Comparison of the Environmental impact of 5 Electric Vehicle Battery technologies using LCA

Transcription

1 Comparison of the Environmental impact of 5 Electric Vehicle Battery technologies using LCA Julien Matheys 1, Jean-Marc Timmermans 1, W out Van Autenboer 1, Joeri Van Mierlo 1, Gaston Maggetto 1, Sandrine Meyer 2, Arnaud De Groof 2, W alterhecq 2, PeterVan den Bossche 3 1 Vrije Universiteit Brussel, Department ofelectrical Engineering and Energy Technology, Belgium 2 Université Libre de Bruxelles, Centre d Etudes Economiques et Sociales de l Environnement, Belgium 3 Erasmus Hogeschool Brussel, Departement Industriële W etenschappen en Technologie, Belgium Abstract The environmental assessment of various electric vehicle battery technologies (Lead-acid, Nickel- Cadmium, Nickel-metal hydride, Sodium nickel-chloride, Lithium-ion)was performed in the context ofthe European end-of-life vehicles directive (2000/53/EC).An environmental single-score based on a life-cycle approach, was allocated to each ofthe studied battery technologies through the combined use ofthe SimaPro software and ofthe life cycle impact assessment (LCIA)method Eco-indicator99.The allocation ofa single-score enables determining which battery technology is to be used preferably in electric vehicles and to indicate how to furtherimprove the overall environmental friendliness ofelectric vehicles in the future. Keywords Electric vehicles, Battery technologies, environment, life-cycle analysis 1 INTRODUCTION The large-scale implementation of battery and hybrid electric vehicles as substitutes for internal combustion engine (ICE) vehicles can form part ofthe solution to modern society s challenges such as urban airpollution, fossil fuel depletion and global warming [1]. This statement is valid independently of the electricity production mix.evidently when using renewable energy sources, the beneficial e fects of applying these technologies are enhanced [2].W hen it comes to the environmental evaluation ofelectric vehicles, the battery is often considered as the majorenvironmental concern. W hateverthe environmental impact ofthe battery might be compared to the complete impact of the electric vehicle, the environmental impact ofthe di ferent battery technologies should be assessed in orderto determine which technology should be preferred.this assessment was performed through the SUBAT-project.The aim is to evaluate the opportunity to keep nickel-cadmium traction batteries for electric vehicles on the exemption list of Directive 2000/53 on End-of-Life Vehicles.The project delivers a complete assessment ofcommercially available and forthcoming battery technologies forbattery-electric and hybrid electric vehicles (lead-acid, nickel-cadmium, nickel-metal hydride, lithium-ion, sodium-nickel chloride.). The assessment is based on technical, economical and environmental evaluations ofthe di ferent battery technologies.in this paper, only the environmental analysis is presented. The impacts of the di ferent technologies should be analysed individually to allow comparison and definition ofthe most environmentally friendly battery technology forelectric vehicles. A life cycle approach is a must when comparing the environmental impact ofthe di ferent battery technologies, because the main environmental burden can be located in di ferent life stages fordi ferent products. The analysis started with a listing of the available technologies for battery and hybrid electric vehicle application.afterwards, a model forthe di ferent battery types has been developed and introduced in the Simapro software tool.this model allows an individual comparison ofthe di ferent phases ofthe life cycle of traction batteries.as often during life cycle assessment (LCA) studies, the main di ficulty encountered while performing this study was the gathering ofappropriate, comparable and accurate data. First ofall, a description ofthe LCA methodology used to compare the di ferent technologies is given.in a second stage, a score is assigned to the di ferent life phases of the batteries.the final step is the compilation ofthese results to obtain an overall environmental score foreach battery type. The attribution of these scores is only possible after normalisation and weighting of the intermediate results.the overall scores ofthe di ferent batteries have been calculated, and the di ferent battery technologies can be ranked according to their environmental performances.finally, a sensitivity analysis has been performed to demonstrate the robustness ofthe results. 