In this blog post, I will explain the scientific reasons why the battery life of smartphones is getting shorter even though the battery capacity is getting bigger.
If you look at a recently released smartphone, you will notice that the battery is much bigger than it used to be. Despite the thinner design and larger screen, the battery capacity is getting bigger and bigger. But why? Is the battery life of a smartphone getting shorter the more you use it? Does turning on Wi-Fi and watching a 10-minute video cause the battery capacity to drop from 100% to 80%? Furthermore, why does the battery level gradually decrease even when not in use? These are some of the frustrations that we often experience in our smartphone usage. To be honest, I’ve been using my smartphone a lot lately, so I often change the battery several times, and I’m experiencing that the battery life is shortening. I want to explain the scientific and material engineering reasons for this reality that bothers and intrigues those of you, including me, who use mobile phones, in an easy-to-understand way.
First, to understand the various factors that affect battery life, we need to know “what’s inside a cell phone battery and what’s going on inside it.” As you know, cell phone batteries are batteries. There are two types of batteries, primary and secondary. Primary batteries are the same type of batteries used in toys that can only be used once and cannot be reused. And the rechargeable battery that can be used repeatedly after charging, like the “mobile phone battery” I’m going to talk about, is a secondary battery. In other words, the mobile phone battery can be charged and discharged.
Now, let’s take a deeper look at the structure of the battery. If you look at your battery, you will see the word “Li-ion.” In other words, there are ions of a substance called lithium (Li) floating around in the battery we use. Here, “ion” refers to a state in which a person who used to be in a stable and happy relationship becomes single and becomes unstable and busy trying to find another person of the opposite sex, or conversely, a state in which a person is anxious because they are dating too many people for their ability, and the former is more likely to stick to stable substances or become unstable by separating from them. The lithium ions mentioned here are in a state where they have lost their electrons, so they are constantly trying to find another ion in the battery. So, how does the movement of these ions affect the operation of the battery?
Lithium ions play a key role in storing and releasing electrical energy in a battery. They move between the (+) and (-) poles of the battery, storing energy through the charging and discharging process and releasing it when needed. There is also an electrolyte in the battery that helps lithium ions move and a separator that regulates the flow of electrons as the ions move to different poles. Without this separator, a direct short circuit would occur inside the battery, which could cause the battery to explode. Although the structure of the battery appears simple, it is actually very complex and precisely designed.
So, what is going on inside? As mentioned above, lithium ions move back and forth between the (+) and (-) poles in search of another ion. However, the direction is not random, but follows a certain rule. If the battery is fully discharged and recharged, lithium ions are released from the material with a (+) pole, and electrons are also released at the same time. The lithium ions are then moved from the (+) pole to the (-) pole and settle in the gaps of the crystals that form the (-) pole. On the other hand, when a battery is used (when discharged), lithium ions and electrons are released together as when charging, and the lithium ions move from the (-) pole to the (+) pole, settling in the crystal gaps of the material that forms the (+) pole, and the electrons are transferred to the (+) pole through a different pathway.
So far, we have talked about what parts make up a mobile phone battery and what reactions occur within it. Now, let’s talk about “why does the battery life of a mobile phone decrease the more you use it?” Factors that determine the life of a lithium-ion secondary battery include the state of the electrodes and the state of the electrolyte. While lithium ions move between the two electrodes, the electrodes repeatedly expand and contract. The reason is that when lithium ions are detached from one electrode, the space between the gaps occupied by the ions is empty, causing the electrode to shrink. On the other hand, when those ions find a new partner, the new partner electrode also expands to accommodate the new ions. This repeated expansion and contraction causes the electrodes to become fatigued, which results in a decline in performance over time. This also gradually reduces the overall capacity of the battery.
In addition, the electrolyte inside the battery undergoes chemical changes over time, which hinders the movement of ions. During this process, impurities are created in the electrolyte, which reduces the battery’s electrical performance. Another factor that reduces the life of a battery is the impact of external temperature. Using or charging a battery at high temperatures accelerates the chemical reactions of the electrolyte and increases the risk of damage to the components inside the battery.
As such, the root cause of the reduction in battery life is that the more a battery is charged and discharged, the more it is fatigued and the shorter its life becomes. It’s like an office worker getting tired from repeating the same work and not getting enough sleep, which damages the body. Now that you know why battery life is short, treat your battery like you would treat your own body, and find ways to extend the life of your battery, just like I do by going to the gym every morning to build a healthy body, and enjoy your battery for a longer period of time.
