Introduction to How Batteries Work

Imagine a world where everything that used electricity had to be plugged in. Flashlights, hearing aids, cell phones and other portable devices would be tethered to electrical outlets, rendering them awkward and cumbersome. Cars couldn't be started with the simple turn of a key; a strenuous cranking would be required to get the pistons moving. Wires would be strung everywhere, creating a safety hazard and an unsightly mess. Thankfully, batteries provide us with a mobile source of power that makes many modern conveniences possible.

While there are many different types of batteries, the basic concept by which they function remains the same. When a device is connected to a battery, a reaction occurs that produces electrical energy. This is known as an electrochemical reaction. Italian physicist Count Alessandro Volta first discovered this process in 1799 when he created a simple battery from metal plates and brine-soaked cardboard or paper. Since then, scientists have greatly improved upon Volta's original design to create batteries made from a variety of materials that come in a multitude of sizes.

Today, batteries are all around us. They power our wristwatches for months at a time. They keep our alarm clocks and telephones working, even if the electricity goes out. They run our smoke detectors, electric razors, power drills, mp3 players, thermostats -- and the list goes on. If you're reading this article on your laptop or smartphone, you may even be using batteries right now! However, because these portable power packs are so prevalent, it's very easy to take them for granted. This article will give you a greater appreciation for batteries by exploring their history, as well as the basic parts, reactions and processes that make them work. So cut that cord and click through our informative guide to charge up your knowledge of batteries.

The history of batteries can be traced back to 1800. Learn about the history of batteries and find out how the Daniell cell battery is constructed.

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Battery History

Batteries have been around longer than you may think. In 1938, archaeologist Wilhelm Konig discovered some peculiar clay pots while digging at Khujut Rabu, just outside of present-day Baghdad, Iraq. The jars, which measure approximately 5 inches (12.7 centimeters) long, contained an iron rod encased in copper and dated from about 200 B.C. Tests suggested that the vessels had once been filled with an acidic substance like vinegar or wine, leading Konig to believe that these vessels were ancient batteries. Since this discovery, scholars have produced replicas of the pots that are in fact capable of producing an electric charge. These "Baghdad batteries" may have been used for religious rituals, medicinal purposes, or even electroplating.

In 1799, Italian physicist Alessandro Volta created the first battery by stacking alternating layers of zinc, brine-soaked pasteboard or cloth, and silver. This arrangement, called a voltaic pile, was not the first device to create electricity, but it was the first to emit a steady, lasting current. However, there were some drawbacks to Volta's invention. The height at which the layers could be stacked was limited because the weight of the pile would squeeze the brine out of the pasteboard or cloth. The metal discs also tended to corrode quickly, shortening the life of the battery. Despite these shortcomings, the SI unit of electromotive force is now called a volt in honor of Volta's achievement.

The history of batteries can be traced back to 1800. Learn about the history of batteries and find out how the Daniell cell battery is constructed.

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The next breakthrough in battery technology came in 1836 when English chemist John Frederick Daniell invented the Daniell cell. In this early battery, a copper plate was placed at the bottom of a glass jar and a copper sulfate solution was poured over the plate to half-fill the jar. Then the zinc plate was hung in the jar, and a zinc sulfate solution was added. Because copper sulfate is denser than zinc sulfate, the zinc solution floated to the top of the copper solution and surrounded the zinc plate. The wire connected to the zinc plate represented the negative terminal, while the one leading from the copper plate was the positive terminal. Obviously, this arrangement would not have functioned well in a flashlight, but for stationary applications it worked just fine. In fact, the Daniell cell was a common way to power doorbells and telephones before electrical generation was perfected.

By 1898, the Colombia Dry Cell became the first commercially available battery sold in the United States. The manufacturer, National Carbon Company, later became the Eveready Battery Company, which produces the Energizer brand.

Now that you know some of the history, click over to the next page to learn the various parts of a battery.

Did You Know?

According to an EPA estimate, Americans purchase nearly 3 billion dry cell batteries every year [source: EPA].

Anatomy of a Battery

Take a look at any battery, and you'll notice that it has two terminals. One terminal is marked (+), or positive, while the other is marked (-), or negative. In normal flashlight batteries, like AA, C or D cell, the terminals are located on the ends. On a 9-volt or car battery, however, the terminals are situated next to each other on the top of the unit. If you connect a wire between the two terminals, the electrons will flow from the negative end to the positive end as fast as they can. This will quickly wear out the battery and can also be dangerous, particularly on larger batteries. To properly harness the electric charge produced by a battery, you must connect it to a load. The load might be something like a light bulb, a motor or an electronic circuit like a radio.

