(365c) Enhancing Lithium-Ion Batteries: A Study of Silicon-Based Anodes and Electrolyte Systems

The growing demand for mobile consumer electronics and renewable energy storage systems has intensified global interest in high-efficiency lithium-ion batteries (LIBs). These advanced LIBs are characterized by increased capacity, extended cycle durability, and reduced weight, making them essential for next-generation devices. While graphite currently serves as the standard anode material in commercial LIBs, its modest theoretical capacity (372 mAh g ^-1 ) limits its use in high-energy applications. In contrast, silicon (Si) offers promise due to its high theoretical capacity (4200 mAh g ^-1 ), widespread availability, and favorable lithium uptake potential (0.4 V vs Li/Li+). However, practical implementation of silicon as an anode material faces challenges related to its substantial volume expansion (400-500%) during operation.

Our research aims to mitigate the volume expansion issue associated with silicon, ultimately leading to the development of high-performance LIBs. To achieve this, we employ both micro-sized (commercial) and nano-sized silicon particles synthesized via magnesiothermic reduction. Initially, silicon particles are combined with graphite to create a finely ground mixture (Si-G). Subsequently, this mixture is integrated with a polymer solution to produce pyrolytic carbon, which acts as a buffer against the mechanical stresses arising from silicon’s volumetric expansion. This process also prevents direct contact between silicon and the electrolyte, thereby stabilizing the solid electrolyte interphase (SEI). The addition of a dopant enhances material conductivity, facilitating electron and lithium ion transport. Furthermore, we introduce synthesized Mxene vanadium carbide (V ₂ C) to enhance charge transport among silicon particles and improve lithium-ion diffusion. Density Functional Theory (DFT) simulations demonstrate that V ₂ C increases Li+ ion mobility within the structure. Morphological and structural analyses using SEM-EDS, TEM, XRD, Raman, and XPS spectroscopy reveal the intricate architecture of the composite, with uniform distribution of silicon, carbon, and Mxene sheets.

We systematically evaluate various liquid electrolytes (including additives) in conjunction with the Si-C composite anode. Galvanostatic Charge/Discharge (GCD) tests, thermal analyses at different temperatures, and other electrochemical characterizations provide insights into electrolyte behavior and the impact of individual components on overall cell performance. The Si-Mxene composite, when employed as an anode, exhibits exceptional electrochemical performance. It achieves a remarkable lithium storage specific capacity of 2010 mAh g ^-1 for micron-sized silicon and ~3150 mAh g ^-1 for nano-sized silicon, even after extensive cycling at high current densities. Notably, volume expansion is reduced from 420% to 153% (for micron-sized silicon) and 33% (for nano-sized silicon). Additionally, the composite demonstrates superior rate capability, delivering a specific capacity of 2438 mAh g ^-1 at a 10 C rate, making it suitable for high-power applications. The electrode exhibits low charge transfer impedance and rapid electron transport, attributed to the unique composite structure comprising Mxene and doping. Overall, our study presents a viable strategy for developing high-capacity lithium-ion batteries based on silicon.