Liquid Electrolyte Solutions

The dissolution of a salt in water was described by Arrhenius as a dissociation of the salt in positive and negative ions of free mobility. This was originally a difficult suggestion to accept because salts were very stable substances. Therefore, for a long time the theory was called Arrhenius dissociation hypothesis. Later it became clear that the process was a reaction of the solvent water with the ions and that the ion-dipole interaction provided the necessary energy for the compensation of the strong lattice energies. For example, the process can be formulated for sodium chloride by the equation 

The enthalpy of solution connected with the solution process is relatively small because it is just the difference between the lattice enthalpy and the enthalpy of solvation of cations and anions. For several years the dissociation theory explained most of the experimental 

A molar conductivity is obtained if the specific conductivity g is divided by the concentration c 

K 7 is measured in S cm , c should be measured in mol cm . Then A is measured in S cm mol. The conductivity of aqueous electrolytes is related to the mobility of cations and anions, and u. Mobility is the rate of motion in a field of one V cm. The independent conductivity of anions and cations was postulated 

The mobility was also used to define transference numbers (also called transport numbers) for anions and cations (Hittorf ) 

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In porous liquid-phase electrodes, all pores are hlled with liquid electrolyte (solution or melt). When part of the pores are gas hlled, the electrodes are called gas-liquid. When the electrode is nonconsumable and chemically inert, its pore structure will remain unchanged during operation (or change very slowly on account of secondary aging processes). The structure of an electrode that reacts changes continuously. 

Liquid surfaces and liquid-liquid interfaces are very common and have tremendous significance in the real world. Especially important are the interfaces between two immiscible liquid electrolyte solutions (acronym ITIES), which occur in tissues and cells of all living organisms. The usual presence of aqueous electrolyte solution as one phase of ITIES is the main reason for the electrochemical nature of such interfaces. 

The ion solvating polymers have found application mainly in power sources (all-solid lithium batteries, see Fig. 2.19), where polymer electrolytes offer various advantages over liquid electrolyte solutions. 

Polymer gels and ionomers. Another class of polymer electrolytes are those in which the ion transport is conditioned by the presence of a low-molecular-weight solvent in the polymer. The most simple case is the so-called gel polymer electrolyte, in which the intrinsically insulating polymer (agar, poly(vinylchloride), poly(vinylidene fluoride), etc.) is swollen with an aqueous or aprotic liquid electrolyte solution. The polymer host acts here only as a passive support of the liquid electrolyte solution, i.e. ions are transported essentially in a liquid medium. Swelling of the polymer by the solvent is described by the volume fraction of the pure polymer in the gel (Fp). The diffusion coefficient of ions in the gel (Dp) is related to that in the pure solvent (D0) according to the equation ... 

Reactions (5.5.30) and (5.5.31) proceed prevailingly during intercalation from solid or polymer electrolytes (cf. Section 2.6) or melts. When using common liquid electrolyte solutions, a co-insertion of solvent molecules (and/or intercalation of solvated ions) very often occurs. The usual products of electrochemical intercalation are therefore ternary compounds of a general composition ... 

Abraham et al. were the first ones to propose saturating commercially available microporous polyolefin separators (e.g., Celgard) with a solution of lithium salt in a photopolymerizable monomer and a nonvolatile electrolyte solvent. The resulting batteries exhibited a low discharge rate capability due to the significant occlusion of the pores with the polymer binder and the low ionic conductivity of this plasticized electrolyte system. Dasgupta and Ja-cobs patented several variants of the process for the fabrication of bonded-electrode lithium-ion batteries, in which a microporous separator and electrode were coated with a liquid electrolyte solution, such as ethylene—propylenediene (EPDM) copolymer, and then bonded under elevated temperature and pressure conditions. This method required that the whole cell assembling process be carried out under scrupulously anhydrous conditions, which made it very difficult and expensive. 

The band bending at the semiconductor/liquid (electrolyte solution) interface can be understood by considering the potential distribution at this interface. In a case where the electrolyte solution contains a redox couple (R/Ox), which causes an electrochemical redox reaction,... 

It is now generally accepted that, given a sufficiently accurate classical force field, molecular dynamics (MD) simulations are capable of predicting thermophysical, structural, dynamical and mechanical properties in quantitative agreement with experiment for a wide variety of materials, including liquids and their mixtures [9-12], polymer melts [13-18], polymer solutions [19-21], polymer electrolytes [22-24] and liquid electrolyte solutions [25]. 

This book focuses on three types of nonaqueous systems—liquid electrolyte solutions, ionically conducting polymers, and molten salts—with emphasis on the more commonly used liquid systems. It provides a review of a variety... 