2 METHODOLOGY LCA allows the practitioner to study the environmental aspects and the potential impacts ofa product throughout its life from raw material acquisition through production, use and final disposal [3]. LCA is one ofthe most e ficient tools to compare the complete environmental burden ofdi ferent products.this is due to the fact that di ferent products may present environmental burdens in di ferent parts oftheirlife cycle. For example, one product may use less resources compared to anotherproduct during the use phase, but this may be at the cost ofmore resources used in its production phase [4]. The life cycle assessment ofa product will never be completely exhaustive; as a consequence, the LCA practitionercan choose to which degree ofdetail to model the assessed life cycle. However, this choice clearly influences the degree ofprecision and correctness ofa study. This study has been performed according to the fouriso standards specifically designed forlca applications (ISO ). 2.1 Assumptions To start with, an appropriate functional unit has to be defined.as the di ferent batteries have various life times and consequently provide varying performances as 97

2 regards the number of charge-discharge cycles, the total lifetime of the battery is not an appropriate functional unit. Different functional units were evaluated, but in the end, it was decided to choose a functional unit corresponding to a battery enabling the car to cover a specific range, with one charge. This one-charge range was set to 60 km when driving up to 80% depth-of-discharge of the battery. Furthermore, the environmental comparison will be based on the impacts of a battery pack (or of the different battery packs) enabling the vehicle to cover a km lifetime range, corresponding to (60km) charge-discharge cycles (80% depth-of-discharge). Depending on the technology, the required number of batteries needed for the functional unit has been determined. The considered battery is applied to a car with a net weight of 888kg (excluding the battery, including the 75kg driver). The system boundaries had to be defined. The assessed time period corresponds to the current state of the technology. The related other life cycles (industrial buildings, trucks, electric power plants, roads, etc.) have not been taken into account. Self-discharge was not considered for any of the assessed technologies because of the great dependence of this parameter on the way the vehicle is used. Neither was the maintenance of the batteries because of the opinion this impact is comparatively small. The electricity consumption has been considered using the European (EU-25, 2003) electricity production mix as a reference. It has been considered that the recycled materials have the same quality as the original materials. A collection rate of 100% was assumed and a recycling rate of 95% was used regarding the recuperated materials (except for the lead-acid recycling technology, which is much older and which is very mature, where the lead metal recycling rate is 98.3%). It was assumed that the electrolyte is neutralized before disposal (except for the lead-acid technology where 90% is recuperated and 10% is neutralized before disposal). Extraction of raw materials, Processing of materials and components, Use phase of the battery, Recycling of discarded batteries, Final disposal or incineration Figure 1 shows a schematized overview of the life cycle of an electric vehicle battery. 2.2 Impact assessment Information available in the literature, information obtained by intensively interrogating the worldwide industry and information obtained through commercially available databases allowed performing the inventory analysis. Starting from the data obtained from these sources, a process tree of each stage of the life of the functional unit was drawn and mass balances linked these subsystems to each other. As an illustration, a process tree for the lead-acid battery is presented in Figure 2. The analysis of the use phase of the batteries can be divided in 3 main parts. First of all, the use phase was studied for an ideal battery (mass = 0 kg, energy efficiency of the battery = 100%). In other words, this is the energy used to move the car (excluding the battery). Secondly, the influences of the varying masses and energy efficiencies of the different battery technologies have been taken into account. The energy consumption of the car varies slightly, depending on the mass of the battery. These differences in energy consumption