Abt life-cycle analysis of different Li-ion chemistries for PHEVs and EVs identifies opportunities for improving environmental profile of batteries
|Generic process flow diagram for lithium-ion batteries for vehicles (color coded to present LCI data sources). Source: “Application of LCA to Nanoscale Technology”. Click to enlarge.|
A recent Abt Associates, Inc. life-cycle study of three Li-ion battery chemistries for plug-in hybrid (PHEV) and battery-electric (BEV) vehicles generated a number of findings and identified opportunities for improving the environmental profile of Li-ion batteries for use in plug-in and electric vehicles.
The study, carried out through a partnership with EPA, the US Department of Energy, the Li-ion battery industry, and academicians, was the first life-cycle assessment to bring together and to use data directly provided by Li-ion battery suppliers, manufacturers, and recyclers. It assessed three currently manufactured Li-ion battery technologies for EVs and two for a PHEV with a 40-mile all-electric range: lithium-manganese oxide (LiMnO2); lithium-nickel-cobalt-manganese-oxide (LiNi0.4Co0.2Mn0.4O2, Li-NCM); and lithium-iron phosphate (LiFePO4). In addition, a single-walled carbon nanotube (SWCNT) anode technology for possible future use in these batteries was assessed.
This partnership was led by EPA’s Design for the Environment (DfE) Program, in the Office of Pollution Prevention and Toxics, and the National Risk Management Research Laboratory, in EPA’s Office of Research and Development.
This type of study had not been previously conducted, and was needed to help grow the advanced-vehicle battery industry in a more environmentally responsible and efficient way, the partners said. Its purpose was to identify the materials or processes within a Li-ion battery’s life cycle that most contribute to impacts on public health and the environment, so that battery manufacturers could use this information to improve the environmental profile of their products, while the technology is still emerging.
The LCA study was conducted consistent with the International Standards Organization (ISO) 14040 series, which stipulates four phases of an LCA: goal and scope definition; life-cycle inventory (LCI); life-cycle impact assessment (LCIA); and interpretation. No comparative assertions, as defined in ISO 14040, were made about the superiority or equivalence of one type of battery system versus another in this study.
Highlights of the conclusions and findings of the study include:
Battery chemistries, components, and materials. The choice of active material for the cathode affects human health and toxicity results. For example, the nickel cobalt manganese lithium-ion (Li-NCM) chemistry relies on rare metals like cobalt and nickel, for which the data indicated significant non-cancer and cancer toxicity impact potential. The other two chemistries use the lower toxicity metals, manganese and iron.
The cathode active materials appear to all require large quantities of energy to manufacture. However, the Li-NCM cathode active material requires 1.4 to 1.5 times as much primary energy as the other two active materials.
The solvent-less Li-ion battery manufacturing method appeared to use very little energy compared to estimates provided in prior studies of cell and pack manufacture. The Abt team was not able to obtain primary data for electricity and fuel consumption from manufacturers using solvent, making it difficult to quantify with any certainty the difference between solvent-less and solvent-based electrode manufacturing.
Choice of materials for cell and battery casing and housing, which are primarily chosen for weight and strength considerations, are among the top process flow contributors to impacts in the upstream and manufacturing stages.
Vehicle/battery types. The authors found that global warming potential (GWP) is one of the few impact categories in which EV batteries show lower impacts than PHEV-40 batteries. However, the GWP benefit only appears when the electricity grid relies less on coal production and more on natural gas and renewables.
Abiotic depletion and eutrophication potential impacts are the only other impact categories in which EV batteries show lower impacts; however, this is only the case when the grid is composed to a large extent by natural gas-based generation facilities.
Accordingly, in regions where the grid is more heavily coal-centric, the study results suggest that PHEV-40 vehicles may be preferable if global warming impacts are highly valued.
The authors emphasized that their study— as well as data contained in a previous study—suggest that, in comparison to internal combustion engine vehicles, there are significant benefits in GWP for both EVs and PHEV-40s, regardless of the carbon intensity of the grid. The Abt analysis did not consider the manufacture of the non-battery components of the vehicle itself, such as the glider and drivetrain.
Life-cycle stages. The use stage of the battery dominates in most impact categories; however, upstream and production is non-negligible in all categories, and relatively important with regard to eutrophication potential, ozone depletion potential, ecological toxicity potential, and the occupational cancer and non-cancer hazard impact categories.
The extraction and processing of metals, specifically aluminum used in the cathode and passive cooling system and steel used in the battery pack housing and battery management system (BMS), are key drivers of impacts.
Recovery of materials in the EOL (end-of-life) stage significantly reduces overall life-cycle impacts, as the extraction and processing of virgin materials is a key contributor to impacts across battery chemistries. This is particularly the case for the cathode and battery components using metals (e.g., passive cooling system, BMS, pack housing and casing).
The analysis underscores the importance of curtailing the extraction of virgin lithium to preserve valuable resources and reduce environmental impacts.
Sensitivity analysis. Lifetime of the battery is a significant determinant of impact results; halving the lifetime of the battery results effectively doubles the non-use stage impacts, resulting in substantial increases in global warming potential, acidification potential, ozone depletion potential, and photochemical oxidation potential (e.g., smog); this is true even for PHEV-40s batteries, which are 3.4 times smaller in terms of capacity.
When examining the sensitivity to changes in the marginal grid mix, impacts tend to be substantially higher when based on an unconstrained charging scenario using the IL grid, which almost exclusively uses coal as a fuel. The low-end of the impact range primarily result from the ISO-NE unconstrained charging scenario, which is predominately natural gas-derived electricity.
