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Life cycle assessment of lithium-ion traction batteries

Despite increased awareness of climate change and governmental goals to reduce anthropogenic greenhouse gas (GHG) emissions, the trend of increasing GHG emissions continues. In consuming about half of global primary oil, the transport sector contributes to about one-fourth of energy-related GHG emissions. Road transport is by far the largest and fastest growing transport segment, mainly due to the rapidly increasing number of light duty vehicles. The estimated one billion light duty vehicles currently in operation are responsible for about half of the transport sector’s energy demand and GHG emissions. Due to increasing standards of living and economic activity, the number of light duty vehicles is expected to more than double by 2050. As such, reducing energy- and fuel carbon-intensities of these vehicles is crucial. Battery electric vehicles (BEVs) have been promoted as a promising alternative to conventional vehicles due to their zero tailpipe emissions and higher powertrain efficiency. However, the change in powertrain technology may introduce unfavourable environmental trade-offs. Because lithium-ion traction batteries are the core of BEVs, understanding their environmental impacts is essential. This thesis assesses the environmental characteristics of lithium-ion traction batteries and evaluates how these influence the overall environmental profile of BEVs.

Environmental impacts associated with the life cycle of a product are best analysed using the method referred to as life cycle assessment (LCA). LCA provides a systematic framework and process for assessing environmental impacts that occur in production, use, and end-of-life treatment of a product. The robustness of an LCA study hinges on its inventory data. Thus, we used industry data where these were available.

This work resulted in the five articles that are included in this thesis. Article I assesses the environmental impacts associated with the production of a lithium-ion traction battery pack and provides a detailed cradle-to-gate inventory based on primary industry data. Article II discusses the energy demand in battery production and the extent to which production volumes can explain the differences in energy demands in the LCA literature. Article III investigates how increasing the battery pack size and range influences the life cycle GHG emissions of BEVs. The article also evaluates the importance of the electricity and its energy sources to these life cycle emissions. Article IV considers prospective materials that may improve the technical performance of energy storage systems used in electric vehicles. Inspired by the holistic life cycle approach of LCA, the article develops an environmental screening framework and evaluates the environmental attributes of nanomaterials in lithium-ion battery cells and proton exchange membrane fuel cells. Article V considers the underlying data and assumptions in LCA studies of lithium-ion traction batteries to identify the causes of differences in reported results.

We find that the life cycle environmental impacts of a lithium nickel-cobalt-manganese oxide traction battery pack are considerable. The production phase is particularly impact intensive due to the significant use of metals and energy. Three production chains associated with the battery cells are found to be particularly impact intensive: manufacture of battery cells, copper in the negative current collector, and nickel sulphate in the positive active material. The other cell and battery pack components have smaller contributions. Impacts associated with the use phase and end-of-life treatment are less significant than those pertaining to production. The indirect impacts associated with the electricity use during operation largely depend on the conversion losses, battery weight, and the energy sources used to generate the electricity that charges the battery. Environmental impacts associated with end-of-life treatment may differ as there are several different industrial recycling schemes for lithium-ion batteries.

Predictably, larger battery packs with more battery cells are more impact intensive than smaller battery packs with fewer cells. Thus, at the current state of the technology, there is a trade-off between driving range and environmental benefits. Prospective electrode materials can potentially allow for longer driving ranges through higher gravimetric energy density. We evaluate nanostructured electrode materials and find that there are indeed promising candidates that may allow for lithium-ion cells with higher gravimetric energy density. However, the use of nanostructured electrode materials may also result in higher production impacts as the synthesis of nanomaterials is generally energy intensive, but this depends on the electrode materials and the methods used to synthesise them.

The large environmental impacts of traction batteries holds repercussions for BEVs. The production of the battery pack alone can result in higher environmental loads in some impact categories than the production of a conventional vehicle. However, BEVs are more energy efficient than conventional vehicles and can compensate for the higher production impacts by having lower use phase impacts, but this depends on the impact intensity of the electricity. As such, BEVs introduce environmental trade-offs between life cycle benefits and disadvantages. Because increasing battery pack size and range result in higher life cycle impacts, BEVs with longer driving ranges generally tend to have larger life cycle environmental impacts than those with shorter driving ranges. In terms of GHG emissions, the ability of BEVs to compensate for the higher production impact depends on the carbon intensity of the electricity used for charging. To ensure and maximize the environmental benefits of the electric powertrain, it is imperative that batteries last as long as the vehicles they power. Production of replacement cells may compromise the ability of BEVs to compensate for higher production impact.

In conclusion, this thesis provides new information and understanding of the environmental characteristics of lithium-ion traction batteries through five articles. The environmental burdens associated with traction batteries hold implications for the environmental sustainability of BEVs. Based on our findings, we identify impact reduction measures that may reduce the environmental burdens associated with lithium-ion batteries.

Name

Linda Ager-Wick Ellingsen

Institution

Norwegian University of Science and Technology (NTNU)

Advisor

Anders Hammer Strømman

Degree

Doctoral

Expected graduation

2017

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