Note: Descriptions are shown in the official language in which they were submitted.
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1. Field of the invention:
The invention relates to a process for the industrial
synthesis of anhydrous lithium imides salts, containing
fluorosulfonyl (FSO2-) or fluorophosphoryl (F2PO-)
electroattractor radical, such as (FSOz);NLi or (F2PO)2NLi.
2. Description of the prior art:
Salts of low basicity anions are widely used in various
industrial fields such as polymerization process, catalysis or
batteries. In this last huge market application, lithium salt
are one of the key component for electrolytes preparation.
Numerous lithium salts have been or are used in lithium
batteries such as CF3SO3Li, LiBF4, LiPF6 or LiN (SO2CF3) 2. In
addition to provide stable and conductive electrolytes when
mixed with suitable organic solvents, lithium salts for
batteries applications need to be obtain in an anhydrous state
(typically with water content inferior to 1000 ppm and
preferably inferior to 100 ppm).
LiPF6 is the main salt used in commercial lithium-ion
("Li-Ion") technology but it presents some drawbacks,
especially a limited thermal stability which lowered the
security of the battery and a poor stability to hydrolysis. On
the other hand, salt such as LiN(SO2CF3)2 are stable up to
300 C and are not sensitive to hydrolysis but, due to cathodic
corrosion of aluminum current collector, this salt is only
used as an additive in Li-Ion technology.
A valuable compromise has been found by replacing CF3- radicals
by fluorine atoms in LiN (S02CF3) 2= Indeed, LiN (SO2F) 2 imide is
in particular more conductive and more stable on storage than
LiPF6. Thus LiN(S02F)2 ("LiFSI") is a valuable substitute of at
least LiPF6.
A few preparation process of LiFSI or its acid form are
described. For example, concerning preparation of the acid,
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bis(fluorosulfonyl)imide (FSO2)2NH ("HFSI") is prepared by
action of fluorosulfonic acid FSO3H with urea H2NC(O)NH2. Pure
acid is then obtained by NaCl treatment of bulk media in
dichloromethane followed by a distillation [Appel &
Eisenhauer, Chem. Ber. 95, 246-8, 1962]. However, toxicity and
corrosive character of fluorosulfonic acid are major drawbacks
of this synthesis. Moreover, yield of the reaction can
fluctuate strongly for several experiments. An other process
implied reaction of (C1SO,) zNH ("HC1SI") with AsF3. (FS02) 2NH is
further isolated after treatment of bulk media by NaCl in
dichloromethane [Ruff & Lustig, Inorg. Synth. 1968, 11, 138-
43]. This process is of poor interest due to the high price of
AsF3 and its toxicity.
From this acid, the preparation of its lithium salt is also
difficult. Contrary to LiPF6, it is possible to prepare lithium
salt of HFSI ("LiFSI") in water solution from the acid and a
lithium source such as lithium carbonate. However, on drying,
it is impossible to abstract the last molecules of water
without decomposing major part of the lithium salt, this is
specific to the lithium cation due to the high reticular
energy of LiF. W095/26056 described a process to produce LiFSI
by reacting (FSO2)2NH and LiF in an aprotic solvent, such as
acetonitrile. This process present several drawbacks, first
the stability of the solvent to strong acid and it is also
rather difficult to dry the obtained slurry to obtain pure
LiFSI as there is a strong interaction between the lithium
salt and acetonitrile solvent.
W002/053494 describe a process to prepare monovalent salt of
HFSI by a "Halex" process in aprotic solvents. Such process is
mainly designed to obtain the potassium salt of HFSI ("KFSI").
LiFSI salt preparation is also described but lead to the
formation of a LiFSI salt containing large amount of impurity
such as FSO3Li.
In the case of phosphoryl derivatives, the reaction of
LiN ( SiMe3) 2 with POF3 lead to the formation of LiN ( POF2) Z after
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elimination of volatile Me3SiF [Fluck & Beuerle,
Z. Anorg. Allg. Chem. 412(1), 65-70, 1975]. However, this
process used costly silyl derivatives and toxic gaseous POF3.
So, it is clear this laboratory process is far from an
industrial one's, moreover the final product contains
undesirable Me3SiF complex with the salt which is difficult to
remove. Moreover, this synthesis is of a limited scope.
Unfortunatly, it appears there is no satisfactory industrial
process to produce anhydrous lithium imides salts, containing
fluorosulfonyl (FSO2-) or fluorophosphoryl (F2PO-)
electroattractor radical such as (FSO2)2NLi or (F2PO)zNLi, and
more generally to produce their acid precursors.
3. Description of the invention:
To overcome those difficulties of salt preparation such as
LiFSI, research has been done on various synthetic pathways,
such as for example lithiation of the acid by alkyllithium in
anhydrous alcane solvent. In fine, as a result of extensive
investigations, a process based on anhydrous HF chemistry has
been designed as the most suitable industrial synthetic
procedure for anhydrous lithium imides salts, containing
fluorosulfonyl (FSO?-) or fluorophosphoryl (F2PO-)
electroattractor radical and characterized in that the
fluorine atoms are covalently bond to the sulfur or phosphorus
atoms, such as (FSO2) zNLi or (F2PO) 2NLi. As a result of research
activities on lithium salt preparation, anhydrous HF chemistry
has also proved effective to produce their acids counterparts.
