Note: Descriptions are shown in the official language in which they were submitted.
CA 02371613 2001-10-26
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Process for the purification of methanide electrolytes
(II)
The invention relates to a process for the preparation
of organic methanide electrolytes in useable quality
for use in electrochemical cells.
The tris(perfluoroalkanesulfonyl)methanide ~~lass of
compounds was described for the first time by Turowsky
et al. in Inorgan. Chem., 1988, 27, 2135-2137 with
reference to tris (trifluoromethanesulfonyl.) methane.
This C-H acidic compound reacts with bases to give the
corresponding salts. The anion is planar, and the
negative charge can be delocalized very well by the
strongly electron-withdrawing substituents.
The lithium salt lithium tris(trifluoromethane-
sulfonyl)methanide has been investigated for some time
with respect to its suitability as conductive salt in
secondary batteries owing to its high conductivity and
good solubility in aprotic solvents. Further advantages
of this salt are its high electrochemical and thermal
stability.
There are two processes for the preparation of such
compounds. According to Turowsky et al., tris[tri-
fluoromethanesulfonyl]methane is prepared by a Grignard
reaction with trifluoromethanesulfonyl fluoride.
A two-step process as described by Koshar et al. in J.
Org. Chem., 1973, 38, 3358-3363, and Benrabah et al. in
J. Chem. Soc. Faraday Trans., 1993, 89(2), 355-359,
likewise gives tris[trifluoromethanesulfonyl]methane.
Both processes give products which require purification
for use as conductive salt. Purification methods used
hitherto, which are based on reaction of the solvated
salt with activated carbon and recrystallization, give
products having a purity of, in general, not greater
CA 02371613 2001-10-26
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than 99.5 which still contain interfering contamina-
tion by water and foreign ions.
However, salts of this quality are not suitable for use
in organic electrolytes.
The object of the present invention is therefore to
provide an inexpensive, easy-to-perform process by
means of which organic methanide electrolytes are
obtained in high-purity form, making the products
prepared suitable for use in battery electrolytes. For
the purposes of the invention, "high-purity" is taken
to mean degrees of purity of greater than 99.5~s.
The obj ect according to the invention is achieved by a
process for the preparation of high-purity methanides
of the formula
M2 [Rl-SOz (CF2) n) -S02-R) (I)
in which
R and R1 are independent of one another,
R is C (SOZRF) z, N (SOzRF) or O,
Rl is C (SOzRF) z or N (S02RF) ,
where ~-
RF i s ( CXFzX+~ ) .
M is H, Li, Na, K, Cs, Rb, Mgl~z, Cal~z, Srl,~z or Bal~z,
n is 1, 2 or 3, and
x is 1, 2, 3 or 4,
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which are suitable as electrolytes, by purification,
characterized in that it comprises the following steps:
(i) reaction of a methanide of the formula (I) with
concentrated sulfuric acid, and fractional rectifica
tion of the resultant free acid of said methanide,
(ii) reaction of the product of the formula (I) in
which M = H obtained from (i) with phosphorus pentoxide
at above the melting point, followed by fractional
rectification,
(iii) taking-up of the product from (ii) in an aprotic
organic solvent, and reaction with metallic Li, Na, K,
Rb, Cs, Mg, Ca, Sr or Ba, or chlorides or hydrides
thereof, or with alkyllithium, to give the
corresponding metal methanides of the formula (I), and,
if necessary, removal of excess reagent.
The process according to the invention gives materials
having a purity of greater than 99.5%, preferably from
99.6% to 99.9%, which are thus suitable for use as
electrolytes in batteries.
Surprisingly, it has been found that the reaction with
concentrated sulfuric acid stabilizes the starting
material and thus enables it to be distilled without
decomposition. In addition, the addition of equivalent
amounts or an -excess of concentrated sulfuric -acid
enables the free acid to be obtained directly from its
salts M2 [Rl-SOZ (CFz)n) -SOa-R] and purified.
