Lithium hexafluoroarsenate LiAsF

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. 

In 1994, Tadiran, an Israeli company, made the discovery described as follows This cell comprises as main components a negative electrode which is Lithium or Lithium alloy, a positive cathode which includes MnOa and an electrolyte which is 1,3-Dioxolane (148) with Lithium hexafluoroarsenate (LiAsFe) and a polymerization inhibitor [143]. 

Silver vanadium oxide is combined with a conductive carbon and a binder like PTFE to make the cathode. The usual electrolyte solution used is lithium hexafluoroarsenate (LiAsFs) in mixed organic solvents, like propylene carbonate and 1,2-dimethoxyethane. 

As a result of their investigation work, Honeywell concluded that electrolyte decomposition at elevated operating temperatures in lithium-vanadium pentox-ide cells could be considerably reduced if the electrolyte were made basic. Thus an electrolyte with the composition 2 m lithium hexafluoroarsenate (LiAsF ) plus 0.4 M lithium borofluoride (LIBF4) is now used in these cells. 

As lithium bromide appeared to initiate the reactions causing electrolyte instabilities, Honeywell investigated other lithium salts for use in reserve battery electrolytes and concluded that lithium hexafluoro-arsenate (LiAsFe) combined with acetonitrile and sulphur dioxide was a suitable electrolyte, which did not exhibit discoloration or deposition of solids during storage. Table 24.1 compares the performance of batteries made up using the lithium bromide- and lithium hexafluoroarsenate-based electrolytes. Clearly, the 0.5 molal lithium hexafluoroarsenate electrolyte is functionally equivalent or superior to the lithium bromide electrolyte. 

Table 11.3 Lithium salts as electrolyte solutes [1] with L1BF4 lithium tetrafluoroborate, LiBF lithium hexafluorophosphate, LiAsFs lithium hexafluoroarsenate, UCIOa lithium perchlorate, Li-triflate lithium trifluoromethanesulfonate Li itnide (LiTFSI) BIS (trifluoromethane) suifonimide lithium...

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