U.S. patent application number 10/381126 was filed with the patent office on 2004-05-20 for method for drying organic liquid electrolytes.
Invention is credited to Lischka, Uwe, Schade, Klaus, Wietelmann, Ulrich.
Application Number | 20040096746 10/381126 |
Document ID | / |
Family ID | 7658628 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040096746 |
Kind Code |
A1 |
Wietelmann, Ulrich ; et
al. |
May 20, 2004 |
Method for drying organic liquid electrolytes
Abstract
A method is described for removing water and other protic
impurities from an organic liquid electrolyte, wherein the organic
liquid electrolyte is brought into contact with one or more
insoluble alkali metal hydride(s) and the insoluble reaction
by-products formed thereby are separated off.
Inventors: |
Wietelmann, Ulrich;
(Friedrichsdorf, DE) ; Schade, Klaus; (Wlesbaden,
DE) ; Lischka, Uwe; (Frankfurt/Main, DE) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
666 FIFTH AVE
NEW YORK
NY
10103-3198
US
|
Family ID: |
7658628 |
Appl. No.: |
10/381126 |
Filed: |
June 13, 2003 |
PCT Filed: |
September 21, 2001 |
PCT NO: |
PCT/EP01/10924 |
Current U.S.
Class: |
429/324 ;
210/702; 429/188 |
Current CPC
Class: |
H01M 10/052 20130101;
H01G 11/34 20130101; H01M 10/0566 20130101; B01D 15/00 20130101;
H01G 11/04 20130101; H01G 11/20 20130101; B01J 20/04 20130101; Y02E
60/10 20130101; H01G 11/58 20130101; H01M 6/162 20130101; Y02E
60/13 20130101 |
Class at
Publication: |
429/324 ;
429/188; 210/702 |
International
Class: |
H01M 010/40; B01D
021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2000 |
DE |
100 49 097.2 |
Claims
1. Method of removing water and other protic impurities from an
organic liquid electrolyte, characterised in that the organic
liquid electrolyte is brought into contact with one or more
insoluble alkali metal hydride(s) and the insoluble reaction
by-products formed thereby are separated off.
2. Method according to claim 1, characterised in that LiH and/or
NaH is used as the alkali metal hydride.
3. Method according to claim 2, characterised in that LiH alone is
used as the alkali metal hydride.
4. Method according to any one of claims 1 to 3, characterised in
that the content of protic compounds in the liquid electrolyte to
be dried is <0.6 mmol/g.
5. Method according to any one of claims 1 to 4, characterised in
that the temperature is from -20 to 150.degree. C.
6. Method according to claim 5, characterised in that the
temperature is from 0 to 90.degree. C.
7. Method according to any one of claims 1 to 6, characterized in
that the amount of metal hydride corresponds at least to the
stoichiometric amount of protic impurities.
8. Method according to claim 7, characterised in that the amount of
metal hydride corresponds to from 2 to 100 times the stoichiometric
amount of protic impurities.
9. Method according to any one of claims 1 to 8, characterised in
that the metal hydride is activated by milling under an inert gas
atmosphere.
10. Method according to any one of claims 1 to 9, characterized in
that the liquid electrolyte is stirred with the metal hydride.
11. Method according to any one of claims 1 to 9, characterised in
that the liquid electrolyte passes over a fixed bed containing the
metal hydride.
12. Method according to any one of claims 1 to 11, characterised in
that the insoluble reaction by-products are separated off by
filtration or centrifugation.
13. Use of the organic liquid electrolyte dried according to any
one of claims 1 to 12 for electrolytic cells or
supercapacitors.
14. Use of the organic liquid electrolyte dried according to any
one of claims 1 to 12 for lithium batteries.
Description
[0001] The present invention relates to a method of removing water
and other protic impurities from organic. liquid electrolytes.
