Treatment of Battery Manufacturing Wastes

Joseph F. Hawumba, Yung-Tse Hung, and Lawrence K. Wang

CONTENTS

32.1 Introduction 1303

32.1.1 Historical, Cultural, and Battery Technology Development 1303

32.2 Overview of the Manufacturing Process 1307

32.2.1 Manufacturing Process 1307

32.3 Battery Chemical Systems 1309

32.3.1 Battery Classification 1309

32.4 Description of Battery Subcategories in the Battery Industry 1310

32.4.1 Subcategories/Subdivision of Batteries 1310

32.4.2 Subcategory A: Cadmium 1311

32.4.3 Subcategory C: Lead 1312

32.4.4 Subcategory D: Leclanche 1313

32.4.5 Subcategory G: Zinc Battery 1315

32.4.6 Subcategory E: Lithium Battery 1316

32.4.7 Subcategory F: Magnesium 1317

32.4.8 Other Battery Types 1318

32.5 Wastewater Characterization 1319

32.6 Health and Environmental Effects of Battery Manufacture 1320

32.6.1 Lead Toxicology 1321

32.6.2 Cadmium Toxicology 1321

32.6.3 Mercury Toxicology 1322

32.6.4 Other Heavy Metals 1322

32.7 Treatment of Battery Manufacturing Waste 1323

32.7.1 Use of Biosorbent in the Treatment of Battery Wastewater 1323

32.7.2 Cleaner Production Options for Battery Manufacture 1324

32.8 Conclusions and Future Prospects 1329

References 1329

The existence and use of batteries is thought to have roots in prehistoric times, whereby, through archeological discoveries, it was discovered that prehistoric people had created an electrochemical cell that would qualify, under today's definition, as a battery. A curiosity found in Baghdad in 1932 was probably representative of battery technology dating as far back as 2500 years.1 Such a primitive

32.1 I NTRODUCTION

32.1.1 Historical, Cultural, and Battery Technology Development battery cell comprised an iron rod that fits into a copper cylinder. Presumably some fluid, which served as an electrolyte, escaped preservation. Notwithstanding its simplicity, such a cell would have provided current to permit primitive jewelers to electroplate precious metals and make copper shine either like gold or as silver.1 Although such archeological evidence provides us with some glimpse into the far past, the history of modern-day battery development begins in the 1780s with the discovery of "animal electricity" by Luigi Galvani (1737-1798), which he published in 1791. This Italian anatomist and physician observed that muscles of a frog's leg would contract when jolted with a static electrical spark delivered from a Leyden jar. In further experiments in bioelectro-genesis, as the knee-jerk reaction came to be called, Galvani noticed that the frog's leg would also react to two different metals being applied to the muscle.1 This behavior was also observed when a dead frog's leg was used in the experiment. From these series of experiments, Galvani deduced that the muscle was producing electricity. It is therefore not surprising that his name has since become intimately associated with electricity to the extent that the process of producing electricity by chemical reaction is termed galvanism.1

More important to the history of the current battery was another Italian physicist, one of Galvani's correspondents, Alessandro Volta (1745-1827). Volta realized that the frog's moist tissue may be replaced by cardboards soaked in salt water, and the frog's muscular response could be replaced by another form of electrical detection. Volta came to believe that contact between his dissimilar metals created the electricity that caused the frog's muscle to contract, thus opposing Galvani's deduction.1 Having already studied the electrostatic phenomenon of capacitance, which required measurements of electric charge and electrical potential, Volta was able to detect electric current flowing through his system, now called the voltaic cell. In its simple construction, the voltaic cell comprised two bowls filled with a salt solution. The bowls were linked together with arcs of metal, one end of the arcs being copper and the other zinc. Besides, each bowl had two ends of two different metal arches in it. The device, the first modern battery, produced electricity by the chemical reactions of the metals in solutions.1

In 1799, Volta invented the battery by placing many voltaic cells in series, literally piling them one above the other. This voltaic pile gave a greatly enhanced electromotive force (emf) for the combination, with a voltage of about 50 V for a 32-cell pile. By 1800, Volta had simplified the arrangement of his bowl-battery into a stack of small disks, alternating zinc and copper with a disk of leather saturated with salt solution separating each metal disk, which generated a substantial electric current (Figure 32.1). In honor of volta's ground-breaking accomplishment, the unit of electrical potential, the volt, was named after him.1 Unfortunately, these early batteries were only useful in limited experimental applications, but were impractical for a large current drain. Such limitations prompted further improvement of the voltaic battery technology. For instance, in 1836, a British chemist John Frederic Daniell improved Volta's cell by moving the copper and zinc into a bath of sulfuric acid to create the gravity or Daniell's cell. However, Daniell's cell did not last long as it suffered from hydrogen accumulation at the cathode. Three years later, William Robert Grove added an oxidizing agent to prevent hydrogen accumulating at the cathode from reducing the voltage the cell produced as it operated. Grove's construction comprised a two-part cell involving a porous pot containing sulfuric acid in which an amalgamated zinc anode was placed. The porous pot was, in turn, placed in a second vessel containing nitric acid and a platinum cathode. In 1841, a German chemist, Robert Wilhelm Bunsen, improved Daniell's cell by substituting cheap carbon for the expensive platinum cathode.1

However, the first enduring invention came from Gaston Planté; then working in France, he developed the first lead-acid storage batteries in 1859 (Figure 32.2a) for use in telegraph equipment.1,2 Notably, Planté's device was not only the first successful storage cell, but was also rechargeable. Further refinement of his battery has, up to date, not been on its electrochemistry, but rather, on the packaging. This battery type is in use today in automobiles and the gelled-electrolyte batteries used in uninterruptible power systems.1 Inasmuch as Planté's device was a great success, yet many other scientists continued in their search for better designs, as well as electrochemical a a a a a a a a

Aircraft Ion Battery Construction
FIGURE 32.1 Volta's 1800 illustration of the voltaic cell from its early development as a series of buckets (a) to a series of cell piles (b-d).

systems. Such efforts yielded more dividends as further contribution to battery development was made by yet another French engineer, George Leclanche, when he developed his wet cell in 1866. In his design, Leclanche used a cathode of manganese dioxide mixed with carbon and an anode of zinc in the form of a rod (Figure 32.2b).

