(444h) High-Capacity Micron Si/Graphite/Vanadium Carbide Composite As Anode for Li-Ion Batteries

The ever-increasing demand for portable consumer electronics and renewable energy storage devices has spurred global interest in high-performance lithium-ion batteries (LIBs). The development of LIBs with enhanced capacity, extended cycle stability, and reduced weight forms the critical strategies necessary to cater to the requirements of next-generation devices [1]. Despite graphite being the commercial anode in LIBs, its relatively low theoretical capacity (372 mAh g^-1) limits its utilization in high-energy applications. Silicon (Si), with its high theoretical capacity of 4200 mAh g^-1, natural abundance, and suitable Li uptake potential (0.4 V vs Li/Li+), emerges as a promising anode material [2]. However, its extensive volume expansion hinders its practical application.

In this work, we combine micron-sized Si particles with graphite. The use of micron Si is cost-effective, and the synthesis process is straightforward. The finely ground mixture (Si-G) is combined with polyacrylonitrile (PAN) to yield amorphous carbon upon carbonization. This assists in buffering the mechanical stresses induced by Si volume expansion. Moreover, it prevents the direct exposure of Si to the electrolyte, thereby stabilizing the solid electrolyte interphase (SEI). The incorporation of a dopant enhances the material’s intrinsic conductivity, leading to an increased capacity by facilitating electron and Li-ion transport channels. To further boost the composite’s performance, synthesized Mxene is incorporated to augment the charge transport between micron Si. The composite’s morphology and structure are examined using various techniques such as SEM-EDS, TEM, XRD, Raman, and XPS spectroscopy, revealing a uniform distribution of Si, C, and Mxene sheets that maintain the sheet architecture.

The composite, when used as an anode, exhibits exceptional electrochemical performance, as evidenced by its remarkable lithium storage specific capacity of 2003 mAh g^-1 (based on the weight of Si) even after prolonged cycling (at 1C rate). At the end of 500 cycles, the volume expansion was reduced to only about 150% of its initial size (from 420%), with an almost intact morphology. Additionally, the composite demonstrates superior rate performance with a specific capacity of ~2440 mAh g^-1 at a 10 C rate, highlighting its potential for high-power applications. Furthermore, the electrode exhibited a low charge transfer impedance and rapid electron transport, which enhanced the electrochemical performance. The improved performance can be attributed to the unique structure comprising Mxene and doping, which significantly augmented the Li-ion diffusion and the active sites. Also, the use of low-cost micron Si with a high tap density is employed. Consequently, this study offers a methodology to develop high-capacity LIBs based on micron silicon.

References

1. Liu, L. Kang, J. Hu, E. Jung, J. Zhang, S.C. Jun, Y. Yamauchi, ACS Energy Lett. 6 (2021) 3011–3019.
2. Zhou, Y. Liu, C. Du, Y. Ren, T. Mu, P. Zuo, G. Yin, Y. Ma, X. Cheng, Y. Gao, Journal of Power Sources. 381 (2018) 156–163.