DESCRIPTION
[Title of Invention]
ELECTROLYTE AND SECONDARY BATTERY
TECHNICAL FIELD
[0001] The present invention relates to an electrolyte containing an aluminum salt
and a solvent, and to a secondary battery using the same.
BACKGROUND ART
[0002] In recent years, small electronic apparatuses represented by a mobile
terminal have been widely used, and it has been demanded to hrther reduce the size and
the weight of the small electronic apparatuses and to achieve their long life.
/
Accordingly, as an electric power source for the small electronic apparatuses, a battery,
in particular, a small and light-weight secondary battery capable of providing high
energy density has been developed. In these days, it has been considered to apply such
a secondary battery to large electronic apparatuses represented by an automobile in
addition to the foregoing small electronic apparatuses.
[0003] As the secondary battery, secondary batteries utilizing various charge and
discharge principles have been proposed. Specially, an aluminum secondary battery
utilizing a precipitation-dissolution reaction of aluminum has attracted attentions. One
reason for this is that, aluminum has a high ionization tendency, and therefore, the
electric charge per unit volume obtained by an oxidation-reduction reaction is high.
That is, aluminum is a greatly prospective material as a material for forming an
electrode or as an electronic charge carrier.
[0004] The aluminum secondary battery includes a cathode, an anode, and an
electrolyte containing an aluminum salt and a solvent. The composition of the
electrolyte functioning as a medium for a charge and discharge reaction largely affects
performance of the battery. Therefore, various studies have been made on the
composition of the electrolyte.
[0005] Specifically, to achieve high capacity and long life, an alkyl sulfone such as
dimethyl sulfone is used (for example, see PLT 1). In this case, as a solvent, an
organic solvent such as a cyclic ester carbonate, a chain ester carbonate, a cyclic ether,
and a chain ether is used.
[0006] Further, to reduce polarization at the time of discharge, an organic halide
such as trimethylphenyl ammonium chloride is used together with an aluminum salt
such as aluminum chloride (for example, see PLTs 2 and 3). In this case, as a solvent,
an organic solvent such as 1,2-dichloroethane is used.
[Citation List]
[Patent Literatures]
[0007] [PLT I]: Japanese Unexamined Patent Application Publication No.
2003- 100347
[PLT 21: Japanese Unexamined Patent Application Publication No. H06-293991
[PLT 31: Japanese Unexamined Patent Application Publication No. H09-259892
SUMMARY OF INVENTION
[0008] To achieve the practical use of the aluminum secondary battery, it is
necessary to smoothly and sufficiently progress a precipitation-dissolution reaction of
aluminum even at comparatively low temperature (such as ambient temperature).
However, in the existing aluminum secondary batteries, the precipitation-dissolution
reaction of aluminum smoothly and sufficiently progresses only at comparatively high
temperature (such as temperature equal to or higher than 50 deg C), and the reaction
efficiency is low. Therefore, in terms of practicality, there is room for improvement.
[0009] In view of the foregoing disadvantage, it is an object of the present
invention to provide an electrolyte capable of decreasing progression temperature of a
precipitation-dissolution reaction of aluminum and a secondary battery using the same.
[0010] An electrolyte according to an embodiment of the present invention includes
an aluminum salt, an alkyl sulfone (Rl-S(=0)*-R2: each of R1 and R2 represents an
alkyl group), and a solvent having a specific dielectric constant of 20 or less. A
content of the solvent is equal to or larger than 30 mol% and is less than 88 mol%, and a
mol ratio between the aluminum salt and the alkyl sulfone (a content of the aluminum
saltla content of the alkyl sulfone) is equal to or larger than 415 and is less than 713.
Further, a secondary battery according to an embodiment of the present invention
includes a cathode, an anode, and an electrolyte, the electrolyte having the foregoing
composition. It is to be noted that a value of the specific dielectric constant is a
measurement value at 25 deg C.