[0002] The lithium batteries (both primary and secondary battery
cells) commonly used today normally contain anhydrous, liquid,
ionically conducting electrolytes in which conducting salts, such
as, for example, LiPF.sub.6, LiBF.sub.4, LiClO.sub.4, lithium
imides, lithium methides or lithium chelato complexes such as, for
example, lithium bis(oxalato)borate, are present in dissolved form.
Many of those conducting salts decompose more or less rapidly in
the presence of protic compounds, such as, for example, water, for
example according to
LiPF.sub.6+H.sub.2O.fwdarw.LiF+2HF.Arrow-up
bold.+POF.sub.3.Arrow-up bold. (1) 1
[0003] The gaseous products (HF, POF.sub.3, etc.) formed during the
hydrolysis of fluorine-containing conducting salts are highly
corrosive and damaging to the other components of the battery, such
as, for example, the cathode materials. For example, HF leads to
the dissolution of manganese spinels and damages the cover layer on
the electrode materials that is important for a long service life.
As a result, the cycle stability of secondary batteries is
impaired. Borate electrolytes are also sensitive to water. In this
case, in part insoluble hydrolysis products form and impair the
functional properties. Although there are conducting salts that are
inert towards water, such as, for example, LiClO.sub.4, negative
effects are to be expected in the presence of water in this case
too, these negative effects being mainly attributable to a
disturbance in the cover layer formation and the build up of
pressure owing to reaction with the anode according to
Li+H.sub.2O.fwdarw.LiOH+H.sub.2.Arrow-up bold. (3)
[0004] It is therefore necessary to reduce the content of protic
impurities to a minimum (H.sub.2O<20 ppm, HF<approx. 30 ppm).
A number of methods have been developed therefor, but they are all
associated with disadvantages.
[0005] In JP 208 7473 it is proposed to mix electrolyte solutions
with a solvent that forms low-boiling azeotropic mixtures with
water, and to remove the water/solvent azeotropic mixture by
distillation. The disadvantages of this method are the undesired
impurities with the entraining solvent and the restriction to
high-boiling electrolyte solvents.
[0006] In U.S. Pat. No. 5,395,486 and in WO 2000038813, inert
fluorinated liquids such as, for example, C.sub.8F.sub.18 are used
as entrainers. A disadvantage of those methods is, inter alia, the
emissions of fluorine-containing substances associated
therewith.
[0007] The method proposed in JP 103 38653 of effecting the drying
of electrolyte solutions by blowing through dry inert gases has the
disadvantage that very expensive (subsequently purified) inert gas
must be used and considerable losses of solvent occur, or the
discharged solvent vapours must be condensed and fed back in a
complex operation.
[0008] Another method described in DE 19827631 and described in a
similar form in JP 2000058119 is based on the physical adsorption
of water and HF on specially pre-treated aluminium oxide. A
disadvantage of the adsorption method is the complex pre-treatment
of the Al oxide (drying for 4 weeks in a stream of nitrogen at
400.degree. C.).
[0009] DE 19827630 describes a method of cleaning battery
electrolytes that consists in bringing a base, fixed to a solid,
for the chemical adsorption of protic impurities into contact with
the electrolyte solution and then separating off the solid cleaning
agent. It is a disadvantage that the amine-containing cleaning
agents fixed to a polymer are expensive and also require
pre-treatment (e.g. drying in vacuo for 4 days at 100.degree.
C.).
[0010] Finally, methods of drying electrolyte solutions by means of
alkali metals are known. For example, F. P. Dousek at al. (Chem.
Listy (1973), 67 (4) 427-432) propose first pre-drying with
molecular sieve and then carrying out final drying by means of
liquid K/Na alloy. In a manner that is in principle similar, JP
01122566 describes cleaning electrolyte solutions by filtering them
through a column packed with solid alkali metals. However, the use
of alkali metals in contact with relatively reactive solvents is
not without risk in terms of safety. Thus it is known that
tetrahydrofuran, for example, is attacked by lithium metal above
approximately 100.degree. C. The other alkali metals may also react
extraordinarily vigorously at moderately elevated temperatures with
the solvents used in lithium battery electrolytes.
