New Insights in to the Lithium Storage Mechanism in Polymer Derived SiOC Anode Materials

Modulation of Free Carbon Structures in Polysiloxane-Derived Ceramics for Anode Materials in Lithium-Ion Batteries

Polymer-derived silicon oxycarbide (SiOC) ceramics have garnered significant attention as novel silicon-based anode materials. However, the low conductivity of SiOC ceramics is a limiting factor, reducing both their rate capability and cycling stability. Therefore, controlling the free carbon content and its degree of graphitization within SiOC is crucial for determining battery performance. In this study, we regulated the free carbon content using divinylbenzene (DVB) and controlled the graphitization of free carbon with the transition metal iron (Fe). Through a simple pyrolysis process, we synthesized SiOC ceramic materials (CF) and investigated the impact of Fe-induced changes in the carbon phase and the amorphous SiOC phase on the comprehensive electrochemical performance. The results demonstrated that increasing the DVB content in the SiOC precursor enhanced the free carbon content, while the addition of Fe promoted the graphitization of free carbon and induced the formation of carbon nanotubes (CNTs). The electrochemical performance results showed that the CF electrode material exhibited a high reversible capacity of approximately 1154.05 mAh g-1 at a low current density of 100 mA g-1 and maintained good rate capability and cycling stability after 1000 cycles at a high current density of 2000 mA g-1.

New insights into the electrochemical performance of precursor derived Si(Nb)OC composites as anode materials for batteries

This work represents a first attempt to synthesize Si(Nb)OC ceramic composites through the polymer pyrolysis or the precursor-derived ceramics (PDC) route for use as a hybrid anode material for lithium-ion batteries (LIB). Electron microscopy, X-ray diffraction, and various spectroscopy techniques were used to examine the micro/nano structural features and phase evolution during cross-linking, pyrolysis, and annealing stages. During the polymer-to-ceramic transformation process, in situ formation of carbon (so-called "free carbon"), and crystallization of t-NbO2, NbC phases in the amorphous Si(Nb)OC ceramic matrix are identified. The first-cycle reversible capacities of 431 mA h g-1 and 256 mA h g-1 for the as-pyrolyzed and annealed Si(Nb)OC electrodes, respectively, exceeded the theoretical Li capacity of niobium pentaoxide or m-Nb2O5 (at approximately 220 mA h g-1). With an average reversible capacity of 200 mA h g-1 and close to 100% cycling efficiency, as-pyrolyzed Si(Nb)OC demonstrates good rate capability. X-ray amorphous SiOC with uniformly distributed nanosized Nb2O5 and graphitic carbon structure likely provides stability during repeated Li+ cycling and the formation of a stable secondary electrolyte interphase (SEI) layer, leading to high efficiency.

Abnormal Graphitization Behavior in Near-Surface/Interface Region of Polymer-Derived Ceramics

The in situ free carbon generated in polymer-derived ceramics (PDCs) plays a crucial role in their unique microstructure and resultant properties. This study advances a new phenomenon of graphitization of PDCs. Specifically, whether in micro-/nanoscale films or millimeter-scale bulks, the surface/interface radically changes the fate of carbon and the evolution of PDC nanodomains, promotes the graphitization of carbon, and evolves a free carbon enriched layer in the near-surface/interface region. Affected by the enrichment behavior of free carbon in the near-surface/interface region, PDCs exhibit highly abnormal properties such as the skin behavior and edge effect of the current. The current intensity in the near-surface/interface region of PDCs is orders of magnitude higher than that in its interior. Ultrahigh conductivity of up to 14.47 S cm^-1 is obtained under the action of the interface and surface, which is 5-8 orders of magnitude higher than that of the bulk prepared under the same conditions. Such surface/interface interactions are of interest for the regulation of free carbon and its resultant properties, which are the core of PDC applications. Finally, the first PDC thin-film strain gauge that can survive a butane flame with a high temperature of up to ≈1300 °C is fabricated.

