Comparative Life Cycle Assessment of Li-ion Batteries through

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Comparative Life Cycle Assessment of Li-ion Batteries through Process-based and Integrated Hybrid Approaches Shipu Zhao, and Fengqi You ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05902 • Publication Date (Web): 13 Feb 2019 Downloaded from http://pubs.acs.org on February 14, 2019

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ACS Sustainable Chemistry & Engineering

Comparative Life-Cycle Assessment of Li-ion Batteries through Process-based and Integrated Hybrid Approaches

Shipu Zhao, Fengqi You* Systems Engineering, College of Engineering Cornell University, Ithaca, New York 14853, USA Last edition date 2/13/2019

Abstract This paper analyzes and compares the life cycle environmental impacts of two major types of Li-ion batteries using process-based and integrated hybrid life-cycle assessment (LCA) approaches. The life cycle inventories (LCIs) of Li-ion battery contain component production, battery assembly, use phase, disposal and recycling and other related background processes. For process-based LCA, 17 ReCiPe midpoint environmental impact indicators and three endpoint environmental impact indicators are considered. As for the integrated hybrid LCA study, life cycle greenhouse gas (GHG) emissions and energy consumption are emphasized. Furthermore, we perform sensitivity analysis of life cycle GHG emissions with respect to the uncertainties in product prices, mass of BMS and cooling system and production efficiency. The integrated hybrid LCA results show that battery cell production is the most significant contributor to the life cycle GHG emissions and the economic input-output (EIO) systems contribute the largest part in life cycle energy consumption for both types of Li-ion batteries. The most significant difference between two Li-ion batteries lies in the disposal and recycling stage. For LiMn2O4 (LMO) battery, disposal and recycling stage only makes up a small portion of less than 10% for life cycle GHG emissions and energy consumption. However, for Li(NixCoyMnz)O2 (NCM) battery, it contributes a significant part with more than 20%. Key words: Li-ion battery, integrated hybrid life cycle assessment, environmental impacts

*Corresponding

Author. Phone: (607) 255-1162; Fax: (607) 255-9166; E-mail: [email protected]

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Introduction Along with the rapid development of battery-powered electric vehicle industry, electrochemical energy storage has gained increasing attentions.1-2 Li-ion battery is an attractive technology for electrochemical energy storage due to its features of high energy density, enhanced rate capabilities and long service life.3 It has been a very active area of research to develop novel and advanced rechargeable Li-ion batteries. However, the production, use and disposal of Li-ion batteries may lead to environmental burdens, and there are very few studies about the corresponding environmental impacts. Currently, most LCA studies about battery technologies are conducted on traction batteries as part of electric vehicles.4-6 Batteries used for hybrid electric vehicles, and plug in hybrids have been studied to the largest extent in recent years.6 Therefore, it is important to quantitatively investigate the environmental impacts of Li-ion batteries from a life cycle perspective. Commercial Li-ion batteries use various types of cathode materials, including LiMn2O4 (LMO), LiFePO4 (LFP), Li(NiCoAl)O2 and Li(NixCoyMnz)O2 (NCM), where x, y, and z denote different possible ratios.7-8 As for anode material, graphite is commonly adopted regardless of different cathode materials.9-11 Different combinations of cathode and anode materials have different properties and may result in different performances, such as energy density and life time. The comparison of life cycle environmental impacts between different types of Li-ion batteries could help to identify the environmental “hotspot” and provide recommendations to future development of Li-ion battery technologies. Existing LCA studies include process-based LCA studies of Li-ion batteries with nanomaterials for electrodes, all-solid-state batteries, batteries with metal anode and lithium metal polymer (LMP) stationary batteries.12-15 Life cycle assessment (LCA) is a systematic methodology for investigating and quantifying the potential environmental impacts. As a well-developed method to quantitatively evaluate the environmental impacts, it has been extensively applied on a wide range of products and processes. The typical process-based LCA includes four phases: goal and scope definition, life cycle inventory analysis (LCI), life cycle impact assessment (LCIA), and interpretation.9 Process-based LCA has specific advantage on technology comparison, because it provides sufficiently detailed information on various types of environmental impacts from each stage of the product’s life cycle. However, traditional process-based LCA excludes many upstream processes and suffers from 2 ACS Paragon Plus Environment

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system boundary truncation.16-18 As a result, the process-based LCA leads to cut-off errors and the environmental impacts are underestimated.18 The EIO-based LCA describes an economy in terms of financial transactions, inputs and outputs, between sectors. The system boundary of EIO-based LCA covers the entire background economy, and it is therefore much more complete than the process-based LCA.19 Nevertheless, EIO-based LCA suffers from aggregation error due to aggregation of industries and commodities, so the accuracy of results from EIO-based LCA could be sacrificed due to its lower resolution.17 The integrated hybrid LCA approach combines the process-based LCA and EIO-based analysis.20 It is widely adopted to reduce the uncertainty in LCA study. The process details within system boundary are studied explicitly by process-based LCA through constructing and analyzing the detailed life cycle inventory associated with each life cycle stages within the systems boundary. Besides, the excluded upstream processes are supplemented by EIO-based LCA to model and analyze the environmental impacts from background economy.16, 20-21 Most existing Li-ion battery LCA studies focus on the process-based analysis,22-25 and to the best of our knowledge no study has conduct to systematically evaluate the “most comprehensive” life cycle environmental impacts of Li-ion battery technologies using the integrated hybrid LCA approach for quantifying both process and EIO environmental impacts. To fill this knowledge gap, in this work, integrated hybrid LCA is adopted to study the environmental impacts of two types of Li-ion batteries with two different cathode materials (NCM and LMO, respectively) produced in UK. This integrated hybrid LCA method leverages the advantages of process-based LCA and EIObased LCA and overcomes their drawbacks. For process-based LCA, 17 ReCiPe midpoint environmental impact indicators and three endpoint environmental impact indicators are studied. As for the integrated hybrid LCA study, life cycle GHG emissions and energy consumption are considered using available data on life cycle inventory and EIO data for UK. Furthermore, we perform sensitivity analysis of GHG emissions with respect to the uncertainties in important factors, including product prices, mass of battery management system (BMS) and cooling system and production efficiency. The results provide recommendations to future development of new Liion battery technologies towards more environmentally sustainable designs. The main novelty of this work is the comparations between process-based LCA and integrated hybrid LCA results for Li-ion batteries.



