Describes the temperature dependence of reaction rates. The basis for calendar ageing models. Degradation rate roughly doubles for every 10°C rise in storage temperature.
Where:
- k = rate constant
- A = pre-exponential factor (frequency factor)
- Ea = activation energy (J/mol)
- R = Universal Gas Constant (8.314 J/mol·K)
- T = absolute temperature (K)
Where Arrhenius Fails and VFT Takes Over
At room temperature, the electrolyte flows easily, like water or a thin oil. However, when temperatures drop below freezing, the chemical nature of its solvents causes it to “gel” and “wax” up, much like diesel fuel left out in the cold. In engineering, we typically calculate the temperature-dependent drop in ionic conductivity using the classical Arrhenius equation. Arrhenius works perfectly when the liquid is in its normal fluid state. But as the temperature drops further and the electrolyte waxes, approaching its glass transition phase, the movement of ions slows to a non-linear halt. This is where Arrhenius breaks down, and we must switch to the VFT (Vogel-Fulcher-Tammann) model to reflect physical reality. VFT dictates a harsh truth: as viscosity approaches infinity, conductivity crashes to zero.
See also: Nernst Equation, Calendar Ageing, Accelerated Testing, Ionic Liquid Electrolytes, Thermal Runaway Modelling at Cell Level