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante's electrochemistry of the lead-acid battery, Leclanche's electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.1,2 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche's chemistry not only usable but also invaluable in some applications. For example, Polaroid's Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1

The progress of battery technology could not wait for the development of plastics. Scientists continued to look for ways of solving the problem of fussy liquids entirely. This came to fruition when battery chemistry was further modified to produce the dry cells. This breakthrough made

Cylindrical Wet Cell Battery

batteries the convenient power source they are today. Credit goes to Carl Gassner of Mainz, Germany, who patented this technology in 1887.1 In constructing his dry cell, Gassner mixed ammonium chloride with plaster of paris to create a paste, with a bit of zinc chloride added to extend the shelf life. The manganese dioxide cathode was dipped in this paste, and both were sealed in a zinc shell, which also acted as the anode. Unlike previous wet cells, Gassner's dry cell was more solid, did not require maintenance, did not spill, and could be used in any orientation. It provided a potential of 1.5 V, and its first mass production was under the brand name the Columbia dry cell. This type of cell was first marketed by the National Carbon Company (NCC) in 1896.

In 1899, the nickel-cadmium battery, the first alkaline battery, was invented by a Swedish scientist named Waldmar Jungner. The special feature of this battery was its potential to be recharged. In construction, nickel and cadmium electrodes in a potassium hydroxide solution, it was the first battery to use an alkaline electrolyte. This battery was commercialized in Sweden in 1910 and reached the Unites States in 1946. The first models were robust and had significantly better energy density than lead-acid batteries, but nevertheless, their wide use was limited because of the high costs.

Although the technology has been refined by over a century of development, the concepts and chemistry are the same as Gassner's first dry cells. Most of today's exotic rechargeable battery systems such as nickel-cadmium, nickel-metal hydride, and the variety of lithium-based cells are twentieth-century developments. It is therefore notable that new chemistries are no longer being discovered through experimentation as the principles of battery design and operation are well known, but rather, new efforts in battery design focus on making the optimal chemistries work in practical cells.1 The growth of battery technology has since revolutionalized and several models of long-lasting battery life have been developed. These range from the nickel metal-hydride battery of the late 1980s to the lithium and lithium-ion batteries of the 1970s and 1990s.

32.2 OVERVIEW OF THE MANUFACTURING PROCESS

Batteries are made up of a positive electrode, a negative electrode, and an electrolytic solution. Battery types differ from each other in the chemical processes involved in the conversion of chemical energy into electrical energy. In essence, the manufacturing process of all batteries covers the making of the positive and negative electrodes, the electrolyte materials, the separators, and the materials that would be used as housing of a complete battery. In addition, the process of conversion of chemical energy into electrical energy in all battery types involves the charge and discharge reactions. During these two reactions the electrolyte plays an active role in the two electrodes. For instance, when lead-acid cells are discharged, the lead dioxide (PbO2) of the positive electrode and sponge lead (Pb) of the negative electrode are both converted to lead sulfate (PbSO4). On charge, the lead sulfate in the positive electrode is converted to lead dioxide (PbO^) and the lead sulfate in the negative electrode is converted to sponge lead. The electrolyte, sulfuric acid, is an active component in the reactions at both electrodes. The basic process of battery manufacture may be performed either manually or by using highly automated machines. The type of process used depends on the size of the company, and its manufacturing capacity. Further, various methods are used all over the world in the manufacture of different parts of a battery, which are firmly linked to the type and electrochemistry of the battery being manufactured. While a few of the major battery manufacturers make their own alloy, oxides, separators, and containers/covers, most of them purchase rather than fabricate these materials.3

32.2.1 Manufacturing Process

In a number of battery types, the anode may be a pure metal, an alloy, or a metal salt, while the cathode may be metal oxide or a mixture of oxides of metals and other elements. Therefore, production of electrodes involves various raw materials that must be processed to the required standards. Although batteries differ in the fine details, they are virtually manufactured following similar process steps. In this chapter, the manufacturing steps are hereby described using, as an example, the production process of the lead-acid reserve battery. The manufacturing process as briefly described by Dahodwalla and Herat3 can be divided into the following sections:

32.2.1.1 Oxide Milling

This is the process in which soft lead (99.97% pure) is converted into lead oxide. To achieve this, solid bars of soft lead are melted at 400-425°C and the molten lead is oxidized to form lead oxide. The lead oxide so formed, along with some percentage (about 26%) of free lead, is then passed into a cyclone separator and a bag filter. This step is important as it allows the particles of lead oxide to be separated from the air stream in these equipments. The separated lead oxide is then transferred using screw conveyors into storage tanks, called silos. However, air emissions from the bag filter contain lead particles, a source of pollution.

32.2.1.2 Grid Casting

Grid casting involves melting bars of lead alloy in a lead melting pot. This is followed by pumping molten lead into the grid molds, which are subsequently cooled by means of cooling water. After the mold has cooled the alloy, it opens to discharge the grid, which is subsequently trimmed to remove the excess lead. The resultant cuttings are then recycled into the lead pot. All these operations take place in one machine, which is completely automated. During this process, different types of lead alloys are used for casting of grids. They may have different thicknesses depending on the thickness of the alloys used. Furthermore, grids are classified on the basis of the type of alloy used and the thickness of the grid casted. It should also be noted that melting of lead causes dross formation as well as generation of some solid wastes. Nevertheless, rejected grids are remelted in the lead melting pot and recycled.

32.2.1.3 Paste Manufacturing

Two types of pastes are manufactured, one for positive plates and the other for negative plates. For the lead-acid batteries, the materials required for paste manufacturing are lead oxide, sulfuric acid, water, and other additives. These additives are different for positive and negative pastes. The ingredients, in the paste mixer, are mixed together in a fixed ratio (ratio of various ingredients depends on the type of grid to be used for plate manufacturing) to form the paste, which is then pasted on the grids. Lead oxide is the major ingredient used in paste manufacture accounting for about 85% of the paste. During paste formation, losses occur due to evaporation and the vapors resulting from the process are treated in a scrubber and then discharged through a stack.