The rest of this article is organized as follows. In Section 2, materials and methods in this study are introduced, including overview of integrated hybrid LCA approach, goal and scope definition, battery technologies, LCI analysis, battery use phase, end-of-life stage of battery pack, impact assessment and life cycle interpretation. The results of process-based LCA, integrated hybrid LCA and sensitivity analysis are presented in Section 3. A conclusion is given in the last section.

Materials and Methods Overview of integrated hybrid LCA approach The term hybrid LCA generically refers to any approach that combines process-based LCA and EIO analysis.21 Hybrid LCA approaches can be further classified into three types, including tiered hybrid LCA, EIO-based hybrid LCA, and integrated hybrid LCA according to how the process-based analysis and EIO-based analysis are combined.18 In tiered hybrid LCA, processbased analysis and EIO-based analysis are treated separately.26 Process-based analysis is adopted for the use and disposal phase and several important upstream processes are also included in process systems; The remaining input requirements and LCI are imported from EIO-based analysis.27 The final results of tiered hybrid LCA can be obtained simply by adding process-based LCI results and EIO-based LCI results. However, the process systems and EIO systems are treated separately in this approach, and the interactions between process systems and EIO systems are not handled systematically and appropriately. In EIO-based hybrid LCA, specific commodity sectors are disaggregated from the whole input-output table to approximate the environmental impacts.28 LCI results up to the pre-consumer stage can be obtained by disaggregating the whole input-output table; LCI results for the remaining stages of the life cycle of the product are added to the LCI results up to the pre-consumer stage. Because EIO-based hybrid LCA approach partly utilizes the tiered hybrid LCA approach, the interactions between life cycle stages of the product might not be fully captured in the analysis results.27 In the integrated hybrid LCA, detailed process analysis is conducted to estimate the environmental impacts of key life cycle processes, and the process system is complemented by the macroeconomic system. The process systems and the macroeconomic systems are integrated systematically by the upstream and downstream cutoff matrices instead of treating them separately in the tiered hybrid LCA approach. Meanwhile, since process-specific data are considered more accurate and reliable than the EIO-based data, the accuracy of analysis is much higher in the integrated hybrid LCA approach than that in the EIO4 ACS Paragon Plus Environment

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based hybrid LCA approach.16-17, 29 The mathematical model of integrated hybrid LCA can be expressed as follows:17, 27, 29

 A E  [ EP , EIO ]  P  CU

1

CD   y  I  AIO   0 

(1)

where E denotes the total environmental impact, including process impact and EIO impact. EP and EIO are the environmental extension vectors of process systems and EIO systems, respectively, representing the environmental impacts for each process and each economic sector. The environmental impact data for each process and each economic sector can be obtained from life cycle inventory data sources, such as Ecoinvent V3.3.30 AP is the physical flow matrix for process systems representing physical flows within the process system boundary, and AIO is the adjusted input-output matrix representing the interdependencies among industrial sectors within the EIO systems. AIO is constructed using the EIO data recently reported for UK. CD and CU are downstream cutoff matrix and upstream cutoff matrix representing the interactions between process systems and EIO systems. y is the functional unit column describing the amount of final products produced per functional unit. The physical flow matrix AP and downstream cutoff matrix CD are given in physical units. The adjusted input-output matrix AIO and upstream cutoff matrix CU are given in monetary units. Downstream cutoff matrix CD represents flows of goods produced by process systems to the EIO systems. In this work, compared with the EIO system for UK, the economic scale of the process system for Li-ion battery life cycle is relatively small. Therefore, in this work we treat Downstream cutoff matrix CD as zero. Upstream cutoff matrix CU represents flows from the EIO systems to the process systems. In order to get CU, we follow the procedures introduced in existing literature.31 Firstly, concordance matrix needs to be created representing correspondence between processes and EIO sectors. Each sector in the EIO system corresponds to a row and each basic process is related to a column in the concordance matrix. Matching sectors and processes are indicated by ones in the matrix and others are zero. Secondly, technical coefficient matrix matching process matrix are created based on the concordance matrix in the first step. Columns of the upstream matrix CU are populated with technical coefficients from domestic use and import table. Thirdly, columns of the matrix from the second step are multiplied with the unit price of the corresponding basic processes to yield price-weighted coefficients. After eliminating double counting of the coefficients, we can get the upstream cutoff matrix CU. 5 ACS Paragon Plus Environment


Goal and scope definition

Fig.1 System boundary of the process-based LCA for Li-ion battery technologies. Only major components are listed in this figure.

