How Do Batteries Work? A Simple Introduction
Dec 29,2022 Basen
We rely on batteries for almost every aspect of our lives. From our cell phones to our laptops to our RVs and cars, batteries quite literally power our mobile world. Because of this, it’s easy to take them for granted. But how do batteries actually work? What goes on inside these portable little cells?
In this article, we explore how they work, why they have positive and negative terminals, and how they keep their charge. Let’s dive in!
What Are the Different Types of Batteries?
The most common types of batteries fall into two different classes: Primary and Secondary.
You can’t recharge primary batteries. They’re generally small, inexpensive, easy to use, and disposed of when they’ve lost their charge (think flashlights, radios, and TV remotes).
On the other hand, you can recharge secondary batteries to their original state, giving them much longer lifespans. Not surprisingly, secondary batteries are typically more expensive but come in a wide range of sizes, depending on their specific use. They power everything from your car starter and radio to your RV, laptop, and cell phone.
Examples of primary batteries include zinc-carbon, which was very popular around World War II, and zinc/alkaline manganese dioxide. This latter is perhaps the most popular primary battery and has slowly replaced the zinc-carbon types. Recently, however, primary lithium metal batteries have become popular for small applications such as watches, hearing aids, and more.
Examples of secondary batteries include lead-acid, nickel-cadmium, nickel-metal hydride, and lithium-ion. Up until recently, lead-acid and nickel-cadmium were the only two rechargeable options. Lead-acid is perhaps the most popular in the automotive industry as SLI (Starting, Lighting, and Ignition) batteries.
Nickel-metal hydride and lithium-ion batteries came along a bit later, and lithium-ion has changed our world greatly. Because of their high energy density, fast recharge times, and long life cycle, more than half of the consumer market now uses lithium-ion batteries. They’re especially popular in mobile electronics such as cell phones, laptops, tablets, and more.
How Do Batteries Work?
The electrochemistry of a battery can seem daunting, but at a high level, it’s relatively easy to understand. The cell of a battery consists of four main parts: an anode, a cathode, an electrolyte, and a separator.
The anode is the negative electrode (located at the negative end of the cell), and the cathode is the positive electrode (located at the positive end of the cell). When a battery releases a charge, the anode oxidizes and releases electrons that move toward the cathode.
The electrolyte provides a solution that allows the transfer of ions (positively or negatively charged particles). The separator prevents contact between the anode and cathode, thus redirecting the electrons through the intended electrical device.
How Do Batteries Create Voltage?
Battery voltage is essentially the difference in electrical charge between a battery’s positive and negative ends. This means that a negatively charged anode has an abundance of negatively charged electrons, while a positively charged cathode has a lack of electrons. The greater the difference in electrons between the two terminals of the battery, the higher the electrical voltage.
The voltage varies between different battery types and is a fundamental characteristic of an individual cell. The chemical reactions inside the battery cell are what determine the voltage, so a smaller cell frequently has the exact same voltage as a larger cell. Most chemical reactions yield around 1.5 to 2 volts which is the voltage of an individual cell.
Because of the low voltage of a cell, most larger batteries have cells in series with each other to increase the voltage. For example, most 12V batteries have 4 to 6 cells in series.
Why Do Batteries Have Negative and Positive Ends?
The negative and positive terminals of a battery are what create the potential electrical charge within the cell. The electrochemistry of a battery houses the potential voltage on one end of the battery and prevents the electrons from traveling to the other end via the separator.
This design allows the battery to store electrical potential until something attaches a circuit, connecting the negative and positive terminals. This allows the electrons to flow freely and creates usable electricity.
How Does Current Flow in a Battery?
This process is critical to how batteries work. Electrons are negatively charged. This means they’re attracted to the positive terminal of a cell. Thus, when discharging, the current flows from the negative end of the cell to the positive end through the circuit it’s connected to.
However, in rechargeable batteries, the electrical current can flow in both directions. When a rechargeable battery connects to its power source, the electrons flow from the positive end to the negative end, therefore replenishing the battery’s charge. The motion of the electrons and how fast they move is called the current. This is measured in amperes.
How Does a Battery Keep Its Charge?
The way a battery cell keeps its charge lies within the electrolyte solution and the separator. Their job is to prevent the electrons from passing from the negative end to the positive end. This allows the battery to sit with an electric charge until it’s ready for use. The voltage is quite literally stored in a way that allows access with a simple circuit. This is the primary function of batteries.
If the separator in the battery fails the battery will short out internally and lose its charge. This is one potential failure mechanism in a damaged battery.
Why Do Batteries Run Out of Power?
Batteries run out of power when all of the electrons from the negative terminal have reached the positive terminal. When this happens, no more negatively charged electrons remain to create an electrical current.
In this case, non-rechargeable batteries basically become useless. However, rechargeable batteries can recharge simply by reconnecting to an appropriate power source. Or, to be more technical, to allow the electrons to flow back to the negative end of the battery. The number of times, or cycles, a rechargeable battery can be recharged and discharged is known as the battery’s lifespan.
Do Batteries Lose Power When Not in Use?
Unfortunately, yes. Nearly all batteries lose some charge even when you don’t have them hooked up to a circuit. This is the self-discharge phenomenon. Internal chemical reactions that decrease the battery’s shelf life cause this phenomenon. Thus, when you use your stored battery, you might find that it has less charge than when you left it.
The rate of self-discharge depends on many factors, however. Namely, the type of battery, temperature, state of charge, and charging current. The batteries with the lowest self-discharge rates include lithium metal, alkaline, and lithium-ion. Lead acid batteries (like your car battery) loose between 5% and 10% per month.
Batteries Are Critical for Portable and Disconnected Power
Can you imagine a world without batteries? We would literally have no way to store electricity. We wouldn’t be able to start our vehicles, carry mobile phones, or even listen to music on the go. Our electronic lives would rely on tethered wires and outlets, and our modern society would look very different.
Thankfully, we do have high-tech batteries that allow us to carry hours of electrical use in our pockets, all thanks to the advancement of lithium-ion technology.