Batteries, from Cradle to Grave - Journal of Chemical Education (ACS

In the Classroom

Batteries, from Cradle to Grave Michael J. Smith* Departamento de Química, Universidade do Minho, 4710-057 Braga, Portugal *[email protected] Fiona M. Gray School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, Scotland

Employers expect graduates to have an area-specific knowledge and to be able to apply instrumental, interpersonal, problem-solving, and systematic skills efficiently. To maximize the number of students achieving high levels of competence, a greater emphasis should be placed on activities intended to develop the appropriate skills within the course structure (1). Problem-based learning (PBL) is a widely applied approach intended to encourage students to learn through the structured exploration of a research problem. Small teams of students are given an open-ended assignment that they research in order to present well-supported, evidence-based solutions or strategies in written or oral format. This approach effectively combines independent learning with written and oral presentation practice. Portable electronic equipment has become an essential component of our everyday lives, and whether the device in question is a remote-controlled toy, a mobile phone, or a laptop computer, it relies on batteries as a source of power. In 2008, the European Union introduced new legislation to regulate the use of toxic chemicals in batteries and to outline a program for the obligatory recycling of spent batteries. This legislation is expected to have a widespread impact on both industry and the consumer, and hence, it is timely to look at key issues such as environmental consequences, public awareness and acceptance, current good practice, challenges and practicalities, and the consequences of legislation that are currently being addressed within Europe, North America, and Asia. We have identified the area of spent-battery recycling as a relevant topic on which to build a PBL activity. Evolving battery design and related disposal issues, relevant to the fields of electrochemistry, environmental chemistry, materials chemistry, electrical engineering and technology, and waste management and recycling, are reviewed to provide key entry points and useful information resources for instructors who wish to adopt this teaching strategy. Problem-Based Learning The problem-based learning (PBL) activity based on battery recycling was successfully implemented with a class of students in the third year of chemistry. The students were introduced to the topic through an oral presentation after completing lecture courses on environmental chemistry and applied electrochemistry. The class was divided into three-member groups, and students were assigned problems. Some examples of these problems are included in the supporting information. A general 162

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perspective of the research, extension, and intended audience were defined, together with a schedule for periodic facilitator contact for discussion of progress and monitoring of group activity. After a period of group activity, the students submitted the results of their research as a short report with supporting bibliography and also as a poster or oral presentation to an audience of colleagues and instructors during a session at the end of the semester. A short text introducing the research assignment and a typical student handout has been provided in the supporting information. Instructor assessment of student learning in this activity was positive and the overall impression was that students performed at a level significantly above their average course grade. This improvement was attributed to the high level of motivation, underlining the importance of authentic problems for students. Our students showed initiative in fact gathering and in the proposal of new solutions to existing problems and invested significant personal effort in self-directed study. The end products delivered as reports, posters, and oral presentations made a useful contribution to student skill development, fully vindicating the PBL approach in undergraduate education. The Chemistry of Batteries Electrochemical power sources or batteries are devices that convert energy stored in chemicals into electrical energy. Strictly speaking, a battery is made up of an assembly of two or more cells connected in a series or parallel configuration (2-7), but over the last few decades the terms cell and battery have become synonymous. Although credit for the original invention that demonstrated the viability of the concept is generally attributed to Alessandro Volta (1800), various, more practical devices were subsequently developed in a sustained effort to improve the efficiency of energy storage and conversion (7). Since the early days of battery science, the development of better portable energy sources has been driven by the needs of manufacturers in the electronics sector. Batteries can be classified as primary (single use) or secondary (rechargeable), with further subdivision into household (for consumer goods such as telephones, flashlights, radios, watches, or computers), industrial (for reserve network power, local backup, or traction), and SLI (for starting, lighting, ignition in vehicles). The principal commercial battery chemistries are listed in Table 1, together with examples of typical applications. Further details of the operational characteristics of these cells may be obtained from refs 2-7.

