Environ. Sci. Technol. 2000, 34, 2299-2304
Life-Cycle Methods for Comparing Primary and Rechargeable Batteries R E B E C C A L . L A N K E Y * ,† A N D FRANCIS C. MCMICHAEL‡ U.S. Environmental Protection Agency, 401 M Street, SW, Washington, D.C. 20460, and Department of Civil and Environmental Engineering and Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
Life-Cycle Assessment (LCA) can be used to improve the environmental performance of products throughout their life cycle. With ongoing discussions about system boundaries, appropriate data, and model limitations, LCA methods are in a constant state of evolution. This paper presents the use of a hybrid LCA approach to product environmental assessment in which two methods of analysis are combined to present the total environmental impact for two battery systems. A quantitative model for product assessment has been developed at Carnegie Mellon. The model is based on economic input-output life-cycle analysis (EIO-LCA) and has been explained in previous works. The EIO-LCA tool allows a user to quantify the direct and indirect relationships among industry sectors and the associated environmental burdens through the materials extraction and manufacturing phases. However, to study environmental effects over a product’s entire life, use and endof-life impacts must also be quantified. This is accomplished using the LCA approach in which an emissions and energy inventory is compiled and the environmental impacts are quantified. In this paper, the above hybrid LCA approach is applied to comparing the total environmental impacts of primary and rechargeable batteries. The primary (non-rechargeable) batteries mainly used in electronic products are zinc-alkaline batteries, and the most widely used consumer rechargeable batteries are nickel-cadmium. It is generally accepted that rechargeable batteries offer environmental advantages over primary batteries. We find that materials use, energy use, and emissions can be quantified over the entire product life cycle to quantitatively show that resource use and emissions are substantially lower if a rechargeable battery can be substituted for a primary battery. However, consumer use patterns will affect the relative environmental benefits of rechargeable batteries. Noting the effect of consumer behavior also determines where uncertainties in the analysis may lie, since behavior is difficult to predict. Recycling batteries will also have associated emissions and energy use. Even accounting for the additional resource consumption and emissions for rechargeable batteries in the use and recycling phases of life, rechargeable batteries will still consume less resources over the entire life cycle when used in applications as a substitute for primary batteries. The assessment methods can also be applied to electronic products in addition to components such as batteries. 10.1021/es990526n CCC: $19.00 Published on Web 04/25/2000
2000 American Chemical Society
Introduction Rechargeable batteries are regularly promoted as the environmental alternative to primary, non-rechargeable batteries. For example, in a consumer electronic application such as a small portable radio, nickel-cadmium (NiCd) batteries of size AA may be substituted for the same size zinc-alkaline batteries. These batteries are often compared on the basis of the number of uses. As is commonly assumed, from a materials viewpoint rechargeable batteries can offer environmental advantages for an equivalent amount of operating time since they are used multiple times. However, rechargeable batteries also require electricity to replenish their store of energy. Primary and rechargeable batteries are often compared on the basis of number of uses versus energy requirements, but there is little offered in the way of comprehensive and quantitative environmental assessments of both products over their entire life cycle. Life-cycle assessment (LCA) is a tool that is used to assess the environmental burdens associated with a product or process in each phase of life. Definitions and methods for life-cycle assessments have been discussed in several publications (see, for example, refs 1-3). The challenges of doing a complete LCA include the difficulty in choosing a boundary, a lack of comprehensive data, potentially high cost, and time intensity of the labor (4). The economic input-output lifecycle assessment (EIO-LCA) software model is a tool that addresses these challenges. However, the EIO-LCA tool only provides an analysis up through the manufacturing phase. To complete the picture of total environmental impacts, lifecycle inventory analysis methods are also used. The following process flow diagrams show the flow of materials and resources through the life cycle of batteries. Figure 1 shows the process flow diagram for primary batteries. After being manufactured, the batteries are used for one cycle by the consumer. After some residence time with the consumer, the batteries are disposed of, typically in municipal solid waste for primary consumer batteries such as zincalkaline batteries. The process flow for rechargeable batteries is shown in Figure 2. After being manufactured, rechargeable batteries are used by the consumer for n cycles, until the end of useful life. After some residence time, rechargeable batteries may be recycled or disposed of in municipal solid waste. If battery materials are recycled, the recovered metals may be used in the production of new batteries, or they may be used for another secondary application.
