Effect of morphology of conducting agent on electrode structure and electrochemical performance for the graphite-silicon composite electrode

Abstract

Silicon has attracted attention as a promising active anode material for lithium-ion batteries (LIBs) due to its high intrinsic capacity of 3579 mAh/g. However, silicon has low electronic conductivity and extreme volume change during lithiation and de-lithiation. Severe volume change of silicon particle leads to the loss of electronic conductive network, pulverization and cracking of Si particle, and electrode failure during repeated cycling. The graphite - silicon composite electrode is being studied as one of the methods to overcome the limitation of silicon-based anode and the low capacity of the conventional graphite anode. The addition of a conducting agent in silicon-based electrode is comparative. The conducting agent forms different conductive network depending on the morphology. It is necessary to design the electrode with the conductive network that allows graphite and silicon to function properly, which can enable the formation of the conductive network with an appropriate structure. The composition of the conducting agent determines the electrode microstructure of the graphite – silicon composite electrode. In order to identify the electrode structure parameters according to the composition of the conductive material in different structures, the pore size distribution, conductivity effectiveness, and electronic conductivity were measured, which is supplemented by scanning electron microscopy (SEM). The effect of the formation of different conductive networks on the electrochemical performance such as rate capability and cycle performance of graphite - silicon composite electrode is evaluated. Separation analysis of graphite and silicon behavior is conducted through each characteristic reaction potential during lithiation and de-lithiation. The difference in capacity decreasing rate was supported by SEM and electrochemical impedance spectroscopy (EIS) after the cycle test. The addition of carbon black in the 0D structure with point-to-point contact enables electrodes with low overpotential, which is advantageous for high-rate capability. However, it is necessary to use carbon nanotube (CNT) to form conductive network with a bridge-like structure to suppress silicon capacity fading during cycling. It is important to design the composition of the conducting agent with desirable conductive network for remarkable electrochemical performance.