lithium hexafluorophosphate
{{chembox
|Verifiedfields = changed
|Watchedfields = changed
|verifiedrevid = 470454337
|ImageFile =lithium hexafluorophosphate.png
|ImageSize =180px
|IUPACName =lithium hexafluorophosphate
|Section1={{Chembox Identifiers
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 146939
|ChEBI = 172376
|InChI = 1/F6P.Li/c1-7(2,3,4,5)6;/q-1;+1
|InChIKey = AXPLOJNSKRXQPA-UHFFFAOYAJ
|SMILES = [Li+].F[P-](F)(F)(F)(F)F
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/F6P.Li/c1-7(2,3,4,5)6;/q-1;+1
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = AXPLOJNSKRXQPA-UHFFFAOYSA-N
|CASNo =21324-40-3
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = T9T8DY51J3
|PubChem = 23688915
}}
|Section2={{Chembox Properties
|Formula = LiPF6
|MolarMass = 151.905 g/mol
|Appearance = white powder
|Density = 2.84 g/cm3
|MeltingPtC = 200
| Solubility = soluble
}}
|Section3={{Chembox Hazards
|GHSPictograms = {{GHS corrosion}}
|GHSSignalWord = DANGER
|HPhrases = {{H-phrases|314}}
|PPhrases = {{P-phrases|280|310|305+351+338}}
|ExternalSDS = [http://www.convachem.com/product/strImg/msds/21324-40-3.pdf External MSDS]
|FlashPt = Non-flammable
}}
|Section4={{Chembox Related
| OtherCations = Sodium hexafluorophosphate
Potassium hexafluorophosphate
Ammonium hexafluorophosphate
| OtherAnions = Lithium tetrafluoroborate
}}
}}
Lithium hexafluorophosphate is an inorganic compound with the formula LiPF6. It is a white crystalline powder.
Production
LiPF6 is manufactured by reacting phosphorus pentachloride with hydrogen fluoride and lithium fluoride{{cite web |last1=Dunn |first1=JB |last2=Gaines |first2=L |last3=Barnes |first3=M |last4=Sullivan |first4=J |last5=Wang M |title=Material and Energy Flows in the Materials Production, Assembly, and End-of-Life Stages of the Automotive Lithium-Ion Battery Life Cycle |url=https://greet.es.anl.gov/files/li-ion |access-date=5 December 2020 |page=28 |date=Sep 2014}}{{cite web |last1=O'Leary |first1=Brian |title=High-Volume Manufacturing of LiPF6, A Critical Lithium-ion Battery Material |url=https://www.energy.gov/sites/prod/files/2014/03/f11/arravt014_es_oleary_2011_p.pdf |access-date=5 December 2020 |page=5 |date=11 May 2011}}
:PCl5 + LiF + 5 HF → LiPF6 + 5 HCl
Suppliers include Targray and Morita Chemical Industries Co., Ltd.
Chemistry
The salt is relatively stable thermally, but loses 50% weight at 200 °C (392 °F). It hydrolyzes near 70 °C (158 °F){{cite journal|last1=Xu|first1=Kang|title=Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries|journal=Chemical Reviews|date=October 2004|volume=104|issue=10|pages=4303–4418|doi=10.1021/cr030203g|pmid=15669157|s2cid=33074301}} according to the following equation forming highly toxic HF gas:
:LiPF6 + 4 H2O → LiF + 5 HF + H3PO4
Owing to the Lewis acidity of the Li+ ions, LiPF6 also catalyses the tetrahydropyranylation of tertiary alcohols.{{cite journal | doi = 10.1055/s-2004-829550 | title = Lithium Hexafluorophosphate-Catalyzed Efficient Tetrahydropyranylation of Tertiary Alcohols under Mild Reaction Conditions | year = 2004 |author1=Nao Hamada|author2=Sato Tsuneo | journal = Synlett | pages = 1802–1804 | issue = 10}}
In lithium-ion batteries, LiPF6 reacts with Li2CO3, which may be catalysed by small amounts of HF:{{cite journal|last1=Bi|first1=Yujing|last2=Wang|first2=Tao|last3=Liu|first3=Meng|last4=Du|first4=Rui|last5=Yang|first5=Wenchao|last6=Liu|first6=Zixuan|last7=Peng|first7=Zhe|last8=Liu|first8=Yang|last9=Wang|first9=Deyu|last10=Sun|first10=Xueliang|title=Stability of Li2CO3 in cathode of lithium ion battery and its influence on electrochemical performance|journal=RSC Advances|volume=6|issue=23|year=2016|pages=19233–19237|issn=2046-2069|doi=10.1039/C6RA00648E|bibcode=2016RSCAd...619233B}}
:LiPF6 + Li2CO3 → POF3 + CO2 + 3 LiF
Application
The main use of LiPF6 is in commercial secondary batteries, an application that exploits its high solubility in polar aprotic solvents. Specifically, solutions of lithium hexafluorophosphate in carbonate blends of ethylene carbonate, dimethyl carbonate, diethyl carbonate and/or ethyl methyl carbonate, with a small amount of one or many additives such as fluoroethylene carbonate and vinylene carbonate, serve as state-of-the-art electrolytes in lithium-ion batteries.{{cite journal|last1=Goodenough|first1=John B.|last2=Kim|first2=Youngsik|title=Challenges for Rechargeable Li Batteries|journal=Chemistry of Materials|date=9 February 2010|volume=22|issue=3|pages=587–603|doi=10.1021/cm901452z}}{{cite journal|last1=Qian|first1=Yunxian|last2=Hu|first2=Shiguang|last3=Zou|first3=Xianshuai|last4=Deng|first4=Zhaohui|last5=Xu|first5=Yuqun|last6=Cao|first6=Zongze|last7=Kang|first7=Yuanyuan|last8=Deng|first8=Yuanfu|last9=Shi|first9=Qiao|last10=Xu|first10=Kang|last11=Deng|first11=Yonghong|title=How electrolyte additives work in Li-ion batteries|journal=Energy Storage Materials|volume=20|year=2019|pages=208–215|issn=2405-8297|doi=10.1016/j.ensm.2018.11.015|s2cid=139865927}}{{cite book |last1=Jow |first1=T. Richard |last2=Borodin |first2=Oleg |last3=Ue |first3=Makoto |last4=Xu |first4=Kang |title=Electrolytes for Lithium and Lithium-Ion Batteries |date=2014 |publisher=Springer: New York |isbn=9781493903023}} This application takes advantage of the inertness of the hexafluorophosphate anion toward strong reducing agents, such as lithium metal, as well as of the ability of [PF6-] to passivate the positive aluminium current collector.Corrosion inhibition of aluminum current collector with molybdate conversion coating in commercial LiPF6-esters electrolytes. 2021. Corrosion Sci. 190/11. S.L. Yang, S.M. Li, Y.B. Meng, M. Yu, J.H. Liu, B. Li. doi: 10.1016/j.corsci.2021.109632.
References
{{Lithium compounds}}
{{Hexafluorophosphates}}