The addition, in accordance with the invention, of
highly hygroscopic sulfuric acid already achieves a
good drying effect, which can be increased further by
addition of sulfur trioxide, corresponding to~ the water
content of the crude product.
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It has also been found that the fractional
rectification of the pure fraction with addition of
phosphorus pentoxide gives a pure product having a
water content of from 5 to 30 ppm, preferably from 10
to 20 ppm. This highly effective drying can be carried
out economically on amounts of any desired size.
The use in accordance with the invention of a solvent
which is used exclusively or proportionately in the
finished electrolyte is particularly advantageous. This
makes isolation of the salt, which is complex,
unnecessary.
In the reaction in process step (iii), gaseous
hydrogen, hydrogen chloride or alkanes form as easily
removable by-products. In this reaction, it was noted
that no decomposition phenomena take place at the
anion, as has been observed in conventional processes
with strong bases.
The reduction of the volume of the electrolyte by
distillation in accordance with the invention has the
crucial advantage that the large excess of desired
oxygen nucleophile present in the solution displaces
undesired nucleophiles from the coordination sphere of
the lithium. This effect allows impurities to be
removed by distillation. A highly concentrated
electrolyte is obtained, which enables low storage and
transport costs-:-
It has been found that the dilution of the highly
concentrated electrolytes can be carried out with any
desired solvents. It is therefore possible, in a simple
manner, to employ the optimum solvent mixture and to
provide electrolytes in any desired concentration.
The purification essentially consists of 3 process
steps, which can preferably be followed by t.wo further
steps.
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1st step:
A methanide of the formula (I) having a purity of from
905 to 99.5 is introduced in batches into concentrated
sulfuric acid (96 - 98~ sulfuric acid), and the mixture
is stirred at temperatures of from 10 to 40°C. The
mixture is preferably reacted with freshly distilled
sulfuric acid at temperatures of from 20 to 30°C. The
sulfuric acid is added in equivalent amounts or in
excess. The rectification apparatus with isothermal
column is baked out under a protective-gas atmosphere.
The distillation bridge must be heatable by means of
heating tapes or the like. This keeps the distillation
bridge at a constant temperature above the respective
melting point. Fractional rectification is carried out
in this apparatus.
2nd step:
The pure fraction from step 1 is mixed with phosphorus
pentoxide in a distillation apparatus which has been
baked out under a protective-gas atmosphere. The
mixture is stirred for from 15 minutes to 5 hours at
temperatures at or below the melting point of the acid.
The reaction is preferably carried out for from 30
minutes to 90 minutes. The mixture is subsequently
subjected to fractional rectification under reduced
pressure.
The fractional rectification of the pure fraction from
step 1 with addition of phosphorus pentoxide gives a
pure product having a water content of, preferably,
from 10 to 30 ppm.
3rd step:
The product from step 2 is dissolved in polar organic
solvents under a dry inert-gas atmosphere. Aprotic
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solvents, such as DMC, DEC, EC, PC, BC, VC, cyclo-
pentanone, sulfolane, DMS, 3-methyl-1,3-oxazolidin-2-
one, y-butyrolactone, EMC, MPC, BMC, EPC, BEC, DPC,
1,2-diethoxymethane, THF, 2-methyltetrahydrofuran, 1,3-
dioxolane, methyl acetate, ethyl acetate, and mixtures
thereof, are particularly suitable. The solution is
mixed with lithium hydride, with metallic lithium (Li),
with lithium chloride, in situ using a lithium positive
electrode, or with alkyllithium. In order to prepare
the sodium, potassium, rubidium, caesium, magnesium,
calcium, strontium or barium compounds, a reaction can
be carried out with metallic sodium (Na), potassium
(K), rubidium (Rb), caesium (Cs), magnesium (Mg),
calcium (Ca), strontium (Sr) or barium (Ba), sodium
chloride, potassium chloride, rubidium chloride,
caesium chloride, magnesium chloride, calcium chloride,
strontium chloride, barium chloride, sodium hydride,
potassium hydride, rubidium hydride, caesium hydride,
magnesium hydride, calcium hydride, strontium hydride,
or barium hydride. The mixture is stirred at
temperatures of from 10°C to 200°C for from 10 minutes
to 24 hours. The reaction is preferably carried out at
temperatures of from 20°C to 100°C for from 25 minutes
to 5 hours. The excess alkali metal reagent or alkaline
earth metal reagent is subsequently filtered aff.