have been simulated and calculated using the Vehicle Simulation Program (VSP) [5]. The life cycle impact assessment methodologies LCApractitioners have at their disposal often differ and the choice of the method to be used remains an important decision [6]. In this study, the chosen LCIA method is Eco-indicator 99 (hierarchist perspective) [7,8,9]. The purpose of this study is to determine which type of traction battery for electric vehicle applications is the most environmentally friendly. This analysis is performed considering the complete battery life cycle. Taking the important number of calculations needed to perform an LCA into account, the use of software is unavoidable. Figure 1:The schematized life cycle of a battery. The interaction of the functional unit with nature is assessed considering the following life stages of the battery: 98 PROCEEDINGS OF LCE2006

3 1 p LC Lead-Acid F.U Range (M1/R1+ R2) 1.08E3 6 p Assembly Lead-acid F.U. Range (M1) 1.21E4 MJ Electricity (due to mass) 2.08E4 MJ Electricity (due to battery efficiency ) 8.61E4 MJ Electricity (f or ideal battery ) 2.07E3 kg Disposal Scenario 1.09E p Assembly monblock lead-acid (opgesplitst) 1.21E4 MJ European mix (2002) 2.08E4 MJ European mix (2002) 8.61E4 MJ European mix (2002) 2.07E3 kg Recycling scenarios (R1 and R2) 1.09E p Separator (/kg) 139 p Case (/kg) 1.32E3 p Electrodes (/kg) 563 p Electroly te (/kg) 2.07E3 p Energy Mix Prodcution 1.03E3 kg Recycling scenario (R2) 1.03E3 kg Recycling scenario (R1) Figure 2: Illustration of a lead-acid process tree with SimaPro. On the basis of technical and commercial interest, a number of battery technologies have been selected and have been analysed quantitatively: lead-acid, nickelcadmium, nickel-metal hydride, sodium-nickel chloride and lithium-ion. Some of the data, required to compare the battery technologies, were extracted from the technical part of the Subat report ( and are presented in Table 1. Specific Energy (Wh/kg) Number of cycles of 1 battery pack Energy efficiency Losses due to heating Pb-acid % NiCd % NiMH % Li-ion % NaNiCl % 7.2% Table 1: Battery properties The results obtained by using SimaPro and ecoindicator 99, are expressed in eco-indicator points. One eco-indicator point being equivalent to one thousandth of the yearly environmental impact of one average European inhabitant. Next to this, to allow an easy comparison of the environmental rating of the different battery technologies, the results were all compared to the environmental impact of the lead-acid battery, which was taken as a reference. 3 RESULTS 3.1 Environmental impact assessment When considering the life cycle of the batteries, a significant impact on the environment is induced by the energy losses in the battery and the energy losses due to the additional mass of the battery (Table 2 and Figure 3). However, this impact is strongly dependent on the way electricity is produced. In the present calculations the European electricity production mix has been used, but this impact would be strongly decreased if renewable energy sources were used more intensively. When analysing the other part of the environmental impact of the battery (excluding the use phase completely), it appears that the lead-acid battery has got the highest impact, followed by nickel-cadmium, lithiumion, nickel-metal hydride and sodium-nickel chloride. Additionally, the recycling phase allows compensation of a significant part of the environmental impacts of the production phase. Eco-indicator Points Figure 3: Environmental impact (in Eco-indicator points) of the assessed technologies, including the losses due to battery masses and to battery efficiencies during use. When including the effects of the losses due to the battery (battery efficiency and battery mass), three technologies have a somewhat higher environmental impact compared to the other two. Inclusion of battery efficiency (table 1) results in a higher environmental impact for nickelcadmium and nickel-metal hydride batteries and in a lower one for lithium-ion batteries as compared to the others. 271 Additional Energy consumption due to battery efficiency Additional Energy due to battery mass Assembly + Recycling Pb-Ac NiCd NiMH Li-ion NaNiCl 13 th CIRP INTERNATIONAL CONFERENCE ON LIFE CYCLE ENGINEERING 99

