Volumetric capacity in battery explorer


How is the volumetric capacity calculated? It looks like the gravimetric capacities are calculated with the Faraday’s laws for electrolysis but applying the same intuition but with the unit cell volume doesn’t seem to recreate the volumetric capacities in the Battery Explorer.

Battery Calculations using Na as working ion


Thanks for asking the question.

I would like to use an example to answer your question.

For electrochemical reaction 0.75Li + Li0.25FePO4 -> LiFePO4 + 0.75e, each LiFePO4 stores 0.75e.
The cell volume is 302.3Å^3 per LiFePO4.
Then it gives you the volumetric capacity = 0.75e/302.3 Å^3;
plug in some of the constants to convert the units:
1Ah = 3600 * 6.25 * 10^18 e and 1Å^3 = 10^-27 L
It will give you that volumetric capacity = 0.75e/302.3 Å^3=441Ah/L.

Fortunately, pymatgen has a insertion_electrode module to calculate the battery cathode properties for you, so that you do not need to worry about it. Here is the usage ( Na battery example) ,

from pymatgen import MPRester
from pymatgen.apps.battery.insertion_battery import InsertionElectrode

mpr = MPRester()
entry1 = mpr.get_entries("mp-763898", inc_structure="final")[0]
entry2 = mpr.get_entries("mp-32486", inc_structure="final")[0]
na_entry = mpr.get_entries("mp-10172", inc_structure="final")[0]

a = InsertionElectrode([entry1,entry2],na_entry)


The output will be:

InsertionElectrode with endpoints at VPO5 and NaVPO5
Avg. volt. = 3.319478280000003 V
Grav. cap. = 144.9496318169905 mAh/g
Vol. cap. = 468.3816011364095

I hope this answers you question, but feel free to let me know if there is a problem.

Best regards,