Impact of blending with polystyrene on the microstructural and electrochemical properties of SiOC ceramic

In this work, we present the electrochemical behavior and microstructural analysis of silicon oxycarbide (SiOC) ceramics influenced by an addition of polystyrene (PS). Polymer-derived ceramics were obtained by pyrolysis (1000 degrees C, Ar atmosphere) of different polysiloxanes prepared by sol-gel synthesis. This method is very effective to obtain desired composition of final ceramic. Two alkoxysilanes phenylthriethoxysilane and diphenyldimethoxysilane were used as precursors. Before pyrolysis polysiloxanes were mixed with PS using toluene as a solvent. Blending with PS affects the microstructure and free carbon content in the final ceramic material. Free carbon phase has been confirmed to be a major lithium storage host. Nevertheless, we demonstrate here that capacity does not increase linearly with increasing carbon content. We show that the amount of SiO4 units in the SiOC microstructure increases the initial capacity but decreases the cycling stability and rate capability of the material. Furthermore, the microstructure of the free carbon influences the electrochemical performance of the ceramic: More ordered graphitic clusters favor better rate capability performance

Organic-inorganic materials for fast charging-discharging processes in energy storage devices

The electrochemical properties of composite material consisting of poly(3, 4-ethylenedioxythiophene) (pEDOT) and iron hexacyanocobaltate (FehcCo) have been investigated for supercapacitors' application. The composite material pEDOT/FehcCo was electrodeposited on titanium or carbon fabric substrate. Prepared electrodes were used in supercapacitors operating in nonaqueous electrolytes (1 M KPF6, 1 M LiPF6 in ethylene carbonate with dimethyl carbonate mixture of solvents). The capacitance values were estimated by galvanostatic and cyclic voltammetry techniques. The material was investigated in symmetric two-electrode cell configuration. The material pEDOT/FehcCo exhibits high capacitance values (~70 F cm-3) and a good cycling performance with a high stability in the tested electrolytes

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

Influence of pyrolysis atmosphere on the lithium storage properties of carbon-rich polymer derived SiOC ceramic anodes

Polymer derived carbon-rich SiOC ceramics are prepared from polysiloxane precursors through a pyrolysis process at 1000 °C using pure argon and argon/hydrogen mixture as pyrolysis atmosphere. The precursor is synthesized from a linear (Si–H)-containing polysiloxane cross-linked with divinylbenzene using hydrosilylation reaction in the presence of a platinum catalyst. Pyrolysis in Ar/H2 mixtures, compared to the treatment under pure Ar, results into a decrease of the concentration of C dangling bonds as revealed by electron spin resonance (ESR) measurements. The amount of free carbon phase is 10 wt.% lower in the sample pyrolysed in a Ar/H2 mixture, while the ratio of hydrogen to free carbon remains constant for both, in Ar and in Ar/H2 pyrolysed samples. The sample prepared under Ar/H2 mixture shows an excellent cycling stability with an increase in the specific capacity of about 150 mAhg− 1 compared to its analogues pyrolysed in pure argon atmosphere

Tailoring of SiOC composition as a way to better performing anodes for Li-ion batteries

Polymer derived silicon oxycarbide (SiOC) ceramics are investigated as potential anodes for lithium ion batteries. Different SiOC ceramics are prepared by pyrolysis (1000 °C and 1400 °C under controlled argon atmosphere) of polysiloxanes ceramic precursors. Preceramic polymers are synthesized using the sol–gel method. Phenyltriethoxysilane (PhTES) and methyltriethoxysilane (MTES) have been used as starting precursors and mixed with different ratios in order to tailor the chemical composition and the structure of the final product. The obtained SiOC ceramics are amorphous with various content of free carbon phase (from approx. 25 to 40 wt.%). The presence of disordered carbons in the ceramic structure is confirmed by the appearance of a well pronounced D band at 1330 cm− 1 in the Raman spectra. Additionally, 29Si MAS-NMR spectra show the presence, in the structure of the materials pyrolysed at 1000 °C, of mixed bond tetrahedra such as: SiO3C, SiO2C2, SiOC3 and SiO4 units. Pyrolysis at an elevated temperature (1400 °C) promotes the phase separation into oxygen rich (SiO4) and carbon rich (SiC4) units with consumption of mixed bonds. Carbon rich SiOC samples exhibit significant reversible capacity and enhanced cycling stability (up to 600 mAh g− 1 measured at a slow current rate of C/20 after 140 cycles of continuous charging–discharging with increasing current density). However, the high irreversible capacity of the first few cycles remains an issue to be solved

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. SiOC ceramics are obtained by pyrolysis of various polysiloxanes synthesized by sol–gel methods. The polysiloxanes contain different organic groups attached to silicon, which influence the chemical composition and the microstructure of the final ceramic product. The structure of the SiOC samples is investigated by XRD, micro-Raman spectroscopy, solid state 29Si MAS-NMR and TEM. All investigated samples remain amorphous. However, at the elevated temperature of pyrolysis a phase separation process begins. During this process the carbon clusters become more ordered, which is reflected in the higher intensity and narrowing of the D1 band and decreasing of the D3 band. Moreover, the elevated temperature of pyrolysis promotes consumption of mixed bonds units, SiO3C, SiO2C2, SiOC3, and increases the share of oxygen rich SiO4 and carbon rich SiC4 tetrahedra. Electrochemical studies show a clear dependence between free carbon content and lithium storage capacity. Carbon-rich samples exhibit significantly higher capacities (∼550 mA h g−1 recorded at low current rate after 140 charge–discharge cycles) compared to carbon-poor samples (up to 360 mA h g−1). Moreover, carbon-rich samples exhibit a lower irreversible capacity during their first cycles compared to low carbon samples

Material Design and Optimisation of Electrochemical Li-Ion Storage Properties of Ternary Silicon Oxycarbide/Graphite/Tin Nanocomposites

In this work, we present the characterization and electrochemical performance of various ternary silicon oxycarbide/graphite/tin (SiOC/C/Sn) nanocomposites as anodes for lithium-ion batteries. In binary SiOC/Sn composites, tin nanoparticles may be produced in situ via carbothermal reduction of SnO2 to metallic Sn, which consumes free carbon from the SiOC ceramic phase, thereby limiting the carbon content in the final ceramic nanocomposite. Therefore, to avoid drawbacks with carbon depletion, we used graphite as a substitute during the synthesis of precursors. The ternary composites were synthesized from liquid precursors and flake graphite using the ultrasound-assisted hydrosilylation method and pyrolysis at 1000 °C in an Ar atmosphere. The role of the graphitic component is to ensure good electric conductivity and the softness of the material, which are crucial for long term stability during alloying–dealloying processes. The presented approach allows us to increase the content of the tin precursor from 40 wt.% to 60 wt.% without losing the electrochemical stability of the final material. The charge/discharge capacity (at 372 mA g−1 current rate) of the tailored SiOC/C/Sn composite is about 100 mAh g−1 higher compared with that of the binary SiOC/Sn composite. The ternary composites, however, are more sensitive to high current rates (above 372 mA g−1) compared to the binary one because of the presence of graphitic carbon