[0011] Modern supercapacitors may also contain an organic
electrolyte which is generally the solution of an ammonium salt in
an aprotic solvent having a high dielectric constant, such as, for
example, acetonitrile or .gamma.-butyrolactone. The ammonium salts
generally have perfluorinated anions such as PF.sub.6.sup.- or
BF.sub.4.sup.-. These are electrochemically stable, not very
nucleophilic and do not become incorporated into the active
electrode masses.
[0012] This type of electrolyte must also have a low water content
(<20 ppm). In order to achieve this, JP 11054378 and JP 11008163
propose adding to the electrolyte adsorbents based on inorganic
oxides, for example aluminosilicates. Such adsorbents are able to
lower the water content and hence improve the reliability, safety
and current characteristics. The disadvantages of this method are
on the one hand that the adsorbents must be pre-treated and on the
other hand that adsorbent remains in the finished capacitor, so
that the specific storage capacity is reduced.
[0013] The object of the present invention is to avoid the
disadvantages of the prior art and to provide a method of removing
water and other protic impurities from organic liquid electrolytes.
Organic liquid electrolytes are to be understood as being solutions
containing lithium salts and/or ammonium salts with
electrochemically resistant anions in aprotic, polar, organic
solvents.
[0014] This method
[0015] is to be generally applicable,
[0016] is not to lead to additional contamination,
[0017] is to use commercially available drying agents that do not
require further conditioning,
[0018] is to be without risk in terms of safety and
[0019] is to yield product solutions having water contents down to
<20 ppm.
[0020] The object is achieved by a method of removing water and
other protic impurities from an organic liquid electrolyte, wherein
the organic liquid electrolyte is brought into contact with one or
more insoluble alkali metal hydride(s) and the insoluble reaction
by-products formed thereby are separated off. The removal of water
and other protic impurities is to be understood as meaning the
partial removal to the complete removal.
[0021] In particular the binary hydrides of lithium (LiH) and
sodium (NaH) that are used as the preferred drying agents are
relatively inexpensive in large amounts and are available in pure
form. Although they are completely insoluble in the aprotic
solvents used for lithium batteries, it has been found that LiH,
NaH and the other alkali metal hydrides KH, RbH and CsH are rapidly
effective insofar as the drying operation is concerned, and very
low residual contents of protic impurities can be achieved. In
addition, it has surprisingly been found that the drying agents in
hydride form used according to the invention are substantially more
advantageous in terms of safety than the alkali metals themselves.
In DSC measurements (differential scanning calorimetry, carried out
in a RADEX apparatus from Systag/Switzerland) on mixtures of LiH or
Li metal repsectiley and lithium bis(oxalato) borate solutions as
well as LiClO.sub.4, and LiPF.sub.6 solutions, it has been found
that the beginning of the dangerous, highly exothermic
decomposition reaction, expressed as the so-called ONSET
temperature (T.sub.ONSET), is significantly higher in the case of
the hydrides (see Table 1).
1TABLE 1 ThermaI decomposition of electrolytes in contact with LiH
and Li metal (Radex experiments) Conducting salt concentration Li
metal LiH Electrolyte (wt. %) T.sub.ONSET T.sub.MAX T.sub.ONSET
T.sub.MAX LiPF.sub.6/EC-DMC 11 145 160 230 (240).sup.1)
LiClO.sub.4/PC- 6 160 165 255 265 DME LOB/EC-DMC 10.5 180 220 240
./..sup.1) .sup.1)T.sub.MAX cannot be determined or is difficult to
determine because the sample vessels have opened T.sub.ONSET =
beginning of the first exothermic reaction (.degree. C.) T.sub.MAX
= maximum of the exothermic reaction (.degree. C.) EC = ethylene
carbonate, DMC = dimethyl carbonate, PC = propylene carbonate, DME
= 1,2-dimethoxyethane, LOB = lithium bis (oxalato) borate
[0022] It will be seen from the comparative data that the hydrides
ensure a high degree of operating safety, which is extremely
important in the case of production on a relatively large
scale.
