Effect of coal tar pitch as carbon source on the electrochemical performance of silicon-carbon composites

Abstract Silicon-carbon composites (SCCs) represent a pivotal class of silicon-based negative electrode materials, exhibiting immense potential for commercial applications. The inclusion of carbon serves to restrict the expansion of silicon and establishes a reliable conductive framework. Pitch, as a carbonaceous precursor, can be utilized for the preparation of SCC exhibiting exceptional electrochemical performance. However, the structural and compositional variations in the carbon pyrolyzed from the pitch with varying softening points result in distinct impacts on the electrochemical properties of SCC, particularly their cycle performance. The coal tar pitch (CTP) with softening points of 80°C and 250°C was selected for synthesizing SCC in this research. The impact of utilizing CTP as a carbon source on the electrochemical performance of SCC and its accompanying structural modifications during cycling were investigated. The pyrolytic carbon with an enhanced graphitization level could be obtained from the CTP and exhibited a softening point of 250°C. The SCC prepared using this CTP revealed superior structural stability and electrochemical performance, with a specific capacity of 1413.4 mAh/g and a capacity retention rate of 76.70% after 100 cycles. The CTP with a softening point of 250°C was further combined with silicon and graphite composites and used as negative electrode materials. The initial reversible specific capacity of 546.1 mAh/g was demonstrated, and it maintained 93.53% of its capacity after 200 cycles. The CTP with a softening point of 250°C can be chosen for the preparation of SCC, ensuring excellent structural stability and electrochemical performance.