[0011] The electrolyte according to the embodiment of the present invention
includes the alkyl sulfone and the solvent (having a specific dielectric constant of 20 or
less) together with the aluminum salt. The content of the solvent and the mol ratio (the
content of the aluminum saltlthe content of the alkyl sulfone) satisfy the foregoing
conditions. In this case, since the dispersion amount of the aluminum salt with respect
to the solvent is increased compared to in a case in which the content of the solvent and
the mol ratio do not satisfL the foregoing conditions, a dimer of the aluminum salt is
easier to be generated. Therefore, since an oxidation-reduction reaction of aluminum
becomes easier to be progressed, progression temperature of a precipitation-dissolution
reaction of aluminum is allowed to be lowered. Thereby, according to the secondary
battery using the electrolyte of the embodiment of the present invention, aluminum is
electrochemically and effectively precipitated and dissolved even at temperature that is
not high. Accordingly, battery capacity is allowed to be stably obtained at ambient
temperature by the precipitation-dissolution reaction of aluminum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] [FIG. 11 FIG. 1 is a triangle phase diagram illustrating compositions of
an electrolyte according to an embodiment of the present invention.
[FIG. 21 FIG. 2 is a cross-sectional view illustrating a configuration of an
electrochemical device including the electrolyte according to the embodiment of the
present invention.
MODE(S) FOR CARRYING OUT THE INVENTION [0013] An embodiment of
the present invention will be hereinafter described in detail with reference to the
drawings. The description will be given in the following order.
1. Electrolyte
2. Electrochemical Device Using Electrolyte
[0014] [l . Electrolyte]
An electrolyte according to an embodiment of the present invention is used for, for
example, an electrochemical device such as an aluminum secondary battery. The
electrolyte contains an alkyl sulfone and a solvent together with an aluminum salt.
The aluminum salt and the alkyl sulfone are dispersed (or dissolved) in the solvent.
However, the electrolyte may contain a material other than the foregoing materials.
[0015] [Aluminum Salt]
The aluminum salt includes one or more of aluminum salts having various anions
described below.
[0016] The aluminum salt contains an anion (negative ion) together with an
aluminum ion ( ~ 1 ~ 'a)s a cation (positive ion). Examples of the anion include a
fluoride ion (F-), a chloride ion (Cl-), an iodide ion (I-), a bromide ion (Br-), a
perchlorate ion (Cloy), a tetrafluoroboric acid ion (BFY), a hexafluorophosphoric acid
ion (PFi), a hexafluoroarsenic acid ion (AsFL), a perfluoroalkyl sulfonic acid ion
(RfS03-: Rf represents a perfluoroalkyl group), and a perfluoroalkyl sulfonyl imide ion
((RfSO&N-). However, the anion may be an ion other than the foregoing ions.
[0017] The aluminum salt may be a complex salt. In this case, examples of the
cation include [AI(cH~cN)~]i~n +w hich acetonitrile is coordinated with an aluminum
ion and [AI(DMSO)~]i~n ' which dimethylsulfoxide ((DMSO: (CH3)2SO) is coordinated
with an aluminum ion. However, the cation in the complex salt may be an ion other
than the foregoing ions.
[0018] Specific examples of the aluminum salt include halogenated aluminum
(AlX3: X represents one of chlorine (Cl), bromine (Br), and iodine (I).). One reason
for this is that the halogenated aluminum is generally available, and an
oxidation-reduction reaction of aluminum is thereby easily progressed.
[0019] [Alkyl Sulfone]
The alkyl sulfone includes one or more of chain compounds represented by
R1-S(=0)2-R2. Each of R1 and R2 represents an alkyl group, and R1 and R2 may be
the same type of group or may be different from each other.
[0020] The electrolyte contains the alkyl sulfone for the following two reasons.