In this work, we conduct process-based LCA and integrated hybrid LCA studies of two Li-ion battery technologies, namely LMO battery and NCM battery. For process systems, a “cradle-tograve” system boundary is considered which includes the whole life cycle of Li-ion batteries as shown in Fig.1. Raw materials extraction, component production, battery manufacturing, use phase and end-of-life stage are considered in this study. For EIO-LCA part, this study adopts a two-region input-output model based on supply and use tables for the UK and the rest of world (ROW).31-32 The reasons for choosing UK to illustrate the integrated hybrid LCA approach are as follows. Firstly, the EIO data recently reported for UK are sufficient to complement the truncated process systems, and the data can also reflect the current economic structure with reasonable accuracy.31 Secondly, as EIO data only models the macroeconomic structure and does not account for the specific price of LIBs, there is always a time delay of several years, before the economic statistics data are published and the corresponding EIO-LCA data become available. The newest EIO data for the US in 2015 only contain 71 industries, which are not sufficient to supplement the process systems, and the EIO data in 2007 with 389 industries may not accurately reflect the current 6 ACS Paragon Plus Environment

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structure of the economy.33 As the data become available, the proposed framework can be applied to other regions and countries, although the present study focuses on the case of UK. The integrated hybrid LCA approach can evaluate the life cycle environmental impacts of Li-ion batteries for both process and EIO environmental impacts. The functional unit is chosen as the production, use, disposal and recycling of one battery pack. Accordingly, the life cycle environmental impacts are evaluated based on this functional unit. The overall structure of the integrated hybrid LCA approach is illustrated by Fig. 2.

Fig.2 Structure of integrated hybrid LCA model for Li-ion battery, including process systems, EIO systems, downstream cutoff flows and upstream cutoff flows.

Battery technologies and LCI analysis In this work the environmental impacts of two battery technologies, LMO Li-ion battery and NCM Li-ion battery, are evaluated. The battery systems include four main components: battery cell, package, BMS, and cooling system.



The battery cell consists of five subcomponents: anode, cathode, cell container, electrolyte and separator.22 For both battery technologies, anode is composed of a copper current collector with a coat of negative electrode paste. Synthetic graphite is the main component of negative electrode, and small amounts of binders are also included.3, 34 The cathode is composed of an aluminum current collector with a coat of positive electrode paste. The positive electrode paste consists mainly of the positive active material, small amounts of carbon black and a binder. For LMO Liion battery, the positive active material is lithium manganese oxide (LiMn2O4); for NCM Li-ion battery the corresponding positive active material is lithium nickel cobalt manganese oxide (Li(NixCoyMnz)O2). A solvent is applied to slurry the mixtures in both the positive and negative electrode pastes. The electrolyte is based on the salt, lithium hexafluorophosphate (LiPF6), in a mixture of solvents.35-36 The separator is a porous polyolefin film. The cell container consists of a multilayer pouch and tabs. Package of battery is composed of three subcomponents: module packaging, battery retention， and battery tray. The BMS includes battery module boards (BMBs), the integrated battery interface system (IBIS), fasteners, a high-voltage (HV) system, and a low-voltage (LV) system. The battery is also equipped with a cooling system for the purpose of thermal management. An aluminum radiator is the main component of the cooling system.37 The LMO Li-ion battery is made with a cathode based on lithium manganese oxide (LiMn2O4) and an anode based on graphite.23 The NCM Li-ion battery is made with a cathode based on lithium nickel cobalt manganese oxide (Li(NixCoyMnz)O2) and a graphite anode.22 The weight of one battery pack for each type of batteries is considered as 250 kg. LMO Li-ion battery and NCM Li-ion battery share the same BMS and cooling system technologies. For LMO Li-ion battery, positive active material lithium manganese oxide (LiMn2O4) is made from manganese oxide (Mn2O3) and lithium carbonate (Li2CO3) through several roasting stages in a rotary kiln.38 Lithium carbonate (Li2CO3) is made from concentrated lithium brine with a carbonation step.39 Manganese oxide (Mn2O3) is produced through a two stage roasting process. For the first stage, manganese carbonate is roasted in an atmosphere low in oxygen content; in the second stage, it is roasted in an environment with a high oxygen content.40 For NCM Li-ion battery, different positive active materials for cathodes with different ratios of nickel, cobalt, and manganese are available on the market.41 The ratio of (1:1:1) is chosen for this study which is used in the literature.42-44 Positive active material, lithium nickel cobalt manganese oxide 8 ACS Paragon Plus Environment

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(Li(Ni1/3Co1/3Mn1/3)O2), is made from lithium hydroxide (LiOH) and nickel cobalt manganese hydroxide (Ni1/3Co1/3Mn1/3(OH)2).45-46 The production process of metal hydroxides consists in the precipitation of the metal hydroxides from an aqueous solution of the metal salts by reaction with a strong base. The products are recuperated by filtration and dried at low temperature.45-46 The base materials for the electrolyte of two types of Li-ion batteries include ethylene carbonate (C3H4O3)

and

lithium

(LiPF6).47-48

hexafluorophosphate

The

production

of

lithium

hexafluorophosphate (LiPF6) uses lithium fluoride (LiF) and phosphorus pentachloride (PCl5).49 The LCIs of Li-ion batteries are established according to the process system boundary and functional unit defined in the previous section. In this study, the process-based LCIs data are built based on two recent process-based LCA studies for LMO Li-ion battery and NCM Li-ion battery,22-23 as well as the Ecoinvent database V3.3.30 In order to make these two types of Li-ion batteries comparable on the same and fair basis, we update the LCIs both for NCM and LMO Liion batteries. We take the same assumptions from the two recent process-based LCA studies mentioned previously.22-23, 50 In the existing literature, there are very limited LCA studies both for NCM and LMO Li-ion batteries. To the best of our knowledge, the LCA study for LMO battery is probably the only one.23 Besides, both studies include detailed LCIs data which can be easily referred to and reproduced to make comparisons with our results. Moreover, these two studies were published in rigorously peer-reviewed journals, Journal of Industrial Ecology and Environmental Science & Technology, respectively, that have been well-recognized by the sustainability community. Therefore, we choose to build LCIs for NCM and LMO Li-ion batteries based on these two LCA studies.22-23 The compositions of BMS and cooling system are shown in Table 1. The LCIs of cathode materials of LMO Li-ion battery and NCM Li-ion battery are shown in Tables 2 and 3, respectively. The LCIs of an anode are shown in Table 4 and the LCIs of lithium hexafluorophosphate are shown in Table 5. These LCI results include raw materials, electricity, heat, transportation, infrastructure and other related parts for production, use phase, disposal and recycling of Li-ion batteries. The processes for raw material inputs cover the corresponding transportation activities. For the EIO systems, this study adopts a two-region input-output model based on supply and use tables for the UK and the rest of world (ROW). Specifically, the resulting adjusted input-output matrix is composed of four parts, including the supply and use tables for the UK and the supply and use tables for the rest of the world (ROW). In each table, there are 224 sectors/commodities considered, including the following broad categories: agriculture, mining, 9 ACS Paragon Plus Environment


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construction, manufacturing, wholesale trade, retail trade, transportation and warehousing, finance, professional and business services, education and health care, arts and entertainment, government, and others. The resulting adjusted input-output matrix has a dimension of 896 × 896.

