SiOx Shell Research Articles

Plasma enabled in-situ deposition of hybrid structured SiOx/C on polymorphous carbon hosts for superior lithium storage

SiOx anode is a potential anode of lithium-ion batteries due to its lower cost, processability, and cycling stability. However, the application of SiOx is still limited by its low conductivity, large volume change and low initial Coulombic efficiency (ICE). This work employs the flexible and controllable active screen plasma to prepare a series of SiOx/C composites with high ICE and specific capacity. The comparative study demonstrates that SiOx/CMK-3 with a hybrid structure supported by the porous structure and three-dimensional carbon skeleton of CMK-3 exhibits better structural stability and higher SiOx loading. Through further temperature regulation, the optimized SiOx/CMK-3 exhibits high rate capability, high ICE (76.7%) and excellent cycling stability (618.9 mAh·g−1 after 4000 cycles at 1Ag-1). The morphology structure and electrochemical behavior analysis reveals that the high capacity and ICE are attributed to the protection of SiOx by nanostructured SiOx, porous carbon structures and SiOx shells, while the pores of CMK-3 can effectively suppress volume expansion and reduce contact with the electrolyte to prevent repeated generation of new SEI. In addition, the carbon matrix and mesoporous channels of CMK-3 endow SiOx/CMK-3 with high conductivity and diffusion kinetics. This study provides new ideas and methods for preparing high-performance silicon-carbon anodes.

Cu3Si-Modified Silicon Nanoparticles Encapsulated within SiOx and Hollow Carbon for Lithium-Ion Battery Anodes

Silicon (Si), a promising anode material for lithium-ion batteries, usually suffers from low capacity retention and poor rate performance due to its huge volume change issue and low electronic conductivity. The synergistic effect brought by the composite of carbon, metal silicide, and silicon is proven to be an effective measure to enhance the performance of silicon-based anodes. Herein, Cu3Si-modified silicon nanoparticles (SiNPs) encapsulated within SiOx and hollow carbon shell (M-Si@H-C) are designed and constructed by an electroless deposition and pyrolysis process, which delivers high specific capacity (1150 mAh g–1 at 0.21 A g–1 and 450 mAh g–1 at 8.4 A g–1) and long cycling stability (86.3% capacity retention after 200 cycles at 1 A g–1). The nanostructure and formation mechanism of the M-Si@H-C is elucidated by employing X-ray diffraction and transmission electron microscopy techniques. The enhancement to the lithium storage performance of the nanostructure is clarified on the basis of the microstructure investigation and electrochemical determination.

SiOx encapsulated FeSi2–Si eutectic nanoparticles as durable anode of lithium-ion batteries

Low-cost and high-efficiency production of silicon-based material is the key to improve the energy density of lithium-ion batteries. Herein, we propose a novel structure of FeSi2–Si eutectic nanoparticles protected by the SiOx shell. FeSi2, as a buffer phase can improve the electrochemical stability of the electrode. A SiOx shell is formed on the surface of the nanoparticles through the passivation process. SiOx encapsulated FeSi2–Si eutectic nanoparticles exhibit excellent capacity of 674.9 mAh/g after 500 charge/discharge cycles. The capacity retention rate is above 90% after the stabilization process. This work provides a new nanomaterial design for high performance silicon-based anode materials of lithium-ion batteries.

Efficiently Luminescent and Stable Lead‐free Cs3Cu2Cl5@Silica Nanocrystals for White Light‐Emitting Diodes and Communication

AbstractThe poor stability of lead‐free Cs3Cu2Cl5nanocrystals (NCs) is the main impediment for their broad practical applications. Here, a sol‐gel reaction using tetraethoxysilane (TEOS) as the silica coating precursor to prepare Cs3Cu2Cl5@SiOxNCs is proposed. Due to the efficient passivation and robust protection of SiOxshells on the NCs surface, Cs3Cu2Cl5@SiOxNCs solution and films exhibit a high photoluminescence quantum yield of 98% and 76%, respectively, and improved stability against water and heat. Cs3Cu2Cl5@SiOxNCs are then used to fabricate warm white light‐emitting diodes (WLEDs), which show a high color‐rendering index of 94 and a proper correlated color temperature of 5049 K, and maintain an excellent thermal (265–360 K) and prolonged operating (380 h) stability. In addition, the good white light emission facilitates the application in visible light communication (VLC). The VLC light source demonstrates a −3 dB bandwidth of 420 kHz, and the achieved data rate of the VLC system reaches 2.65 Mbps using orthogonal frequency division multiplexing modulation with a bit loading. As a result, lead‐free Cs3Cu2Cl5@SiOxNCs with an efficient optical performance and an excellent stability might promote the development of stable NCs and extend the applications in optoelectronics.

