The reason smartphone batteries are getting bigger but lasting less time is due to damage to the electrodes and electrolyte that occurs during the repeated charging and discharging of lithium ions. This degrades battery performance and reduces its lifespan. To prevent this, it’s important to keep your battery at the right temperature and improve your charging habits.
If you look at modern smartphones, you’ll notice that the batteries are quite a bit bigger than they used to be. Despite thinner designs and bigger screens, battery capacity is still increasing. But why is it that the more you use your phone, the more your battery deteriorates? Is the battery capacity dropping from 100% to 80% just because you turned on Wi-Fi and watched a video for 10 minutes? Better yet, why is the battery slowly dwindling even when it’s not in use? These are some of the common puzzles in our smartphone experience. To be honest, I use my smartphone a lot these days, and I’ve noticed that I’m often swapping batteries multiple times, which leads to shorter battery life. I’m going to try to demystify the scientific and materials science reasons for this frustrating and curious reality for cell phone users like myself.
First, to understand the many factors that affect battery life, we need to know a little bit about “what’s inside a cell phone battery and what’s going on.” A cell phone battery is, as you probably know, a cell. There are two types of batteries: primary and secondary. Primary cells are literally the kind of “batteries” in toys that you use once and can’t use again. Secondary cells are the kind of cells that you can use and recharge and use again, like the cell phone battery I’m talking about. In other words, cell phone batteries can be charged and discharged.
Now, if you look at your battery, you’ll see the word Li-ion, which means that there are ions of a substance called lithium (Li) floating around in your battery, and ions are electrons that either attach themselves to a stable substance and become more attached to it, or they detach themselves and become unstable, like when a person who was in a couple and had a stable, happy life becomes single and becomes insecure and busy looking for someone else, or vice versa, when a person becomes insecure because they’re dating more people than they should be. The lithium ions we’re talking about here are in a state of electron withdrawal, so they’re constantly trying to find another home in the battery. So how does this behavior affect the operation of the battery?
Lithium ions are the key to storing and releasing electrical energy in a battery. They move between the (+) and (-) poles of the battery, storing energy and releasing it when needed through the process of charging and discharging. Inside the battery, there is an electrolyte that allows the lithium ions to move, and a separator that regulates the flow of electrons as they move from one pole to the other. Without this separator, there would be a direct short circuit within the battery, which could cause the battery to explode. So while the structure of a battery looks simple, it’s actually very complex and sophisticated.
So what’s going on inside? As we wrote above, the lithium ions move back and forth between the (+) and (-) poles in search of the other side, but the direction is not random, it has a certain order to it. When a battery is depleted and charged, lithium ions are released from the material that makes up the (+) pole and electrons are released at the same time. The lithium ions then move from the (+) pole to the (-) pole and settle in the gaps in the crystals that make up the (-) pole. On the other hand, when the battery is used (discharged), as when it is charged, the lithium ions and electrons escape together, and the lithium ions move from the (-) pole to the (+) pole, settling in the crystal gaps of the material that makes up the (+) pole, while the electrons are transferred to the (+) pole through a different pathway.
So far, we’ve talked about the components that make up a cell phone battery and the reactions that take place within it. Now we’re going to talk about “why the more you use your cell phone, the shorter the battery life.” The factors that determine the lifespan of a lithium-ion secondary battery include the condition of the electrodes and the state of the electrolyte. As lithium ions move between two electrodes, the electrodes expand and contract: when a lithium ion leaves one electrode, the space between the gaps it occupied is empty, causing the electrode to shrink, and when the ion finds a new mate, the new mate’s electrode also shrinks to accommodate the new mate. This cycle of expansion and contraction fatigues the electrodes, causing them to degrade over time. This causes the overall capacity of the battery to gradually decrease as well.
Additionally, the electrolyte inside the battery will undergo chemical changes over time that impede the movement of ions. This process causes impurities to form in the electrolyte, which reduces the electrical performance of the battery. Another factor that can reduce the lifespan of a battery is the effect of external temperature. When batteries are used or charged at high temperatures, the chemical reactions in the electrolyte accelerate, increasing the risk of damage to the components inside the battery.
At the root of these causes of reduced battery life is the fact that the more you charge and discharge a battery, the more you fatigue it, which reduces its lifespan. Now that you know why battery life is shortened, I hope you will treat your battery like your own body and find ways to make it last longer, just like I do by going to the gym every morning to build a healthy body.
