Novel mesoporous Si@C microspheres as anodes for lithium-ion batteries

Flexible Carbon Nanotubes Confined Yolk-Shelled Silicon-Based Anode with Superior Conductivity for Lithium Storage

The further deployment of silicon-based anode materials is hindered by their poor rate and cycling abilities due to the inferior electrical conductivity and large volumetric changes. Herein, we report a silicon/carbon nanotube (Si/CNT) composite made of an externally grown flexible carbon nanotube (CNT) network to confine inner multiple Silicon (Si) nanoparticles (Si NPs). The in situ generated outer CNTs networks, not only accommodate the large volume changes of inside Si NPs but also to provide fast electronic/ionic diffusion pathways, resulting in a significantly improved cycling stability and rate performance. This Si/CNT composite demonstrated outstanding cycling performance, with 912.8 mAh g-1 maintained after 100 cycles at 100 mA g-1, and excellent rate ability of 650 mAh g-1 at 1 A g-1 after 1000 cycles. Furthermore, the facial and scalable preparation method created in this work will make this new Si-based anode material promising for practical application in the next generation Li-ion batteries.

Fabrication of noble metal nanoparticles decorated on one dimensional hierarchical polypyrrole@MoS2 microtubes

Herein, we present a facile strategy to fabricate noble metal (Ag, Au, Pd) decorated on PPy@MoS₂ microtubes. As a proof of application, the ternary PPy@MoS₂@Au hybrids reveal excellent enzyme-like catalytic performance.

Interactive Fe2O3/porous SiO2 nanospheres for photocatalytic degradation of organic pollutants: Kinetic and mechanistic approach

A uniformly distributed mesoporous silica nanospheres has been successfully synthesized. Silica nanospheres have been loaded with different content of Fe₂O₃ nanoparticles synthesized by the sol-gel process followed by calcination to form the Fe₂O₃ supported on silica nanospheres composite. The as-synthesized photocatalyst has been characterized for crystal structure, morphology, stability, surface area and also surface composition was determined. The photocatalytic oxidation ability of the composite photocatalyst was evaluated by degrading aqueous solutions of Methylene Blue and Congo red dyes under visible light having intense absorption in the wavelength range between 550 and 560 nm. The prime significance of silica is to act as catalyst support for uniform distribution of hematite particles for enhanced catalytic reactivity. Highest degradation has been achieved with 20 wt % loading of hematite nanoparticles indicating the less agglomeration and availability of more catalytic sites. Furthermore, colorless organic pollutants 2-chlorophenol and 2, 4-dichlorophenol have been degraded with high efficiency in the presence of H₂O₂ oxidizer. The scavenger experiments confirmed that hydroxyl radicals are the majorly participating species in this catalytic system. The composite system also shows good recyclability of the materials and advocates the promising nature of the designed system for multiple hazardous environmental contaminants.

Metal-Organic Frameworks-Derived Mesoporous Si/SiOx @NC Nanospheres as a Long-Lifespan Anode Material for Lithium-Ion Batteries

Silicon (Si)-based anode materials with suitable engineered nanostructures generally have improved lithium storage capabilities, which provide great promise for the electrochemical performance in lithium-ion batteries (LIBs). Herein, a metal-organic framework (MOF)-derived unique core-shell Si/SiO_x @NC structure has been synthesized by a facile magnesio-thermic reduction, in which the Si and SiO_x matrix were encapsulated by nitrogen (N)-doped carbon. Importantly, the well-designed nanostructure has enough space to accommodate the volume change during the lithiation/delithiation process. The conductive porous N-doped carbon was optimized through direct carbonization and reduction of SiO₂ into Si/SiO_x simultaneously. Benefiting from the core-shell structure, the synthesized product exhibited enhanced electrochemical performance as an anode material in LIBs. Particularly, the Si/SiO_x @NC-650 anode showed the best reversible capacities up to 724 and 702 mAh g^-1 even after 100 cycles. The excellent cycling stability of Si/SiO_x @NC-650 may be attributed to the core-shell structure as well as the synergistic effect between the Si/SiO_x and MOF-derived N-doped carbon.

