Thermal stability electrolytes

Synthetic polymers and natural polymers suitable for drilling muds are listed in Tables 1-7 and 1-8, respectively. Polyacrylamides are eventually hydrolyzed in the course of time and temperature. This leads to a lack of tolerance toward electrolyte contamination and to a rapid degradation inducing a loss of their properties. Modifications of polyacrylamide structures have been proposed to postpone their thermal stability to higher temperatures. Monomers such as AMPS or sulfonated styrene/maleic anhydride can be used to prevent acrylamide comonomer from hydrolysis [92]. 

Polydrill is a sulfonated polymer for filtration control in water-based drilling fluids [1775]. Tests demonstrated the product s thermal stability up to 200° C and its outstanding electrolyte tolerance. Polydrill can be used in NaCl-saturated drilling fluids as well as in muds containing 75,000 ppm of calcium or 100,000 ppm of magnesium. A combination of starch with Poly drill was used successfully in drilling several wells. The deepest hole was drilled with 11 to 22 kg/m of pregelatinized starch and 2.5 to 5.5 kg/m of Polydrill to a depth of 4800 m. Field experience with the calcium-tolerant starch/Polydrill system useful up to 145° C has been discussed in detail [1774]. 

This material was first synthesized in the middle 1960s by E.I. Du Pont de Nemours and Co., and was soon recognized as an outstanding ion conductor for laboratory as well as for industrial electrochemistry. The perfluorinated polymeric backbone is responsible for the good chemical and thermal stability of the polymer. Nation membrane swollen with an electrolyte solution shows high cation conductivity, whereas the transport of anions is almost entirely suppressed. This so-called permselectivity (cf. Section 6.2.1) is a characteristic advantage of Nation in comparison with classical ion-exchange polymers, in which the selective ion transport is usually not so pronounced. 

There are a few reports of poly(naphthalene) thin films. Yoshino and co-workers. used electrochemical polymerization to obtain poly(2,6-naphthalene) film from a solution of naphthalene and nitrobenzene with a composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate. Zotti and co-workers prepared poly( 1,4-naphthalene) film by anionic coupling of naphthalene on. platinum or glassy carbon electrodes with tetrabutylammonium tetrafluoroborate as an electrolyte in anhydrous acetonitrile and 1,2-dichloroethane. Recently, Hara and Toshima prepared a purple-colored poly( 1,4-naphthalene) film by electrochemical polymerization of naphthalene using a mixed electrolyte of aluminum chloride and cuprous chloride. Although the film was contaminated with the electrolyte, the polymer had very high thermal stability (decomposition temperature of 546°C). The only catalyst-free poly(naphthalene) which utilized a unique chemistry, Bergman s cycloaromatization, was obtained by Tour and co-workers recently (vide infra). 

On the other hand, since most of these reactions are thermally activated, their kinetics are accelerated by the rise in temperature in an Arrhenius-like manner. Therefore, within a much shorter time scale, the adverse effect of these reactions could become rather significant during the storage or operation of the cells at elevated temperatures. In this sense, the long-term and the thermal stability of electrolytes can actually be considered as two independent issues that are closely intertwined. The study of temperature effects on electrolyte stability is made necessary by the concerns over the aging of electrolytes in lithium-based devices, which in practical applications are expected to tolerate certain high-temperature environments. The ability of an electrolyte to remain operative at elevated temperatures is especially important for applications that are military/space-related or traction-related (e.g., electric or hybrid electric vehicles). On the other hand, elevated tem-... 

When conducting a differential scanning calorimetry (DSC) study on the stability of carbonaceous anodes in electrolytes, Tarascon and co-workers found that, before the major reaction between lithiated carbon and fluorinated polymers in the cell, there was a transition of smaller thermal effect at 120 °C, marked peak (a) in Figure 28. They ascribed this process to the decomposition of SEI into Li2C03, based on the previous understanding about the SEI chemical composition and the thermal stability of lithium alkyl carbonates.Interestingly, those authors noticed that the above transition would disappear if the carbonaceous anode was rinsed in DMC before DSC was performed, while the other major processes remained (Figure 28). Thus,... 