Porous Silicon Oxycarbonitride Ceramics with Palladium and Pd2Si Nanoparticles for Dry Reforming of Methane

Pd-containing precursor has been synthesized from palladium acetate and poly(vinly)silazane (Durazane 1800) in an ice bath under an argon atmosphere. The results of ATR-FTIR and NMR characterizations reveal the chemical reaction between palladium acetate and vinyl groups in poly(vinyl)silazane and the hydrolyzation reaction between –Si–H and –Si–CH=CH₂ groups in poly(vinyl)silazane. The palladium nanoparticles are in situ formed in the synthesized precursors as confirmed by XRD, XPS, and TEM. Pd- and Pd₂Si-containing SiOCN ceramic nanocomposites are obtained by pyrolysis of the synthesized precursors at 700 °C, 900 °C–1100 °C in an argon atmosphere. The pyrolyzed nanocomposites display good catalytic activity towards the dry reforming of methane. The sample pyrolyzed at 700 °C possesses the best catalytic performance, which can be attributed to the in situ formed palladium nanoparticles and high BET surface area of about 233 m² g⁻¹.

Core-shell structured monodisperse carbon-rich SiO1.31C1.46H0.81 ceramic spheres as anodes for high-capacity lithium-ion batteries

SiOC ceramic material is a promising anode material for lithium-ion batteries. However, due to its intrinsically low electronic conductivity, it often suffers from a much lower specific capacity than the theoretical value, poor rate capability and serious potential hysteresis. In this paper, we report a core-shell structured monodisperse carbon-rich SiO_1.31C_1.46H_0.81 submicron ceramic sphere with a free carbon content of 13.7 wt%, which is synthesized by directly annealing polysiloxane spheres derived from vinyltrimethoxysilane without adding external carbon resources. The SiO_1.31C_1.46H_0.81 sphere has a unique microstructure, the core of which is organically assembled by large amounts of SiO_1.31C_1.46H_0.81 primary particles of less than 20 nm and coated by a shell of 20-50 nm. As anodes for lithium-ion batteries, it presents much higher reversible capacity, initial Coulomb efficiency (ICE) and rate performance than the SiOC-based ceramic materials reported in the literature to date. At 100 mA g^-1, its first reversible capacity and ICE reach ∼1107 mAh g^-1 and 78.2%, respectively. At 1600 mA g^-1, its stable discharge capacity is still as high as 610 mAh g^-1. The excellent electrochemical performance is attributed to the moderate composition, spherical morphology and unique microstructure of the synthesized material.

Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides

The present work elaborates on the correlation between the amount and ordering of the free carbon phase in silicon oxycarbides and their charge carrier transport behavior. Thus, silicon oxycarbides possessing free carbon contents from 0 to ca. 58 vol.% (SiOC/C) were synthesized and exposed to temperatures from 1100 to 1800 °C. The prepared samples were extensively analyzed concerning the thermal evolution of the sp2 carbon phase by means of Raman spectroscopy. Additionally, electrical conductivity and Hall measurements were performed and correlated with the structural information obtained from the Raman spectroscopic investigation. It is shown that the percolation threshold in SiOC/C samples depends on the temperature of their thermal treatment, varying from ca. 20 vol.% in the samples prepared at 1100 °C to ca. 6 vol.% for the samples annealed at 1600 °C. Moreover, three different conduction regimes are identified in SiOC/C, depending on its sp2 carbon content: (i) at low carbon contents (i.e., <1 vol.%), the silicon oxycarbide glassy matrix dominates the charge carrier transport, which exhibits an activation energy of ca. 1 eV and occurs within localized states, presumably dangling bonds; (ii) near the percolation threshold, tunneling or hopping of charge carriers between spatially separated sp2 carbon precipitates appear to be responsible for the electrical conductivity; (iii) whereas above the percolation threshold, the charge carrier transport is only weakly activated (Ea = 0.03 eV) and is realized through the (continuous) carbon phase. Hall measurements on SiOC/C samples above the percolation threshold indicate p-type carriers mainly contributing to conduction. Their density is shown to vary with the sp2 carbon content in the range from 1014 to 1019 cm-3; whereas their mobility (ca. 3 cm2/V) seems to not depend on the sp2 carbon content.