The internal workings of a battery are typically housed within a metal or plastic case. Inside this case are a cathode, which connects to the positive terminal, and an anode, which connects to the negative terminal. These components, more generally known as electrodes, occupy most of the space in a battery and are the place where the chemical reactions occur. A separator creates a barrier between the cathode and anode, preventing the electrodes from touching while allowing electrical charge to flow freely between them. The medium that allows the electric charge to flow between the cathode and anode is known as the electrolyte. Finally, the collector conducts the charge to the outside of the battery and through the load.

On the next page, we'll explore how the cathode, anode, electrolyte, separator and collector work together to produce an electrical current and keep your portable devices going strong.

Powered by Air?

Researchers are currently developing a battery in which the electrodes would be lithium and, amazingly, oxygen from the air. Such an advancement would dramatically decrease battery weight and could boast five to 10 times the energy of traditional lithium-ion batteries. While this technology still has a number of obstacles to overcome, it could one day revolutionize the electric car industry [source: Rahim].

Battery Reactions and Chemistry

A lot happens inside a battery when you pop it into your flashlight, remote control or other wire-free device. While the processes by which they produce electricity differ slightly from battery to battery, the basic idea remains the same.

When a load completes the circuit between the two terminals, the battery produces electricity through a series of electromagnetic reactions between the anode, cathode and electrolyte. The anode experiences an oxidation reaction in which two or more ions (electrically charged atoms or molecules) from the electrolyte combine with the anode, producing a compound and releasing one or more electrons. At the same time, the cathode goes through a reduction reaction in which the cathode substance, ions and free electrons also combine to form compounds. While this action may sound complicated, it's actually very simple: The reaction in the anode creates electrons, and the reaction in the cathode absorbs them. The net product is electricity. The battery will continue to produce electricity until one or both of the electrodes run out of the substance necessary for the reactions to occur.

Modern batteries use a variety of chemicals to power their reactions. Common battery chemistries include:

  • Zinc-carbon battery: The zinc-carbon chemistry is common in many inexpensive AAA, AA, C and D dry cell batteries. The anode is zinc, the cathode is manganese dioxide, and the electrolyte is ammonium chloride or zinc chloride.
  • Alkaline battery: This chemistry is also common in AA, C and D dry cell batteries. The cathode is composed of a manganese dioxide mixture, while the anode is a zinc powder. It gets its name from the potassium hydroxide electrolyte, which is an alkaline substance.
  • Lithium-ion battery (rechargeable): Lithium chemistry is often used in high-performance devices, such as cell phones, digital cameras and even electric cars. A variety of substances are used in lithium batteries, but a common combination is a lithium cobalt oxide cathode and a carbon anode.
  • Lead-acid battery (rechargeable): This is the chemistry used in a typical car battery. The electrodes are usually made of lead dioxide and metallic lead, while the electrolyte is a sulfuric acid solution.

The best way to understand these reactions is to see them for yourself. Go to the next page for some hands-on battery experiments.

Gas vs. Electric

Despite all its drawbacks, gasoline continues to be the dominant fuel for automobiles. Why haven't batteries caught on? One of the biggest problems is with energy density -- the amount of energy a fuel can store in relation to its weight, which is measured in watt-hours per kilogram. Gasoline has an energy density of about 13,000 watt-hours per kilogram, while the best lithium-ion batteries currently available can hold only 200 watt-hours per kilogram [source: Manjoo].

Battery Experiments: Voltaic Pile

If you want to learn more about the electrochemical reactions that occur in batteries, you can actually build one yourself using simple household materials. One thing you should buy before you start is an inexpensive ($10 to $20) volt-ohm meter at your local electronics or hardware store. Make sure that the meter can read low voltages (in the one-volt range) and low currents (in the five-to-10 milliamp range). With this equipment on hand, you'll be able to see exactly how well your battery is performing.

You can create your own voltaic pile using quarters, foil, blotting paper, cider vinegar and salt. Cut the foil and blotting paper into circles, then soak the blotting paper in a mixture of the cider vinegar and salt. Using masking tape, attach a copper wire to one of the foil discs. Now stack the materials in this order: foil, paper, quarter, foil, paper, quarter, and so on until you have repeated the pattern 10 times. Once the last coin is on the stack, attach a wire to it with masking tape. Finally, attach the free ends of the two wires to an LED, which should light up. In this experiment, the copper in the quarter is the cathode, the foil is the anode, the cider vinegar-salt solution is the electrolyte, and the blotting paper is the separator.

A homemade battery can also be made from copper wire, a paper clip and a lemon. First, cut a short piece of copper wire and straighten out the paper clip. Use sandpaper to smooth out any rough parts on the ends of either piece of metal. Next, gently squeeze the lemon by rolling it on a table, but be careful not to break the skin. Push the copper wire and the paper clip into the lemon, ensuring that they are as close together as possible without actually touching. Finally, connect your volt-ohm meter to the ends of the paper clip and the copper wire, and see what kind of voltage and current your battery produces.