32.2.1.4 Grid Pasting

Plates are formed as a result of applying paste onto grids using machines. The pasting machine is divided into four sections, namely, feeding, pasting, drying, and collection. The grids are fed onto the conveyor belt by a feeding mechanism and the paste is applied on them. The pasted grids are passed between rollers where even spreading of paste occurs. Subsequently, the paste is dried in a flash drier and the dried plates are collected and stacked at the extreme end of the pasting machine. The plates are moved into different sections, namely, pasting, drying, and collection, with the help of the belt conveyor system. Finally, the plates are classified depending on the thickness of paste on a particular type of grid. Reject plates and excess paste applied onto the grids are generated in this section. Also, washing of equipment generates wastewater streams, which are contaminated with "paste," which essentially contains lead.

32.2.1.5 Plate Curing

Curing is the process of exposing plates pasted positive and negative to a regime of (a) controlled time (minimum 32 h), (b) temperature (30-35°C), and (c) relative humidity (> 90%). This process converts the free lead into lead oxide, using oxygen from the surrounding air. The plates are allowed to cure for a minimum of 32 h. Care is also taken to ensure that the maximum temperature of the plate does not exceed 60°C. The cured plates are then parted.

32.2.1.6 Plate Parting

This operation is also performed using machines. The cured plates are fed into the parting machine by mechanical means. The plates are parted in the machine and then collected when the operation is completed manually. The parted plates are thereafter stacked for use in battery assembly. More rejects are also generated in this section as well as some lead dust. The ventilation system in this area ensures that the lead dust generated is removed from the work area and discharged into the atmosphere through a baghouse filter.

32.2.1.7 Battery Assembly

The first operation in this area is that of enveloping of positive plates. This envelope, which may be a polythene sheet, acts as a separator that electrically isolates the positive and negative electrodes. A mechanical vacuum system is used to feed positive and negative plates for automatic stacking. The positive and negative plates are stacked together in the desired sequence and encased. However, before the plates are encased, several other processes such as lug brushing, melting of lugs, cast-on strap, intercell welding, and fixing covers are carried out. After the plates are assembled in the container, they are mounted on a conveyor for the finishing operations that involve a shear test, heat sealing, terminal burning, and leak testing. The product at this stage is called a dry uncharged battery. The number and types of positive and negative plates in each battery depend on the type of battery being manufactured. Nevertheless, for a particular type of battery having a specified capacity, the number and types of positive and negative plates are generally fixed. The activities in this section generate rejects of plates, dross, and lead dust. The vacuum system generates lead dust due to feeding of plates, which is discharged to the atmosphere through a baghouse filter.

32.2.1.8 Charging

The dry uncharged battery now needs to be charged by the addition of an electrolyte, which in the case of the lead-acid battery is sulfuric acid. Accordingly, the battery is filled with sulfuric acid (a specific gravity of 1245-1255 at 25°C) and placed on tables and then cooled with water. The operations of filling and emptying sulfuric acid from the battery are performed automatically using machines. Acid is filled by gravity flow into the cell to a level considerably above the plate tops. The positive and negative terminals of the battery are connected to the electric connections and the electric current is passed for a fixed duration of time during which the battery is charged. Different batteries have different currents for charging and different charging systems are, therefore, used. Charging is indicated as complete when there is no change in specific gravity over a 3-h period. Thereafter, the sulfuric acid is emptied from the batteries, a new solution of sulfuric acid is filled, and the battery is washed, labeled, tested, and packed. It should be noted here that the quantity of sulfuric acid filled in a battery varies with the type of battery manufactured. In case it is a wet-charged battery, it would be ready at this stage for distribution and use. Wastewater streams are generated in this section as a result of charging and washing the batteries. This wastewater is acidic and contains sulfuric acid.

32.3 BATTERY CHEMICAL SYSTEMS

Among the most important factors in designing products around batteries (and batteries themselves) is the amount of power a battery of a given size and weight can produce. After all, the energy source for a device should not handicap the ready use of that device. The chemical reactions in the cell are the most important factor constraining energy density and the usefulness of batteries. In fact, the entire history of battery technology has been mostly a matter of finding and refining battery chemistries to pack more energy in ever-smaller packages. Today's batteries use a variety of chemical systems, some dating from the late nineteenth century as mentioned previously, and some hardly a decade old. The diversity results from each having distinct benefits for particular applications. The following battery chemistries are the most popular for portable computer, cell phone, power system, and peripheral applications.

32.3.1 Battery Classification

Batteries are broadly divided into two main classes, namely: (a) primary batteries or cells, which irreversibly (within limits of practicality) transform chemical energy into electrical energy. This happens because of the exhaustion of the initial supply of reactants to the extent that energy cannot be readily restored to the battery by electrical means. In other words, primary batteries are one-way batteries that create new electricity from chemical reaction that permanently transforms the cells. As a consequence, the anode, cathode, and electrolyte are permanently and irreversibly changed and the batteries are disposed of. For this reason, primary batteries are often also referred to as either disposable or nonrechargeable batteries.1,4 (b) Secondary batteries or cells, which may be recharged when their chemical reactions are reversed by applying electrical energy to the cells, thereby restoring their original composition. In essence, rather than operating as producers of power, the secondary batteries merely store it. For that matter, they are often called storage batteries or simply rechargeable batteries. Despite this seemingly inexhaustible capacity to store energy, secondary batteries are not indefinitely rechargeable. This loss of rechargeability is due to dissipation of the active materials, loss of electrolyte, and internal corrosion.1

32.4 DESCRIPTION OF BATTERY SUBCATEGORIES IN THE BATTERY INDUSTRY

32.4.1 Subcategories/Subdivision of Batteries

Based on the anode material employed, eight (8) subdivisions (A-H) have been developed by the U.S. EPA.5 As may be noted (Table 32.1), the zinc anode is divided into two groups (subcategories D and G) based on the electrolyte types. This difference is also reflected in the substantial differences in the manufacture, as well as the waste generated by the two groups. Although a subcategory of nuclear batteries is indicated, hardly any data exist that describes its construction, leave alone the waste characteristics. Similar paucity in information exists on thermal batteries (such as calcium batteries), whose production and use are limited to few operations, especially in

