Why does storing Li-ion battery at 100% charge damage them?

[XTAR Light]

When you plan to store some 18650 Li-ion batteries for a long time, it's suggested to charge to a voltage around 3.6V, and maintain at around 40%-80% charge. It's not suitable to keep the Li-ion batteries at a 100% full charge. It's because the higher the voltage, the more electrochemically active the battery components are. Some harmful erosion and chemical reactions are accelerated.

Batteries produce electricity through a chemical reaction. High performance lithium batteries use a lithium material that is intentionally designed to be "sponge-like". In order to maximize the surface area available for chemical reactions. Like the sponge, the battery will struggle to find space for lithium ion once it approaches fully charged. It leads to heat and unwanted chemical reactions with the electrolyte, which converts lithium ions into lithium metal. This can be reversed with discharging. But over time, it may loose available lithium ions and the space to move into. Storing at 100% removes the ability to dissolve the lithium metal during discharge and can become permanent.

And everything is cumulative. Voltage, temperature, time, all contribute to the batteries' degradation at increasing rates. So if you plan to store lithium-ion batteries for an extended period, it's best to store them at a partial charge, around 50%. This state minimizes stress on the electrodes and electrolyte, preventing degradation during storage.

 

[DRW]

I'd like to add that storage is not the same as ready for use.

All of my lights are fully charged and ready for use. If the battery starts to fail, I replace it - it is consumable.

Preppers come to mind regarding storage of cells for use after Armageddon.

Seasonal equipment like eBikes and garden equipment would likely benefit from storing the batteries as suggested above.

 

[Monocrom]

When you plan to store some 18650 Li-ion batteries for a long time, it's suggested to charge to a voltage around 3.6V, and maintain at around 40%-80% charge....

Appreciate the detailed explanation.

 

[KITROBASKIN]

Agree with all above, but our go-to flashlights will have 80-90% except if I make a mistake charging, then no big deal if 100%. I just use that flashlight as soon as practical. Being an avid flashlight person, we have plenty of flashlights around for emergencies so that keeping stuff around at 100% is not needed; one light depletes, just grab another. We have solar capability to charge if challenges are extended. Things start going really bad, I'll charge to 100% but portable light will probably not be the highest priorities.

 

[thermal guy]

What is a long time??

 

[Rossymeister]

I've kept 18650's fully charged, and im getting 3-4 years out of a set before noticing any major loss in capacity, or voltage drop under load. The tradeoff is completely worth it to me.

 

[Bucur]

My "trick" is to live by newer standards but to think by older parameters. A contemporary flashlight with a fully charged 1 x 18650 battery has more than enough power and runtime for emergencies I would expect to encounter with my car. Thus, a flashlight with an 80% charged 21700 would outperform it anyway. With this "trick" in mind, I keep a Fenix E35 V3.0 at 80% charge level in my car and I feel like I am even better prepared than I could be with a fully charged 18650 powered light: long term storage problem solved!