By now you should be well acquainted with the basic principles by which batteries discharge electricity. Read on to discover how some batteries can be recharged.

Rechargeable Batteries

With the rise in portable devices such as laptops, cell phones, MP3 players and cordless power tools, the need for rechargeable batteries has grown substantially in recent years. Rechargeable batteries have been around since 1859, when French physicist Gaston Plante invented the lead acid cell. With a lead anode, a lead dioxide cathode and a sulfuric acid electrolyte, the Plante battery was a precursor to the modern-day car battery.

Non-rechargeable batteries, or primary cells, and rechargeable batteries, or secondary cells, produce current exactly the same way: through an electrochemical reaction involving an anode, cathode and electrolyte. In a rechargeable battery, however, the reaction is reversible. When electrical energy from an outside source is applied to a secondary cell, the negative-to-positive electron flow that occurs during discharge is reversed, and the cell's charge is restored. The most common rechargeable batteries on the market today are lithium-ion (LiOn), though nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) batteries were also once very prevalent.

When it comes to rechargeable batteries, not all batteries are created equal. NiCd batteries were among the first widely available secondary cells, but they suffered from an inconvenient problem known as the memory effect. Basically, if these batteries weren't fully discharged every time they were used, they would quickly lose capacity. NiCd batteries were largely phased out in favor of NiMH batteries. These secondary cells boast a higher capacity and are only minimally affected by the memory effect, but they don't have a very good shelf life. Like NiMH batteries, LiOn batteries have a long life, but they hold a charge better, operate at higher voltages, and come in a much smaller and lighter package. Essentially all high-quality portable technology manufactured these days takes advantage of this technology. However, LiOn batteries are not currently available in standard sizes such as AAA, AA, C or D, and they're considerably more expensive than their older counterparts.

With NiCd and NiMH batteries, charging can be tricky. You must be careful not to overcharge them, as this could lead to decreased capacity. To prevent this from happening, some chargers switch to a trickle charge or simply shut off when charging is complete. NiCd and NiMH batteries also must be reconditioned, meaning you should completely discharge and recharge them again every once in a while to minimize any loss in capacity. LiOn batteries, on the other hand, have sophisticated chargers that prevent overcharging and never need to be reconditioned.

Even rechargeable batteries will eventually die, though it may take hundreds of charges before that happens. When they finally do give out, be sure to dispose of them at a recycling facility.

Next, let's take a look at battery arrangement.

Battery arrangement determines voltage and current. Check out serial battery arrangements, parallel arrangements and what maximum current is about.

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Battery Arrangement and Power

In many devices that use batteries -- such as portable radios and flashlights -- you don't use just one cell at a time. You normally group them together in a serial arrangement to increase the voltage or in a parallel arrangement to increase current. The diagram shows these two arrangements.

The upper diagram shows a parallel arrangement. The four batteries in parallel will together produce the voltage of one cell, but the current they supply will be four times that of a single cell. Current is the rate at which electric charge passes through a circuit, and is measured in amperes. Batteries are rated in amp-hours, or, in the case of smaller household batteries, milliamp-hours (mAH). A typical household cell rated at 500 milliamp-hours should be able to supply 500 milliamps of current to the load for one hour. You can slice and dice the milliamp-hour rating in lots of different ways. A 500 milliamp-hour battery could also produce 5 milliamps for 100 hours, 10 milliamps for 50 hours, or, theoretically, 1,000 milliamps for 30 minutes. Generally speaking, batteries with higher amp-hour ratings have greater capacities.

The lower diagram depicts a serial arrangement. The four batteries in series will together produce the current of one cell, but the voltage they supply will be four times that of a single cell. Voltage is a measure of energy per unit charge and is measured in volts. In a battery, voltage determines how strongly electrons are pushed through a circuit, much like pressure determines how strongly water is pushed through a hose. Most AAA, AA, C and D batteries are around 1.5 volts.

Imagine the batteries shown in the diagram are rated at 1.5 volts and 500 milliamp-hours. The four batteries in parallel arrangement will produce 1.5 volts at 2,000 milliamp-hours. The four batteries arranged in a series will produce 6 volts at 500 milliamp-hours.

Battery technology has advanced dramatically since the days of the Voltaic pile. These developments are clearly reflected in our fast-paced, portable world, which is more dependent than ever on the portable power source that batteries provide. One can only imagine what the next generation of smaller, more powerful and longer-lasting batteries will bring.

For more information on batteries and related topics, check out the links on the next page.

Lots More Information

Sources

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