Surprisingly, when the cathode material, LiCo02, was in the presence of these thermally stable salts, Lilm and LiMe, much higher reactivity was detected than that in the presence of LiPFe, as indicated by the total absence of any combustion suppression on SHR that had been observed with LiPFe. DSC results of LiCoOz in the presence of Lilm- or LiBeti-based electrolytes confirmed the above observation, which showed the onset thermal decomposition of LiCo02 to be at 280 °C, whereas in LiPFe-based electrolytes the same thermal event was much suppressed in terms of heat evolution as the concentration of LiPFe increased. In other words, the presence of Lilm and LiBeti did not introduce any increase in the thermal stability of the electrode, while LiPFe, although believed to be thermally unstable, efficiently suppressed the thermal decomposition of the cathode. 

With few exceptions, these new electrolyte solvents focus on possible improvements in low-temperature performance, while new salts are intended to offer higher thermal stability. This divided directions of pursuit after the targeted improvements is apparently created by the fact that solvent and salt, respectively, impose the upper and lower temperature limits of the current state-of-the-art electrolytes. 

Handa et al. reported the synthesis of a phosphorus equivalent of Barthel s salts in which the hexavalent phosphorus(V) was coordinated by three bidentate ligands. 1.2-benzenediolato-O.C7. Its thermal stability is similar to that of its boron counterparts, and moderate ion conductivity was achieved in nonaqueous media. The authors attributed the less-than-satisfactory ion conduction to the large size of the anions, which increased the viscosity of the resultant electrolyte solutions. The anodic stability limit, as measured by voltammetry on a Ni electrode, was below 3.7 V. A preliminary test of this salt in EC/ THF was conducted in a lithium cell using the low potential cathode. V2O5. and the authors believed that this salt could be a superior electrolyte solute, judging from the utilized cell capacity that was close to the theoretical value. 

The thermal stability of LiFAP was also studied by Aurbach and co-workers in EC/DEC/DMC solution using ARC. As compared with LiPFe, LiFAP delayed the onset thermal decomposition of the electrolyte by 10 °C however, the self-heating became much more severe once the reactions started. The above ARC was conducted in the absence of electrode materials. 

Figure 74. Improved thermal stability of an electrolyte by flame retardant HMPN (a, left) DSC traces for baseline electrolyte with (1.68%) and without HMPN in the presence of a fully lithiated graphite anode (Reproduced with permission from ref 523 (Figure 5). Copyright 2000 The Electrochemical Society.) (b, right) SHR of baseline electrolyte with (10.0%) and without HMPN in the presence of metallic lithium. (Reproduced with permission from ref 523 (Figure 6). Copyright 2000 The Electrochemical Society.)...

The early patent disclosures have claimed the application of a wide spectrum of gas-evolving ingredients and phosphorus-based organic molecules as flame retarding additives in the electrolytes. Pyrocarbonates and phosphate esters were typical examples of such compounds. The former have a strong tendency to release CO2, which hopefully could serve as both flame suppressant and SEI formation additive, while the latter represent the major candidates that have been well-known to the polymer material and fireproofing industries.The electrochemical properties of these flame retardants in lithium ion environments were not described in these disclosures, but a close correlation was established between the low flammability and low reactivity toward metallic lithium electrodes for some of these compounds. Further research published later confirmed that any reduction of flammability almost always leads to an improvement in thermal stability on a graphitic anode or metal oxide cathode. 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

Room-temperature ionic liquids are attractive due to their chemical and thermal stability, negligible vapor pressure, high ionic conductivity, and ample electrochemical window. Their properties can be varied by a rational choice of the cations and of the anions and can represent an important iodide source for an I /I3 -based electrolyte (Fig. 17.12). 

The use of quasi-solid-state electrolytes usually reaches the goal of a superior thermal stability with respect to liquid electrolytes cells can survive prolonged periods (accelerated aging of 1000 h) at relatively high temperatures (55-80°C) under... 

These liquids have been studied primarily for their applications as electrolytes in electrochemical technologies such as electroplating, batteries, and alloy preparations. They have excellent chemical and thermal stabilities and are good solvents for highly charged complex ions of high or low oxidation states. The Lewis acidities can be varied with the composition of the liquid. 

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