Battery systems

Finally, the conversion of the primary metal into the product and the form which are actually utilized in the battery system should be considered. For example, the electrode materials in lead acid batteries are normally cast lead or lead-alloy grids. The materials utilized in NiCd batteries are cadmium oxide and high surface area nickel foams or meshes. Technically, all of these factors should be considered to produce a detailed life cycle analysis. However, again, these differences are generally quite small compared to the principal variables - composition, performance and spent battery disposal option. 

The SEI data is based mainly on earlier emission numbers for NiCd battery manufacturing, whereas the OECD monograph data represents updated emissions in the European Union as of 1994 compared to total volumes of cadmium utilized for NiCd battery production, based on information from the International Cadmium Association. All of this data indicates that most of the cadmium remains in the product and is not lost during NiCd battery manufacturing. A similar conclusion can be inferred with respect to nickel and cobalt, the other materials in a NiCd battery which might be likely to be regarded as hazardous and contribute to an adverse environmental impact. Iron, of 

Percent of Total Cadmium SEI Report OECD Monograph 

In each group, from left to right Cadmium Plating Consumer NlCds Pigments Stabilizers Industrial NlCds 

In addition, two sets of data from the Battery Association of Japan (BAJ), formerly known as the Japan Storage Battery Association (JSBA), equally clearly demonstrate that the levels of cadmium emissions to air and water in Japan have decreased steadily over the period from 1980 through 1992 in spite of the greatly accelerated production of NiCd batteries in Japan during that same time period (Mukunoki and Fujimoto 1996). Japan is the world s largest producer of NiCd batteries, and currently accounts for over 70% of the world s NiCd battery production. If there is any country where potential enviromnental contamination by cadmium from NiCd battery manufacture should be 

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The pot extractor is a batch extraction plant in which extraction and solvent recovery from the exhausted soHds can be carried out in a single vessel. These extractors are normally agitated vessels having capacities in the range of 2 to 10 m, beyond which the battery system becomes a preferred technical alternative. 

Fig. 1. Schematic representation of a battery system also known as an electrochemical transducer where the anode, also known as electron state 1, may be comprised of lithium, magnesium, zinc, cadmium, lead, or hydrogen, and the cathode, or electron state 11, depending on the composition of the anode, may be lead dioxide, manganese dioxide, nickel oxide, iron disulfide, oxygen, silver oxide, or iodine.

Batteries are miniatuie chemical leactois that convert chemical energy into electrical energy on demand. The thermodynamics of battery systems foUow direcdy from that for bulk chemical reactions (10). For the general reaction... 

Fig. 7. (a) Simple battery circuit diagram where represents the capacitance of the electrical double layer at the electrode—solution interface, W depicts the Warburg impedance for diffusion processes, and R is internal resistance and (b) the corresponding Argand diagram of the behavior of impedance with frequency, for an idealized battery system, where the characteristic behavior of A, ohmic B, activation and C, diffusion or concentration (Warburg... 

When a battery produces current, the sites of current production are not uniformly distributed on the electrodes (45). The nonuniform current distribution lowers the expected performance from a battery system, and causes excessive heat evolution and low utilization of active materials. Two types of current distribution, primary and secondary, can be distinguished. The primary distribution is related to the current production based on the geometric surface area of the battery constmction. Secondary current distribution is related to current production sites inside the porous electrode itself. Most practical battery constmctions have nonuniform current distribution across the surface of the electrodes. This primary current distribution is governed by geometric factors such as height (or length) of the electrodes, the distance between the electrodes, the resistance of the anode and cathode stmctures by the resistance of the electrolyte and by the polarization resistance or hinderance of the electrode reaction processes. 

Table 4. Rechargeable Battery Systems in Various Stages of Research and Development ...

Table 1. Rechargeable Alkaline Storage Battery Systems...

The aimual production value of small, sealed nickel—cadmium cells is over 1.2 biUion. However, environmental considerations relating to cadmium are necessitating changes in the fabrication techniques, as well as recovery of failed cells. Battery system designers are switching to nickel —metal hydride (MH) cells for some appHcations, typically in "AA"-si2e cells, to increase capacity in the same volume and avoid the use of cadmium. 

Because the nickel—iron cell system has a low cell voltage and high cost compared to those of the lead—acid battery, lead—acid became the dorninant automotive and industrial battery system except for heavy-duty appHcations. Renewed interest in the nickel—iron and nickel—cadmium systems, for electric vehicles started in the mid-1980s using other cell geometries. 

Silver—Iron Cells. The silver—iron battery system combines the advantages of the high rate capabiUty of the silver electrode and the cycling characteristics of the iron electrode. Commercial development has been undertaken (70) to solve problems associated with deep cycling of high power batteries for ocean systems operations. 

Lithium as an anode in alkaline electrolyte has been considered in the battery system shown in Figure 29. Even though lithium reacts dkecdy with water, it was possible to operate the battery because of a protective lithium hydroxide film that forms on the anode. However, the film was not totally protective and units exhibited poor efficiency and were very complex. 

A second class of important electrolytes for rechargeable lithium batteries are soHd electrolytes. Of particular importance is the class known as soHd polymer electrolytes (SPEs). SPEs are polymers capable of forming complexes with lithium salts to yield ionic conductivity. The best known of the SPEs are the lithium salt complexes of poly(ethylene oxide) [25322-68-3] (PEO), —(CH2CH20) —, and poly(propylene oxide) [25322-69-4] (PPO) (11—13). Whereas a number of experimental battery systems have been constmcted using PEO and PPO electrolytes, these systems have not exhibited suitable conductivities at or near room temperature. Advances in the 1980s included a new class of SPE based on polyphosphazene complexes suggesting that room temperature SPE batteries may be achievable (14,15). 

The Na—S system is expected to provide significant iacreases ia energy density for sateUite battery systems (69). In-house testing of Na—S cells designed to simulate midaltitude (MAO) and geosynchronous orbits (GEO) demonstrated over 6450 and over 1400 cycles, respectively. 

A battery system closely related to Na—S is the Na—metal chloride cell (70). The cell design is similar to Na—S however, ia additioa to the P-alumiaa electrolyte, the cell also employs a sodium chloroalumiaate [7784-16-9J, NaAlCl, molten salt electrolyte. The positive electrode active material coasists of a transitioa metal chloride such as iroa(Il) chloride [7758-94-3] EeQ.25 or nickel chloride [7791-20-0J, NiQ.25 (71,72) in Heu of molten sulfur. This technology is in a younger state of development than the Na—S. 

As of this writing, there is Httle commercialization of advanced battery systems. Small rechargeable lithium button cells have been commercialized, however, by Sanyo, Matsushita (Panasonic), and Toshiba. These cells are intended for original equipment manufacturer (OEM) use in appHcations such as memory backup and are not available to the general consumer. 

Efforts to develop commercially viable EV versions of advanced battery systems continue. The ultimate goal is to develop battery technology suitable for practical, consumer-acceptable electric vehicles. The United States Advanced Battery Consortium (USABC) has been formed with the express purpose of accelerating development of practical EV batteries (83). 

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