[0023] The method according to the invention can be used with all
organic liquid electrolytes, that is to say, for example, solutions
of
[0024] fluorides, such as MPF.sub.6, MAsF.sub.6, MBF.sub.4
[0025] perchlorates MClO.sub.4
[0026] lithium iodide LiI
[0027] triflates MSO.sub.3R.sub.F
[0028] imides MN(SO.sub.2R.sub.F).sub.2
[0029] methides M[C(SO.sub.2R.sub.F).sub.3]
[0030] chelatoborates M[L.sub.2B]
[0031] chelatophosphates M[L.sub.3P]
[0032] where M=Li or NR.sub.4 (R=H or alkyl having from 1 to 10
carbon atoms, also cyclic)
[0033] R.sub.F=perfluorinated alkyl radical having from 1 to 10
carbon atoms, also cyclic
[0034] L=bidentate ligand having two O atoms, such as, for example,
oxalate, catecholate, salicylate, also partially or wholly
fluorinated
[0035] in aprotic solvents having a high dielectric constant, such
as
[0036] carbonates, e.g. dimethyl carbonate, diethyl carbonate,
ethylene carbonate, propylene carbonate, ethylmethyl carbonate,
[0037] nitriles, e.g. acetonitrile, adipic acid dinitrile, glutaric
acid dinitrile,
[0038] lactones, e.g. .gamma.-butyrolactone,
[0039] amides, e.g. dimethylformamide, N-methylpyrrolidone,
[0040] ethers, e.g. tetrahydrofuran, 2-methyltetrahydrofuran,
1,2-dimethoxyethane (monoglyme), 1,3-dioxolan,
[0041] acetals, e.g. 1,1-diethoxymethane
[0042] carbonic acid esters, e.g. ethyl formate, propyl formate,
diethyl oxalate
[0043] boric acid esters, e.g. tributyl borate, trimethyl
borate
[0044] phosphoric acid esters, e.g. tributyl phosphate, trimethyl
phosphate
[0045] sulfur compounds, e.g. dimethyl sulfoxide, sulfolane
[0046] and mixtures thereof.
[0047] The alkali metal reacts energetically and irreversibly with
proton-active substances according to;
MH+X--H.fwdarw.MX.dwnarw.+H.sub.2.Arrow-up bold. (4)
[0048] X=HO, halogen, RCOO, RO and the like
[0049] R=alkyl
[0050] In order that the reaction (4) associated with the evolution
of gas is not too vigorous, the hydride is preferably added in
portions to the liquid electrolyte. In a further preferred
embodiment of the invention, the content of proton-active
substances, for example water, is not to exceed a particular upper
limit of 0.6 mmol/g active H concentration, for example 1% water.
Although liquid electrolytes containing larger amounts of
impurities can also be dried while observing the safety precautions
known to the person skilled in the art, it is recommended in such
cases first to use a different drying method and to carry out only
the final drying using the method according to the invention.
[0051] The drying method according to the invention can be carried
out as described below by way of example.
[0052] An alkali metal hydride is added in portions, preferably
with stirring, to the moist liquid electrolyte optionally
contaminated with other proton-active substances. This operation is
preferably carried out in a temperature range from -20 to
150.degree. C., particularly preferably from 0 to 90.degree. C. The
drying operation can readily be monitored by measuring the volume
of gas that develops. In some cases (mainly when significant
amounts of acid are present, e.g. 0.1 mmol/g HCl), the evolution of
gas is very vigorous and foaming occurs. Cooling is then necessary.
Otherwise, the reaction is scarcely noticeably exothermic.
Depending on the activity of the drying agent, a subsequent
reaction phase at room temperature or elevated temperature (up to
90.degree. C., sometimes up to 12020 C.) is necessary to complete
the drying.
