I am working with lithium ion batteries having the cathode material as NMC i.e. LiNixMnyCozO2, wherein x + y + z = 1. The proportion of Nickel, Manganese and Cobalt in the cathode varies, but mostly Nickel is either equal to or greater than the amount of Manganese and Cobalt in the cathode (for example NMC-111, NMC-532, NMC-622, NMC-811 are the commonly reported chemistries in literature).
I tried doing Energy dispersive X-ray spectroscopy on the surface of my battery cathode to find out the proportion of Nickel, Manganese and Cathode. The results I obtained were: Ni - 20%, Mn - 20%, Co - 60%. I repeated the EDXS procedure at ten different locations on the battery cathode and still got the same results with 1% error in the values. This result is far from what I expected and I suspect the reason for this is that I am scanning only the surface of the cathode.
So I have two questions regarding this:
1) Should I expect the EDXS results to be different and correct if I perform it on the cross-section of my battery cathode?
2) What are other cheap techniques which can get me the elemental composition of the cathode? One of my friends suggested me ICP-MS (inductively coupled plasma mass spectrometry), which is way too expensive for me.