Table 1. Compositions of BMS and cooling system.22 Component and subcomponent

Mass (kg)

BMS

9.40E+0 IBIS

4.50E+0

IBIS fasteners

3.00E-1

High Voltage system

3.20E+0

Low Voltage system

1.40E+0

Cooling system

1.00E+1 Radiator

9.10E+0

Manifolds

4.20E-1

Clamps & fasteners

2.40E-1

Pipe fitting

2.00E-2

Thermal pad

2.20E-1

Table 2. Life cycle inventories of lithium manganese oxide. Input

Unit

Value

Note

Manganese oxide

kg

9.18E-1

Manganese component23

Lithium carbonate

kg

2.15E-1

Lithium component51

Oxygen

kg

7.15E-1

Liquid, for oxidizing atmosphere51

Nitrogen

kg

7.86E-1

Liquid, for inert atmosphere23

Water

kg

3.40E+0

For suspension: 3 parts water, 1 part Mn2O3 and Li2CO3 powder23

Electricity

kWh

5.00E-3

Mechanical drive of the rotary kiln23

Process heat

MJ

1.53E+1

Furnace for rotary kiln23

Transport lorry

tkm

5.64E-1

Ecoinvent V3.330

Transport train

tkm

3.23E+0

Ecoinvent V3.330 10

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Infrastructure chemical plant

unit

4.00E-10

kg

1.00E+0

Ecoinvent V3.330

Functional unit Lithium manganese oxide

Table 3. Life cycle inventories of lithium nickel cobalt manganese oxide. Input

Unit

Value

Note

Lithium hydroxide

kg

2.50E-1

Lithium component50

Nickel sulfate

kg

5.42E-1

Nickel component22

Cobalt sulfate

kg

5.42E-1

Cobalt component22

Manganese sulfate

kg

5.23E-1

Manganese component22

Sodium Hydroxyde

kg

8.36E-1

Aqueous solution of metal salts50

Process heat

MJ

5.50E-1

Mechanical drive of the rotary kiln22

Transport lorry

tkm

3.67E-1

Ecoinvent V3.330

Transport train

tkm

2.15E+0

Ecoinvent V3.330


unit

4.00E-10

Ecoinvent V3.330

kg

1.00E+0

Functional unit Lithium nickel cobalt manganese oxide

Table 4. Life cycle inventories of an anode. Input

Unit

Value

Note

Latex

kg

1.85E-2

Binder50

Water

kg

4.24E-1

Solvent of the binder23

Graphite

kg

4.94E-1

Active material22

Carbon black

kg

1.59E-2

Conductive carbon23

Copper

kg

5.70E-1

Negative current collector Cu22

Sulfuric acid

kg

8.08E-2

For treatment of alu foil23

Process heat

MJ

1.22E+0

Evaporating water50

Electricity

kWh

2.00E-3

Mechanical drive for pumping slurry50 11



Transport lorry

tkm

1.13E-1

Ecoinvent V3.330

Transport train

tkm

4.70E-1

Ecoinvent V3.330


unit

4.00E-10

Ecoinvent V3.330

kg

1.00E+0

Functional unit Anode for Li-ion battery

Table 5. Life cycle inventories of lithium hexafluorophosphate. Input

Unit

Value

Note

Lithium fluoride

kg

1.97E-1

86.7% conversion of lithium23

Phosphorous pentachloride

kg

1.98E+0

86.7% conversion of phosphorus chloride23

Hydrogen fluoride

kg

4.04E+0

Overspill: 532%23

Nitrogen

kg

1.25E-3

Liquid, for inert atmosphere22

Lime

kg

7.44E+0

Neutralisation and disposal of HF22

Electricity

kWh

5.39E-1

Heat pump24

Electricity

kWh

2.00E-3

For pumps, stirring, milling of LiPF623

Transport lorry

tkm

1.37E+0

Ecoinvent V3.330

Transport train

tkm

8.19E+0

Ecoinvent V3.330


unit

4.00E-10

Ecoinvent V3.330

Functional unit Lithium kg hexafluorophosphate

1.00E+0

Battery use phase In battery use phase, Li-ion batteries are assumed on an average midsized EV with a weight of 4,270 lb and an average driving distance of 200,000 km during a 10-year service life.52-53 One battery pack is supposed to power the EV on the whole life time. The driving mix of the vehicle is 55% urban and 45% highway.54


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End-of-life of battery pack In existing literature, there are different methods for Li-ion recycling including “recycledcontent” approach and “avoided burden” approach.55 At the end-of-life stage, the metal materials in the battery pack are expected to be recycled and other components of the battery pack are treated as landfill.54 We adopt the “recycled-content” approach in the end-of-life stage of Li-ion batteries.56 The main purpose of recycling is material recovery and the recycling procedures are assumed using current recycling technologies, including hydrometallurgical and pyrometallurgical recovery.57-58 In this study, the recovered materials are not treated as raw materials for battery production because materials for battery production are required to have high quality and purity. The recycling processes for metal materials are shown in Table 6. Table 6. Recycling processes for metal materials. Material

