Battery knowledge · Electrochemistry fundamentals
Cell voltage
The difference between the positive and negative electrode potentials at equilibrium: for NMC against graphite about 3.7 V. It is set by the chemistry, and the difference in Gibbs free energy of the cell reaction per unit charge. [1]
- Also called
- electromotive force, EMF
- Unit
- V
- Relationship
- E = E₊ − E₋ = −ΔG / nF
Example
Subtract equilibrium electrode potentials
If two illustrative electrode potentials are 4.0 V and 0.2 V versus the same reference, their equilibrium cell voltage is 3.8 V. Under load, resistance and polarization change the measured terminal voltage.
Explore the graph
A spontaneous forward cell reaction has negative Gibbs energy and positive equilibrium voltage under this convention.
At 3.7 V, ΔG = -357 kJ/mol reaction for n = 1.
ΔG = −nFE
Illustrative model. Equilibrium relation at fixed temperature and pressure. No reaction chemistry, activity model or loaded voltage is calculated.
Use in Lemonergy
Connect reaction sites and transport paths.
This is a reference concept. No executable Lemonergy block has been verified for this term.
References & further reading
Technical references
- Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing
IUPAC · 2011
Technical reference · Physical-chemistry notation, thermodynamics, electrochemistry and transport quantities.