4 Production Additional Recycling Total Energy Pb-acid NiCd NiMH Li-ion NaNiCl Table 2: Environmental scores (Eco-indicator points) of the life stages of the assessed battery technologies. 3.2 Sensitivity analysis A sensitivity analysis has been performed as the results need to be reliable. This analysis consisted in the modification of the assumptions made during the development of the model. The consequences of these modifications on the results were analysed. The sensitivity analysis assessed the effects of the assumptions (concerning average battery composition, energy consumption, etc.) and of possible variations in the collected data on the results. This analysis was performed by varying the assumed parameters. The implemented variations included calculations using different relative sizes of the components of the battery (10% more weight of one component, compensated by an equivalent decrease of another component). This resulted in the alteration of the proportional masses of the electrodes, electrolytes and cases. Also, the recycling efficiencies and rates were modified as well as the required energy to produce and recycle the different types of batteries. The calculations of the environmental impacts were performed over again for each of the alterations included in the functional unit data. Figure 4 summarizes the relative environmental scores as well as the results of the sensitivity analysis. Figure 4 only includes the results originating from production, recycling and the energy losses due to the battery mass and to the battery efficiency, but not the energy use in the hypothesis of an ideal battery, as this parameter doesn t vary from one battery technology to another. Moreover; this energy use is related to the use of the vehicle and not to the battery itself. The bars in Figure 4 represent the relative environmental impacts of every battery type, considering the lead-acid as a reference. The overall environmental score of the lead-acid battery has been set to 100. The error bars represent the intervals containing all the results obtained during the sensitivity analysis. Figure 4 shows that the assumptions didn t have any significant impact on the results as the conclusions remain the same within the error bars. This reveals the results of this study are reliable and demonstrates the robustness of the model. It should be noted that data concerning the environmental impacts of the electrolytes of the lithium-ion batteries were very difficult to obtain, as these electrolytes are very specific and new. As a consequence, these impacts have not been taken into account in this study. Also, no realistic data were obtained concerning the energy consumption during the manufacturing of the sodium-nickel chloride batteries. As a consequence, the environmental impacts of both the lithium-ion and the sodium-nickel chloride batteries could be slightly higher than the results shown in Figure 4. Environmental impact Lead-acid Nickelcadmium 97.7 Nickel-metal hydride 55.2 Lithium-ion 46.5 Sodium-nickel chloride Figure 4: Graphical overview of the relative environmental scores (including the sensitivity analysis). The lead-acid technology has been taken as a comparison basis and set to 100. Finally, other one-charge ranges have been assumed (50 or 70 km instead of 60 km). The results of the changes in the one-charge range are discussed separately from the other results of the sensitivity analysis, as they imply the establishment of new and different functional units, which are consequently not to be directly compared. The environmental impacts of the batteries presenting 50 and 70 km one-charge ranges, are shown in figure 5. These results are based on the same reference as figure 4 (lead-acid with a 60 km range = 100). It appears that the absolute environmental impacts are different from the ones obtained using the 60 km range. But the main trends, and thus the conclusions, stay the same within each of the assessed same-range batteries. 100 PROCEEDINGS OF LCE2006

5 Environmental Impact km 60km km Lead-acid Nickel-cadmium Nickel-metal hydride Lithium-ion Sodium-nickel chloride Figure 5: Graphical comparison of the environmental impacts of the different battery types when assuming three different ranges.the 60km range lead-acid battery has been kept as a comparison basis and set to CONCLUSIONS An essential conclusion is that the impacts of the assembly and production phases are compensated to a important extent when collection and recycling of the batteries is efficient and performed on a large scale. Excluding the energy losses occurring during the use phase (due to the battery efficiencies and the additional masses of the batteries), results in the following environmental ranking (decreasing environmental