U.S. patent application number 11/098742 was filed with the patent office on 2005-08-18 for electrolyte for lithium battery, and lithium battery containing electrolyte.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Kato, Toshimitsu, Kotato, Minoru, Mine, Norioki.
Application Number | 20050181286 11/098742 |
Document ID | / |
Family ID | 19086660 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050181286 |
Kind Code |
A1 |
Kato, Toshimitsu ; et
al. |
August 18, 2005 |
Electrolyte for lithium battery, and lithium battery containing
electrolyte
Abstract
An electrolyte for a lithium battery contains ethylene sulfite,
which includes chloroethanol in an amount of not more than 1000
ppm. A lithium battery includes an electrolyte, which contains
chloroethanol in an amount of not more than 1000 ppm.
Inventors: |
Kato, Toshimitsu; (Mie,
JP) ; Mine, Norioki; (Mie, JP) ; Kotato,
Minoru; (Ibaraki, JP) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN AND BERNER, LLP
1700 DIAGONAL ROAD
SUITE 300 /310
ALEXANDRIA
VA
22314
US
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Tokyo
JP
|
Family ID: |
19086660 |
Appl. No.: |
11/098742 |
Filed: |
April 5, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11098742 |
Apr 5, 2005 |
|
|
|
10227242 |
Aug 26, 2002 |
|
|
|
Current U.S.
Class: |
429/340 |
Current CPC
Class: |
C07D 331/02 20130101;
H01M 10/0567 20130101; H01M 6/168 20130101; H01M 10/052 20130101;
Y02E 60/10 20130101; H01M 10/0569 20130101 |
Class at
Publication: |
429/340 |
International
Class: |
H01M 006/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2001 |
JP |
2001-259262 |
Claims
What is claimed is:
1. An electrolyte for a lithium battery consisting of ethylene
sulfite, said ethylene sulfite containing chloroethanol in an
amount of not more than 1000 ppm.
2. A lithium battery comprising an electrolyte, said electrolyte
containing chloroethanol in an amount of not more than 1000
ppm.
3. An electrolyte according to claim 1, wherein said ethylene
sulfite is obtained by a method of reacting ethylene glycol with
thionyl chloride by a process including a rectification A, and
providing at least one process which is another purification
selected from the group consisting of washing with basic water,
dehydration by refluxing, distillation (rectification B), and
absorption before or after the rectification A.
4. An electrolyte according to claim 3, wherein said method further
comprises a simple distillation process of said raw ethylene
sulfite or rectified ethylene sulfite which is conducted before
said refining process.
5. An electrolyte according to claim 3, wherein said absorbing
process employs at least one absorbent selected from the group
consisting of complex metal oxide, activated carbon and metal
oxide.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application of a patent application
Ser. No. 10/227,242 filed on Aug. 26, 2002.
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0002] The present invention relates to an electrolyte for a
lithium battery formed of refined ethylene sulfite, and lithium
battery containing the electrolyte.
[0003] Ethylene sulfite is used as a raw material in various fields
of organic synthesis, and a solvent or an additive for an
electrolyte of a lithium secondary battery or the like.
[0004] Examples of conventional methods for producing the ethylene
sulfite are:
[0005] i) a method of reacting ethylene glycol and thionyl
chloride;
[0006] ii) a method of reacting ethylene glycol and dimethyl
sulfite;
[0007] iii) a method of reacting ethylene oxide and sulfur
dioxide;
[0008] iv) a method of depolymerizing polyethylene sulfite.
[0009] Among these methods, the method of reacting ethylene glycol
and thionyl chloride has been considered advantageous industrially
due to safety and low costs.
[0010] D. S. Bleslow and H. Skolnic, Chem. Heterocycl. Compound.,
1966, 21-1,1 describes the method of reacting ethylene glycol and
thionyl chloride for producing ethylene sulfite without solvent and
catalyst.
[0011] However, ethylene sulfite produced by the above conventional
methods contains a large amount of impurities.
[0012] The ethylene sulfite produced by the conventional methods is
unsuitable for a solvent and an additive for an electrolyte for a
lithium secondary battery, since the ethylene sulfite contains
impurities so much that the electrolyte does not have good storage
stability. For example, the electrolyte containing the ethylene
sulfite produced by the conventional methods tends to cause an
increase of acid content during preservation. When the electrolyte
is used for a lithium secondary battery, the battery is increased
in its internal pressure due to the electrolyte which sometimes
damages a canister of the battery.
