JP2002280063A - Electrolyte and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte having high conductivity and superior thermal stability and oxidation stability, and a battery using the same. SOLUTION: A rolled electrode 20 having a band positive electrode 21 and a negative electrode 22 rolled via a separator 23 is provided in a battery can 11. The separator 23 is impregnated with the electrolyte. The electrolyte contains a solvent and a lithium salt dissolved in the solvent and additionally contains a compound as an additive of a molecular weight of 500 or less having an NS structure with nitrogen and sulfur bonded. The compound having the NS structure is 1,1'-sulfonyldiimidazole or the like. Thus, the thermal stability and the oxidation stability can be improved while maintaining high conductivity of the electrolyte and battery properties including cycle property, high- temperature property and storage stability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrolyte used for an electrochemical device such as a battery, and a battery using the same.

[0002]

2. Description of the Related Art In recent years, portable electronic devices typified by a camera-integrated VTR (video tape recorder), a cellular phone or a laptop computer have become widespread, and their miniaturization, weight reduction and continuous driving for a long time are strongly demanded. Have been. Along with this, research and development for improving the energy density of batteries, particularly secondary batteries, as those portable power sources have been actively promoted. Above all, lithium ion secondary batteries or lithium secondary batteries are expected to provide a higher energy density than conventional nonaqueous electrolyte secondary batteries such as lead batteries and nickel cadmium batteries.

Conventionally, as an electrolyte of this lithium ion secondary battery or lithium secondary battery, one in which LiPF ₆ is dissolved as an electrolyte salt in a carbonate-based non-aqueous solvent such as propylene carbonate or diethyl carbonate has a conductivity of It is widely used because it is high and stable in terms of potential.

[0004]

However, LiP
F ₆ is not satisfactory in thermal stability, and therefore has a problem in that the cycle characteristics or storage characteristics of the battery deteriorate. Such characteristic deterioration occurs even when the thermal decomposition of LiPF ₆ slightly occurs in the electrolyte.

[0005] LiPF₆As other electrolyte salts,
Than LiBF_Four, LiCF_ThreeSO _Three, LiClO_FourAh
Rui or LiAsF₆Etc. are also known. However, Li
BF _FourHas high thermal and oxidative stability but high electrical conductivity
Low, LiCF_ThreeSO_ThreeHas high thermal stability but high conductivity
Low oxidation stability and charging at high voltage of 4V or more
There has been a problem that satisfactory discharge characteristics cannot be obtained. Also,
LiClO_FourAnd LiAsF₆Has high conductivity but good
There was a problem that good cycle characteristics could not be obtained.

In recent years, LiN (CF ₃ SO ₂ )
₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ or LiN (C ₄
F ₉ SO ₂ ) (CF ₃ SO ₂ ) and the like can be obtained as a relatively high conductivity and have high thermal stability, and are therefore expected as electrolyte salts. However, since these electrolyte salts are inferior in oxidative stability, when used as an electrolyte salt of a lithium ion secondary battery having a charging voltage of more than 4 V, good conductivity, cycle characteristics and storage characteristics are simultaneously obtained. There was a problem that it could not be realized.

[0007] These problems are not limited to the conventional lithium ion secondary battery or lithium secondary battery, but secondary batteries recently developed by the inventors for realizing higher energy density, for example, The same applies to a secondary battery in which the capacity of the negative electrode is represented by the sum of a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium.

The present invention has been made in view of such problems, and an object of the present invention is to provide an electrolyte having high conductivity, excellent thermal stability and oxidation stability, and a battery using the same. .

[0009]

The electrolyte according to the present invention comprises:
It includes a compound having a molecular weight of less than 500 and having an NS structure in which nitrogen (N) and sulfur (S) are bonded.

[0010] The battery according to the present invention comprises an electrolyte together with a positive electrode and a negative electrode.
It is less than 00 and includes a compound having an NS structure in which nitrogen and sulfur are bonded.

Another battery according to the present invention is provided with an electrolyte together with a positive electrode and a negative electrode, and the capacity of the negative electrode is the sum of a capacity component due to absorption and desorption of light metal and a capacity component due to precipitation and dissolution of light metal. Wherein the electrolyte has a molecular weight of less than 500 and contains a compound having an NS structure in which nitrogen and sulfur are bonded.

The electrolyte according to the invention has a molecular weight of 500
, And contains a compound having an NS structure in which nitrogen and sulfur are bonded, so that the conductivity is high and the thermal stability and the oxidation stability are improved.

In the battery according to the present invention and other batteries, since the electrolyte according to the present invention is provided, the conductivity and stability of the electrolyte are high, a high discharge capacity is obtained, and the cycle characteristics, high temperature characteristics and storage stability are obtained. Etc. are improved.

[0014]

Embodiments of the present invention will be described below in detail.