Highly Selective Photocatalytic CO2 Reduction to CH4 by Ball-Milled Cubic Silicon Carbide Nanoparticles under Visible-Light Irradiation.

The ultimate goal of photocatalytic CO2 reduction is to achieve high selectivity for a single product with high efficiency. One of the most significant challenges is that expensive catalysts prepared through complex processes are usually used. Herein, gram-scale cubic silicon carbide (3C-SiC) nanoparticles are prepared through a top-down ball-milling approach from low-priced 3C-SiC powders. This facile mechanical milling strategy ensures large-scale production of 3C-SiC nanoparticles with an amorphous silicon oxide (SiOx) shell and simultaneously induces abundant surface states. The surface states are demonstrated to trap the photogenerated carriers, thus remarkably enhancing the charge separation, while the thin SiOx shell prevents 3C-SiC from corrosion under visible light. The unique electronic structure of 3C-SiC tackles the challenge associated with low selectivity of photocatalytic CO2 reduction to C1 compounds. In conjugation with efficient water oxidation, 3C-SiC nanoparticles can reduce CO2 into CH4 with selectivity over 90%.

Self-confined vapour-liquid-solid growth of SnS/SiOx core/shell nanowires

Tin sulfide/silicon oxide (SnS/SiOx) core/shell nanowires (NWs) were synthesized by a catalyst-free chemical vapor deposition (CVD) technique using SnS powder as the source material. The morphology and microstructure of the as-prepared NWs were characterized, and it was found that the NWs have core/shell structures composed of crystalline orthorhombic SnS cores and amorphous SiOx shells. Interestingly, there were holes encapsulated in the core/shell NWs to separate the SnS cores into segments. Based on the examinations on the morphology evolution of the NWs, we propose a self-confined vapour-liquid-solid (VLS) growth mechanism, in which silicon oxide shells confined the lateral growth of SnS cores resulting in the formation of core/shell NWs.

Large scale synthesis of Si3N4@SiOx core-shell structure nanowires by direct nitridation

In this work, millimeter-scale Si3N4@SiOx core-shell structure nanowires were synthesized using the direct nitridation method without the use of catalysts. The silicon powders used as raw materials were pretreated at 1300 °C for 3 h under ammonia. The ammonia was then converted into a nitrogen/hydrogen gas mixture and heated at 1350 °C for another 5 h. The morphology and structure of the as-obtained nanowires were investigated in detail. The Si3N4@SiOx nanowires with a core-shell structure were composed of a crystalline α-Si3N4 core and an amorphous SiOx shell. The formation of the α-Si3N4 core nanowire is due to the reaction of the N2 gas with the byproduct SiO gas. However, the formation of the amorphous SiOx shell is related to the deposition location of the samples. For the inner part of the samples, the SiOx shell derives from the deposition of the byproduct SiO gas at 1350 °C, while the SiOx shell of the external part of the samples likely derives from the oxidation of the silicon nitride core during the cooling process.

Double-shell-structured Si@SiOx@C composite material for long-life lithium-ion storage

Double-shell-structured Si@SiOx@C composite material was prepared by aqueous etching with ammonium hydroxide and citric acid pyrolysis. The combination of Si with a double shell of SiOx and carbon shell has outstanding structural advantages. As Si anode has high specific capacity, SiOx is more stable during cycling and carbon has high conductivity. The excellent stability of SiOx during cycling compared with Si is profit from Li-oxide and Li-silicate generated by the reaction of Li+ with Si and O elements, which help to lead excellent cyclic performance. The Si@SiOx@C composite electrode demonstrates excellent electrochemical performance with high cyclic stability. The composite electrode has an initial reversible specific capacity of 575.3 mAhg−1 and capacity retention as high as 74.7% even after 400 cycles. The method used for the preparation of double-shell-structured Si@SiOx@C composite is easy and mass-productive, which could be applied for long-life lithium-ion battery anode materials.

