Note: Descriptions are shown in the official language in which they were submitted.
CA 02328020 2000-12-08
Alkylspiroborate salts
for use in electrochemical cells
The invention relates to a process for the preparation
of spiroborate salts, and to their use in electro
chemical cells.
Lithium ion batteries are amongst the most promising
systems for mobile applications. The areas of applica-
tion extend from high-quality electronic equipment (for
example mobile telephones, camcorders) to batteries for
electrically driven motor vehicles.
Rechargeable lithium batteries have been commercially
available since the early 1990s.
These batteries consist of a negative electrode, a
positive electrode, a separator and a non-aqueous
electrolyte. The negative electrode is typically
Li (MnMez) 204, Li (CoMez) O2, Li (CoNixMeZ) OZ or other lithium
intercalation and insertion compounds. Positive elec-
trodes can consist of lithium metal, carbon, graphite,
graphitic carbon or other lithium intercalation and
insertion compounds or alloy compounds. The electrolyte
can be a solution containing lithium salts, such as
LiPF6, LiBF4, LiC109, LiAsF6, LiCF3S03, LiN (CF3S0z) 2 or
LiC(CF3S02)3 and mixtures thereof, in aprotic solvents.
In LiPF6, a highly hydrolysis-sensitive and thermally
unstable substance is currently used as conductive salt
in many lithium ion batteries. In contact with atmos-
pheric moisture and/or residual water from the solvent,
hydrofluoric acid HF immediately forms. In addition to
the toxic properties, HF has an adverse effect on the
cycle behaviour and thus on the performance of the
lithium battery, since metals from the electrodes may
be dissolved out.
US 4505997 describes lithium imides and US 5273840
describes lithium methanides. Both salts have high
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- 2 -
positive-electrode stability and form solutions of high
conductivity in organic carbonates. Aluminium, the
negative-electrode charge eliminator in lithium ion
batteries, is passivated to an inadequate extent, at
least by lithium imide. Lithium methanide, by contrast,
can only be produced and purified at very great
expense. In addition, the electrochemical properties,
such as oxidation stability and passivation of alumi
nium, are highly dependent on the purity of the
methanide.
In lithium bis[5-fluoro-2-olatobenzenesulfon-
ato(2-)0,0']borate(1-), a conductive salt is described
which, owing to its properties, is regarded as a highly
promising conductive salt for use in lithium ion
batteries. However, the high-cost and complex synthesis
of the precursors is problematic.
Anionic chelate complexes of the borate anion are
described in EP 698301. On use of organic aromatic
diols or aromatic hydroxy acids as ligands, very high
thermal stability and good delocalization of negative
charge is observed. The lack of oxidation stability or
inadequate conductivity in aprotic solvents, which are
employed as standard in electrochemical cells, prove to
be disadvantageous. The known spiroborates have
optimized conductivity at the same time as inadequate
oxidation stability or optimized oxidation stability at
the same time as inadequate conductivity.
The object of the present invention is therefore to
provide materials which have improved conductivity and
are electrochemically stable.
The object according to the invention is achieved by
borate salts of the general formula
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Ra R~ Y_
Mx+ ~ B
R3 RZ x
iy
in which:
M is a metal ion, tetraalkylammonium ion,
PRaRbR~Rd, P (NRaRb) kR~mRd4-k-m (where k - 1 - 4, m - 0 - 3
and k + m _< 4),
C (NRaRb) (NR~Rd) (NReRf) , C (RZ) 3, tropylium or
heterocyclic rings containing P, N, S or 0, or fused
heterocyclic systems containing these rings,
where Ra to Rf are H, alkyl or aryl (C1-Ca), which may
be partially substituted by F, Cl or Br,
RZ is an aromatic or substituted aromatic ring,
x and y are 1, 2, 3, 4, 5 or 6,
R1 to R4 may be identical or different alkoxy or
carboxyl radicals (C1-Ce, ) which are optionally bonded
directly to one another via a single or double bond.