First, in this case, since the aluminum salt is easily solvated, aluminum is
electrochemically activated. Thereby, an oxidation-reduction reaction of aluminum is
easily progressed. Secondly, in this case, since the oxidizing characteristics of the
electrolyte (characteristics of oxidizing a substance other than the electrolyte) is
suppressed, the reactivity thereof is reduced. Thereby, in the case where the electrolyte
is used together with a metal material in an electrochemical device, the metal material is
less likely to be corroded. Examples of the metal material include a metal package
member, a metal electrode, and a metal lead.
[0021] Though types (carbon number and combination) of R1 and R2 are not
particularly limited, each carbon number is preferably equal to or less than 4, since
superior solubility and superior compatibility are thereby obtained. In this case,
examples of each of Rl and R2 include a methyl group, an ethyl group, an n-propyl
group, an i-propyl group, an n-butyl group, an i-butyl group, an s-butyl group, and a
t-butyl group. In particular, the sum of the carbon number of R1 and the carbon
number of R2 is preferably from 4 to 7 both inclusive, since thereby, a higher effect is
obtainable.
[0022] Specific examples of the alkyl sulfone include dimethyl sulfone,
methylethyl sulfone, methyl-n-propyl sulfone, methyl-i-propyl sulfone, methyl-n-butyl
sulfone, methyl-i-butyl sulfone, methyl-s-butyl sulfone, methyl-t-butyl sulfone, diethyl
sulfone, ethyl-n-propyl sulfone, ethyl-i-propyl sulfone, ethyl-n-butyl sulfone,
ethyl-i-butyl sulfone, ethyl-s-butyl sulfone, ethyl-t-butyl sulfone, di-n-propyl sulfone,
di-i-propyl sulfone, n-propyl-n-butyl sulfone, and di-n-butyl sulfone, since these
compounds are generally available, and easily exercise the foregoing advantageous
function of the alkyl sulfone. It goes without saying that the alkyl sulfone may be a
compound other than the foregoing compounds as long as the compound has the
structure represented by Rl -S(=0)2-R2.
[0023] [Solvent]
Examples of the solvent include one or more of nonaqueous solvents having a
specific dielectric constant of 20 or less (hereinafter referred to as "low polarity
solvents"). Such nonaqueous solvents are less likely to affect the solvation of an
aluminum salt. Therefore, in the case of using one or more of such nonaqueous
solvents, while inhibition of the solvation of the aluminum salt is suppressed, the
aluminum salt and the alkyl sulfone are dispersed in the solvent. Further, since the
viscosity of the electrolyte is lowered, the aluminum salt and the alkyl sulfone are easily
dispersed. However, the solvent may further contain a solvent other than the low
polarity solvent.
[0024] The low polarity solvent is a solvent having low dielectric characteristics
and low protogenic characteristics (low electron releasing characteristics). However, a
value of the specific dielectric constant is a measurement value at 25 deg C.
[0025] In the case where the specific dielectric constant is within the foregoing
range, the type of the low polarity solvent is not particularly limited. Examples of the
low polarity solvent include organic solvents such as an aromatic hydrocarbon, ether,
ketone, ester acetate, a chain ester carbonate, and a halide of each thereof. The
aromatic hydrocarbon is an aromatic ring or a compound obtained by introducing a
hydrocarbon group to an aromatic ring. Examples of the aromatic hydrocarbon
include benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, and 1-methyl
naphthalene. Examples of the ether include diethyl ether and tetrahydrofuran.
Examples of the ketone include 4-methyl-2-pentanone. Examples of the ester acetate
include methyl acetate and ethyl acetate. Examples of the chain ester carbonate
include dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. The halide
is obtained by substituting each of part or all of hydrogen groups in each of the
foregoing aromatic hydrocarbon and the like by a halogen. Examples of the halide
include a fluorinated compound. In addition thereto, other type of ester and/or the like
may be used.
[0026] Specially, the low polarity solvent preferably dissolves the aluminum salt
and the alkyl sulfone sufficiently. One reason for this is that, in this case, since the
aluminum salt and the alkyl sulfone are uniformly dispersed, a higher effect is
obtainable. It is to be noted that, in the case where the solubility is evaluated, for
example, the solubility is examined by mixing the aluminum salt, the alkyl sulfone, and
the low polarity solvent at a mixture ratio (weight ratio) of 10:60:30.