impact): lead-acid, nickel-cadmium, lithium-ion, nickelmetal hydride, sodium-nickel chloride. Looking at the global results, the following environmental ranking is obtained (decreasing environmental impact): nickel-cadmium, lead-acid, nickel-metal hydride, lithiumion and sodium-nickel chloride. Globally three battery technologies (lead-acid, nickel-cadmium and nickel-metal hydride) have very comparable environmental impacts. It can consequently be stated that, taking the sensitivity analysis into account, these technologies have a higher environmental impact than the lithium-ion and the sodiumnickel chloride batteries. When the calculations are performed with batteries having different energy storage capacities (batteries allowing the coverage of different ranges with a single charge), the main conclusions remain the same. In other words, three of the assessed technologies (lead-acid, nickel-cadmium and nickel-metal hydride) have a similar environmental burden, which is higher than the burdens of the other two technologies, lithium-ion and sodiumnickel chloride. However, these results could be mitigated due to the great rareness of environmental data concerning some aspects of the lithium-ion and the sodium-nickel chloride batteries (for example concerning the electrolyte). When analyzing the results of this study, it should be kept in mind that the environmental impacts of the batteries of electric vehicles are small compared to the impact of the rest of the vehicle as well as compared to its use when using the current electricity production mix (whatever the used battery technology might be). Additionally it should be remembered that the latter impacts are also small when comparing them to the environmental burden caused by vehicles equipped with internal combustion engines [1]. Therefore the results of this study should be seen as an indication on how to even enhance the environmental friendliness of electric vehicles. When compiling these conclusions with the technical and economic conclusions provided by the Subat project the following conclusion is drawn. The will to improve the environmental friendliness of transportation (by improving the environmental friendliness of batteries for electric vehicles) should not discourage the electric vehicle manufacturers. Some time should be provided to the vehicle manufacturers to adapt their production modes and to integrate some more environmentally sound battery technologies in their vehicles. During the discussions the consortium had with various stakeholders, it appeared this cannot be performed within 4 years from now (2006). ACKNOW LEDGMENTS This research has been made possible thanks to the support and funding of the European Commission through the 6th Framework Program (Action 8.1.B.1.6; EU-project n ). REFERENCES [1] Maggetto, G. & Van Mierlo (2001). Electric Vehicles, Hybrid Electric Vehicles and Fuel Cell Electric Vehicles: State of the Art and Perspectives. Annales de Chimie - Science des matériaux, 26 (4), [2] Van Mierlo, J., Timmermans, J.-M., Maggetto, G., Van den Bossche, P., Meyer S., Hecq, W., Govaerts, L. & Verlaak, J. (2004). Environmental rating of vehicles with different alternative fuels and 13 th CIRP INTERNATIONAL CONFERENCE ON LIFE CYCLE ENGINEERING 101

6 drive trains: a comparison of two approaches. Transportation Research Part D 9, [3] ISO (1997). Environmental management Life cycle assessment Principles and framework. International Standard ISO [4] Finnveden G. (2000). On the limitations of Life Cycle Assessment and Environmental Systems Analysis Tools in General. International Journal of LCA 5, [5] Van Mierlo, J. & Maggetto, G. (2004). Innovative Iteration Algorithm for a Vehicle Simulation Program. IEEE Transactions on vehicular technology 53 (2), [6] Dreyer L.C., Niemann A.L. & Hauschild M.Z. (2003). Comparison of Three Different LCIA Methods: EDIP97, CML2001 and Eco-indicator 99. International Journal of LCA 8 (4), [7] VROM (Ministerie van Volkshuisvesting, Ruimtelijke Ordening en Milieubeheer) (1999). The Ecoindicator 99: A damage oriented method for Life Cycle Impact Assessment. Methodology Report, Publicatiereeks productenbeleid, nr. 1999/36A. The Netherlands. [8] SimaPro (2004). Introduction to LCA with SimaPro, PRé Consult, Amersfoort, The Netherlands, pp. 71. [9] SimaPro (2005). Online 12th January 2005: [ ] CONTACT Julien Matheys Vrije Universiteit Brussel, Department of Electrotechnical Engineering and Energy Technology, Pleinlaan 2, B-1050 Brussels, Belgium, jmatheys@ vub.ac.be 102 PROCEEDINGS OF LCE2006