[0013] Thus, there has been required ethylene sulfite having high
purity in order to improve performance of the battery.
SUMMARY OF THE INVENTION
[0014] It is an object of the present invention to overcome
aforementioned problems and provide an electrolyte for a lithium
battery formed of refined ethylene sulfite, and lithium battery
containing the electrolyte.
[0015] Ethylene sulfite is produced by reacting ethylene glycol
with thionyl chloride, and the ethylene sulfite contains
chloroethanol in an amount of not more than 1000 ppm.
[0016] A method is for refining raw ethylene sulfite which is
obtained by reacting ethylene glycol with thionyl chloride by a
process including a rectification process A, wherein the method
further has at least one purification process which is conducted
before or after the rectification process A, and which is selected
from the group consisting of a washing process with basic water, a
dehydration process by refluxing, a distillation (rectification B)
process, and an absorption process.
[0017] An electrolyte for a lithium battery consists of ethylene
sulfite, wherein the ethylene sulfite contains chloroethanol in an
amount of not more than 1000 ppm.
[0018] A lithium battery has an electrolyte, wherein the
electrolyte contains ethylene sulfite containing chloroethanol in
an amount of not more than 1000 ppm.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] A chlorine content in the ethylene sulfite is found to have
an influence to the storage stability of the electrolyte, and that
chloroethanol contained in the ethylene sulfite significantly
influences the storage stability of the electrolyte and stability
of the lithium secondary battery containing the electrolyte.
[0020] The refined ethylene sulfite can be produced by producing
the raw or crude ethylene sulfite by reacting ethylene glycol and
thionyl chloride, and rectifying the crude ethylene sulfite to
produce refined ethylene sulfite.
[0021] <Production Method of the Raw Ethylene Sulfite>
[0022] Reaction of ethylene glycol and thionyl chloride to produce
the raw or crude ethylene sulfite can be conducted either with or
without a solvent and/or catalyst.
[0023] Examples of the solvent are: hydrocarbon halogenides such as
methylene chloride; esters such as ethyl acetate; nitriles such as
acetonitrile; ethers such as tetrahydrofuran and dimethoxyethane;
and aromatic hydrocarbons such as toluene, but the solvent is not
limitative thereto.
[0024] The catalyst may be at least one basic compound, and
examples thereof are inorganic bases such as sodium carbonate,
potassium carbonate, sodium hydroxide, potassium hydroxide and
calcium hydroxide, and organic bases such as N-methyl piperidine
and N-ethyl morpholine.
[0025] Reaction temperature can be in a range of -20 to 100.degree.
C., preferably of 0 to 80.degree. C. Reaction time can be in a
range of 0.5 to 10 hours, preferably of 0.5 to 5 hours.
[0026] When the reaction product contains the solvent(s), the raw
ethylene sulfite can be produced by distilling the reaction
product. The raw ethylene sulfite also contains unreacted ethylene
glycol, by-produced chloroethanol, and other impurities. The raw
ethylene sulfite contains salt(s) of a basic compound and hydrogen
chloride when the reaction process employs a catalyst of the basic
compound. The salt can be removed from the raw ethylene sulfite by
filtration, washing or rinsing, extraction and so on.
[0027] <Refining the Raw Ethylene Sulfite>
[0028] Raw ethylene sulfite which is obtained by reacting ethylene
glycol with thionyl chloride is refined by a process including a
rectification process A, and by at least one purification process
selected from the group consisting of a washing process with basic
water, a dehydration process by refluxing, a distillation
(rectification B) process, and an absorption process which is
conducted before or after the rectification process A.
[0029] <Simple Distillation Process>
[0030] The simple distillation process can be conducted under
either normal pressure or reduced pressure, and can be conducted at
an internal temperature not higher than 100.degree. C.
[0031] <Rectifying Processes (Rectification A and Rectification
B)>
[0032] The rectifying process (rectification A and rectification B)
can be conducted with a rectifying column normally having
theoretical plates of 2 to 15 preferably 3 to 10 under either
normal or reduced pressure, preferably at an internal temperature
not higher than 100.degree. C., and at a reflux ratio of about 3 to
15.