Silicon Oxycarbide-Graphite Electrodes for High-Power Energy Storage Devices

Herein we present a study on polymer-derived silicon oxycarbide (SiOC)/graphite composites for a potential application as an electrode in high power energy storage devices, such as Lithium-Ion Capacitor (LIC). The composites were processed using high power ultrasound-assisted sol-gel synthesis followed by pyrolysis. The intensive sonication enhances gelation and drying process, improving the homogenous distribution of the graphitic flakes in the preceramic blends. The physicochemical investigation of SiOC/graphite composites using X-ray diffraction, ²⁹Si solid state NMR and Raman spectroscopy indicated no reaction occurring between the components. The electrochemical measurements revealed enhanced capacity (by up to 63%) at high current rates (1.86 A g⁻¹) recorded for SiOC/graphite composite compared to the pure components. Moreover, the addition of graphite to the SiOC matrix decreased the value of delithiation potential, which is a desirable feature for anodes in LIC.

Experimental validation of a building block of passive devices and stochastic analysis of PICs based on SiOC technology

Silicon oxycarbide (SiOC) with a wide tunable refractive index window and low absorption coefficient has emerged as an appealing material platform in integrated photonics. Its physical, optical and chemical properties can be tailored over a large window through changes in composition. The circuit simulation based on the building-block approach is a useful framework for deep exploitation of the potential of photonics in the large-scale integration of complex circuits. In this manuscript, the simulation and experimental results of the waveguide and directional coupler based on SiOC technology have been investigated. A simplified model for the coupling coefficient, within defined limits of width, coupling length and gap, of parallel waveguides of the directional coupler has been proposed and validated experimentally. The building blocks of the waveguide and directional coupler have been prepared and parametrized. The proposed models of these passive devices have been exploited in commercially available circuit simulator for the circuit and stochastic simulations of SiOC based photonic circuits.

In Vitro Cytocompatibility Assessment of Ti-Modified, Silicon-oxycarbide-Based, Polymer-Derived, Ceramic-Implantable Electrodes under Pacing Conditions

Polymer-derived ceramics (PDC) have recently gained increased interest in the field of bioceramics. Among PDC's, carbon-rich silicon oxycarbide ceramics (SiOC) possess good combined electrical and mechanical properties. Their durability in aggressive environments and proposed cytocompatibility makes them an attractive material for fabrication of bio-MEMS devices such as pacemaker electrodes. The aim of the present study is to demonstrate the remarkable mechanical and electrical properties, biological response of PDCs modified with titanium (Ti) and their potential for application as pacemaker electrodes. Therefore, a new type of SiOC modified with Ti fillers was synthesized via PDC route using a Pt-catalyzed hydrosilylation reaction. Preceramic green bodies were pyrolyzed at 1000 °C under an argon atmosphere to achieve amorphous ceramics. Electrical and mechanical characterization of SiC_xO_2(1-x)/TiO_xC_y ceramics revealed a maximum electrical conductivity of 10 S cm^-1 and a flexural strength of maximal 1 GPa, which is acceptable for pacemaker applications. Ti incorporation is found to be beneficial for enhancing the electrical conductivity of SiOC ceramics and the conductivity values were increased with Ti doping and reached a maximum for the composition with 30 wt % Ti precursor. Cytocompatibility was demonstrated for the PDC SiOC ceramics as well as SiOC ceramics modified with Ti fillers. Cytocompatibility was also demonstrated for SiTiOC20 electrodes under pacing conditions by monitoring of cells in an in vitro 3D environment. Collectively, these data demonstrate the great potential of polymer-derived SiOC ceramics to be used as pacemaker electrodes.