If M"+ is a tetraalkylammonium ion conforming to the
general formula [NR' R" R" ' R" " J , the radicals R' to
R " " may be identical or different, optionally bonded
directly to one another via a single or double bond and
have the meaning CnF,2n+i-X~Hx, where n - 1 - 6 and x - 0
- 13.
Particularly suitable are borate salts conforming to
the formula (I) which are characterized in that M, x, y
and R1 to R4 are as defined, and
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R1 to R4 are optionally partially or fully substituted
by electron-withdrawing groups selected from the group
consisting of
F, C1, N (CnF(2n+1-x)Hx) 2r 0 (CnF(2n+1-x)I"~x) r S~2 (CnF(2n+1-x)Hx)
where
n is 1, 2, 3, 4, 5 or 6, and
X is 0 to 13.
Surprisingly, it has been found that the salts accord-
ing to the invention have very high electrochemical
stability. The compounds of the formula (I), besides
the thermal stability which is typical of borates, at
the same time have high oxidation stability.
It has been found that the salts according to the
invention have high ionic conductivity in aprotic
solvents. Suitable solvents are the customary battery
solvents, preferably selected from the group consisting
of dimethyl carbonate, diethyl carbonate, propylene
carbonate, ethylene carbonate, ethyl methyl carbonate,
methyl propyl carbonate, y-butyrolactone, methyl
acetate, ethyl acetate, methyl propionate, ethyl pro-
pionate, methyl butyrate, ethyl butyrate, dimethyl
sulfoxide, dioxolane, sulfolane, acetonitrile, acrylo-
nitrile, tetrahydrofuran, 2-methytetrahydrofuran and
mixtures thereof.
The borate salts of the formula (I) and mixtures
thereof can be used in electrolytes for electrochemical
cells. They can be employed as conductive salts or
additives . They can likewise be used in proportions of
between 1 and 99% in combination with other conductive
salts which are used in electrochemical cells. Examples
of suitable conductive salts are those selected from
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the group consisting of LiPF6, LiBF9, LiC109, LiAsF6,
LiCF3S03, LiN (CF3S02) 2 and LiC (CF3S02) 3 and mixtures
thereof.
The electrolytes may also contain organic isocyanates
(DE 199 44 603) for reducing the water content. The
electrolytes may likewise contain organic alkali metal
salts (DE 199 10 968) as additive. Suitable alkali
metal salts are alkali metal borates of the general
formula
L1+ B- ( OR1 ) m ( ~RZ ) p
in which
m and p are 0, l, 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
are each, individually or together, an aromatic ring
from the group consisting of phenyl, naphthyl,
anthracenyl and phenanthrenyl, which may be unsubsti
tuted or mono- to 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 hydroxy-
carboxylic acids and aromatic hydroxysulfonic acids,
which may be unsubstituted or mono- to tetrasubstituted
by A or Hal,
and
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Hal is F, Cl or Br
and
A is alkyl having 1 to 6 carbon atoms, which may be
mono- to trihalogenated.
Likewise suitable are alkali metal alkoxides
(DE 9910968) 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
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.
CA 02328020 2000-12-08
In addition, compounds of the general formula
C ( LR1 (CR2R3) xJ iAx) yKtJ + -N (CF3) 2
where
Kt is N, P, As, Sb, S or Se,
A is N, P, P (0) , 0, S, S (0) , SO2, As, As (0) , Sb or
Sb (O) ,
R1, RZ 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 poly-
substituted and/or unsubstituted phenyl, substituted
and/or unsubstituted heteroaryl,
A can be included in R1, RZ and/or R3 in various
positions,
Kt can be included in a cyclic or heterocyclic ring,
the groups bonded to Kt may be identical or different,
where
n is 1-18
m is 3-7
k is 0 or 1-6
<.;
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1 is 1 or 2 in the case where x - 1 and 1 in the
case where x = 0
x is 0 or 1
y is 1-4,
may be present (DE 9941566).
