Unraveling the Effect of Conductive Additives on Li-Ion Diffusion Using Electrochemical Impedance Spectroscopy: A Case Study of Graphene vs Carbon Black

As an indispensable part of the electrodes in lithium-ion batteries, conductive additives play an important role not only in electron transport, but in the electrode structure as they form carbon-binder domains (CBD) that are located in the voids among active materials. The latter is expected to have a significant effect on Li-ion diffusion in the electrode, but has been paid little attention to in previous research. Accordingly, two typical types of conductive additives with distinct structures, including carbon black and graphene, are employed in LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811) electrodes to investigate this important issue in this work by quantitative analysis of Li-ion diffusion resistance (R ion ) and charge transfer resistance (R ct ) by electrochemical impedance spectroscopy (EIS) using a symmetric cell configuration combined with the transmission line model (TLM). The EIS results confirm that addition of graphene is more effective to enhance Li-ion diffusion compared with carbon black. Meanwhile, for constructing better CBD, graphene and carbon black are equally crucial, and the combination of both is necessary to achieve the best rate performance, as Li-ion diffusion, electronic conductivity, and charge transfer process which is affected by the electroactive surface area in the electrode should be taken into consideration at the same time.