TABLE 32.1

Battery Subcategories, Types, and Construction Materials

Subcategory

A—Cadmium

B—Calcium

E—Lithium

Anode Materials

Cadmium anode

Calcium anode Lead anode

Zinc anode

Lithium anode

F—Magnesium Magnesium anode

H—Nuclear Other types

Zinc anode, alkaline electrolyte

Radioisotopes Variable

Cathode Materials

Nickel, mercury, and silver

Lead oxide

Carbon, silver chloride, and air

Iodine, sulfur dioxide, thionyl chloride, and iron disulfide

Carbon, vanadium pentoxide, and magnesium chloride

Manganese dioxide, nickel hydroxide, mono- and divalent oxides of silver, atmospheric oxygen

Variable

Battery Type

Secondary

Secondary

Primary and secondary

Secondary

Primary and secondary

Primary and secondary

Examples

Nickel-cadmium, mercury-cadmium, and silver-cadmium Thermal batteries for military and atomic applications Lead-acid batteries used for starting, lighting, and ignition (SLI)

Zinc-air batteries, carbon-zinc batteries, and silver chloride-zinc batteries Lithium-iron disulfide batteries, lithium-ion batteries, and lithium polymer batteries Magnesium-based thermal batteries

Nickel-zinc batteries and alkaline manganese cells

Nickel-metal hydride cells, sodium-sulfur batteries, redox batteries, and unusual batteries

Source: Rosch, W., Batteries: History, Present, and Future of Battery Technology, EXTREMETECH. Available at http:// www.extremetech.com/, June 2001; U.S. EPA, Battery Manufacturing, U.S. Environmental Protection Agency, Washington, DC, 1981. N.G. = Not given.

military and space exploration programs. Therefore, these two subcategories are out of the scope of this chapter. However, in the subsequent paragraphs, brief descriptions of other subcategories are provided.

32.4.2 Subcategory A: Cadmium

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes; nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures; nylon and polypropylene, for use in manufacturing the cell separators; and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.14 A typical example is the nickel-cadmium battery described below.

32.4.2.1 Nickel-Cadmium

The most popular rechargeable/storage batteries in consumer electronic equipment are nickel-cadmium cells, often called NiCads. As the name implies, these batteries use cathodes made from nickel and anodes from cadmium. Their most endearing characteristic is the capability to withstand a huge number of full charge/discharge cycles, often in the range of 500-1000 cycles, without deteriorating past the point of usefulness. NiCads also are of relatively lightweight, have a good energy storage density (although about half that of alkaline cells), and tolerate trickle charging (when properly designed). On the downside, cadmium is toxic, thus the requirement for warning labels that implore the user to be cautious with them and properly dispose of them.1 In most batteries the output voltage declines as the battery discharges. This is so because the reactions within the cell increase its internal resistance. This is, however, not the case with NiCads. The NiCads batteries have a very low internal resistance, meaning they can create high currents that change little as the cell discharges. Consequently, the NiCad cell produces a nearly constant voltage until it becomes almost completely discharged, at which point its output voltage falls precipitously. This constant voltage is an advantage to the circuit designer because fewer allowances need to be made for voltage variations. However, the constant voltage also makes determining the state of a NiCad's charge nearly impossible. As a result, most battery-powered computers estimate the remaining battery power from the time they have been operating and the known battery capacity rather than actually checking the battery state. NiCads are known for another drawback: memory. When some NiCads are partly discharged, then later recharged, they may lose capacity. Chemically, recharging NiCads before they are fully discharged often results in the formation of cadmium crystals on the anodes of the cell. The crystals act like a chemical memory system, marking a second discharge state for the cell. When the cell gets discharged to this secondary discharge state, its output abruptly falls despite further capacity being available within the cell. In subsequent cycles, the cell remembers this second discharge level, which further aggravates the situation by reinforcing the memory of the second discharge state. The full capacity of the cell would only be recovered by nudging the cell past this second discharge state. This should erase the memory and restore full cell capacity. This situation would soon change as newer NiCads are free from memory effects.

Another problem encountered by manufacturers and users of NiCads batteries is the breakdown, by electrolysis, of water. This ought to be prevented; otherwise the cells may explode. As with lead-acid batteries, NiCads are also prone to electrolysis-mediated breaking down of water in the electrolyte into potentially explosive hydrogen and oxygen. Battery manufacturers take great steps to reduce this effect. Commercially available NiCads are sealed to prevent leakage. They are also designed so that they produce oxygen before hydrogen, which reacts internally to shut down the electrolysis reaction. To prevent sealed cells from exploding should gas somehow build up inside them, their designs usually include resealable vents. As a matter of fact, there is a great risk of getting an explosion if a NiCad cell is encased in such a way that it cannot vent. Cadmium anode batteries are produced in a broad range of sizes and configurations corresponding to varied applications (Table 32.2). They range from a cylindrical cell with capacities of <1 A-h to large rectangular batteries for industrial applications with capacities in excess of 100 A-h.1

32.4.3 Subcategory C: Lead

The lead subcategory encompasses the lead-acid reserve cells and more familiar lead-acid storage batteries. This subcategory of batteries is the largest both in terms of number of plants and in volume of production, as well as the total volume of wastewater generated. The raw materials for all lead anode battery types include lead, lead oxide, lead alloys, sulfuric acid, material for making separators, as well as battery cases, covers, and filter caps. Carbon, barium sulfate, and some fibrous materials may be used as additional materials in the manufacture of electrodes.5 Although lead anode batteries are manufactured using similar materials and employing the same basic chemistry, they differ significantly in configuration depending on the end use. For instance, lead-acid battery products include cells with immobilized electrolyte for use in portable tools, lanterns; conventional rectangular batteries for use in automotive SLI applications; sealed batteries for SLI use, and a wide variety of batteries designed for industrial applications. Like the NiCads, lead anode batteries are also rechargeable. Besides, these types of batteries may be described as wet charged such as the SLI or dry charged such as damp-charged batteries (damp batteries) and dehydrated plate batteries (dehydrated batteries). Damp and dehydrated batteries may sometimes be described as gelled lead-acid cells.1 Dehydrated batteries are manufactured by charging the electrodes in open tanks (open formation), which is subsequently followed by rinsing and dehydration processes. Thereafter the batteries are assembled and shipped to various destinations. The wet-charged batteries, on the other hand, may be manufactured by either closed formation processes or open formation processes. Of the three categories, the dehydrated plate batteries afford significantly longer shelf life than wet and damp batteries. Most uninterruptible power systems rely on gelled lead-acid cells for their power reserves. In this application, they require little maintenance. A typical example, described below, is the wet-charged lead-acid battery.