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Vol. 87 No. 2 February 2010 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed800053u Published on Web 01/12/2010

In the Classroom Table 1. Chemistry Present in Household, Industrial and SLI Batteries Principal Components Designation PRIMARY

SECONDARY

Anode/Negative

Electrolyte

Cathode/Positive

Typical Applications

Zinc-carbon

Zinc sheet

NH4Cl or ZnCl2

MnO2, C (mix)

Used in a wide range of small portable electronic devices; low-cost modest discharge performance; 1.5 V cell potential

Alkaline-manganese

Zinc powder

KOH

MnO2, C (mix)

Improved performance version of the ZnC cell, more energy and power but also more expensive; 1.5 V cell potential

Mercury

Zinc powder

NaOH or KOH

HgO, C (mix)

Previously used in hearing aids, cameras, and calculators, discontinued because of Hg toxicity; 1.35 V cell potential

Lithium

Lithium foil

Organic solvent and Li salt

MnOp, C (mix)

Available in range of systems with various cathodes with voltages between 1.5 and about 3.6 V; excellent performance; expensive

Zinc-air

Zinc powder

KOH

Air, C

Principal niche market of hearing aids; good cell performance with nominal 1.4 V, but high self-discharge rate

Zincsilver oxide

Zinc powder

KOH

Ag2O, C (mix)

Typical application in watches or calculators; good discharge performance, but expensive because of Ag content; nominal 1.55 V cell potential

NiCd

Cd

KOH

NiO(OH)

Substantial market presence in portable devices; high cycle life, but suffers from memory effect; nominal 1.2 V cell potential; Cd is toxic

NiMH

AB5 or AB2 Intermetallic compound

KOH

NiO(OH)

Substitute for traditional NiCd cell; improved in both electrochemical and environmental performance; nominal 1.2 V cell potential

Lead-acid

Pb

H2SO4

PbO2

Generally used in SLI applications, traction battery, or as a reserve power source; high toxicity; nominal 2 V; easy to recycle

Lithium ion

C, Lix

Organic solvent and Li salt

Li(1-x)MnOp

High performance cell widely used in portable electronic equipment; low environmental impact; nominal 3.6-3.7 V cell potential

Li-poly or LiPo

C, Lix

Polymer gel and Li salt

Li(1-x)MnOp

Proposed as substitute for Li ion, probably cheaper and safer with comparable performance; nominal 3.7 V

All commercial batteries are made up of two electrodes, the anode and the cathode, and an electrolyte. The efficiency of the battery chemistry depends on the chemical reactions taking place at the electrodes and the nature of the electrolyte present. In addition to these active components, batteries must also contain inactive components that have support functions and ensure cell operation. These inactive components include the casings (often made of steel) and separators, seals, or labels (typically fabricated from polymers, paperboard, or paper). The active components that are currently of greatest environmental concern are those based on cadmium, lead, and mercury, and to a lesser degree copper, nickel, lithium, silver, and zinc (8). Precise up-to-date estimates of the number of household batteries produced are difficult to obtain (9), but approximate annual sales in the United States, Europe, and Japan are about 4, 5.5, and 1.9 billion, respectively (6, 10-13). The secondary cell market share is between 10 and 14% of annual sales, and this is made up of a mixture of nickel-cadmium (NiCd),

r 2010 American Chemical Society and Division of Chemical Education, Inc.

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nickel-metal hydride (NiMH), and lithium ion (Li ion) batteries. Batteries and Environmental Issues Battery components present no threat to human health or to the environment while the battery is in normal use. However, when subjected to careless disposal within the household or workplace, inevitable damage and degradation of the battery housing changes this situation. The environmental impact of batteries in landfills (11-14) depends on the battery chemistry, the residual capacity of the battery, the local conditions of temperature, moisture, and oxygen content, the design and maintenance of the landfill, and the proximity of surface or groundwater. Batteries identified for household use are mainly zinccarbon, alkaline-manganese, zinc-air, zinc-silver oxide, and lithium types. This group of primary batteries continues to make