EIO-LCA Model The EIO-LCA model used in this paper is a tool that has been developed to complement LCAs that use an inventory analysis approach (as described in ref 5), and the EIO-LCA model and methods have been described in previous works (4, 6). The EIO-LCA model can be used to calculate resource demands and environmental and economic effects for the manufacture of a given monetary demand in an industry sector, thereby simplifying a LCA up through the manufacturing stage of life. However, a complete LCA also considers the stages of life beyond manufacturing. This life-cycle comparison of two battery sectors uses a hybrid LCA approach, using EIO-LCA results for the resource extraction through manufacturing phases, using inventory analysis * Corresponding author phone: (202)260-1547; fax: (202)260-0816; e-mail:
[email protected]. † U.S. Environmental Protection Agency. ‡ Carnegie Mellon University. VOL. 34, NO. 11, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Process flow diagram for primary batteries.
FIGURE 2. Process flow diagram for rechargeable batteries. methods combined with EIO-LCA for the use phase, and giving a qualitative assessment of the recycling and disposal phases. The EIO-LCA model quantifies the direct and indirect relationships between industry sectors within an economic system and quantifies their respective environmental burdens. The data used in EIO-LCA has been developed from a variety of public data sets and assembled for various commodity sectors. Primarily, the data are self-reported and are subject to measurement error and reporting requirement gaps. The major data sources include the 1992 commodity input-output matrix of the U.S. economy as developed by the U.S. Department of Commerce, the 1992 Census of Manufacturers, the U.S. Environmental Protection Agency (EPA) 1995 Toxics Release Inventory (TRI), the 1995 Annual Survey of Manufacturers, and the 1993 biannual U.S. EPA report on Resource Conservation and Recovery Act (Subtitle C) (RCRA) hazardous waste. The data that are used are the most recently available compiled figures from these sources, and the EIO-LCA database is regularly updated as more recent data become publicly available. CMU-ET is a weighting method for toxic emissions to account for their relative hazard by using occupational exposure standards (7). External costs are calculated from conventional air pollutant emissions and estimates of pollution damage taken from the economics literature. For further details on the EIO-LCA software model, the reader is referred to the previously given references or to the EIO-LCA web site (http://www.eiolca.net).
Methods In this paper, the EIO-LCA model is used to compare two industry sectors, primary batteries, categorized as “dry and wet primary batteries,” with a Standard Industrial Classification (SIC) code of 3962 (EIO No. 580200) and rechargeable batteries, categorized as “storage batteries,” with an SIC code of 3961 (EIO No. 580100). These sectors provide the most disaggregated data that are available for these types of batteries. In 1992 in the United States, the total industry output for the primary battery sector was $1.78 billion and 2300
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for the secondary battery sector was $3.40 billion. Both of the industrial sectors manufacture primary and secondary batteries; about 98% of the revenue made by the primary sector comes from primary batteries, and about 2% is made from the rechargeable battery commodity. In 1992, the rechargeable battery industrial sector made 99% of its output as rechargeable batteries and about 1% as primary batteries. Although each makes several commodities in addition to batteries, each may be approximated by its principal commodity. In consumer electronic products, the primary (nonrechargeable) batteries most often used are zinc-alkaline batteries, and the rechargeable batteries most widely used are NiCd. To make a comparison of primary and rechargeable batteries, the analysis must account for the ability to recharge batteries. To offer environmental improvements, the environmental burdens associated with the use of a rechargeable battery must be less than the use of an equivalent number of primary batteries. If the rechargeable batteries are recycled at end of life, this will further reduce the environmental burden by decreasing the amount of raw materials needed to manufacture the batteries. As an example, this analysis considers a lower bound substitution of 200 primary batteries for one rechargeable battery and assumes a cost for rechargeable batteries to be 4 times that of primary batteries as an upper bound. Substitution has technical requirements such as voltage level, power, and energy required for an application. LCA can provide a method to evaluate the environmental impact of batteries that may be substituted for each other. One difficulty of the hybrid method described here lies in the aggregated nature of the industry sector data. For example, several types of batteries may be included in the storage battery sector. In this sector, a substantial fraction of the output is in starting-lighting-ignition (SLI) batteries. However, to apply the hybrid model in this paper, we consider that the data for the storage battery sector is representative of one type of rechargeable battery, NiCd, and we use the EIO-LCA results with use and end-of-life results for NiCd batteries.