4th step:
The volume of--_ the solution from step 3 is, . if
necessary, reduced to 2/3 to 1/4. The solvent is
preferably reduced to 1/3. The distillation is carried
out at atmospheric pressure at the boiling point of the
corresponding solvent. The distillation can also be
carried out under reduced pressure. The boiling points
shift correspondingly.
CA 02371613 2001-10-26
5th step:
The high-viscosity electrolyte can be diluted to any
desired extent with any desired solvents and solvent
mixtures. Suitable solvents and solvent mixtures are
all those employed in electrochemical storage media.
The composition of the electrolyte can thus be matched
in accordance with the specific requirements.
The inexpensive process which can be carried out using
simple reagents and apparatuses gives products in good
yields in a quality which is suitable for use in
batteries. No explosive or toxic by-products are formed
in this process.
The methanides can also be employed in proportions of
from 1 to 99% in combination with other conductive
salts which are used in electrochemical cells. Examples
of suitable conductive salts are those selected from
the group consisting of LiPF6, LiBF4, LiClO~, LiAsF6,
LiCF3S03, LiN (CF3S02) 2 and LiC (CF3S02) 3, and mixtures
thereof. The electrolytes can also contain organic
isocyanates (DE 199 44 603) for reducing the water
content. The electrolytes may also contain organic
alkali metal salts (DE 199 10 968) as additive.
Suitable alkali metal salts are alkali metal borates of
the general formula
Li+ B-(OR1)m(ORz)p
in which --
m and p are 0, 1, 2, 3 or 4, where m + p = 4, and
R1 and RZ are identical or different,
are optionally bonded directly to one another via a
single or double bond,
are each, individually or together, an aromatic or
aliphatic carboxylic, dicarboxylic or sulfonic acid
radical, or
CA 02371613 2001-10-26
are each, individually or together, an aromatic ring
from the group consisting of phenyl, naphthyl,
anthracenyl and phenanthrenyl, which may be
unsubstituted or mono- or tetrasubstituted by A or Hal,
or
are each, individually or together, a heterocyclic
aromatic ring from the group consisting of pyridyl,
pyrazyl and bipyridyl, which may be unsubstituted or
mono- to trisubstituted by A or Hal, or
are each, individually or together, an aromatic hydroxy
acid from the group consisting of aromatic
hydroxycarboxylic acids and aromatic hydroxysulfonic
acids, which may be unsubstituted or mono- to
tetrasubstituted by A or Hal,
and
Hal is F, C1 or Br
and
A is alkyl having 1 to 6 carbon atoms, which may be
mono- to trihalogenated.
Likewise suitable are alkali metal alkoxides of the
general formula
- Li+ OR- -
in which R
is an aromatic or aliphatic carboxylic, dicarboxylic or
sulfonic acid radical, or
is an aromatic ring from the group consisting of
phenyl, naphthyl, anthracenyl and phenanthrenyl, which
may be unsubstituted or mono- to tetrasubstituted by A
or Hal, or
CA 02371613 2001-10-26
_ g _
is a heterocyclic aromatic ring from the group
consisting of pyridyl, pyrazyl and bipyridyl, which may
be unsubstituted or mono- to trisubstituted by A or
Hal, or
is an aromatic hydroxy acid from the group consisting
of aromatic hydroxycarboxylic acids and aromatic
hydroxysulfonic acids, which may be unsubstituted or
mono- to tetrasubstituted by A or Hal,
and
Hal is F, C1 or Br
and
A is alkyl having 1 to 6 carbon atoms, which may be
mono- to trihalogenated.