[0027] Further, the specific dielectric constant is preferably equal to or less than 10,
and is more preferably equal to or less than 2.4. One reason for this is that, in this case,
the foregoing advantageous function of the low polarity solvent is easily exercised.
Examples of the low polarity solvent having a specific dielectric constant equal to or
less than 10 include an aromatic hydrocarbon and a chain ester carbonate. Examples
of the low polarity solvent having a specific dielectric constant equal to or less than 2.4
include an aromatic hydrocarbon.
[0028] [Contents ofAluminum Salt, Alkyl Sulfone, and Low Polarity Solvent]
FIG. 1 illustrates a triangle phase diagram of compositions of the electrolyte. In
FIG. I, a full line A is a line indicating a case that the content of the low polarity solvent
is 30 mol%, a dashed line B is a line indicating a case that the content of the low
polarity solvent is 88 mol%, a full line C is a line indicating a case that the mol ratio
(the content of the aluminum saltlthe content of the alkyl sulfone) is 415, and a dashed
line D is a line indicating a case that the mol ratio is 713.
[0029] The content of the low polarity solvent in the electrolyte is equal to or larger
than 30 mol% and is less than 88 mol%, and is more preferably from 30 mol% to 84
mol% both inclusive. One reason for this is that, in this case, the content of the low
polarity solvent becomes appropriate, and therefore, the dispersion amount of the
aluminum salt with respect to the low polarity solvent is increased.
[0030] Further, the mixture ratio between the content (mol%) of the aluminum salt
and the content (mol%) of the alkyl sulfone is equal to or larger than 415 and is less than
7/3, and is more preferably from 415 to 513 both inclusive at a mol ratio (the content of
the aluminum saltlthe content of the alkyl sulfone). One reason for this is that, in the
case where the low polarity solvent satisfies the foregoing conditions, the mixture ratio
between the aluminum salt and the alkyl sulfone becomes appropriate, and therefore, the
dispersion amount of the aluminum salt with respect to the low polarity solvent is
further increased.
[0031] Accordingly, a range of electrolyte composition, that is, a range within
which the respective contents of the aluminum salt, the alkyl sulfone, and the low
polarity solvent fall is the range surrounded by the full lines A and C and the dashed
lines B and D in FIG 1. However, as seen in the foregoing conditions, while dots
(contents) on the full lines A and C are included in the range, dots (contents) on the
dashed lines B and D are not included in the range.
[0032] [Method of Forming Electrolyte]
In forming the electrolyte, the aluminum salt, the alkyl sulfone, and the low
polarity solvent are mixed to disperse the aluminum salt and the alkyl sulfone in the low
polarity solvent. In this case, though mixing order thereof is not particularly limited,
specially, the aluminum salt is preferably dispersed after the low polarity solvent and the
alkyl sulfone are mixed. One reason for this is that, in this case, generation of reaction
heat is suppressed, and the dispersion amount of the aluminum salt tends to be further
increased. In the case where the dispersion amount of the aluminum salt is increased,
the content of the aluminum salt in the electrolyte is increased, and therefore, a dimer of
the aluminum salt is easily generated. Thereby, even if temperature of the electrolyte
is not increased, an oxidation-reduction reaction of the aluminum salt is easily and
significantly progressed.
[0033] [Function and Effect of Electrolyte]
The electrolyte contains the alkyl sulfone and the low polarity solvent together
with the aluminum salt. The content of the low polarity solvent is equal to or larger
than 30 mol% and is less than 88 mol%. The mol ratio (the content of the aluminum
salt/the content of the alkyl sulfone) is equal to or larger than 4/5 and is less than 7/3.