Recycling process

Aluminum

Hydrometallurgical recovery57

Copper

Pyrometallurgical recovery58

Lithium


Cobalt


Manganese


Nickel

Pyrometallurgical recovery58

Impact assessment To evaluate the life cycle environmental impacts of these two battery technologies, life cycle inventory results are converted into corresponding environmental impacts under different impact categories. Impact categories can be further classified into midpoint impact categories and endpoint impact categories.59 Midpoint impact categories can evaluate the direct environmental impacts, and endpoint impact categories can estimate the ultimate environmental impacts. Midpoint characterization factors can be obtained according to equivalency principles, and endpoint characterization factors can be obtained by multiplying the midpoint characterization potentials with the damage characterization factors of the reference substance.60-62 LCIA methods based on midpoint categories are midpoint-oriented methods, such as the method defined in the 13 ACS Paragon Plus Environment


Handbook of Life Cycle Assessment.9 LCIA methods based on endpoint categories are endpointoriented methods, such as the Eco-indicator 99 and the state-of-the-art ReCiPe methods.63-64 For process system analysis, we choose the endpoint-oriented LCIA method, ReCiPe, to quantify the life cycle environmental impacts of Li-ion battery technologies. For ReCiPe approach, impact categories and characterization methods are applied to evaluate the environment profile of Li-ion batteries. There are a total of 17 impact categories addressed at the midpoint level. These midpoint impact categories are further aggregated into three endpoint impact categories. A total endpoint environmental impact score can be obtained according to the ReCiPe method. Fig. 3 illustrates the relationship between these midpoint and endpoint impact categories.

Fig. 3 Illustration of midpoint and endpoint environmental impact categories

For integrated hybrid LCA part, two environmental indicators, life cycle GHG emissions and energy consumption, are considered. Life cycle GHG emissions and energy consumption for Liion batteries from process systems and EIO systems are systematically evaluated by the integrated hybrid LCA method. For life cycle GHG emissions, we choose the global warming potential (GWP) indicator applying a time frame of 100 years reported by Intergovernmental Panel on Climate Change (IPCC), as a characterization factor for global warming impact assessment.65 The 14 ACS Paragon Plus Environment

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integrated hybrid LCA approach66-67 adopted in this study can be applied to other environmental impact indicators in addition to GHG emissions and energy consumption, if the corresponding EIO data are available. Specifically, the environmental impact data corresponding to each sector in the EIO system are required in the integrated hybrid LCA approach. However, only GHG emissions and energy consumption data are available for the case of UK in 224 economic industries. Therefore, we only consider GHG emissions and energy consumption for the EIO system in this study. For energy consumption, it refers to the cumulative energy consumption for the whole life cycle of Li-ion batteries which sums up various types of primary energies used by each stage for the whole life cycle of Li-ion batteries. Raw material production, component assembly, use phase, disposal and recycling of Li-ion batteries are considered in this study Energy consumption for the end-of-life stage of Li-ion batteries consists of the energy consumption for recycling of metal materials and landfill of other components. Life cycle interpretation All the results from life cycle impact assessments will be summarized, and comparison will be made between LMO Li-ion battery and NCM Li-ion battery. For process-based LCA, 17 midpoint impact indicators and three endpoint impact indicators according to the ReCiPe LCIA method are addressed. Only cradle-to-gate LCA results are presented for process-based LCA due to lack of environmental impact data for battery use phase in 17 midpoint impact indicators and three endpoint impact indicators for ReCiPe LCIA method. For integrated hybrid LCA, we concentrated on two impact indicators, GHG emissions and energy consumption. Both cradle-to-gate and cradle-to-grave LCA results are presented for integrated hybrid LCA approach. More insightful suggestions are presented following sensitivity analysis. For the LCA results, the total environmental impacts for Li-ion batteries are divided into six parts, including battery cell, package, BMS, cooling system, disposal & recycling and EIO system. Battery cell part includes cell production and pack assembly is considered in package part. To demonstrate the effect of input parameter fluctuations and quantify the corresponding influences, we perform a sensitivity analysis by varying input parameters, including mass of BMS and cooling system, production efficiency and product prices. The results of sensitivity analysis can insinuate the actual range of error margins. To further investigate the influence of uncertain parameters on sustainability indicators, a comprehensive uncertainty analysis based on Monte 15 ACS Paragon Plus Environment


Carlo simulation is conducted. The results of Monte Carlo simulation can show the probability distributions of sustainability indicators with respect to uncertain parameters.

Results and Discussion Environmental profile Fig. 4 and 5 show the cradle-to-gate environmental profiles of LMO Li-ion battery and NCM Li-ion battery, respectively. According to ReCiPe LCIA method, 17 midpoint impact indicators are considered in this study. For environmental profile analysis, we only consider the process systems for Li-ion batteries and the EIO systems are not considered. Each impact indicator is normalized, and the total indicator of each category is 100%. From Fig. 4, it can be found that battery cell is the most significant contributor for 13 environmental impact indicators in the environmental profile of LMO Li-ion battery, including agricultural land occupation (41.9%), climate change for ecosystems (66.9%), marine ecotoxicity (90.1%), natural land transformation (92.9%), terrestrial acidification (66.3%), terrestrial ecotoxicity (86.1%), climate change for human health (62.5%), human toxicity (75.8%), ionizing radiation (43.8%), particulate matter formation (38.4%), photochemical oxidant formation (69.2%), fossil depletion (57.2%) and metal depletion (84.1%). Packaging accounts for the largest part in the remaining four environmental impact indicators, including freshwater ecotoxicity (42.5%), freshwater eutrophication (45.1%), urban land occupation (42.9%) and ozone depletion (41.6%). Battery cell has dominant contributions in 13 environmental indicators for LMO Li-ion battery. In addition to battery cell, package also have significant contribution in all environmental indicators. However, cooling system and BMS only make up small portions for all environmental indicators.