Lithium complex salts of the formula
Rs
R5 O~ ,O
S~0
Li ~ t ,OR ~
2
OR
R3
where __
Rl and RZ are identical or different, are optionally
bonded directly to one another via a single or double
bond, and are each, individually or together, an
aromatic ring from the group consisting of phenyl,
naphthyl, anthracenyl and phenanthrenyl, which may be
unsubstituted or mono- to hexasubstituted by alkyl (C1
to C6) , alkoxy groups (C1 to C6) or halogen (F, C1 or
Br) ,
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or are each, individually or together, an aromatic
heterocyclic ring from the group consisting of pyridyl,
pyrazyl and pyrimidyl, which may be unsubstituted or
mono- to tetrasubstituted by alkyl (C1 to C6), alkoxy
groups (C1 to C6) or halogen (F, C1 or Hr) ,
or are each, individually or together, an aromatic ring
from the group consisting of hydroxybenzocarboxyl,
hydroxynaphthalenecarboxyl, hydroxybenzosulfonyl and
hydroxynaphthalenesulfonyl, which may be unsubstituted
or mono- to tetrasubstituted by alkyl (C1 to C6), alkoxy
groups (C1 to C6) or halogen (F, C1 or Br) ,
R3 - R6 may each, individually or in pairs and
optionally bonded directly to one another via a single
or double bond, have the following meanings:
1. alkyl (C1 to C6) , alkoxy (C1 to C6) or halogen (F,
C1 or Br)
2. an aromatic ring from the groups consisting of
phenyl, naphthyl, anthracenyl and phenanthrenyl, which
may be unsubstituted or mono- to hexasubstituted by
alkyl (C1 to C6) , alkoxy groups (C1 to C6) or halogen
(F, C1 or Br) .
pyridyl, pyrazyl and pyrimidyl, which may be
unsubstituted o-r- mono- to tetrasubstituted by alkyl (C1
to C6) , alkoxy groups (C1 to C6) or halogen (F, C1 or
Br) ,
which are prepared by the following process
(DE 199 32 317):
a) chlorosulfonic acid is added to 3-, 4-, 5- or 6-
substituted phenol in a suitable solvent,
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b) the intermediate from a) is reacted with chloro-
trimethylsilane, and the reaction mixture is
filtered and subjected to fractional distillation,
c) the intermediate from b) is reacted with lithium
tetramethoxyborate(1-) in a suitable solvent, and
the end product is isolated therefrom,
may also be present in the electrolyte.
The electrolytes may likewise comprise compounds of the
following formula (DE 199 41 566)
C ( [R1 (CR2R3) x] lAx) YKt] + ~N (CF3) 2
where
Kt = N, P, As, Sb, S or Se,
A = N, P, P (O) , O, S, S (O) , 502, As, As (O) , Sb or
Sb (O) ,
Rl , R2 and R3
are identical or different
and are H, halogen, substituted and/or unsubstituted
alkyl CnH2n+i, substituted and/or unsubstituted alkenyl
having 1-18 carbon atoms and one or more double bonds,
substituted and/or unsubstituted alkynyl having 1-18
carbon atoms and one or more triple bonds, substituted
and/or unsubstituted cycloalkyl CmH2m_1, mono- or
polysubstituted and/or unsubstituted phenyl, or substi-
tuted and/or unsubstituted heteroaryl,
A can be included in R1, R2 and/or R3 :in various
positions,
Kt can be included in a cyclic or heterocyclic ring,
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the groups bonded to Kt may be identical or different,
where
n = 1-18
m = 3-7
k = 0 or 1-6
1 = 1 or 2 in the case where x - 1 and 1 in the case
where x = 0
x = 0 or 1
y = 1-4.