An eggshell-structured N-doped silicon composite anode with high anti-pulverization and favorable electronic conductivity

Silicon is the most promising anode alternative for the next generation of lithium-ion batteries. However, the capacity of Si anodes quickly fades because of its large volume change during lithiation/delithiation, which heavily prevents its practical use. To alleviate this problem, herein, we design and prepare a microscale N-doped Si composite that has an eggshell structure. Mechanical milling of the sintered Si-xLiNH2 mixtures under a CO2 atmosphere leads to the successful in situ creation of a ~10 nm thick amorphous Li2CO3 and SiOx shell containing well-dispersed Si3N4 nanocrystals on the surface of Si microparticles. The fine and dispersed Si3N4 nanocrystals significantly enhance the mechanical properties of the amorphous shell, providing it with remarkable hardness and toughness, consequently hindering the pulverization of the micro-Si particles during lithiation/delithiation. Moreover, doping with N improves the electrical conductivity of the Si composites, and the in situ-formed Li2CO3 contributes to a stable SEI layer on the electrode surface. Thus, the N-doped micro-Si composite with an eggshell structure demonstrates excellent electrochemical properties including a high initial reversible capacity (1820 mA h g−1), a reasonable cycle performance (1020 mA h g−1 after 600 cycles), and a good rate capability (1117 mA h g−1 at 2000 mA g−1).

Nitrogen Plasma-Treated Core-Bishell Si@SiOx@TiO2-δ: Nanoparticles with Significantly Improved Lithium Storage Performance.

Si-based anode materials have attracted considerable attention because of their ultrahigh reversible capacity. However, poor cycling stability caused by the large volume change during cycling prevented the commercial application of Si anodes for lithium-ion batteries (LIBs). To overcome these challenges, in the present study, we designed a nitrogen plasma-treated core-bishell nanostructure where the Si nanoparticle was encapsulated into a SiOx shell and N-doped TiO2-δ shell. Here, the SiOx inside the shell and the TiO2 outside the shell act as binary buffer matrices to accommodate the large volume change and also help to stabilize the solid electrolyte interphase films on the shell surface. More importantly, the plasma-induced N-doped TiO2-δ shell with many Ti3+ species and oxygen vacancies plays a key role in improving the electrical conductivity of Si anodes. Owing to the synergistic effects of SiOx and N-doped TiO2-δ bishells, the cycling stability and rate performance of Si anodes are significantly enhanced. The as-obtained sample exhibits superior cycling stability with a capacity retention of 650 mA h g-1 at 200 mA g-1 after 300 cycles. This strategy is favorable for improving the electrochemical performances of Si-based anodes to employ in practical LIBs.

Oxygen precipitate positive charge evolution upon annealing of oxygen implanted silicon

Oxygen precipitates (OPs) formed by the annealing of oxygen implanted silicon samples at diverse temperatures in the ranges from 700°C to 1100°С have been investigated with capacitance-voltage and transmission electron microscopy techniques. An increase of the OP sizes with the increasing temperature was found to accompany with a decrease of the OP embedded positive charge being inversely proportional to the formers. The obtained result showed that the positive charge is localized in SiOx shell of predominantly stoichiometric OP core.

Strain engineering of core–shell silicon carbide nanowires for mechanical and piezoresistive characterizations

This study evaluated the mechanical properties and piezoresistivity of core–shell silicon carbide nanowires (C/S-SiCNWs) synthesized by a vapor–liquid–solid technique, which are a promising material for harsh environmental micro electromechanical systems (MEMS) applications. The C/S-SiCNWs were composed of a crystalline cubic (3C) SiC core wrapped by an amorphous silicon dioxide (SiOx) shell; however, TEM observations of the NWs showed that hexagonal polytypes (2H, 4H , and 6H) were partially induced in the core by a stacking fault owing to a Shockley partial dislocation. The stress–strain relationship of the C/S-SiCNWs and SiC cores without an SiOx shell was examined using MEMS-based nanotensile tests. The tensile strengths of the C/S-SiCNWs and SiC cores were 7.0 GPa and 22.4 GPa on average, respectively. The lower strength of the C/S-SiCNWs could be attributed to the SiOx shell with the surface roughness as the breaking point. The Young’s modulus of the C/S-SiCNWs was 247.2 GPa on average, whereas that of the SiC cores had a large value with scatter data ranging from 450 to 580 GPa. The geometrical model of the SiC core based on the transmission electron microscopy observations rationalized this scatter data by the volume content of the stacking fault in the core. The piezoresistive effects of the C/S-SiCNW and SiC core were also evaluated from the I–V characteristics under uniaxial tensile strain. The gauge factor of –30.7 at 0.008 ε for the C/S-SiCNW was approximately two-times larger than that of –15.8 at 0.01 ε for the SiC core. This could be caused by an increase of the surface state density at the SiOx/SiC interface owing to the positive fixed oxide charge of the SiOx shell.

