1 Introduction

As society moves from fossil-fuel vehicles towards electric vehicles (EV), it is able to selectively access cheaper, cleaner, and renewable electricity sources; however, the life cycle profile shifts from use-related emissions burdens to more material and manufacturing associated concerns. Light duty vehicles are responsible for approximately 10 % of global energy use and greenhouse gas emissions (Hawkins et al. 2013; Solomon et al. 2007); whereas, on a cradle-to-grave basis, the resource and environmental loading at the production stage of EVs can be largely offset compared to fossil-fueled internal combustion engine formats by advantages at the use phase (Ellingsen et al. 2014; Hawkins et al. 2013; Simon and Weil 2013). Nonetheless, a major consideration, and the subject of this paper, is the initial material, environmental, and energy costs associated with electric vehicles, particularly the production of large lithium-ion (Li-ion) battery packs.

Commercialization of EVs and plug-in hybrid vehicles by major automotive manufacturers is underway and technological advances in battery performance combined with the regulatory push for low and zero-emission vehicles have made common electric mobility a growing reality (Bennion and Thornton 2009; MacLean and Lave 2003). Significantly, at the end of its useful life in the vehicle, EV Li-ion battery packs will retain approximately 80 % of their performance, allowing the pack to be applied in a second application, such as a stationary energy storage system (ESS) (Ahmadi et al. 2014a, b; Heymans et al. 2014). As such, used EV batteries can be re-purposed for a second use. Re-purposing requires a modest effort for disassembly, testing for degradation and failure, packaging the batteries for second use, adding electrical hardware, control systems, and safety systems to the re-purposed packs (Ahmadi et al. 2014b; Cready et al. 2003). Re-purposed batteries present energy and environmental opportunities to store intermittent low-emission renewable energy such as wind and solar by harmonizing supply and demand, or to ease electrical grid congestion by providing time of day electricity load leveling in a distributed fashion (Ahmadi et al. 2014a; Shokrzadeh and Bibeau 2012). Reuse may be particularly desirable from an economic perspective given that the recycled value of end-of-life battery packs may be diminishing if lower cost iron and manganese chemistries become popular (Wang et al. 2014). Cascaded use also has the potential to mitigate waste disposal risks, for example in the context of emerging regulations and concerns of handling and transporting spent Li-ion batteries (Richa et al. 2014). The technical and economic features of battery reuse have been proposed by automakers, governments, and utility companies (Cready et al. 2003; Williams and Lipman 2010; Wolfs 2010). However, there are limited studies regarding environmental assessment of second use of the batteries (Casals et al. 2015; Cicconi et al. 2012; Richa et al. 2015).

In our previous studies, factors affecting the state-of-health of the EV Li-ion battery were assessed and new concept of energy efficiency fade was introduced as an important limitation for reuse of EV batteries (Ahmadi et al. 2014a). Moreover, the potential impact of battery reuse on life cycle greenhouse gas emissions and energy usage of the battery in first and second uses was evaluated, the significance of quantifying the comprehensive environmental impacts of reuse of EV batteries was emphasized (Ahmadi et al. 2014a, b). Other studies considered operational simulation with respect to the use of the technology only, including economic and policy considerations (Heymans et al. 2014; Van Lanen et al. 2015). Extending this work, in order to investigate environmental benefits and impacts of this technology more broadly, the present study assesses a Li-ion battery pack through its entire life cycle including manufacturing, EV use, re-manufacturing, reuse into stationary application and recycling. Future publications are anticipated on risk, safety and business feasibility of EV battery reuse.

Because of comprehensive and systematic view of impact categories across all stages of the life cycle of a product system, life cycle assessment (LCA) has been applied to assessing the environmental aspects of EVs (Hawkins et al. 2013; Majeau-Bettez et al. 2011; Zackrisson et al. 2010). In the present study, two scenarios are compared through their stages from an environmental assessment standpoint. “Conventional” scenario includes mobility by an internal combustion engine vehicle (ICEV) and stationary application of reactive power from a natural gas peaking power plant; while “cascaded” scenario includes mobility by an EV and a stationary energy storage system (ESS) provided by re-purposed vehicle batteries that are charged at an optimal time of clean electricity availability, thus avoiding the use of peaking power plants. Note that the cascaded scenario will also avoid the need to construct reactive peak power plant capacity in the first place (recognizing that in itself this potentially provides significant environmental advantage). Avoidance of new construction of peaking and back-up power generation capacity is a more complex political and electrical reliably question beyond the scope of the current work.