[0034] In this case, aluminum is electrochemically activated by the alkyl sulfone,
and an oxidation-reduction reaction of aluminum is less likely to be influenced by the
low polarity solvent. Therefore, the oxidation-reduction reaction of aluminum
becomes easier to be progressed smoothly and sufficiently. Further, in this case, a
dimer of the aluminum salt is more easily generated according to increase of the
dispersion amount with respect to the low polarity solvent compared to a case in which
the content of the low polarity solvent and the mol ratio do not satisfy the foregoing
conditions. Therefore, the oxidation-reduction reaction of aluminum becomes easier to
be progressed.
[0035] Accordingly, since the oxidation-reduction reaction of aluminum becomes
significantly easier to be progressed, progression temperature of a
precipitation-dissolution reaction of aluminum is allowed to be lowered. That is, even
if temperature of the electrolyte is not excessively increased, the
precipitation-dissolution reaction of aluminum is allowed to be progressed smoothly
and sufficiently at ambient temperature. Specifically, the favorable
precipitation-dissolution reaction of aluminum is allowed to be achieved at 15 deg C or
more, preferably at 20 deg C or more, and more preferably at 25 deg C or more. In
this case, further, reactivity of the electrolyte is suppressed by the alkyl sulfone, and
therefore, corrosion of the metal material by the electrolyte is allowed to be suppressed.
[0036] In particular, in the case where the low polarity solvent is an aromatic
hydrocarbon such as toluene, a higher effect is obtainable. In addition thereto, in the
case where each of carbon numbers of R1 and R2 in the alkyl sulfone is equal to or less
than 4, or the alkyl sulfone is ethyl-n-propyl sulfone, etc., a higher effect is obtainable.
[0037] [2. Electrochemical Device Using Electrolyte]
Next, a description will be given of a usage example of the foregoing electrolyte.
A secondary battery will be herein taken as an example of electrochemical devices.
The electrolyte is used for the secondary battery as follows.
e
[0038] [Configuration of Secondary Battery]
FIG. 2 illustrates a cross-sectional configuration of a secondary battery. The
secondary battery herein described is an aluminum secondary battery in which capacity
is obtained by a precipitation-dissolution reaction of aluminum at the time of charge and
discharge.
[0039] In the secondary battery, an outer package can 14 containing a cathode 11
and an outer package cup 15 containing an anode 12 are swaged with a separator 13 and
a gasket 16.
[0040] The outer package can 14 and the outer package cup 15 are package
members to contain the cathode 11, the anode 12, and the like. For example, the outer
package can 14 and the outer package cup 15 are made of a metal material such as
aluminum, an aluminum alloy, and stainless steel.
[0041] In the cathode 1 1, a cathode active material layer 1 1 B is formed on one
surface of a cathode current collector 11A. The cathode current collector 11A may be
made of, for example, aluminum, nickel (Ni), stainless steel, or the like. The cathode
active material layer 11B contains other material such as a cathode binder and a cathode
electric conductor as necessary together with a cathode active material. Examples of
the cathode active material include a disulfide such as titanium disulfide and
molybdenum sulfide. Examples of the cathode binder include a polymer material such
11
as polyvinylidene fluoride and polytetrafluoroethylene. Examples of the cathode
electric conductor include graphite, carbon black, acetylene black, and Ketjen black.
[0042] In the anode 12, an anode active material layer 12B is formed on one surface
of an anode current collector 12A. The anode current collector 12A may be made of,
for example, copper (Cu), nickel, stainless steel, or the like. The anode active material
layer 12B may be made of aluminum or an aluminum alloy. Examples of elements
configuring the aluminum alloy include one or more of silicon (Si), manganese (Mn),
chromium (Cr), nickel, and copper.
[0043] The separator 13 separates the cathode 11 from the anode 12, and passes
aluminum ions while preventing current short circuit resulting from contact of both
electrodes. The separator 13 is formed of, for example, a porous film made of a
synthetic resin, ceramics, or the like. Examples of the synthetic resin include
polytetrafluoroethylene, polypropylene, and polyethylene. The separator 13 may be a
laminated film in which two or more types of porous films are laminated. The
separator 13 is impregnated with the foregoing electrolyte. The electrolyte is what we
call an electrolytic solution (liquid electrolyte).
