Carbon materials have drawn remarkable attention as promising anode materials for high performance sodium-ion batteries (SIBs). Developing carbon-based anodes is important for the practical utilization of SIBs in energy storage technologies. Herein, hard carbon spheres encapsulated with graphene networks are prepared by a large-scalable and low-cost method, which deliver better electrochemical performance, such as rate capability and long-cycling life with respect to the ever reported hard carbon materials. The electrochemical test indicates that the as-prepared hard carbon anode exhibits a reversible capacity of 140 mA h g⁻¹ under a current density up to 10 A g⁻¹. Of special interest is that the capacity of 122 mA h g⁻¹ is maintained after 4000 cycles, corresponding to the high capacity retention of 87.1%. The robust and flexible structure of the G-HCS material could facilitate a fast electron and sodium ion transport rate, and sustain fast sodium storage at a high current rate owing to the construction of conductive graphene networks with outstanding electrical conductivity, enabling good contact between hard carbon sphere particles and graphene nanosheets. These results provide a rewarding avenue to design and optimize advanced carbon anode materials for next-generation SIBs.

Outdoor insulators are often subject to corona discharges and the problem is becoming more prevalent with the increasing use of higher transmission voltage levels. For polymeric insulators, exposure to such discharges can alter the chemical structure of basic polymer and degrade surface properties. This paper investigates the effect of micro and/or nano fillers in silicone rubber composites in suppressing such damage. Four different types of samples are fabricated: pristine silicone rubber (PR), 30wt% micron–sized silica/silicone rubber (MC), 27.5wt% micron + 2.5wt% nano silica/silicone rubber (NMC), and 5wt% nano silica/silicone rubber (NC) composites. Samples are exposed to AC corona using a needle to ground-plane electrode setup. Experimental results are analyzed based on five different measurement methods: phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), Surface roughness and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that NC shows a strong resistance to partial discharges and hydrophobicity loss. In the area below the needle tip, higher hydrophobicity loss and higher recovery are observed as compared to the vicinity region. Variations in surface roughness, appearance of crackles, voids, pits, surface splitting into blocky structures and damages to chemical structure of silicone rubber are appreciably retarded in NC as compared to PR, MC and NMC. Based on NMC results, it is found that addition of nano–sized silica can be an attractive approach to improve the corona resistance of micron–sized silica filled silicone rubber.

Silicone rubber is a hydrophobic polymer which is widely employed for high voltage outdoor insulation. The material offers excellent electrical performance under contaminated environments. However, pristine silicone rubber has low thermal properties and this may cause tracking and erosion failure due to severe dry band arcing and ohmic heating on the insulating surface. This work investigates the effect of material thermal characteristics on the tracking and erosion resistance of silicone rubber filled with micron sized alumina tri-hydrate (ATH), aluminum nitride (AlN) and boron nitride (BN) particles. Composites with different loading were synthesized by dispersing particles in pristine room temperature vulcanizing (RTV) silicone rubber and IEC 60587 inclined plane test (IPT) was conducted to evaluate tracking and erosion resistance. Apart from physical parameters and leakage current, an infrared thermal imager was used to measure the surface temperature distribution during the course of IPT. Experimental results showed tracking and erosion resistance is significantly enhanced with addition of BN particles followed by ATH. AlN composites exhibit poor tracking and erosion resistance, similar to pristine silicone rubber. It is concluded that addition of BN-composites improves ability to impede the tracking and erosion process, the reasons being better thermal stability and enhanced thermal conduction in the discharge region. On the other hand, infrared analysis revealed thermal accumulation is remarkably higher in AlN-composites which promotes dry band arcing and results in tracking and erosion failure.

Increasing demands in minimization of fire risks and meeting fire safety requirements by polymers require advances in knowledge of flame-retardant materials suitable for use in fire-retardancy applications. The present work represents the seminal review of alginate/polymer-based materials as flame retardants. Alginates are suitable for this application as they represent alternatives to petroleum-based polymer feedstocks. The content of the present work is structured into four sections: synthesis and structure, including alginate synthesis and modification by polymeric conjugation; properties, including four-stage mechanism of thermal degradation; applications, including commercial information on alginates and polymers; and flame retardancy, including comprehensive summaries of test methods and published data, discussion of key parameters, eight fire retardancy mechanisms, four char generation mechanisms, and extensive quantitative analysis of polymer char formation. The final section culminates in a first-principles approach to the prediction of quantitative polymer char formation. The goal of the review is to provide guidance for the application of alginates and alginates conjugated with fire-retardant polymers as a new generation flame retardant material.