Electrospinning Equipment: Enhancing Lithium-Ion Battery Anodes with Silicon-Carbon Nanofibers in Porous Biochar

With the booming development of the electric vehicle and renewable energy storage fields, the demand for high-energy-density and long-life lithium-ion batteries has been increasing rapidly. The traditional graphite anode, with a theoretical capacity of only 372 mAh/g, struggles to meet the performance requirements of next-generation batteries. Silicon-based materials, boasting a high theoretical capacity of 4200 mAh/g and abundant resources, have emerged as highly promising alternatives. However, during charge-discharge cycles, silicon undergoes a 300% volume expansion, leading to issues such as electrode pulverization, active material detachment, and rapid capacity fading. Moreover, this expansion causes the SEI layer to form and rupture repeatedly, increasing impedance and degrading performance. To overcome these limitations, a research team led by Professor Jianfeng Dai from the School of Materials Science and Engineering at Lanzhou University of Technology developed a novel silicon-carbon nanofiber/carbonized Poria powder composite through electrospinning machine and a simple heat treatment process. This composite can effectively mitigate silicon's volume expansion and improve cycling stability and rate performance. This research was published under the title "Enhancement of lithium-ion battery anodes performance by anchoring silicon–carbon nanofibers in porous biochar frameworks" in the internationally renowned journal J Mater Sci: Mater Electron.

The pore structure of CPP (carbonized Poria powder) provides an ideal support framework for silicon-carbon nanofibers. It can effectively absorb and redistribute the stress generated by silicon's volume changes during charge and discharge, thereby preventing electrode pulverization and cracking. This porous structure not only enhances the mechanical strength of the composite material but also provides channels for electrolyte penetration, increasing the contact area between the active material and the electrolyte and thus improving the efficiency of electrochemical reactions.

Figure 1: SEM images of Si@CNFS (a, b); SEM image of CPP (c); SEM images of Si@CNFS/CPP (d, e)

The one-dimensional Si@CNFS (silicon-carbon nanofiber) framework effectively buffers the volume expansion of silicon during charge and discharge. This structure offers mechanical support to silicon particles, limiting the damage to the electrode structure caused by volume changes. At the same time, the one-dimensional framework provides a fast pathway for lithium-ion transport, ensuring efficient ion diffusion and thus enhancing the electrochemical performance of the electrode.

Figure 2: TEM images of Si@CNFS/CPP (a, b, c); diffraction speckle image of Si (d); EBSD images of Si@CNFS (e, f)

The Si@CNFS/CPP composite exhibits excellent electrochemical performance at a current density of 0.1 A g⁻¹, with an initial discharge capacity of 1579.7 mAh g⁻¹ and a charge capacity of 1455.5 mAh g⁻¹. After 1000 cycles, the discharge capacity remains at 1277.2 mAh g⁻¹, with a capacity retention rate of 80.8% and an average capacity loss of only 0.0201% per cycle. These results indicate that the composite has outstanding cycling stability and capacity retention capabilities.

Figure 3: Cycling performance curve of Si@CNFS/CPP and SEM images of the electrode sheet surface before and after cycling

The hierarchical pore structure (including macropores and mesopores) of the Si@CNFS/CPP composite significantly promotes electron and ion transport, enabling it to achieve high-performance operation within a wide current density range from 0.1 to 2 A g⁻¹. Cyclic voltammetry analysis shows that at higher scan rates, the pseudocapacitive contribution reaches 91.56%, exceeding the 89.14% of Si@CNFS. This indicates improved surface reactivity and faster kinetics of the material, thereby enhancing its electrochemical performance.

Figure 4: Cyclic voltammetry (CV) curves of Si@CNFS/CPP at different scan rates (a); Pseudocapacitive contribution analysis of Si@CNFS/CPP (b, c); Cyclic voltammetry (CV) curves of Si@CNFS at different scan rates (d); Pseudocapacitive contribution analysis of Si@CNFS (e, f)

The coulombic efficiency of the Si@CNFS/CPP composite is 76.08% in the first cycle. As the number of cycles increases, the coulombic efficiency gradually improves, reaching 92.91% and 96.80% in the second and third cycles, respectively. This improvement reflects the formation of a stable SEI (solid electrolyte interface) layer. In addition, after 100 cycles, the Warburg coefficient of the composite is only 9.91 Ω s⁻¹/², indicating its low ion diffusion resistance and excellent ion transport properties. These properties are attributed to the material's porous structure and conductive network, which jointly provide efficient channels for the rapid transport of lithium ions.

Figure 5: Cyclic voltammetry (CV) curves of Si@CNFS/CPP, Si@CNFS, and CNFS (a, b, c); Voltage-capacity curves of Si@CNFS/CPP and Si@CNFS in the first three cycles (d, e); Comparison of coulombic efficiency of Si@CNFS/CPP and Si@CNFS materials during the first three charge-discharge cycles (f)

It is worth noting that the nitrogen doping in CNFS (nitrogen-doped carbon nanofibers) significantly improves the conductivity and electrochemical activity of the material. The introduction of nitrogen atoms not only modifies the electronic structure of the carbon framework but also increases the active sites, providing more opportunities for lithium-ion adsorption and insertion. This modification further enhances the overall electrochemical performance of the material.

In conclusion, the preparation and performance of Si@CNFS/CPP effectively address the issues of volume expansion and cycling stability in silicon-based anode materials. The synergistic effect between porous biochar and silicon-carbon nanofibers may offer a promising approach for improving the performance of lithium-ion batteries.

Article Source: https://doi.org/10.1007/s10854-025-14660-y