[0015] An electrolyte according to one embodiment of the present invention includes, for example, an electrolyte salt and a solvent that dissolves the electrolyte salt. The electrolyte salt is for imparting ionic conductivity by dissociation. As the electrolyte salt,
Light metal salts and the like, specifically, lithium (L
i) Salt, sodium (Na) salt or potassium (K)
Alkali metal salts such as salts, or magnesium (Mg)
One or two or more salts or alkaline earth metal salts such as calcium (Ca) salts or aluminum (Al) salts are used depending on the purpose.

As the lithium salt, for example, Li
AsF ₆ , LiPF ₆ , LiBF ₄ , LiClO ₄ , L
iB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ S
O ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ S
O ₂ ) ₂ , LiN (C ₄ F ₉ SO ₂ ) (CF ₃ S
O ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiAlCl ₄ ,
LiSiF ₆ , LiCl, LiBr and the like can be mentioned, and any one of them or a mixture of two or more thereof may be used. Among them, LiPF ₆ is preferable because high conductivity can be obtained and the oxidation stability is excellent,
LiBF ₄ is preferable because of its excellent thermal stability and oxidation stability. LiClO ₄ is preferable because high conductivity can be obtained. LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ can obtain relatively high conductivity, and thermal stability can be obtained. Is also preferred.

The content of the electrolyte salt (concentration) in the range of 0.5mol / dm ³ ~2.0mol / dm ³ in the solvent, or 0.5mol / kg~2.0mol / kg
Is preferably within the range. This is because the ionic conductivity of the electrolyte can be increased within this range.

The solvent is composed of, for example, a non-aqueous solvent such as a liquid organic solvent. The liquid non-aqueous solvent is, for example, one composed of one or more non-aqueous compounds and having an intrinsic viscosity at 25 ° C. of 10.0 mPa · s or less. In addition, the intrinsic viscosity in a state where the electrolyte salt is dissolved is 1
It may be 0.0 m · Pa or less, and when a plurality of non-aqueous compounds are mixed to form a solvent, the intrinsic viscosity in the mixed state may be 10.0 m · Pa or less. As such a non-aqueous solvent, various non-aqueous solvents conventionally used can be used. Specifically, cyclic carbonate such as propylene carbonate or ethylene carbonate, chain ester such as diethyl carbonate, carboxylate such as methyl propionate or methyl butyrate, and γ-butyrolactone, sulfolane, 2-methyltetrahydrofuran or dimethoxyethane And the like. In particular, from the viewpoint of oxidation stability,
It is preferable to use a mixture of carbonate esters.

This electrolyte also contains, as an additive, a compound having a molecular weight of less than 500 and soluble in a solvent having an NS structure in which nitrogen and sulfur are bonded. Thus, in this electrolyte, thermal stability and oxidation stability can be improved while maintaining high conductivity. The molecular weight of the compound having the NS structure is 5
The reason why the molecular weight is less than 00 is that if the molecular weight is too large, it is difficult to dissolve in a solvent and the electric conductivity is lowered. In addition,
The molecular weight of the compound having the NS structure is more preferably 350 or less.

The compound having the NS structure includes, for example, a compound having a molecular structure in which nitrogen and SO ₂ shown in Chemical formula 3 are bonded. Specifically, 1,1′-sulfonyldiimidazole (1,1′-s) represented by the structural formula
N-bismethylthiomethylene-p-toluenesulfonamide (N- [bis (methylthio) metylene] -p-toluenesulfonamid) represented by the structural formula
e) or 1-p-tolysulfonyl pyrrolr represented by the structural formula of Chemical formula 6, etc., and one or more of these are used in combination.

[0021]

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[0022]

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[0023]

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[0024]

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The content of the compound having the NS structure is as follows:
The content is preferably in the range of 0.01% by mass or more and less than 20.0% by mass, more preferably in the range of more than 0.01% by mass and 10% by mass or less based on the solvent. This is because a higher improvement effect can be obtained within this range.

The electrolyte may be a so-called liquid electrolyte comprising these electrolyte salts, a liquid solvent and additives, but may further contain a polymer compound holding them, and form a gel. It may be. In this case, the type and amount of the polymer compound are preferably adjusted so that the ionic conductivity is 1 mS / cm or more at room temperature.

Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and polyhexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, and polyphosphazene. , Polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, a polymer compound having a structure of polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable from the viewpoint of electrochemical stability.

Some of these high molecular compounds do not have ion conductivity, but some of them can dissociate the electrolyte salt and have ion conductivity, and either of them may be used. However, the electrolyte salt can be dissociated,
The polymer compound having ion conductivity also functions as a solvent. Therefore, such a polymer compound is included in the solvent when defining the content of the electrolyte salt or the content of the compound having the NS structure.

The amount of the polymer compound added to the electrolyte is
Usually, it is preferably in the range of 5% by mass to 50% by mass of the electrolytic solution, though it depends on the compatibility of both.

This electrolyte can be produced, for example, by dissolving an electrolyte salt in a solvent and then adding a compound having an NS structure. In the case of forming a gel, for example, the electrolyte can be produced by mixing the electrolytic solution with a monomer which is a starting material of a polymer compound, and polymerizing the monomer.

