Lithium hexafluorophosphate

Structural formula
General
Surname	Lithium hexafluorophosphate
other names	Lithium phosphorus hexafluoride LHFP LFP
Molecular formula	Li [PF 6 ]
Brief description	white odorless solid
External identifiers / databases
CAS number 21324-40-3 EC number 244-334-7 ECHA InfoCard 100.040.289 PubChem 23688915 Wikidata Q2583808
properties
Molar mass	151.91 g mol −1
Physical state	firmly
density	1.5 g cm −3 (20 ° C)
Melting point	200 ° C
solubility	soluble in water
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 301-314-372 P: 260-280-301 + 330 + 331 + 310-303 + 361 + 353-304 + 340 + 310-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Lithium hexafluorophosphate is an inorganic compound consisting of lithium , more precisely the cation Li ⁺ , and the hexafluorophosphate anion PF ₆ ^- , so that the empirical formula LiPF ₆ results. LiPF ₆ is the lithium salt of the volatile hexafluorophosphoric acid . The white crystalline powder is mainly used in the electrolyte in lithium batteries and lithium batteries used. Due to its properties , LiPF ₆ is overall better suited for this application than possible alternatives, so that it is used in almost all Li cells.

LiPF _{6 also} serves as a catalyst in the conversion of tertiary alcohols into tetrahydropyran .

Properties of salt and electrolytes

Pure, solid lithium hexafluorophosphate is stable when heated up to 107 ° C. Above this temperature it begins to decompose. This creates solid lithium fluoride LiF and gaseous phosphorus pentafluoride PF ₅ :

${\displaystyle {\ce {LiPF6 -> LiF + PF5 ^}}}$,

The decomposition reaction is only so pronounced above 160 ° C that a significant increase in pressure occurs due to the evolution of gas, and it only proceeds rapidly above the melting point of 200 ° C.

In the presence of water , e.g. B. humidity , the product when LiPF _{6 is} heated is not PF ₅ , but hydrogen fluoride HF and the phosphorus oxide fluoride POF ₃ :

${\displaystyle {\ce {LiPF6 + H2O -> LiF + 2HF ^ + POF3 ^}}}$,

the decomposition reaction starts at a lower temperature than in the absence of water.

The electrical conductivity of the solutions of LiPF ₆ in aprotic solvents is - compared to other lithium salts - extraordinarily high. In carbonic acid ester mixtures (solvents made from organic carbonates) such as the battery-relevant mixture EC / DMC , a higher conductivity is obtained than in solutions of the same concentration of lithium perchlorate or lithium tetrafluoroborate , e.g. B. 11.2 mS cm ⁻¹ for a one molar solution of LiPF ₆ in EC / DMC (50:50). LiPF ₆ is not as toxic as lithium hexafluoroarsenate (V) LiAsF ₆ . In addition, it forms a passivating , AlF ₃ -containing layer on aluminum foils in lithium ion accumulators, which are required as current collectors , so that corrosion is minimized there. Due to the combination of these properties, LiPF _{6 is} used as an electrolyte in almost all lithium-ion accumulators and lithium batteries. The concentration of the electrolyte solution is often approximately one molar, since the conductivity decreases again when the concentration is increased further.

See also

• other inorganic hexafluorophosphates with monovalent cation:
  • Ammonium hexafluorophosphate
  • Sodium hexafluorophosphate
  • Potassium hexafluorophosphate
  • Silver hexafluorophosphate
• Applications for LiPF ₆ :
  • Lithium-ion accumulator
  • Lithium battery
    • Lithium carbon monofluoride battery

Individual evidence

1. ↑ ^{a b c d} Entry on lithium hexafluorophosphate (1-) in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
2. ↑ ^{a b} Entry on 3-lithium hexafluorophosphate at ChemicalBook , accessed on November 27, 2013.
3. ↑ John B. Goodenough, Youngsik Kim: Challenges for Rechargeable Li Batteries . In: Chem. Mater. , 2010, Volume 22, pp. 587-603. doi : 10.1021 / cm901452z .
4. ↑ ^{a b c d e} Wesley A. Henderson: Electrolytes for lithium and lithium-ion batteries . Ed .: T. Richard Jow, Kang Xu, Oleg Borodin, Makoto Ue (=  Modern Aspects of Electrochemistry . No. 58 ). Springer, 2014, ISBN 978-1-4939-0301-6 , ISSN  2197-7941 , Nonaqueous Elektrolytes: Advances in Lithium Salts, p. 5-26 , doi : 10.1007 / 978-1-4939-0302-3 .
5. ↑ Hamada, N .; Tsuneo S .: Lithium Hexafluorophosphate-Catalyzed Efficient Tetrahydropyranylation of Tertiary Alcohols under Mild Reaction Conditions . In: Synlett . No. 10, 2004, p. 1802. doi : 10.1055 / s-2004-829550 .
6. ↑ ^{a b c d} Hui Yang, Guorong V. Zhuang, Philip N. Ross Jr .: Thermal stability of LiPF ₆ salt and Li-ion battery electrolytes containing LiPF ₆ . In: Journal of Power Sources . tape 161 , no. 1 . Elsevier, October 20, 2006, p. 573-579 , doi : 10.1016 / j.jpowsour.2006.03.058 ( osti.gov ).
7. Jump up ↑ Qingsong Wang, Jinhua Sun, Shouxiang Lu, Xiaolin Yao, Chunhua Chen: Study on the kinetics properties of lithium hexafluorophosphate thermal decomposition reaction . In: Solid State Ionics . tape 177 , no. 1-2 . Elsevier, January 16, 2006, p. 137-140 , doi : 10.1016 / j.ssi.2005.09.046 ( elsevier.com ).
8. ↑ Xiang-Guo Teng, Fa-Qiang Li, Pei-Hua Ma, Qi-Du Ren, Shi-You Li: Study on thermal decomposition of lithium hexafluorophosphate by TG-FT-IR coupling method . In: Thermochimica Acta . tape 436 , no. 1-2 . Elsevier, October 1, 2005, p. 30–34 , doi : 10.1016 / j.tca.2005.07.004 ( elsevier.com ).