Science Journal

How Heat Affects the Phone's Battery

I know that heat is the greatest enemy of all devices but I wondered how heat reduce the lifespan of a phone's battery. Does it literally burn the capacity of the battery? And it is true that battery lasts longer if it put inside the fridge? So ofcourse as usual, I consulted Google.

I learned that the phone's chip today temporarily slows down the operating speed to reduce temperature and save the phone from severe damage which is why playing game apps or heavily multi-tasking make phone hangs to frustrate the user and stop him/her from using it. Overheating affects two main areas in phone's battery which leads to reduced capacity. First, System-on-chip (SOC) a microchip with all the necessary electronic circuits and other parts that a system or device needed on a single integrated circuit (a semiconducting chip which consists of thousands or millions of tiny resistors, capacitors, and transistors). If it frequently overheats, it can be damaged permanently which can slows down the applications, performance or might not function anymore. Second, the battery Lithium-ion or Li-ion in short, this compound is sensitive to heat and if the phone is stored at over 30 degrees Celsius, it will be damaged. Also, Li-ion ages and degrade even it is not used and only last 2-3 years. So, do not avoid "not using it" because everything ages and nothing stays forever.

Li-ion

The answers I found did not satisfy me so I searched further about Lithium-ion and how it chemically decays, which contributes to losing capacity. Li-ion has two parts, Cathode, the positive electrode and made of non-metallic lithium and Anode, negative electrode composing of carbon. When phone charges, the ions from cathode go to the anode, otherwise when used, the ions from anode go to the cathode. Since its charging and discharging are both chemical reactions, it gradually degrades cathode. As Lithium ions move across the cathode, it is being oxidized leaving something like a rust blocking the way of ions to flow, thus reducing capacity. Repeated subtraction and addition of ions alters the structure of lithium material, making it less receptive to future exchanges. It's like a rag that is soaked and wrung a few hundred times. So 300 or 500 full cycles lose 70% capacity and overheating and erratic charging speeds up the cathode degradation.

How to prolong Battery's Life

Experts recommended partial discharges and charges because it extends battery's life before capacity drops to 70% of their original capacity. And store it at low temperature but manufacturers do not recommend to store batteries in a refrigerator because there is a possibility that it can form condensation when it is not removed from the fridge. If the battery gets wet, the rate of discharge increases. The wet surface of the battery can form a conductive path between the two terminals.