Four Phosphonium-based Ionic Liquids. Synthesis, Characterization and Electrochemical Performance as Electrolytes for Silicon Anodes

Herein, we describe the synthesis, characterization and electrochemical performance of four phosphonium-based ionic liquids (ILs) as electrolytes, Physicochemical properties such as viscosity, density, ionic conductivity, and thermal stability of ILs and conventional organic solvent ethylene carbonate (EC)/diethyl carbonate (DEC) were experimentally determined at different temperatures. All ILs showed thermal stability greater than 300 degrees C, surpassing the stability of the conventional organic solvent, whose flash points were 145 and 23 degrees C for EC and DEC, respectively. Nevertheless, at room temperature, all ILs are much more viscous than EC/DEC. The composite Si -[P-2224][FSI] (triethyl-n-butylphosphonium bis(fluoromethylsulfonyl)imide) and Si-EC/DEC anodes exhibit initial specific capacities at 0.15 A/g of 2409 and 2631 mAh/g, respectively. This demonstrates that despite the inferior transport properties of ILs, short alkyl-substituted phosphonium ILs like [P-2224][FSI] are potentially competitive for the new generation of electrolytes for LIBs. NMR, DSC, TGA, and galvanostatic discharged/charged were used as characterization techniques.Peer reviewe

In situ-formed nitrogen-doped carbon/silicon-based materials as negative electrodes for lithium-ion batteries

The development of negative electrode materials with better performance than those currently used in Li-ion technology has been a major focus of recent battery research. Here, we report the synthesis and electrochem-ical evaluation of in situ-formed nitrogen-doped carbon/SiOC. The materials were synthesized by a sol-gel pro-cess using 3-(aminopropyl)triethoxysilane (APTES), sodium citrate and glycerol. The electrochemical performance of pyrolyzed materials was studied using poly(acrylic acid) binder and commercial organic elec-trolyte. Our reported approach enables changes in both the amount of nitrogen and the morphology as a func-tion of the molar ratio of APTES:citrate and reaction time. Spherical-shaped NC/SiOC composite electrodes deliver a delithiation capacity of 622 mAh/g at 0.1 A/g and an initial coulombic efficiency of-63%, while in the large bulk material, respective values of 367 mAh/g and-55% were obtained. After 1000 charge/dis-charge cycles at 1.6 A/g, the latter material exhibits 98% of the initial capacity once it returned to lower cur-rent cycling. Overall, our results indicate that NC/SiOC materials are quite promising for electrochemical applications since both their large capacity and stability demonstrate superior performance compared to tradi-tional graphite. Moreover, our synthesis is simple and, more importantly, environmentally friendly chemicals, such as sodium citrate and glycerol, are used.Peer reviewe

Kinetic and Thermodynamic Studies on the Adsorption of Reactive Red 239 by Carra Sawdust Treated with Formaldehyde

In this study, carra sawdust pre-treated with formaldehyde was used to adsorb reactive red 239 (RR239). The effects of several experimental conditions, including the concentration of dye, sorbent dosage, temperature, ionic strength, stirring speed and solution pH, on the kinetics of the adsorption process have been studied, and the experimental data were fitted to pseudo-second-order model. A study of the intra-particle diffusion model indicates that the mechanism of dye adsorption using carra sawdust is rather complex and is most likely a combination of external mass transfer and intra-particle diffusion. The experimental data obtained at equilibrium were analyzed using the Langmuir and Freundlich isotherm models, and the results indicated that at this concentration range, both models can be applied for obtaining the equilibrium parameters. The maximum dye uptake obtained at 298 K was found to be 15.1 mg g(-1). In contrast to the usual systems, the reactive dye studied in the present work is strongly attached to the sawdust even after several washes with water, allowing it to be discarded as a solid waste.FAPESP [2010/08646-9, 2012/02117-0, 2009/53199-3]FAPESPINCT in Bioanalytics (FAPESP) [08/57805-2]INCT in Bioanalytics (FAPESP)CNPq [490116/2007-8]CNP