The process for the preparation of the compounds is
characterized in that an alkali metal salt of the
general formula
D+ -N ( C F3 ) 2
where D+ is selected from the group consisting of
alkali metals, is reacted, in a polar organic solvent,
with a salt of the general formula
2 0 L ( C R1 ) CRZR3 ) x ] iAX ) YKt J + -E
where
Kt, A, R1, R2, R3, k, 1, x and y are as defined above,
and
-E is F-, C1-, Br-, I-, BF4-, C104-, As F6-, SbF6- or PF6-.
The compounds according to the invention may also be
present in electrolytes comprising compounds of the
formula
X- ( CYZ ) m-S02N ( CR1RZR3 ) 2
where
X is H, F, C1, CnFzn+1, CnF2n-1 Or (S02) kN (CR'R'R3) 2.
Y is H, F or Cl
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_ g -
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 perfluorinated
alkylsulfonyl fluorides with dimethylamine in organic
solvents (DE 199 466 73).
Lithium complex salts of the formula
Rs
Rs O.~S.O
Li ~ Ot ~OR ~
R' / O~B 2
OR
R~
where
R1 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, Cl or
Br) ,
or are each, individually or together, an aromatic
heterocyclic ring from the group consisting of pyridyl,
pyrazyl and pyrimidyl, which may be unsubstituted or
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mono- to tetrasubstituted by alkyl (C1 to C6), alkoxy
groups (C1 to C6) or halogen (F, C1 or Br) ,
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 or mono- to tetrasubstituted by alkyl (C1
to C6), alkoxy groups (C1 to C6) or halogen (F, Cl 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,
b) the intermediate from a) is reacted with chlorotri-
methylsilane, and the product is filtered and subjected
to fractional distillation,
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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.
It is also possible to use electrolytes comprising
complex salts of the general formula (DE 199 51 804)
M"+ [ EZ ] 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
BR1RZR3 A1R1RZR3 PR1RZR3R4R5 AsRIRZR3R4R5 and VR1RZR3R4R5
R1 to RS are identical or different, are optionally
bonded directly to one another via a single or double
bond, and are each, individually or together,
a halogen (F, C1 or Br),
an alkyl or alkoxy radical (C1 to CB), which may be
partially or fully substituted by F, C1 or Br,
an aromatic ring, optionally bonded via oxygen, from
the group consisting of phenyl, naphthyl, anthracenyl
and phenanthrenyl, which may be unsubstituted or mono-
to hexasubstituted by alkyl (C1 to C8) 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 C8) or F, C1 or Br, and
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- 12 -
Z is OR6, NR6R', CR6R'Re, OSO2R6, N ( SO2R6 ) ( SO2R~ ) ,
C ( SO2R6 ) ( SOZR~ ) ( SO2R8 ) or OCOR6, where
R6 to Re 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 phos-
phorus Lewis acid/solvent adduct with a lithium or
tetraalkylammonium imide, methanide or triflate.
It is also possible for additives such as silane
compounds of the general formula
SiR1R2R3R9
where R1 to R9 are H
CyF2y+1-zHz
OCyF2y+~-zHz
OC ( 0 ) CyF2y+~-zHz
OSO2CyF2y+~-zHz
and 1 <_ x < 6
1 <_ y <_ 8 , and
0 5 z <_ 2y + 1
and
R1-R4 are identical or different
and are an aromatic ring from the group consisting of
phenyl and naphthyl, which may be unsubstituted or
monosubstituted or polysubstituted by F, CyF2y+i-zHz.
OCyF2y+1-zHzi OC (0) CyF2y+i-zHzi OSO2CyF2y+1-zHzi N (CnF2n+1-zI"Iz) 2i
or
is a heterocyclic aromatic ring from the group consist-
ing of pyridyl, pyrazyl and pyrimidyl, each of which
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' - 13 -
may be monosubstituted or polysubstituted by F,
CyF2y+i-ZHZ. OCyFzy+i-ZHZ, OC (O) CYFZy+i-ZHZ. OSOZCyF2y+i-ZHZ.