In Situ Transmission Electron Microsopy of Oxide Shell-Induced Pore Formation in (De)lithiated Silicon Nanowires

Silicon (Si) nanowires with a silicon oxide (SiOx) shell undergoing lithiation and delithiation were examined by in situ transmission electron microscopy (TEM). Large pores formed in the nanowires during the delithiation cycle. We found that the oxide shell constrains the expansion of the Si nanowires during lithitation and then induces pore formation in the nanowires. We propose that the SiOx shell prevents the vacancies that result from the loss of lithium from escaping the Si core, leading to pore nucleation and growth. It is also possible that the difference in mechanical properties of the expanding and contracting Si nanowire and SiOx shell contribute to the observed pore formation. This in situ study reaffirms the need to directly observe structural changes that occur during cycling in battery materials, especially when modified by coatings.

Forming-free resistive switching in solution-processed silicon nanocrystal thin film

We report a forming-free resistive switching using a solution-processed silicon nanocrystal (Si NC) thin film. A Si NC thin film is formed on an ITO/glass substrate by spin-coating a colloidal Si NC solution in air. The Si NC thin film shows bipolar resistive switching without a forming process. Electrical characteristics at low temperatures and in various gas environments suggest that a non-stoichiometric SiOx shell on Si NCs contributes to the resistive switching. We propose that the origin of the resistive switching is a conductive filament of oxygen vacancies on the SiOx shell by an electric field.

Formation of SiOx shell on Si nanoparticles and its effects on electrochemical properties as a Li-ion battery's anode

Crystalline Si core–amorphous SiOx shell nanoparticles were synthesized from SiCl4 using an atmospheric microwave plasma process and their microstructures were investigated. It was found that the amorphous SiOx shell thickness was determined by varying the applied microwave power. The increase of applied power directly increased the length of the flame at the end of the plasma. Through observation of the microstructures with varying lengths of the flame, it was found that a highly crystalline Si phase was formed in the plasma and amorphous SiOx phase was formed in the flame. The longer flame resulted in the thicker SiOx shell around the Si core. The electrochemical properties of the varying SiOx shell thicknesses were also investigated in that the synthesized Si-SiOx nanoparticles were used as anode materials in a lithium-ion battery (LIB). Thin shells such as native oxide did not influence the electrochemical behaviour of the Si core, whilst some shells were too thick to allow Li-ions to react with the Si core. Using Si-SiOx nanoparticles with the optimum SiOx:Si ratio of 18:82, the following electrochemical properties were obtained: a first reversible capacity of 932 mAh/g, an initial columbic efficiency (ICE) of 52.5%, and a capacity retention of 83.7% at the 100th cycle.

A novel combined experimental and multiscale theoretical approach to unravel the structure of SiC/SiOx core/shell nanowires for their optimal design.

In this work we propose a realistic model of nanometer-thick SiC/SiOx core/shell nanowires (NWs) using a combined first-principles and experimental approach. SiC/SiOx core/shell NWs were first synthesised by a low-cost carbothermal method and their chemical-physical experimental analysis was accomplished by recording X-ray absorption near-edge spectra. In particular, the K-edge absorption lineshapes of C, O, and Si are used to validate our computational model of the SiC/SiOx core/shell NW architectures, obtained by a multiscale approach, including molecular dynamics, tight-binding and density functional simulations. Moreover, we present ab initio calculations of the electronic structure of hydrogenated SiC and SiC/SiOx core/shell NWs, studying the modification induced by several different substitutional defects and impurities into both the surface and the interfacial region between the SiC core and the SiOx shell. We find that on the one hand the electron quantum confinement results in a broadening of the band gap, while hydroxyl surface terminations decrease it. This computational investigation shows that our model of SiC/SiOx core/shell NWs is capable to deliver an accurate interpretation of the recorded X-ray absorption near-edge spectra and proves to be a valuable tool towards the optimal design and application of these nanosystems in actual devices.

