Charge Capacity of an Electrode Based On Its Material

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Recently I've been researching parallel plate capacitors and was wondering what effects the material had on the charge capacity of the plate. I found one source for measuring the capacity based on its material, but haven't seen any textbook evidence to support it yet. Any feedback on the accuracy of the formula is greatly appreciated.

https://www.researchgate.net/post/H...material_LiMn15Ni05O4_for_lithium_ion_battery

"The Practical specific capacity can be calculated as follow by the Voltage-time curve from the galvanostatic cycling test:

Qpractical = (i*A*tcut off ) / ( 3600*Mw) mAh g-1

where:

i is the current density in A m-2

A the area in m2

tcutoff is the time to reach the cut off potential (Vcutoff) in seconds

Mw is the molecular weight of the active material used in the electrode.

For example for the LiNi1/3Co1/3Mn1/3O2 cathode material

The Theoretical capacity is Q=277.8 mAh g-1 (considering Mw= 96.46 g/mol and n=1) The Practical capacity:

Depends on the C rate used and also on the voltage range investigated (cut off voltage values). When cycled at C/30 in the 2.5-4.3V voltage range LiNMC generally delivers 165 mAh g-1.

The reason why practical capacity is lower than theoretical capacity is that not all the Li can be removed from the lattice of the host material. The rest of the Li is removed above the cutoff potential. Therefore, it is not accessible."
 

Answers and Replies

  • #2
Baluncore
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Recently I've been researching parallel plate capacitors and was wondering what effects the material had on the charge capacity of the plate.
A chemical cell or a battery of cells is quite different to an electrical capacitor.

In a capacitor, where C = q / v; the capacitance is due only to the dielectric constant of the insulation, and is quite independent of the conductor material.

In a chemical cell, the voltage is determined by the electro-chemistry of the chemicals in the electrolyte and chemical reaction with the conductive plates.
 
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In a chemical cell, the voltage is determined by the electro-chemistry of the chemicals in the electrolyte and chemical reaction with the conductive plates.
Thank you for the clarification! I was worried the usual capacitor math wouldn't be as exact.
 

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