Investigation of Polyacrylonitrile-Derived Multiple Carbon Shell Composites for Silicon-Based Anodes in Lithium-Ion Batteries

The aim of manufacturing silicon-carbon (Si/C) composites for lithium-ion batteries is to embed silicon particles into a carbon matrix or shell, which results in improved electrical conductivities and cycling stability by avoiding the direct solid electrolyte interphase (SEI) formation on the silicon surfaces. In this study, we explore the production of Si/C composites containing one (single) and two (multiple) carbon shells, achieved through the carbonization of polyacrylonitrile. We thoroughly analyze the carbonization process of polyacrylonitrile and investigate the structural, physical, and electrochemical properties of the resulting Si/C composites. Our findings indicate that the increase of the carbon fraction and the second thermal treatment during the manufacturing of multiple carbon shells (MCS) have a significant impact on the conductivity of the powders, increasing it by one order of magnitude. We also discover that the MCS cover the silicon surface more effectively, as revealed through etching in a NaOH solution and subsequent elemental analysis. The MCS composite, containing 30 wt.% silicon, exhibits the best cycling performance in half-cells at 0.5 C, with an initial capacity of 776 mAh g-1 and a capacity retention of 83.0 % after 100 cycles. This work includes the synthesis of silicon-carbon composites containing a single or multiple carbon shells as active materials for anodes in lithium-ion batteries. Herein we reveal the significantly advantageous physicochemical and electrochemical properties of composites with multiple carbon shells such as reduced specific surface areas, increased specific electrical conductivities, improved silicon embedding and improved cycling performance during electrochemical testing. image