TABLE 32.2

Standard Designs, Shapes, and Sizes

Design Type Shape Height

Height (mm)

Diameter (mm)

AAAA AAA

Cylindrical

Cylindrical

Cylindrical

Cylindrical

Cylindrical

Rectangular

Cylindrical

Rectangular

42.5

44.5

50.5

50.0

61.5

48.5

29.35

48.5

Source: Rosch, W., Batteries: History, Present, and Future of Battery Technology, EXTREMETECH. Available at http://www.extremetech.com/, June 2001.

32.4.3.1 Lead-Acid Battery

The most common storage batteries in the world are the lead-acid batteries used to start automobiles, which are not only the heirs to Plante's first designs but are also almost identical. They have anodes made from porous lead and cathodes made from lead oxide, both soaked in a sulfuric acid electrolyte. The lead in the cells and the highly corrosive sulfuric acid electrolyte not only make these batteries inherently heavy but also cumbersome and dangerous. Furthermore, the acid and its fumes are capable of damaging nearby objects (particularly metals), while overcharging cells results in electrolysis of the water component of the internal acid to release hydrogen. The hydrogen released by the electrolysis is highly combustible and if mixed with air and exposed to a spark, an explosion may occur. Besides, the breakdown of the water in the cells also has another effect: it reduces the overall amount of water in the cell. As a result, too little water is available, which reduces the reaction area inside the cell, thereby reducing its capacity. Eventually, the cells would deteriorate by atmospheric action and the electrodes may either flake or possibly shut out a cell entirely, thereby reducing its capacity to zero.1

Early lead-acid cells consequently required regular maintenance to keep the water/acid inside the cell at the proper level. Since only the water electrolyzes in the battery, it is the only one needed to be replaced regularly. To avoid contaminating the battery chemistry, manufacturers recommend the use of distilled water in replenishing the battery. In stationary applications, lead-acid batteries were once encased in glass. Not only would such designs resist the internal acid, but also they would allow maintenance workers to quickly assess the condition of the cells. For automotive applications, however, a more shatterproof case is required for which engineers developed hard rubber or plastic enclosures. In addition, the convenience of using lead-acid batteries is immensely increased by sealing the cells. The result is the so-called maintenance-free battery. Since the vapors within the sealed cell cannot escape, electrolysis losses are minimized. For this reason, maintenance-free batteries never need water. But on the downside, maintenance-free batteries are not entirely trouble-free. They still have acid sloshing around inside them, which may leak out through the battery vent, thereby either damaging the battery compartment or the equipment in which the battery is located. To overcome these shortcomings, two ways of eliminating the slosh have been developed. One way is to keep the liquid acid (electrolyte) inside a plastic separator (typically a microporous polyolefin or polyethylene) between cell electrodes. The second alternative is to chemically combine the liquid electrolyte with other compounds that turn it into a gel (a colloidal form like gelatin), which is less apt to leak out.

Having had over 150 years of technical development behind them, lead-acid batteries can be custom-tailored to specific applications, such as those requiring deep discharge cycles (e.g., where the batteries are used as the sole power source for electrical equipment) and for battery backup uses such as in large uninterruptible power supply systems in data centers. Moreover, lead-acid cells not only have low internal resistance but also experience no memory effect as do some more exotic cell designs, such as NiCads. This enables these cells to produce enormous currents and have a moderately long, predictable life.1

32.4.4 Subcategory D: LeclancH

The Leclanche battery subcategory is a type of zinc battery that uses an acidic electrolyte and zinc anode. The major raw materials used in the manufacture of batteries in this subcategory include zinc, mercury, carbon, manganese dioxide, ammonium chloride, zinc chloride, silver chloride paper, starch, flour, and pitch (or similar materials) for sealing cells. Plastics are also used in producing flat cells for photographic use. The zinc is most often obtained as sheet zinc preformed into cans, which serve as both cell anode and container. However, some facilities form and clean the cans on-site. Zinc powder may also be used in one such type of cells. Where mercury is used to amalgamate the zinc and to reduce internal corrosion in the battery, it is generally added with the cell electrolyte or the separator. It amounts to approximately 1.7% by weight of the zinc contained in these cells. Plants involved in the manufacture of cells in this subcategory produce conventional carbon-zinc Leclanche cells as well as silver chloride-zinc and carbon-zinc air cells. All of these batteries have in common the use of an acidic (chloride) electrolyte and a zinc anode. In this respect they differ from subcat-egory G, which, although it has a zinc anode, uses an alkaline electrolyte.

A wide variety of cells and battery configurations and sizes are produced in this subcategory comprising cylindrical cells in sizes from AAA to No. 6, flat cells, which are stacked to produce rectangular 9-V transistor batteries, various rectangular lantern batteries, and flat sheet batteries for photographic applications. Cells of this subcategory are of the primary type (Table 32.1). Although the above cell configurations are used in the construction of this cell subcategory, there are some differences in the manufacturing process. These differences arise from the differences in the cell separators chosen, that is, cooked paste, uncooked paste, or paste paper. Another notable difference may arise from the electrolyte used. For instance, among carbon-zinc air batteries, only dry cells, which use ammonium chloride in the electrolyte, are included in this subcategory; otherwise carbon-zinc air depolarized batteries, which use alkaline electrolyte, are not included in the Leclanche subcategory, but rather, included in subcategory G, the zinc battery. Typical examples described below are the carbon-zinc and zinc-air battery types.

