Abstract
The electrification of transport systems is essential for improved city air quality and reduced noise, may also contribute to enhanced energy security and decreased greenhouse gas emissions. The key enabler of the large-scale uptake of electric vehicles (EVs) are improved lithium-ion batteries (LIBs), offering higher mass specific energies, volumetric energy densities, potential differences and energy efficiencies. Most LIBs used in automotive applications combine nickel-cobalt-manganese (NCM) oxide cathodes with graphite (Gr) anodes intercalating lithium ions from organic electrolyte solutions of lithium salts. Two widely reported modifications include increasing the nickel content in cathodes and introducing silicon-graphite (SiGr) composite anodes, enabling increased energy storage capacities.
Technological developments in EVs and LIBs have triggered a growing interest in using Life Cycle Assessment (LCA) to quantify the environmental burdens of electrified mobility (Ellingsen et al., 2014; Kim et al., 2016). Figure 1 compares the global warming potential (GWP) (kg CO2-eq. (battery kW h)- 1) of battery manufacturing at different locations, for reports that allowed the production footprint to be distinguished. The indication that despite the higher coal intensity in its electricity mix, China's LIB manufacturing has a lower GWP production footprint than other regions is counter-intuitive and raises the need for more detailed analysis. An important additional aim of this work is to consider whether the high environmental burdens of producing LIBs can be counter-balanced by extended EV use periods and the parameters that affect these. Since nickel-rich cathodes and silicon-based anodes are considered the most promising modifications for next-generation LIBs in the near-term, their combined environmental performance is studied.
This paper reports on the development of a detailed unit process-based Life Cycle Inventory model, built to assess the production of current and future NCM batteries in China. The definition of the studied product system and LCI model is followed by the introduction of four different battery production scenarios, which were developed to assess the impacts of producing batteries in China, study the introduction of silicon in anodes and examine the effects of two novel cathode chemistries with increased nickel content (NCM622, NCM811). A detailed presentation of the production phase impacts is provided, based on the ReCiPe 1.08 Midpoint characterisation method. The production phase analysis is complemented by the development of a gate-to-gate model, assessing the environmental impact of using a LIB in a passenger vehicle in China.
The results indicate that the GWP of producing a LIB in China is 250 kg CO2-eq (battery kW h)-1, which is 40% higher than previously estimated (Ellingsen et al., 2014) and significantly higher than earlier reported values for China (Hao et al., 2017; Yu et al., 2018). The mismatch with the latter two studies is due to the fundamentally different assumptions made when modelling the production phase. This work provides the means to make sensible comparisons, using the same model and assumptions, and accurately benchmark the performance of different scenarios. It is shown that copper production for anode current collectors makes the most important contribution towards all human toxicity and ecotoxicity categories, with the next most important contribution coming from nickel sulfate production for mixed metal oxide cathodes. Furthermore, the manufacturing of next-generation LIBs is estimated to have a slightly increased impact intensity on a per battery pack basis, with the increased nominal energy capacity effectively reducing the impacts on a per kW h basis. The use of LIBs in China primarily affects the GWP, as a result of the high coal intensity of the local electricity mix.
References
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Figure 1