Silicon (Si) anodes have emerged as a promising candidate for next-generation lithium-ion batteries (LIBs) due to their high theoretical capacity of 4200 mAh/g, which is approximately ten times higher than that of conventional graphite anodes. However, the practical application of Si anodes is hindered by their poor electrical conductivity (~10^-3 S/cm) and significant volume expansion (>300%) during lithiation, leading to mechanical degradation and capacity fading. To address these challenges, MXenes—a family of two-dimensional transition metal carbides and nitrides—have been employed as conductive coatings. Recent studies demonstrate that Ti3C2Tx MXene-coated Si anodes exhibit a remarkable enhancement in conductivity, reaching up to 10^2 S/cm, while maintaining structural integrity over 500 cycles. This improvement is attributed to the intrinsic metallic conductivity of MXenes (~10^4 S/cm) and their ability to form a conformal, flexible layer that accommodates volume changes.
The interfacial engineering between MXene coatings and Si particles plays a critical role in optimizing electrochemical performance. Advanced characterization techniques, such as in situ transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), reveal that the MXene-Si interface facilitates efficient charge transfer with a low interfacial resistance of ~5 Ω·cm². Furthermore, the hydrophilic nature of MXenes enables uniform dispersion of Si particles during electrode fabrication, reducing agglomeration and enhancing electrode homogeneity. Experimental results show that MXene-coated Si anodes achieve a specific capacity of 2500 mAh/g at 0.1 C with a Coulombic efficiency exceeding 99.5%, outperforming uncoated Si anodes by ~40%. This performance is sustained at higher current densities, with a capacity retention of 80% after 1000 cycles at 1 C.
The mechanical robustness imparted by MXene coatings significantly mitigates the pulverization of Si anodes during cycling. Nanoindentation studies reveal that the Young’s modulus of MXene-coated Si electrodes increases from ~50 GPa to ~120 GPa, enhancing their resistance to fracture. Additionally, the layered structure of MXenes acts as a buffer layer, reducing stress concentrations and preventing crack propagation. Finite element simulations corroborate these findings, showing that the maximum von Mises stress in MXene-coated Si particles decreases by ~60% compared to bare Si particles. These mechanical improvements translate into superior cycling stability, with capacity retention exceeding 85% after 500 cycles at 0.5 C.
The scalability and cost-effectiveness of MXene-coated Si anodes have been demonstrated through pilot-scale production using roll-to-roll manufacturing techniques. By optimizing the MXene synthesis process—such as reducing etching time from 24 hours to 2 hours—the production cost has been lowered to $10/kg for Ti3C2Tx MXenes. Moreover, the use of aqueous-based slurries for electrode fabrication eliminates the need for toxic solvents, aligning with green chemistry principles. Large-format pouch cells incorporating MXene-coated Si anodes exhibit energy densities exceeding 350 Wh/kg with minimal capacity fade (<5%) over 200 cycles under practical operating conditions.
Future research directions include exploring alternative MXene compositions (e.g., Mo2CTx and Nb2CTx) to further enhance conductivity and mechanical properties. Computational studies predict that Mo2CTx-coated Si anodes could achieve conductivities exceeding 10^3 S/cm due to their higher density of states near the Fermi level. Additionally, hybrid coatings combining MXenes with other conductive materials (e.g., graphene or carbon nanotubes) are being investigated to create synergistic effects for ultrahigh-performance LIBs.
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