[0053] The amount of drying agent to be used is determined on the
one hand by the "activity" of the metal hydride used and on the
other hand by the concentration of the proton-active
impurity--generally water. The water content is normally determined
by Karl Fischer titration. The amount of drying agent used is
preferably such that it corresponds at least to the amount of water
determined by Karl Fischer titration (or an alternative water
determination). In order to shorten the reaction times, the drying
agent can preferably be used in a stoichiometric excess (e.g. from
2 to 100 times). The excess to be used in a particular case is
given by the activity of the hydride and the precise manner in
which the drying operation is carried out. The drying ability is
dependent on the "active surface area" of the metal hydride, i.e.
the activity is better the finer the degree of distribution of the
metal hydride. The drying ability of the metal hydride is
additionally dependent on the nature of the pre-treatment,
[0054] The "fresher" a metal hydride, the more active it is in
general. Metal hydrides that have been in contact with air or
moisture are "passivated" and must generally be activated. This may
be effected by milling under an inert gas atmosphere. This
operation may take place separately from the point of view of space
or in situ, i.e. during drying of the electrolyte.
[0055] It has been found that the commercially available hydride
grades are sufficiently active to dry an electrolyte to water
contents <20 ppm within a few hours. In order to assist the
drying operation intensive stirring is preferably carried out, on a
laboratory scale, for example, using a high-speed propeller
stirrer. Drying may also be carried out by passing the liquid
electrolyte over a fixed bed containing the metal hydride (e.g. a
column).
[0056] When the drying operation is complete, residues of the
drying agent and insoluble reaction products must be separated off.
It has been found that the alkali metal hydroxide formed according
to (4) is completely insoluble in the solvents and solvent mixtures
mentioned above. Accordingly, the undesirable reaction by-products
can be separated off by means of a simple solid/liquid separating
operation such as filtration or centrifugation.
[0057] The clear solutions prepared in this manner have extremely
low water contents (and equally low contents of other proton-active
substances). They can be used without further treatment as
electrolytes for electrolytic cells, preferably lithium batteries,
or electrolytic two-layer capacitors (supercapacitors).
[0058] The subject of the invention is. explained in greater detail
below by means of examples:
EXAMPLES 1 TO 6
Drying of Various Electrolyte Solutions
[0059] Various electrolyte solutions indicated in Table 2 were
dried under different drying conditions with the aid of the method
according to the invention. The general experimental set-up was as
follows:
[0060] The crude electrolyte solution in question was placed in a
multi-necked flask which had been rendered inert and was equipped
with a KPG stirrer, a device for adding solids, and a thermocouple.
A sample was removed by means of a plastics syringe and its water
content was checked by Karl Fischer titration.
[0061] The amount of LiH specified in Table 2 was then added, and
stirring was carried out under the conditions likewise indicated in
Table 2. After the given drying times, samples were again removed
and were clarified by filtration by means of syringe attachment
filters (e.g. Minisart SRP, 0.45 .mu.m pore size from Sartorius),
and their water content was checked again,
[0062] The dried solutions were then clarified by filtration over
glass filter frits.
2TABLE 2 Drying conditions for various electrolytes H.sub.2O Amount
Drying Drying H.sub.2O content Amount of LiH temperature time
content Ex. Electrolyte solution (ppm) (g) (g) (.degree. C.) (hrs)
(ppm) 1 LiClO.sub.4/PC-DME 870 150 0.8 room temp. 25 265 2 " " " "
" 15 15 3 LiClO.sub.4/PC-DME 340 8000 3.4 70 2 100 4 " 340 8000 4.7
70 5 10 5 LOB/PC-DME 340 1010 4.8 40 24 55 6 LOB/EC-DMC 120 2600
15.4 70 24 <20
[0063] As will be seen from Table 2, the degree of drying depends
on the conditions chosen in each case. In order to achieve residual
water contents of <20 ppm, drying times of from 5 to 24 hours
are necessary in the described Examples.
* * * * *