[0033] The rectification A and the rectification B may be conducted
under either the same condition or different conditions.
[0034] <Washing Process with Basic Water>
[0035] The washing process can be conducted with water or a basic
water dissolved therein a basic inorganic salt such as sodium
hydrogen carbonate, and is continued until the water phase becomes
neutral. In this washing process, the amount of washing Water or
the number of application is not limitative.
[0036] <Dehydration Process by Total Reflux Distillation>
[0037] The process is conducted at an internal temperature not
higher than 100.degree. C. and at a pressure not higher than 20
Torr, so as to discharge water out of the system in the form of
non-condensed gas. The time of processing can be normally in a
range of 1 to 5 hours.
[0038] <Absorption Process>
[0039] The absorption process employs an absorbent which may be
complex metal oxide such as molecular sieves, activated carbon, or
metal oxide such as aluminum oxide (Al.sub.2O.sub.3) and magnesium
oxide (MgO). The amount of the absorbent can be 10% or less to the
ethylene sulfite, but is not limitative thereto. The process can be
either a batch or a continuous process.
[0040] <Combination of Refining Process>
[0041] The raw ethylene sulfite is refined preferably by the simple
distillation, the first rectifying process and at least one
refining process, wherein the refining process can be conducted
either before or after the first rectifying process. Combinations
of the first rectifying process and the refining process(es)
include the absorbing process and the rectifying process; the
washing process, the dehydration process by total reflux
distillation and the rectifying process: and the washing process,
the dehydration process by total reflux distillation, the absorbing
process and the rectifying process.
[0042] The above method provides the refined ethylene sulfite. The
refined ethylene sulfite contains chlorine in an amount not more
than 500 ppm, preferably not more than 200 ppm, and also contains
chloroethanol in an amount not more than 1000 ppm, preferably not
more than 400 ppm.
[0043] <Determination of Total Chlorine Content in Ethylene
Sulfite>
[0044] A sample is diluted with an inert solvent for ethylene
sulfite (for example, toluene) and is burned in an oxyhydrogen
flame combustor. The resulted product is absorbed in a water
solution of hydrogen peroxide. Chlorine ion content in the water
solution is determined by ion chromatography, and the total
chlorine content is calculated.
[0045] <Determination of Contents of Ethylene Sulfite,
Chloroethanol and Ethylene Glycol>
[0046] A sample is diluted by an inert solvent for ethylene sulfite
(for example, toluene) and is subjected to a gas chromatograph
(column: dimethyl polysiloxane type, detector: Flame Ionizaion
Detector (FID)). The contents of ethylene sulfite, chloroethanol
and ethylene glycol are expressed in percentage by area
respectively.
[0047] The ethylene sulfite containing not more than 1000 ppm
chloroethanol according to the embodiment is useful for a solvent
and an additive of the electrolyte for the lithium battery,
especially for the lithium secondary battery.
[0048] The electrolyte for a lithium battery according to another
aspect of the invention contains at least one lithium electrolyte,
at least one solvent, and ethylene sulfite containing not more than
1000 ppm chloroethanol. The ethylene sulfite containing not more
than 1000 ppm chloroethanol can be prepared according to the
above-described method. The lithium electrolyte may be a lithium
compound such as lithium borofluoride, lithium phosphate
hexafluoride, lithium perchlorate, and lithium
trifluoromethanesulfonate. The solvent may be a usual one for an
electrolyte such as a cyclic carbonate including ethylene carbonate
and propylene carbonate; a chane carbonate including dimethyl
carbonate and methyl ethyl carbonate; an ether group including
tetrahydrofuran and 1,2-diethoxyethane; and a lactone group such as
.gamma.-butyrolactone. The ethylene sulfite containing not more
than 1000 ppm chloroethanol can be used for either the solvent or
the additive. The ethylene sulfite having the reduced amount of
chloroethanol has a good storage stability, and the acid content
therein can be kept low for a long time of storage, so that it is
useful for the electrolyte for the lithium battery especially for
the lithium secondary battery. On the other hand, the electrolyte
consisting of ethylene sulfite containing more than 1000 ppm
chloroethanol has inferior storage stability.