This paper provides several contributions. First is a methodological contribution regarding the use of a complex functional unit useful for product systems with cascaded (multiple) applications. Second is the assessment of the potential environmental costs and advantages of reusing of EV Li-ion battery packs in a stationary ESS. Third are insights into the importance of the state-of-health of a Li-ion battery and its significance in the energy efficiency of the second use application.

The LCA study is conducted to assess the Li-ion battery pack during its life cycle, including battery manufacturing, use in the EV, re-manufacturing, reuse in a stationary ESS, and recycling. To address uncertainty of predicting aspects of the state-of-health of the battery, a sensitivity analysis is surveyed regarding key parameters is presented.

This study uses comprehensive information about environmental concerns of the re-purposed Li-ion battery technology reused in the ESS to help decision-makers in the field of power generation and energy storage systems to improve the future strategies and policies. It is targeted that the results of this study would be supportive for making decision about re-purposing of used batteries after their end-of-life in the EVs and utilizing them in the stationary applications. Moreover, the knowledge and structure of this LCA study could be applicable for battery production companies and automakers in their choices about future electric mobility.

2 Methods

The product system of this study is a Li-ion battery pack used in two applications to deliver energy in a cascaded manner: the first is in an EV that provides personal transportation and the second is in a stationary power ESS. In this study a Li-ion battery pack with cell chemistry of LiFePO4 cathode and graphite anode is considered. It is assumed that the production of this lithium material is conducted by hydrothermal synthesis through the reaction of iron sulfate, phosphoric acid and lithium hydroxide (Majeau-Bettez et al. 2011). The material content of battery components and the processes used to manufacture, use, re-manufacture, reuse, and recycling phases are estimated based on secondary data and stated assumptions (Majeau-Bettez et al. 2011; Hischier et al. 2007; Simon and Weil 2013). Other Li-ion chemistries are in use or under development that involve different materials, including more significant critical materials such as cobalt, but these are not considered in this study; however, the study results are still useful.

There are two sequential functions performed in the cascaded product system, and this presents a multi-function system problem that is well identified in LCA (Ekvall and Tillman 1997). However because the system focuses on a component (the battery pack) rather than a final end-product (e.g., the vehicle), there is a methodological complication. This kind of cascaded system is relatively unusual in LCA but is identified as especially important to battery reuse (Richa et al. 2015), given the economic scale of potential cascaded use. The co-product problem approach used in the present study is a system expansion, which is favored in ISO guidance because it avoids co-product allocation; however, the reference flow selected to describe the functional unit is somewhat unusual. The battery pack provides storage of energy for use in the EV for transportation and again for energy storage in a stationary application. These two energy deliveries are summed over the full-life of the battery pack, and it is this total energy provision that is used as the functional unit, measured in kWh.

The battery pack is assumed used for eight years in the EV, followed by re-manufacturing into the stationary ESS application for ten additional years. The assumption of the 8-year life time is based on auto manufacturer warranties for the battery lifespan in the electric vehicles. The choice of 10 years for the ESS is an assumption made in this study partly because it is consistent with and comparable to previous published studies (Ahmadi et al. 2014a, b). The technical rationale is that in an ESS batteries can be carefully managed for power load, climate, depth-of-discharge, and other factors because of the nature of stationary position in comparison to a more demanding mobile EV application. Moreover, if in order to support the investment in an ESS, a significant lifetime is need to justify the cost of the power plant and installation. Based on additional details listed below, over the 8-year life of the EV, the battery pack delivers 35,040 kWh and the vehicle provides 160,000 km of transportation service. For the conventional system, this distance is converted into the quantity of gasoline fuel that would be consumed in a conventional ICEV, thus providing equivalency of transportation distance for mobility in the first use phase. The second use is similarly compared: over ten years each of the ESS and the conventional grid-electricity system provide 29,004 kWh of energy for stationary use (like a commercial building or residential household), making this portion of the energy system equivalent and comparable. Therefore, the battery pack and the corresponding conventional system each deliver a total of 64,044 kWh of stored energy over the 18-year life. In the LCA, to facilitate calculation and comparisons, this quantity is reduced to a measure of “one kilowatt-hour (kWh) delivered by the battery pack over its full life,” which is used as the reference flow.