The process for the preparation of these compounds is
characterized in that an alkali metal salt of the
general formula
D+ N(CF3)z (II)
where D+ is selected from the group consisting of the
alkali metals, is reacted, in a polar organic solvent,
with a salt of the general formula
C ( ~Rl ) CRZR3 ) x] iAX) YKt ] + -E ( I I I )
where
Kt , A, R1, Rz , R~ , k, 1, x and y are as def fined above ,
and
~E is F-, C1-, Br-, I-, BF4-, C104-, AsF6-, SbF6- or PF6-.
However, use can also be made of electrolytes
comprising compounds of the general formula (DE 199 53
638)
X- ( CYZ ) n,- SOZN ( CRIRzR3 ) 2
where
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X is H, F, C1, CnFzn+i. CnFzn-~ or (SOz) kN (CR1RZR3) z.
Y is H, F or C1
Z is H, F or C1
R1, Rz and R3 are H and/or alkyl, fluoroalkyl or cyclo-
alkyl
m is 0-9 and, if X = H, m $ 0
n is 1-9
k is 0 if m = 0 and k = 1 if m = 1-9,
prepared by reacting partially or perf:Luorinated
alkylsulfonyl fluorides with dimethylamine in organic
solvents, and complex salts of the general formula
(DE 199 51 804)
MX+ ~EZJ Y X/y
in which
x and y are 1, 2, 3, 4, 5 or 6
M"+ is a metal ion
E is a Lewis acid selected from the group consisting
of -- -
BR1R2R3 , A1R1R2R3 , PR1RZR3R4R5 , AsRIRZR3R4R5 and VR1R2R3R4R5 ,
R1 to RS are identical or different, are optionally ,
bonded directly to one another via a single or double
bond, and each, individually or together, have the
following meanings:
a halogen (F, C1 or Br),
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an alkyl or alkoxy radical (C1 to C8), which can be
partially or fully substituted by F, C1 or Br,
an aromatic ring, optionally bonded via oxygen, from
S the group consisting of phenyl, naphthyl, anthracenyl
and phenanthrenyl, which may be unsubstituted or mono-
to hexasubstituted by alkyl (C1 to Ce) or F, C1 or Br,
an aromatic heterocyclic ring, optionally bonded via
oxygen, from the group consisting of pyridyl, pyrazyl
and pyrimidyl, which may be unsubstituted or mono- to
tetrasubstituted by alkyl (C1 to Ce) or F, C1 ar Br, and
Z i s OR6 , NR6R' , CR6R'R8 , OS02R6 , N ( SOzR6 ) ( SOzR' ) ,
C ( S02R6 ) ( SOZR' ) ( SOzRe ) or OCOR6 , where
R6 to R8 are identical or different, are optionally
bonded directly to one another via a single or double
bond and are each, individually or together,
hydrogen or as defined for R1 to R5,
prepared by reacting a corresponding boron or
phosphorus Lewis acid/solvent adduct with a lithium or
tetraalkylammonium imide, methanide or triflate.
They can also be employed in mixtures which comprise
the borate salts (DE 199 59 722) of the general formula
y_
MX+
Rs R2 X f ,
in which
M is a metal ion or tetraalkylammonium,
CA 02371613 2001-10-26
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x and y are 1, 2, 3, 4, 5 or 6,
Rl to R'' are identical or different and are alkoxy or
carboxyl radicals (C1-Ce), which are optionally bonded
directly to one another via a single or double bond.
These electrolytes can be employed in electrochemical
cells having negative electrodes made fram common
lithium intercalation and insertion compounds, but also
with negative-electrode materials consisting of lithium
mixed-oxide particles coated with one or more metal
oxides or polymers.
Lithium mixed-oxide particles coated with one or more
metal oxides are obtained by a process (DE 199 22 522)
which is characterized in that the particles are
suspended in an organic solvent, a solution of a
hydrolysable metal compound and a hydrolysis solution
are added to the suspension, and the coated particles
are then filtered off, dried and optionally calcined.