[0049] <Determination of Acid Content in Electrolyte>
[0050] A precisely weighed sample is dissolved in cold pure water,
and then the water is titrated by alkali where the indicator is BTB
(bromothymol blue) changing yellow to blue. The amount of the
titrant is converted to the acid content expressed as hydrofluoric
acid content.
[0051] The ethylene sulfite refined through the above processes is
normally reduced in content of unreacted ethylene glycol to 2000
ppm or less, so that it is also useful for the solvent and the
additive for the electrolyte of the battery, preferably the
secondly battery.
EXAMPLES AND COMPARATIVE EXAMPLES
[0052] Without further elaboration, it is believed that one skilled
in the art, using the preceding description, can utilize the
present invention to its fullest extent. The following embodiments
are, therefore, to be construed as merely illustrative, and not
limitative in any way whatsoever, of the remainder of the
disclosure.
[0053] The present invention is further illustrated by the
following Examples and Comparative Examples. The determination is
conducted as follows.
[0054] <Determination of Total Chlorine Content in Ethylene
Sulfite>
[0055] A sample was diluted with toluene and was burned in an
oxyhydrogen flame combustor. The resulted product was absorbed in a
water solution of 3% hydrogen peroxide. Chlorine ion content in the
water solution was determined by ion chromatography, and the total
chlorine content was calculated.
[0056] <Determination of Contents of Ethylene Sulfite,
Chloroethanol and Ethylene Glycol>
[0057] A sample was diluted by toluene and was subjected to a gas
chromatograph (GC 14A manufactured by Shimadzu Corporation having a
column of HR-1) in such a manner that the temperature was held at
80.degree. C. for 5 minutes and then raised to 220.degree. C. at a
rate of 8.degree. C./min, and then held for 10 minutes, and an
injector and a detector (FID) were kept at 250.degree. C. The
contents of ethylene sulfite, chloroethanol and ethylene glycol
were expressed in percentage by area respectively, where the limits
of detection of chloroethanol and ethylene glycol were both 25
ppm.
[0058] <Determination of Acid Content in Electrolyte>
[0059] A precisely weighed 10 g sample was dissolved in 100
cm.sup.3 pure water of 5.degree. C. or lower, and then the water
was titrated by alkali where the indicator was BTB (bromothymol
blue) changing yellow to blue. The amount of the titrant was
converted to the acid content expressed as hydrofluoric acid
content.
[0060] <Production (I) of Raw Ethylene Sulfite>
[0061] 1 kg of ethylene glycol (available from Mitsubishi Chemical
Corporation) was held in a flask having a capacity of 2 liters. The
flask was evacuated to reduce the internal pressure to 30 Torr at a
room temperature, and then nitrogen gas was introduced into the
flask to substitute the atmosphere. After that, a total amount of
2.1 kg of thionyl chloride (available from Kishida Chemicals Ltd.,
purity: 95%) was dropped into the flask for 6 hours, while
agitating the contents in the flask, through which the internal
temperature rose up to 45.degree. C. After finished dropping the
thionyl chloride, the contents were aged at an internal temperature
of 68.degree. C. for 70 minutes, and then the flask was evacuated
to 35 Torr and kept at an internal temperature of 63.degree. C. for
25 minutes. The resulted reaction product was thin-brown liquid
containing ethylene sulfite of 97.04%, chloroethanol of 0.47% and
ethylene glycol of 1.30%.
[0062] The product was simple-distilled at a pressure of 20 Torr
with a heat medium having a constant temperature of 85.degree. C.
The initial distillate which was 5% of the total distillate was cut
off and removed therefrom. The product distillate thus distilled at
a yield of 86% was the raw ethylene sulfite which contained
ethylene sulfite of 97.7%, chloroethanol of 0.28%, ethylene glycol
of 1.6% and total chlorine of 5300 ppm.
[0063] It should be noted that the raw ethylene sulfite thus
obtained was employed as a starting raw ethylene sulfite in the
later-described Examples 1 to 4 respectively as well as the
below-described rectifying process, so that the raw ethylene
sulfite is sometimes referred to as parent raw ethylene sulfite
hereinafter.
[0064] The parent raw ethylene sulfite was rectified with a
rectifying column having ten theoretical plates and a heat medium
having a temperature of 91.degree. C., wherein the reflux ratio was
kept at 10 until 5% of the distillate was distilled out initially,
and after that, the ratio was kept at 5.