Si nanoparticle clusters in hollow carbon capsules (SNC@C) as lithium battery anodes: toward high initial coulombic efficiency

Large volumetric expansion and structural pulverization have been major problems in Si-based anode materials for Li-ion batteries. To overcome this limitation, yolk-shell structured Si-carbon structures have been proposed to allow for the reversible structural breathing of Si nanoparticles confined inside the carbon shell. However, initial coulombic efficiency (ICE) of the yolk-shell structured anodes is highly decreased mainly due to their extremely high specific surface area (SSA) and the resulting excessive formation of solid electrolyte interphase (SEI) over the carbon shell. Here, instead of using a single Si nanoparticle-containing yolk-shell structure, we propose a novel structure comprising hollow carbon capsules internally encapsulating Si nanoparticle clusters (SNC@Cs). To implement this structural design, Si nanoparticle clusters are encompassed by a polystyrene matrix (SNC@PS) by emulsion polymerization, followed by coating with a polydopamine (PDA) layer (SNC@PS@PDA). Then, after annealing them for carbonization, SNC@Cs are finally prepared, which can decrease the SSA by a factor of one-third compared to the conventional yolk-shell structures. These SNC@C particles have shown remarkably high ICE values of up to 81%. Moreover, the cycling stability could be improved up to 100 cycles because the properly confined Si cluster inside the stable carbon capsule mitigates structural pulverization during repeated lithiation-delithiation processes of Si nanoparticles.

Solutions for the problems of silicon-carbon anode materials for lithium-ion batteries

Lithium-ion batteries are widely used in various industries, such as portable electronic devices, mobile phones, new energy car batteries, etc., and show great potential for more demanding applications like electric vehicles. Among advanced anode materials applied to lithium-ion batteries, silicon-carbon anodes have been explored extensively due to their high capacity, good operation potential, environmental friendliness and high abundance. Silicon-carbon anodes have demonstrated great potential as an anode material for lithium-ion batteries because they have perfectly improved the problems that existed in silicon anodes, such as the particle pulverization, shedding and failures of electrochemical performance during lithiation and delithiation. However, there are still some problems, such as low first discharge efficiency, poor conductivity and poor cycling performance, which need to be improved. This paper mainly presents some methods for solving the existing problems of silicon-carbon anode materials through different perspectives.

Two-Dimensional Porous Sandwich-Like C/Si-Graphene-Si/C Nanosheets for Superior Lithium Storage

A novel two-dimensional porous sandwich-like Si/carbon nanosheet is designed and successfully fabricated as an anode for superior lithium storage, where a porous Si nanofilm grows on the two sides of reduced graphene oxide (rGO) and is then coated with a carbon layer (denoted as C/Si-rGO-Si/C). The coexistence of micropores and mesopores in C/Si-rGO-Si/C nanosheets offers a rapid Li⁺ diffusion rate, and the porous Si provides a short pathway for electric transportation. Meanwhile, the coated carbon layer not only can promote to form a stable SEI layer, but also can improve the electric conductivity of nanoscale Si coupled with rGO. Thus, the unique nanostructures offer the resultant C/Si-rGO-Si/C electrode with high reversible capacity (1187 mA h g^-1 after 200 cycles at 0.2 A g^-1), excellent cycle stability (894 mA h g^-1 after 1000 cycles at 1 A g^-1), and high rate capability (694 mA h g^-1 at 5 A g^-1, 447 mA h g^-1 at 10 A g^-1).

A Tremella-Like Nanostructure of Silicon@void@graphene-Like Nanosheets Composite as an Anode for Lithium-Ion Batteries

Graphene coating is receiving discernable attention to overcome the significant challenges associated with large volume changes and poor conductivity of silicon nanoparticles as anodes for lithium-ion batteries. In this work, a tremella-like nanostructure of silicon@void@graphene-like nanosheets (Si@void@G) composite was successfully synthesized and employed as a high-performance anode material with high capacity, cycling stability, and rate capacity. The Si nanoparticles were first coated with a sacrificial SiO2 layer; then, the nitrogen-doped (N-doped) graphene-like nanosheets were formed on the surface of Si@SiO2 through a one-step carbon-thermal method, and the SiO2 layer was removed subsequently to obtain the Si@void@G composite. The performance improvement is mainly attributed to the good conductivity of N-doped graphene-like nanosheets and the unique design of tremella nanostructure, which provides a void space to allow for the Si nanoparticles expanding upon lithiation. The resulting electrode delivers a capacity of 1497.3 mAh g(-1) at the current density of 0.2 A g(-1) after 100 cycles.

