Degradation of lithium ion battery in a prolonged storage period

Will the brand new li-ion battery degrade while sitting on a shelf unused?

The answer is yes. Degradation happens, sometimes permanent damaged.

For example, a lithium ion battery pack of 14.8V 2200mAh, when leaving factory, SOC is at 30%, or 600 mAH. We all have heard about the famous the phenomenon of “self-discharge” of all types of batteries, some people call it “battery leakage” although for lithium there is no physical leakage.

Self-discharge rate of li-ion battery is 10 micro amps / hour, it can be calculated as 1-2mA in a day. Therefore, with a battery at 30% state of charge, this battery is expected to be completely exhausted after 1 year.

In addition, the battery has other electrical components like IC, BMS, and other resistors that also contribute to power consumption and shorten this period. When the battery’s power is completely exhausted, the separator membrane dries up, and the electrolyte level reaches 0, the battery loses its ability to reactivate, which is when the battery in unable to hold a charge.

So if you buy new batteries and have no plan to use them very soon, Store no more than 4-5 months. You should charge the new batteries to SOC 40% and check the voltage every 2 months.

 

What happens when a lithium ion battery is left unused for too long?

Li-ion batteries that have been left unused for a long time are not uncommon. However, you must understand that li-ion batteries are a power source, providing energy convenience, but when used, safety principles must be followed. In industry, this type of battery is operated by trained, technically knowledgeable people.

For li-ion batteries in use, when they are exhausted to the protection voltage, the protection circuit will automatically cut off the power. At this time, the battery has very little power left, only about 5%. Then, if you forget the battery for a long time, the following phenomena will occur:

The battery is completely exhausted, sometimes it won’t turn on anymore (many people call it a FAULTY battery):

This phenomenon is due to self-discharge or natural aging over time, which is a typical characteristic of li-ion. In addition, the electronic components attached to the battery pack such as circuits, BMS… also consume electricity continuously. If not used for many months, a fully charged lithium battery can also be completely exhausted.

Battery degradation: irreversible loss of capacity:

After a period of non-use and “forgetting”, you take out the battery to charge and use it again and find that it runs out of battery quickly. The reason is because the chemical reactions inside the battery have created a SEI film on the cathode or lithium plating has occurred on the anode. Lithium ions, instead of moving freely, are “retained” in an unwanted way and reduce the battery’s ability to store electricity. See more: Causes of lithium-ion battery death 

Increased Internal Resistance:

The coating on the SEI cathode also increases the internal resistance of the battery. High resistance reduces the discharge capacity (current supply) and reduces the battery life. See also High internal resistance affects battery performance 

Explosion when recharging:

This is a rare phenomenon and extremely dangerous.  There’s a high chance that users haven’t used battery for an extended period of time, voltage of each cell has go lower than 2V each. This is when tree-shaped branches called “dendrites” appear on the surface of the anode. These dendrites sometimes ventures through the separator, making it become conductive inside the battery. People call this “inner short circuit”.

 

CONCLUSION 

If you have no intention of using the lithium-ion battery for a long time, please follow the guidelines for proper  storage of lithium-ion batteries. 

Please avoid discharge the battery completely, recharge as soon as possible, normally a charge should be applied when SOC is 20%.