So, the basic description of the process illustrated in the
case of LiFSI is illustrated below:
FSO NH + LiF anhydrous HF
( 2)2 (FSO2)2NLi + HF
Indeed, the process to obtain an anhydrous lithium salt
consist of an acid-base reaction between an acid imide,
containing fluorosulfonyl (FSO2-) or fluorophosphoryl (F2PO-)
electroattractor radical, and a base LiM used as lithium
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cation source, preferably choose such as the HM species,
formed during lithiation of the imide, is volatile as with
LiCl or LiF which produce HCl and HF.
For example when operated at 180 C in an autoclave, this
reaction lead to the formation of LiFSI of good purity.
The R&D activities on fluorinated imide lithium salt
preparation as also allows to design an efficient process to
obtain their acid counterparts from their chlorine derivatives
in anhydrous HF, i.e from imides containing chlorosulfonyl
(C1S02-) or chlorophosphoryl (Cl2PO-) electroattractor radical
and characterized in that the chlorine atoms are covalently
bond to the sulfur or phosphorus atoms, such as (C1SO2)2NH or
(C12PO)2NH. This process is illustrated below in the case of
bis(fluorosulfonyl)imide (HFSI):
(CISO2)2NH anhydrous HF (FSO2)2NH + HCI
Indeed, the fluorinated acid is obtained by a
chlorine/fluorine exchange operated in anhydrous HF. It may be
necessary to distillate the bulk media after reaction to
obtain the pure acid.
The effectiveness of such reaction is non-obvious, it has been
showed that when operated in an autoclave, the reaction
proceed efficiently at temperature reaching or above 60 C. The
anhydrous HF was then evaporated and the resulting product
distillated to obtain pure HFSI.
It is also possible by a combination of both processes to
obtain directly lithium salt such as LiFSI from the chlorine
counterpart:
anhydrous HF --Jf
(CISO 2)2NH + LiF (FSO2)2NLi + HCI
An other possibilities is to obtain directly lithium salt such
as LiFSI from the lithiated chlorine counterpart:
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anhydrous HF --Of
(CISO2)2NL (FSO2)2NLi + HCI
The availability of acid imide containing (FSO2-) or (F~PO-)
electroattractor radical from their chlorine equivalent
(C1S02-) or (C12PO-) radical is particularly useful as it
allows to extend the scope of available precursor to produce
lithium imide salt containing (FSO2-) or (F2PO-) radical.
It has also been put in evidence that HFSI could be obtained
from HC1SI by bulk reaction with KHF2.
The present invention is illustrated by the following
examples, which are only used as an illustrative purpose
without intended to provide any limitation for man of the art.
Preparation of HFSI: Reaction of 1 gr HN(SO2C1)2 with 4 gr HF
in an autoclave was done as various temperatures. Results are
resumed in Table 1. It appears that an efficient Cl/F exchange
could be performed. After evaporation of HF and distillation
of bulk media, pure HFSI is obtained in a yield of at least
50%.
Time (hours) Temperature Yield
12 RT 0%
24 RT 0%
12 30 3-5%
12 50 7-10%
4 110 24%
7 120 50%
5 120 55%
2 130 55%
Table 1: Synthesis of HFSI in HF
Preparation of HFSI: Reaction of 1 gr HN(SO2C1)2 with 10 gr HF
in an autoclave was done as various temperatures. It appears
that an efficient Cl/F exchange is performed at 60 C and above
after 2 hours reaction. After evaporation of HF and
distillation of bulk media, pure HFSI is obtained in a yield
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of at least 50%. The reaction was also performed in gas phase
with a yield of at least 50%. The reaction was also performed
with CF;SOzNHSOzCl and FSO2NHSO2C1, '9F NMR show fluorine pic
relative to HFSI and CF3SO2NHSO2F after distillation of
reactive media.
Preparation of FSI: Reaction of 10 gr HN(SO?-Cl)2 with 5 KHF2
equivalents was performed in bulk at 100-160 C in Teflon
recipient under argon. After three hours, a sample of reaction
media in CD3CN was analyzed by 19F NMR, showing a peak
characteristic of the (FSO?)2N- anion.
Preparation of HFSI: Reaction of 10 gr HN(SO-9C1)2 with 4 gr HF
in an autoclave was done. Reaction mixture without chlorine
traces were obtained at 65-70 C temperatures. After
distillation, product obtained was identified by 19F NMR as
HN(SO?F)2=HF adduct.
Preparation of LiFSI: Reaction of 1 gr of HN(SO2F)2 and an
equimolar quantity of LiF in 5 ml of HF, at 180 C during
1 hour in an autoclave, gave nearly quantitative yield of
LiFSI (> 99%) contaminated with a small amount of LiOSO2F - as
determined by 19F NMR.
Preparation of LiFSI: Reaction of 1 gr HN(SO2C1)2 with 364 mg
LiF in an autoclave containing 10 ml of HF was done at 120 C
during two hours. 15F NMR show a peak characteristic of the
(FSO2)2N- anion and 'H NMR no peak characteristic of acidic
proton in HFSI. The reaction was also performed with
CF3SO2NHSO2C1, '9F NMR show fluorine pic relative to CF3SO2N SO2F
anions.
Preparation of LiFSI: Reaction of 1 gr LiN(SO2C1)2 with 400 mg
LiF in an autoclave was done at 100 C during two hours. 19F NMR
show a peak characteristic of the (FSO2)2N anion.