TABLE 1. Resource Use for a Given Demand ($106) primary
fertilizers ($)
fuels
ores (t)
ores ($) water use (106 L) electricity (106 kWh) fuel conversion (TJ)
nitrogenous ammonium nitrate ammonium sulfate organic fertilizers phosphatic fertilizers super phosphates bituminous coal (t) natural gas (t) liquefied natural gas (t) liquefied petroleum gas (t) motor gasoline (t) kerosene (kg) aviation and jet fuel (t) light and heavy fuel oil (t) iron copper bauxite gold silver ferroalloy lead and zinc uranium and vanadium intake recycled and reused discharged untreated
storage
$100
$100
$2
$100S/$100P
$100P/$2S
65 2 200 4 100 26 000 14 2 600 26 000 7 000 500 800 990 880 450 3 100 11 000 19 000 840 16 000 340 21 000 93 000 8 900 3 100 5 100 1 400 63 1 400
95 2 400 5 600 24 000 7 2 200 23 000 7 600 540 670 1700 870 430 4 100 2 800 68 000 1100 66 000 800 9 400 758 000 57 000 1 900 2 900 870 96 1 400
1.9 48 110 478 0.14 43 466 152 11 13 34 17 8.6 82 56 1 400 22 1 300 16 190 15 000 1 100 38 58 17 1.9 28
1.5 1.1 1.4 0.93 0.50 0.83 0.9 1.1 1.1 0.84 1.7 1.0 0.9 1.3 0.3 3.7 1.3 4.1 2.3 0.4 8.2 6.5 0.62 0.57 0.60 1.5 1.0
34 45 37 54 100 60 56 46 46 60 29 51 51 38 190 14 39 12 21 110 6.1 7.7 81 87 83 33 49
A more detailed analysis of the disaggregated data is beyond the scope of this paper. However, a thorough analysis would involve first manually disaggregating the EIO-LCA data into different battery types. Within the storage battery sector, for example, this can be estimated by examining the data on the sectors that purchase these types of batteries. For the phases following manufacture, data on the use, disposal, and recycling for each battery type represented would be collected. These data would be used proportionately to their representation in the storage battery sector to form a complete environmental assessment using the described hybrid method. Disaggregating and combining the data as described above is a thesis-level project. An additional requirement for the comparison of two battery types is a substitution model, whereby a rechargeable battery is considered equivalent to a given number of primary batteries for use in an equivalent function. Such a substitution model is described in the next section.
Results and Discussion Materials Acquisition and Manufacturing Phases. When considering a $100 million demand in both sectors, the resource use and emissions for the rechargeable battery sector often equal or exceed the impacts of the primary battery sector. For some resources, such as iron and ferroalloy, the demand of the primary battery sector exceeds the demand of the storage battery sector by more than a factor of 3. However, a fair comparison of the impact of each battery type depends on whether one type can substitute for the other. If a primary and a secondary battery can serve equivalent functions, then this means that n primary batteries may be replaced with a single secondary battery. Depending on the electrochemistry and the mode of use, n may be several hundred or larger. During the life-cycle phases of raw materials extraction through manufacturing, resources will be consumed and environmental impacts will result. The EIO-LCA software can simplify LCA by providing impact data for the raw materials extraction through manufacturing phases. Tables 1 and 2 compare the resource consumption and environ-
mental impacts for a demand of $100 million in both primary batteries and rechargeable batteries. If the demand for either of these commodities decreases by $100 million, then the sign of the emissions would change, and we would expect decreases in emissions by the same amounts. Tables 1 and 2 also give results for a demand of $2 million in the storage battery sector. Suppose we compare rechargeable batteries that function for 200 cycles to a primary battery that functions for a single cycle, and also suppose that the secondary battery costs 4 times that of an equivalent primary battery. For this case of equivalent functionality, the rechargeable battery has a net cost of 4 ÷ 200 ) 1/50th of the cost of the primary battery. Increasing the number of discharge cycles and decreasing the price difference will also favor the rechargeable battery over the primary battery. Thus, a demand of $100 million in the dry and wet primary battery sector would be equivalent to a $2 million demand in the storage battery sector. To show the relative burdens, the last two data columns report relative resource use and environmental impacts. One column shows simply the relative burdens of a $100 million demand in the storage battery sector to a $100 million demand in the dry and wet primary battery sector. The other column reports the relative burden of the $100 million demand for primary batteries to an equivalent demand in rechargeable batteries, which based on the substitution model used is a $2 million demand. Unrounded data were used to calculate the ratios. When taking recharging capability into account, rechargeable batteries that substitute for primary batteries consume much less resources than primary batteries. From a mass impact, secondary batteries use less materials than primary batteries. The use of rechargeable batteries requires 81 times less water resources and almost 33 times less electricity. The converted fuel equivalent demand is about 49 times less for rechargeable batteries than for primary ones. Similar savings in emissions and waste generation are shown in Table 2. Considered on a one-to-one cost basis, the environmental burdens associated with the manufacture of rechargeable batteries are often twice the burdens associated with primary VOL. 34, NO. 11, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Environmental Impacts for a Given Demand ($106) primary
conventional pollutants (t)
SO2 CO NO2 volatile organic compds lead (particulate) particulate matter