As described above, since the electrolyte according to the present embodiment contains a compound having an NS structure and a molecular weight of less than 500, thermal stability and oxidation stability can be improved. Therefore, if an electrochemical element such as a battery is formed using this electrolyte, its characteristics can be further improved.

Such an electrolyte is preferably used, for example, in the following secondary batteries. Here, an example of a secondary battery using lithium as an electrode reactive species will be described with reference to the drawings.

FIG. 1 shows a sectional structure of a secondary battery using the electrolyte according to the present embodiment. This secondary battery is a so-called cylindrical type. A band-shaped positive electrode 21 and a negative electrode 22 are provided inside a substantially hollow cylindrical battery can 11.
Electrode body 20 is wound with a separator 23 interposed therebetween.
have. The battery can 11 is made of, for example, nickel-plated iron, and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are respectively arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

At the open end of the battery can 11, a battery cover 14 is provided.
And a safety valve mechanism 15 provided inside the battery lid 14.
And Positive Temperature Coefficie
nt; PTC element) 16 and caulked via a gasket 17, and the battery can 11
The inside is closed. The battery cover 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery cover 14 via the thermal resistance element 16, and when the internal pressure of the battery becomes higher than a certain level due to an internal short circuit or external heating, the disk plate 15a is inverted. Then, the electrical connection between the battery cover 14 and the spirally wound electrode body 20 is cut off. Thermal resistance element 1
Reference numeral 6 denotes an element for limiting the current by increasing the resistance value when the temperature rises and preventing abnormal heat generation due to a large current, and is made of, for example, a barium titanate-based semiconductor ceramic. The gasket 17 is made of, for example, an insulating material, and its surface is coated with asphalt.

The wound electrode body 20 is wound around, for example, a center pin 24. Positive electrode 2 of wound electrode body 20
1 is connected to a positive electrode lead 25 made of aluminum or the like, and the negative electrode 22 is connected to a negative electrode lead 26 made of nickel or the like. The positive electrode lead 25 is electrically connected to the battery cover 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

FIG. 2 is an enlarged view of a part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode mixture layer 21b is provided on both surfaces of a positive electrode current collector 21a having a pair of opposing surfaces. Although not shown, the positive electrode mixture layer 21b may be provided only on one side of the positive electrode current collector 21a. Positive electrode current collector 21a
Has a thickness of, for example, about 5 μm to 50 μm, and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode mixture layer 21b has a thickness of, for example, 80 μm to 250 μm and includes a positive electrode material capable of inserting and extracting lithium as a light metal. When the positive electrode mixture layer 21b is provided on both surfaces of the positive electrode current collector 21a, the thickness of the positive electrode mixture layer 21b is the total thickness thereof.

As the positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing compound such as lithium oxide, lithium sulfide or an intercalation compound containing lithium is suitable. You may use it. In particular, to increase the energy density, a lithium composite oxide represented by the general formula Li _x MO ₂ or an intercalation compound containing lithium is preferable. In addition, M is preferably one or more transition metals. Specifically, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), aluminum (Al), vanadium (V) and titanium ( At least one of Ti)
Species are preferred. x differs depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. In addition, LiM having a spinel type crystal structure is also used.
n ₂ O ₄ or LiF having an olivine type crystal structure
ePO _{4 is} also preferable because a high energy density can be obtained.

Incidentally, such a positive electrode material includes, for example, lithium carbonate, nitrate, oxide or hydroxide,
It is prepared by mixing and pulverizing a transition metal carbonate, nitrate, oxide or hydroxide to have a desired composition, followed by calcination in an oxygen atmosphere at a temperature in the range of 600 ° C to 1000 ° C. Is done.

The positive electrode mixture layer 21b also contains, for example, a conductive agent, and may further contain a binder, if necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black and Ketjen black, and one or more of them are used in combination. Further, in addition to the carbon material, a metal material or a conductive polymer material may be used as long as the material has conductivity. Examples of the binder include synthetic rubbers such as styrene-butadiene rubber, fluorine rubber and ethylene propylene diene rubber, and polymer materials such as polyvinylidene fluoride, and one or more of them are mixed. Used as For example,
When the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use a highly flexible styrene-butadiene-based rubber or a fluorine-based rubber as the binder.

The negative electrode 22 has, for example, a structure in which a negative electrode mixture layer 22b is provided on both surfaces of a negative electrode current collector 22a having a pair of opposing surfaces. Although not shown, the negative electrode mixture layer 22b may be provided only on one side of the negative electrode current collector 22a. The negative electrode current collector 22a is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electric conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electric conductivity. The thickness of the negative electrode current collector 22a is preferably, for example, about 6 μm to 40 μm. 6μ
If the thickness is smaller than m, the mechanical strength is reduced, the anode current collector 22a is easily broken in the manufacturing process, and the production efficiency is reduced. The volume ratio becomes larger than necessary,
This is because it becomes difficult to increase the energy density.

