Hi Vivek,
I suggest you get a differential capacity curve, e.g. dQ/dV, from your original curve. It will be of a bit trouble. But you will know almost the exact voltage position under a certain (dis)charging current density. Please, see the following link:
http://www.ultimate-electronics.co.uk/battery-article/FaqTips/Function-Of-Battery.htm
Regards,
Hi Vivek,
Voltage of battery maybe having no plateau, single plateau or multiple plateau all have advantages as well as disadvantages. Typical example could be,
- Having a sloppy profile (no plateau) will be useful to know the state of charge/discharge by measuring the voltage. In case of constant voltage (plateau) just by measuring voltage you cannot say anything about the state of charge/discharge. Thus a sloppy profile could be advantageous to know the state of charge and for some other applications it may not be useful. But, knowing state of charge/discharge is one of the important practical applications. The state of charge could be known by Coulomb counting in case of the battery having a plateau (as the voltage does not change much).
More points,
- Having a plateau might have constant energy density (ED = Voltage * Capacity) where as a sloppy profile will have varying energy density depending on the state of charge/discharge (though we can mention an average ED).
- Having multiple plateau indicates multi phase transitions.
- Higher the voltage plateau, higher the energy ED multiple plateau means lower and lower ED as the plateau voltage decreases.
- Constant voltage (plateau) indicates two-phase behavior while sloppy profile indicates a solid-solution-like behavior.
A lot more points that are not mentioned so may be i'll add more points later. Hope this helps you to start thinking more about it.
Thank you Professor Yousif and Sathanagopalan for your comments.
Professor Yousif, I tried to plot the dQ/dV curve but as there is voltage plateaus so at some points we will have dV = 0, which results dQ/dV to be infinity? Please correct me if i am wrong. Then in such cases what should be the path forward? Kindly let me know your opinion? Thank you for your time.
The question as phrased above is very general. A number of different explanations are possible. Here is one that adds to that which has already been presented. I will restrict the discussion to a special case not mentioned previously.
As usually defined, a battery contains n cells where the value of n is greater than or equal to unity. I will refer to the case where n is greater than one, i.e., a multicell battery. In that case, the battery contains cells that are not identical. This is the consequence of wiring cells in series from a production line. The production cells have a distribution of capacities that meet some established quality standards and a single nameplate capacity is given to the generic cell. The nameplate cell capacity does not mean that the cells are identical. So, when a multicell battery is discharged, a series of voltage plateaus appears that represents the time when the lower capacity cells drop out and the higher capacity cells continue to deliver their remaining capacity. There is an obvious point to be made here. The end of discharge is determined by the first cell that drops out. Clearly, if one chooses the end of discharge voltage as zero volts, that means that the summation of the cell voltages is zero volts. Some of the cells have been reversed. Doing that tends to accelerate the deterioration of the battery.
I hope that this comment is relevant to the situation that you are addressing.
Asla Bish it is too late to reply. you can plot differential Voltage then it will not be infinity. i.e. dV/dQ on y axis and Voltage on x axis. if you want, i will send you a paper, it deals with both differential capacity and differential voltage.
Asla Bish Check this journal, it will compare both techniques i.e. differential votlage and capacity.
I. Bloom, A. N. Jansen und e. al., „Differential voltage analyses of high-power, lithium ion cells 1. Technique and application,“ Journal of Power Sources, Bd. 139, pp. 295-303, 2005
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