[0044] [Operation of secondary Battery]
In the secondary battery, for example, a charge and discharge reaction is generated
as follows. At the time of charge, due to a reduction reaction, aluminum ions extracted
from the cathode 11 reach the anode 12 through the electrolyte, and therefore, aluminum
is precipitated in the anode 12. In contrast, at the time of discharge, due to an
oxidation reaction, aluminum is dissolved in the anode 12, and therefore, aluminum ions
are eluted from the anode 12 into the electrolyte.
[0045] [Method of Manufacturing Secondary Battery]
The secondary battery is manufactured, for example, by the following procedure.
First, the cathode active material layer 11B containing a cathode active material is
formed on one surface of the cathode current collector 11A by using a coating method
or the like to form the cathode 11. Subsequently, the anode active material layer 12B
containing an anode active material is formed on one surface of the anode current
collector 12A by using a coating method or the like to form the anode 12.
Subsequently, the cathode 11 is contained in the outer package can 14, and the anode 12
is contained in the outer package cup 15. Finally, the outer package can 14 and the
outer package cup 15 are swaged with the separator 13 impregnated with the foregoing
electrolyte and the gasket 16. Thereby, the secondary battery is completed.
[0046] [Function and Effect of Secondary Battery]
According to the secondary battery, since the separator 13 is impregnated with the
foregoing electrolyte, progression temperature of a precipitation-dissolution reaction of
aluminum is lowered. Therefore, aluminum is effectively precipitated and dissolved
electrochemically even at temperature that is not high. Accordingly, battery capacity is
obtainable stably by the precipitation-dissolution reaction of aluminum at ambient
temperature. Other functions and other effects are similar to those of the electrolyte.
Examples
[0047] Next, Examples of the present invention will be described in detail.
[0048] [Examples 1 to 181
A low polarity solvent (toluene: TOL) and an alkyl sulfone (ethyl-n-propyl sulfone:
ENPS) were mixed. Thereafter, an aluminum salt (aluminum chloride: AlC13) was
dispersed to prepare liquid electrolytes (electrolytic solutions). In this case, the
mixture ratio of the foregoing three components was adjusted so that compositions
illustrated in Table 1, that is, contents of the low polarity solvent and mol ratios (the
content of the aluminum salt/the content of the alkyl sulfone) illustrated in Table 1 were
obtained. When the electrochemical characteristics of the electrolytic solutions were
examined, results illustrated in Table 1 were obtained. In Table 1, as content values of
the respective components, values rounded to two places of decimals are shown.
[0049] As the electrochemical characteristics, first, progression degrees of
precipitation-dissolution reactions of aluminum were evaluated by using each
electrolytic solution (2 cm3). Specifically, a current flowing at the time of an
oxidation-reduction reaction of aluminum was measured by using a cyclic voltammetry
(three-electrode method cell) in the air (25 deg C) and in a constant-temperature bath
(60 deg C). In this case, a side-derivatized molybdenum electrode (diameter: 1.5 mm)
available from BAS Inc. was used as a working electrode, and an aluminum wire
(diameter: 1.0 mm) available from Nilaco Corporation was used as a reference electrode
and a counter electrode. Further, the sweep rate was 10 mV/s. The electric potential
(V) of the working electrode with respect to the electric potential (V) of the reference
electrode was changed in the range from -1.0 V to +1.7 V (mol ratio: 513 or less) both
inclusive, and in the range from -1.0 V to +1.0 V (mol ratio: 713). Based on the
measurement results, in the case where both current densities (mA/cm2) at the time of
an oxidation reaction and at the time of a reduction reaction of aluminum were equal to
or larger than 3 mA/cm2, it was evaluated as "white circle (o)", and in the case where
both current densities (rn~lcma~t )th e time of an oxidation reaction and at the time of a
reduction reaction of aluminum were less than 3 mA/cm2, it was evaluated as "cross
(x)".