The system boundary of this study contains the entire manufacturing sequence of Li-ion battery, first use in the EV, re-purposing, second use in the ESS, and recycling. This includes all major processes, significant materials and energy flows to the point where materials are extracted or emitted to the natural environment (see also Electronic Supplementary Material). Battery production and vehicle production are assumed to occur in East Asia. Use, re-manufacturing, and reuse phases are assumed to occur within the Province of Ontario, Canada. This geographic boundary therefore relies on the Ontario electricity grid mix (and associated aggregate emission factors) for vehicle use and reuse in the ESS as the reference cascaded scenario. The Ontario grid (IESO 2012a, b) provides power that is modestly clean: a mix of nuclear (56.5 %), hydroelectricity (22.3 %), natural gas (14.6 %), coal (2.8 %), and renewables (3.8 %). The time boundary for production and use phase of vehicle life time is assumed to be 8 years. In other words, the study covers the current situation and it is estimated that future Li-ion batteries utilization in EVs will be in a larger scale than present.

Figure 1 provides details on unit processes in the study system (see Electronic Supplementary Material for more details). As can been seen, three main steps are defined in the system boundary including step A (battery pack manufacturing (1A), battery pack first use in EV (2A)), step B (battery pack re-manufacturing (1B), battery pack second use in ESS (2B)), and step 3 (recycling). Steps 1 and 3 have been assessed in previous studies and this study attempts to advance the results for EV application based on Ontario grid mix. The new concept of this analysis is related to step 2 which assesses the environmental impacts of EV batteries re-purposing and reusing in the different application. As summarized in Fig. 1, the cell container, module and battery packaging and electronics of the used battery pack are newly made during re-manufacturing, and it is assumed that the required electricity and heat for re-manufacturing processes would be 30 % of that required in the original first manufacturing process. The reuse phase includes charging and discharging of the re-purposed Li-ion battery in an ESS, with electricity provided by Ontario grid mix for charging the battery during its extended life in ESS. The total power delivered by a re-purposed Li-ion battery pack during its extended life is calculated based on following assumptions:

Fig. 1
figure 1

Flow-diagram of the system functions and related unit processes

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  • Daily peaking power delivery of a re-purposed battery is about 6.079 kWh.

  • Assumed roundtrip efficiency for this process is 85 % and transmission efficiency would be 90 %.

  • A rate of 1 C is defined as the current that is equivalent to the full capacity of the battery being charged or discharged.

  • It is assumed that every day one cycle (charging/discharging) happens, so the total number of the battery cycling would be 3650 cycles over ten year in the ESS.

  • Depth of discharge (DOD), 75 %

Step 3 qualitatively considers the significance of recycling process of Li-ion batteries, which is based on Ecoinvent databases of the laptop Li-ion batteries. Recycling processes for the Li-ion batteries are included; however, there is no credit applied to the recovery of materials at the end-of-life: this assumption is conservative for the comparison being made, as in the present study the scope is one Li-ion battery, not the whole vehicle. Note that the recycling step for the Li-ion battery is not changed by the re-purposing step, as outlined in our earlier work (Heymans et al. 2014).

The chosen method to weight and model the results is classification and characterization with ReCiPe 08 Midpoint (H) which is applied into the SimaPro, LCA software tool (Saha and Goebel 2009). ReCiPe Midpoint (H) version 1.06, includes 18 impact categories and includes all the impact categories selected for this given the availability of LCI data). ReCiPe is a follow-up of two methods: Eco-indicator 99 and CML 2002 methods. It integrates and harmonizes midpoint and endpoint approach in a consistent framework (JRC 2010). Cumulative energy demand (CED) method is also used to express the primary energy use over the whole life cycle. This method contains direct use as well as the indirect use of renewable and nonrenewable resources (Frischknecht et al. 2007). Given the data sources used, 6 of the possible 18 ReCiPe indicator categories are calculated in final LCIA category results: global warming potential (GWP), particulate matter formation potential (PMFP), freshwater eutrophication potential (FEP), photochemical oxidant formation potential (POFP), metal depletion potential (MDP), and fossil depletion potential (FDP). Nonetheless, this includes categories related to air, water, and natural resources is sufficient to cover the main environmental areas identified in the literature as relevant to EV battery analysis (Ellingsen et al. 2014; Hawkins et al. 2013; Majeau-Bettez et al. 2011; Notter et al. 2010).

