How Do Batteries Work?
You scour every store on the web or at your local mall looking for the perfect gift to give a kid this holiday season. You can hardly wait to see the light in their eyes when they switch on that talking, walking robot.
Oh, but wait a second. You forgot the batteries.
Nearly two-thirds of shoppers admitted in a recent survey that they had forgotten to buy the batteries needed for toys and other gifts. These gift givers risk going from superhero to superzero in the flick of a switch.
We know how this happens. You can always find batteries at checkout counters during the holidays, but they’re rarely offered at an online point of sale. Though we all recognize them, very few of us know how they work, not to mention the practical plusses and minuses of the various battery chemistries now on the market. Let’s take a closer look at how batteries work so next time you’re buying a battery-using gadget, maybe you’ll think twice before checkout.
All batteries work the same way: by taking advantage of the fact that different metals have different electrochemical potential, depending on the number of electrons in their outermost shell. Some are electron takers — they “want” more electrons — while others are givers. When two metals with different potentials are placed in a conductive fluid or paste and then connected by an external wire, chemical reactions occur that free electrons and cause them to flow through that wire from the givers to the takers, producing an electric current.
Without the external connection, nothing happens, which is why batteries can last for years when they’re not in use.
In primary batteries (disposable) the metal that gives up electrons in a battery is called the anode; the one that receives them, the cathode. The conductive substance with which the two metals react to free the electrons is called the electrolyte. Any variations to improve battery performance or meet specific needs involve changes to the anode, cathode or electrolyte.
Readers who are chemists will note that the above is a significant over-simplification. There’s much more to the story — but every battery in the world has at least these three components.
A wide variety of batteries have been developed, but when it comes to the familiar disposable AAs and AAAs that power toys and household gadgets, four varieties stand out.
Each features a different chemistry, but they all share the same cylindrical design. From the outside, it looks like the cathode and anode are located at either end, as in primitive batteries, but in fact, the cathode is a cylinder wrapped around the anode, the two being separated by the electrolyte. Electricity is conducted to the external contact via a central carbon tube. Carbon is a good conductor and resistant to chemical degradation over time.
- Zinc/carbon batteries date back to the 1860s, and represent the oldest technology still manufactured. Like Volta’s first battery, they have a zinc cathode. The anode is manganese dioxide, and the electrolyte is ammonium chloride. These batteries provide the least power of any available, but they are also the least expensive.
- “Heavy-duty” batteries. This name is a misnomer, because these batteries, although two to three times more powerful than zinc/carbon, are still at the low end of the power and shelf life spectrum. The primary chemical difference between zinc carbon and heavy-duty batteries is the heavy-duty electrolyte: zinc chloride instead of ammonium chloride.
- Alkaline batteries, named for their electrolyte, are 500% to 700% more powerful than zinc/carbon and have a shelf life four to nine times longer. Although the use of an alkaline, rather than an acidic electrolyte, would appear to be their main differentiating feature, the improved performance is generally attributed to refinements to the anode and cathode. The zinc of the anode is powdered, which means a larger surface area to react with the electrolyte. The electrolyte itself, manganese dioxide, like the batteries discussed above, is said to be purer and denser in alkaline batteries.
- Primary lithium batteries offer at least twice as much energy (measured in volts) as alkaline batteries. The key to their higher performance is the use of lithium instead of zinc as a cathode. Lithium atoms have only one electron in their outer shell, which means their electrochemical potential is very high in comparison with zinc. While primary batteries still have a large market share, secondary (rechargeable) batteries have been growing rapidly due to the introductions of smart devices and electrification of vehicles. There is a bright future for lithium ion batteries and many innovations are taking place in this space.
A Bright Future
Batteries are a very hot focus of research and investment. Electronic vehicles (EVs) are one of the most important catalysts of innovation, but it’s likely that new offerings in many categories will continue to appear. For now, however, what’s important is that the right batteries appear when someone special opens your electronic holiday gift.