Stable and efficient Li-ion battery anodes prepared from polymer-derived silicon oxycarbide-carbon nanotube shell/core composites

We demonstrate synthesis and electrochemical performance of polymer-derived silicon oxycarbide-carbon nanotube (SiOC-CNT) composites as a stable lithium intercalation material for secondary battery applications. Composite synthesis was achieved through controlled thermal decomposition of 1,3,5,7-tetramethyl 1,3,5,7-tetravinyl cyclotetrasiloxane (TTCS) precursor on carbon nanotubes surfaces that resulted in formation of shell/core type ceramic SiOC-CNT architecture. Li-ion battery anode (prepared at a loading of~ 1.0 mg cmˉ²) showed stable charge capacity of 686 mAh gˉ¹ even after 40 cycles. The average coulombic efficiency (excluding the first cycle loss) was 99.6 %. Further, the post electrochemical imaging of the dissembled cells showed no apparent damage to the anode surface, highlighting improved chemical and mechanical stability of these composites. Similar trend was observed in the rate capability tests, where the SiOC-CNT anode (with 5 wt.% loading in TTCS) again showed stable performance, completely recovering the first cycle capacity of ~ 750 mAh gˉ¹ when the current density was brought back to 50 mA gˉ¹ after cycling at higher current densities

Preparation of Nanocrystalline TiO 2

Nanocrystalline TiO2 electrodes were prepared using binder-free TiO2 paste on conductive ITO-PEN substrates by the doctor-blade method at significantly low temperature (140 °C), and the electrodes were further processed under different compressions (10–60 MPa) in order to improve interparticle connections and adhesion between the nanoparticles and the ITO-PEN substrate. TiO2 electrodes compressed at 30 and 40 MPa had relatively less cracks with low crack width. Electrode compressed at 30 MPa showed the highest internal surface area. Electrode prepared at this compression showed the best dye-sensitized solar cell (DSC) performance with Voc of 805 mV, Jsc of 9.24 mA cm–2, and an overall efficiency of 4.39%. Electrochemical impedance spectroscopy (EIS) studies of the sandwiched cells employing bare nanocrystalline TiO2 electrode and Pt counter electrode in I–/I3– electrolyte showed that electrode compression significantly influences the stability of the cells. EIS data suggested that degradation/corrosion processes may take place on ITO-PEN for sandwiched cells made by TiO2 electrodes compressed at all pressures. Thirty and 40 MPa compressions showed a minor degradation of ITO. The recombination dynamics at the TiO2/electrolyte interface were influenced by the changes in the nanostructured electrode internal surface area, changes in electron transport properties (due to improved sintering), and possible degradation/corrosion of ITO-PEN. Open-circuit voltage decay (OCVD) measurements showed that the DSC made by the 30 MPa compressed TiO2 electrode had the highest decay time, indicating low recombination properties, which is in a good agreement with other data

Electrically conductive silicon oxycarbide thin films prepared from preceramic polymers

This work focuses on silicon oxycarbide thin film preparation and characterization. The Taguchi method of experimental design was used to optimize the process of film deposition. The prepared ceramic thin films with a thickness of c. 500 nm were characterized concerning their morphology, composition, and electrical properties. The molecular structure of the preceramic polymers used for the preparation of the ceramic thin films as well as the thermomechanical properties of the resulting SiOC significantly influenced the quality of the ceramic films. Thus, an increase in the content of carbon was found beneficial for the preparation of crack-free thin films. The obtained ceramic films exhibited increased electrical conductivity as compared to monolithic SiOC of similar chemical composition. This was shown to correlate with the unique hierarchical microstructure of the SiOC films, which contain large oxygen-depleted particles, mainly consisting of highly graphitized carbon and SiC, homogeneously dispersed in an oxygen-containing amorphous matrix. The matrix was shown to also contain free carbon and to contribute to charge carrier transport between the highly conductive large particles. The ceramic thin films possess electrical conductivities in the range from 5.4 to 8.8 S/cm and may be suitable for implementation in miniaturized piezoresistive strain gauges