Rong Yang

Activated porous carbon materials with ultrahigh specific surface area derived from banana peels for high-performance lithium–sulfur batteries

A series of banana peels derived porous carbon (BPPC) materials were fabricated by pyrolysis carbonization with different numbers of KOH activation. The Brunauer–Emmett–Teller tests indicated the number of activation effectively improves the specific surface area and pore volume of the BPPC. Amongst, the BPPC-2 (activated twice) possesses ultrahigh specific surface area (2044.57xa0m2xa0g−1) and large pore volume (2.40xa0cm3xa0g−1) on account of the improved hierarchical porous microstructure. After S loading process, the resultant C/S composites were introduced as cathode material in Li–S batteries. The S/BPPC-2 composite cathode exhibited a higher initial specific capacity (1481.54xa0mAhxa0g−1 at 0.1xa0C) and a better reversible capacity (351 mAhxa0g−1 after 300 cycles at 1xa0C) than those of others. It also exhibited excellent high rate performance even at 5xa0C. The enhanced electrochemical performances were ascribed to the improved specific surface area and larger pore volume of the BPPC-2, which effectively facilitated the intimate contact between sulfur and the conductive matrix, accommodating severe volume change. Besides, the micro/mesopores provided high adsorption power to inhibit the dissolution of polysulfides. This research suggested that the activation number played a key role in improving the electrochemical performance of composite cathode in Li–S batteries.

Preparation and Electrochemical Properties of Coral-like Li2FeSiO4/C Cathode Material by Two-Step Precipitation Method

Lithium iron silicate (Li2FeSiO4) cathode materials have been synthesized by a soft chemical method combined with spray drying, being both simple and economical. Superxa0P, as a new kind of nanoscale carbon black, was added in the synthesis process. The phase and microstructure of the samples were characterized by x-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. The results show that the obtained Li2FeSiO4 possessed coral-like morphology with size range from 250xa0nm to 450xa0nm. Superxa0P was decorated on the surface of the Li2FeSiO4 particles. Furthermore, the electrochemical properties of the products were tested, indicating that the as-obtained Li2FeSiO4/C composite presented high specific discharge capacities and stable cycling performance, which can be attributed to the coral-like morphology and Superxa0P coating.

The hierarchical porous structure of carbon aerogels as matrix in cathode materials for Li-S batteries

For Li-S batteries, commercial application was hindered by the insulating nature of S and the solubility of polysulfide. Porous carbon materials had proven themselves to be an ideal immobilizer host for S impregnation. Herein, carbon aerogels (CAs) with tunable pore microstructure were synthesized from resorcinol-formaldehyde reaction with increasing catalyst concentration and pyrolysis under high temperature. The results demonstrated that the catalyst concentration played a key role in tuning the porous microstructure of the CAs. In addition, potassium hydroxide (KOH) was introduced to activate the obtained CAs. The activated carbon aerogels (A-CAs) with hierarchical porous structure exhibited the highest specific surface area (1837.4xa0m2xa0g−1) and the largest total pore volume (2.276xa0cm3xa0g−1), which combined the advantages of both mesoporous and microporous. The effects of porous microstructure, specific surface area, and pore volume of the CAs and A-CAs on S incorporation were studied. The S/A-CAs exhibited significantly improved reversible capacity (1260xa0mAhxa0g−1 at a rate of 0.1 C), enhanced high-rate property, and excellent cycling performance (229xa0mAhxa0g−1 after 500xa0cycles at 1 C) as a cathode for Li-S batteries.

An efficient process to fabricate spherical hierarchical LiFePO 4 /C cathode composites with controllable coating thickness

Hierarchical lithium iron phosphate/carbon (LiFePO4/C) microspheres were fabricated successfully using a facile spray drying-assisted coprecipitation method. A relatively short calcination time and a relatively low calcination temperature were adopted to prepare the hierarchical LiFePO4/C microspheres. The hierarchical microspheres consisted of nanoparticles with a uniform coating of amorphous carbon. The thickness of the carbon layer was controlled by the addition of glucose. The hierarchical LiFePO4/C microspheres exhibited a high tap density and a large specific surface area. The electrochemical properties of the sample were investigated. The sample exhibited a better rate capability and a better cyclability than the coral-like LiFePO4/C cathode material, and these were ascribed to the highly uniform carbon coating and the self-assembled nanoparticles.