Analyze and understand the overcharge of lithium battery

People often have a misunderstanding when charging: it is best to maintain full power. Perhaps for OCD, when the battery power jumps from 100% to 99%, it will take his life. But actually keeping the phone in charge is not a recommended behavior, especially after the device is fully charged still continue to charge, the phone battery can't really handle this.

Lithium batteries are not omnipotent

There are many elders who will always tell you when you get your first mobile phone. The new mobile phone must be fully discharged first, then fully charged for 12 hours, then fully discharged, and it needs to be repeated three times. At the beginning, you must be honestly done according to the words of your elders. In fact, smart phones that have already used lithium batteries no longer need such a troublesome battery maintenance process.

It is a nickel-hydrogen battery that needs to perform multiple discharge charging processes. This battery has a strong memory, and the process of repeating charging and discharging is also to obtain the maximum charging limit for the nickel-hydrogen battery. Today's mobile phones use lithium batteries. There is no need to repeat such a complicated battery memory process. So, will the lithium battery always maintain the highest power limit?

The answer is definitely no. Although the lithium battery is known for its durability, it is inevitable that the upper limit of its power will be lost during the battery charging and discharging process. This loss is formed over time, and the cause of the loss is in addition to the normal charging. Charging is the culprit.

How to understand overcharge

Overcharge is actually very well understood, that is, the mobile phone continues to charge the mobile phone battery when the display is full. In this case, we call the mobile phone overcharged. Continued charging with the battery full is caused by a change in the structure of the positive electrode material, resulting in a loss of capacity, and a violent chemical reaction between the liberating oxygen and the electrolyte, and the worst result is an explosion.

[Science] How to correctly understand the overcharge of lithium batteries?

In real life, there are many cases in which mobile phones explode while charging. For example, Xinhua net reported that on March 4, 2015, a 23-year-old girl was charged and her mobile phone was burnt. The Shanxi Evening News also reported that on June 15, 2015, an 18-year-old boy was charged with electric shock while charging his mobile phone. The reason for these tragedies can be attributed to damage to the battery itself, the charger has no IC protection, and the power supply itself has quality problems. When the current is still being input after the charging is completed, since the battery capacity has reached the upper limit, most of the current is converted from electric energy to heat energy, and the battery starts to heat up.

General knowledge also tells us that the best way to save the battery is at room temperature and dry, whether it is nickel-metal hydride or lithium battery. When overcharging occurs, there is no doubt that the heat energy of the current conversion will be largely emitted, causing the lithium battery positive electrolyte to react, consuming the maximum capacity of the lithium battery, and when the heat is accumulated to a certain extent, such events as fire and explosion are caused. It is possible to happen.

In the face of such low security, natural mobile phone manufacturers and charger manufacturers will not sit idly by. After all, when users have security problems, they must be unlucky, so there is a lot of attention when charging mobile phones, especially the mobile phones and chargers that are currently charging with USB ports are very particular.

In order to prevent overcharging, they really fight

In fact, most mobile phones now have IC protection. The charger itself also monitors voltage and current. In order to protect the safety of the battery and the user, trickle charging is often used on mobile devices.

When using the USB port for charging, if the loss on the wire is not calculated, the USB charging port will negotiate with the mobile phone to charge and match the appropriate current, so that the mobile phone will not lose most of the current due to the high current input. The battery is low, such as about 10%.

At this time, the battery is charged most efficiently, and the current reaches the highest state. As the capacity increases, the current required by the mobile phone will gradually decrease. Even when the last 10%~20% of the remaining power reaches the full powers, the mobile phone will request a small current to charge the battery, thereby achieving the purpose of protecting the battery. The method, also known as trickle charging, is the current mainstream mobile phone charging solution, in order to reduce the loss of the upper limit of the capacity and extend the battery life.

In addition to the overcharge protection provided by the mobile phone battery, there is also a way to rely on the charging socket to prevent overcharging. To provide over-charge protection, the socket must first provide a stable voltage. The higher the voltage fluctuation, the more the current will be affected. Especially in China, the voltage fluctuations at night time are frequent, and it is very important to ensure the stability of the USB port output voltage. Generally speaking, the voltage of the USB charging port is 5V. Some USB charging ports that can intelligently distribute the current will slightly lower the voltage of the charging port when the mobile phone battery is near full power, so as to reduce the input current and relieve the battery pressure.

These methods have a good inhibitory effect on the overcharge of the mobile phone, but in the end it is because we did not unplug the power supply when the mobile phone is fully charged, so that the mobile phone continuously repeats the process of discharging and charging, resulting in a reduction in the upper limit of the capacitance.

Overcharging is not a trivial matter

For ordinary mobile phone users, overcharging is really not a trivial matter. The life of the mobile phone battery directly affects the time you use this mobile phone. If you let the mobile phone cope with overcharge, I believe that the battery will die in less than a year.

If you can see a slight bump on the back of the battery, it's probably due to overcharging. To put it in a big way, overcharging even directly affects your safety. Those poor quality batteries of fake cell phones can't be guaranteed to let off fireworks or something. If you want to avoid overcharging fundamentally, it seems that you should start from time control.

The page contains the contents of the machine translation.