The negative electrode mixture layer 22b is composed of one or more negative electrode materials capable of occluding and releasing lithium as a light metal. A binder similar to that of the agent layer 21b may be included. The thickness of the negative electrode mixture layer 22b is, for example, 8
0 μm to 250 μm. The thickness of the negative electrode mixture layer 2
When 2b is provided on both surfaces of the negative electrode current collector 22a, it is the total thickness thereof.

It should be noted that, in the present specification, the term "storage / release of light metal" means that light metal ions are electrochemically stored / released without losing their ionicity. This includes not only the case where the occluded light metal exists in a perfect ionic state but also the case where the occluded light metal exists in a state that cannot be said to be a perfect ionic state. Such cases include, for example, occlusion by electrochemical intercalation reaction of light metal ions with respect to graphite. Further, occlusion of light metals by forming an intermetallic compound or an alloy can also be mentioned.

Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon and graphitizable carbon. These carbon materials are preferable because a change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good charge and discharge cycle characteristics can be obtained. Particularly, graphite is preferable because it has a large electrochemical equivalent and can obtain a high energy density.

As the graphite, for example, the true density is 2.10
g / cm ³ or more, preferably 2.18 g / cm ³
The above is more preferable. In order to obtain such a true density, the C-axis crystallite thickness of the (002) plane must be 1
It is necessary to be 4.0 nm or more. Also, (00
2) The spacing between the surfaces is preferably less than 0.340 nm, and more preferably 0.335 nm or more and 0.337 nm or less.

The graphite may be natural graphite or artificial graphite.
In the case of artificial graphite, for example, it can be obtained by carbonizing an organic material, performing a high-temperature heat treatment, and pulverizing and classifying. The high-temperature heat treatment is performed by, for example, carbonizing at 300 ° C. to 700 ° C. in an inert gas stream such as nitrogen (N ₂ ) as necessary,
The temperature is raised from 900 ° C to 1500 ° C at a rate of 1 ° C to 100 ° C per minute, the temperature is maintained for about 0 hours to 30 hours, and calcined, and heated to 2000 ° C or more, preferably 2500 ° C or more. This is performed by maintaining the temperature for an appropriate time.

Coal or pitch can be used as the starting organic material. For the pitch, for example, tars obtained by pyrolyzing coal tar, ethylene bottom oil or crude oil at a high temperature, asphalt, etc. (vacuum distillation, normal pressure distillation or steam distillation), thermal polycondensation, extraction, Examples include those obtained by chemical polycondensation, those produced at the time of wood reflux, polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, and 3,5-dimethylphenol resin.
These coals or pitches have a maximum of 400
It exists as a liquid at about ℃, and aromatic rings are condensed and polycyclic by being held at that temperature, and it is in a laminated orientation state, and then becomes a solid carbon precursor at about 500 ° C. or higher, that is, semi-coke. (Liquid phase carbonization process).

Examples of the organic material include condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphen, and pentacene, and derivatives thereof (for example, carboxylic acids and carboxylic anhydrides of the above compounds). , Carboximides), or mixtures thereof. Further, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine and derivatives thereof;
Alternatively, a mixture thereof can be used.

The pulverization may be carried out before or after carbonization or calcination, or during the heating process before graphitization. In these cases, heat treatment for graphitization is finally performed in a powder state. However, to obtain graphite powder with high bulk density and high breaking strength, heat treatment is performed after molding the raw material,
It is preferable to pulverize and classify the obtained graphitized molded body.

For example, when producing a graphitized molded body, coke as a filler and binder pitch as a molding agent or a sintering agent are mixed and molded. And the pitch impregnating step of impregnating the sintered body with the melted binder pitch is repeated several times, followed by heat treatment at a high temperature. The impregnated binder pitch is carbonized and graphitized in the above heat treatment process. By the way, in this case,
Since filler (coke) and binder pitch are used as raw materials, it is graphitized as a polycrystal, and since sulfur and nitrogen contained in the raw materials are generated as a gas during heat treatment, minute holes are formed in the passage. It is formed. Accordingly, the vacancies facilitate the progress of the insertion and extraction reaction of lithium, and also have the advantage of high industrial processing efficiency. In addition, as a raw material of the molded body, the moldability itself,
A filler having sinterability may be used. In this case, it is not necessary to use a binder pitch.

As the non-graphitizable carbon, the (002) plane spacing is 0.37 nm or more and the true density is 1.70 g / cm.
With less than ^3, differential thermal analysis in air (Differen
Those which do not show an exothermic peak above 700 ° C. in tial thermal analysis (DTA) are preferred.

