Carbon-Coated SiO2 Composites as Promising Anode Material for Li-Ion Batteries

Porous silica-based materials are a promising alternative to graphite anodes for Li-ion batteries due to their high theoretical capacity, low discharge potential similar to pure silicon, superior cycling stability compared to silicon, abundance, and environmental friendliness. However, several challenges prevent the practical application of silica anodes, such as low coulombic efficiency and irreversible capacity losses during cycling. The main strategy to tackle the challenges of silica as an anode material has been developed to prepare carbon-coated SiO₂ composites by carbonization in argon atmosphere. A facile and eco-friendly method of preparing carbon-coated SiO₂ composites using sucrose is reported herein. The carbon-coated SiO₂ composites were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, transmission and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, cyclic voltammetry, and charge–discharge cycling. A C/SiO₂-0.085 M calendered electrode displays the best cycling stability, capacity of 714.3 mAh·g⁻¹, and coulombic efficiency as well as the lowest charge transfer resistance over 200 cycles without electrode degradation. The electrochemical performance improvement could be attributed to the positive effect of the carbon thin layer that can effectively diminish interfacial impedance.     

Double-Shelled Hollow SiO2@N-C Nanofiber Boosts the Lithium Storage Performance of [PMo12O40]3−

Polyoxometalates (POMs)-based materials, with high theoretical capacities and abundant reversible multi-electron redox properties, are considered as promising candidates in lithium-ion storage. However, the poor electronic conductivity, low specific surface area and high solubility in the electrolyte limited their practical applications. Herein, a double-shelled hollow PMo₁₂−SiO₂@N−C nanofiber (PMo₁₂−SiO₂@N−C, where PMo₁₂ is [PMo₁₂O₄₀]³⁻, N−C is nitrogen-doped carbon) was fabricated for the first time by combining coaxial electrospinning technique, thermal treatment and electrostatic adsorption. As an anode material for LIBs, the PMo₁₂−SiO₂@N−C delivered an excellent specific capacity of 1641 mA h g⁻¹ after 1000 cycles under 2 A g⁻¹. The excellent electrochemical performance benefited from the unique double-shelled hollow structure of the material, in which the outermost N−C shell cannot only hinder the agglomeration of PMo₁₂, but also improve its electronic conductivity. The SiO₂ inner shell can efficiently avoid the loss of active components. The hollow structure can buffer the volume expansion and accelerate Li⁺ diffusion during lithiation/delithiation process. Moreover, PMo₁₂ can greatly reduce charge-resistance and facilitate electron transfer of the entire composites, as evidenced by the EIS kinetics study and lithium-ion diffusion analysis. This work paves the way for the fabrication of novel POM-based LIBs anode materials with excellent lithium storage performance.     

Electrophoretic Deposition of Binder‐Free MnO2/Graphene Films for Lithium‐Ion Batteries

Binder‐free, nano‐sized needlelike MnO₂ ‐submillimeter‐sized reduced graphene oxide (nMnO₂‐srGO ) hybrid films with abundant porous structures were fabricated through electrophoretic deposition and subsequent thermal annealing at 500 °C for 2 h. The as‐prepared hybrid films exhibit a unique hierarchical morphology, in which nMnO₂ with a diameter of 20—50 nm and a length of 300—500 nm is randomly anchored on both sides of srGO . When evaluated as binder‐free anodes for lithium‐ion half‐cell, the nMnO₂‐srGO composites with a content of 76.9 wt% MnO₂ deliver a high capacity of approximately 1652.2 mA •h•g⁻¹ at a current density of 0.1 A•g⁻¹ after 200 cycles. The high capacity remains at 616.8 mA •h•g⁻¹ (ca. 65.1% capacity retention) at a current density as high as 4 A•g⁻¹. The excellent electrochemical performance indicates that the nMnO₂‐srGO hybrid films could be a promising anode material for lithium ion batteries (LIBs ).     

