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Reasons for the Explosion of Cell Phone Batteries

Since the second half of 2016, the media has frequently reported the news of a fire and explosion accident involving a smartphone of a well-known international brand. Many people get puzzled:

The cell phone has neither materials and components that are prone to fire and explosion, nor is it under high pressure and high temperature. How can fire and explosion happen?

Tracing the cause, we must start with the cell phone battery.

Reasons why cell phone batteries explode

Smartphones use lithium-ion batteries. In the early 1990s, lithium-ion batteries began to become a common component in devices such as cell phones. The working principle of lithium-ion batteries with small volume and high energy is as follows:

The battery has a positive electrode, a negative electrode, a separator (also known as a diaphragm) and electrolyte. The charging and discharging function of the battery is realized by lithium ions moving back and forth between the positive electrode and the negative electrode.

Specifically, when charging, the current of the charger drives out the lithium ions in the positive electrode, and the driven out lithium ions move to the negative electrode through the electrolyte between the positive electrode and the negative electrode. Discharging is just the opposite of charging, and these lithium ions move back from the negative electrode to the positive electrode through the electrolyte to provide power for the mobile phone.

What needs to be emphasized here is that the positive and negative electrodes must not be in direct contact during charging and discharging. Otherwise, a short circuit will occur, causing abnormal heating of the battery, and even dangerous accidents such as fire and explosion.

Reasons for the Explosion of Cell Phone Batteries
Reasons for the Explosion of Cell Phone Batteries

So, how to keep the positive and negative electrodes in the battery not in direct contact with each other? At the same time, there is enough electrolyte between the positive and negative electrodes for lithium ions to move back and forth. 

In this situation, the separator is playing a key role. The separator is actually a non-conductive thin film, which can not only isolate the positive and negative electrodes, but also allow sufficient electrolyte between the two electrodes for lithium ions to move.

The unique advantages of lithium-ion batteries are:

Compared with nickel metal hydride, nickel cadmium and other batteries, it not only has low toxicity, low cost, fast charge and discharge, high output power, and long service life. And also light weight and high energy density, that is, storing more energy in a smaller volume, so that its battery life can be extended.

The direct cause: poor battery manufacturing process

Some cell phone battery producers blindly make some inappropriate changes on the battery out of competition needs and the pursuit of profit maximization. They clearly know that the energy density of current mobile phone batteries is close to the limit and there is very little room for improvement.

But in order to provide more energy in a smaller volume, they can only take risks to squeeze the space occupied by the isolation film. And install a little more positive and negative electrode materials to improve the energy density of the battery and the battery life of the cell phone. However, this ultra-thin separator has particularly strict requirements on the processing technology, and a little carelessness may cause quality defects or defects.

This further leads to a short circuit of the battery, which is the direct cause of the fire and explosion of the mobile phone.

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