Quantification of the Carbon-Coating Effect on the Interfacial Behavior of Graphite Single Particles

Abstract

The effect of carbon coating on the interfacial charge transfer resistance of natural graphite (NG) was investigated by a single-particle measurement. The microscale carbon-coated natural graphite (NG@C) particles were synthesized by the simple wet-chemical mixing method using a phenolic resin as the carbon source. The electrochemical test results of NG@C using the conventional composite electrodes demonstrated desirable rate capability, cycle stability, and enhanced kinetic property. Moreover, the improvements in the composite electrodes were confirmed with the electrochemical parameters (i.e., charge transfer resistance, exchange current density, and solid phase diffusion coefficient) analyzed by a single-particle measurement. The surface carbon coating on the NG particles reduced the interfacial charge transfer resistance (R ct ) and increased the exchange current density (i 0 ). The R ct decreased from 81−101 (NG) to 49−67 Ω cm 2 (NG@C), while i 0 increased from 0.25−0.32 (NG) to 0.38−0.52 mA cm −2 (NG@C) after the coating process. The results suggested both electrochemically and quantitatively that the outer uniformly coated surface carbon layer on the graphite particles can improve the solid−liquid interface and other kinetic parameters, therefore enhancing the rate capabilities to obtain the high-power anode materials.