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u cl ltur im al at e c land ha o fre nge ccu fre shw , ec pati sh at os on w er ys at er eco tem eu to s na tu ma trop xici ra t l l rine hic y an at e te d tr cot ion rre a ox str nsf ici te ial orm ty rre ac at id io s cl u im rb trial ific n a at an e c la eco tion t ha nd ox ng oc ic e, c it hu upa y m ti hu an on m h io an ealt ni pa sin tox h rti i cu o g ra city la zo te n dia ph ma e de tion ot tte pl oc e h r fo tio fo emi rm n rm ca at i faotio l ox on ssn id il a m dep nt et al leti de on pl et io n

ric

ag ric u cl ltur im al at e c land ha o fre nge ccu fre shw , ec pati sh at os on w er ys at er eco tem eu to s na tu ma trop xici ra t l l rine hic y an at e te d tr cot ion rre a ox str nsf ici te ial orm ty rre ac at id io s cl u im rb trial ific n a at an e c la eco tion t ha nd ox ng oc ic e, c it hu upa y m ti hu an on m h io an ealt ni pa sin tox h rti i cu o g ra city la zo te n dia ph ma e de tion ot tte pl oc e h r fo tio fo emi rm n rm ca at i faotio l ox on ssn id il a m dep nt et al leti de on pl et io n

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ag

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100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

Package

Package Battery cell

Battery cell BMS

BMS

Cooling system

Fig. 4 Cradle-to-gate environmental profile for one pack of LMO Li-ion battery.

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

Cooling system

Fig. 5 Cradle-to-gate environmental profile for one pack of NCM Li-ion battery.

From Fig. 5, it can be found that NCM Li-ion battery has a similar environmental profile with

that of LMO Li-ion battery. Battery cell is the most significant contributor for all the 17

environmental impact indicators in the environmental profile of NCM Li-ion battery, including

agricultural land occupation (59.7%), climate change for ecosystems (62.4%), freshwater

17



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ecotoxicity (71.7%), freshwater eutrophication (67.2%), marine ecotoxicity (97.9%), natural land transformation (78.2%), terrestrial acidification (89.3%), terrestrial ecotoxicity (79.0%), urban land occupation (65.0%), climate change for human health (62.0%), human toxicity (74.7%), ionizing radiation (65.0%), ozone depletion (72.0%), particulate matter formation (82.0%), photochemical oxidant formation (74.1%), fossil depletion (64.5%) and metal depletion (83.4%). Battery cell has dominant contribution in all of the environmental impact indicators, and cooling systems only makes up a small portion in all environmental indicators for NCM Li-ion battery. Compared with the environmental profile of LMO Li-ion battery, the main difference lies in the package part. For NCM Li-ion battery, package only makes up a small portion for all environmental impacts, but it is much more significant in the environmental profile of LMO Liion battery. 180% 160% 140% 120% 100% 80% 60% 40% 20% 0% Ecosystem

Human health NCM

Resources

Total impact

LMO

Fig. 6 Comparison between one pack of NCM Li-ion battery and LMO Li-ion battery in three endpoint impact indicators and total environmental impact.

According to ReCiPe LCIA method, 17 midpoint impact indicators are aggregated into three endpoint indicators: human health, ecosystem quality and resources quality. The comparison of three endpoint impact indicators and total environmental impact between LMO Li-ion battery and NCM Li-ion battery are provided in Fig. 6. The NCM Li-ion battery is used as the standard for normalization. NCM Li-ion battery has lower impact in ecosystem quality and resources quality, but it performs worse in human health. Besides, NCM Li-ion battery has higher total 18 ACS Paragon Plus Environment

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environmental impact than LMO Li-ion battery. The most significant difference lies in ecosystem impact, where LMO Li-ion battery has over 60% higher impact. Integrated Hybrid LCA Results For the integrated hybrid LCA of Li-ion batteries, we consider two key environmental impact categories, the life cycle GHG emissions and energy consumption in this work, due to the limited availability of data in environmental extension vectors corresponding to the EIO systems. Different from tiered hybrid LCA approach68 sectors in the EIO systems are treated in an aggregated way in the integrated hybrid LCA approach. Therefore, we cannot get the environmental impacts corresponding to specific EIO sectors.66-67 To convert the GHG emissions into carbon dioxide equivalents, we adopt the 100-year global warming potential (GWP) factors in the fifth assessment report by IPCC.69 Following the integrated hybrid LCA approach, we can calculate both the direct and indirect life cycle environmental impacts. In Fig.7 and 8, we summarize the breakdowns of cradle-to-gate life cycle GHG emissions and life cycle energy consumption of LMO Li-ion battery and NCM Li-ion battery, respectively. In our research, we consider 224 economic sectors for the EIO system and we focus on the environment impacts of Li-ion batteries. Due to the large number of economic sectors considered in the EIO system, explicit listing of sector-level environmental impacts in the EIO system could not be presented in a clear way. Therefore, in integrated hybrid LCA results, we treat the EIO system as a whole and only present the aggregated environmental impacts caused by the entire EIO system instead of specifying the major environmental impacts by departments separately. It can be found that the cradle-to-gate life cycle GHG emissions and life cycle energy consumption have different breakdowns. For LMO and NCM Li-ion batteries, battery cell contributes the most life cycle GHG emissions with 53.9% for LMO Li-ion battery and 55.0% for NCM Li-ion battery. EIO systems contribute a relatively small portion of around 10% of the life cycle GHG emissions. However, for life cycle energy consumption, EIO systems become the most significant part, which contributes 49.2% of the life cycle energy consumption for LMO Li-ion battery and 47.6% for NCM Li-ion battery. Battery cell becomes the second largest source of life cycle energy consumption for both Li-ion batteries. Fig. 9 and 10 provide the integrated hybrid LCA results for cradle-to-gate life cycle GHG emissions and life cycle energy consumption for LMO and NCM Li-ion batteries, respectively. For LMO Li-ion battery, the life cycle GHG emissions is 2,336 kg CO2-eq. per battery pack and life cycle energy consumption is 58,804 MJ per battery pack, respectively. For NCM Li-ion battery, 19 ACS Paragon Plus Environment