[0050]
[Table 11
Table 1
Example 1
Composition Evaluation
25 deg
C
o
Low polarity solvent 60 deg
C
o
Type
TOL
Content
(mol%)
56.26
Aluminum salt
Type
AICI,
mol
ratio
41.5
Content
(mol%)
19.44
Alkyl sulfone
Type
ENPS
Content
(mol%)
24.30
[0051] In the case where the electrolyte contained the alkyl sulfone and the low
polarity solvent together with the aluminum salt, when the content of the low polarity
solvent and the mol ratio were in the appropriate ranges, an oxidation-reduction reaction
of aluminum was progressed smoothly and sufficiently in the vicinity of -1 .O V and +1.0
V not only under high temperature conditions (60 deg C), but also under ambient
temperature conditions (25 deg C). Thereby, a sufficient amount of current flowed
both at the time of an oxidation reaction and at the time of a reduction reaction. With
regard to the appropriate ranges, the content of the low polarity solvent was equal to or
larger than 30 mol% and less than 88 mol%; and the mol ratio was equal to or larger
than 415 and less than 713.
[0052] On the other hand, in the case where the content of the low polarity solvent
and the rnol ratio were out of the foregoing appropriate ranges, under high temperature
conditions, an oxidation-reduction reaction of aluminum was progressed and therefore a
sufficient amount of current flowed. In contrast, in the case where the content of the
low polarity solvent and the mol ratio were out of the appropriate ranges, under ambient
temperature conditions, an oxidation-reduction reaction of aluminum was less likely to
be progressed, and therefore, almost no current flowed.
[0053] The foregoing results showed the following fact. In the case where the
electrolyte contains the alkyl sulfone and the low polarity solvent together with the
aluminum salt, when the contents of the foregoing three components (mol ratio) are
appropriate, a specific advantage that an oxidation-reduction reaction of the aluminum
salt is easily progressed without high temperature conditions is obtainable. Therefore,
only by setting the contents of the foregoing three components appropriately, a more
sufficient electric charge is obtained by a precipitation-dissolution reaction of aluminum
even at ambient temperature.
[0054] [Examples 19 to 281
As shown in Table 2, electrolytic solutions were prepared and the electrochemical
characteristics thereof were examined by a procedure similar to that of Example 6
except that types of the low polarity solvent and alkyl sulfone were changed. In this
case, as low polarity solvents, benzene (BEZ), o-xylene (OXY), m-xylene (MXY),
p-xylene (PXY), and 1-methyl naphthalene (MN) were used. Further, as alkyl sulfones,
ethyl-i-propyl sulfone (EIPS), ethyl-n-butyl sulfone (ENBS), ethyl-i-butyl sulfone
(EIBS), ethyl-s-butyl sulfone (ESBS), and di-n-propyl sulfone (DNPS) were used.
[0055]
[Table 21
[0056] Even if the types of the low polarity solvent and the alkyl sulfone were
changed, a sufficient amount of current flowed at the time of an oxidation reaction and
at the time of a reduction reaction of aluminum not only under high temperature
conditions (60 deg C), but also under ambient temperature conditions (25 deg C).
