The Nyquist plots are fitted to an equivalent circuit model (Figure ) to evaluate 𝑅𝑅 𝑐𝑐𝑡𝑡 and then used to determine 𝑗𝑗 𝑡𝑡 from Eq. [11]. The exchange current density demonstrates a dependency on lithium concentration that can be described by a form of the Butler-Volmer equation (see Figure ): 16