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],... 

According to the depth profile of lithium passivated in LiAsF6 / dimethoxyethane (DME), the SEI has a bilayer structure containing lithium methoxide, LiOH, Li20, and LiF [21]. The oxide-hydroxide layer is close to the lithium surface and there are solvent-reduction species in the outer part of the film. The thickness of the surface film formed on lithium freshly immersed in LiAsF /DME solutions is of the order of 100 A. 

Li PC, EC, DME /LiAsF, SNIFTIR, EMIRS R0C02Li, Li2C03, peroxides, ketals [181]... 

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. 

Further, tungsten oxysulfide films, WOyS, have shown promising behavior as positive electrodes in microbatteries, unlike WS2 that is not suitable as cathode in lithium cells. Using amorphous thin films of WO1.05S2 and WO1.35S2.2 in the cell Li/LiAsFe, 1 M ethyl-methyl sulfone (EMS)/W03,Sz, Martin-Litas et al. [80] obtained current densities up to 37 xA cm between 1.6 and 3 V. In these cathode materials, 0.6 and 0.8 lithium per formula unit, respectively, could be intercalated and de-intercalated reversibly. 

Scheme 2. Reaction between LiAsFe and Ether Solvents...

The above process was observed only in the initial cycles. Nevertheless, any electrochemical reduction of As(V) would raise concern about the safety of using LiAsFe in a commercial battery, because, while arsenate in its high oxidation state (V) is not particularly toxic, As(III) and As(0) species From the electrochemical point of view, however, the above reduction could be a benefit, especially for lithium ion cells, since an SET formed on an anode at > 1.0 V vs lithium would be very stable during the operation of a lithium ion cell according to a semi-empirical rule, ° which will be discussed in more detail in section 6. 

Very similar to the case of LiC104, an SEI formed from LiAsFe-based electrolytes, either on a lithium or carbonaceous anode, mainly consists of alkyl carbonates or Li2COs rather than LiF, as one would expect from the behavior of its close structural brothers LiPFe or LiBF4. This can be attributed to the much less labile As—F bond that is resistive to hydrolysis. 

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. 

LiAsFe. According to the ionics studies on the limiting properties in various solvents, this excellent conductivity results from the combination of its ionic mobility and dissociation constant, although in neither category does LiPFe stand at the most outstanding position " ... 

---