The Use And History Of Battery Power Engineering Essay
A battery, which is actually an electric cell, is a device that produces electricity from a chemical reaction. Strictly speaking, a battery consists of two or more cells connected in series or parallel, but the term is generally used for a single cell. A cell consists of a negative electrode; an electrolyte, which conducts ions; a separator, also an ion conductor; and a positive electrode. Continue with How Batteries Work/Battery Typeshttp://inventors.about.com/library/inventors/blbattery.htm
Extract: Nasa Jet Propulsion Laboratory Report By Sandra M. Dawson
Return Battery History
A battery, which is actually an electric cell, is a device that produces electricity from a chemical reaction. Strictly speaking, a battery consists of two or more cells connected in series or parallel, but the term is generally used for a single cell. A cell consists of a negative electrode; an electrolyte, which conducts ions; a separator, also an ion conductor; and a positive electrode. The electrolyte may be aqueous (composed of water) or nonaqueous (not composed of water), in liquid, paste, or solid form. When the cell is connected to an external load, or device to be powered, the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. When the external load is removed the reaction ceases.
A primary battery is one that can convert its chemicals into electricity only once and then must be discarded. A secondary battery has electrodes that can be reconstituted by passing electricity back through it; also called a storage or rechargeable battery, it can be reused many times.
One of the first space batteries was the Silver-Zinc battery, which dominated the industry in the 60's. This is a premium system with very high specific power and energy, but is quite expensive due to the use of silver. They are still used in selected applications, such as launch vehicles (rockets) and torpedoes. Mars Pathfinder also used a Silver-Zinc battery, but it was designed to be rechargeable. They have a relatively short cycle life, and are not used for multi-year missions. This type of battery is used commonly in the commercial market as hearing aid batteries.
Batteries come in several styles; the most familiar are single-use alkaline batteries. NASA spacecraft usually use rechargeable nickel-cadmium or nickel-hydride batteries like those found in laptop computers or cellular phones. Engineers think of batteries as a place to store electricity in a chemical form.
Battery technology is part of the power system, storing and discharging energy on each orbit of the spacecraft. The batteries help provide a constant source of power to the spacecraft by storing energy when excess is provided by the solar cells and discharging stored energy when the solar cells are not providing any during periods of eclipse.
Nickel-Cadmium has been the most common space battery since the 70's. They were used in all commercial communications satellites, in most earth orbiters, and in some space probes. They are generally a prismatic (resembling, or being a prism) design, and packaged very efficiently. This means that the batteries can be stored on the spacecraft in a very compact form, eliminating the need for extraneous space. They have been known to last for ten to twenty years in space. They are still in use in selected space applications, including small satellites and for missions that encounter very severe radiation environments.
This battery uses nickel oxide in its positive electrode (cathode), a cadmium compound in its negative electrode (anode), and potassium hydroxide solution as its electrolyte. The Nickel Cadmium Battery is rechargeable, so it can cycle repeatedly. A nickel cadmium battery converts chemical energy to electrical energy upon discharge and converts electrical energy back to chemical energy upon recharge. In a fully discharged NiCd battery, the cathode contains nickel hydroxide [Ni(OH)2] and cadmium hydroxide [Cd(OH)2] in the anode. When the battery is charged, the chemical composition of the cathode is transformed and the nickel hydroxide changes to nickel oxyhydroxide [NiOOH]. In the anode, cadmium hydroxide is transformed to cadmium. As the battery is discharged, the process is reversed, as shown in the following formula.
Cd + 2H2O + 2NiOOH —> 2Ni(OH)2 + Cd(OH)2
Nickel cadmium is the most commonly used battery for Low Earth Orbit (LEO) missions. A spacecraft battery consists of series-connected cells, the number of which depends upon bus voltage requirements and output voltage of the individual cells.
The Nickel-Hydrogen battery is currently the most popular space battery. It can be considered a hybrid between the nickel-cadmium battery and the fuel cell. The cadmium electrode was replaced with a hydrogen gas electrode. This battery is visually much different from the Nickel-Cadmium battery, because the cell is a pressure vessel, which must contain over one thousand pounds per square inch (psi) of hydrogen gas. It is significantly lighter than nickel-cadmium, but is more difficult to package, much like a crate of eggs. It is the longest-lived space battery yet built, with 10 to 20 year lifetimes being common. This battery is too expensive for commercial applications, and few terrestrial examples have been built.
Nickel-hydrogen batteries are sometimes confused with Nickel-Metal Hydride batteries, the batteries commonly found in cell phones and laptops. The nickel-metal hydride system is rarely used in space due to its limited life. Nickel-hydrogen, as well as nickel-cadmium batteries use the same electrolyte, a solution of potassium hydroxide, which is commonly called lye.
Incentives for developing nickel/metal hydride (Ni-MH) batteries comes from pressing health and environmental concerns to find replacements for the nickel/cadmium rechargeable batteries. Due to worker's safety requirements, processing of cadmium for batteries in the U.S. is already in the process of being phased out. Furthermore, environmental legislation for the 1990's and the 21st century will most likely make it imperative to curtail the use of cadmium in batteries for consumer use. In spite of these pressures, next to the lead-acid battery, the nickel/cadmium battery still has the largest share of the rechargeable battery market. Further incentives for researching hydrogen-based batteries comes from the general belief that hydrogen and electricity will displace and eventually replace a significant fraction of the energy-carrying contributions of fossil-fuel resources, becoming the foundation for a sustainable energy system based on renewable sources. Finally, there is considerable interest in the development of Ni-MH batteries for electric vehicles and hybrid vehicles.