32.4.4.1 Carbon-Zinc

Carbon-zinc cells are probably the most common batteries in the world, known under a variety of names including dry cell and flashlight battery. When you think of batteries, it is likely that carbon-zinc cells first come to mind. One company alone, Energizer, sells over 6 billion carbon-zinc cells each year. They are the lowest-priced primary cells. They also have the lowest storage density of any common battery. In the basic carbon-zinc cell, the "carbon" in the name is a cathode current collector, which is a carbon rod in the center of the cell. The actual materials used in the manufacture of the cathode are a mixture of manganese dioxide, carbon conductor, and electrolyte. The zinc, in addition to serving as the anode, forms the metal shell of the battery. The electrolyte is a complex mixture of chemicals that typically include ammonium chloride and manganese dioxide. Therefore, the electrolyte is the chief difference between Leclanche and zinc cells of subcategory G that use alkaline electrolytes.1

32.4.4.2 Zinc-Air

Of the current battery technologies, the one offering the densest storage is zinc-air. One reason is that one of the components of its chemical reaction is external to the battery. Zinc-air batteries use atmospheric oxygen as their cathode reactant, hence the "air" in the name. Small holes in the battery casing allow air to react with a powered zinc anode through a highly conductive potassium hydroxide electrolyte. Originally created for use in primary batteries, zinc-air batteries were characterized by long stable storage life, at least when kept sealed from air and thus inactive. A sealed zinc-air cell loses only about 2% of its capacity after a year of storage. Once air infiltrates the cell, zinc-air primary cells last only for months, whether under discharge or not. Some battery makers have adapted zinc-air technology for secondary storage. Zinc-air cells work best when frequently or continuously used in low-drain situations. The chief drawback of zinc-air batteries is, however, its high internal resistance, which means zinc-air batteries must be huge enough to satisfy high current needs as for notebook PCs, which means an auxiliary battery pack about the size of the PC itself. Zinc-air secondary cells have been only crudely adapted to portable PC applications. One of the first products, the PowerSlice XL, developed jointly by Hewlett-Packard Co. and AER Energy Resources Inc., demonstrated the shortcomings of zinc-air technology for high-current computer use. The product developed for the HP OmniBook 600 notebook PC weighed 7.3 lb, more than the computer itself, but could power the OmniBook only for about 12 h. Energizer has also adapted zinc-air technology to small button cells aimed at hearing aids. Charging a battery is not simply a matter of preventing a dead battery from sucking in the entire output of a power plant (as would be its natural tendency). Cell chemistry is extremely sensitive to the electricity applied to it. If the voltage applied is too low, the cell will output current instead of accepting it. If too high, undesirable reactions would take place, which would, in turn, destroy the cell. This is so because raising the voltage inevitably raises the current to such high levels that it would eventually cause the cell to overheat. In addition, trying to charge a cell beyond its capacity can result in the production of explosive gases and an explosion itself.1

32.4.5 Subcategory G: Zinc Battery

Batteries of this subcategory resemble the Leclanche cells in having a zinc anode, while they differ inasmuch as the electrolyte is alkaline. As such, batteries in this subcategory may be referred to or described as zinc anode alkaline electrolyte batteries. These batteries are at present manufactured using six different cathode reactants, namely, manganese dioxide, mercury oxide, nickel hydroxide, monovalent and divalent oxides of silver, and atmospheric oxygen (Table 32.1). The raw materials used in producing these batteries include zinc, zinc oxide, mercury, manganese dioxide, carbon, silver, silver oxide, silver peroxide, mercury oxide, nickel and nickel compounds, cadmium oxide potassium hydroxide, sodium hydroxide, steel, and paper. Zinc and zinc oxide are used to manufacture anodes, while mercury is used both to manufacture mercuric oxide cell cathode material and to amalgamate zinc anode to limit corrosion and self-discharge. Other cathode materials may be made from (a) manganese dioxide, which is blended with carbon to form cathodes for alkaline manganese cells; (b) silver, which is used to produce silver oxide and silver peroxide cathodes as well as wire screens that serve as support grids for cell electrodes; and (c) nickel and nickel compounds, which are used to produce cathodes for nickel-zinc batteries. The electrolytes used in these cells are either potassium hydroxide or sodium hydroxide. Finally, the batteries are encased in steel material, while paper and plastics, respectively, are used as separators and insulating components.

Typically, the alkaline zinc batteries construction (as opposed to chemistry) differs significantly from ordinary carbon-zinc cells. Alkaline cells are effectively turned inside out. Unlike the zinc battery of subcategory D, the shell of the alkaline battery is nothing more than a protective shell, which does not play a part in the overall chemical reaction. The anode of the cell is a gelled mixture of powered zinc combined with the electrolyte (which itself is a mixture of potassium hydroxide and water), and the combination is linked to the negative terminal of the cell by a brass spike running up the middle of the cell. The cathode, a mixture of carbon and manganese dioxide, surrounds the anode and electrolyte, separated by a layer of nonwoven fabric, such as polyester. This is the construction of a Duracell alkaline battery.1 Depending on the application, alkaline cells can last for 4-9 times the life of more traditional carbon-zinc cells. The advantage is greatest under heavy loads that are infrequently used, that is, something that draws heavy current for an hour once a day rather than a few minutes of each hour. In this respect, an alkaline zinc anode cell is better than typical carbon-zinc cells, which nominally produce 1.5 V, a voltage only available when little current is drawn from the cell during its initial discharge. As the load increases the voltage of the cell diminishes and the charge of the cell also decreases.