It is assumed that 17 % of the battery pack mass is packaging, plus 3 % for the battery management system (BMS), which comprises electronics and casing. There is an uncertainty about the conceptual border between “manufacturing” and “material production”; it is deemed that “material production” is taken as being limited to pure metals, simple plastics, or raw chemicals (Majeau-Bettez et al. 2011; Rydh and Sandén 2005). Freight transportation is excluded from this assessment because of its negligible portion in the raw material usage and emissions. The manufacturing facilities are not included in this study. The grid mix is estimated based on Ontario long-term plans and predicted mix from 2012 to 2030 (IESO 2012a, b, 2013; LTEP 2010; Mallia and Lewis 2012).

In order to have a comprehensive perspective of environmental implications of battery pack performance during its extended lifetime, the comparison for the first use of the battery pack in EV is to an ICEV based on results derived from a public and transparent study by Hawkins et al. (2013). The environmental performance of the re-purposed battery pack in the second use is compared to natural gas generated power, which is chosen as the source for new marginal production in the province. Figure 2 presents the main scenarios to represent the complex functional unit that includes both first use and second use together: the “conventional” system (ICEV plus stationary power with natural gas) and the “cascaded” system (EV plus ESS by re-purposed battery pack). Both are assessed in their provision of one kilowatt-hour delivered by the battery pack. In order to conduct the comparison for the mobility phase, the results of Hawkins et al. (2013) study that uses a functional unit of 1 km driven by the vehicle are adjusted to the 1 kWh reference flow used in the present study, using United States Environmental Protection Agency (EPA) datasets (see Electronic Supplementary Material).

Fig. 2
figure 2

Overall comparison flowchart of cascaded and conventional systems. Analysis of the processes in the dashed-line boxes is based on previous research (largely Hawkins et al. 2013) whereas processes indicated by solid-line boxes provide new analysis

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3 Results

3.1 Energy use

The primary energy use over the Li-ion battery pack life cycle is expressed by CED, as depicted in Fig. 3. Five main energy sources are considered: non-renewable (fossil), non-renewable (nuclear), renewable (biomass), renewable (wind, solar, geothermal), and renewable (water). Regarding the battery charging source of electricity, renewables such as biomass, wind, solar, and geothermal have negligible portions of associated environmental impacts of energy usage of the battery pack in comparison with other energy sources. Use phase energy usage is significantly higher than other phases; however, the energy consumption of reuse phase is also major. As mentioned above, long-term charging of the battery pack, 8 years in first use in EV and 10 years in second use in ESS by Ontario electricity grid mix which uses significant nuclear and fossil fuel resources. As would be expected, high percentages of nuclear source usage are related to use and reuse phases because of importance of this energy source in Ontario grid mix. The main source of energy use in manufacturing phase is associated with heat from natural gas and European electricity grid mix, which have been applied mostly for production of positive electrode, cell container, and BMS. The energy consumption of recycling of the battery pack is negligible in contrast with energy usage of the battery pack life cycle.

Fig. 3
figure 3

The Li-ion battery pack energy usage (cumulative energy demand) for phases of the battery pack life

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3.2 Environmental impact category indicator results

Results for Li-ion battery pack during its entire life cycle are presented in Fig. 4. The results of the study indicate that the potential environmental impacts of the Li-ion battery pack differ significantly between its life cycle phases. In Fig. 4, life cycle of the battery is divided into five phases: battery pack manufacturing, use in EV, re-manufacturing, reuse in ESS, and recycling at the end-of-life. As can been seen, all impact indicator results associated with the manufacturing phase of the battery pack life are considerably greater than other phases except fossil depletion impact which use phase has more significant impact. Metal depletion and FEP are the highest relative impacts of the battery pack manufacturing phase, while they are the lowest impacts of other phases. Figure 4a presents GWP associated with the battery pack over its life cycle. The total amount of greenhouse gas emissions is 0.25 kg CO2 eq. per 1 kWh delivered by the battery pack. The result shows that 40 % of this quantity is generated from battery pack manufacturing phase; however battery use and reuse produce significant emissions (31 and 26 %). Manufacturing of the positive electrode is the main source of the GWP indicator in the manufacturing phase, which significantly generated from polytetrafluoroethylene production (14 %). Major contributions to the GWP for battery pack use and reuse are the electricity source (Ontario grid mix). Because of long-term (18-year) usage of electricity for the battery charging, greenhouse emissions would be more meaningful and shows that the magnitude of the emissions of battery pack manufacturing is greater than those of use and reuse phases. Re-manufacturing phase contributes 3 % to the GWP, which majorly results from heating by natural gas throughout re-assembly process.