N (CnF2n+~-ZHZ) z (DE 100 276 26) to be present.
The compounds according to the invention may also be
employed in electrolytes comprising lithium fluoro-
alkylphosphates of the following formula
Li+[PFx (CYF2y+i-ZHZ) s-X~
in which
1 <_ x <_ 5
3 S y <_ 8
0 < z < 2y + 1
and the ligands (CyFzy+i-ZHZ) may be identical or
different, where the compounds of the general formula
Li+[PFa(CHbF~(CF3)d)eJ
in which a is an integer from 2 to 5, b = 0 or 1, c = 0
or 1, d = 2 and
a is an integer from 1 to 4, with the provisos that b
and c are not simultaneously each = 0, and that the sum
of a + a is equal to 6, and the ligands (CHbF~ (CF3) a)
may be identical or different, are excluded (DE 100 089
55). The process for the preparation of the lithium
fluoroalkylphosphates is characterized in that at least
one compound of the general formula
3 5 HmP ( CnH2n+1 ) 3-m ( I I I ) ,
OP (CaH2n+1) 3 ( IV) .
ClmP ( CaHzn+1 ) 3-m ( V ) .
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- 14 -
FmP ( CnH2n+1 ) 3-m ( VI ) ,
Clop (CnHZn+1) 5-0 (VII) ,
FoP ( CnH2n+1 ) s-o ( ~1I I I ) ,
in which in each case
0 < m < 2, 3 < n < 8 and 0 < o < 4,
is fluorinated by electrolysis in hydrogen fluoride,
the resultant mixture of fluorination products is
separated by extraction, phase separation and/or
distillation, and the resultant fluorinated alkyl-
phosphorane is reacted with lithium fluoride in an
aprotic solvent or solvent mixture with exclusion of
moisture, and the resultant salt is purified and
isolated by conventional methods.
The compounds according to the invention may also be
employed in electrolytes which comprise salts of the
formula
2 5 Li [ P ( OR1 ) a ( 0R2 ) b ( 0R3 ) c ( 0R4 ) dF'e ~
in which 0 < a + b + c + d < 5 and a + b + c + d + a -
6, and R1 to R4, independently of one another, are
alkyl, aryl or heteroaryl radicals, where at least two
of R1 to R4 may be bonded directly to one another by a
single or double bond (DE 100 16 801). The compounds
are prepared by reacting phosphorus(V) compounds of the
general formula
P(OR1)a(0R2)b(OR3)c(0Rq)dF'e
in which 0 < a + b + c + d <_ 5 and a + b + c + d + a =
5, and R1 to R4 are as defined above, with lithium
fluoride in the presence of an organic solvent.
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The electrolyte may also comprise ionic liquids of the
general formula
K+A-
in which:
K+ is a cation selected from the group consisting of
R1 R1
R6 ~ ~ R2 R6 ~ R2
R5 N"R3 R5 ~ N~N
R4 R4
R1
R6 ~ + N R6 ( + R2
RS N R3 RS N R3
R4 R4
R5 R1 R5 ~R1
~N
~N/.~-~N'
R4 ~ R2 R4 g R2
R3
RS ~R1 ~R1
R4 p R2 R4 N R2
I
R3
where R1 to RS are identical or different, are option-
ally bonded directly to one another by a single or
double bond, and each, individually or together, have
the following meaning:
H,
- halogen,
CA 02328020 2000-12-08
- 16 -
- alkyl radical (C1 to C8), which may be partially or
fully substituted by further groups, preferably F, C1,
N (CnF(2n+1-x)Hx) 2. O (CnF(2n+1-x)Hx) . S02 (CnF(2n+1-x)Hx) . CnF(2n+1-x)-
Hx where 1 < n < 6 and 0 < x <_ 13
and
A- is an anion selected from the group consisting of
[B(OR1)n(ORZ)m(OR3)o(OR4)p~
where 0 5 n, m, o, p 5 4 and
m + n + o + p = 4
where R1 to R4 are different or identical in pairs, are
optionally bonded directly to one another by 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 monosubstituted or polysubstituted by
CnF(2n+1-x>Hx. where 1 < n < 6 and 0 < x <_ 13, or halogen
(F, Cl or Br),
an aromatic heterocyclic ring from the group consisting
of pyridyl, pyrazyl and pyrimidyl, which may be unsub
stituted or monosubstituted or polysubstituted by
CaF(Zn+i-x)Hx. where 1 < n < 6 and 0 < x <_ 13, or halogen
(F, C1 or Br),
an alkyl radical (C1 to Ce) , which may be partially or
fully substituted by further groups, preferably F, Cl,
N (CnF(2n+1-x)Hx) 2. O (CnF(2n+1-x)Hx) . S02 (CnF(2n+1-x)Hx) .
