Batteries, Secondary Cells

Abstract

Alkaline electrolyte storage battery systems are suitable in applications where high currents are required, because of the high conductivity of the electrolyte. Additionally, the electrolyte, usually an aqueous solution containing 25–40% potassium hydroxide, KOH, does not enter into the chemical reaction. Thus concentration and cell resistance are invariant with state of discharge, and these battery systems give high performance and have long cycle life. Battery system designers are switching to nickel–metal hydride (MH) cells for many applications, typically in “AA”‐size cells. Many of the most recent applications for alkaline storage batteries require higher energy density and lower cost designs than were previously available. Materials such as foam or fiber nickel, Ni, mats as substrates, and new processing techniques including plastic bound, pasted, or electroplated electrodes, have enabled the alkaline storage battery to meet these new requirements, while reducing environmental problems in the manufacturing plants. The most recent innovations in materials relate to the development of metal–hydride alloys for the storage and electrochemical utilization of hydrogen. Improvements in materials science and electrical circuits have led to better separators, seals, welding techniques, feedthroughs, and charging equipment. A number of different types of nickel oxide electrodes have been used in nickel–cadmium cells and nickel–MH cells. Almost all the methods described for the nickel electrode have been used to fabricate cadmium electrodes. The solid‐state chemistry of the nickel electrode is complex. There are various hydrated and nonhydrated nickel hydroxides that have slightly different crystal habitats and electrochemical potentials. Most sealed cells are based on the principles appearing in patents of the early 1950s. The majority of cells in commercial production use sintered positive (nickel) electrodes, and either sintered or pasted negative (cadmium) electrodes. Pocket cells and tubular cells are also used. The fabrication of sintered electrode batteries can be divided into five principal operations: preparation of sintering‐grade nickel powder; preparation of the sintered nickel plaque; impregnation of the plaque with active material; assembly of the impregnated plaques (often called plates) into electrode groups and into cells; and assembly of cells into batteries. Other methods to fabricate nickel–cadmium cell electrodes include those for the button cell, used for calculators and other electronic devices. Nickel–cadmium cells represent over one sixth of the market for all storage batteries, including lead–acid, manufactured in the world. The uses for nickel‐cadmium cells are divided into three categories: pocket cells are used in emergency lighting, diesel starting, and stationary and traction applications where the reliability, long life, and low temperature performance characteristics warrant the extra cost over lead–acid storage batteries; sintered, vented cells are used in extremely high rate applications, such as jet engine and large diesel engine starting; and sealed cells, both the sintered and button types, are used in computers, phones, cameras, portable tools, electronic devices, calculators, and in space applications, where nickel–cadmium is optimum because it can be recharged a great number of cycles. There has been renewed interest in alkaline storage batteries for electric and hybrid electric vehicle applications. Initially, in the 1990's many electric vehicle types used nickel cadmium and nickel‐iron battery designs. More recent interest has been in commercially available hybrid electric vehicles, which use a combination of a combustion engine and a battery, most of these have used nickel MH batteries. The silver–zinc battery had the highest attainable energy density of any rechargeable system in use in the early 1990s, and its use was limited almost exclusively to the military for various aerospace applications such as satellites and missiles, submarine and torpedo propulsion applications, and some limited portable communications applications. Zinc electrodes for secondary silver–zinc batteries are made by one of three general methods: the dry‐powder process, the slurry‐pasted process, or the electroformed process. Silver–zinc cells have one of the flattest voltage curves of any practical battery system known. Silver–zinc cells are usually manufactured as either low or high rate cells. Other silver positive electrode systems include silver–cadmium cells , used in satellite applications where the nonmagnetic property of the silver–cadmium battery is of utmost importance, and silver–iron cells , which combine the advantages of the high rate capability of the silver electrode and the cycling characteristics of the iron electrode; commercial development has been undertaken to solve problems associated with deep cycling of high power batteries for ocean systems operations. Nickel–zinc cells offer potential advantages over other rechargeable alkaline systems. The limited life of nickel–zinc batteries is the principal drawback to widespread use. With the proposed development of the nickel–hydrogen system for electric vehicles, limited attention was directed to the development of a silver–hydrogen cell. Other cell systems include zinc–oxygen cells, iron–air cells, hydrogen–oxygen cells, and mechanically rechargeable batteries. Potassium hydroxide is the principal electrolyte of choice for the above batteries because of its compatibility with the various electrodes, good conductivity, and low freezing point temperature. Alkaline batteries generate hydrogen and oxygen gases under various operating conditions. In vented batteries free ventilation should be provided to avoid hydrogen accumulations surrounding the battery. Alkaline batteries are capable of high current discharges and accidental short circuits should be avoided. The recycling of these batteries is discussed. The lead–acid battery is one of the most successful electrochemical systems and the most successful storage battery developed. The lead–acid battery consists of a number of cells in a container. These