Fig. 4
figure 4

Life cycle impact assessment indicator results for 1 kWh of power delivered by the Li-ion battery pack cascaded use for six indicators: a global warming potential (GWP), b photochemical oxidation formation potential (POFP), c particulate matter formation potential (PMFP), d freshwater eutrophication potential (FEP), e metal depletion potential (MDP), and f fossil-resource depletion potential (FDP)

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There is a similar trend for POFP associated with battery pack manufacturing, use and reuse phases. BMS production is the major source of photochemical oxidants in manufacturing, mostly associated with the gold applied in the integrated circuit of this system. It is notable that the main source of this emission in the use and reuse phases (35 %) associated with the electricity grid mix, generated from natural gas power plants. The production of module and battery packaging is the main source of NMVOC emissions of the re-manufacturing phase. Figure 4c shows PMFP throughout the battery pack life and illustrates the significant impact of manufacturing, use, and reuse phases, over 18 years in contrast with the manufacturing phases. Production of the negative substrate generates the main part of this emission for manufacturing phase, which largely is related to use of copper in this component. Use phase of the battery pack life also have a significant portion in the particulate matter which is related to Ontario grid mix in which natural gas plays the main role in this emission. The re-manufacturing phase is minor in the amount of emissions, and slightly less than recycling phase. In Fig. 4d, the FEP is illustrated for different phases of the pack life. Likewise other environmental categories, manufacturing is the main sources of this emission with this difference that the use and reuse phase have minor portions in the total fresh water eutrophication (5.7 and 4.7 %) and re-manufacturing phase has less than 1 % of P eq. emissions; however, it is even lower than amount of P eq. emissions of recycling phase. The negative substrate production has the greatest portion of FEP in the manufacturing phase (36 %).

As can been seen in Fig. 4e, metal depletion potential is an anomaly compared to the other indicators. Ninety-four percent of this indicator is associated with the manufacturing phase which mainly relates to negative electrode substrate and subsequently to copper production (57 %). BMS production is significant for metal depletion indicator of the manufacturing phase, related to integrated circuit (20 %): gold is used in the production of the integrated circuit and is the main contribution to this indicator. Chromium used in the BMS has higher contribution to metal depletion than tin used. Aluminum is used in the cell container, and nickel and iron in the BMS. The main metal depletion associated with the use and reuse phases of the battery pack life cycle are related to uranium of nuclear source of electricity grid mix. Re-manufacturing forms 0.47 % of this impact category, related aluminum used in the battery pack packaging.

As can been seen in Fig. 4f, the use phase is the main source of the fossil depletion indicator (37 %). The natural gas used in power plants in Ontario is the major contribution to the fossil depletion impact indicator (53 %). Hard coal in electricity generation is the next most significant fossil source. Reuse phase is same due to the battery pack is powered by the same grid mix. The fossil depletion impact associated with the manufacturing phase is largely due to medium voltage electricity, which is used in the battery pack production and whose generation includes hard coal and lignite. Fossil depletion impact is the most significant impact category of re-manufacturing phase and it generates from cell container and battery packaging production. The battery packaging is the main reason of fossil depletion impact of the re-manufacturing phase.

3.3 Comparison to conventional system

As mentioned in the “Methods” section, in order to have a comprehensive evaluation of the battery pack environmental performance during its life cycle, a comparison is conducted between the battery pack first use in EV and ICEV powered by gasoline (Hawkins et al. 2013) as well as the battery pack second use in ESS and stationary application powered by natural gas sources. Indicator results are presented in Fig. 5. Five main phases of the battery pack life are compared with conventional scenario including the battery pack and EV powertrain production versus ICEV powertrain production, battery pack first use in EV versus ICEV use, battery pack re-manufacturing, re-purposed battery pack second use in ESS versus stationary systems powered by natural gas, and recycling of the battery pack. Note that for the conventional scenario, the environmental burdens of re-manufacturing and recycling phases are zero, as these are not present.

Fig. 5
figure 5

Life cycle impact indicator results for cascaded use of Li-ion battery pack versus conventional ICEV system, for six life cycle impact assessment indicators: a global warming potential (GWP), b photochemical oxidation formation potential(POFP), c particulate matter formation potential (PMFP), d freshwater eutrophication potential (FEP), e metal depletion potential (MDP), and f fossil-resource depletion potential (FDP)

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For the powertrains alone, across all the environmental indicators considered, the EV powertrain production is higher than for the ICEV powertrain production. This result mostly comes from the needed material for large battery packs production. The obvious difference between numbers of greenhouse gases in the use of the ICEV versus the EV highlights the effect of electrified vehicles and clean grid mix applied in the battery charging on the GWP.

