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I am working on charging lithium-ion batteries (NMC chemistry, max. charge voltage is 4.2 V).

In charging mode, after the cell has reached 4.2 V, the charger goes to CV mode, and after this, charging ends (based on cut-off current).

As I understand it: in CV mode the battery chemistry stabilizes; due to this we may get good capacity and life cycle.

What happens if we charge the battery to 4 V (not up to 4.2 V) using CC mode and eliminate the CV mode? This means we are not charging to 100% (capacity is not an issue in my application and I want to reduce the charge time).

Can we eliminate CV mode when charging? And when charging like this, will there be any battery degradation/life cycle/capacity issues?

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2 Answers 2

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Can we eliminate CV mode and use it?

Yes.

And when charging like this, will there be any battery degradation/life cycle/capacity issues?

On the contrary. You would be at about 70% of maximum capacity, but have a huge increase in cycle life, see the third table in the article BU-808: How to Prolong Lithium-based Batteries at Battery University.

Not discharging them below, say, 20% will also increase cycle life, at the expense of usable capacity, of course.

Charging faster by increasing the CC current will probably reduce cycle life as well.

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    \$\begingroup\$ Agreed. Fol solar systems it's quite recommended not to fully charge in order to get more cycles out of the battery packs. \$\endgroup\$
    – Overmind
    Commented Aug 25, 2020 at 12:08
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    \$\begingroup\$ If you maintain Vcell between 50% and 80% with twice the cells your lifetime Wh may be 5x 500 cycles so 3.5 to 4V is a good plan IF you monitor battery current minimize time above 3.8V and below 3.6 for optimum life span but suboptimal capacity (roughly) \$\endgroup\$
    – D.A.S.
    Commented Aug 25, 2020 at 13:14
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    \$\begingroup\$ The answer is right. When cycle life is your main concern, you may sacrifice battery capacity by charging to anything less than 4.2V. The CV phase is only needed if you want to reach maximum SoC. In particular, this is very good if your battery spends a lot of time in a fully charged state, since 100% SoC means a highly energetic state and thus higher degradation (this is why we are never storing Li-ion cells at full charge capacity).. \$\endgroup\$
    – Diego
    Commented Aug 26, 2020 at 7:31
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you can charge to 4 volts instead of 4.2V no problems, but why ? Charging in CC mode up to 4 volts, and skiping CV mode will not charge your battery to its full capacity. Is this an issue or not ? If you want to reduce charge time, you just increase the current in CC mode instead. Say, your capacity is 2000mAh, then check battery manufacturer specification to establish what is the maximum safe charge current you can use, and charge the battery to 4.2V in CC mode (that is if you want to make use of its full capacity/cycle). Why do you have to charge it so quickly ?

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  • \$\begingroup\$ Also forgot to mention, not charging your battery to 100% may reduce the battery life. Li-Pol / Li-Ion batteries like to be charged to 100% and discharged to 0% to obtain maximum life-span possible, especially the first couple of cycles for a new battery .... \$\endgroup\$
    – citizen
    Commented Aug 25, 2020 at 11:26
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    \$\begingroup\$ I am not sure where you got that, but that isnt for Li-ion, it is for NiCd ehich is completly different \$\endgroup\$
    – Ahmed Eshra
    Commented Aug 25, 2020 at 11:46
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    \$\begingroup\$ "Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles." \$\endgroup\$
    – ocrdu
    Commented Aug 25, 2020 at 11:46
  • \$\begingroup\$ where did you read that ? Any references ? I'd love it if it were true ;-) Going from 300 cycles to 2400 cycles just like that... Can we get 10000 cycles ? \$\endgroup\$
    – citizen
    Commented Aug 25, 2020 at 11:52
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    \$\begingroup\$ @ citizen not charging to 100% helps life-cycle, it does not reduce it. \$\endgroup\$
    – Overmind
    Commented Aug 25, 2020 at 12:07

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