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up the majority of batteries consumed, accounting for about 90% of the portable battery market (6, 11-14). The commercial success of aqueous electrolyte-based batteries (zinc-carbon, alkaline-manganese, zinc-air, and zinc-silver oxide) is due to low material costs, ease of manufacture, and performance characteristics that are suitable for a wide range of electronic devices with modest energy and power requirements. Although these batteries are based on some of the oldest chemistries, they have been subjected to continuous improvement. It is noteworthy that the alkaline-manganese, zinc-air, and zinc-silver oxide miniature batteries (coin or button format) may contain small quantities of mercury as a corrosion-suppressing additive for the anode. In Europe, for example, the marketing of button batteries containing more than 2% of mercury by mass and other batteries containing more than 0.0005% of mercury has been prohibited since January 2000. In addition, silver oxide, zinc-air, and alkaline button batteries that contain between 0.0005% and 2% per cell must also be labeled as not for household waste disposal. The mercury-content restrictions have motivated structural changes: the introduction of zinc alloy powder anodes, the development of new corrosion suppressors, and modified cathode formulations to maintain prelegislation performance. The lithium nonaqueous primary-battery technology has also progressed significantly since the early 1970s (15, 16). Although substantial market growth has been observed, the cost of lithium-based primary batteries is only justified in specific applications where high cell performance is essential. Of all the systems under consideration here, it is the lead-acid battery predominantly used in SLI, traction, and industrial energy storage that is the most successfully recycled (Figure 1). The greatest contribution to this situation lies in factors such as the inherent value of the scrap metal, the effective spent-battery collecting procedure, the relatively simple structure of the battery, and the straightforward nature of the leadsmelting process. The NiCd secondary battery has been commercially available since 1950 and effectively dominated the household secondary-battery market until about 1990. It is still produced in the standard battery packaging (cylindrical, button, and flat prismatic formats) for household use and in industrial, large-scale

batteries that contest the commercial terrain occupied by lead-acid batteries. However, the highly toxic cadmium anode, along with the nickel oxide hydroxide cathode and the concentrated potassium hydroxide electrolyte, present an environmental dilemma. In 1990, NiMH cells with their improved electrochemical performance became available commercially and also occupied a more favorable environmental position. While the electrolyte and cathode compositions are similar to those of a NiCd cell, a hydrogen storage anode of nickel-cobalt-rare-earth metal alloy replaced the toxic cadmium electrode. NiMH technology is generally viewed as being a stopgap, to be superseded by lithium-based battery technology. There has been significant electrochemical development in this sector; first with the launch of the lithium-ion cell and more recently with the lithium polymer (Li-poly) cell. A move to lithium-based batteries (both primary and secondary) represents an advance in terms of environmental impact. Although the anodic materials are nontoxic, lithium-ion cells contain flammable electrolytes and may also contain moderately toxic composite cathodes. Li-poly cells contain similar anode and cathode constituents but incorporate a polymeric gel electrolyte. The advantages of this new cell format, such as high electrochemical and safety performance and a thin-cell profile that allows manufacturers to adapt cells to fit available space in new devices, will lead to significant growth of this battery in the market and will require alterations in disposal strategies. Legislation Although there are differences in the way countries approach health and environmental issues, the content of the regulations applied to industry is similar. In Europe (17-19), Asia (19, 20), and North America (21-25), the first stages of regulation involved limitation of dangerous substance content in household batteries. Subsequent legislation regulated the collection and disposal or recycling of industrial and household batteries. Representation of the battery manufacturing industry from the outset has permitted consensual positions to be established and resulted in the associations of manufacturers and importers (26-32) that assume responsibility for coordination

Figure 1. Recycling procedure of lead-acid batteries. (UPS is uninterruptible power supply.)

