Silicon oxycarbide (SiOC) ceramics have garnered significant attention as anode materials for lithium-ion batteries due to their tunable chemical composition, minimal volume expansion, and high theoretical capacity. However, achieving simultaneous control over the structure and composition of both the SiOC tetrahedral phase and free carbon remains a formidable challenge. To address this, we introduce a concept leveraging the Si-H induced carbon-deficiency effect in precursors. Through a controlled reduction reaction, partial replacement of Si-OH with Si-H groups facilitates carbon free radical migration during pyrolysis, promoting the rearrangement of both SiOC phases and free carbon structures. By tailoring Si-H precursors and optimizing pyrolysis conditions, we synthesized SiOC ceramics with high reversible phase content (SiO2C2 and SiO3C) and highly ordered free carbon. The M1-Ph-25% sample demonstrated an impressive reversible capacity of 849 mAh g- 1 after 250 cycles at 0.5 A g- 1. Furthermore, in a full cell coupled with LiFePO4 (LFP), over 100 mAh g- 1 was achieved after 550 cycles at 0.2 A g- 1. This study provides valuable insights into the controlled fabrication of SiOC ceramics with tailored compositions and structures, offering a promising route for improving SiOC-based anodes in energy storage applications.

SiOC anode is considered as a candidate for the next generation of lithium ion batteries, because of its appealing specific capacity and relative small volume expansion. However, the inherent inferior electron conductivity blocks its development. Recently, controlling the amount of free carbon domains is adopted to modify the performance, ignoring the influence of free C on the SiOC phases change and their synergistic effect on the performance. The crosslinking and polymerization competition between divinylbenzene and polymethylsilsesquioxane was coordinated to regulate the free carbon and phase composition of SiOC ceramics, and a durable SiOC anode with high ceramic yield was prepared. The result is that, keeping the proportion of free C about 10% and increasing the SiO3C and SiO2C2 phases ratios can obtain good anode within limited cycle life (440 cycle in this work), and increasing free C amount further is necessary for durable long cycle life. Herein, SDVB-2 anode with 12% free C delivers 698.7 mAh g-1 at a current density of 100 mA g-1 after 100 cycles, and SDVB-1 anode with 20.6% free C shows excellent stable long cycle performance at the current density of 0.5 A g-1, the remaining capacity is 476 mAh g-1 after 500 cycles.

It is necessary to design a scalable composite material with a rational structure for Li-ion batteries and electromagnetic wave absorption. Herein, we developed a modified precursor-driven method of spacer-assisted oxidation to prepare heterogeneous multi-interface SiOC-based composite ceramic nanoparticles. The outstanding structural design regulated by the ratio of raw materials tailored its functional potential in the fields of Li-ion batteries and electromagnetic wave absorption. The addition of a small amount of iron-sol produced small-sized ceramic nanoparticles bridged by carbon ribbons, which can provide efficient charge transfer kinetics and volumetric buffering capacity. Used in Li-ion battery anodes, it exhibited a specific discharge capacity of 514.4 mAh/g after 1000 cycles at a current density of 0.5 A/g with durable long cycling performance. In addition, the addition of high iron-sol induced the formation of porous core-shell nanoparticles and performed excellent electromagnetic wave absorption ability. The ceramic nanoparticles with carbon content of about 30% had the lowest reflection loss in the X-band of -55.5 dB, and the effective absorption range was 8.48-12.4 GHz, which basically covered the entire X-band. This strategy enriches the preparation and application of multifunctional composite ceramic nanoparticles.

