Thermal behavior salts effects

In contrast to that of solvents, the effect of the electrolyte solute, LiPFe, on the thermal decomposition of the cathode, LiCo02, was found to be suppression instead of catalyzation. The SHR of a partially delithiated cathode was measured in a series of electrolytes with various salt concentrations, and a strong suppression of the self-heating behavior was found as the concentration of LiPEe increased above 0.50 M. The mechanistic rationale behind this salt effect is still not well understood, but the authors speculated that the salt decomposition coated the cathode with a protective layer that acted as a combustion retardant. On the basis of these results, the authors recommended a higher salt concentration (>1.50 M) for LiCo02-based lithium ion cells is preferred in terms of thermal safety. 

The interplay of these various effects is very well demonstrated in a study of the thermal behavior of 45 different salts prepared by the reaction of five different substituted imidazoles and nine different Brensted acids [9]. The study shows particularly well that predictions based on any one of the parameters that can affect melting points alone will often fail. 

Pitawala et al., (2007) studied the combined effect of both plasticizer and nano-ceramic filler on the thermal behavior and conductivity of (PEO)g-lithium trifiuoromethanesulphonate (LiCFjSOj or LiTf) composite polymer electrolyte. The formula (PE0)gLiCFjS03 denotes the chemical composition of the polymer-salt complex in which 9 is the molar ratio of (ethylene oxide (EOl/LiCF SOj). According to their work, addition of 15 wt% Aip lowered the and T of (PEO)gLiTf from 58 °C and °Cto 51 °C and -50 °C, respectively and the con-... 

The combined effects of a divalent Ca counterion and thermal treatment can be seen from studies of PMMA-based ionomers [16]. In thin films of Ca-salts of this ionomer cast from methylene chloride, and having an ion content of only 0.8 mol%, the only observed deformation was a series of long, localized crazes, similar to those seen in the PMMA homopolymer. When the ionomer samples were subject to an additional heat treatment (8 h at 100°C), the induced crazes were shorter in length and shear deformation zones were present. This behavior implies that the heat treatment enhanced the formation of ionic aggregates and increased the entanglement strand density. The deformation pattern attained is rather similar to that of Na salts having an ion content of about 6 mol% hence, substitution of divalent Ca for monovalent Na permits comparable deformation modes, including some shear, to be obtained at much lower ion contents. 

The 3-mercapto-1,2-dithiolium salts (39a) also suffer deprotonation on addition of water. This behavior is the basis of a simple and effective method of purification, which is particularly useful for aryl-substituted trithiones. 48 The tendency towards charge neutralization in the alkylmercapto-1,2-dithiolium ions is also the reason for the relative ease of removal of the alkyl group (cf. thermal dealkylation, transmethylation), as well as for the extremely labile bonding of other groups such as acyl—, —S02—, —SO—, —S2C1, and halogen to the exocyclic S atom of the corresponding 3-mercapto-1,2-dithiolium derivatives. 

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