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In the Classroom

of battery elimination or recycling. Despite legislation to regulate disposal and recycling, poor public knowledge of the legislation, lack of enforcement, and insufficient budget allocation to regulation (33, 34) have been the major contributors to ineffective application of these new laws. The Disposal Option Many batteries still end up in landfills or are incinerated because of inefficient national collection and recycling schemes. This is undesirable because of the risk of hazardous chemicals contributing to leachate from landfill (a 25 g NiCd phone battery can contaminate 750,000 L of groundwater to the maximum acceptable concentration limit) or to emissions from incineration plants. For incineration, the quantities of hazardous emissions depend on furnace temperature, the volatility of the battery elements, and the efficiency of local treatments applied to the furnace emissions. Some heavy elements may be concentrated in the furnace slag and require specific and expensive secondary treatment. Where disposal is the only end-of-life option, it is possible to treat heavy metals by stabilization and inertization to avoid leaching. These processes reduce the toxicity by making insoluble or immobilizing the hazardous waste and involve chemical reactions between constituents in the waste or with species in a solid matrix added to the residue. Inertization is generally considered to be financially nonviable. It requires a battery collection scheme, and unlike recycling, the inertized materials have no residual commercial value. Battery Collection and Sorting Strategies Although certain segments of the battery market benefit from specific collection routines (for example the lead-acid batteries or large capacity installations of industrial batteries), the most challenging market segment is that of household batteries. These batteries are widely dispersed, use a broad variety of chemistries, and represent a large portion of the overall cell market. Efficient collection of household batteries depends on legislation and the willingness of the population to recycle spent cells. Recent studies (32) confirm that high recycling rates, measured as a percentage of the mass of recycled batteries to

the mass of batteries sold for any given financial year, can be achieved. In Belgium (27), for example, the collection rate per person is the highest in the world. To achieve this, it was necessary to invest in an intense and continuous public-awareness campaign to inform the population about national laws, to motivate participation in collection programs, and to change battery disposal habits. The Belgian program involves schools, public and private services, civic associations, point-of-sale outlets (supermarkets, jewelers, photographic shops, pharmacies, toy stores), and municipal ecoyards. Most collection programs are intended for all types of household batteries, with sorting taking place at the recycling installation. As most recycling treatments are sensitive to batterytype purity, the sorting is a critical phase in the process. Various types of automatic sorting equipment have been developed based on magnetic, photographic, UV label detection, and X-ray fingerprinting. Improvements in sorting rates over the last 10 years mean that identification and selection can now be achieved at rates of up to 24 batteries per second with a recognition efficiency of about 99%. This phase of battery treatment no longer represents the limiting step of the recycling process. Recycling Procedures for Batteries The diversity of battery chemistries has led to a correspondingly wide range of recycling treatments. Regardless of the treatment method undertaken, the preliminary processing stage involves removal of labels, opening of cell casings, and destroying seals and separators by procedures based on mechanical cutting, chopping, or pounding, vacuum milling, cryogrinding, or pyrolysis (Figure 2). The secondary stages of recycling are broadly classified as hydrometallurgic or pyrometallurgic. Hydrometallurgic techniques applied to the cell fragments include acid, alkaline, or solvent extraction. These procedures yield metal solutions that are subsequently subjected to precipitation, selective reactions, electrolysis, or electrodialysis to isolate the purified materials. Pyrometallurgic procedures, using high temperatures to separate metals, may be subdivided by the final destiny of the recycled material. One subdivision relates to treatments that ultimately incorporate the processed battery material as a

Figure 2. General recycling procedure for all types of batteries.


