Highly Conductive Ultrafine N-Doped Silicon Powders Prepared by High-Frequency Thermal Plasma and Their Application as Anodes for Lithium-Ion Batteries

Abstract

Silicon materials are widely regarded as highly promising candidate anodes for the next generation of lithium-ion batteries. However, the violent volume expansion and low intrinsic conductivity hinder their practical application. In this study, ultrafine N-doped silicon powders (N-doped Si) were prepared by using high-frequency thermal plasma (HF-plasma) technology, in which nanocrystallization and N doping were conducted in a single step without the formation of the Si 3 N 4 phase. Through characterization of X-ray photoelectron spectroscopy, X-ray diffraction, and Raman analysis, it is ascertained that N is doped in silicon after HF-plasma treatment. According to the UV−vis and conductivity tests, N-doped Si has a notably narrower bandgap and a higher conductivity than those of undoped Si. N-doped Si with a submicrosphere (N−Si-0.5) delivered a reversible capacity of 974.1 mA h g −1 at 0.2 A g −1 after 50 cycles and an initial Coulombic efficiency (ICE) of 88.72%. Even at 6 A g −1 , N−Si-0.5 can still exhibit a high reversible capacity of 200.5 mA h g −1 , while Si without doping (N−Si-0.0) only gives a reversible capacity of 526.8 mA h g −1 at 0.2 A g −1 after 50 cycles with an ICE of 85.81% and an unnoticeable capacity at 6 A g −1 . It is clear that Si shows higher ICE, better cycle stability, and rate performance. For further enhancement of the electrochemical performances of N-doped Si, the Si nanowires (NW-Si) were prepared. Experimental results showed that the initial capacity, ICE, and rate performance all gradually improved as the N 2 flow rate increased. NW-Si-1.0 has an initial capacity of 2725.7 mA h g −1 and an ICE of 80.18%. Even at 6 A g −1 , it can provide a reversible capacity of 584.7 mA h g −1 . The enhanced electrochemical performances of N-doped Si can be ascribed to the introduction of the N dopant and nanowire, which raised carrier concentration, accelerated electron transfer, and alleviated volume expansion.

Recent Advances in Conductive Polymers-Based Electrochemical Sensors for Biomedical and Environmental Applications

“…Commonly used anode materials include chromium, gold, nickel, palladium, and titanium platinum-coated electrodes, as well as indium tin oxide-coated glass plates. Additionally, semiconductor materials such as n-doped silicon [ 22 ], cadmium sulfide [ 23 ] and semi-metallic graphite [ 24 ] are employed for the electrochemical growth of CPs films. This synthetic approach enables the preparation of independent, homogeneous, self-doped thin films while also allowing for copolymerization and grafting reactions to occur if desired.…”

Silicon-Based Nanocomposite Anodes with Excellent Cycle Life for Lithium-Ion Batteries Achieved by the Synergistic Effect of Two Silicides

“…[11][12][13] Several approaches have been employed to address the aforementioned limitations. They include the synthesis of nanostructured Si materials (i.e., nanoparticles, nanowires, and nanorods) to relieve Si-generated stress, [14][15][16][17][18][19] Si coating using conductive materials to reduce the electrical resistivity of Si, 20,21 doping of Si with impurities (e.g., phosphorus and boron) to improve its electrical conductivity and alter its phase transition behavior, [22][23][24][25][26][27] and prelithiation of Si to enhance the initial CE. [28][29][30] Furthermore, we proposed futuristic Si-based active materials, e.g., binary silicide/Si composites, to address the limitations of Si.…”