Recently I did an experiment, I prepared 2 groups of Li sheet, one group is fresh, another group is sunk in electrolyte for 48h to form SEI layer.
Then I test the EIS curve (100KHz-10mHz) , I found fresh Li-Li symmetric cell has only 1 semi-circle, and another groups have 2 semi-circle,
The groups are noted as:
Li - Li : Fresh Li to fresh Li symmetric cell
Li- Li' : Fresh Li to aged Li cell
Li'- Li' Aged Li to aged Li cell
Is it because of the formation of SEI that the latter 2 groups emerges additional semi-cirle?
Then which is ascribed to Rsei, which is ascribed to Rct?
According to the Phase-Log frequecy diagram, the frequency of the only semi-circle in Li-Li cell is also very high, so it may still be Rsei?
Then how to explain the formation of new semi-circle in Li-Li' and Li'-Li' group?
Thanks for your answer
Hope for your instruction , thanks ~
Dear Fangzheng Liu ,
nearly all your Z-spectra have very high[1] Z-values[2], due to (curtained) Li sheet surface-contamination, that contribute to high-Z errors (random and systematic errors, in Z-measurements). In order to avoid/minimize such errors I recommend you to repeat the same exp.
So, try, please, to repeat, more carefully, the same, using, initially, 'clean Li' sheet[3] (and very shiny Li-) surfaces, 'analytically clean Li' for such a special class for analytical purposes (in research exp.).
Also, you must use the same, meaningful, (Z'-Z'') scales in your Nyquist plots.
1. apart the better (and normal Z-values) case, the case after Li-cycling.
2. for a common (laboratory cell) electrodes' area, of about 1cm2.
3. Li sheet should have, initially, shiny surfaces.
Yeah thanks for your recommendations . I will try another same experiment.
indeed I have a extremely high z value at initial stage, But how to explain it decrease so sharply after several charge/discharge process？ is that because the newly formed SEI has much smaller impedance？ Thank you
Yes, compared with bare Li metal, the SEI has much larger contact area with the electrolyte. So the impedance is decreased
Dear Fangzheng Liu ,
a major Z-healing effect, e.g. Z-decrease ('so sharply') after a single (or small N1[1], number of Li-cycles) charge/discharge process occurs due to
a) pin-holes of contamination (and Li2O framework) on Li sheet surface(s),
Also, another, additional, but minor Z-healing effect occurs after several(-N[2], number of Li-cycles) charge/discharge processes, in your case, due to
b) a progressive dendritic Li formation.
1. N1
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