Considering the theoretical specific capacity and the w% of both silicon and graphite, we can obtain two values of active material mass and charging current for C/20 for example. How can we determine the charging current for C/20 for the entire Si/graphite composite anode? Thanks in advance.
Hi Zineb,
As mentioned by Sascha, you can calculate the 1C current by using weighted average theoretical capacity, based on only activate material, or total electrode loading. Actually, the definition of "C-Rate" comes from industry and at the beginning, people will usually first test their cell under certain low current density to test the specific capacity of the cell, then use this obtained capacity as the reference and determine the C-rate current density. I think this is more reasonable based on the meaning of C-rate.
However, since more and more people are using theoretically calculated value as C-rate current, you can also use this but remember to mention the 1C current in your paper. As for me, I prefer to use current density instead of C rate. Currently, C rates used in literature varies from 0.1 C to several hundreds C, and for most of the situation, the charge-discharge time does not follow the "1/C" rule, which makes the "C-rate" meaningless. If you use different current densities, people will not misunderstand you. In addition, I would prefer to calculate the actual charge-discharge time and convert that to actual C-rate and present this in the paper.
I am not sure if i understood you correctly but I will take a shot at anyway. It is the sum.
For instance, mass of active material *(wt % Si*its theoretical capacity + wt % Graphite*its theoretical capacity) = Capacity (Ah). When you define things as "C/20", what you really saying is: it takes 20 hours to charge and 20 hours to discharge. So your current will be,
Current = Capacity/20.
I hope this helps. Hey, correct me if I misunderstood you incorrectly or if i am wrong.
Dear Zineb Benzait,
to the best of my knowledge, there is no strict definition for the dependency of C/20 for composite electrodes. There are a plenty of options, which I all encountered while reading articles or looking a datasheets for commercially available electrode materials:
1) 1C related to the theoretical capacity of the active material with the highest mass proportion
2) 1C related to the weighted average of the theoretical capacity of all active materials
3) one of the two above, but related to the overall mass of the electrode including binders, additives etc.
4) one of the three above, but related to the measured capacity for your sample in the one discharging cycle.
In my humble opinion, you need to define the reference value for your capacity and make sure, the actual charging current density is given.
Kind regards,
Sascha Wolter
Hi Zineb,
As mentioned by Sascha, you can calculate the 1C current by using weighted average theoretical capacity, based on only activate material, or total electrode loading. Actually, the definition of "C-Rate" comes from industry and at the beginning, people will usually first test their cell under certain low current density to test the specific capacity of the cell, then use this obtained capacity as the reference and determine the C-rate current density. I think this is more reasonable based on the meaning of C-rate.
However, since more and more people are using theoretically calculated value as C-rate current, you can also use this but remember to mention the 1C current in your paper. As for me, I prefer to use current density instead of C rate. Currently, C rates used in literature varies from 0.1 C to several hundreds C, and for most of the situation, the charge-discharge time does not follow the "1/C" rule, which makes the "C-rate" meaningless. If you use different current densities, people will not misunderstand you. In addition, I would prefer to calculate the actual charge-discharge time and convert that to actual C-rate and present this in the paper.
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