As shown in Fig. 5, for the full product systems (mobility plus stationary power) in conventional and cascaded scenarios, indicator results show that conventional scenario yielded higher environmental costs than cascaded scenario regarding selected impact category indicators, except metal depletion. The higher metal depletion impact of the cascaded scenario, as shown in Fig. 5, originated mainly from EV powertrain production, particularly from the battery production. The differences were small for particulate matter formation, but particularly large for freshwater eutrophication. The fossil fuel (gasoline) used in ICEV use phase caused the larger impact for freshwater eutrophication with the conventional scenario.

3.4 Sensitivity analysis

A number of factors can be considered in a sensitivity analysis. The effect of electricity mix was analyzed and results were found to be as obvious if the grid is shifted from Ontario to a cleaner renewable energy mix or to higher emission factor sources (see “Discussion”). Previous research on EV battery reuse examined energy and greenhouse gas impacts over first-use and second-use lifetimes (Ahmadi et al. 2014a, b), and identified the importance of battery degradation as a determinant of feasibility of reuse. This issue is examined in more detail in this section.

The loss of the state-of-health, due to degradation of chemistry in the Li-ion battery over its life cycle is assessed. Energy efficiency is assumed to fade by 20 % after eight years in the vehicle, and an additional 15 % after ten more years in the stationary application, for a total energy efficiency degradation of 35 % (Ahmadi et al. 2014a). The energy efficiency fade follows an exponential trend during about first year of the battery cycling in EV (first 300–350 charge/discharge cycles) and then it follows a progressive linear trend. Additional, after being re-purposed and used in an ESS, the battery energy efficiency continues to fade resulting in a further 15 % loss (Ahmadi et al. 2014a). This scenario is compared to a reference scenario where energy efficiency fade is assumed to be zero. Fade in energy efficiency affects the greenhouse gas emissions and energy use of Li-ion batteries by increasing electricity usage during both phases of the battery pack’s life. The manufacturing, re-manufacturing, and end-of-life phases of the battery pack are not affected; consequently the effect on non-energy indicators like POFP and FEP is negligible, and on metal depletion is about 2 %. However, the fossil depletion indictor increases 17 % during first use and by 25 % during second use; and GWP increases 47 and 67 %, respectively. This confirms that battery degradation is as an important factor, particularly as it affects energy efficiency in the environmental performance in an ESS using reused battery packs.

4 Discussion

4.1 Electricity mix

The energy sources in electricity generation are important variables in LCA studies, and vary significantly from region to region. The baseline Ontario grid is a moderately clean mix of energy generation technologies (over 80 % based on nuclear and hydro power sources), and needs to be adjusted if considered in other regions. In areas utilizing coal power electricity, obviously the portions of fossil energy sources increase in both first use and reuse and there is greater fossil depletion during 18 years of battery pack use, as well as emissions increase accordingly. If clean wind electricity is assumed to be used to recharge the battery packs in vehicle and reuse phases, the manufacturing and re-manufacturing phases account for significantly higher portions of energy and environmental emissions. It means that advantages associated with the use of the electric battery pack are even more important because of the extended life of the system from 8 to 18 years. Future work needs to consider charging at times when the emission factor of the grid can be a considered, which depends on which power generation plant/technologies contribute power to the grid’s the overall emission factor; thus charging could be done to coincide with low emission factor periods and discharging done at high emission factor periods. Additionally, this kind of analysis could be developed to include different carbon pricing scenarios in different jurisdictions. These considerations need to be factored into smart grid designs which may utilize re-purposed batteries, for example to manage electricity hubs to optimize economic advantages while providing local pollution reductions as well as global greenhouse gas benefits (Van Lanen et al. 2015).

4.2 Battery degradation

Energy efficiency of a battery refers to the fraction of energy that is used to charge the battery versus the energy delivered from the battery during use (Ahmadi et al. 2014b). Unfortunately, as the battery degrades over time it experiences energy efficiency fade in association with capacity and power fade. Surprisingly, this concept and its measurement are relatively new, as they have not been a concern for manufacturers of electric vehicles; instead the focus has been on battery capacity and power output, which correspond to vehicle mileage and power, respectively. However, for stationary applications like an ESS, energy efficiency equates to round-trip charging requirements and overall electrical energy use, and thus it directly determines overall energy use and economics in stationary applications. In the present study, sensitivity to energy efficiency fade is assessed as batteries are cascaded from first use to second use.