Lithium mixed-oxide particles coated with one or more
polymers are obtained by a process (DE 199 46 066)
which is characterized in that particles are suspended
in a solution comprising polymers selected from the
group consisting of polyimides, polyanilines, poly-
pyrroles, polythiophenes, polyacetylenes, polyacrylo-
nitriles, carbonized polyacrylonitriles, poly-p-phenyl-
enes, polyphenylenevinylenes, polyquinolines, polyquin-
oxalines, polyphthalocyanine-siloxanes, polyvinylidene
fluorides, polytetrafluoroethylenes, polyethyl meth
acrylates, polymethyl methacrylates, polyamides, co
polymers with vinyl ethers, cellulose, polyfluoro
ethylenes, polyvinyl alcohols and polyvinylpyridines,
and derivatives thereof, and the coated particles are
then filtered off, dried, and optionally calcined.
The examples below are intended to illustrate the
invention in greater detail, but without representing a
limitation.
~
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Examples
Example 1
Purification of dicaesium hexafluoropropane-1,3-bis-
[sulfonylbis(trifluoromethanesulfonyl)methanide]
1st step:
Preparation of dicaesium hexafluoropropane-1,3-bis-
[sulfonylbis (trifluoromethanesulfonyl) methanide] as
described in P 19733948 (purity 97.5-99.5%). The
methanide was introduced in portions into freshly
distilled sulfuric acid, and the mixture was stirred at
room temperature for fifteen minutes. The round-bottom
flask was subsequently connected to a distillation
apparatus with isothermal column which had been baked
out under an argon atmosphere, and the mixture was
subjected to fractional rectification at a pressure of
10 Pa. The distillation bridge was provided with a
heating tape from the column head in order to obtain a
constant temperature above the respective melting point
in the bridge. The ground-glass joints were provided
with Teflon sleeves.
Weighed-out amount of
Cs2 [ (CF3SO2) 2C-SO2- (CFZ) 3-SO2-C (CF3SO2) 2] 640 g (0. 6 mol)
Boiling point of _the acid 170-173°C [10. .Pa]
Yield of the acid 68%
2nd step:
A portion of the pure fraction of H2 [ (CF3S0z) zC-S02- ~
(CF2) 3-S02-C (CF3S02) z] from step 1 was mixed with
phosphorus pentoxide, and the flask containing the
mixture was connected to the distillation apparatus,
which had been baked out under an argon atmosphere. The
CA 02371613 2001-10-26
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mixture was melted, stirred for one hour at 180°C under
atmospheric pressure and subjected to fractional
rectification under reduced pressure.
Weighed-out amount of
H2 [ (CF3S02) zC-SOZ- (CFz) a-SOa-C (CF3S02) 2] 174 g
Added amount of phosphorus pentoxide 18 g
Pressure 10 Pa
3rd step:
124 .6 g (0 . 149 mol) of H2 [ (CF3S02) 2C-SOZ- (CFz) 3-SOz-
C (CF3S02) 2] were dissolved in 300 ml of diethyl
carbonate under a dry inert-gas atmosphere and reacted
with 2.5 g (0.315 mol) of lithium hydride. When the
addition was complete, the electrolyte was stirred for
30 minutes, and the excess lithium hydride was
subsequently separated off via a filter.
4th step:
The volume of the electrolyte was reduced to 100 ml at
room temperature and a pressure of 10-5 Pa.
5th step:
The colourless electrolyte, which was now of high
viscosity, was diluted with 200 ml of solvent mixture
(ethylene carbonate:dimethyl carbonate 1:1) to give
300 ml of an electrolyte which was 1 molar with respect
to Li+ .
Even at the maximum amplification of the 19F-NMR
spectrum, no fluorine-containing impurities were
detected (purity > 99.90 .
-18-
A water content of 32 ppm was found.