CnF(zn+i-x)Hx where 1 < n < 6 and 0 < x <_ 13,
or OR1 to OR4
CA 02328020 2000-12-08
> . _ 17 _
individually or together, are an aromatic or aliphatic
carboxyl, dicarboxyl, oxysulfonyl or oxycarboxyl
radical, which may be partially or fully substituted by
further groups, preferably F, C1, N (CnF(zn+i-x)Hx) 2.
O (CnF(2n+1-x)Hx) i SOZ (CnF(2n+1-x)Hx) r CnF(2n+1-x)Hx where 1 < ri <
6 and 0 < x <_ 13 (DE 100 265 65). Ionic liquids K+A-,
where K+ is defined as above and
A- is an anion selected from the group consisting of
PFx(CyFZy.,)_z~6.x
and 1 <_ x < 6
1 <_ y <_ 8 and
0 <_ z <_ 2y + 1
may also be present (DE 100 279 95).
The compounds according to the invention may be
employed in electrolytes for electrochemical cells
which comprise positive-electrode material consisting
of coated metal cores, selected from the group
consisting of Sb, Bi, Cd, In, Pb, Ga and tin or alloys
thereof (DE 100 16 024). The process for the
preparation of this positive-electrode material is
characterized in that
a) a suspension or sol of the metal or alloy core in
urotropin is prepared,
b) the suspension is emulsified with C5-C12-hyrocarbons,
c) the emulsion is precipitated onto the metal or alloy
cores, and
d) the metal hydroxides or oxyhydroxides are converted
into the corresponding oxide by heating the system.
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The compounds according to the invention can also be
employed in electrolytes for electrochemical cells with
negative electrodes comprising customary lithium inter-
s calation and insertion compounds, but also with
negative-electrode materials consisting of lithium
mixed oxide particles which are coated with one or more
metal oxides (DE 199 22 522) by suspending the
particles in an organic solvent, adding a solution of a
hydrolyzable metal compound and a hydrolysis solution
to the suspension, and then filtering off, drying and
optionally calcining the coated particles. They can
also consist of lithium mixed oxide particles which are
coated with one or more polymers (DE 199 46 066),
obtained by a process in which the particles are
suspended in a solvent, and the coated particles are
subsequently filtered off, dried and optionally
calcined. The compounds according to the invention can
likewise be employed in systems with negative
electrodes which consist of lithium mixed oxide
particles which are coated with one or more layers of
alkali metal compounds and metal oxides (DE
100 14 884). A process for the preparation of these
materials is characterized in that the particles are
suspended in an organic solvent, an alkali metal salt
compound suspended in an organic solvent is added,
metal oxides dissolved in an organic solvent are added,
a hydrolysis solution is added to the suspension, and
the coated particles are subsequently filtered off,
dried and calcined. The compounds according to the
invention can likewise be employed in systems which
comprise positive electrode materials containing doped
tin oxide (DE 100 257 61). This positive electrode
material is prepared by
a) adding urea to tin chloride solution,
b) adding urotropin and a suitable dopant compound to
the solution,
CA 02328020 2000-12-08
- 19 -
c) emulsifying the resultant sol in petroleum ether,
d) washing the resultant gel and removing the solvent
by suction, and
e) drying and heating the gel.