Note that this study has identified a key policy practice that is needed for the advancing the overall reuse concept. Specifically, there is a need to assess the state-of-health of the battery at the time of removal from vehicle service. Critical is to know the effective remaining capacity, current charge efficiency, and if there are any failed cells within the pack. For example, a battery pack would have a ‘state-of-health’ assessment report at the end of vehicle life. This assessment would require access to original equipment manufacturer (OEM, or the vehicle manufacturer) battery management system sensor codes and/or assessment service equipment. Since this data is closely controlled commercial property, there is need for one of many potential service scenarios, such as: the OEMs require their authorized service and dealer networks to provide this service (and an associated report) at a reasonable cost, or automotive recyclers develop that capacity and capabilities to assess battery pack and cell health. Note that such a report would allow automotive recycling facilities to direct the pack to an appropriate future use, including: material cycling (for highly degraded and/or damaged packs), stationary ESS systems (for packs with useable operational capabilities), or potentially return to vehicle use (for relatively new and undamaged packs).

4.3 Technical challenges of battery pack re-manufacturing

One limitation in this study is the lack of empirical data on battery life, collection, assessment, and re-manufacturing of batteries for the ESS. Battery life is an important subject of future study: empirical efforts would likely be most enlightening. Re-manufacturing process starts by recognition and collection of the used EV batteries at their end-of-life from EV owners. The energy in transportation of the collected batteries to a central re-purposing depot is not considered, and although economically costly, is likely not energetically significant. The collected batteries recovery stage includes sorting function and then disassembly process of packs into modules and testing the failure rate of cells. Re-assembly process contains installation of new module and packaging for the battery and related electronics as well as the needed electricity for testing and activating it for second application in the ESS. However, if original equipment manufacturers of vehicles were to consider design for disassembly the re-purposing process could be more efficient and less complex (Ahmadi et al. 2014a; Herrmann et al. 2012; Tomić and Kempton 2007).

There are also data gaps regarding the battery cycling experience during a long term process. Most of present experimental data in previous studies was limited to a period of less than 1-year under laboratory conditions. Also, there is a significant limitation in literature regarding the EV batteries re-manufacturing and second use of them in stationary applications. There is lack of real data about lifetimes and end-of-life of the batteries, including recycling of EV Li-ion batteries. Fundamental uncertainties are related to the life expectancy assumptions in first and second uses of the batteries, as these are varying by charge/discharge rates, depth of discharge, and operation conditions. Limited data about failure rate of cells, which is critical for effectiveness of battery pack re-purposing, causes uncertainties in the evaluation of state of-health of the re-purposed battery packs to be used in stationary ESS. These factors present opportunity for future applied and laboratory research. Future work should consider maintenance-induced failure modes during the re-purposing process, for example using a simulation that considers failed cell “change-out” during the second use and the resulting overall steady-state pack voltage performance.

Lastly, with respect to battery reuse, there are a number of qualitative challenges and potential barriers to EV battery reuse. These include regulatory, risk, safety, and business feasibility of EV battery availability and collection. It is suggested that reuse needs to include an assessment of the “quality” of each used battery pack as it is removed from vehicle service. Vehicle manufacturers and some dealers have the appropriate computer codes to assess quality, however perhaps recyclers or other parties need this capacity. A pack that is close to new in quality could be reused in another vehicle; whereas a pack with expected degradation up to 80 % is suitable for stationary re-purposing. Some packs may require limited maintenance, whereas some packs may be damaged beyond any potential reuse. Thus, collection and testing protocols of used battery packs will have to be established within the automotive recycling sequence, and/or perhaps at vehicle dealers. Safety, fire, and other and risks associated with reusing EV Li-ion batteries have been raised, including risk of fire and explosion (Long et al. 2012; Mikolajczak et al. 2011). Initial work using failure mode and effects analysis, and fault tree analysis has considered probabilities and severity of incidents and in complex applications (Ahmadi et al. 2014b; Gaffney et al. 2014). Safety systems and containment may have to be added to ESS systems to manage potential moisture exposure, fire protection and other hazards that differ from the vehicle use of the battery pack. Improvement of cell design, separator quality and cell construction could make the Li-ion batteries safer for their extended applications and emphasize more that safety and associated liability may be as serious barrier to technology implementation (Gaffney et al. 2014). It is recommended to consider the effect of failure rate of cells on the re-manufacturing phase in future analysis and to develop more refined technical understandings of battery degradation and state-of-health chemistry of a battery given a known history of use, thus leading to new vehicle powertrain control strategies. Moreover, future research should look at human related impacts, in addition to economic and environmental performance.

