[SOLVED] Li-ion CC then CV charging definition explanation

Hi,

Curiosity: I am trying to understand Li-ion cell charging, not a battery pack which needs charge balancing. Have read a few web pages and pdfs so far. I have understood the following:

> Ideal usage (i.e. discharge) temperature is 18°C to 21°C.
> Discharge to ~10% to 20% and no lower.
> Charge to ~90% or is 100% fine?
> Allow to discharge to ~10% to 20% before charging to maximize lifecycle.
> Do not allow a cell to fall below 2.5V.
> Can use/discharge from -20°C up to +60°C (or preferaby +55°C).
> Can fast charge from +5°C to +45°C. Below +5°C, need to reduce charge current. Do not charge below 0°C.
> Self-discharge is ~3% to 5% per month and must recharge at least every 12 months.
> Store at ~ 40% to ~50% charge, not 100%.
> Charging is implemented via constant current at a steadily increasing voltage then at a constant voltage above the battery's nominal voltage.

a) Are the above points correct/factual?
b) Is sensing low voltage and nominal voltage a way of knowing when to charge and when to stop charging the cell?
c) What in real, practical, circuit implementation terms does the last point mean? Can you e.g. charge a 3.7V, 1A cell at, for example, a fixed 100mA and fixed 4V continuously from 2.5V to 3.7V and then disconnect the charger or is the method more complex than just using a CC source until nominal voltage is reached? How is the 10% to 20% sensed and how is fully-charged sensed - via the cell voltage only?

TIA

d123 said:

How is the 10% to 20% sensed and how is fully-charged sensed - via the cell voltage only?

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The instructions tell what's ideal. I suppose the ideal requires instruments that inform us about every detail of what's going on the battery. Voltage, current level, temperature, elapsed time, etc.

The most correct method is to keep track of Amp-hours drawn out of the cell since it was fully charged. Furthermore to do that you need a 'smart' charger that knows exactly how to detect ful charge. Voltage reading gives a rough idea because you need to apply greater than cell voltage in order to push current into it.

Hi,

Many battery manufacturers provide documents "how to charge"...

Did you go through https://batteryuniversity.com ?

Klaus

You charge it at a recommended (by its manufacturer) current but limit the voltage to 4.20V if you want to go to a full charge. There is a graph at batteryuniversity.com that shows the charge capacity at lesser voltages. At 4.20V the charge is about 70% of 100% capacity. When the charging current drops to a percentage (5%?) of the beginning charging current then a cell is 100% full charge capacity.

My Lithium battery manufacturers say do not store at a full charge, store at 3.7V to 3.8V per cell then charge before using. They say 3.0V or less damages a cell.

Who recommends killing a Lithium battery cell by discharging to 10%-20%?
71%-76% of its fully charged voltage is as low as it should go and when its load should be disconnected.
Do not fully charge? Of course a battery lasts longer if you don't use it, but most people want a full charge so that the discharge can last longer.

Hi,

Thanks for the helpful input.

Audioguru said:

Who recommends killing a Lithium battery cell by discharging to 10%-20%?
71%-76% of its fully charged voltage is as low as it should go and when its load should be disconnected.
Do not fully charge? Of course a battery lasts longer if you don't use it, but most people want a full charge so that the discharge can last longer.

Click to expand...

This pdf says to wait to charge until the battery is at 10% to 20% of capacity. I'll take your word for it. Also, saw a couple of documents that say charging to 90% of capacity extends cell life.

You said, "Discharge to ~10% to 20%" but did not say "of its capacity". If you discharge to ~10% to 20% of its voltage then you will kill it.
It is difficult to measure its capacity but simple to measure its voltage. My Lithium powered products give a warning when a cell's voltage has dropped to 3.2V and the product shuts off when the voltage has dropped to 3.0V per cell.

Yes, if you do not fully charge a lithium battery then its life lasts longer if you don't use it often and don't charge it many times (the same as not using it). But then each discharge lasts for a shorter time and you will probably charge it many more times which reduces its lifetime.
Most people want a discharge to last as long as is possible, so they fully charge the battery.