Effect of combinations of additives on the performance of lithium ion batteries

Commercial lithium-ion batteries have excellent performance at room temperature for a few years. However, the calendar life and thermal stability (>50 °C) need to be improved for many applications, including electric vehicles. We have conducted an investigation of the effect of thermal stabilizing additives, including dimethyl acetamide, vinylene carbonate, and lithium bis(oxalato) borate, on the performance of lithium ion batteries stored at 70 °C for one month. The reactions of the lithium hexafluorophosphate/carbonate electrolyte, with and without electrolyte additives, with the surface of the electrodes after initial formation cycling have been analyzed via a combination of IR-ATR and XPS.     

Effect of gelator structures on electrochemical properties of ionic-liquid supramolecular gel electrolytes

Bis(4-acylaminophenyl)methane (G1) and bis(4-acylaminophenyl)ether (G2) with varied acyl chains were found to be efficient gelators for the gelation of imidazole-based ionic liquids. The supramolecular gel electrolytes were formed via the self-assembly of these gelators in ionic liquids. The minimum gelator concentrations (MGCs) for the gelation of ionic liquids depend on the chemical structures of the gelators. The longer the acyl chains, the lower the MGCs. Polarized optical microscopy images of the ionic-liquid gels reveal the formation of spherical crystallites resulting from the fibrillar aggregates of the gelators. In addition, the phase transition temperatures of the ionic-liquid gels increase with an increase of the acyl chain length of the gelators. The impedance spectra of the ionic-liquid gels indicate that the temperature dependence of the conductivity follows the classical Arrhenius equation. The conductivities of ionic-liquid gels also decrease with an increase of the acyl chain length, but the differences in conductivities between the gels and corresponding ionic liquids are in one order of magnitude. The ionic-liquid gels possess a stable electrochemical window.     

Reversibility of electrochemical magnesium deposition from tetrahydrofuran solutions containing pyrrolidinyl magnesium halide

In this paper we reported for the first time the electrochemical behavior of pyrrolidinyl magnesium halide (C₄H₈NMgX, X = Br and Cl) dissolved in tetrahydrofuran (THF) with regard to potential application as electrolytes for rechargeable magnesium batteries. C₄H₈NMgX/THF solutions were characterized in term of conductivity, anodic stability, and reversibility of magnesium deposition and dissolution. Furthermore, the effect of metal substrates on magnesium deposition process was studied. Simple preparation, high cycling reversibility and moderate anodic stability of C₄H₈NMgBr/THF solution indicate the feasible application as the electrolyte for rechargeable magnesium batteries.     

On the measurement of the real values of individual ionic activities: A chemical engineering perspective

This work demonstrates the perfect analogy between the standard method for determining activities in non-electrolyte mixtures and the method used for the determination of ionic activities in electrolyte solutions. For the case of electrolyte solutions, the general procedure of solving three equations with three unknowns is discussed and the reasons why this procedure failed to work for the case of KCl solutions are recapitulated. A modified iteration procedure implemented in this work gives convergence of the solution after three iterations. The crucial difference between eliminating the junction potential, by combination of independent equations, and the use of a proper estimate of its value is emphasized. A new model-free calibration procedure is proposed and sample calculations of K⁺ and Cl⁻ activities in KCl aqueous solutions are presented. Values of K⁺ and Cl⁻ activities in KCl aqueous solutions obtained by this new procedure and by a variety of other methods and researchers are compared.     

Improved ceramic and electrical properties of CaZrO3-based proton-conducting materials prepared by a new convenient combustion synthesis method

The present work emphasizes the features of a new combustion synthesis method suitable for easy synthesis and sintering of CaZrO₃-based materials as promising proton-conducting electrolytes for electrochemical applications in solid oxide electrochemical devices. Sc- and In-doped CaZrO₃ compounds are selected to be the objects of investigation and their crystal structure properties as well as microstructural, thermal and electrical characteristics are studied by the means of X-ray diffraction analysis, high-temperature dilatometry, scanning electron spectroscopy, impedance and 4-probe DC conductivity techniques. The established properties are critically compared with previously obtained data to confirm the prospects of the proposed method synthesis for the preparation of Zr-based proton-conducting ceramic materials. It is found that CaZr_0.95Sc_0.05O_3–δ exhibits predominantly protonic conductivity under wet air atmospheres below 700 °C; while, CaZr_0.9In_0.1O_3–δ demonstrates a certain value of electronic conductivity along with ionic one.     