Such non-graphitizable carbon can be obtained, for example, by heat-treating an organic material at about 1200 ° C., and pulverizing and classifying. The heat treatment is, for example, 3
After carbonization at 00 ° C to 700 ° C (solid carbonization process),
The temperature is raised from 900 ° C. to 1300 ° C. at a rate of 1 ° C. to 100 ° C. per minute, and the temperature is maintained for about 0 to 30 hours. The pulverization may be performed before or after carbonization, or during the heating process.

As the organic material used as a starting material, for example, furfuryl alcohol or furfural polymer or copolymer, or furan resin which is a copolymer of these polymers and other resins can be used. . Also,
Phenol resin, acrylic resin, vinyl halide resin, polyimide resin, polyamide imide resin, polyamide resin, conjugated resin such as polyacetylene or polyparaphenylene, cellulose or derivatives thereof, coffee beans, bamboo, shellfish including chitosan, bacteria Biocelluloses utilizing the same can also be used. Furthermore, the atomic ratio H / of hydrogen atoms (H) and carbon atoms (C)
A compound in which a functional group containing oxygen (O) is introduced (so-called oxygen cross-linking) into petroleum pitch in which C is, for example, 0.6 to 0.8 can also be used.

The oxygen content of this compound is preferably at least 3%, more preferably at least 5% (see JP-A-3-25253). The oxygen content affects the crystal structure of the carbon material, and at a higher content, the physical properties of the non-graphitizable carbon can be increased.
This is because the capacity of the negative electrode 22 can be improved.
Incidentally, petroleum pitch is, for example, coal tar, tar bottoms obtained by pyrolyzing ethylene bottom oil or crude oil at high temperature, or asphalt,
It is obtained by distillation (vacuum distillation, normal pressure distillation or steam distillation), thermal polycondensation, extraction or chemical polycondensation. Examples of the oxidative crosslinking method include nitric acid,
A wet method in which an aqueous solution of sulfuric acid, hypochlorous acid, or a mixed acid thereof is reacted with petroleum pitch, a dry method in which an oxidizing gas such as air or oxygen is reacted with petroleum pitch, or sulfur, ammonium nitrate, ammonium persulfate, A method of reacting a solid reagent such as ferric chloride with petroleum pitch can be used.

The organic material used as a starting material is not limited to these, and any other organic material may be used as long as it is an organic material that can be made non-graphitizable carbon through a solid phase carbonization process by oxygen crosslinking or the like.

Examples of the non-graphitizable carbon include those produced using the above-mentioned organic materials as starting materials, and those described in JP-A-3-3-1.
A compound containing phosphorus (P), oxygen and carbon as main components described in 37010 is also preferable because it shows the above-mentioned physical property parameters.

Examples of the negative electrode material capable of inserting and extracting lithium include metals and semiconductors capable of forming alloys and compounds with lithium, and alloys and compounds thereof. These are preferable because a high energy density can be obtained, and it is more preferable to use them together with a carbon material because a high energy density can be obtained and excellent cycle characteristics can be obtained.

As such a metal or semiconductor,
For example, tin (Sn), lead (Pb), aluminum (A
l), indium (In), silicon (Si), zinc (Z
n), antimony (Sb), bismuth (Bi), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr)
And yttrium (Y). These alloys or compounds, e.g., chemical formula Ma _s Mb _t
Li _u, or include those represented by the chemical formula Ma _p Mc _q Md _r. In these chemical formulas, Ma represents at least one of a metal element and a semiconductor element capable of forming an alloy or a compound with lithium; Mb represents at least one of a metal element and a semiconductor element other than lithium and Ma; Represents at least one kind of non-metallic element, and Md represents at least one kind of metallic element and semiconductor element other than Ma. Also, s, t, u,
The values of p, q and r are s> 0, t ≧ 0, u ≧
0, p> 0, q> 0, r ≧ 0.

Among them, a group 4B metal element or semiconductor element, or an alloy or compound thereof is preferable.
Particularly preferred are silicon or tin, or alloys or compounds thereof. These may be crystalline or amorphous.

For such alloys or compounds,
To give an example, LiAl, AlSb, CuMgS
b, SiB_Four, SiB₆, Mg_TwoSi, Mg_TwoSn, N
i_TwoSi, TiSi_Two, MoSi_Two, CoSi_Two, Ni
Si_Two, CaSi_Two, CrSi_Two, Cu_FiveSi, FeS
i_Two, MnSi_Two, NbSi_Two, TaSi_Two, VS
i _Two, WSi_Two, ZnSi_Two, SiC, Si_ThreeN_Four, S
i_TwoN_TwoO, SiO_v(0 <v ≦ 2), SnO_w(0 <
w ≦ 2), SnSiO_Three, LiSiO or LiSn
O and the like.

As the negative electrode material capable of inserting and extracting lithium, other metal compounds or polymer materials can be used. Examples of other metal compounds include oxides such as iron oxide, ruthenium oxide, and molybdenum oxide, and LiN _3. Examples of polymer materials include polyacetylene, polyaniline, and polypyrrole.