A wide range of cell sizes, electrical capacities, and configurations are manufactured in both primary (nonrechargeable) and secondary (rechargeable) categories. Ordinarily, alkaline batteries cannot be recharged because the chemical reactions in the cell to cannot be readily reversed. If one attempts to recharge an ordinary zinc cell, it acts more like a resistor than a storage cell, turning the electricity applied to it into heat, which may cause the cell to heat up enough to explode. For this reason, it is advisable never to attempt to recharge ordinary alkaline zinc anode batteries. The Renewal batteries produced are currently the rechargeable type of this subcategory. The Renewal design relies on a two-prong attack on carbon-zinc technology. The Renewal cell is fabricated

TABLE 32.3

Nominal Voltage and Storage Density of Various Battery Types

Battery Type Nominal Voltage (V) Storage Density (wh/kg)

Lead acid Nickel-cadmium

40-60 60-80 90-100 100-110 130-150

Nickel-metal hydride Circular lithium ion Prismatic lithium ion Polymer lithium ion

Source: Rosch, W., Batteries: History, Present, and Future of Battery Technology, EXTREMETECH. Available at http://www.extremetech.com/, June 2001.

differently from a standard cell, with a special battery charger and a microprocessor. More importantly, in recharging Renewal batteries, the Renewal charger adds power in a series of pulses, while a microprocessor in the charger monitors how each pulse affects the cell to prevent overheating. However, even with such a novel charger, Renewal cells have a limited life, typically between 25 and 100 charge-discharge cycles (Table 32.3). Accordingly, Renewal cells cost only about twice as much as standard alkaline cells.1

32.4.6 Subcategory E: Lithium Battery

This subcategory encompasses the manufacture of batteries, which employ lithium as the reactive anode material. However, this classification may not account for the recent developments in lithium battery technologies, which use either the lithium ion or the lithium polymer not as anodes but rather as cathodes and "complexed" electrolytes, respectively.1 Therefore, in addition to the traditional lithium anode batteries, these newly developed variants are conveniently classified under the lithium battery subcategory and their construction is described in detail under Sections 32.4.6.2 and 32.4.6.3, respectively. A variety of cathode materials that have been applied earlier in the manufacture of lithium cells include iodine, sulfur dioxide, thionyl chloride, and iron disulfide, which were predominant in the 1970s and 1980s (Table 32.1). Lithium battery technology has greatly developed to various designs based on lithium ion as well as lithium polymer battery technologies, respective-ly.1 Typical examples described below are the lithium-iron disulfide, lithium-ion, and lithium polymer battery types.

32.4.6.1 Lithium-Iron Disulfide

The lithium-iron disulfide battery, also known as voltage-compatible lithium battery, is a sandwich of a lithium anode, a separator, and an iron disulfide cathode with an aluminum cathode collector. Unlike other lithium technologies, lithium-iron disulfide cells are not rechargeable. Compared to the alkaline cells, lithium-iron disulfide cells are lighter (weighing about 66% of same-size alkaline cells), higher in capacity, and longer in life. Even after 10 years of shelf storage, lithium-iron disulfide cells still retain most of their capacity. Lithium-iron disulfide cells operate best under heavier loads. In addition, they can supply power for about 260% the time of a same-size alkaline cell, when used under high-current applications. On the contrary, this advantage is lost at lower loads and at very light loads where such a capacity may disappear entirely. Lithium-iron disulfide cells may be used wherever zinc-carbon batteries are used, although they are cost effective only under high-current loads such as in flashlights, motor-driven devices, and powerful electronics. They are not a wise choice for clocks and portable radios.1

32.4.6.2 Lithium Ion

Batteries based on lithium metal were developed and manufactured in the 1970s, and in the 1980s some companies introduced commercial rechargeable cells based on metallic lithium. Such batteries quickly earned a reputation for doubtful safety. To prevent problems caused by reactive metallic lithium, battery makers refined their designs to keep the lithium in its ionic state. In this way, they were able to reap the electrochemical benefits of lithium-based cells without the safety issues associated with the pure metal. In lithium-ion cells, the lithium ions are absorbed into the active material of the electrodes rather than being plated out as metal. The typical lithium-ion cells use carbon for its anode and lithium cobalt dioxide as the cathode. The electrolyte is usually based on a lithium salt in solution. Lithium batteries offer higher storage densities than nickel-metal hydride cells (Table 32.3). Besides, lithium-ion cells also lack the memory effect that plagued early NiCads. On a downward side, however, current lithium cells have a higher internal resistance than NiCads and consequently cannot deliver high currents.1 Moreover, the life of lithium cells is more limited than that of nickelbased designs, although lithium-ion cells withstand hundreds of charge/recharge cycles. Since lithium-ion cells use a liquid electrolyte (although one that may be constrained in a fabric separator), cell designs are limited to the familiar cylindrical battery form.

32.4.6.3 Lithium Polymer

The lithium solid polymer cell is today's brightest new battery technology and is a refinement of the familiar lithium chemistry. As a matter of fact, most battery makers and computer makers are switching to the lithium solid polymer cell design. A typical lithium polymer cell substitutes the liquid electrolytes required in conventional lithium-ion cells by a solid polymer, polyacrylonitrile containing a lithium salt, which is integrated into a polymer plastic separator between the anode and the cathode. Since there is no liquid electrolyte, the solid polymer cell does not require the chunky cylindrical cases of conventional batteries. Instead, the solid polymer cells can be formed into flat sheets or prismatic (rectangular) packages that are better able to fit the nooks and crannies of notebook computers. Although the energy density of solid polymer cells is similar to ordinary lithiumion cells, PC manufacturers can shape them to better fit the space available in a PC, squeezing more capacity into each machine. For example, simply by filling the empty space that would appear in the corners around a cylindrical cell, a solid polymer battery can fit in about 22% more chemistry and energy capacity. In addition, solid polymer batteries are lighter and environmentally friendly because they have no metal shell and contain no flammable solvent.1

32.4.7 Subcategory F: Magnesium

The magnesium subcategory encompasses such batteries as magnesium-carbon batteries, magnesium-vanadium pentoxide thermal cells, ammonia-activated magnesium anode cells, magnesiumair batteries, and several different types of magnesium reserve cells that use metal chloride cathodes. A wide variety of raw materials are used in the manufacture of magnesium anode batteries and such materials are in tandem with the diversity of cell types manufactured. While the anode is magnesium in each case, various raw materials are used for cathode manufacturing including magnesium dioxide, barium chromate, lithium chromate, magnesium hydroxide and carbon (for magnesium-carbon batteries), vanadium pentoxide (for thermal batteries), copper chloride, lead chloride, silver and silver chloride (for magnesium reserve cells), and m-dinitrobenzene (for ammonia-activated cells). As for the electrolyte, raw materials such as magnesium perchlorate, magnesium bromide, and ammonia are used. Separators, on the other hand, are most often made from either Kraft paper or cotton.67 This battery system is characterized by its good shelf life in inactivated state and its capability to operate well at extremely low temperatures of the order of -60°C and below. The battery system gives nearly flat discharge over 75% of its total discharge capacity and can be activated with water. Basing on the above characteristics, this battery system finds application in meteorological equipment such as Radiosonde or Rawin Transmitter, Radio reporting, and ozone sonde, among others, which are used for monitoring the climatic conditions at high-altitude regions where the ambient temperature is of the order of -80°C. The batteries are also required to operate the instruments for <3 h only. Besides operating much more efficiently at extremely low temperatures and possessing a long shelf life, a 112-V battery pack weighs nearly half as much as a Leclanche cell pack of the same power output.8