The compounds according to the invention can likewise
be employed in systems comprising positive electrode
materials containing reduced tin oxide (DE 100 257 62).
This positive electrode material is prepared by
a) adding urea to a tin chloride solution,
b) adding urotropin to the solution,
c) emulsifying the resultant sol in petroleum ether,
d) washing the resultant gel and removing the solvent
by suction,
e) drying and heating the gel, and
f) exposing the resultant Sn02 to a reducing gas stream
in an aeratable oven.
The borate salts according to the invention are thus
particularly suitable as conductive salts or additives
for electrochemical cells. They are suitable for use in
batteries, in particular lithium ion batteries, and
supercapacitors.
A general example of the invention is explained in
greater detail below.
For the preparation of the borate salts according to
the invention, a lithium tetraalcoholatoborate or a 1:1
mixture of lithium alkoxide with a corresponding borate
CA 02328020 2000-12-08
- 20 -
is introduced in an aprotic solvent. This solution is,
if necessary, warmed somewhat so that the borate
dissolves.
Lithium tetraalcoholatoborates which are suitable for
the reaction are the derivatives of methanol, ethanol,
propanol, but also of other short-chain alcohols.
However, particular preference is given to the use of
the derivatives of methanol or ethanol since these
alcohols, owing to their low boiling point, can be
removed from the reaction mixture at relatively low
temperatures after the complex formation has taken
place.
For the complex formation, a suitable hydroxyl or
carboxyl compound is added at room temperature in a
ratio of 2:1 or 4:1, if necessary under a protective-
gas atmosphere. In order to complete the reaction, the
reaction solution is, if necessary, subsequently
stirred for some time at a temperature between 60 and
150°C, preferably between 60 and 120°C. The subsequent
stirring may be superfluous in the case of complex-
formation reactions which proceed very quickly.
It is possible to use aprotic solvents, preferably
selected from the group consisting of acetonitrile,
acetone, nitromethane, dimethylformamide, toluene,
dimethyl carbonate, diethyl carbonate, dimethylacet
amide and dimethyl sulfoxide. Particular preference is
given to toluene.
The alcohol formed during the reaction is, if it inter-
feres with the subsequent isolation of the complex salt
prepared, separated off with application of a slight
vacuum and possibly by slight warming to about 50 to
60°C. Depending on the solubility of the lithium
complex salt prepared in the aprotic solvent used, the
reaction mixture is evaporated or the solvent is
distilled off completely, and, if crystallization does
CA 02328020 2000-12-08
- 21 -
not take place spontaneously, cooled for several hours
at a temperature of from 0 to 10°C. The crystalline
product is separated off in a conventional manner and
dried by slow warming.
Particularly suitable for the complex formation are
alkoxides and dialkoxides which are hydroxylated in
adjacent positions, such as perfluoropinacolate, per-
fluoroglycolate and 1,2-dihydroxyperfluoropropylate.
The following examples are intended to illustrate the
invention in greater detail, but without restricting
it.
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Examples
Example 1
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Preparation of lithium bis[perfluoropinacolyl-
0,0'(2-)]borate(1-)
2 mol of perfluoropinacole are dissolved in toluene.
This solution is added to a suspension of 1 mol of
lithium methanolatoborate in toluene. The reaction
mixture is heated to 100°C, and the methanol formed is
distilled off.
On cooling, colourless, needle-shaped crystals preci-
pitate.
The salt is purified by recrystallization and dried to
constant weight under reduced pressure.
Example 2
Electrochemical stability of the electrolytes in EC/DMC
In each case, a number of cyclic voltammograms were
recorded successively in a measurement cell containing
platinum electrode, lithium counterelectrode and
lithium reference electrode. To this end, the potential
was firstly increased from the rest potential to 6 V
against Li/Li+ at a rate of 20 mV/s, and then reduced
back to the rest potential.