Understanding the effects of electrode meso-macropore structure and solvent polarity on electric double layer capacitors based on a continuum model

The structures of electrode meso-macropore and the solvent polarity are the crucial factors dominating the performance of the electric double layer capacitors (EDLCs), but their impacts are usually tangled and difficult to decouple and quantitate. Here the effects of electrode meso-macropore structure and solvent polarity on the specific capacitance of an EDLC are quantitatively investigated using a steady-state continuum model. The simulation results indicate the specific capacitances are significantly affected by the meso-macropore surface structure. The specific capacitances significantly decrease for both convex surface structures but obviously increase for both concave surface structures, with the increase of curvature radius from 1 to 20 nm. As for solvents, the polar solvent with high saturated dielectric permittivity improves the capacitance performance. Moreover, the electrode meso-macropore structure is of more concern compared with solvent polarity when aiming at enhancing the specific capacitance. These results provide fundamentals for the rational design of porous electrodes and polar electrolytes for EDLCs.     

Biorefinery process water effluent treatments by salt coagulation

Acid pretreatment is one of the critical pretreatments for the biorefinery. However, little information is available on water effluent that results from this acidic pretreatment compared to alkaline pretreatment. In this study, the wastewaters from an integrated modern magnesium bisulphite pulp mill (acidic) were utilized as models for the acid pretreatment effluents of a modern biorefinery. The coagulation technique, using high valency electrolytes, was applied for the treatment of treated and untreated process water from the pulp mill. The effectiveness of some electrolytes and the selectivity of the coagulation process were compared by measuring the removal extent of critical contaminants such as organics, phosphorus and colour. The salt coagulation process was found to be selective for colour and total phosphorus removal from the wastewater, achieving more than 90% removal of contaminants.     

Highly Efficient Electrochemiluminescence of Functionalized Tris(2,2′‐bipyridyl)ruthenium(II) and Selective Concentration Enrichment of Its Coreactants

An enhanced electrochemiluminescence (ECL) efficiency is obtained from the ruthenium complex tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) by introduction of an ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF₄). Upon addition of 1 % (v/v) BMImBF₄ to 0.1 mM Ru(bpy)₃²⁺ solution, a maximum increase in ECL intensity is obtained both at an indium tin oxide (ITO) electrode (15‐fold) and at a glassy carbon (GC) electrode (5‐ to 6‐fold). Furthermore, upon addition of 1 % (v/v) BMImBF₄ to 5 μM Ru(bpy)₃²⁺/100 mM co‐reactant systems at a GC electrode, IL adsorption occurs at the electrode surface, which results in a change of the polarity of the electrode surface. Such functionalization greatly improves the functions of both Ru(bpy)₃²⁺ and ionic liquids, as is demonstrated in the sensitive and selective concentration enrichment of the Ru(bpy)₃²⁺ co‐reactants.     

Effects of electrolytes on the electrochemical performance of Si/graphite/disordered carbon composite anode for lithium-ion batteries

The influences of LiBF₄, LiClO₄, lithium bis(oxalato) borate (LiBOB), LiPF₆ with VC and without VC, and the mixed electrolytes composed of different ratios of LiBOB and LiPF₆ or LiClO₄ on the electrochemical properties of Si/graphite/disordered carbon (Si/G/DC) composite electrode were systematically investigated by constant current charge-discharge and electrochemical impedance spectra (EIS) techniques. Scanning electron microscopy (SEM) was used to observe the change of electrodes in morphology after given cycle numbers. X-ray photoelectron spectroscopy (XPS) was employed to understand the influences of different mixed electrolytes on the composition of SEI layers. The results showed that Si/G/DC composite electrode in the mixed electrolytes presented better electrochemical performance than in single electrolyte. The compactness and compositions of SEI layers intensively influenced the cycle performance of Si/G/DC composite materials. LiBOB and additive VC had a good synergistic effect on the formation of the dense SEI layers. In particular, Si/G/DC in 0.5 M LiBOB + 0.38 M LiPF₆ electrolytes containing VC exhibited a high reversible capacity and excellent cycle performance.