Dear Everyone, I am new to this battery field and want to know how to get x (amount of lithium (de)inserted) from the galvanostatic charge/discharge profile for any materials. I have attached reference for your quick understanding. (Ref:
The thermodynamic origin of hysteresis in insertion batteries, W. Dreyer et al. Nat Mat. 9, pages 448–453 (2010) ) Thanks in advance!
Hello,
First of all, some corrections should be made in the equation Nguyen mentioned. Using specific capacity is erroneous and total capacity with unit of Coulomb should be used instead.
Furthermore, n is the amount of material formed during the reaction and x is the number of electrons (unit charge) takes place in the proess. Therefore, x is always a positive integer.
The final and correct equation for x can be derived from Faraday's law according to:
Q [C] = (xFm)/M = xFn
x [-] = (QM)/(Fm)
where Q is the amount of charge goes through the electrolyte during the electrolysis (operation), F is the Faraday-constant, m is the mass of the active material in gramms, M is the molar weight of the active material in gramm/mole and n is the amount of material formed during the reaction. The active material is the Li in this case.
So, it can be seen that x in LixFePO4 is different than x in the Faraday equation. In the chemical formula, x is related to the amount of Li in the electrode which is changing during the charge/discharge. Since it is an amount of something its unit is mole/dm3 and called as concentration. Usually, it is normalised so its value is in the range of 0-1. (For clarity, the actual Li concentration is divided by the total concentration of the given electrode which is a material constraint)
The concentartion of Li in the electrode is related to the state-of-charge (SOC) but none of them can be directly measured in most cases. However, I usually approximate the concentration by dividing the amount of charge consumed by the reaction so far (Q = current multiplied by time) and the total capacity. It gives only a rough estimation of concentration in % but works well in quasi-equilibrium (less than 0,2 C) discharge.
The current concentration can be then derived from the overall concentration of Li in the electrode, if necessary.
I hope it helps.
Regards,
Bence
- Badges
- Science topic
- Similar topics
- Electrochemistry
- Battery