Hi! I was wondering, what exactly damages L-ion cells when charging at a <1C rate? Is it heat, internal resistance, or something pertaining to the cell's physical construction?
Thanks!
I wouldn't say Li Ion batteries are "damaged" by charging at a low rate. They do have a limited lifetime (based on current battery technology) - they slowly degrade over time. A dodgy charger that even slightly overcharges them, or a device that overdischarges them, will damage the battery, resulting in much faster degradation.
IIRC one of the big factors in degradation is the state of charge during storage - they do best at around 60%, and degrade more rapidly when stored fully charged or fully discharged. This is why most electronic devices you buy come with the battery half-charged.
epicface2304:
I was wondering, what exactly damages L-ion cells when charging at a <1C rate?
Most all batteries degrade over time when they are charged and discharged, they dont last forever.
Probably best to ask a chemist if you want a more specific answer, its not the Arduinos fault.
What about a >1C charging rate? How do phones charge in 45 minutes without destroying their batteries? I'm trying to make a high-current charger.
Designing fast chargers for Lithium batteries requires a great deal of care and experience, get it wrong and your battery can explode, burn down your house etc.
If you need to ask basic questions about charging LiPo, assume you dont have the experience to design and build one.
They can be as much as 25p to buy, why take the risk ?
1C is not a magical rate. It all depends on the exact chemistry. E.g. I have modern Lipos which are specified for 10C charging rates and others specified for only 2C. 1C used to be the recommended rate for the early ones but that was years ago.
Lithium charging requires a specific CC/CV charging regime and provided you stick to that the charge rate is rather less important.
Steve
epicface2304:
What about a >1C charging rate? How do phones charge in 45 minutes without destroying their batteries?
They use batteries rated for higher charging rate, and a high current charging controller IC. It's worth noting that fast charging does shorten the overall life of the battery (my tablet has options to disable fast charge, and also to not charge it past 60% to maximize lifespan of the batteries...) - but that's considered acceptable in a cellphone since they're designed for a 2-year lifecycle anyway.
epicface2304:
I'm trying to make a high-current charger.
Use an IC designed for that purpose.
Don't screw around when working with charging of a lithium battery - when abused severely enough, those batteries can burst into flame.