Nickel-cermet electrodes for high-temperature electrochemical devices made using nanomaterials

Characteristics of nickel-cermet anodes obtained from weakly aggregated NiO nanopowders made by wire electric blasting (NiO/WEB) were studied. Electrodes made of NiO/WEB nanopowders have low sheet resistance (<0.1 Ohm) and high electrochemical activity (R _η = 0.06–0.09 Ohm cm² at 850–900°C). Prolonged studies of symmetric cells of the (0.9H₂ + 0.1H₂O) Ni-SSZ + CeO₂/YSZ/CeO₂ + Ni-SSZ (0.9H₂ + 0.1H₂O) type at the temperature of 850°C showed that the electrodes preserve sufficiently high activity (R _η < 0.1 Ohm cm²) for 1000 h. Using a NiO-WEB powder allows not performing presynthesis of nickel-cermet and decreasing the anode baking temperature to 1200°C.     

How xerogel carbonization conditions affect the reactivity of highly disperse SiO<Subscript>2</Subscript>–C composites in the sol–gel synthesis of nanocrystalline silicon carbide

A transparent silicon polymer gel was prepared by sol–gel technology to serve as the base in the preparation of highly disperse SiO₂–C composites at various temperatures (400, 600, 800, and 1000°C) and various exposure times (1, 3, and 6 h) via pyrolysis under a dynamic vacuum (at residual pressures of ~1 × 10^–1 to 1 × 10^–2 mmHg). These composites were X-ray amorphous; their thermal behavior in flowing air in the range 20–1200°C was studied. The encapsulation of nascent carbon, which kept it from oxidizing in air and reduced the reactivity of the system in SiC synthesis, was enhanced as the carbonization temperature and exposure time increased. How xerogel carbonization conditions affect the micro- and mesostructure of the xerogel was studied by ultra-small-angle neutron scattering (USANS). Both the carbonization temperature and the exposure time were found to considerably influence structure formation in highly disperse SiO₂–C composites. Dynamic DSC/DTA/TG experiments in an inert gas flow showed that the increasing xerogel pyrolysis temperatures significantly reduced silicon carbide yields upon subsequent heating of SiO₂–C systems to 1500°C, from 35–39 (400°C) to 10–21% (1000°C).     

High reversible capacity and rate capability of ZnCo2O4/graphene nanocomposite anode for high performance lithium ion batteries

A facile and straightforward method was adopted to synthesize ZnCo₂O₄/graphene nanocomposite anode. In the first step, pure ZnCo₂O₄ nanoparticles were synthesized using urea-assisted auto-combustion synthesis followed by annealing at a low temperature of 400 °C. In the second step, in order to synthesize ZnCo₂O₄/graphene nanocomposite, the obtained pure ZnCo₂O₄ nanoparticles were milled with 10 wt% reduced graphene nanosheets using high energy spex mill for 30 s. The ZnCo₂O₄ nanoparticles, with particle sizes of 25–50 nm, were uniformly dispersed and anchored on the reduced graphene nanosheets. Compared with pure ZnCo₂O₄ nanoparticles anode, significant improvements in the electrochemical performance of the nanocomposite anode were obtained. The resulting nanocomposite delivered a reversible capacity of 1124.8 mAh g⁻¹ at 0.1 C after 90 cycles with 98% Coulombic efficiency and high rate capability of 515.9 mAh g⁻¹ at 4.5 C, thus exhibiting one of the best lithium storage properties among the reported ZnCo₂O₄ anodes. The significant enhancement of the electrochemical performance of the nanocomposite anode could be credited to the strong synergy between ZnCo₂O₄ and graphene nanosheets, which maintain excellent electronic contact and accommodate the large volume changes during the lithiation/delithiation process.     