Silicon has been considered as a potential alternative of anodes for advanced lithium ion battery as it possesses high capacity and abundance. However, it encounters excessive volume expansion and inferior electoral conductivity, which imposes restrictions on its further development. In order to address these two problems, yolk-shell structure is employed, in which there is a suitable void for the expansion with a shell to protect the core and promote the conductivity. Here, by the inspiration from the egg holders and inverse-opal structure, an egg-stacking-like Si/C composite (ES) anode with spherical air holes was fabricated to gather the yolk-shell particles in a 3D carbon network with abundant channels allowing electrolyte to enter the material, which can facilitate the cycling performance. The half-cell battery assembled with these anodes presents high capacity and good rate performance, with a capacity reduction of only 2-7% per current density. And the cycling performance of ES anode is also praiseworthy that it delivers a high reversible discharge capacity of 2175 mAh g(-1) after 300 cycles at 0.5 A g(-1). This kind of structure design is expected to be applicative for most of large-volume-change anodes. (C) 2019 Elsevier B.V. All rights reserved.

In this work, porous core-shell structured Co2Si@SiC/C/SiOC/SiO2/Co(3)O(4)nanoparticles were fabricated by a polymer-derived ceramic approach. The in situ formation of mesopores on the shell, microstructural, and phase evolution of resulting nanoparticles were investigated in detail. The obtained nanoparticles-paraffin composites possess a very low minimum reflection coefficient (RCmin) -60.9 dB, broad effective absorption bandwidth 3.50 GHz in the X-band and 15.5 GHz in the whole frequency range (from 2.5 to 18 GHz). The results indicate outstanding electromagnetic wave (EMW) absorbing performance among all the reported cobalt-based nanomaterials, due to the reasons as follows: (a) The unique core-shell structure as well as complex phase composition of SiC/C/SiOC/SiO2/Co(3)O(4)in the shell, result in a large number of heterogeneous interfaces in the nanoparticles; (b) Nanoparticles have both dielectric and magnetic loss; (c) Mesopores in the shell prolong the propagation path of EMW, thereby increasing the absorption/reflection ratio of EMWs. Thanks to the material structure design, the resulting core-shell structured cobalt-containing ceramic nanoparticles have great potential for thin and high-performance EMW absorbing materials applied in harsh environment.

In order to address the issue of large volume expansion and poor electrical conductivity of Fe3O4-based anodes for lithium-ion batteries, carbon and SiOx/SiC heterojunction double-shell coated Fe3O4(FexSiy) nanocomposites were synthesized by crosslinking, pyrolysis and decarbonization of sol particles. The particles were produced by the reaction of iron carbonyl with liquid polycarbosilane using pitch as isolator, which is a low cost and easy to scale up preparation method. It is found that the double-shell structure of the nanoparticles not only solves the problem of comminution of Fe3O4 during cycling, but also ensures stable cycling and superior rate performance. The FeOSiC-30 anode delivers a high reversible capacity (1357.2 mAh g(-1) for 550 cycles at 1 A g(-1) and 1060.7 mAh g(-1) for 2500 cycles at 5 A g(-1)). The excellent electrochemical performance can be contributed to the novel structure: 1) the uniform carbon layer can improve the electrical conductivity and ensure the formation of a stable SEI; 2) different active materials can relieve the stress caused by volume variation and also contribute additional capacity; 3) the small particle size can offer a strong kinetic of electrochemical reactions and lithium ion transfer. These results can strongly support the improvement of the capacity of Fe3O4-based anodes by the unique multi-function structural design, also providing new pathways for the design of other electrode materials.

The Cover Feature shows carbon and SiC double-shell coated SiOx/Fe3O4(FexSiy) heterojunction nanocomposites, which are fabricated by using a simple method that is expected to be widely applied to the preparation of other nanoparticles. These nanocomposites demonstrate excellent performance and cycle life over 2500 cycles in lithium-ion battery testing, which can be attributed to its unique composite structure of various materials and its small particle size. More information can be found in the Article by P. Wu et al. on page 3606 in Issue 14, 2019 (DOI: 10.1002/celc.201900250).