[0065] The refined ethylene sulfite distilled at a yield of 71.8%,
had a purity of 99.30%, and contained chloroethanol of 0.14%,
ethylene glycol of 0.38% and total chlorine of 1600 ppm.
Example 1
[0066] The above parent raw ethylene sulfite was subjected to an
absorbing treatment with an activated carbon (Sekado BW-50,
produced by Shinagawa Chemicals Ltd.) as an absorbent, wherein the
activated carbon was added in the raw ethylene sulfite in an amount
of 10% and then the ethylene sulfite was agitated for 5 hours. The
ethylene sulfite was further rectified in the same manner as the
above Production (I).
[0067] The ethylene sulfite was rectified at a yield of 68%, and
had a purity of 99.5%, and contained chloroethanol of 0.09%,
ethylene glycol of 0.18% and total chlorine of 480 ppm.
Example 2
[0068] The parent raw ethylene sulfite was added with a sodium
hydrogen carbonate saturated solution in an amount of 30% by
weight, was agitated for one hour and then left at rest for 30
minutes, and after that, the water phase was removed. After the
resultant was added with water in an amount of 20% by weight, it
was agitated for one hour. After it was left at rest for 30
minutes, the water phase was removed. The ethylene sulfite thus
washed two times was dehydrated by dehydration process by total
reflux distillation at an internal temperature of 70.degree. C. and
at a pressure of 20 Torr for 5 hours, while discharging water out
of the system. The dehydrated ethylene sulfite was further
rectified in the same manner as the Production (I).
[0069] The ethylene sulfite was rectified at a yield of 60.1%, and
contained chloroethanol of 0.09%, ethylene glycol of 0.05% and
total chlorine of 110 ppm.
Example 3
[0070] The refined ethylene sulfite obtained in Example 2 was
further treated by the absorbing treatment with a molecular sieve
of 5A as an absorbent, wherein the absorbent was added into the
refined ethylene sulfite in an amount of 3%, and then the ethylene
sulfite was agitated for 5 hours. After that, the treated ethylene
sulfite was rectified in the same manner as the Production (I).
[0071] The ethylene sulfite was rectified at a yield of 54%, and
contained chloroethanol of 0.01%, ethylene glycol of 0.01% or less
and total chlorine of 40 ppm or less.
Example 4
[0072] 440 kg of ethylene glycol (available from Mitsubishi
Chemical Corporation) was held in a reaction vessel having a
capacity of 1 m.sup.3. The vessel was evacuated to reduce the
internal pressure to 30 Torr at a room temperature, and then
nitrogen gas was introduced into the vessel to substitute the
atmosphere. After that, a total of 900 kg of thionyl chloride
(available from Kishida Chemicals Ltd., purity: 95%) was dropped
into the vessel for 12 hours, while agitating the contents in the
vessel, through which the internal temperature rose up to
35.degree. C. Having finished dropping the thionyl chloride, the
contents were aged at an internal temperature of 68.degree. C. for
70 minutes, and then the vessel was evacuated to 95 Torr and kept
at an internal temperature of 69.degree. C. for 3 hours.
[0073] The reaction product was simple-distilled at a pressure of
20 Torr with a heat medium having a constant temperature of
85.degree. C. The initial distillate which was 5% of the total
distillate was cut off and removed to obtain the raw ethylene
sulfite. The raw ethylene sulfite was added with a sodium hydrogen
carbonate saturated solution in an amount of 30% by weight, and was
agitated for one hour. After it was left at rest for 30 minutes,
the water phase was removed. After the resultant was added with
water in an amount of 20% by weight, it was agitated for one hour.
After it was left at rest for 30 minutes, the water phase was
removed. The ethylene sulfite thus washed two times was dehydrated
by dehydration process by total reflux distillation at an internal
temperature of 70.degree. C. and at a pressure of 20 Torr for 5
hours, while discharging water out of the system. The dehydrated
ethylene sulfite was rectified with a rectifying column having ten
theoretical plates and a heat medium having a temperature of
90.degree. C., wherein the reflux ratio was kept at 10 until 5% of
the distillate was distilled out initially and after that, the
ratio was kept at 5. The refined ethylene sulfite was further
treated by the absorbing treatment with a molecular sieve of 5A as
an absorbent, wherein the absorbent was added into the refined
ethylene sulfite in an amount of 3%, and then the ethylene sulfite
was agitated for 5 hours. After that, the treated ethylene sulfite
was rectified with the rectifying column having ten theoretical
plates and a heat medium having a temperature of 90.degree. C.,
wherein the reflux ratio was kept at 10 until 5% of the distillate
was distilled out initially, and after that, the ratio was kept at
5.