32.4.8 Other Battery Types

Apart from the classical subcategories described above, there are other cell subcategories that do not fit into the above classification. Such cells include (a) the sodium/sulfur battery that uses liquid sulfur for the positive electrode, (b) redox batteries, (c) unusual batteries such as the urine battery, ampoule battery, thin-film battery, and homebrew battery,9 and (d) nickel-metal hydride batteries, which have, as one of the electrodes, metal alloys that have a very high capacity to store atomic hydrogen, and hence called hydrides. Although the technologies for the sodium/sulfur, redox, and unusual batteries are very interesting, their practical applications are still limited, and therefore no further discussion is devoted to them in this chapter. However, the metal-hydride technology is finding such an application in the manufacture of rechargeable batteries that are currently used in a number of devices. This technology development shall be explored briefly by looking at the nickelmetal hydride battery.

32.4.8.1 Nickel-Metal Hydride

Nickel-metal hydride (NiMH) batteries are related to sealed nickel-cadmium batteries (Table 32.4) and only differ from them in that, instead of cadmium, hydrogen is used as the active element at a hydrogen-absorbing negative electrode (anode). This electrode is made from a metal hydride, usually alloys of lanthanum and rare earths (LiNi5 or ZrNi2) that serve as a solid source of reduced hydrogen that can be oxidized to form protons.1,10,11 In properly designed systems, hydrides can provide a storage sink of hydrogen that can reversibly react in battery cell chemistry. The most common cells that use hydride cathodes carry over the nickel anodes from NiCad cell designs. These cells typically have an electrolyte of a diluted solution of potassium hydroxide, which is alkaline in nature. Substituting hydrides for cadmium in battery cells has several advantages: (a) the environmentally undesirable cadmium is eliminated, which, in turn, removes the constraints on cell manufacture, usage, and disposal imposed because of concerns over cadmium toxicity; (b) the elimination of cadmium also means that the cells are free from the memory effect that plagues NiCad cells; (c) hydrogen is so much better as a cathode material that cells based on nickel and metal hydrides have a storage density about 50% higher than NiCads. In practical terms, it means that cells of the same size and about the same weight can power a notebook computer for about 50% longer; and (d) its incorporation into products currently using NiCads because of the many design similarities between the two chemistries is possible.1,11

Cells based on nickel and metal hydrides are not perfect. Their chief drawback is that most of such cells have a substantially higher self-discharge rate than do NiCad cells. Some NiMH cells lose as much as 5% of their capacity per day, although this figure is coming down with more refined cell designs. As with NiCads, NiMH cells have a nominal output voltage of 1.2 V that remains relatively flat throughout the discharge cycle, falling precipitously only at the end of the useful charge of the cell. In many ways NiMH cells are interchangeable with NiCads. They have a similar ability to supply high currents, although not quite as much as NiCads. NiMH cells also endure many charge/ discharge cycles, typically up to 500 full cycles, but they are not a match for NiCads. Although the discharge characteristics of NiMH and NiCads are similar, the two cell types react differently during charging. Specifically, NiCads are essentially endothermic while being charged and NiMH cells are

TABLE 32.4

Summary Comparison of Nickel-

Application Feature

Nominal voltage Discharge capacity Discharge profile Discharge cutoff voltages High-rate discharge capability High-temperature (>35°C) discharge capability Charging process

Charge termination techniques

Operating temperature limits

Self-discharge rate

Cycle life

Mechanical fit

Mechanical properties

Selection of sizes/shapes/capacities

Handling issues

Environmental issues

Metal Hydride Application Features

Comparison of Nickel-Metal Hydride with Nickel-Cadmium Batteries

NiMH up to 40% greater than NiCd

Equivalent

Equivalent

Effectively the same rates

NiMH slightly better than standard NiCd cells

Generally similar; multiple step constant current with overcharge control recommended for fast charging NiMH Generally similar but NiMH transitions are more subtle. Backup temperature termination recommended Similar, but with NiMH, cold temperature charge limit is 15°C NiMH slightly higher than NiCd

Generally similar, but NiMH is more application dependent

Equivalent

Equivalent

NiMH product line more limited Similar

Reduced with NiMH because of elimination of cadmium toxicity concerns

Source: Energizer: Nickel-Metal Hydride Application Manual, June 2001, Eveready battery Co. Inc., www.data.energizer.com.

exothermic, that is, they produce heat. As the NiMH cell approaches full charge, its temperature can rise dramatically. Consequently, chargers are best designed for one or the other type of cell.

32.5 WASTEWATER CHARACTERIZATION

As may be noted from the foregoing description of a typical battery manufacturing process (Section 32.2.1), water is used in preparing reactive materials and electrolytes, in depositing reactive materials on supporting electrode structures (grids), in charging electrodes, and removing impurities, as well as washing finished cells, production equipment, and manufacturing area/work places. As a consequence, wastewater flow, pattern of water use, and waste characteristics are similar among the subcategories, albeit varying widely among different battery manufacturing units.5 Table 32.5 summarizes the prominent constituents of wastewater streams generated from various battery subcate-gory plants. For instance, high levels of lead, oxides of lead, sulfates, and suspended solid (SS) material and the low pH due to the acidic electrolyte used, that is, sulfuric acid, characterize lead acid manufacturing plants.3 Wastewater characterized by high levels of cadmium, nickel, silver, zinc, and mercury are the most dominant pollutants in cadmium anode, zinc anode, Leclanche cells, lithium anode, and calcium thermal battery plants.5 In addition, barium, z

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