Climate change is causing us to have increasingly longer summers and with increasingly higher temperatures. This affects not only people, but also the machines and devices we use every day, including the mobile phone.
It is not that we are going to melt the phone in summer, but it is true that at extreme temperatures it will not work the same. Our phones are made of plastic housings, or aluminum if it is high-end, printed circuits and a battery. Of these basic components, the battery is undoubtedly the most temperature sensitive.
It is clear that extreme temperatures do not suit batteries, but how does heat affect them? To see the full picture, one would have to distinguish between two sources of heat. The first one would be that overheating that we notice when we try to do a thousand things at once with the mobile. In this case it would be best to close applications and let it cool.
The increase in the internal temperature of the batteries is a problem known as "thermal runaway".
The simple explanation is that this rapid increase in temperature favors a series of events that further increase the temperature, until the generation of gases (by evaporation of the electrolyte or from secondary reactions) causes an increase in pressure that causes the battery swells and even explodes or catches fire.
In addition to this, above 120 degrees the separator begins to melt resulting in internal short circuits. As expected that does not help the battery does not explode, but do not worry, it is very rare to do so. The second source of heat would be the weather.
Like humans, batteries work best at room temperature, between 15 and 35 degrees depending on who is asked.
There are lithium-ion batteries with different chemicals and different characteristics, but they can usually work in a range of -20 to 60 degrees, although many devices do not allow charging outside the range of 0 to 45 degrees. This means that we could make a call one summer afternoon in Cordoba, or from the top of a mountain in the Alps. At least in theory. Most likely, in a very cold environment our mobile phone will turn off in a short time (in fact, it happened on top of the Rigi). Luckily for those of us who live in the south of the peninsula, for the mobile to turn off due to heat the temperature has to be hellish.
Phones with Android or iOS operating systems usually warn when the device suffers from extreme temperatures.
Like humans, batteries work best at room temperature, between 15 and 35 degrees
If what worries you is if the battery of your mobile will suffer the consequences, know that in the short term very hot or very cold temperatures will not damage the battery. However, prolonged exposure to extreme temperatures will cause irreversible damage. When the temperature rises a little, the battery capacity increases slightly, although aging processes are also accelerated and capacity is lost in the long run, which determines the usage time.
Electrolyte and electrodes
Going into more detail, the continuous use of a high-temperature lithium-ion battery affects the electrolyte, the electrodes and its protective layer. In the electrolyte we can find a lithium salt that carries the ions from one electrode to another. This salt decomposes with temperature, so it stops transporting ions.
The structure of some active materials – such as lithium oxides, cobalt nickel and manganese used in the cathode – can be altered with temperature, so that the mobility of ions inside is slower, even limited. On the other hand, the glue that holds the active material particles together loses effectiveness and peels off, causing the necessary electrical contact for electrochemical reactions to be lost. The protective layer of the electrodes, especially the anode, also undergoes major changes. The increase in temperature alters the proportion between its components, helping them to dissolve and remain others. Unfortunately for battery users, the components that remain are the ones with the greatest resistance to the passage of lithium ions.
In summary, the continued use of a high-temperature lithium-ion battery causes electrode degradation and loss of capacity due to increased resistance. But high temperatures are not the only enemy of the durability of lithium-ion batteries. Below zero degrees the ionic conductivity of the electrolyte decreases considerably, while the chemical reactions of the materials with the lithium ions are slower. This situation increases the internal resistance of the batteries and, again, we find a considerable loss of capacity.
How to act
So what to do to protect our mobile battery from high temperatures? If it has already been heated too much, turn it off, remove the charger and let it cool. But do not cool it in the fridge, because sudden temperature changes do not feel good to the battery.
If it has not yet been heated, it is advisable to make moderate use and not run heavy applications (navigation, video, games, etc.), do not expose it directly to sunlight and, above all, do not forget it in the car On a hot day!
Juan Luis Gómez Cámer, Assistant Professor Doctor in Inorganic Chemistry, University of Córdoba
This article was originally published in The Conversation. Read the original.
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