Lithium tetrafluoroborate

Names IUPAC name Other names Identifiers ChemSpider ECHA InfoCard 100.034.692 Edit this at Wikidata UNII Properties LiBF₄ Molar mass 93.746 g/mol Appearance White/grey crystalline solid Odor odorless Density 0.852 g/cm³ solid Melting point 296.5 °C (565.7 °F; 569.6 K) Boiling point decomposes Very soluble^[1] Hazards Occupational safety and health (OHS/OSH): Harmful, causes burns,
hygroscopic. NFPA 704 (fire diamond) Safety data sheet (SDS) External MSDS Related compounds Tetrafluoroborate, Nitrosyl tetrafluoroborate

Lithium tetrafluoroborate is an inorganic compound with the formula Li BF₄. 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.^[2]

Although BF₄⁻ has high ionic mobility, solutions of its Li⁺ salt are less conductive than other less associated salts.^[2] As an electrolyte in lithium-ion batteries, LiBF₄ offers some advantages relative to the more common LiPF₆. It exhibits greater thermal stability^[3] and moisture tolerance.^[4] For example, LiBF₄ can tolerate a moisture content up to 620 ppm at room temperature whereas LiPF₆ readily hydrolyzes into toxic POF₃ 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.

Because LiBF₄ 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:^[5]

LiBF₄ → LiF + BF₃

LiBF₄ is a byproduct in the industrial synthesis of diborane:^{[5] [6]}

8 BF₃ + 6 LiH → B₂H₆ + 6 LiBF₄

LiBF₄ can also be synthesized from LiF and BF₃ in an appropriate solvent that is resistant to fluorination by BF₃ (e.g. HF, BrF₃, or liquified SO₂):^[5]

LiF + BF₃ → LiBF₄