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I'm looking at this battery: SLB08115L1401CV

I was under the impression that the chemistry of a lithium ion cell dictates the charged/discharged voltage levels. That certainly seems to be the case with larger cells. Every one I've ever seen follows a similar curve, where ~4.2 V = full charge and the voltage starts falling off around 3.5 V.

This cell does not. Full charge on its curve is approximately 2.75 V. Why is that?

Discharge curve from datasheet

The datasheet is very sparse and doesn't explain anything peculiar about the chemistry.

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    \$\begingroup\$ The clue is "Over 10000 cycles lifetime". That pretty much pins it down as Lithium Titanate, and the voltage range is right for LTO. \$\endgroup\$
    – user16324
    Commented Oct 28, 2021 at 21:33
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    \$\begingroup\$ Lithium-Ion is not a single chemistry but a family of chemistries with varying characteristics. \$\endgroup\$
    – jcaron
    Commented Oct 28, 2021 at 21:33
  • \$\begingroup\$ @jcaron In that case how are we supposed to design product with these batteries, without knowing the chemistry? For example what would happen if this cell were discharged to zero, etc ,etc? Others have inferred LTO chemistry from the voltage, but it seems silly that the designer would be required to make such a guess. \$\endgroup\$
    – Drew
    Commented Oct 29, 2021 at 6:08
  • \$\begingroup\$ @Drew you are supposed to know either the chemistry or, better, the charge/discharge characteristics of the battery you are using. A lot of parameters depend not only on the chemistry, but on other battery design peculiarities as well. Times when the only available rechargeable chemistries were lead-acid and NiCd alcaline are gone. \$\endgroup\$
    – fraxinus
    Commented Oct 29, 2021 at 7:43
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    \$\begingroup\$ @Drew The product listing on DigiKey specifically lists this as a 2.4V battery. Like anything else, you design based on the datasheets - not intuitions or speculations on the chemistry or physics inside. The charge and discharge cutoff voltages are specified in the datasheet. If you discharge to zero you are operating outside of the regime dictated by the datasheet - so don't. It's up to you to make sure you stop discharging when the cell voltage gets too low (1.8V in this case) and it's up to you to make sure you don't charge beyond the max cutoff voltage. \$\endgroup\$
    – J...
    Commented Oct 29, 2021 at 17:30

1 Answer 1

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The voltage of any cell depends upon the particular materials used for the electrodes.

The cell voltage of 2.4V indicates it is probably a lithium-titanate-oxide (LTO) cell.

Although these cells have a lower energy density than other types the cell can potentially have a longer life, many thousands of cycles. It is also much safer with very much lower probability of catching fire if mistreated.

The longer life is due in part to the characteristic that LTO does not change its physical structure as much as other types when charged and discharged. With other types the electrode physically swells during charging, the physical deformation can ultimately lead to loss of capacity.

Lithium-titanate_battery

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