Field-emission property of self-purification SiC/SiOx coaxial nanowires synthesized via direct microwave irradiation using iron-containing catalyst

SiC/SiOx coaxial nanowires were rapidly synthesized via direct microwave irradiation in low vacuum atmosphere. During the preparation process, only graphite, silicon, silicon dioxide powders were used as raw materials and iron-containing substance was employed as catalyst. Comprehensive characterizations were employed to investigate the microstructure of the products. The results showed that a great quantity of coaxial nanowires with uniform sizes and high aspect ratio had been successfully achieved. The coaxial nanowires consist of a silicon oxide (SiOx) shell and a β-phase silicon carbide (β-SiC) core that exhibited in special tube brush like. In additional, nearly all the products were achieved in the statement of pure SiC/SiOx coaxial nanowires without the existence of metallic catalyst, indicating that the self-removal of iron (Fe) catalyst should be occurred during the synthesis process. Photoluminescence (PL) spectral analysis result indicated that such novel SiC/SiOx coaxial nanowires exhibited significant blue-shift. Besides, the measurement results of field-emission (FE) demonstrated that the SiC/SiOx coaxial nanowires had ultralow turn-on field and threshold field with values of 0.2 and 2.1 V/μm, respectively. The hetero-junction structure formed between SiOx shell and SiC core, lots of emission sites, as well as clear tips of the nanowires were applied to explain the excellent FE properties.

Si-SiOx nanoparticles Synthesis for Lithium-Ion Battery Anode Material By Atmospheric Pressure Microwave Plasma

Si-SiOx nanoparticles with core-shell structure were synthesized by atmospheric microwave plasma using tetrachloride silicon. Crystalline Si core and amorphous SiOx shell could be controlled by various process conditions. In order to determine the Si-SiOx core-shell ratio for application to anode materials in lithium-ion battery, microstructures and electrochemical properties of synthesized Si-SiOx nanoparticles with various core-shell ratios were investigated. From a result of HR-TEM analysis, there are Si nanoparticles with thickness of 1~3 nm SiOx shell which are only native oxide layer on crystalline Si core. Typical electrochemical behaviour of Si such as high initial reversible capacity and poor retention was observed in those nanoparticles. The shell thickness of Si-SiOx nanoparticles affects the electrochemical properties such as first reversible capacity, retention. For example, nanoparticles with shell thickness of 10 nm exhibited the first reversible capacity of about 1,274 mAh/g and retention at 50th cycle of about 94.8 %. As a result, electrochemical properties could be controlled by the core-shell ratios of Si-SiOx nanoparticles.

Quantitative relationships between microstructures and electrochemical properties in Si core-SiOx shell nanoparticles for Li-ion battery anodes

Abstract Nanoparticles having four different ratios of crystalline silicon (Si) cores and amorphous SiOx shells were synthesized by using a microwave-generated plasma. Their microstructures were analyzed to find quantitative relationships with electrochemical properties. By measuring XRD, SEM, HR-TEM, and Raman spectra of four samples with different core-shell microstructures, the quantitative fractions of crystalline Si core and amorphous SiOx shell in the nanoparticles were calculated. Also, electrochemical properties of the nanoparticles were measured and compared with the calculated fractions. The electrochemical properties such as the initial reversible capacity, the initial coulombic efficiency, and the capacity retention exhibited tendencies remarkably similar to those implied by the calculated fractions. Analysis of each sample's dQ/dV profile also gave us good evidence of understandable relationships between the fractions and electrochemical properties. Details of calculating the fractions from microstructural data are given, with suitable consideration having been given to the fact that several assumptions could lead to errors during the analysis. The approach introduced in this research offers a good means of analysis with which to further the optimal design of nanoparticle microstructure for Li-ion battery anodes.

Effect of hydrogen on the microstructure and electrochemical properties of Si nanoparticles synthesized by microwave plasma

We synthesized silicon (Si) nanoparticles using an atmospheric microwave plasma process, and investigated the effects of hydrogen (H2) injection on their microstructure during the synthesis. Two nozzles were applied to inject H2 (swirling and rectilinear H2). Our microstructural analysis indicated that the amount and method of H2 injection were critical for completion of the reaction from silicon tetrachloride (SiCl4) to Si, as well as to obtain highly crystalline Si nanoparticles. The swirling H2 was especially critical due to its formation of vortex flow, which allowed relatively long residence time of the H-ions in plasma. The Si nanoparticles synthesized by the atmospheric plasma process had core-shell structures that consisted of crystalline Si cores with amorphous SiOx shells of 5–15 nm thickness. We also investigated the feasibility of the synthesized Si nanoparticles as anode materials in a lithium-ion battery (LIB). For the core-shell structured Si nanoparticles, we obtained the first reversible capacity of 1204 mAhg−1, and a capacity retention of 82.2% at the 50th cycle.