What does it mean if the OCV of a lithium-ion half-cell decreases after assembly in the glove box? Because usually it should be close to 3V, but when we tested our cell, their OCV was around 2.3V and it got less over time! (This is a type of coin cell with metal oxide as the positive electrode and lithium foil as the negative electrode).
Hello, it's normal that the OCV of the coin cell change after the assembly, especially the decrease, because even with no external current (and this is due to many possible phenomena) Lithium ions are inserted in the material or sometimes removed. Also, it can be caused by impurities that react with the electrolyte or Lithium. So these are the likely causes of the OCV change. Other unlikely causes can be electrolyte leakage or short circuit. Also the change in the temperature from the glove box to the testing room can cause the change in OCV.
Thanks Ayoub El Bendali .
I asked this question because I read in the literature that after the formation cycling, first verify that the cell holds a voltage ( >3 V), If the cell doesn’t hold a voltage, the cell may have shorted and cannot be used.
So if the half-cell voltage decreases how we can use it for electrochemical tests?
Fatemeh Shekofteh , Ah, I understand, so if you are following a protocol described in some paper or something, then you just don't do the test, but if you are doing research and want to discover something, then in this case do the test, and one interesting finding is to make your own threshold and say that 80% of the cells with an OCV less than 2.85V, for example, are not working (which is a typical result that will lead the authors in the literature to make a verification test to not waste your testing resources). So it depends on your objective—is it applying a protocol or testing your materials?
Yes, there is a protocol. In fact, after coating the copper foil with the anode active material, I have to test it. The cyclability test should be performed in the voltage range of 0.01 to 3 volts.
As far as I know, the cell must be activated before any test (known as formation process). And I think this is achieved for anode material firstly by discharging and then charging at a low rate current.
But if the half-cell voltage before activation was low, for example around 2 volts, that means the cell is not suitable at all and another cell should be prepared or the activation should be done in such a way that the voltage of the cell reaches 3 volts, then cycling tests be done?
Hello, Fatemeh Shekofteh , i understand, but i suggest you do the test anyways and see how it goes. especially if you don't have a constraint about the number of tests that you can do. drop in voltage can be just a short circuit during handeling, and may in most cases not affect your results a lot.
Dear Fatemeh Shekofteh ,
if you notice that the voltage appears to 'became lower and lower', in the case of anodic materials' half Li-cells, then it is quite NORMAL, e.g. it is not any problem ('something like self-discharge').
Also, the CVs' potential window of common&useful anodic materials' half-cells must be: 0 V(min), up to 1.5 V (max).
Dear Ioannis Samaras
Could you please explain what you mean by it is "Normal" for anodic materials?
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