Salts LiAsF

Dioxolane-l, 2-dimethoxyethane-Li2 B1()C11() exhibited chemical stability towards the components of a lithium-titanium disulfide cell and showed promise as an electrolyte in such cells [98], Among various systems composed of an ether-based solvent and a lithium salt, THF-LiAsF6 was the least reactive to lithium at elevated temperature and gave the best cycling efficiency [99, 100], Tetrahydrofu-ran-diethyl ether-LiAsF(i afforded lithium electrode cycling efficiency in excess of 98% [101],... 

The maximum ionic conductivities of the complexes XV/LiAsF and XV/ LiCl04 at the same temperature are 5x10 and 6x10 S cm respectively [10]. XV is completely amorphous from -100 to +100 °C. Its Tg is -74 °C in the absence of salt. Its dimensional stability is considerably higher than that of the linear MEEP with a similar molecular weight, and it forms free-standing films. 

The anodic stability of the AsFe" anion proved to be high. In proper solvents, such as esters rather than ethers, the electrolyte based on this salt can remain stable up to 4.5 V on various cathode surfaces.The combination of cathodic and anodic stability would have made LiAsFe a very promising candidate salt for both lithium and lithium ion batteries had the toxicity not been a source of concern. Instead, it was never used in any commercialized cells but is still frequently used in laboratory tests even today. ... 

Like LiAsFe, LiBF4 is a salt based on an inorganic superacid anion and has moderate ion conductivity in nonaqueous solvents (Table 3). It was out of favor in the early days of lithium battery research because the ether-based electrolytes containing it were found to result in poor lithium cycling efficiencies, which decayed rapidly with cycle number. ° The reactivity of LiBF4 with lithium was suspected as discoloration occurred with time or heating. 

Aurbach et al. and Andersson et al. also detected the presence of surface layers on cathodes with XPS. The former authors noted that the presence of salts (LiPFe and LiAsFe) played a crucial role in changing the surface state of cathode materials due to their acidic nature, because pure solvents do not change the native surface layer, Li2C03, when brought into... 

Surface chemical characterization of the passivation layer on the Al surface has been performed mainly via XPS, and the interpretation of results generated by various researchers still remains controversial. Because salt anions with active fluorine (LiPFe, LiAsFe, and LiBF4) are able to form stable surface layers on Al and protect it from corrosion, early studies had suggested that fluoride species such as LiF and AIF3 are crucial to the protection. 

Lithium tetrafluoroborate, (LiBF4), lithium hexafluorophosphate, (LiPF6), lithium hexafluoroarsenate, (LiAsF ), lithium trifluoromethane sulfonate, (LiSOjCFj), are the electrolyte salts of the 21st Century. The performance of lithium ion cells, primary and secondary lithium cells depends on the purity of these compounds. Several hundred tons of these materials have been produced and many more tons — and perhaps thousands of tons — will be required in the near future. One of the largest automotive producers predicts that there may be a market for 10-15 million pounds of these salts. The demand for Lithium ion primary cells is also very huge in electronics, computers, communication systems and military applications. 

The recent example of the ab initio structure determination of the polymer electrolyte Poly (ethylene oxide)6 LiAsFe by Bruce et is a notable example of the complex structures that can be determined from powder diffraction on a pulsed neutron source. Polymer electrolytes consist of salts dissolved in solid high molecular weight polymers, and represent a unique class of solid coordination compounds. Their importance lies in their potential in the development of truly all-solid-state rechargeable batteries. The structure of the 6 1 complex is particularly important, as it is a region where the conductivity increases markedly. The structure of the complex is distinct from all known crystal structures of PEO salt complexes (see Figure 7). The Li-i- cations are arranged in rows, with each row located inside a cylindrical surface formed by two PEO chains, with the PEO chains adopting a previously unobserved conformation. Furthermore the anions are located outside the PEO cylinders and are not coordinated with the cations. 

The onset potentials reported in Table 12 were estimated from the deflection points in the I versus E curves. However, if we determine the oxidation onset potential according to the potentials in which the anodic current exceeds a predetermined value, such as 0.5 mA/cm, it is then clear from Auborn s data that the anodic stability of the above salts is according to the following order LiAsFe, LiBp4, LiPF > LiC104, LiSOsCFs. 

The third group involves LiC104 and LiAsFe. These two salts are usually not acidic and are only moderately reactive on the Li surfaces, depending on the solvents. In ethers, their reduction processes are pronounced and may dominate the Li surface chemistry, while in the more reactive solvents such as alkyl carbonates and esters, solvent reduction processes usually dominate the Li surface chemistry. LiC104 reduction on the Li surfaces contributes LiCl and Li20 as obvious surface species [77-80]. However, there is some evidence for the formation of species of the LiC10 c type (4 > x) [216]. LiAsFe reduction contributes LiF and species of the Li jAsFy type as obvious surface species [101-105,159,217] (see Scheme 8). 

Fig. 1.12 Ionic conductivity of EC PC (50 50 v v) and 2-MeTHF EC PC (75 12.5 12.5 v v v) mixtures with LiAsF for different temperatures and salt concentrations [5]...

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