4.4 Resource use and metal “depletion”

The extended lifetime of a battery needs to be considered more broadly for the resource consequences of this technology. Note that the necessity for end-of-life treatment of batteries does not change with re-purposing. Reuse delays the end-of-life treatment by 10 years, but the final end-of-life treatment of the battery pack is still needed. A converse consideration arising from re-purposing in that there is that delay in the recycling availability of metals and other materials, although this delay in processing recycled Li-ion batteries may permit the development of new technologies and practices.

This LCA study evaluates a limited number of environmental impact indictors however future work could extend assessment to more impact categories, including human toxicity. The “metal depletion” indicator is of particular note. LCA studies that flag “metal depletion” being of concern need to be considered carefully. Measures of “fossil depletion” or other metrics of non-renewable fuel resource consumption are more accepted. However, conventional indicators used in LCA to assess raw material natural resource use have been criticized as not particularly meaningful or useful (see for example, Sonnemann et al. 2015). This includes the ReCiPe “metal depletion” indicator used in the present study. Extraction and processing of metal resources correspond to environmental emissions, and are significant for production of metals used in batteries, including lithium, copper, cobalt, aluminum, nickel, and gold. Utilization of metals in batteries raises concerns for resource depletion (McManus 2012), for example with respect to availability and balance between virgin and recycled resources of lithium (Gaines et al. 2011). In recent years, such concerns are considered under the “critical materials” discussion, including recent work in this area using the EV as a case study (Gemechu et al. 2015). Results in the present study confirm the environmental significance of metal production in the battery system, but still show lower indicator results compared to the conventional system for five of the six indicators (see Fig. 5). The last indicator, the ReCiPe “metal depletion” metric suggests that by extending the life of the battery pack from 8 to 18 years in the cascaded system there is a potential resource trade-off: more raw materials are utilized compared to the conventional ICEV scenario, which is more fossil-fuel intensive. However, given the previous discussion, it is suggested that although “metal depletion” indicator is increased by battery pack reuse, this is tangible different compared to the five other LCA indicators that show decreased impacts over the whole battery pack life cycle. Extending the life of an EV battery pack may raise issues of material resource availability by keeping the base material in a useful manufactured application longer. If implemented on a large scale, additional lithium, copper, aluminum, and other metals would need to be mined in order to satisfy demand resulting from a delay in material recycling. This would be an interesting analysis, basically to consider energy versus material resource sustainability under various future scenarios.

Cascaded use of such a material intensive component allows for significant economic and environmental investments in battery pack production to be offset through its longer-term application. The LCA results confirm the environmentally feasible performance of EV Li-ion batteries and the importance of the development of second use applications of the battery packs. Results could be helpful to automakers, governments, utility companies, and energy providers in decisions about the operational use of electric vehicles, second use options, policy, and economic support for re-manufacturing. As such, the reuse of EV battery packs could bring new opportunities for material efficiency and in the development of renewable energy sources and the smart grid.

5 Conclusions

The study characterizes the extended lifetime of Li-ion battery packs using a complex functional unit to cover both use and reuse phases over an 18-year lifetime. Methodologically, the use of a complex functional unit proved valuable in studying a product system with cascaded (multiple) applications, although more development of this kind of approach is needed. In this case for most impact categories, the cascaded use system appears significantly beneficial compared to the conventional system. Battery pack components such as electrodes, substrates and the battery management system are contributors to several of the potential environmental impacts assessed. However, it is the battery pack use and reuse stages that dominate energy demand and air emissions. Energy efficiency fade (as part of battery state-of-health) is a considerable determinant of potential performance for second use, more so than first use in the electric vehicle. Although this technology has not yet developed commercially, which limits the reliability of assumptions made in the analysis; it appears that cascaded use of battery packs can be beneficial in the necessary transition to cleaner power sources for both mobility and to support stationary applications seeking to shift time-use of power generation.