The nickel/metal hydride battery operates in concentrated KOH (potassium hydroxide) electrolyte. The electrode reactions in a nickel/metal hydride battery are as follows:
Cathode (+): NiOOH + H2O + e- Ni(OH)2 + OH- (1)
Anode (-): (1/x) MHx + OH- (1/x) M + H2O + e- (2)
Overall: (1/x) MHx + NiOOH (1/x) M + Ni(OH)2 (3)
The KOH electrolyte can only transport the OH- ions and, to balance the charge transport, electrons must circulate through the external load. The nickel oxy-hydroxide electrode (equation 1) has been extensively researched and characterized, and its application has been widely demonstrated for both terrestrial and aerospace applications. Most of the current research in Ni/Metal Hydride batteries has involved improving the performance of the metal hydride anode. Specifically, this requires the development of a hydride electrode with the following characteristics: (1) long cycle life, (2) high capacity, (3) high rate of charge and discharge at constant voltage, and (4) retention capacity.
These systems are different from all of the previously mentioned batteries, in that no water is used in the electrolyte. They use a non-aqueous electrolyte instead, which is composed of organic liquids and salts of lithium to provide ionic conductivity. This system has much higher cell voltages than the aqueous electrolyte systems. Without water, the evolution of hydrogen and oxygen gases is eliminated and cells can operate with much wider potentials. They also require a more complex assembly, as it must be done in a nearly perfectly dry atmosphere.
A number of non-rechargeable batteries were first developed with lithium metal as the anode. Commercial coin cells used for today's watch batteries are mostly a lithium chemistry. These systems use a variety of cathode systems that are safe enough for consumer use. The cathodes are made of various materials, such as carbon monoflouride, copper oxide, or vanadium pentoxide. All solid cathode systems are limited in the discharge rate they will support.
To obtain a higher discharge rate, liquid cathode systems were developed. The electrolyte is reactive in these designs and reacts at the porous cathode, which provides catalytic sites and electrical current collection. Several examples of these systems include lithium-thionyl chloride and lithium-sulfur dioxide. These batteries are used in space and for military applications, as well as for emergency beacons on the ground. They are generally not available to the public because they are less safe than the solid cathode systems.
The rechargeable lithium battery field is a growing area for space, and the latest technology for space is the Lithium Ion battery. The high voltage lithium-ion cells are moving into space for short to moderate length missions. They are easy to package, and very light. In this system, the lithium metal anode is replaced with a carbon electrode which inserts lithium ions from the electrolyte, storing them in a solid solution phase. This configuration has improved safety over previous lithium rechargeable, and yet gives good rate capability.
The next step in lithium ion battery technology is believed to be the lithium polymer battery. This battery replaces the liquid electrolyte with either a gelled electrolyte or a true solid electrolyte. These batteries are supposed to be even lighter than lithium ion batteries, but there are currently no plans to fly this technology in space. It is also not commonly available in the commercial market, although it may be just around the corner.
In retrospect, we have come a long way since the leaky flashlight batteries of the sixties, when space flight was born. There is a wide range of solutions available to meet the many demands of space flight, 80 below zero to the high temperatures of a solar fly by. It is possible to handle massive radiation, decades of service, and loads reaching tens of kilowatts. There will be a continued evolution of this technology and a constant striving toward improved batteries.
A voltaic pile
The first battery was created by Alessandro Volta in 1800. To create his battery, he made a stack by alternating layers of zinc, blotting paper soaked in salt water, and silver. This arrangement was known as a voltaic pile. The top and bottom layers of the pile must be different metals. If you attach a wire to the top and bottom of the pile, you can measure a voltage and a current from the pile. The pile can be stacked as high as you like, and each layer will increase the voltage by a fixed amount.
In the 1800s, before the invention of the electrical generator (the generator was not invented and perfected until the 1870s), the Daniell cell was extremely common for operating telegraphs and doorbells. The Daniell cell is also known by three other names:
Crowfoot cell (because of the typical shape of the zinc electrode)
Gravity cell (because gravity keeps the two sulfates separated)
Wet cell (because it uses liquids for the electrolytes, as opposed to the modern dry cell)
The Daniell Cell
The Daniell cell is a wet cell consisting of copper and zinc plates and copper and zinc sulfates. To make the Daniell cell, the copper plate is placed at the bottom of a glass jar. Copper sulfate solution is poured over the plate to half-fill the jar. Then a zinc plate is hung in the jar and a zinc sulfate solution is poured very carefully into the jar. Copper sulfate is denser than zinc sulfate, so the zinc sulfate "floats" on top of the copper sulfate. Obviously, this arrangement does not work very well in a flashlight, but it works fine for stationary applications.
If you have access to zinc sulfate and copper sulfate, you can try making your own Daniell cell. In the next section, we'll show you how to do it.
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