A comparison of lithium diffusion between Graphite/LFP 18650 power and energy cells with low and high current pulses

This study gives a new estimation model to evaluate the voltage-increase due to a step-up current in both lithium-ion power and energy cells. The step-up current analysis is similar to the GITT technic developed in the literature, but with tests at low or high C-rate and for a longer time. The power cell voltage-increase follows a square root of time dependency which is commonly observed in the literature. On the contrary, a superimposed transient overvoltage in the energy cell is observed. The transient overvoltage has the capacity to distort the characterization of diffusion as modelled by existing models. This paper proposes a phenomenological approach to model the transient overvoltage in the energy cell. This work gives a method to model the phenomenon and is a first step to clarify the origin of the phenomenon. It can also help improving the estimation of the diffusion parameters.