Lithium battery chemistry experts: charging questions.....

[pullin-gs]

Questions regarding Lithium Ion 4.2V battery chemistries.
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Q1) How much capacity would I leave on the table if I choose to charge at constant current .2C, abruptly stopping charge cycle once 4.2V is reached (vs mainting charge cycle and dropping current until .1C current load at 42V is reached).
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Q2) What implications are there (plating, etc.) if I choose to charge at .1C for entire charge cycle with hard cutoff once 4.2V is reached?
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Solar charging solution currently provides:
*)Delivers .2C max (probably more like .1C in practice though).
*)It provides constant voltage up to 42V/2amps....less depending on Solar Panel output.
*)Pack is 10S6P 29E Sanyo build.
*)Has hard disconnect once 42V is reached across 10S pack.
*)Once it disconnects from pack (open circuit). Will not reestablish charge cycle without operator intervention.

 

[flat tire]

Depends on the internal resistance of the battery but not very much capacity should be lost CC charge to 4.2v at that slow rate. Like a couple %. .2C is close to many people's CV phase current cutoff. You won't cause any special damage to the batteries by charging at .1C.

 

[john61ct]

I'm no expert but

the SoC% "sacrificed" will vary by the specific chemistry and from one maker to another.

The only true measure of **usefully stored** power, is precisely controlled load tests. Counting coulombs on the way in is not accurate after amps start to taper, especially toward the end.

I have only measured with LFP, but below can I think be applied to LCO, NMC and other LI chemistries.

Assuming the voltage maximum is constant.

A. hold Absorb / CV until current tapers to zero

B. hold Absorb / CV until current tapers to .01C

C. hold Absorb / CV until current tapers to .05C

D. no Absorb / CV at all, just stop when V setpoint is reached

Overall from A to D might be "sacrificing" as much as 6-8%

Between each increment, 1-3%

Varying the charge rate when below .03C will not affect resulting SoC for B & C.

Also, voltage setpoint can be reduced without impacting endpoint SoC much, just hold CV a bit longer.

Not as true for "just stop" no-CV "charging To" a given voltage,

the **lower** the charge current rate, the **higher** the resulting SoC when charge is cut off.

At **higher** rates, say over .5C, voltage can go higher to get closer to "vendor profile 100%" than would be safe for lower rates.

At lower rates you need to be more careful to terminate earlier in the taper, it is entirely possible to overcharge even at voltages much lower than vendor spec'd.

 

[john61ct]

You won't cause any special damage to the batteries by charging at .1C.

In fact for LI, lower rates are healthier for longevity, assuming CV not held too long.

Some lead chemistries require high initial charge rates, even over .4C, but not lithium ones.

The only reason to use high rates with LI is speeding up the charge cycle.

 

[pullin-gs]

Thanks for the prompt&quality responses.
v/r,

P

 

[spinningmagnets]

I highly recommend to charge to 4.1V as a max. If you Google Jeff Dahn, and making a lithium battery last, he will spell it out with all the details.