Porous Molybdenum Carbide Nanostructures Synthesized on Carbon Cloth by CVD for Efficient Hydrogen Production

Molybdenum carbide (Mo₂C) is a promising noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER), due to its structural and electronic merits, such as high conductivity, metallic band states and wide pH applicability. Here, a simple CVD process was developed for synthesis of a Mo₂C on carbon cloth (Mo₂C@CC) electrode with carbon cloth as carbon source and MoO₃ as the Mo precursor. XRD, Raman, XPS and SEM results of Mo₂C@CC with different amounts of MoO₃ and growth temperatures suggested a two-step synthetic mechanism, and porous Mo₂C nanostructures were obtained on carbon cloth with 50 mg MoO₃ at 850 °C (Mo₂C-850(50)). With the merits of unique porous nanostructures, a low overpotential of 72 mV at current density of 10 mA cm⁻² and a small Tafel slope of 52.8 mV dec⁻¹ was achieved for Mo₂C-850(50) in 1.0 m KOH. The dual role of carbon cloth as electrode and carbon source resulted into intimate adhesion of Mo₂C on carbon cloth, offering fast electron transfer at the interface. Cyclic voltammetry measurements for 5000 cycles revealed that Mo₂C@CC had excellent electrochemical stability. This work provides a novel strategy for synthesizing Mo₂C and other efficient carbide electrocatalysts for HER and other applications, such as supercapacitors and lithium-ion batteries.     

Simplified Synthesis of Biomass-Derived Si/C Composites as Stable Anode Materials for Lithium-Ion Batteries

Synthesis of silicon/carbon (Si/C) composites from biomass resources could enable the effective utilization of agricultural products in the battery industry with economical as well as environmental benefits. Herein, a simplified process was developed to synthesize Si/C from biomass, by using a low-cost agricultural byproduct “rice husk (RH)” as a model. This process includes the calcination of RH for SiO₂/C and the reduction of SiO₂/C by Al in molten salts at a moderate temperature. This process does not need the removal of carbon before thermal reduction of SiO₂, which is thought to be necessary to avoid the formation of SiC at elevated temperatures. Thus, carbon derived from biomass can be directly used for Si/C composites for anode materials. The resultant Si/C shows a high reversible capacity of 1309 mAh g⁻¹ and long cycle life (300 cycles). This research advocates a new and simplified strategy for the synthesis of RH-based biomass-derived Si/C, which is beneficial for low-cost, environmentally friendly, and green energy storage applications.     

Flower-like SnO2 nanoparticles grown on graphene as anode materials for lithium-ion batteries

Tin oxide (SnO₂)/graphene composite was synthesized from SnCl₂?·?2H₂O and graphene oxide (GO) by a wet chemical-hydrothermal route. The GO was reduced to graphene nanosheet (GNS) and flower-like SnO₂ nano-crystals with size about 40 nm were homogeneously distributed on the surface of GNS. The SnO₂/graphene composites delivered a superior first discharge capacity of 1941.9 mAhg^?1 with a reversible capacity of 901.7 mAhg^?1 at the current density of 100 mAg^?1. Moreover, even at higher densities of 200 and 500 mAg^?1, the SnO₂/graphene composite still maintained enhanced cycling stability. After 40 cycles, the discharge capacity was still maintained at 691.1 mAhg^?1 at the current density of 100 mAg^?1. The SnO₂/graphene composite displayed an outstanding Li-battery performance with large reversible capacity and enhanced rate performance, which can be attributed to the highly uniform distribution of SnO₂ nanoparticles and high reduction degree of graphene. This result strongly indicates that the SnO₂/graphene composite was a promising anode material in high-performance lithium-ion batteries.     

Slope‐Dominated Carbon Anode with High Specific Capacity and Superior Rate Capability for High Safety Na‐Ion Batteries

The comprehensive performance of carbon anodes for Na‐ion batteries (NIBs) is largely restricted by their inferior rate capability and safety issues. Herein, a slope‐dominated carbon anode is achieved at a low temperature of 800 °C, which delivers a high reversible capacity of 263 mA h g^?1 at 0.15C with an impressive initial Coulombic efficiency (ICE) of 80 %. When paired with the NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the reversible capacity at 6C is still 75 % of that at 0.15C, and 73 % of the capacity is retained after 1000 cycles at 3C. The enhanced Na storage performance could be attributed to the unique microstructure with randomly oriented short carbon layers and the relatively higher defect concentration. Given its robustness, such a low‐temperature carbonization strategy could also be applicable to other precursors and provide a new opportunity to design slope‐dominated carbon anodes for high safety, low‐cost NIBs with excellent ICE and superior rate capability.     

