Tech 101: How Batteries Work
The first “modern” battery consisted of an apparatus made with metal plates and brine soaked cardboard and was invented by an Italian physicist named Count Alessandro Volta in 1799. Since then, the materials used have changed tremendously, but the basic principle has remained the same. When a device is connected to a battery, a reaction takes place that generates electricity. This is called an electrochemical reaction.
Mankind’s appetite for electricity has grown exponentially since the 1800s. Today, batteries are found in a vast variety of devices from wristwatches and alarm clocks to smartphones and laptops. Lets look at a few of the most common batteries that we find around us everyday.
If you look at any battery today, be it a pencil cell or a car battery, the first thing you’ll notice is that it has two terminals marked + and – . On pencil cells and flashlight batteries like AA, AAA, C or a D cell battery, the terminals are at opposite ends of the battery. On higher capacity batteries like a 9V or a car battery the terminals are located together on top of the battery. If a wire is connected to both terminals, electricity will flow from the -’ve terminal to the +’ve terminal as fast as possible. This will drain the battery very quickly and is dangerous when applied to larger batteries.
A battery consists of five main components. There is a cathode, which connects to the +’ve terminal, an anode, which connects to the -’ve terminal, a seperator, which prevents the anode and cathode from touching each other, an electrolyte, which allows the charge to flow from the anode to the cathode and lastly a collector, which conducts the electricity out of the battery.
When you put a battery in a device, it completes the load circuit. What happens next differs from battery to battery but the idea remains the same. The anode goes through an oxidation reaction in which two or more ions from the electrolyte react with the anode material and creates a new compound and two or more electrons. At the same time, the cathode goes through a reduction reaction in which the cathode material, ions and free electrons combine to form other compounds. While this sounds very complicated, its actually very easy. The anode reacts with the electrolyte to create electrons and the cathode reacts with the electrolyte to absorb electrons. The end result is electricity. A battery will last as long as it has materials to continue the reaction at both electrodes.
A few commonly found batteries include:
- Zinc Carbon Battery: This type of battery chemistry is commonly found in many cheap AA, AAA, C and D cell batteries. The anode is Zinc, the cathode is Manganese Dioxide and the electrolyte is Ammonium Chloride or Zinc Chloride.
- Alkaline Battery: This is also another commonly found battery chemistry. 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: Lithium ion batteries are used in high performance devices that require frequent charging. These include phones, laptops, tablets and even electric cars. While the exact components of Lithium Ion batteries vary, the most common practice is to have a lithium cobalt oxide cathode and a carbon anode.
- Lead Acid: This is the typical car battery. It consists of lead dioxide and metallic lead electrodes that are suspended in a Sulfuric Acid solution.
The two main categories of batteries are Primary (one time use) batteries and Secondary (rechargeable) batteries. The only difference between the two is that when an external current is applied to a secondary battery, the electrochemical reaction happens in reverse, which restores the charge of the battery. There are three main types of rechargeable batteries, Lithium Ion (LiOn), Nickle Metal Hydride (NiMH) and Nickle Cadmium (NiCd). NiCd batteries were the first widely available rechargeable batteries but they suffered from a problem known as the memory effect. These batteries, if not fully discharged during every use, would quickly start to loose power.
NiCd batteries were largely replaced by NiMH batteries which boasted a much larger capacity as well as a reduced memory effect. The only problem with NiMH batteries was their relatively short 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.
An offshoot of the LiOn technology is the Lithium Polymer (LiPo) battery. While LiOn batteries are the norm for most laptops, LiPo batteries offer significant advantages in space as well as weight savings. These types of batteries consist of an anode and cathode material that has been laminated onto a microperforated plastic sheet which, as the name implies, allows the passage of ions but seperates the anode from the cathode. This allows LiPo batteries to created in almost any shape from round to square and anywhere in the middle. Most mobile phones and tablets have these batteries as they boast the highest charge density of any battery available in the market today.
Looking to the future, many people believe that the days of the battery are numbered and that they will soon be replaced by fuel cells. While we look forward to the day we have to start popping H2 cartridges into our phones once a month, it is still a while away.