In this secondary battery, lithium metal starts to precipitate on the negative electrode 22 when the open circuit voltage (that is, the battery voltage) is lower than the overcharge voltage in the charging process. That is, when the open circuit voltage is lower than the overcharge voltage, lithium metal is deposited on the negative electrode 22, and the capacity of the negative electrode 22 is based on the capacity component due to insertion and extraction of lithium and the capacity component due to deposition and dissolution of lithium metal. And the sum of Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and the lithium metal function as the negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is the base material when the lithium metal is deposited. It has become.

The overcharge voltage refers to an open circuit voltage when the battery is overcharged. For example, one of the guidelines set by the Japan Storage Battery Association (Battery Manufacturers Association) is “lithium”. Guideline for Secondary Battery Safety Evaluation Standards ”(S
"Full charge" as defined and defined in BA G1101)
Refers to a voltage higher than the open circuit voltage of the battery. In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, the standard charging method, or the recommended charging method used to determine the nominal capacity of each battery. Specifically, in this secondary battery, for example, the battery is fully charged when the open circuit voltage is 4.2 V, and the negative electrode capable of inserting and extracting lithium in a part of the open circuit voltage in the range of 0 V or more and 4.2 V or less. Lithium metal is deposited on the surface of the material.

As a result, in this secondary battery, a high energy density can be obtained, and the cycle characteristics and the rapid charging characteristics can be improved. This is similar to a so-called lithium secondary battery using lithium metal or a lithium alloy for the negative electrode in that lithium metal is deposited on the negative electrode 22, but deposits lithium metal on a negative electrode material capable of inserting and extracting lithium. This is considered to be because the following advantages are obtained.

First, it is difficult to deposit lithium metal uniformly in a so-called lithium secondary battery, which causes deterioration of cycle characteristics. However, a negative electrode material capable of inserting and extracting lithium is generally used. In this secondary battery, lithium metal can be uniformly deposited because the surface area is large. Secondly, in a so-called lithium secondary battery, the volume change accompanying the precipitation and elution of lithium metal is large, which also causes deterioration of the cycle characteristics. In this secondary battery, a negative electrode capable of inserting and extracting lithium is used. The lithium metal precipitates also in the gaps between the particles of the material, so that the volume change is small. Third, in a so-called lithium secondary battery, the larger the amount of lithium metal deposited / dissolved, the greater the above problem. However, in this secondary battery, lithium is inserted / extracted by a negative electrode material capable of inserting / extracting lithium. Also contributes to the charge / discharge capacity, which means that the amount of lithium metal deposited and dissolved is small in spite of the large battery capacity. Fourth, in a so-called lithium secondary battery, when rapid charging is performed, lithium metal is more unevenly deposited, thereby further deteriorating the cycle characteristics. However, in this secondary battery, lithium is initially stored and charged. Since lithium is occluded in the detachable negative electrode material, rapid charging becomes possible.

In order to obtain these advantages more effectively, for example, the maximum deposition capacity of the lithium metal deposited on the negative electrode 22 at the maximum voltage before the open circuit voltage becomes the overcharge voltage is determined as follows. It is preferable that the charge capacity is 0.05 times or more and 3.0 times or less of the charge capacity of the detachable negative electrode material. If the amount of lithium metal deposited is too large, a problem similar to that of a so-called lithium secondary battery occurs. If the amount is too small, the charge / discharge capacity cannot be sufficiently increased. Also, for example, the discharge capacity of the negative electrode material capable of inserting and extracting lithium is preferably 150 mAh / g or more. This is because the greater the ability to insert and extract lithium, the smaller the amount of lithium metal deposited. The charge capacity of the negative electrode material is obtained, for example, from the amount of electricity when a negative electrode using lithium metal as a counter electrode and using the negative electrode material as a negative electrode active material is charged to 0 V by a constant current / constant voltage method. The discharge capacity capacity of the negative electrode material is obtained, for example, from the quantity of electricity when the battery is discharged to 2.5 V over 10 hours or more by the constant current method.

The separator 23 is made of, for example, a porous film made of a synthetic resin such as polytetrafluoroethylene, polypropylene or polyethylene, or a porous film made of ceramic. The structure may be modified. Above all, a polyolefin porous film is preferable because it has an excellent short-circuit prevention effect and can improve battery safety by a shutdown effect. In particular, polyethylene is 100
Since the shutdown effect can be obtained in the range of not less than 160 ° C. and the electrochemical stability is excellent, it is preferable as the material forming the separator 23. In addition, polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

The porous film made of polyolefin is prepared, for example, by kneading a liquid polyolefin composition in a molten state with a low-volatility solvent in a liquid state in a molten state to form a uniform high-concentration solution of the polyolefin composition. Molded by
It is obtained by cooling into a gel-like sheet and stretching.

