the largest source of cradle-to-gate environmental impacts. Disaggregated analysis of LIB refinement pathways at Redwood Materials provides important insights into the performance and potential of different refinement processes. While pyrometallurgical processing is widely considered as more environmentally intensive than hydrometallurgy, Redwood Materials' RC pathway exhibits much lower environmental impacts than current Hy-containing pathways reported in practice and in literature (Fig. ). The optimized conditions of RC processing minimizes the combustion of carbon-containing LIB materials, significantly reducing CO2-eq emissions while simultaneously generating products that are amenable for hydrometallurgical separation. Because chemical consumables such as H2O2 are important contributors to hydrometallurgy, environmental impacts of Hy processes could be reduced through more sustainable (e.g., electrochemical) production methods . Our findings also advocate the refinement products of mixed metal sulfates over the single salts, indicating that the further separations among Ni and Co salts can be avoided. An emerging alternative LIB recycling technology, "direct recycling", recovers functional battery materials without decomposition into substituent elements, and is reported to exhibit comparable environmental impacts to Redwood Materials methods . However, direct recycling is still under development and warrants further assessment after process optimization and industrial-scale implementation.