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the life cycle GHG emissions is 2,126 kg CO2-eq. per battery pack and life cycle energy consumption is 59,563 MJ per battery pack. LMO Li-ion battery has more life cycle GHG emissions and less life cycle energy consumption than NCM Li-ion battery. However, the differences in life cycle GHG emissions and energy consumption between NCM and LMO Li-ion batteries are not significant. The EIO systems play a key role in evaluating the life cycle environmental impacts of Li-ion batteries especially in life cycle energy consumption. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% GHG emissions Package

Battery cell

Energy consumption BMS

Cooling system

EIO

Fig. 7 Breakdowns of cradle-to-gate life cycle energy consumption and life cycle GHG emissions for LMO Li-ion battery. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% GHG emissions Package

Battery cell

Energy consumption BMS

Cooling system

EIO

Fig. 8 Breakdowns of cradle-to-gate life cycle energy consumption and life cycle GHG emissions for NCM Li-ion battery.


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GWP 100 kg CO2-eq. per battery pack

2500 2000 1500 1000 500 0 NCM Package

Battery cell

LMO BMS

Cooling system

EIO

Fig. 9 Integrated hybrid LCA results of cradle-to-gate life cycle GHG emissions for LMO and NCM Li-ion batteries. 70000

Energy consumption per battery pack (MJ)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60000 50000 40000 30000 20000 10000 0 NCM Package

Battery cell

LMO BMS

Cooling system

EIO

Fig. 10 Integrated hybrid LCA results of cradle-to-gate life cycle energy consumption for LMO and NCM Li-ion batteries.

Fig. 11 and 12 provide the integrated hybrid LCA results for cradle-to-grave life cycle GHG emissions and life cycle energy consumption for LMO and NCM Li-ion batteries, respectively. For LMO Li-ion battery, the life cycle GHG emissions is 25,845 kg CO2-eq. per battery pack and life cycle energy consumption is 640,475 MJ per battery pack, respectively. For NCM Li-ion battery, the life cycle GHG emissions is 26,452 kg CO2-eq. per battery pack and life cycle energy 21 ACS Paragon Plus Environment


consumption is 655,687 MJ per battery pack. NCM Li-ion battery has more life cycle GHG emissions and life cycle energy consumption than LMO Li-ion battery. The main reason for higher cradle-to-grave life-cycle GHG emissions and life cycle energy consumption is that NCM Li-ion battery contains cobalt and nickel in the cathode part and the recycling processes of cobalt and nickel have relatively higher environmental impacts compared with recycling processes of aluminum, copper, lithium and manganese. Besides, production and processing of these metal materials also have significant impacts on environment. For cradle-to-grave life cycle GHG emissions, battery use phase makes up dominant part both for NCM and LMO Li-ion batteries. It also accounts for the second largest part in cradle-to-grave life cycle energy consumption. 30000 GWP 100 kg CO2-eq. per battery pack

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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25000 20000 15000 10000 5000 0 NCM Battery production

LMO

Battery use phase

Disposal & recycling

EIO

Fig. 11 Integrated hybrid LCA results of cradle-to-grave GHG emissions for LMO and NCM Li-ion batteries.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Energy consumption per battery pack (MJ)

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700000 600000 500000 400000 300000 200000 100000 0 NCM Battery production

LMO

Battery use phase

Disposal & recycling

EIO

Fig. 12 Integrated hybrid LCA results of cradle-to-grave life cycle energy consumption for LMO and NCM Li-ion batteries.

Sensitivity Analysis

Fig. 13 Sensitivity analysis of LMO Li-ion battery in cradle-to-gate life cycle GHG emissions. The ranges for each input parameter are presented on the figure while the bars represent the variations in GHG emissions as input parameters are varied from their mean values.



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Fig. 14 Sensitivity analysis of NCM Li-ion battery in cradle-to-gate life cycle GHG emissions. The ranges for each input parameter are presented on the figure while the bars represent the variations in GHG emissions as input parameters are varied from their mean values.

In order to further quantify the influences brought about by input parameters, sensitivity analysis is conducted.70 The results of sensitivity analysis of LMO Li-ion battery and NCM Li-ion battery in cradle-to-gate life cycle GHG emissions are presented in Fig. 13 and 14, respectively. The horizonal bars describe the deviations in cradle-to-gate life cycle GHG emissions associated with changes in the input parameters. The ranges of each input parameter are presented on the figures. These two figures demonstrate that changing input parameters regarding mass of BMS and cooling system, production efficiency, and product prices can potentially change the cradleto-gate life cycle GHG emissions. The sources of input parameters are shown in Table 7. Table 7. Ranges, mean values and sources of input parameters. Input parameter