Two-Dimensional SnSe2/CNTs Hybrid Nanostructures as Anode Materials for High-Performance Lithium-Ion Batteries

Tin diselenide (SnSe₂), as an anode material, has outstanding potential for use in advanced lithium-ion batteries. However, like other tin-based anodes, SnSe₂ suffers from poor cycle life and low rate capability due to large volume expansion during the repeated Li⁺ insertion/de-insertion process. This work reports an effective and easy strategy to combine SnSe₂ and carbon nanotubes (CNTs) to form a SnSe₂/CNTs hybrid nanostructure. The synthesized SnSe₂ has a regular hexagonal shape with a typical 2D nanostructure and the carbon nanotubes combine well with the SnSe₂ nanosheets. The hybrid nanostructure can significantly reduce the serious damage to electrodes that occurs during electrochemical cycling processes. Remarkably, the SnSe₂/CNTs electrode exhibits a high reversible specific capacity of 457.6 mA h g⁻¹ at 0.1 C and 210.3 mA h g⁻¹ after 100 cycles. At a cycling rate of 0.5 C, the SnSe₂/CNTs electrode can still achieve a high value of 176.5 mA h g⁻¹, whereas a value of 45.8 mA h g⁻¹ is achieved for the pure SnSe₂ electrode. The enhanced electrochemical performance of the SnSe₂/CNTs electrode demonstrates its great potential for use in lithium-ion batteries. Thus, this work reports a facile approach to the synthesis of SnSe₂/CNTs as a promising anode material for lithium-ion batteries.     

Synthesis and characterization of LiNi1/3Co1/3Mn1/3O2 cathode material for rechargeable lithium batteries by polyacrylic acid-assisted sol–gel method

Nanocrystalline LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials are synthesized by sol–gel method using polyacrylic acid as a chelating agent. The effects of the calcination temperature and calcination time on the structure, morphology, and electrochemical performances of the LiNi_1/3Co_1/3Mn_1/3O₂ electrode materials are investigated by X-ray diffraction, scanning electron microscopy and charge–discharge cycling test, respectively. All experiments show that the microscopic structural features and the morphology properties are deeply related with the electrochemical performance. The results show that the nanocrystalline LiNi_1/3Co_1/3Mn_1/3O₂ with a particle size of 80 nm sintered at 700 °C for 2 h presents good α-NaFeO₂ layer structure and the best electrochemical performance. When it is discharged between 4.4 and 2.8 V at 20 mAg^?1, the initial specific capacity of the LiNi_1/3Co_1/3Mn_1/3O₂ obtained at 700 °C for 2 h is 169.2 mAhg^?1. The investigated electrode materials retain 151 mAhg^?1 after 30 cycles when cycled at 20 mAg^?1.     

High temperature thermo-photocatalysis driven carbon removal in direct biogas fueled solid oxide fuel cells

Solid oxide fuel cells (SOFCs) can directly convert renewable biogas into electricity with high efficiency at high temperature, however the long-term stability of SOFCs is significantly affected by the carbon deposition on the anode during cell operation. Herein, we report a novel carbon removal approach by high temperature infrared light driven photocatalytic oxidation. Upon the comparison of electrochemical performance of Ni-YSZ anode and TiO₂ modified Ni-YSZ anode in the state-of-the-art single cell (Ni-YSZ/YSZ/LSCM), the modified anodes exhibit markedly improved peak powder density with simulated biogas fuel (70% CH₄+ 30% CO₂) at 850 °C with less coking after 40 h operation. The high activity and carbon deposition resistance of the modified anode is possibly attributed to the in situ generated hydroxyl radical from the reduced TiO_x powder under high temperature infrared light excitation, which is supported by detailed analysis of microstructural information of anodes and the powder-based thermo-photocatalytic experiments.     

