Lithium tetrafluoroborate is an inorganic compound with the formula LiBF4. 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, LiBF4 offers some advantages relative to the more common LiPF6. It exhibits greater thermal stability and moisture tolerance. For example, LiBF4 can tolerate a moisture content up to 620 ppm at room temperature whereas LiPF6 readily hydrolyzes into toxic phosphoryl fluoride (POF3) and hydrogen fluoride (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 LiBF4 and other alkali-metal salts thermally decompose to evolve boron trifluoride (BF3), the salt is commonly used as a convenient source of the chemical at the laboratory scale:
LiBF4 → LiF + BF3
Production LiBF4 is a byproduct in the industrial synthesis of diborane:
8 BF3 + 6 LiH → B2H6 + 6 LiBF4 It can also be synthesized from LiF and BF3 in an appropriate solvent that is resistant to fluorination by BF3 (e.g. HF, Bromine trifluoride (BrF3), or liquified Sulfur dioxide (SO2):
LiF + BF3 → LiBF4
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