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*Not evaluated by this method

Sweden and Netherlands appear to be much more concerned about cadmium and therefore their actions against nickel-cadmium batteries are not surprising. The conclusion must be that life cycle impact assessment values are, at best, estimates which are heavily biased towards particular area's, country's, organization's or individual's points of view and are often not really scientifically based. Of the five techniques considered above, only the U.S. EPA method appears to be largely based on scientifically established toxicological endpoints for human health and the environment, and even in the establishment of those endpoints, there are a considerable number of assumptions and judgments made as to the relative weighting factors utilized and surrogate compounds employed which affect the ultimate impact assessment.

Life Cycle Analysis of Battery Systems

If the total energy and emissions of a battery during its entire lifetime production, use, maintenance and disposal are established, then divided by the total lifetime energy of the battery, the total emissions per kilowatt-hour of energy may be derived. These are separated into specific materials, usually elements, compounds or groups of compounds, for which specific environmental and/or human health impact assessment values are available. Utilizing these values, the overall relative life cycle environmental impact of a particular battery system may be established and compared to other battery systems. As previously discussed, these analyses involve many assumptions and generalizations. In point of fact, accurate analyses can only be carried out on a specific battery composition with specific battery performance. Even then, the assumptions inherent in the impact assessment values, the manufacturing processes, the disposal options and all of the other steps discussed in this review create a large area of uncertainty. These uncertainties notwithstanding, it is useful and interesting to carry out an analysis on a specific battery to show how some of these variables will affect the overall analysis.

At the 8th International Conference on Nickel-Cadmium Batteries in Prague, Czech Republic, a paper (Morrow 1998) was presented which discussed the relative effects of performance and recycling on the life cycle impact assessment of nickel-cadmium batteries. An AA-sized NiCd battery with an assumed composition of 30%Ni - 15%Cd - l%Co was studied even though the references and data in Table I clearly show that these compositions could vary widely. The AA-sized consumer cell is, of course, a small (23-gram) sealed consumer cell, and thus there are no emissions during its use, maintenance or recharging, which would be small even if it were a vented cell. The range of performance parameters chosen were those previously presented in Table V. While the voltage for an AA-sized NiCd battery has remained the same over the years, the capacity of this cell and thus its unit energy have increased over the years. In 1990, the best AA-sized NiCd had a capacity of 0.5 ampere-hours, whereas in 2000, the best commercially available NiCd capacity in this size is about 1.2 ampere-hours. In addition, cycle life has generally improved, so that today's batteries have a higher total lifetime energy than yesterday's batteries. This statement is probably true of all battery systems, not just the nickel-cadmium system.

If we assume that better than 98% of a battery's total environmental impact is contained in the battery itself and whether or not it is disposed of by incineration, land filling or recycling, then it becomes a relatively simple exercise to compute the environmental impacts of AA-sized NiCd batteries under the compositional and performance assumptions made above. A 23-gram NiCd battery will contain 6.90 grams of nickel, 3.45 grams of cadmium and 0.23 grams of cobalt. From previous analyses, these three materials in the NiCd battery will be the ones which will produce the largest adverse environmental effects even though there may be moderate amounts of steel, plastic, copper and electrolyte present as well. If we assume that the entire weight of the battery upon disposal represents an emission or output to the environment, then the "heavy metal waste" generated per kilowatt-hour of total lifetime battery energy is as summarized in Table VIII. Two figures are shown, one for the lowest lifetime energy (420 watt-hours) and one for the highest lifetime energy (1680 watt-hours).

It is immediately obvious that the highest energy NiCd exhibits the lowest amount of heavy metal waste generated when expressed in terms of grams per kilowatt-hour of total lifetime battery energy. The lowest energy NiCd correspondingly exhibits the highest amount of heavy metal waste per unit of lifetime battery energy. As expected, the amounts of the individual heavy metal wastes generated are directly proportional to the battery's assumed composition. If higher or lower nickel, cadmium or cobalt contents are utilized, then the values for those metals will shift in direct proportion.

Table VIII. Heavy Metal Waste Generated for AA-Sized NiCd* Batteries

Waste Generated, grams per KW-hr Element Highest Energy Lowest Energy

Cadmium 2.05 8.21

Cobalt 0.14 0.55

Nickel 4.10 16.43

Once the ranges of heavy metal wastes generated have been established for an AA-sized NiCd battery of an assumed composition, the next step in the analysis is to assess the environmental and human health impacts of those wastes. While there are many different techniques for assessing the environmental and human health impacts of various materials, the preferred method which will be utilized in this analysis is the one developed for the U.S. Environmental Protection Agency by the University of Tennessee (Davis et al. 1994). This method considers all the major human health and environmental effects including persistence and bioaccumulation which are really relevant to organic compounds but not to metals. This method also includes weighting factors for the actual total levels of emissions. Under this ranking and scoring system, "inherent hazard values" are assigned to various chemicals depending on their quantitative effects on human health and environmental toxicological endpoints. These human health endpoints include both acute and chronic effects, ingestion as well as inhalation, carcinogenicity considerations and other effects such as mutagenicity and reproductive effects. A set of appropriate factors for aquatic and terrestrial organisms are similarly incorporated into the scoring system.

The human health and environmental factors are then multiplied by the exposure potential which includes parameters expressing biological oxygen demand half-life, hydrolysis half-life and an aquatic bioconcentration factor. It is felt that this system is probably one of the better impact assessment systems available today because it assigns impact values based on quantitative scientific data rather than subjective "concern" over a chemical which is often based on perception rather than scientific data. On the other hand, the bioaccumulation and persistence factors have already been shown to be not particularly relevant to metals per se. In the future, alternative evaluation systems such as solubility and transformation characteristics of metals and metal compounds, and models such as the biotic ligand model will be found to be much more appropriate for evaluating the human health and environmental impacts of battery metals.

If the environment impact assessment values for the U.S. EPA method shown in Table VII are combined with the heavy metal waste data for nickel, cadmium and cobalt shown in Table VIII, environmental impact assessment values per unit of total battery energy for each of the three metals may be derived. The sum of these three values then yields an approximate environmental impact value for an AA-sized NiCd battery of an assumed composition and an assumed range of performance and total lifetime energy. The lowest impact values are associated with the highest set of performance parameters of capacity and cycle life, while the highest impact values are associated with the lowest set of capacity and cycle life performance parameters. This data may be further analyzed to establish the respective impact values when various percentages of the NiCd batteries are recycled. Such an analysis is shown in Table IX for two levels of recycling, 0% and 40%. For each level of recycling, the range of impact values for each element corresponding to the highest and lowest performance parameters are shown. As expected, recycling of 40% of the NiCd batteries results in a 40% reduction in the environmental impact values associated with NiCd batteries. What is perhaps more surprising is that performance can have a marked effect on the total life cycle environmental impact associated with NiCd batteries. The data indicate that, if both capacity and cycle life of an AA-sized NiCd battery can simultaneously be realized at the top end of the assumed ranges, then total life cycle risks may be reduced by a factor of four compared to those batteries with performance at the bottom end of the assumed ranges.

Table IX. Environmental Impact Values per Kilowatt-Hour Lifetime Energy For AA-Sized NiCd Batteries at Two Recycling Levels

Element

Environmental Impact Values per KW-hr 0% Recycling 40% Recycling

Nickel

Cadmium

Cobalt

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