As the low volatile solvent, for example, nonane,
Low volatile aliphatic or cyclic hydrocarbons such as decane, decalin, p-xylene, undecane or liquid paraffin can be used. The mixing ratio of the polyolefin composition and the low-volatile solvent is 100% by mass of the total of both.
The content of the polyolefin composition is preferably from 10% by mass to 80% by mass, and more preferably from 15% by mass to 70% by mass. If the amount of the polyolefin composition is too small, swelling or neck-in becomes large at the die exit during molding, and sheet molding becomes difficult. on the other hand,
If the amount of the polyolefin composition is too large, it is difficult to prepare a uniform solution.

When a high-concentration solution of the polyolefin composition is molded with a die, in the case of a sheet die, the gap is preferably, for example, 0.1 mm or more and 5 mm or less. Further, the extrusion temperature is preferably from 140 ° C. to 250 ° C., and the extrusion speed is preferably from 2 cm / min to 30 cm / min.

The cooling is performed to at least the gelling temperature or lower. As a cooling method, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a roll cooled by a refrigerant, or the like can be used. The high-concentration solution of the polyolefin composition extruded from the die may be taken at a take-up ratio of 1 to 10 and preferably 1 to 5 before or during cooling. If the take-up ratio is too large, neck-in becomes large, and breakage tends to occur during stretching, which is not preferable.

The stretching of the gel-like sheet is preferably performed by biaxial stretching, for example, by heating the gel-like sheet and using a tenter method, a roll method, a rolling method or a combination thereof. At that time, either vertical or horizontal simultaneous stretching or sequential stretching may be used, but simultaneous secondary stretching is particularly preferable.
The stretching temperature is preferably equal to or lower than the temperature obtained by adding 10 ° C. to the melting point of the polyolefin composition, and more preferably equal to or higher than the crystal dispersion temperature and lower than the melting point. If the stretching temperature is too high, an effective molecular chain orientation due to stretching cannot be performed due to melting of the resin, which is not preferable.If the stretching temperature is too low, the softening of the resin becomes insufficient and the film breaks during stretching. This is because it is easy to perform stretching at a high magnification.

After stretching the gel-like sheet, it is preferable to wash the stretched film with a volatile solvent to remove the remaining low-volatile solvent. After washing, the stretched film is dried by heating or blowing, and the washing solvent is volatilized. As the cleaning solvent, for example, pentane, hexane,
A volatile substance such as a hydrocarbon such as hebutane, a chlorinated hydrocarbon such as methylene chloride or carbon tetrachloride, a fluorocarbon such as ethane trifluoride, or an ether such as diethyl ether or dioxane is used. The washing solvent is selected according to the low-volatile solvent used, and used alone or in combination. The washing can be performed by a method of immersing in a volatile solvent for extraction, a method of sprinkling with a volatile solvent, or a method of combining these. This washing is performed until the residual low-volatile solvent in the stretched film becomes less than 1 part by mass with respect to 100 parts by mass of the polyolefin composition.

The separator 23 is impregnated with the electrolyte according to the present embodiment. This electrolyte contains a lithium salt as an electrolyte salt. In the present embodiment, since the electrolyte contains a compound having a NS structure in which nitrogen and sulfur are bonded to each other and having a molecular weight of less than 500, the conductivity, thermal stability, and oxidation stability of the electrolyte are high. Cycle characteristics, high-temperature characteristics, storage stability, and the like can be improved while maintaining a high discharge capacity.

This secondary battery can be manufactured, for example, as follows.

First, for example, a positive electrode material is prepared by mixing a positive electrode material capable of inserting and extracting lithium, a conductive agent, and a binder, and this positive electrode mixture is mixed with N-methyl-2-pyrrolidone or the like. To a paste-like positive electrode mixture slurry. The positive electrode mixture slurry is applied to the positive electrode current collector 21a, the solvent is dried, and then compression-molded by a roll press or the like to form the positive electrode mixture layer 21b, and the positive electrode 21 is manufactured.

Next, for example, a negative electrode material is prepared by mixing a negative electrode material capable of inserting and extracting lithium and a binder, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone. To form a paste-like negative electrode mixture slurry.
The negative electrode mixture slurry is applied to the negative electrode current collector 22a, the solvent is dried, and then compression-molded by a roll press or the like to form the negative electrode mixture layer 22b, thereby producing the negative electrode 22.

Subsequently, the positive electrode lead 2 is connected to the positive electrode current collector 21a.
5 is attached by welding or the like.
The negative electrode lead 26 is attached to “a” by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound via the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 sandwiched between the pair of insulating plates 12 and 13 are housed inside the battery can 11. After housing the positive electrode 21 and the negative electrode 22 inside the battery can 11, an electrolyte is injected into the inside of the battery can 11,
3 impregnated. After that, the battery lid 14, the safety valve mechanism 15, and the thermal resistance element 16 are fixed to the open end of the battery can 11 by caulking via the gasket 17.

The positive electrode lead 25 and the negative electrode lead 2
After attaching 6, the electrolyte may be applied to the positive electrode mixture layer 21b and the negative electrode mixture layer 22b, and the positive electrode 21 and the negative electrode 22 may be wound via the separator 23. After that, as described above, it is stored inside the battery can 11,
The battery cover 14 is fixed. Thereby, the secondary battery shown in FIG. 1 is formed.