Silicon Oxycarbide-Tin Nanocomposite as a High-Power-Density Anode for Li-Ion Batteries

Tin-based materials are an emerging class of Li-ion anodes with considerable potential for use in high-energy-density Li-ion batteries. However, the long-lasting electrochemical performance of Sn remains a formidable challenge due to the large volume changes occurring upon its lithiation. The prevailing approaches toward stabilization of such electrodes involve embedding Sn in the form of nanoparticles (NPs) in an active/inactive matrix. The matrix helps to buffer the volume changes of Sn, impart better electronic connectivity and prevent particle aggregation upon lithiation/delithiation. Herein, facile synthesis of Sn NPs embedded in a SiOC matrix via the pyrolysis of a preceramic polymer as a single-source precursor is reported. This polymer contains Sn 2-ethyl-hexanoate (Sn(Oct)2) and poly(methylhydrosiloxane) as sources of Sn and Si, respectively. Upon functionalization with apolar divinyl benzene sidechains, the polymer is rendered compatible with Sn(Oct)2. This approach yields a homogeneous dispersion of Sn NPs in a SiOC matrix with sizes on the order of 5-30 nm. Anodes of the SiOC/Sn nanocomposite demonstrate high capacities of 644 and 553 mAh g-1 at current densities of 74.4 and 2232 mA g-1 (C/5 and 6C rates for graphite), respectively, and show superior rate capability with only 14% capacity decay at high currents.

Importing Tin Nanoparticles into Biomass-Derived Silicon Oxycarbides with High-Rate Cycling Capability Based on Supercritical Fluid Technology

Silicon oxycarbides (SiOC) are regarded as potential anode materials for lithium-ion batteries, although inferior cycling stability and rate performance greatly limit their practical applications. Herein, amorphous SiOC is synthesized from Chlorella by means of a biotemplate method based on supercritical fluid technology. On this basis, tin particles with sizes of several nanometers are introduced into the SiOC matrix through the biosorption feature of Chlorella. As lithium-ion battery anodes, SiOC and Sn@SiOC can deliver reversible capacities of 440 and 502 mAh g^-1 after 300 cycles at 100 mA g^-1 with great cycling stability. Furthermore, as-synthesized Sn@SiOC presents an excellent high-rate cycling capability, which exhibits a reversible capacity of 209 mAh g^-1 after 800 cycles at 5000 mA g^-1 ; this is 1.6 times higher than that of SiOC. Such a novel approach has significance for the preparation of high-performance SiOC-based anodes.

Silicon oxides: a promising family of anode materials for lithium-ion batteries

Silicon oxides have been recognized as a promising family of anode materials for high-energy lithium-ion batteries (LIBs) owing to their abundant reserve, low cost, environmental friendliness, easy synthesis, and high theoretical capacity. However, the extended application of silicon oxides is severely hampered by the intrinsically low conductivity, large volume change, and low initial coulombic efficiency. Significant efforts have been dedicated to tackling these challenges towards practical applications. This Review focuses on the recent advances in the synthesis and lithium storage properties of silicon oxide-based anode materials. To present the progress in a systematic manner, this review is categorized as follows: (i) SiO-based anode materials, (ii) SiO2-based anode materials, (iii) non-stoichiometric SiOx-based anode materials, and (iv) Si-O-C-based anode materials. Finally, future outlook and our personal perspectives on silicon oxide-based anode materials are presented.

First-principles calculation of lithium insertion into homogeneous a-SiC2/5O6/5as high performance anode

Amorphous silicon oxycarbide is considered as a promising anode material for new generation of lithium-ion batteries, and figuring out the lithiation mechanism is crucial for its application.

Synthesis and electrochemical performance of a polymer-derived silicon oxycarbide/boron nitride nanotube composite

Synthesis of a new type of composite consisting of boron nitride nanotubes (BNNTs) filler in polymer-derived ceramic silicon oxycarbide (SiOC) for electrochemical applications is demonstrated.

