Ultra-light energy storage devices that bestow both high power density and high energy storage along with miniature size, minimal cost, and stable performance are currently the need of the hour for high-speed electronic devices. To achieve high energy storage density in dielectric capacitors, the breakdown strength and dielectric constant should be enhanced, along with decreased dielectric loss. Most of the contemporary dielectric materials fail to maintain the high dielectric permittivity, low dielectric loss and high breakdown strength simultaneously. Traditionally, combining glass ceramics, such as SiO2, with dielectric materials has been thought to be a possible way to minimize loss of tanδ as well as maximize dielectric permittivity, especially for high temperature applications. However, the high production cost and low breakdown strength still hinder commercial prospects. Interestingly, the presence of free-carbon domains found in polymer derived silicon oxycarbides (SiOC) were observed to demonstrate enhanced dielectric permittivity by virtue of improved interfacial polarisation. Further, the ever-existent demands in Li-ion batteries for alternative anode materials to graphite to achieve increased capacity, longer life high-rate capabilities can also be envisaged through SiOC based polymer derived ceramics wherein, the free carbon network acts as storage centres for Li+ ions.
Briefly, silicon oxycarbides are well-known advanced ceramics because of their unique structure composed mainly of a Si–O–C glass phase with a free carbon region. Furthermore, modifying the processing parameters and the composition of the pre-ceramic polymer allows for a considerable variation in the mechanical and functional properties of these ceramics. However, very few authors reported on the dielectric properties of SiOC and metal modified SiOCs for energy storage devices. Moreover, the modification of silicate glass networks with transition metal oxides has been demonstrated to result in in-situ nano crystallized amorphous structure and, as a result, significant improvement in interfacial polarization, which eventually enhances dielectric permittivity and decreases tanδ losses as well was observed. Further, SiOC/metal oxide materials have demonstrated increased rate capability and cyclic stability. However, SiOC modified with transition metal-oxide precursors for LIB anodes have not been explored yet.
Hence, in this study through precursor-derived ceramic methodology hafnium modified poly methyl hydro siloxane was synthesised. The mixture solution taken in 1:1 (v/v) ratio was cross-linked at 250 °C and pyrolyzed at 900 °C under an argon atmosphere. The powders were sintered at 1200 °C using the spark plasma sintering technique to produce SiOC/HfO2 nano composites. X-ray diffractograms confirmed the crystallization of tetragonal HfO2 in these composites. The presence of free carbon with D and G peaks was confirmed through Raman spectroscopy. Electron microscopy was used to explore morphological features. The dielectric permittivity of the SiOC/HfO2 composites at room temperature and 1kHz frequency showed a value of εr ~15 and loss of tanδ ~ 0.05 compared to SiOC (εr ~7 and tanδ ~ 0.5). This work provides a pathway for cost-effective, tuneable, and fully functional SiOC/HfO2 composites for next-generation dielectrics. Further investigation of the dielectric properties of SiOC and SiOC/HfO2 composites with increased temperature and transition metal-modified siloxanes (Si(Ti)OC and Si(Nb)OC) as potential anode materials for LIBs is underway and will be discussed in the subsequent studies.