li-ion charge current vs fullness in capacity

[TranceAddict]

i find that when applies lower charge current to battery, when it is about to reach full state the voltage of the battery will ramp up slowly until it reach 4.20 to trigger the charger cut-off. whereas higher charge rate will cause it ramp very fast to 4.20 triggering cut-off resulting lesser capacity. in both setting the battery were cool by fan so temperature we same and constant, internal resistance increase due to heat can be neglected.

is this true?

anyone did discharge test to calculate capacity in the aforementioned scenario before?

 

[45/70]

I'm not sure if this is what you mean Trance, but the CV stage should be the same regardless of whether you're charging at a slow, or a fast rate. One exception to this, is a "Fast" charge. With a "Fast" charge the cutoff is generaly at 1/5th the original charge current, as opposed to the standard 1/10th that a normal charge uses. So, a "Fast" charge will result in somewhat less capacity of the cell.

Does this help any?

Dave

 

[TranceAddict]

the algorithm in any sophisticated charger should be charge-sense-charge-sense... when it sense the voltage is close to 4.20v it will change to CV state.

but one phenomenon is when large CC is applied, the voltage tend to ramp up, and when the circuit is opened voltage also tend maintain longer before it fall back to the actual and stable stage. i wonder if charger will confuse in this case and alter to CV state, and ultimately cut-off if the voltage fall down too slowly. thus resulting in lesser capacity

 

[TranceAddict]

Re: li-ion charge rate vs fullness in capacity

it is confirmed that higher charge rate brings lower capacity.

When charging at higher currents, the cell voltage rises more rapidly due to overvoltage in the electrode reactions and the increased voltage across the internal resistance of the cell. The constant-current stage becomes shorter, but the overall charge cycle time is not reduced because the percentage of time in the constant voltage stage increases proportionately.

source: http://powerelectronics.com/mag/power_charging_liion_batteries/

 

[tsmith35]

Re: li-ion charge rate vs fullness in capacity

source: http://powerelectronics.com/mag/power_charging_liion_batteries/

LOL. Love this excerpt from the article:
"In the fourth and final stage, the constant voltage charging is terminated. Unlike nickel-based batteries, it is not recommended to continue to trickle charge Li-ion batteries, which can cause plating of metallic lithium, a condition that makes the battery unstable. The result can be sudden, automatic and rapid disassembly."

Rapid disassembly...

 

[45/70]

Re: li-ion charge rate vs fullness in capacity

it is confirmed that higher charge rate brings lower capacity.

Quote: When charging at higher currents, the cell voltage rises more rapidly due to overvoltage in the electrode reactions and the increased voltage across the internal resistance of the cell. The constant-current stage becomes shorter, but the overall charge cycle time is not reduced because the percentage of time in the constant voltage stage increases proportionately.

I always just figured that the proportionately longer CV period of the faster charge rate, compensated enough that it ended up working out to the same amount of charge. Maybe not. There doesn't seem to be any reference to the faster charge rate yielding lower capacity, could be though.

Dave