Nonaqueous liquid electrolyte solutions may be divided into subgroups according to several criteria based on the differences among the various polar aprotic solvents. The first division can be between protic or polar aprotic nonaqueous solvents and nonpolar solvents. In polar aprotic and protic nonaqueous systems, conductivity is achieved by the dissolution of the electrolytes and the appropriate charge separation of the dissolved species, allowing for their free migration under the electrical field. In nonpolar systems the conductance mechanism may be more... 

Electrochemical windows of nonaqueous liquid electrolyte solutions and what determines them. 

Stability of electrodes in liquid electrolyte solutions, corrosion problems. Especially interesting is the electrochemistry of active metals. 

V. CONDUCTIVITY OF LIQUID ELECTROLYTE SOLUTIONS BASED ON POLAR APROTIC SOLVENTS... 

In this chapter, the above issues are dealt with point by point. The emphasis is on experimental aspects related to liquid electrolyte solutions, since these are the most commonly used and have the broadest applications. 

A great deal of effort was dedicated to the study of Li electrodes in polymeric electrolyte systems [112-115], These can serve as alternatives for the liquid electrolyte solutions in which dendrite formation is such a severe problem. 

While most of this chapter is devoted to liquid electrolyte solutions, an intensive amount of work is currently devoted to R D of polymeric electrolyte systems for Li batteries. Of particular importance are polymeric electrolyte systems that maintain high room temperature conductivity (the order of 10 3 S/cm, which is comparable to the conductivity of Li salt solutions in many polar aprotic systems) [382],... 

It was possible to improve the interfacial properties of Li metal anodes in liquid electrolyte solutions using additives that modify the Li-surface chemistry, such as C02 [23-27] and HF [28,29], Using PEO-based gel electrolyte systems effectively suppressed dendritic deposition of lithium [30], In Section C we report on a very good charge-discharge performance of lithium metal anodes in PVdF-HFP gel electrolyte systems. Furthermore, addition of C02 to the PVdF-HFP gel electrolyte system considerably improves the charge/discharge characteristics [31]. 

Carbon powder mixed with polymeric binder (PVdF, PTFE) has been widely used as anode material for lithium ion batteries and as the electrode material for EDLC with liquid electrolyte solutions. When such composite electrodes composed of carbon powder and polymer binder were used in all-solid-state EDLC, the performance was not good enough because of poor electrical contact between the electrode s active mass and the electrolyte. By having the electrolyte inside the composite electrode, the contact between the active mass in the electrode and the electrolyte can be considerably improved and hence the capacitance can... 

Continuous mixtures Phase equilibria of mixtures Polar and associating liquids Electrolyte solutions... 

Dry cell — Popular name of batteries made by the addition of starch, flour (Paul Schmidt, 1899), or other gelling agents to the liquid electrolyte solution which then shows no typical properties of a water-like liquid anymore, in particular it is nonspillable. One of the first representatives of this class of primary cells was designed by -> Leclanche. 

Kavan [28] and Kijima et al. [29] have used the electrochemical method to synthesize carbyne. This technique may be realized by classical electrochemistry whereby the charge transfer reaction occurs at interface of a metal electrode and liquid electrolyte solution. Electrons in reaction were supplied either through redox active molecules or through an electrode, which contacts an ionically conducting solid or liquid phase and the precursor. In general, the structure and properties of electrochemical carbon may differ considerably from those of usual pyrolytic carbons. The advantage of this technique is the synthesis of carbyne at low (room) temperature. It was shown that the best product was prepared by cathodic defluorination of poly(tetrafluoroethylene) and some other perhalo-//-alkanes. The carbyne... 

Lin M. S., Hung N. and Wrighton M. S. (1982), Interface energetics for n-type semiconducting strontium titanate and titanium dioxide contacting liquid electrolyte solutions and competitive photoanodic decomposition in non-aqueous solutions , J. Electroanal. Chem. 135, 121-143. 

The first section of this book covers liquids and. solutions at equilibrium. I he subjects discussed Include the thcrmodvnamics of solutions, the structure of liquids, electrolyte solutions, polar solvents, and the spectroscopy of solvation. The next section deals with non-equilibrium properties of solutions and the kinetics of reactions in solutions. In the final section emphasis is placed on fast reactions in solution and femtochemistry. The final three chapters involve important aspects of solutions at interfaces. Fhese include liquids and solutions at interfaces, electrochemical equilibria, and the electrical double layer. Author W. Ronald Fawcett offers sample problems at the end of every chapter. The book contains introductions to thermodynamics, statistical thermodynamics, and chemical kinetics, and the material is arranged in such a way that It may be presented at different levels. Liquids, Solutions, and Interfaces is suitable for senior undergr.iduates and graduate students and will be of interest to analytical chemists, physical chemists, biochemists, and chemical environmental engineers. 

The subject matter in this monograph falls into three general areas. The first of these involves liquids and solutions at equilibrium. These subjects are discussed in chapters 1-5, and include the thermodynamics of solutions, the structure of liquids, electrolyte solutions, polar solvents, and the spectroscopy of solvation. 

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