Analyze the reason why lithium batteries are not resistant to freezing

"Oh, my mobile phone is just full of electricity. How do I shut it down when I go out for a while?" Yes, in the winter in the north, is this scene very common and similar? Regarding the fact that the mobile phone automatically shuts down the pot in a low temperature environment, it may be necessary to have the lithium battery back on the back. As for why, we need to understand how lithium batteries work.

A lithium ion battery refers to a secondary battery composed of two compounds capable of reversibly intercalating and deintercalating lithium ions as a positive and negative electrode. When discharged, lithium atoms are ionized from the anode surface of the graphite crystal into lithium ions and electrons, and Lithium atoms are synthesized at the cathode, and a potential difference is formed between the positive and negative electrodes to generate a current, so that the charge and discharge of the lithium battery are achieved by chemical changes.

According to our high school chemistry knowledge, the reaction speed of chemical reactions is different at different temperatures. Under low temperature conditions, the electrolyte moves quite slowly, which affects the transfer activity of lithium ions between positive and negative electrodes, resulting in battery charge and discharge. Performance has dropped dramatically. Therefore, in one sentence, the power of the lithium battery at low temperature did not disappear, but it was too cold to be released. Sometimes we put the phone into the close pocket and warm it for a while, and the phone can be turned on again.

Secondly, the automatic shutdown of the mobile phone is a security consideration for the mobile phone manufacturer, ensuring that the battery can work normally and shut down deliberately. Apple officially stated that the normal operating temperature of the iPhone is between 0-35 degrees Celsius and the storage temperature is -20-45 °C. Why are there such demanding requirements?

This is related to the structure of the lithium battery. It is afraid that when the temperature is too low, the internal electrolyte will crystallize, thereby piercing the diaphragm inside the battery, causing a short circuit and causing thermal runaway. The battery operating temperature will rise instantaneously, and the chemical reaction will occur. Further intensified, the heat generated by these reactions in turn further heats the battery, and eventually the battery will overheat. Like the Samsung Galaxy Note7, the phone has a spontaneous combustion explosion, which is very dangerous! When you look at the fate of Samsung Note7's global recall, you know that low temperatures can cause irreversible damage to the battery and can lead to serious safety accidents.

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