Tunable Synthesis of Hierarchical Yolk/Double-Shelled SiOx@TiO2@C Nanospheres for High-Performance Lithium-Ion Batteries

This work reports the preparation of unique hierarchical yolk/double-shelled SiO_x@TiO₂@C nanospheres with different voids by a facile sol-gel method combined with carbon coating. In the preparation process, SiO_x nanosphere is used as a hard template. Etch time of SiO_x yolk affects the morphology and electrochemical performance of SiO_x@TiO₂@C. With the increase in etch time, the yolk/double-shelled SiO_x@TiO₂@C with 15 and 30 nm voids and the TiO₂@C hollow nanospheres are obtained. The yolk/double-shelled SiO_x@TiO₂@C nanospheres exhibit remarkable lithium-ion battery performance as anodes, including high lithium storage capacity, outstanding rate capability, good reversibility, and stable long-term cycle life. The unique structure can accommodate the large volume change of the SiO_x yolk, provide a unique buffering space for the discharge/charge processes, improve the structural stability of the electrode material during repeated Li⁺ intercalation/deintercalation processes, and enhance the cycling stability. The SiO_x@TiO₂@C with 30 nm void space exhibits a high discharge specific capacity of ≈1195.4 mA h g⁻¹ at the current density of 0.1 A g⁻¹ after 300 cycles and ≈701.1 mA h g⁻¹ at 1 A g⁻¹ for over 800 cycles. These results suggest that the proposed particle architecture is promising and may have potential applications in improving various high performance anode materials.     

PEO-LITFSI-SiO2-SN System Promotes the Application of Polymer Electrolytes in All-Solid-State Lithium-ion Batteries

All-solid-state polymer lithium-ion batteries are ideal choice for the next generation of rechargeable lithium-ion batteries due to their high energy, safety and flexibility. Among all polymer electrolytes, PEO-based polymer electrolytes have attracted extensive attention because they can dissolve various lithium salts. However, the ionic conductivity of pure PEO-based polymer electrolytes is limited due to high crystallinity and poor segment motion. An inorganic filler SiO₂ nanospheres and a plasticizer Succinonitrile (SN) are introduced into the PEO matrix to improve the crystallization of PEO, promote the formation of amorphous region, and thus improve the movement of PEO chain segment. Herein, a PEO₁₈−LiTFSI−5 %SiO₂−5 %SN composite solid polymer electrolyte (CSPE) was prepared by solution-casting. The high ionic conductivity of the electrolyte was demonstrated at 60 °C up to 3.3×10⁻⁴ S cm⁻¹. Meanwhile, the electrochemical performance of LiFePO₄/CSPE/Li all-solid-state battery was tested, with discharge capacity of 157.5 mAh g⁻¹ at 0.5 C, and capacity retention rate of 99 % after 100 cycles at 60 °C. This system provides a feasible strategy for the development of efficient all-solid-state lithium-ion batteries.     

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.     

Enhancement of water barrier properties and tribological performance of hybrid glass fiber/epoxy composites with inclusions of carbon and silica nanoparticles

Water barrier properties and tribological performance (hardness and wear behavior) of new hybrid nanocomposites under dry and wet conditions were investigated. The new fabricated hybrid nanocomposite laminates consist of epoxy reinforced with woven and nonwoven tissue glass fibers and two different types of nanoparticles, silica (SiO₂) and carbon black nanoparticles (C). These nanoparticles were incorporated into epoxy resin as a single nanoparticle (either SiO₂ or C) or combining SiO₂ and C nanoparticles simultaneously with different weight fractions. The results showed that addition of carbon nanoparticles with 0.5 and 1 wt% resulted in maximum reduction in water uptake by 28.55% and 21.66%, respectively, as compared with neat glass fiber reinforced epoxy composites. Addition of all studied types and contents of nanoparticles improves hardness in dry and wet conditions over unfilled fiber composites. Under dry conditions, maximum reduction of 47.26% in weight loss was obtained with specimens containing 1 wt% carbon nanoparticles; however, in wet conditions, weight loss was reduced by 17.525% for specimens containing 0.5 wt% carbon nanoparticles as compared with unfilled fiber composites. Diffusion coefficients for different types of the hybrid nanocomposites were computed using Fickian and Langmuir models of diffusion. Copyright © 2017 John Wiley & Sons, Ltd.     

