Everything we write here still holds. However, the finger-type reference electrode is no longer available. The good news is that we now have an even better solution: The mesh-type reference electrode.
Sometimes a finger-shaped reference electrode can be better than our standard ring-shaped reference electrode. The finger reference measures the electrical potential in the middle of the stack instead of at the outer edge of the cell stack. This can help to minimize artifacts caused by inhomogeneities of the electric field. The finger is made of stainless steel and coated with polyimide, except for the measurement area at the end of the finger. Different geometries of the finger are available.
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The finger-shaped reference electrode is considered useful for several scenarios:
It can be employed as a stainless steel pseudo-reference electrode.
It can be coated by the user with a reference material (e.g. LTO).
It can be lithiated or delithiated by the user in-situ after cell assembly.
All these scenarios are perfectly supported by our PAT battery testers, like the PAT Tester-x-8 and EL-Software. This is shown here using the example of a cell consisting of NCM and graphite. After building the cell, the stainless steel finger is first electroplated with lithium utilizing the NCM electrode as the lithium source.
Pre-lithiation of the finger-shaped stainless steel electrode (R) from the NCM electrode (1)
In the second step, the lithiated finger is used as a stable reference electrode when cycling the NCM / graphite cell. Switching between the two modes is easy to do in the test script. No cable connections need to be changed, as would be necessary with a conventional battery tester.
Once lithiated, the R electrode serves as a true reference when cycling the NCM / graphite cell.
Conclusion: EL-Software and the PAT-Core make pre-lithiating a simple task.
About the author
Dr. Matthias HahnSenior Scientist, Co-founder of EL-CELL
Matthias has a PhD in physical chemistry and brings over 15 years of hands-on research experience in electrochemistry, gained at institutions such as Honeywell, Daimler, and the Paul Scherrer Institute.
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