“…Generally, the semicircle in the high and medium frequency region is related to the charge transfer process, and the value of the diameter corresponds to the value of charge transfer resistance (R ct ). The inclined line in the low frequency region represents the Warburg impedance, which is associated with the lithium-ion diffusion in the prepared cathode materials [31]. Approximately, the values of R ct for sample a, b, c and d were estimated to be 79, 84, 70 and 196 V, respectively.…”