Constructing Novel Si@SnO2 Core-Shell Heterostructures by Facile Self-Assembly of SnO2 Nanowires on Silicon Hollow Nanospheres for Large, Reversible Lithium Storage

Developing an industrially viable silicon anode, featured by the highest theoretical capacity (4200 mA h g(-1)) among common electrode materials, is still a huge challenge because of its large volume expansion during repeated lithiation-delithiation as well as low intrinsic conductivity. Here, we expect to address these inherent deficiencies simultaneously with an interesting hybridization design. A facile self-assembly approach is proposed to decorate silicon hollow nanospheres with SnO2 nanowires. The two building blocks, hand in hand, play a wonderful duet by bridging their appealing functionalities in a complementary way: (1) The silicon hollow nanospheres, in addition to the major role as a superior capacity contributor, also act as a host material (core) to partially accommodate the volume expansion, thus alleviating the capacity fading by providing abundant hollow interiors, void spaces, and surface areas. (2) The SnO2 nanowires serve as a conductive coating (shell) to enable efficient electron transport due to a relatively high conductivity, thereby improving the cyclability of silicon. Compared to other conductive dopants, the SnO2 nanowires with a high theoretical capacity (790 mA h g(-1)) can contribute outstanding electrochemical reaction kinetics, further adding value to the ultimate electrochemical performances. The resulting novel Si@SnO2 core-shell heterostructures exhibit remarkable synergy in large, reversible lithium storage, delivering a reversible capacity as high as 1869 mA h g(-1)@500 mA g(-1) after 100 charging-discharging cycles.

Synthesis of Ultrathin Si Nanosheets from Natural Clays for Lithium-Ion Battery Anodes

Two-dimensional Si nanosheets have been studied as a promising candidate for lithium-ion battery anode materials. However, Si nanosheets reported so far showed poor cycling performances and required further improvements. In this work, we utilize inexpensive natural clays for preparing high quality Si nanosheets via a one-step simultaneous molten salt-induced exfoliation and chemical reduction process. This approach produces high purity mesoporous Si nanosheets in high yield. As a control experiment, two-step process (pre-exfoliated silicate sheets and subsequent chemical reduction) cannot sustain their original two-dimensional structure. In contrast, one-step method results in a production of 5 nm-thick highly porous Si nanosheets. Carbon-coated Si nanosheet anodes exhibit a high reversible capacity of 865 mAh g(-1) at 1.0 A g(-1) with an outstanding capacity retention of 92.3% after 500 cycles. It also delivers high rate capability, corresponding to a capacity of 60% at 20 A g(-1) compared to that of 2.0 A g(-1). Furthermore, the Si nanosheet electrodes show volume expansion of only 42% after 200 cycles.

Template-Assisted Hydrothermal Synthesis of Li₂MnSiO₄ as a Cathode Material for Lithium Ion Batteries

Lithium manganese silicate (Li2MnSiO4) is an attractive cathode material with a potential capacity above 300 mA h g(-1) if both lithium ions can be extracted reversibly. Two drawbacks of low electronic conductivity and structural collapse could be overcome by a conductive surface coating and a porous structure. Porous morphology with inner mesopores offers larger surface area and shorter ions diffusion pathways and also buffers the volume changes during lithium insertion and extraction. In this paper, mesoporous Li2MnSiO4 (M-Li2MnSiO4) prepared using MCM-41 as template through a hydrothermal route is compared to a sample of bulk Li2MnSiO4 (B-Li2MnSiO4) using silica as template under the same conditions. Also, in situ carbon coating technique was used to improve the electronic conductivity of M-Li2MnSiO4. The physical properties of these cathode materials were further characterized by SEM, XRD, FTIR, and N2 adsorption-desorption. It is shown that M-Li2MnSiO4 exhibits porous structure with pore sizes distributed in the range 9-12 nm, and when used as cathode electrode material, M-Li2MnSiO4 exhibits enhanced specific discharge capacity of 193 mA h g(-1) at a constant current of 20 mA g(-1) compared with 120.1 mA h g(-1) of B-Li2MnSiO4. This is attributed to the porous structure which allows the electrolyte to penetrate into the particles easily. And carbon-coated M-Li2MnSiO4 shows smaller charge transfer resistance and higher capacity of 217 mA h g(-1) because carbon coating retains the porous structure and enhances the electrical conductivity.

A plum-pudding like mesoporous SiO2/flake graphite nanocomposite with superior rate performance for LIB anode materials

A novel kind of plum-pudding like mesoporous SiO₂ nanospheres (MSNs) and flake graphite (FG) nanocomposite (pp-MSNs/FG) was designed and fabricated via a facile and cost-effective hydrothermal method.

A strategy for suitable mass production of a hollow Si@C nanostructured anode for lithium ion batteries

Si with high theoretical capacity has long suffered from its large volume variation and low electrical transport linked to poor cycling stability and rate performance.