Is Fast charging bad for battery?

From “5V 1A” to “60W”, there are countless jokes about charging speed. These classic jokes also always remind mobile phone manufacturers that fast charging has become a rigid need for mobile phone users.

In recent years, the charging speed of mobile phones has continued to break through, and more than one 100W fast charger has appeared on the market. The soaring charging speed inevitably makes users worry: will fast charging harm the battery?

To figure out whether fast charging will damage the battery, we must first understand the factors that affect battery life.

Including Apple, almost all smartphones at this stage use lithium-ion batteries. The reason is that lithium-ion batteries have the characteristics of higher power density and smaller size, which are perfect for smartphones.

The charging and discharging of lithium-ion batteries, in principle, is the flow of lithium ions between the positive electrode and the negative electrode of the battery. In this process, the active substances of the battery will be irreversibly consumed. Over time, the performance of the battery will degrade and the capacity will become lower.

In addition, abnormal temperature and voltage during charging will also have a great impact on the decay rate of the battery.

Here is the principle of fast charging. Power (P) = voltage (U) x current (I), fast charging either increases the current when the voltage remains the same, or increases the voltage when the current remains the same, or both.

On the other hand, mobile phone manufacturers have also developed many new technologies to reduce the heat generated during charging, but heat generation is still unavoidable.

So we can conclude that even when fast charging is not used, the battery of the mobile phone will naturally decay. The fast charging of the mobile phone will speed up the loss of the battery and accelerate the process of the degradation of the mobile phone battery.

That is to say, fast charging hurts the battery, that’s for sure.

Frequent fast charging does harm the battery as opposed to slow charging.

1. Accelerate the polarization of battery cells. Generally, during the charging process of lithium-ion batteries, the migration rate of Li+ diffused inside the electrode is smaller than that of the electrolyte, and the diffusion inside the electrode is the control step of the Li+ diffusion rate. When the continuous charging current is large, the ion concentration at the electrode increases, the polarization intensifies, and the battery terminal voltage cannot be directly proportional to the charged amount/energy.
2. It may lead to crystallization of the cell during the charging process, and the control of lithium ions is actually very weak. We can only guarantee that lithium ions will migrate to the surface of the negative electrode, but we cannot guarantee that the lithium ions will be evenly distributed on the surface of the negative electrode. Fast charging of lithium batteries means that lithium ions are quickly released and “swim” to the negative electrode. At this time, the negative electrode material needs to have fast lithium intercalation ability.

So, should we reject fast charging?

The replacement cycle for most mobile phone users is about two years. Within this time, the loss of the battery caused by fast charging is completely acceptable.

To give a simple example: OPPO once mentioned at the Reno Ace conference that although its charging power is as high as 65W, it has passed 800 charge and discharge tests, and the rated capacity is still greater than 80%.

We can refer to the national recommended standard: 400 times of charge and discharge tests, rated capacity ≥ 60%. As long as this level is reached, the battery loss is well within a reasonable range.

In contrast, the user’s own “bad habits” have a greater impact on battery life. For example, many users like to play mobile phones while charging, which will cause the mobile phone to heat up during charging and accelerate the aging of the battery. We also cannot ignore the series of benefits brought by fast charging. Faster charging speed allows users to use the fragmented time to charge. For example, the iQOO 5 Pro, which supports 120W ultra-fast flash charging, can fully charge a phone in 15 minutes. In actual use, maybe you can charge the battery from 0 to 100% while you are having breakfast, bringing a series of conveniences to life and work.

Therefore, although fast charging will cause certain damage to the battery, the application of fast charging will always have more advantages than disadvantages. So, how many watts of fast charging are you using on your phone now? How is the experience?