Batteries

Batteries

Introduction

Batteries are major part of everyday life all over the world. Without them, we would not be able to live life as we know it. They give us the lightweight, portable energy to run the devices we need in our everyday lives. The problem with batteries being such a big part of our lives is that the average person does not consider the environmental hazards. We use them until they don't work anymore and then throw them in the garbage without a second thought. It is hard to believe that something so essential could also be so dangerous to the environment.

Batteries work by converting chemical energy into electrical energy. Every battery has a positive end called an anode and a negative end called a cathode. Electrons collect on the negative end of the battery and flow through whatever you attach by wire on their way back to the positive side of the battery. The electrical current through the battery is caused by the voltage difference between the anode and cathode. As the current passes through the battery it is pushed through an electrolyte that can be either solid or liquid. This process causes a chemical reaction that produces electrons. As long as the chemical reaction takes place, the battery will continue to work.

History

In 1876 Count Luigi Galvani found that when the tissues of a dead frog were touched by two different metals, they twitched. This started the thinking that there could be an electrical pathway from an anode to a cathode. Count Alessandro Volta took this thinking to the next level and made the first real battery in 1800. He did this by alternating layers of zinc, blotting paper soaked in salt water, and silver. His battery is called a voltaic pile and is pictured below. When a wire is attached to both ends, the voltage can be measured. The batteries that we use today are just variations of Volta's original. They have plates of reactive chemicals that are separated by polarized barriers (Brain, 2000).

Figure 1: Voltaic pile (Brain, 2000)

These batteries that we use today are almost never used alone. They are usually put together in groups either serially or in parallel to gain either higher voltage or current. When cells are arranged in series the voltage of the individual cells adds together. When cells are arranged in parallel the voltage does not add, but the current will increase by the number of cells in the arrangement. In the figure below, the top four cells are arranged in parallel so the voltage remains the same as an individual cell, but the current produced is increased by four times the current of a single cell. The bottom four cells are arranged in series so their individual voltages of 1.5 are added together for a total of 6 volts (Brain, 2000).

Figure 2: Cells in Parallel and Series (Brain, 2000)

Types of Batteries

There are two main types of batteries used today. The first is primary cells, which are non - rechargeable and are usually thrown away after one use. Some of the primary cell batteries include Alkaline, Carbon-Zinc, Mercury Oxide, Silver Oxide, and Lithium Primary. The other types of batteries are called secondary cells. These can be recharged and used over and over. They will eventually die, but can be charged and used many times. Some of the different types of secondary cells include nickel cadmium, nickel metal hydride, lithium ion, and lead acid. As environmental concerns grow, these reusable secondary cells are becoming more popular (Brophy).

Primary Cells

Alkaline and Carbon-Zinc cells are the most common battery used by consumers. The difference between the two is that alkaline batteries have zinc and manganese-oxide electrodes with an alkaline electrolyte and the carbon-zinc batteries have carbon and zinc electrodes with an acidic paste for the electrolyte. Both of these batteries are used in low drainage appliances like flashlights, toys, and other household items. It is because of their wide range of uses that they are so popular. These batteries were made with mercury until the early 1990's to keep internal gasses from forming and causing leaks. New technology and concern for the environment caused this practice to be stopped in the United States by 1993. It was made illegal in 1996 by the Mercury-Containing and Rechargeable Battery Management Act (NEMA 2002). Since the practice of using mercury stopped these batteries are safe to throw away.

Mercury oxide batteries are not widely used anymore because, as the name implies, they are made with mercury. These batteries last a lot longer than either alkaline or carbon-zinc and will remain stable under very high temperatures. Because of these features, they are still used by the military and in some medical applications (Brophy). Federal law states that these mercury oxide batteries can only be sold if the manufacturer clearly identifies a collection site for recycling (NEMA 2002).

Silver oxide batteries are small cells that are coin shaped and used in many watches, calculators and hearing aids. They are sometimes referred to as button cells. Because of their small size and lack of other options to reduce gas buildup inside these batteries, small amounts of mercury are still used. Federal regulations limit this mercury content to 25 milligrams per button cell (NEMA 2002). Because of this mercury content, these batteries should be taken to collection sites and recycled. Since they are so small and used in everyday things, most people don't assume they are harmful to the environment and are often just thrown in the trash.

Lithium primary batteries are used in cameras, watches, and for memory backup in computers. They have a very long shelf life, have a very short recovery time and can thus supply power surges to devices like a camera flash. Their voltage remains constant until all of the lithium metal has reacted so there is no reactive lithium left when they are disposed of.

Secondary Cells

The oldest and most widely used small rechargeable battery is nickel cadmium. It is used in laptop computers, cell phones, tools and many other devices. The electrodes are nickel and cadmium with potassium hydroxide used as the electrolyte (Brain, 2000). Although cadmium is a known carcinogen, these types of batteries remain one of the most popular rechargeable cells. There are many reasons they remain popular. They are very adaptable to different charging rates and operate well through a wide range