In this work, we report a novel kind of Si3N4/SiC composite fibers, which exhibit a controlled gradient Si3N4(shell)/SiC(core) structure. These composite fibers are fabricated through a controlled nitridation and pyrolysis process on electron irradiation-cured polycarbosilane fibers. Structural and chemical analysis based on Elemental Analyzer, FT-IR, Raman spectroscopy, electron probe micro-analyzer, X-ray photoelectron spectroscopy, and X-ray diffraction confirm the gradient structure of obtained fibers, which consist a shell with high Si3N4 content and a SiC core. The as-fabricated fibers exhibit dense and smooth surfaces, and no microscopic holes or defects were observed. The effects of nitridation temperature on mechanical properties and electrical resistivity were also investigated. Combined with high mechanical properties and lightweight, the present gradient Si3N4/SiC fibers open a new strategy to fabricate multifunctional and electromagnetic wave absorbing materials.

In this work, novel core-shell structured Fe3Si@C/SiC/Fe3O4/SiO2 nanoparticles were fabricated via a polymer-derived ceramic approach, starting from sol-like polycarbosilane-encapsulated polynuclear carbonyl iron nanoparticles and with pitch as an isolator to avoid aggregation during polymer-to-ceramic transformation. Elemental analysis, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscope, vibrating sample magnetometer and vector network analyzer were employed to investigate the composition, nano/microstructure, morphology, and dielectric/magnetic properties. The results show that the size of obtained Fe3Si@C/SiC/Fe3O4/SiO2 nanoparticles is in the range of 2-200 nm. And the unique core-shell structure with the hetero-interface combined with simultaneous dielectric and magnetic loss endow Fe3Si@C/SiC/Fe3O4/SiO2 nanoparticles outstanding electromagnetic (EM) wave absorbing performance. With a sample thickness of 4.5 mm, the minimum reflection coefficient (RC) of the composites Fe3Si@C/SiC/Fe3O4/SiO2 mixed with paraffin wax reaches -44.7 dB, indicating that more than 99.99% EM waves can be attenuated by the composites. By adjusting the sample thicknesses, the effective bandwidth (the bandwidth of RC values lower than -10 dB) amounts 9.5 GHz (from 2.5 to 12.0 GHz), covering the whole C and X bands.

Different mass fraction of iron-containing silicon carbide(Fe/SiC)ceramics was successfully prepared by firstly synthesizing iron(Fe)-containing precursor via blending Fe colloids formed by the reaction of liquid polycarbosilane(PCS)and carbonyl iron with solid PCS and then the cross-linking and pyrolysis.The effects of the introduction of Fe on the component, structure, and magnetic and dielectric properties were systematically studied.When the mass fraction of iron is less than 8.94%, Fe element can significantly promote the decomposition of SiC xOyand generate β-SiC,and the crystallization peak of β-SiC is sharper with increased Fe.But when the Fe mass fraction increases to 11.78%, the main product is Fe3Si; Fe-SiC ceramics are all ferromagnetic,and their saturation magnetization increases exponentially with the increase of iron.Fe/SiC ceramic with 4.19%Fe has a minimum -9.4 dB reflection loss at 12.4 GHz.The bandwidths of less than -5 dB for Fe/SiC cermic with 4.19%and 8.94% Fe are 2.4 GHz and 3.7 GHz,respectively, which can be used as good microwave-absorption materials.

Polycarbosilane (PCS) fiber was irradiated by electron beam at low dose in a flowing N2/O2 mixture with O2 concentration of 1%. After the pyrolysis of the irradiated precursor fibers, SiC fibers with high strength of 2.4 GPa were obtained. Microstructural evolutions of the resultant fibers were explored. It was found that during the irradiation, free radicals were formed in the PCS and were oxidized by oxygen as Si–OH groups. The Si–OH groups then transformed into Si–O–Si linkage and resulted in further cross‐linking of the PCS during pyrolysis. A remarkable structure gradient along the fiber diameter was formed under the coupled effects of irradiation and oxidation. The content of oxygen decreased from the fiber surface to the core, whereas the crystallinity of β‐SiC increased in the same direction. The electrical resistivity of the as‐prepared ceramic fiber was 80.7 Ω cm, showing good potential for being as electromagnetic wave absorber.

