Researchers at the Norwegian University of Science and Technology (NTNU) have designed and applied a life cycle analysis to examine three of the leading vehicle battery types to determine which does the best job of powering the vehicle while causing the least amount of environmental impact during its production.  For most the knowledge is clear that the lithium-ion technology seems best, but careful analysis from raw materials to disposal is a major factor that can reveal some advantages in the investment portion of the battery storage equation.

The NTNU team’s results have been published in the April 20, 2011 edition of the scientific journal Environmental Science and Technology. The study shows, to some relief that when the full battery cycle is considered, iron phosphate lithium-ion (LFP) batteries come out on top followed by the nickel cobalt manganese lithium-ion (NCM) and the nickel metal hydride (NiMH) battery.

The team members are Guillaume Majeau-Bettez a PhD candidate in NTNU’s Industrial Ecology Programme; Troy R. Hawkins, a researcher in the programme; and Anders Hammer Strømman, an associate professor in the program.

Battery Construction Components. For more info check the study paper linked in the post's text. Click image for the largest view.

To prepare the paper the team conducted a life cycle analysis of the three battery types and looked at 11 different types of environmental impacts from their production. These impacts included everything from greenhouse gas emissions to freshwater ecotoxicity, freshwater eutrophication and human toxicity at the front end of the raw material to construction stage.

For high density energy storage hopes the team was surprised to find that except for ozone depletion potential, the NiMH battery performed significantly worse than the two Lithium-ion batteries for all impact categories. The researchers attributed this difference to the greater use phase efficiency of Li-ion relative to NiMH, and the fact that each kilogram of Lithium-ion battery is expected to store between 2 to 3 times more energy than the other battery types over the course of its lifetime.

The press release offers the team observations, “The NCM and LFP batteries contain at least an order of magnitude less nickel and virtually no rare earth metals. Among Lithium-ion batteries, our analysis points to overall environmental benefits of LFP relative to NCM, which can be explained by a greater lifetime expectancy and the use of less environmentally intensive materials.”

Digging in deeper the team found for all three batteries, the energy requirements for their manufacture were a major cause of greenhouse gas emissions. One component of the analysis demonstrated the environmental significance of using polytetrafluoroethylene as dispersant/binder in the electrode paste.  Its production was responsible for more than 97% of the ozone depletion potential of all three batteries, along with 14 -15% of the greenhouse gas production from the two Lithium-ion batteries, mostly due to the halogenated methane emissions.

The final shipping and the production of the cell containers, module packaging, separator material, and electrolyte contribute relatively little to causing environmental damage, with collectively less than 10% of any impact category.

The paper is a trove of worthwhile data for making battery choices.  The team points out the importance of the choice of the functional unit for the life cycle analysis. While the production of NiMH causes the least energy requirement and greenhouse gas emissions impact per kilogram of battery in the simplest calculation, its lower energy density makes it score worst both relative to its nominal energy capacity and the researchers’ storage-based functional unit.  That suggests its cheaper to buy – but costs more to use.

The team offers a sensible observation, “A shift from NiMH to Li-ion may thus be viewed positively. Though associated with important uncertainties, our results point to a higher than expected level of environmental impacts for the production and use of traction batteries. This inventory and life cycle analysis provide a basis for further benchmarking and focused development policies for the industry.”

In non-academic terms that means NiMH subject to some uncertainty, falls short compared to Lithium-ion technology in the battery building stage of a battery lifecycle.  Lithium-ion’s lower weights, less total materials and lower energy demands offers significant savings over Nickel Metal Hydride when battery capacity is the metric that matters to consumers.  Spreading the manufacturing energy use and emissions over the battery capacity and lifecycle put Lithium-ion up on top.

In electric vehicles the seemingly higher Lithium-ion cots will be counter balanced by less weight or more range.  The next question is going to be about the recycling costs across the range of electric vehicle batteries.  That field, which is still quite immature as the demand isn’t there yet, will offer even more information on the long-term costs of electrical storage and how the technologies will compare.

As chemical to electricity conversion improves, and efficiency gains come, the battery demand will be leavened.  While Lithium-ion isn’t cheap or likely to ever get cheap, it’s the technology of the day and looking better with each research step.


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