cells contain positive (PbO 2 ) and negative (Pb) electrodes or plates, separators to keep the plates apart, and sulfuric acid, H 2 SO 4 , electrolyte. The battery reactions are highly reversible, so that the battery can be discharged and charged repeatedly. Each cell has a nominal voltage of 2 V and capacities typically vary from 1 to 2000 ampere‐hours. The many cell designs available for a wide variety of uses can be divided into three main categories: automotive, industrial, and consumer. Automotive batteries as a category constitute starting, lighting, and ignition (SLI) for cranking of internal combustion engines battery sales. Industrial batteries are used for heavy‐duty application such as motive and standby power. Consumer batteries are used for emergency lighting, security alarm systems, cordless convenience devices and power tools, and small engine starting. This is one of the fastest growing markets for the lead–acid battery. Automotive and industrial motive power batteries have the standard free electrolyte systems and operate only in the vertical position. Two types of batteries having immobilized electrolyte systems are also made. They are most common in consumer applications, but their use in industrial and SLI applications is increasing. Lead sulfate is formed as the battery discharges, and sulfuric acid is regenerated as the battery is charged. The open circuit voltage of the lead–acid battery is the function of the acid concentration and temperature. The battery voltage is obtained by multiplying the cell voltage by the number of cells. The corrosion of the lead grid at the lead dioxide electrode is one of the primary causes of lead–acid battery failure. At high discharge rates, such as those required for starting an engine, the voltage of the lead–acid battery drops sharply, primarily because of the resistance of the lead current collectors. This voltage drop increases with the cell height and becomes significant even at moderate discharge rates in large industrial cells. Researchers have developed a model which has been used to improve grid designs for automotive batteries. The shelf life of the lead–acid battery is limited by self‐discharge reactions. High temperatures reduce shelf life significantly. The lead–acid battery is comprised of three primary components: the element, the container, and the electrolyte. Whereas automotive batteries have the majority of the market, other types of lead–acid batteries are making inroads into various applications (eg, for back up power systems, telecommunications, load leveling equipment). The proliferation of portable electronic devices has fueled rapid market growth for the rechargeable battery industry. Miniaturization of electronics coupled with consumer demand for lightweight batteries providing ever longer run times continues to spur interest in advanced battery systems. Interest also continues to run strong in electric vehicles (EVs) and the large auto manufacturers continue to develop prototype EVs. Advanced batteries continue to play a strong role in other applications such as load leveling for the electric utility industry and satellite power systems for aerospace. Secondary battery systems have been based on aqueous electrolytes. The use of water imposes a fundamental limitation on battery voltage because of the electrolysis of water. The application of nonaqueous electrolytes affords a significant advantage in terms of achievable battery voltages. By far the most actively researched field in nonaqueous battery systems has been the development of practical rechargeable lithium batteries based on the use of lithium metal, Li, or a lithium alloy, as the negative electrode. The use of lithium as a negative electrode for secondary batteries offers a number of advantages. Realization of the technology to commercialize these advantages has been slow. A key technical problem in developing practical lithium batteries has been poor cycle life attributable to the lithium electrode. The highly reactive nature of freshly plated lithium leads to reactions with electrolyte and impurities to form passivating films that electrically isolate the lithium metal. An important class of electrolytes for rechargeable lithium batteries are solid electrolytes. Of particular importance is the class known as solid polymer electrolytes (SPEs), polymers capable of forming complexes with lithium salts to yield ionic conductivity. The lithium or lithium alloy negative electrode systems employing a liquid electrolyte can be categorized as having either a solid positive electrode or a liquid positive electrode. Systems employing a solid electrolyte employ solid positive electrodes to provide a solid‐state cell. The most important rechargeable lithium batteries are those using a solid positive electrode within which the lithium ion is capable of intercalating. These intercalation, or insertion, electrodes function by allowing the interstitial introduction of the Li + ion into a host lattice. Intercalation electrodes have found wide application in systems employing both solid or liquid electrolytes. The use of high temperature lithium cells for electric vehicle applications has been under development since the 1970s. Advances in the development of lithium alloy–metal sulfide batteries. Because sulfur is not conductive, a current collection network of graphite is required. The cell is operated at about 350°C. The Na–S battery couple is a strong candidate for applications in both EVs and aerospace. The Na–S system is expected to provide significant increases in energy density for satellite battery systems. A battery system closely related to Na–S is the Na–metal chloride cell. The cell design is similar to Na–S; however, in addition to the β‐alumina electrolyte, the cell also employs a sodium chloroaluminate, NaAlCl 4 , molten salt electrolyte. The positive electrode active material consists of a transition metal chloride such as iron(II) chloride, FeCl 2 , or nickel chloride, NiCl 2 , in lieu of molten sulfur. This technology is in a younger state of development than the Na–S. The ultimate goal is to develop battery technology suitable for practical, consumer‐acceptable electric vehicles.