The characteristic curve shown in Figure 1 is obtained.
The electrolyte is thus suitable for use in lithium ion
batteries with transition-metal negative electrode.
CA 02328020 2000-12-08
.,
Example 3
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Ionic conductivity of the conductive salt in EC/DMC
Conductive salt Solvent Conductivity
(1:1) [mS/cm]
Lithium bis[perfluoropinacolyl- EC/DMC 5.4
O,0'(2-)]borate(1-)
LiPF6 EC/DMC 5.0
Li [N (S02CF3) 2] EC/DEC 5. 8
The concentration of the conductive salt in the solvent
is 0.3 mol/1. The measurements were carried out at a
temperature of 25°C.
The salts according to the invention have conducti-
vities which are interesting for use in electrochemical
cells and are comparable with known conductive salts,
such as lithium hexafluorophosphate or lithium imide.
Example 4
Preparation of tetramethylphosphonium bis[oxalato-
0,0'(2-)]borate(1-) via lithium bis[oxalato-0,0'(2-)]-
borate(1-)
Lithium bis[oxalato-0,0'(2-)]borate(1-) (prepared in
accordance with DE 198 29 030) is reacted with
tetramethylphosphonium chloride at room temperature in
acetonitrile to give tetramethylphosphonium bis-
(oxalato-0,0'(2-)]borate(1-). The resultant lithium
chloride is filtered off at 50°C, and the product is
recrystallized from acetonitrile/methyl tert-butyl
ether.
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Example 5
Preparation of tetraethylammonium bis[oxalato-0,0'-
(2-)]borate(1-)
Oxalic acid, tetraethylammonium hydroxide and boric
acid are suspended in toluene in the molar ratio 2:1:1.
After the stoichiometric amount of water formed in the
reaction has been removed by azeotropic distillation,
the crude product is recrystallized a number of times
from acetonitrile/DMC.
Instead of in toluene, the reaction can also be carried
out analogously in any other aprotic solvent which
forms an azeotrope with water. In this case, diethyl
carbonate, in which the crude product can also be
recrystallized directly, has proven particularly
successful.
1H-NMR (200 MHz, DMSO, TMS)
1.2 ppm (t)
3.20 ppm (q)
Example 6
Preparation of lithium bis[malonato-0,0'(2-)]borate(1-)
Malonic acid, lithium carbonate and boric acid are
suspended in toluene in the molar ratio 2:0.5:1. After
the stoichiometric amount of water formed in the
reaction has been removed by azeotropic distillation,
the crude product is recrystallized a number of times
from acetonitrile.
Lithium hydroxide can also be employed instead of
lithium carbonate. In this case, the malonic
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acid: lithium hydroxide: boric acid molar ratio changes
to 2:1:1.
1H-NMR (200 MHz, DMSO, TMS)
3.45 ppm (s)
Example 7
Preparation of tetramethylphosphonium bis[malonato-
0,0'(2-)]borate(1-) via lithium bis[malonato-0,0'(2-)]-
borate(1-)
Lithium bis[malonato-0,0'(2-)]borate(1-) is reacted
with tetramethylphosphonium chloride at room tempera-
ture in acetonitrile to give tetramethylphosphonium
bis[malonato-0,0'(2-)]borate(1-). The lithium chloride
formed is filtered off at 50°C, and the product is
recrystallized from acetonitrile/methyl tert-butyl
ether.
Example 8
Preparation of tetraethylammonium bis[malonato-0,0'-
(2-)]borate(1-)
Oxalic acid, tetraethylammonium hydroxide and boric
acid are suspended in toluene in the molar ratio 2:1:1.
After the stoichiometric amount of water formed in the
reaction has been removed by azeotropic distillation,
the crude product is recrystallized a number of times
from acetonitrile/DMC.
Instead of in toluene, the reaction can also be carried
out in any other aprotic solvent which forms an
azeotrope with water. In this case, diethyl carbonate,
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from which the crude product can also be recrystallized
directly, has proven particularly successful.