[0074] The ethylene sulfite was rectified at a yield of 62%, and
contained chloroethanol in an amount below the limit of detection,
ethylene glycol in an amount below the limit of detection, and
total chlorine of 40 ppm or less.
[0075] <Stability of Electrolyte Added with the Above Ethylene
Sulfite>
[0076] An electrolyte was prepared as follows: Ethylene carbonate
of 286 g and ethylmethyl carbonate of 514 g were mixed. Having been
added with a molecular sieve 4A of 5.1 g as an absorbent, the
mixture was dehydrated for 5 hours. The mixture was then filtrated
by filter of 1 .mu.m. The filtered mixture was added with
commercially available LiPF.sub.6 of 114 g little by little, and
then stirred for 30 minutes. After that, the mixture was filtrated
by a filter of 1 .mu.m again so as to prepare the electrolyte. The
electrolyte contained acid of 9.5 ppm and water of 5.1 ppm.
[0077] Five samples i), ii), iii), iv) and v) consisting of the
electrolyte were prepared, and each of the samples ii) to iv) was
added with ethylene sulfite in an amount of 2 wt %
respectively.
[0078] To the first sample i), ethylene sulfite was not added.
[0079] To the second sample ii), ethylene sulfite which was
prepared in Example 3 containing chloroethanol of 0.01% was
added.
[0080] To the third sample iii), ethylene sulfite which was
prepared in Example 3 and further the chloroethanol were added till
its concentration in ethylene sulfite became 0.21%.
[0081] To the fourth sample iv), ethylene sulfite which was
prepared in Example 3 and further added with the chloroethanol till
its concentration in ethylene sulfite became 0.35% was added.
[0082] To the fifth sample v), ethylene sulfite which was prepared
in Example 4 containing chloroethanol in an amount less than 25 ppm
which was below the limit of detection was added.
[0083] Each of the samples i) to v) of the electrolyte was stocked
in a stainless steel (SUS No. 304: American Iron and Steal
Institute) container and held at a temperature of 25.degree. C. in
an atmosphere of nitrogen. Acid contents of the samples were
determined on the first day and after ten days. The results are
shown in Table 1.
1TABLE 1 Concentration of Acid content No. of chloroethanol in
Initial acid after10 days electrolyte ethylene sulfite content
(ppm) (ppm) i) -- 9.5 13.5 (No ethylene sulfite was added) ii)
0.01% 9.4 19.2 iii) 0.21% 13.8 33.2 iv) 0.35% 13.9 38.5 v) below 25
ppm 9.6 13.6
[0084] <Stability of Batteries Containing the
Electrolyte>
[0085] Batteries i) to v) are produced with the above electrolytes
i) to v) and a battery casing having a size of 5 cm.times.9
cm.times.6 mm made of a laminate film having an aluminum sheet and
resin layers on both sides thereof. The batteries are kept at
25.degree. C. for one month, and then observed the appearances
thereof. The results will become as shown in Table 2. It should be
noted that the serial number of the battery corresponds to that of
the electrolyte.
2 TABLE 2 No. of battery Apperance i) Very slight expansion is
observed. ii) Very slight expansion is observed. iii) Expansion is
observed. iv) Expansion is observed. v) Very slight expansion is
observed.
[0086] The refined ethylene sulfite of the invention includes a
very small amount of impurities, so that it will exhibit excellent
storage stability when it is added to an electrolyte for a
battery.
[0087] The foregoing is considered illustrative only of the
principles of the invention. Further, since numerous modifications
and changes will readily occur to those skilled in the art, it is
not desired to limit the invention to the exact construction and
operation shown and described. Accordingly, all suitable
modifications and equivalents may be resorted to that fall within
the scope of the appended claims.
[0088] The disclosure of Japanese Patent Application No.
2001-259262 filed on Aug. 29, 2001 is incorporated herein as a
reference.
* * * * *