Lithium tetrafluoroborate
# Lithium tetrafluoroborate

Lithium tetrafluoroborate is an inorganic compound with the formula $LiBF_4.$ It is a white crystalline powder. It has been extensively tested for use in commercial secondary batteries, an application that exploits its high solubility in nonpolar solvents.

## Applications

Although $BF_4^−$ has high ionic mobility, solutions of its $Li^+$ salt are less conductive than other less associated salts. As an electrolyte in lithium-ion batteries, $LiBF_4$ offers some advantages relative to the more common $LiPF_6.$ It exhibits greater thermal stability and moisture tolerance. For example, $LiBF_4$ can tolerate a moisture content up to 620 ppm at room temperature whereas $LiPF_6$ readily hydrolyzes into toxic $POF_3$ and HF gases, often destroying the battery's electrode materials. Disadvantages of the electrolyte include a relatively low conductivity and difficulties forming a stable solid electrolyte interface with graphite electrodes.

## Thermal stability

Because $LiBF_4$ and other alkali-metal salts thermally decompose to evolve boron trifluoride, the salt is commonly used as a convenient source of the chemical at the laboratory scale:

    $LiBF_4$ → LiF + $BF_3$

## Production

$LiBF_4$ is a byproduct in the industrial synthesis of diborane:

    8 $BF_3$ + 6 LiH → $B_2H_6$ + 6 $LiBF_4$

$LiBF_4$ can also be synthesized from LiF and $BF_3$ in an appropriate solvent that is resistant to fluorination by $BF_3$ (e.g. HF, $BrF_3,$ or liquified $SO_2):$

    LiF + $BF_3$ → $LiBF_4$