However, with ozone depletion and occupational cancer hazard, lower impacts are observed under the IL smart charging scenario, due to lower emissions of halogenated compounds and formaldehyde, respectively.
Abt based the analysis of the EOL impacts on the high-end of the ranges of recovery rates provided by the recyclers for each battery material. When conducting the sensitivity analysis and comparing the impact results between the low- and high-end of the ranges provided, the authors found that the impacts were not highly sensitive to the rate within these ranges, with the exception of the occupational non-cancer and, to a lesser extent, cancer categories.
The study results show that recovery of the materials in the EOL stage for use as secondary materials in the battery does significantly mitigate impacts overall, especially from the upstream processing and extraction stages, across battery chemistries.
Nanotechnology. Nanomaterials such as SWCNTs are being researched and developed to improve the energy density and ultimate performance of the batteries.
SWCNT anodes made by laser vaporization result in electricity consumption that is orders of magnitude greater than that of battery-grade graphite anodes. In addition, the ratio of the SWCNT anode to the graphite anode for primary energy use is similar to the ratio for the environmental and human health impact categories, except for ozone depletion potential (where the ratio is lower) and the occupational non-cancer hazard (where the ratio is higher).
The Abt authors noted that over time, the manufacturing process for SWCNTs will become much more energy-efficient. The high pressure carbon monoxide (HiPCO) process for SWCNT production, first reported in the literature in 1999 and patented (applied) in 2004, has already seen the electrical energy required per gram of nanotube reduced by more than an order of magnitude. However, they added, the break-even impact analysis suggests that significant additional energy efficiency gains will have to be met to be comparable to the battery grade graphite anode in terms of energy requirements per gram of material.
The Abt study also identified a number of opportunities for improving the environmental profile of Li-ion batteries for use in plug-in and electric vehicles were identified:
Increase the lifetime of the battery. A lifetime of 10 years was assumed by the partnership, as it represents the anticipated lifetime the battery manufacturers seek to achieve. As shown in the sensitivity analysis, halving the lifetime of the battery results in notable increases across all impact categories for both PHEV-40 and EV batteries; therefore, future battery design changes should focus on increasing the battery lifetime in order to reduce overall impacts.
Reduce cobalt and nickel material use. These metals showed higher toxicity impacts; specifically, non-cancer and cancer impact potential. Reducing the use of and/or exposure to these materials in the upstream, manufacturing, and EOL stages would be expected to reduce the overall potential toxicity impacts.
Reduce the percentage of metals by mass. The Abt team found that metals were a key driver of environmental and toxicity impacts—especially those found in the passive cooling system, battery management system, pack housing, and casing, which were strong contributors to impacts. Accordingly, reducing the use of metals by mass in these components, in particular, should reduce the overall life-cycle impacts of the battery systems.
Incorporate recovered material in the production of the battery. Given the off-set of impacts from the use of recovered materials—as opposed to virgin materials (especially metals)—in the EOL stage, impacts can be reduced if battery manufacturers work with recyclers to maximize the use of secondary materials in the manufacture of new batteries.
Use a solvent-less process in battery manufacturing. The solvent-less process was found to have lower energy use and lower potential environmental and health impacts.
Reassess manufacturing process and upstream materials selection to reduce primary energy use for the cathode. The active material for the cathode, and the cathode manufacturing process itself, were significant contributors to impacts across the categories. Manufacturers can reduce impacts by carefully considering the choice of active material, and assessing their manufacturing process for energy efficiency gains.
Produce the SWCNT anode more efficiently for commercialization. Given the fact that the cradle-to-gate energy use and associated impacts of the SWCNT anode, as currently manufactured, are currently orders of magnitude greater than the battery grade graphite anode, SWCNT anode laboratory research that focuses on lowering the energy intensity of manufacturing processes, in tandem with improving technology performance, will help to improve the overall environmental profile of the technology, before it is commercialized.
his study demonstrates how the life-cycle impacts of an emerging technology and novel application of nanomaterials (i.e., the SWCNT anode) can be assessed before the technology is mature, and provides a benchmark for future life-cycle assessments of this technology. Identifying opportunities for reducing environmental and human health impacts throughout the life cycle of the Li-ion battery should be done on a continuous basis, as the technology evolves and the market share for electric vehicles expands.—“Application of LCA to Nanoscale Technology”
The Abt team also suggested a number of areas for future research, including:
Reducing uncertainty regarding the energy and fuel use for the processes necessary for component and battery manufacture, and differences in energy use due to battery chemistry and size;
Clarifying the actual potential for exposure, in the case of cobalt, and elements that contribute to toxicity, in the case of complex lithium chloride brines from saline lakes, to help understand their contribution to potential occupational impacts;
Research to more realistically characterize the changes in lifetime across chemistries, and differences between EV and PHEV-40 batteries;
Estimating the changes to the grid that would be expected to result from large increases in demand from the increased use of PHEVs and EVs;
Further research on the eventual disposition of recovered and recycled materials—especially for the rare and strategically important metals used in battery production, to allow manufacturers, recyclers, and the scientific community to better understand the benefits and detriments of current recycling technologies, and to help characterize the extent to which secondary material markets might come to substitute for virgin mined material; and
Additional research on nanomaterials that may be used to increase the energy density and performance of Li-ion batteries for vehicles, to ensure that upstream impacts (e.g., energy use and toxicity) do not outweigh potential performance and environmental benefits in the use stage.