Unit

Mean value

Lower bound

Upper bound

Mass of BMS

kg

9.40

7.2054

10.8050, 54

2.50E+9

2.20E+950

4.30E+950

Number of battery packs produced per factory Mass of cooling system

kg

10.00

7.4071

20.1054

Price of copper

EUR

5.52

2.4772

8.9872

Price of manganese ore

EUR

0.005

0.00273

0.00773


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Price of carbon black

EUR

0.86

0.6474

0.9974

Price of nickel sulfate

EUR

2.85

2.2875

3.4275

Price of aluminum

EUR

1.44

1.1472

2.4572

From Fig. 13 and 14, variations in mass of BMS and cooling system, as well as production efficiency, have significant effects on life cycle GHG emissions. We use the number of battery packs produced in the same plant to represent production efficiency in this sensitivity analysis. Larger number of battery packs produced in a plant implies a higher production efficiency. It is obvious that increasing mass of BMS and cooling system can lead to higher life cycle GHG emissions. Higher production efficiency results in lower life cycle GHG emissions. The upstream cutoff matrix in the integrated hybrid LCA approach represents commodity flows in monetary terms from the product sectors in the EIO systems to the process systems. Therefore, we need price data of EIO product sectors to construct the upstream cutoff matrix, and variations in product prices can affect the integrated hybrid LCA results. Results of sensitivity analysis show that higher product prices will result in higher life cycle GHG emissions. However, variations in product prices do not have significant effects on life cycle GHG emissions. Variations in product prices can only affect the life cycle GHG emissions from EIO systems. It is reasonable to assume that reliable results of the life cycle GHG emissions are dependent on accurate input parameters. However, it is not uncommon that fluctuation exists in input parameters. Fluctuations in input parameters for Li-ion batteries may result from battery production, use phase, disposal and recycling processes and estimation in LCI data. Therefore, several parameters, such as mass of BMS, mass of cooling system, battery pack production efficiency and driving distance exhibit inherent uncertainties in the integrated hybrid LCA approach. Therefore, probability distributions are applied to the key input parameters. Simulation methods are further used to investigate the influence of uncertain parameters on sustainability indicators introduced above. To simulate the probability distribution of cradle-to-grave life cycle GHG emissions for LMO and NCM Li-ion batteries, Monte Carlo simulations are conducted using the Oracle Crystal Ball add-in for Excel. Each simulation consists of 100,000 Monte Carlo runs, used to develop GHG emissions probability distributions. For each run, Crystal Ball randomly selects input parameters based on the predefined probability distributions for four input parameters: 25 ACS Paragon Plus Environment


mass of BMS, mass of cooling system, battery pack production efficiency and driving distance. Mass of BMS, mass of cooling system, battery pack production efficiency and driving distance are assigned to lognormal distributions.

Fig. 15 Probability distribution of cradle-to-grave GHG emissions for LMO Li-ion battery. 90% confident region is shown as blue part.


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Fig. 16 Probability distribution of cradle-to-grave GHG emissions for NCM Li-ion battery. 90% confident region is shown as blue part.

The probability distributions of cradle-to-grave GHG emissions for LMO and NCM Li-ion batteries are shown in Fig. 15 and 16, respectively. GHG emissions for LMO and NCM Li-ion batteries have similar probability distributions. Both probability distributions almost have the same 90% confident intervals, although they have different peak values. Besides, both probability distributions demonstrate a wide range of GHG emissions, with the highest bars representing the values of the highest probabilities. The asymmetric profile of both distributions results from the nonlinear relationship between the input parameters and the corresponding sustainability indicators. It can be seen that GHG emissions in both cases are found to be unstable to the presence of parameter uncertainties. In other words, changes in input parameters can lead to relatively significant changes in GHG emissions for Li-ion batteries. Therefore, to apply simple and scalable manufacturing methods with less GHG emissions can lead to more environmentally sustainable Li-ion battery technologies.

Conclusion We evaluated and compared the life cycle environmental impacts of LMO and NCM Li-ion batteries through process-based LCA and integrated hybrid LCA approaches. The integrated hybrid LCA approach emphasized the advantages of process-based LCA and EIO-based LCA and overcame the drawbacks of them. The integrated hybrid LCA approach could estimate the total environmental impacts resulted from both the process systems and the EIO systems. For processbased LCA, 17 ReCiPe midpoint environmental impact indicators and three endpoint environmental impact indicators were studied. As for the integrated hybrid LCA, life cycle GHG emissions and energy consumption were emphasized. Furthermore, we performed sensitivity analysis of cradle-to-gate life cycle GHG emissions with respect to the uncertainties in mass of BMS and cooling system, product prices, and production efficiency. Monte Carlo simulations were conducted to simulate the probability distributions of life cycle GHG emissions for LMO and NCM Li-ion batteries. The results of the process-based LCA showed that battery cell production contributed to the most significant part in most of the environmental impact indicators. The results of the integrated hybrid LCA revealed that battery cell production was the most significant contributor in life cycle GHG emissions, and the EIO systems contributed the largest part in life 27 ACS Paragon Plus Environment


cycle energy consumption. The most significant difference between two Li-ion batteries lied in the disposal and recycling stage. For LMO Li-ion battery, disposal and recycling stage only made up a small portion of less than 10% for life cycle GHG emissions and energy consumption. However, for NCM Li-ion battery, it contributed a much larger part with more than 20%. From the results, we can find that the EIO systems play a key role in evaluating the life cycle environmental impacts of Li-ion batteries especially in life cycle energy consumption. To systematically evaluate the environmental impacts of Li-ion batteries and avoid cutoff errors, integrated hybrid LCA approach is necessary as the data become available. Meanwhile, we can figure out the influences of macroeconomic fluctuations on environmental impacts from results of integrated hybrid LCA approach. However, due to limited data availability, current integrated hybrid LCA studies can only analyze some specific environmental impact categories. As shown by the environmental profiles of two Li-ion batteries, process-based LCA has specific advantage on technology comparison, because it provides sufficiently detailed information on various types of environmental impacts. Therefore, results from process-based LCA can make good compensations for integrated hybrid LCA results. Process-based LCA and integrated hybrid LCA are both required when evaluating the environmental impacts of Li-ion batteries. A potential future direction of this research is to investigate a variety of recycling process and emerging recycling methods for Li-ion batteries.

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For Table of Contents Use Only. Synopsis: Process-based and integrated hybrid life cycle assessment of Li-ion batteries to evaluate and compare environmental impacts.


Comparative Life Cycle Assessment of Li-ion Batteries through

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