The commercial Nicalon 202 SiC fiber was exposed in thermal air to degum and heat treated in argon gas from 1 100 to 1 400 ℃.Change of the chemical,structural and electrical properties of the resultant fibers as a function of thermal treatment temperature were studied.The results showed that the SiCx Oy phase decom-posed evidently above 1 200 ℃,which led to the formation and crystallization of SiC.With the raise of the heat-ing temperature,the tensile strength of fiber decreased,the specific conductivity and dielectric loss of the fiber increased.Moreover,after heating at 1 400 ℃ the fracture behavior of the fiber turned to intergranular mode from amorphous brittleness mode.

In order to investigate the oxidation-curing mechanism of polycarbosilane（PCS） green fibers,the products during oxidation-curing of PCS green fibers in different temperature zone were analyzed by IR,1H NMR and GC-MAS,and the oxidation-cured PCS fibers were analyzed by IR.It was found that the major reactions occurred during oxidation-curing were the oxidation of Si—H bonds and the formation of Si—OH groups.And the condensation reactions were took place between the Si—OH groups to produce Si—O—Si linkages,which were responsible for curing.When the curing temperature was over 150℃,the Si—CH3 groups were also oxidized into Si—OH,further promoting the curing process.At the same time,the side chains of PCS molecule were decomposed to small molecule during oxidation-curing,forming big molecule by condensation of the Si—OH groups.The higher the oxidation-curing temperature,the higher the molecular mass of the products.It was essential to discharge the gas during the oxidation-curing,and the decomposed products can be avoided to be adhesion on the surface of the fibers and make the fibers sticking.

The effects of polypropylene on the processing of low‐oxygen silicon carbide (SiC) fibers by the polycarbosilane (PCS) route have been studied. Polypropylene acts as a high‐temperature solvent for PCS, reducing the spinning temperature. A small amount of polypropylene (≤5 wt%) significantly improves the spinning ability and the tensile strength of the as‐spun precursor fibers because of its excellent fiber‐forming ability. During blending and spinning, no noticeable chemical interaction has been detected between PCS and polypropylene. In the early stage of electron beam irradiation of the polypropylene‐containing precursor fibers, free radicals are formed from both PCS and polypropylene. They combine with each other, forming a cross‐linked structure and promoting the curing. The introduction of polypropylene has no detrimental effects on the properties of the final SiC fibers.

Silicon carbide (SiC) fibers are prepared using an iron‐containing polycarbosilane (Fe‐PCS) as the precursor. Iron pentacarbonyl [Fe(CO)5] is first reacted with low‐molecular‐weight liquid PCS to form an iron‐containing colloid. The colloid is then added into high‐molecular‐weight solid PCS to form Fe‐PCS. Formation of the iron‐containing colloid as well as the SiC fiber processing has been studied. It is found that during the preparation of the colloid, the iron pentacarbonyl first decomposes under heat into nanosized carbonyl derivatives and CO. CO then reacts with liquid PCS at the interface, rendering liquid PCS cross‐linked and hence the particles encapsulated. At a higher temperature, the derivatives further decompose into nanosized iron particles. The iron exists as nanosized α‐Fe domains (∼5 nm) and is highly uniformly distributed inside the ceramic fibers. Ceramic fibers containing 3.64 wt% iron have a good combination of tensile strength (2.37 GPa), electrical resistivity (0.46 Ω·m) and magnetic properties (a saturation magnetization of 1.48 A·m2/kg and a coercivity of 5094 A/m).

Polycarbosilane (PCS) precursor fibers were irradiated using electron beam at low dose and under low oxygen partial pressure. They were then annealed at inert atmosphere, and pyrolyzed at high temperature under nitrogen to give silicon carbide fibers. The chemical reactions occurring during irradiation and annealing were studied. The results show that Si—H bonds in the molecular structure of PCS react with oxygen under electron beam bombarding to get Si—OH groups. During annealing, Si—OH groups undergo dehydration condensation reactions to produce Si—O—Si linkage, resulting in cross-linking. Silicon carbon fibers prepared at 1 250 ℃ have a shell-core structure. The shell is oxygen-rich, and the core is oxygen-deficient. The average tensile strength and tensile modulus are 2.4 GPa and 170.1 GPa, respectively.