[0057] From the foregoing results of Table 1 and Table 2, the following fact was
confirmed. That is, since the electrolyte of the present invention contains the alkyl
sulfone and the low polarity solvent together with the aluminum salt, and the content of
Table 2
Example 6
Example 19
Example 20
Example 21
Example 22
Example 23
Example 24
Example 25
Example 26
Example27
Example28
25 deg
C
o
o
o
o
o
o
o
o
o
o
o
Low polarity
Type
TOL
BEZ
OXY
MXY
PXY
MN
Evaluation
60 deg
C
o
o
o
o
o
o
o
o
o
o
o
--
solvent
Content
(mol%)
62.32
62.32
Composition
Type
AICI,
AICIz
mol
ratio
413
413
-
Aluminum salt
Content
(mol%)
21.53
21.53
Alkyl
Type
ENPS
ELPS
ENBS
ELBS
ESBS
DNPS
ENPS
sulfone
Content
(mol%)
16.15
16.15
the low polarity solvent and the mol ratio (the content of the aluminum saltlthe content
of the alkyl sulfone) are in the appropriate ranges, a precipitation-dissolution reaction of
aluminum is smoothly and sufficiently progressed even at ambient temperature (25 deg
C). Thereby, in a secondary battery using the electrolyte according to the present
invention, a battery capacity is stably obtained by a precipitation-dissolution reaction of
aluminum at ambient temperature.
[0058] The present invention has been described with reference to the embodiment
and Examples. However, the present invention is not limited to the aspects described
in the embodiment and Examples, and various modifications may be made. For
example, the electrolyte of the present invention is applicable not only to the secondary
battery but also to other electrochemical device such as a capacitor.
[0059] Further, in the embodiment and Examples, with regard to the content of the
solvent (specific dielectric constant of 20 or less), the description has been given of the
appropriate range derived from the results of Examples. However, the description
does not totally deny a possibility that the content is out of the foregoing range. That
is, the foregoing appropriate range is the range particularly preferable for obtaining the
effects of the present invention. Therefore, as long as the effects of the present
invention are obtained, the content may be out of the foregoing range in some degrees.
The same is similarly applicable to the mol ratio (the content of the aluminum salt/the
content of the alkyl sulfone) and the specific dielectric constant of the solvent.

CLAIMS
1. An electrolyte comprising:
an aluminum salt;
an alkyl sulfone (R1-S(=0)2-R2: each of R1 and R2 represents an alkyl group);
and
a solvent having a specific dielectric constant of 20 or less, wherein
a content of the solvent is equal to or larger than 30 rnol percent and is less than
88 rnol percent, and
a rnol ratio between the aluminum salt and the alkyl sulfone (a content of the
aluminum salt/a content of the alkyl sulfone) is equal to or larger than 415 and is less
than 713.
2. The electrolyte according to claim 1, wherein
the content of the solvent is from 30 rnol percent to 84 rnol percent both
inclusive, and
the rnol ratio between the aluminum salt and the alkyl sulfone is from 415 to 513
both inclusive.
3. The electrolyte according to claim 1, wherein the specific dielectric constant of
the solvent is equal to or less than 10.
4. The electrolyte according to claim 1, wherein the solvent is an aromatic
hydrocarbon.
5. The electrolyte according to claim 1, wherein the solvent is one of benzene,
toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, and 1 -methyl naphthalene.
6. The electrolyte according to claim 1, wherein each of carbon numbers of the
R1 and the R2 in the alkyl sulfone is equal to or less than 4.
7. The electrolyte according to claim 1, wherein the alkyl sulfone is one of
ethyl-n-propyl sulfone, ethyl-i-propyl sulfone, ethyl-n-butyl sulfone, ethyl-i-butyl
sulfone, ethyl-s-butyl sulfone, and di-n-propyl sulfone.
8. The electrolyte according to claim 1, wherein the electrolyte is used for a
secondary battery.
9. A secondary battery comprising:
a cathode;
an anode; and
an electrolyte, wherein
the electrolyte includes
an aluminum salt,
an alkyl sulfone (Rl-S(=O)*-N: each of RI and R2 represents an alkyl group),
a solvent having a specific dielectric constant of 20 or less,
a content of the solvent is equal to or larger than 30 mol percent and is less than
88 mol percent, and
a mol ratio between the aluminum salt and the alkyl sulfone (a content of the
aluminum salt/a content of the alkyl sulfone) is equal to or larger than 415 and is less
than 713.
Dated this 12/04/20 13
ATTORNEY FOR THE APPLICANT[S]
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