Unraveling the role of binder concentration on the electrochemical behavior of mesocarbon microbead anode in lithium-ion batteries: understanding the formation of the solid electrolyte interphase

Binders play a significant role in the electrochemical performance of anodes in lithium-ion batteries. In this study, mesocarbon microbead (MCMB) electrodes are fabricated with various binder concentrations of 4.5 wt% (MCMB-4.5), 7.5 wt% (MCMB-7.5), and 10 wt% (MCMB-10) to evaluate the optimum content of binder for a MCMB anode. The cyclic voltammetry (CV) profiles indicate a slow kinetic process of lithiation/delithiation in the MCMB-10 anode. The results demonstrate that MCMB-7.5 has the highest lithium diffusion coefficient, which represents the improved lithium diffusion kinetics of MCMB-7.5. The step-by-step electrochemical impedance spectroscopy (EIS) studies indicate that a highly conductive solid electrolyte interphase (SEI) film is formed from 0.1 to 0.01 V on MCMB-7.5 anode that not only makes up the increase of SEI resistance (R-SEI), relating to the expansion of MCMB volume, but also leads to a decrease of the R-SEI. The MCMB-4.5, MCMB-7.5, and MCMB-10 show self-discharge rates of 0.99, 0.28, and 1.09% per week, respectively. Thus, the MCMB-7.5 has the lowest level of parasitic reactions between the active material and electrolyte. Furthermore, the 7.5% binder concentration provides the best capacity retention along 100 cycles at 0.5 C rate, which can suggest as the optimum concentration of CMC/SBR for MCMB anodes.