How to extend your battery lifetime
Lithium-ion batteries degrade over their lifetime, however there some best practices which you can follow to extend their useful life.
Reduce time at high state-of-charge
Batteries generally degrade fastest when they are fully charged. The reason for this is that a layer forms on the anode called the solid electrolyte interphase (SEI). This SEI is important for battery operation as it prevents direct contact of the electrolyte with the lithiated graphite, which would otherwise cause rapid degradation of the cell. However, over time this SEI grows and consumes lithium-ions which results is a combination of capacity fade (less accessible energy) and power fade (less power).
Keeping devices at 100% state-of-charge (SOC) generally accelerates this SEI layer growth and thus its recommended (where possible) to only charge up to ~85% SOC. The drawback of doing this however, is that there is less energy available as the whole SOC range is not used. Many phones and electric vehicles offer options to limit the maximum SOC to extend the battery lifetime.
Don’t let the battery get too hot
If a lithium-ion battery exceeds a temperature of ~70 °C it can enter into thermal runaway, where the SEI layer decomposes leading to the exothermic reactions between the anode and electrolyte. If temperature keeps increasing this can melt the polymer separator in the battery, causing a short circuit, as well as the decomposition of the cathode and electrolyte which can lead to a battery fire.
Temperatures below 70 °C can still cause damage to the battery, with warmer conditions accelerating degradation. This happens because the growth of that SEI layer accelerates at warmer temperatures, leading to decreased capacity and power
An optimum temperature is often ~20 °C and thus batteries should be stored away from heat sources.
Avoid fast charging
Whilst fast charging your battery can shorten the time needed for charging, this can lead to accelerated degradation of your battery, especially at low temperatures.
The reason for this is that when charging your batteries, lithium-ions move from the cathode to the anode. Here, the ideal reaction is for the lithium-ions to intercalate into the anode. However, if this is done too quickly then instead of going into the anode, this can instead plate on the surface of the anode.
An analogy for this, is people trying to get onto a train. If too many people try to get on at the same time then even if there is space inside the train, people will get stuck near the entrances.
If this lithium plating occurs dramatically, this can lead to the formation of metallic lithium dendrites which can accelerate degradation and potentially cause internal short circuits which lead to the failure of the battery.
Many devices such as mobile phones allow you to turn this fast charging on and off, and whilst there are smart ways to get fast charging with minimal additional degradation, a safer option is to not use it unless is needed.
Don’t over-discharge your batteries
Many lithium-ion batteries have a recommended operating voltage range of 4.2V-2.7V. The reason why we have these limits stem from the electrochemical stability of the materials in a battery. Overcharging the battery can lead to decomposition of the electrolyte. Overdischarging the battery, can instead lead to dissolution of the copper current collectors, which can facilitate the formation of copper dendrites which can short circuit your battery.
Whilst, the battery management system might protect against overdischarge during normal operation, if not using your device for a while, self-discharge of the battery could cause it to enter into the regime where the copper current collector dissolves.
Therefore, consider periodically charging your battery to a storage SOC of ~30% which strikes a balance between low SOCto minimise SEI layer growth, but high enough to account for some self-discharge.