Silicon Oxycarbide/Carbon Nanohybrids with Tiny Silicon Oxycarbide Particles Embedded in Free Carbon Matrix Based on Photoactive Dental Methacrylates

A new facile scalable method has been developed to synthesize silicon oxycarbide (SiOC)/carbon nanohybrids using difunctional dental methacrylate monomers as solvent and carbon source and the silane coupling agent as the precursor for SiOC. The content (from 100% to 40% by mass) and structure (ratio of disordered carbon over ordered carbon) of the free carbon matrix have been systematically tuned by varying the mass ratio of methacryloxypropyltrimethoxysilane (MPTMS) over the total mass of the resin monomers from 0.0 to 6.0. Compared to the bare carbon anode, the introduction of MPTMS significantly improves the electrochemical performance as a lithium-ion battery anode. The initial and cycled discharge/charge capacities of the SiOC/C nanohybrid anodes reach maximum with the MPTMS ratio of 0.50, which displays very good rate performance as well. Detailed structures and electrochemical performance as lithium-ion battery anodes have been systematically investigated. The structure-property correlation and corresponding mechanism have been discussed.

Silicon oxycarbide ceramics as anodes for lithium ion batteries: influence of carbon content on lithium storage capacity

We report here on the synthesis and characterization of silicon oxycarbide (SiOC) in view of its application as a potential anode material for Li-ion batteries.

Supercritical fluid assisted biotemplating synthesis of Si–O–C microspheres from microalgae for advanced Li-ion batteries

Si–O–C microspheres were synthesized from microalgaes served as biological templates and carbon sources with the assistance of supercritical CO₂ fluid. As anodic materials, Si–O–C microspheres exhibited remarkable electrochemical performance.

High rate capabilities of HF-etched SiOC anode materials derived from polymer for lithium-ion batteries

Polymer-derived silicon oxycarbide (SiOC) composites have recently attracted considerable attention because of their potential as high capacity electrode for rechargeable lithium ion batteries.

Polysiloxane-functionalized graphene oxide paper: pyrolysis and performance as a Li-ion battery and supercapacitor electrode

Exfoliated graphene oxide (GO) and polysiloxane were blended and pyrolyzed to synthesize free-standing SiOC–graphene composite papers.

New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics

Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

Lithium species in electrochemically lithiated and delithiated silicon oxycarbides

The work described herein deals with efforts to make a persuasive correlation between structural characteristics and electrochemical lithium storage for a silicon oxycarbide prepared from poly(methylhydrogensiloxane) and divinylbenzene. Structural characterization reveals that the silicon oxycarbide includes excess free carbon in an amorphous network. The reversibility of lithiation and delithiation in the silicon oxycarbide reaches 74% between 0.005 and 3 V relative to lithium at the first cycle but falls to only ca. 30% between 0.4 and 3 V. We found two resonances at 0 and 2.4 ppm in the (7)Li magic angle spinning nuclear magnetic resonance spectrum of the silicon oxycarbide lithiated to 0.4 V, whose contributions are 67 and 33%, respectively, and thus are in good agreement with the reversibility observed between 0.4 and 3 V. The fully lithiated silicon oxycarbide shows a single resonance at ca. 3-9 ppm, which tends to broaden at lower temperatures to -120 °C, whereas the fully delithiated silicon oxycarbide has a single resonance at 0 ppm. These results indicate that both reversible and irreversible lithium species have ionic natures. The Li K edge in electron energy loss spectroscopy does not show clearly any identified near-edge fine structures in the inner part of the silicon oxycarbide after delithiation. Near the surface, on the other hand, LiF and oxygen- and phosphorus-containing compounds were found to be the major constituents of a solid electrolyte interface (SEI) layer. Over repeated lithiation and delithiation, the SEI layer appears to become thick, which should in part trigger capacity fading.