N-Doped Porous Carbon Derived from Solvent-Free Synthesis of Cross-Linked Triazine Polymers for Simultaneously Achieving CO2 Capture and Supercapacitors

It is highly desirable to design advanced heteroatomic doped porous carbon for wide application. Herein, N-doped porous carbon (NPC) was developed via the fabrication of high nitrogen cross-linked triazine polymers followed by pyrolysis and activation with controllable porous structure. The as-synthesized NPC at the pyrolysis temperature of 700 °C possessed rich nitrogen content (up to 11.51 %) and high specific surface area (1353 m² g⁻¹), which led to a high CO₂ adsorption capability at 5.67 mmol g⁻¹ at 298.15 K and 5 bar pressure and excellent stability. When the activation temperature was at 600 °C, such NPC exhibited a superior electrochemical performance as anode for supercapacitors with a specific capacitance of 158.8 and 113 F g⁻¹ in 6 M KOH at a current density of 1 and 10 A g⁻¹, respectively. Notably, it delivered an excellent stability with capacity retention of 97.4 % at 20 A g⁻¹after 6000 cycles.     

Surface Chemistry and Structure of Silicon Oxycarbide Gels and Glasses

In this study, the surface chemistry and structure of methyl-substituted silica gels and porous oxycarbide glasses were investigated. FTIR was used to measure the relative concentration of Si−CH₃ and Si−OH as a function of the degree of methyl-substitution and the pyrolysis temperature. The gels and glasses were further heated, dehydrated or hydrated, in situ, within the FTIR spectrometer. In the temperature range of 800–850°C, high surface area oxycarbide glasses were created with no detectable surface hydroxyl groups. Oxycarbide glasses synthesized in argon at 700°C displayed a weak band for surface hydroxyl groups and reversible physisorption of water, while those synthesized at 850/900°C showed a complete absence of surface hydroxyl groups and the formation of vicinal silanols upon chemisorption of water. Isolated silanols were observed upon heat treatment in vacuum. Formation of aromatic carbon species was found to correlate with the decomposition of the methyl groups. The oxycarbide surface is quite stable to densification (presumably due to elemental carbon on the pore surfaces). In the absence of oxygen, porous silicon oxycarbide glass powders maintain surface areas >200 m²/g at 1200°C. However, oxidizing species in the atmosphere deplete the aromatic carbon species, and the glasses lose surface area.     

Locally Concentrated Ionic Liquid Electrolytes Enabling Low-Temperature Lithium Metal Batteries

Lithium metal is a promising anode material for next-generation high-energy-density batteries but suffers from low stripping/plating Coulombic efficiency and dendritic growth particularly at sub-zero temperatures. Herein, a poorly-flammable, locally concentrated ionic liquid electrolyte with a wide liquidus range extending well below 0 °C is proposed for low-temperature lithium metal batteries. Its all-anion Li⁺ solvation and phase-nano-segregation solution structure are sustained at low temperatures, which, together with a solid electrolyte interphase rich in inorganic compounds, enable dendrite-free operation of lithium metal anodes at −20 °C and 0.5 mA cm⁻², with a Coulombic efficiency of 98.9 %. As a result, lithium metal batteries coupling thin lithium metal anodes (4 mAh cm⁻²) and high-loading LiNi_0.8Co_0.15Al_0.05O₂ cathodes (10 mg cm⁻²) retain 70 % of the initial capacity after 100 cycles at −20 °C. These results, as a proof of concept, demonstrate the applicability of locally concentrated ionic liquid electrolytes for low-temperature lithium metal batteries.