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component in steel production; the other subdivision involves specific processes designed to yield purified elements for reentry into a variety of industrial feedstocks. While the nickel, chromium, and manganese residues from recycled batteries are acceptable components in steel production, the quantities of cadmium, copper, and zinc must be carefully monitored to avoid deterioration of the steel's properties. At the extremely high furnace temperatures used in steel production, any residual zinc and cadmium (and mercury, should it be present) will evaporate, oxidize, and be emitted from fume stacks as flyash loaded with hazardous dust. Although useful, this strategy for battery waste treatment carries certain limitations. Various companies specialize in the production of purified zinc, cadmium, lead, mercury, and nickel using batteries as feedstock. These pure elements are supplied to other metallurgic companies as raw material, and the slag or bottom-ash containing unwanted residues is separated for use in road or building foundations. Procedures for recycling lithium battery feedstocks, also represented in Figure 2, have been developed by various companies. In the Toxco (hydrometallurgic) treatment (35), lithium is recovered as the metal or lithium hydroxide. Initial processing of battery feedstock involves cryogrinding and reacting with water to produce hydrogen, which can be burnt off above the reaction liquid. In pyrometallurgic procedures, component recovery is limited to cobalt and steel-making residues. Other treatments (not shown) involve a combined pyro-hydrometallurgical process where punctured cells are subjected to incineration and cobalt is subsequently recovered from metallic waste through the application of standard hydrometallurgical procedures. With alternative, less vigorous, purely hydrometallurgical procedures (36), electrolyte and electrode material may also be recovered from the disassembled cells. This latter option is more attractive, and even with fluctuations in the market value of recycled materials, the fundamental profitability of the process is supported by the sale of products rather than from charges levied on battery end-users. Future of Battery Technology and Recycling Information provided by manufacturers and recycling agencies confirms that treatment of battery residues has arrived at a critical moment when old responsibilities are being addressed with new strategies. More than ever before, the current consumer generation is being made aware of its duty to adopt a socially and scientifically correct response to preserve the quality of our environment. An ever-increasing number of equipment manufacturers are using high-performance lithium-based secondary cells in their products. Such cells are increasingly of the Li-poly class and pose an interesting conundrum. With foil-bag containers substituting the traditional steel casing, they have minimal recyclable content and combine competitive electrochemical performance with negligible environmental impact. Future versions of Li-poly secondary cells may represent a truly ecological choice of a power source in which the toxic chemical content is so low that they can safely be disposed of as municipal solid waste. Significant advances are also being made in fuel-cell technology with several companies involved in the design and manufacture of high-performance fuel cells adapted to the portable electronics, back-up energy, and traction markets (37-41). These hydrogen or methanol-fuelled cells draw their 166


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chemical energy from a quick-fill reservoir outside the cell (or stack) structure. As the source of chemical energy is not part of the cell, the task of recycling these units is greatly simplified. The use of precious-metal catalysts in the composite electrode component of these cells also provides a strong economic motivation for end-of-life collection and recycling treatment. Even before the routines for end-of-life processing of current primary and secondary cells have become well established and before widespread collection strategies have been implemented at a local level, there are clear indications that a new fuel cell-based power source is gaining commercial viability and that the portable electronics industry is prepared to welcome this innovation. Literature Cited 1. Tuning Educational Structures in Europe; The Tuning Management Committee, University of Deusto: Deusto, Spain, 2006. Document available at http://www.tuning.unideusto.org/ tuningeu/ (accessed Nov 2009). 2. Modern Batteries: An Introduction to Electrochemical Power Sources, 2nd ed.; Vincent, C. A., Scrosati, B., Eds.; Arnold: London, 1997. 3. Crompton, T. R. Battery Reference Book, 3rd ed.; Elsevier Science: London, 2000. 4. Dell, R. M.; Rand, D. A. J. Understanding Batteries; RSC Publishing: London, 2001. 5. Handbook of Batteries, 3rd ed.; Linden, D., Reddy, T. B., Eds.; McGraw-Hill: New York, 2002. 6. Pistoia, G. Batteries for Portable Devices; Elsevier Science: London, 2005. 7. Heise, G. W.; Cahoon, C. N. Primary Batteries; John Wiley & Sons, Inc.: New York, 1960; Vol. 1. 8. The Sigma Aldrich Library of Safety Data, 2nd ed.; Lange, R., Ed.; Sigma-Aldrich Corp.: Milwaukee, WI, 1988. 9. Galligan, C.; Morose, G. An Investigation of Alternatives to Miniature Batteries Containing Mercury; Lowell Center for Sustainable Production, University of Massachusetts Lowell: Lowell, MA, 2004. document available at http://sustainableproduction.org (accessed Nov 2009). 10. Directive of the European Parliament and of the Council on Batteries and Accumulators and spent Batteries and Accumulators; Commission Staff Working Paper, Brussels (2003), http://www.epbaeurope. net/PositionPapers/RD%20como%20presentation%20final%20june%2004%20for%20web.pdf 11. Broussely, M. Spent Battery Collection and Recycling. In Industrial Applications of Batteries: From Cars to Aerospace and Energy Storage; Pistoia, G., Ed.; Elsevier Science: London, 2007; Chapters 14 and 15. 12. Hurd, D. J.; Muchnik, D. M.; Schedler, T. M. Recycling of Consumer Dry Cell Batteries: Pollution Technology Review, no. 213; Notes Data Corp.: Park Ridge, NJ, 1993; pp 210-243. 13. Lund, H. F. The McGraw-Hill Recycling Handbook; McGraw-Hill Professional: New York, 2001. 14. Pistoia, G.; Wiaux, J.-P.; Wolsky, S. P. Used Battery Collection and Recycling; Industrial Chemistry Library, Vol. 10; Elsevier Science: New York, 2001; pp 369-372. 15. Vincent, C. A. Solid State Ionics 2000, 134, 159–167. 16. Tamura, K.; Horiba, T. J. Power Sources 1999, 81-82, 156–161. 17. The Battery Directive, Accumulators and Waste Batteries Disposal, Official Journal of the European Union, 26.9.06, Directive 2006/66/EC, 2006, http://europa.eu/legislation_summaries/


