First, the case where transport of the charged species is limited
by the transport in the active material was investigated. Previous
studies have provided analytical expressions of the degree of
discharge as a function of the discharge rate in the case of a pure
diffusional process. A formula involving an infinite sum of terms,
valid over the entire C-rate range has been found, [30] as well as
simple formulas only valid for long or short discharge times [31]. In
here we rely on the analysis of the numerical solution of the
diffusion problem, which can be reduced to the following
approximation