I am trying to make a LiNi0.5Mn1.5O4 cathode without the addition of carbon black to study the phenomenon of SEI layer formation.
Unfortunately, when the cell is charged at C/20, the cell reach instantly to upper cutoff voltage.
Can anyone suggest a solution for this problem? Why is this happening? I was expecting the cell wouldn't behave like this in the absence of carbon black.
I suspect it is the low electrical conductivity of the cathode without the addition of carbon black. I assume open circuit voltage is normal before you start the test, but reaches the upper cutoff voltage quickly just as you explained. If everything is setup correctly this would indicate there is a very high polarization, most likely ohmic polarization (IR drop) due to the decreased electrical conductivity.
Do you have access to electrochemical impedance spectroscopy (EIS)? You can quickly test your battery 1MHz - 1Hz at 5mV to generate an impedance spectra that will tell you your ohmic resistance. It should be less than 5 ohms at high frequency.
I suspect it is the low electrical conductivity of the cathode without the addition of carbon black. I assume open circuit voltage is normal before you start the test, but reaches the upper cutoff voltage quickly just as you explained. If everything is setup correctly this would indicate there is a very high polarization, most likely ohmic polarization (IR drop) due to the decreased electrical conductivity.
Do you have access to electrochemical impedance spectroscopy (EIS)? You can quickly test your battery 1MHz - 1Hz at 5mV to generate an impedance spectra that will tell you your ohmic resistance. It should be less than 5 ohms at high frequency.
Zachary Neale Thank you very much for a very satisfying answer to my query, I will try to follow your suggestion.
When you access EIS then test your battery in the range 1MHz - 0.01Hz, with an Vac amplitude 1 to 5mV and a Vdc polarization near a value corresponding to 10% to 50% SOC of your common WE (with carbon black).
Also, in next (say in 5) steps of the testing WE (with less carbon black) try to reduce, step by step, the carbon black percentage, adding (more) binder percentage. So, in all (say 5) steps, you keep the percentage of your active material the same. Finally, in the last step of the testing WE (without any carbon black), try to replace all the carbon black percentage (Hcarbon black) with (more, HbinderAtEnd=HInitial_Binder+Hcarbon black) binder, keeping the percentage of your active material, again, the same.
Hi Ioannis Samaras, I am curious why Vdc polarization should be non-zero. I have always done EIS with Vdc equal to 0. Is there a reason to add polarization, and should I be testing batteries this way?
Hi Zachary Neale, we test batteries starting[1] EIS, always, with the common case of the Vdc polarization[2] value: Vdc=OCV, where idc=0A.
Also, the Vdc polarization parameter is used to sense for any possible energy (E) correlation with the EIS (Z-)properties.
So, we are measuring (Z-)impedance spectra scanning with the tool of the parametric Vdc,j value[3] or energy Ej level (candidate redox) value[3] of the device (battery).
_ _ _ _ _
1. if, only, a simple case of EIS spectrum measurement for a single Vdc polarization.
2. A case for Vdc=0V, where idc is very high (in theory idc-->oo), is out of most batteries' scope, out of any (full cell) real battery scope.
3. Vdc,j=Ej/e, where idc=0A.
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