Battery special topic: mobile phone low temperature shut down, why is lithium battery not antifreeze?

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"Oh, my phone is just full of electricity. How can I go out for a while and turn off my own phone? " Yes, in the winter in the North, is this kind of scene very common and similar? With regard to the automatic shutdown of the phone at low temperatures, it may be necessary to put a lithium battery on the back. As for why, we need to understand how lithium batteries work.

Lithium-ion batteries refer to the use of two compounds capable of reversibly embedding and deem-bedding lithium ions as secondary batteries composed of positive and negative poles. When discharging, lithium atoms Ionize lithium ions and electrons from the anode surface of the graphite crystal, and in the cathode. Synthesize lithium atoms at the cathode, The current is generated by forming a potential difference between the positive and negative poles, so the charge and discharge of the lithium battery is achieved by chemical changes.

According to our high school chemical knowledge, chemical reactions react at different temperatures at different speeds. Electrolytes move quite slowly at low temperatures, which affects the transfer activity of lithium ions between positive and negative poles, resulting in a sharp decrease in battery charge and discharge performance.. So a word is, low temperature lithium battery power does not disappear, but too cold to release, sometimes we put the mobile phone into the personal pocket warm for a while, mobile phone can boot again.

Secondly, automatic cell phone shutdown is the mobile phone manufacturer in the security considerations, to ensure that the battery can work and deliberately shut down. Apple officially stated that the normal operating temperature of the iPhone is between 0-35 degrees Celsius and the storage temperature is -20-45 degrees Celsius. Why is there such a harsh requirement?

This is related to the structure of the lithium battery. It is afraid that the internal electrolyte will crystallize when the temperature is too low, thus piercing the diaphragm inside the battery, causing a short circuit and causing thermal runaway. The temperature of the battery will rise instantaneously. The chemical reaction will further intensify. The heat generated by these reactions, in turn, further heats the battery, and eventually the battery will overheat. Like Samsung Galaxy Note 7, mobile phones spontaneously explode, which is very dangerous! As you can see from the fate of Samsung note 7's global recall, cold temperatures can cause irreversible damage to batteries and serious safety incidents.

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