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29. Rechargeable Battery Recycling Corporation (RBRC). http:// www.rbrc.org/call2recycle/ (accessed Nov 2009). 30. Portable Rechargeable Battery Association (PRBA. http://www. prba.org/ (accessed Nov 2008). 31. European Battery Recycling Association. http://www.ebrarecycling. org (accessed Nov 2008). 32. Recycling around Europe. European Portable Battery Association, European Portable Battery Association, Bruxelles, Belgium. http://www.epbaeurope.net/recycling.html (accessed Jan 2009). 33. Rogulski, Z.; Czerwinski, A. J. Power Sources 2006, 159, 454–458. 34. Bernardes, A. M.; Espinosa, D. C. R.; Tenorio, J. A. S. J. Power Sources 2003, 124, 586–592. 35. Toxco Inc., Anaheim, CA. http://www.toxco.com/ (accessed Nov 2009). 36. Lain, M. J. Power Sources 2001, 97-98, 736–738. 37. Cook, B. An Introduction to Fuel Cells and Hydrogen Technology; Heliocentris: Vancouver, 2001; http://www.fuelcellstore.com/ products/heliocentris/INTRO.pdf (accessed Nov 2009). 38. Plugpower, Fuel Cell systems, Hydrogen, the fuel of the future. http://www.plugpower.com/technology/fuelcelloverview.aspx (accessed Jan 2009). 39. Medis Technologies Ltd., 805 Third Avenue, 15th floor, New York, NY 10022, Medis 24-7 Power Pack product specification sheet, http://fuelcellstore.com/products/medis/Powerpack-specsheet.pdf (accessed Jan 2009). 40. Ballard Power Systems Inc., 4343 North Fraser Way, Burnaby BC, V5J 5J9, Canada, Ballard delivers first prototypes of third generation long-life fuel cell for residential cogeneration, http://www. ballard.com (accessed Nov 2009). 41. Honda Motor Company. Honda Fuel Cell Power FCX, Press information 2004.12, http://world.honda.com/FuelCell/FCX/ FCXPK.pdf and Honda's Clarity advanced fuel cell vehicle, http://automobiles.honda.com/fcx-clarity/ (accessed Dec 2009).

Supporting Information Available Examples of student research problems; text introducing the research assignment and a typical student handout. This material is available via the Internet at http://pubs.acs.org.


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Batteries, from Cradle to Grave - Journal of Chemical Education (ACS

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