Life-cycle analysis, by global region, of automotive lithium-ion nickel manganese cobalt batteries of varying nickel content

The batteries in electric vehicles can account for one-third of their production greenhouse gas (GHG) emissions; thus, it is important to understand how these batteries' environmental performance is affected by both the battery's chemistry and production location. In this study, we examined how transitioning to higher-nickel, lower-cobalt, and high-performance automotive lithium nickel manganese cobalt oxide (NMC) lithium-ion batteries (LIBs) from the base NMC111 would influence the environmental impacts of LIB production. Tran-sitioning from NMC111 cathodes to cathodes with higher nickel and lower cobalt contents results in a potential increase in the energy density (i.e., increased driving range) of the batteries and is thus favored in the industry. This study utilized the Greenhouse gases, Regulated Emissions, and Energy use in Technology (GREET) life-cycle assessment model to conduct the environmental analysis by focusing on the differences among global regions with respect to production conditions (electricity grid, mineral extraction methods, etc.) and examining them on the basis of a set of scenarios for current production conditions to better understand how regional supply-chain variations impact environmental performance. The environmental impact of the transition relative to the GREET baseline conditions was such that the GHG emission levels for NMC532, NMC622, and NMC811 showed re-ductions of 0.3%, 5.3%, and 7.5%, respectively, relative to NMC111, while the SO(x)emission levels increased significantly-by 130%, 130%, and 142%, respectively-relative to NMC111. These increases in the SOx emissions levels were correlated with increasing nickel content and were due to the production pathway of the nickel precursor. Through further scenario analysis, we showed that lower SOx emission levels could be attained when the nickel precursor was produced exclusively from mixed hydroxide precipitate (MHP) instead of Class I nickel-although this change resulted in higher GHG emission levels with the current MHP supply chain. Regional variability of the electricity grid profiles also influenced the environmental impacts of LIB production. The use of hydro-powered electricity resulted in reduced GHG emissions levels; however, water consumption levels increased compared to the baseline conditions. Among other scenarios, we also investigated the best-and worst-case-scenario supply chains based on GHG emission levels. In this case, the best-case scenario is the scenario with the lowest GHG emissions, while the worst has the highest. For the NMC811 LIB, the GREET baseline, currently dominant, and worst-case-scenario supply chains showed GHG emission levels of 121%, 173%, and 347%, respectively, relative to the best-case-scenario supply chain. This study highlights the sensitivity of an LIB's life-cycle environmental performance to its supply chain, thereby suggesting a path toward improving the battery's environmental performance, namely, supply-chain decarbonization.

Automated summary

In this study, the environmental impacts of lithium-ion battery production were analyzed, and it was found that transitioning to higher-nickel, lower-cobalt materials can reduce greenhouse gas emissions, but increase sulfur dioxide emissions. Changing the production pathway of the nickel precursor can lower sulfur dioxide emissions. The variability of electricity sources also affects the environmental impacts of battery production.