Advancements in Li-Ion Battery Efficiency: A Study on Silicon-Vanadium Carbide Composite Anodes and Liquid Electrolytes
Authors: Choudhury Rohit , Meduri Praveen 
Published: December 2024

The escalating need for mobile consumer electronics and renewable energy storage systems has ignited worldwide attention in high-efficiency lithium-ion batteries (LIBs). The advancement of LIBs, characterized by augmented capacity, prolonged cycle durability, and diminished weight, constitutes the pivotal approaches requisite to meet the demands of future-generation devices [1]. At present, graphite serves as the standard anode material in commercial LIBs. However, its relatively modest theoretical capacity (372 mAh g-1) restricts its utilization in high-energy devices. Conversely, Silicon (Si) emerges as a promising substitute owing to its high theoretical capacity (4200 mAh g-1), abundant availability, and favourable lithium uptake potential (0.4 V vs Li/Li+) [2]. Nevertheless, the practical application of silicon as an anode material is impeded by its significant volume expansion (400-500%) during operation [3].

In this study, our primary objective is to alleviate the volume expansion issue of silicon (Si), thereby leading to the fabrication of high-performance LIBs. To achieve this, Si, in both micro (commercial) and nano size (synthesized using magnesiothermic reduction), have been employed. Initially, Si particles are amalgamated with graphite to form a finely ground mixture (Si-G). This mixture is subsequently combined with a polymer solution to yield pyrolytic carbon, which serves to buffer the mechanical stresses induced by the volumetric expansion of Si. This process also prevents the direct contact of Si with the electrolyte, thereby stabilizing the solid electrolyte interphase (SEI). The integration of a dopant enhances the inherent conductivity of the material, leading to an increase in capacity by facilitating the transport of electrons and lithium ions. To further enhance the performance of the composite, synthesized Mxene vanadium carbide (V2C) is introduced, which promotes charge transport among the Si particles and aids in increasing the lithium-ion diffusion through the material. Density Functional Theory (DFT) simulations are performed to demonstrate that the addition of V2C increases the mobility of Li+ ions through the structure. The morphology and structure of the composite are examined using a range of techniques, including SEM-EDS, TEM, XRD, Raman, and XPS spectroscopy. These analyses reveal the intricate structure of the materials with a uniform distribution of Si, C, and Mxene sheets, with the sheet architecture being preserved.

We also tested different liquid electrolytes (along with additives) with a Si-C composite material as an anode. Galvanostatic Charge/Discharge (GCD) tests, thermal analysis at different temperatures, and other electrochemical characterizations are performed to study the behaviour of the electrolytes and how their individual components affect the overall electrochemical performance of the cell.

The Si-Mxene composite, when employed as an anode, demonstrates exceptional electrochemical performance. This is substantiated by its remarkable lithium storage specific capacity of ~2000 mAh g-1, for micron Si and ~3100 mAhg-1 (for nano Si) which it retains even after prolonged cycling at a high current density. The volume change was reduced from 420% to 150% (for micron Si) and 33% (for nano Si). Furthermore, the composite exhibits superior rate performance, delivering a specific capacity of 2440 mAh g-1 at a 10 C rate, underscoring its suitability for high-power applications. Additionally, the electrode showcases a low charge transfer impedance and rapid electron transport, contributing to its enhanced electrochemical performance. This improvement can be attributed to the unique structure of the composite, which comprises Mxene and doping. This structure significantly augments the diffusion of Li ions and the number of active sites. Consequently, this study presents a viable strategy for the development of high-capacity lithium-ion batteries (LIBs) based on silicon.