This secondary battery operates as follows.

In this secondary battery, when charged, lithium ions are detached from the positive electrode mixture layer 21b, and the separator 2
First, the negative electrode mixture layer 22
The lithium contained in b is stored in a negative electrode material that can be inserted and extracted. When charging is further continued, in the state where the open circuit voltage is lower than the overcharge voltage, the charge capacity exceeds the charge capacity capacity of the negative electrode material capable of inserting and extracting lithium, and the surface of the negative electrode material capable of inserting and extracting lithium is charged. Lithium metal begins to precipitate. Thereafter, lithium metal continues to be deposited on the negative electrode 22 until charging is completed. As a result, the appearance of the negative electrode mixture layer 22b changes from black to golden, and further to white silver when, for example, a carbon material is used as the negative electrode material capable of inserting and extracting lithium.

Next, when discharge is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and the positive electrode mixture layer 21 is passed through the electrolyte impregnated in the separator 23.
b. When the discharge is further continued, the negative electrode mixture layer 22
The lithium ions occluded in the negative electrode material capable of occluding and releasing lithium in b are released and occluded in the positive electrode mixture layer 21b via the electrolytic solution. Therefore, in this secondary battery, characteristics of both a so-called lithium secondary battery and a lithium ion secondary battery, that is, high energy density and good charge / discharge cycle characteristics can be obtained.

Particularly, in the present embodiment, since the electrolyte contains a compound having an NS structure and a molecular weight of less than 500,
The conductivity of the electrolyte is kept high, the thermal stability and the oxidation stability are improved, and the cycle characteristics, high temperature characteristics, storage stability, and the like are further improved.

As described above, according to the present embodiment, since a compound having an NS structure and a molecular weight of less than 500 is contained, it is possible to improve thermal stability and oxidation stability while maintaining high conductivity of the electrolyte. Can be. Therefore, a high discharge capacity can be obtained, and battery characteristics such as cycle characteristics, high-temperature characteristics, and storage stability can be further improved.

In the above description, the capacity of the negative electrode 22 depends on the capacity component due to insertion and extraction of lithium, and the capacity of lithium deposition / desorption.
The secondary battery represented by the sum of the capacity component due to dissolution has been described as an example, but the electrolyte according to the present embodiment can be similarly used for a secondary battery having another configuration.

As a secondary battery having another structure, for example, a so-called lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium, or a capacity of the negative electrode in which lithium metal is deposited and deposited. A so-called lithium secondary battery represented by a capacity component due to dissolution is exemplified.
Lithium ion secondary batteries, for example, occlude lithium
The secondary battery has the same configuration as the above secondary battery except that the amount of the detachable negative electrode material is relatively larger than the positive electrode material, and lithium metal does not precipitate on the negative electrode during charging. Further, the lithium secondary battery has the same configuration as the above-described secondary battery except that, for example, the negative electrode is made of lithium metal or the like.

Therefore, the same effects as those of the above secondary battery can be obtained for these secondary batteries by using the electrolyte according to the present embodiment. That is, the thermal stability and the oxidative stability can be improved while keeping the conductivity of the electrolyte high, and a high capacity can be obtained, and the cycle characteristics, high-temperature characteristics, storage stability, and the like are further improved. be able to.

[0087]

EXAMPLES Further, specific examples of the present invention will be described in detail. 1 and 2 in the following embodiment.
Was manufactured as shown in FIG. Therefore, here, the description will be made with reference to FIGS.

(Examples 1 and 2) In Examples 1 and 2, the capacity of the negative electrode 22 is represented by the sum of the capacity component due to insertion and extraction of lithium and the capacity component due to deposition and dissolution of lithium metal. A secondary battery was manufactured.

First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) were converted into Li ₂ CO ₃ : CoC
O ₃ was mixed at a ratio of 0.5: 1 (molar ratio) and calcined in air at 900 ° C. for 5 hours to obtain a lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode material. Next, 91 parts by mass of the lithium-cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which was uniformly applied to both surfaces of a positive electrode current collector 21a made of a 20 μm-thick strip-shaped aluminum foil and dried. Then, the mixture was compression-molded with a roll press machine to form a positive electrode mixture layer 21b, and the positive electrode 21 was produced. After that, a positive electrode lead 25 made of aluminum was attached to one end of the positive electrode current collector 21a.

Further, pitch coke was prepared as a negative electrode material capable of inserting and extracting lithium, and 90 parts by mass of the pitch coke was added to polyvinylidene fluoride 10% as a binder.
The mixture was mixed with parts by mass to prepare a negative electrode mixture. Next, after dispersing this negative electrode mixture in N-methyl-2-pyrrolidone as a solvent to form a slurry, the mixture is uniformly applied to both surfaces of a negative electrode current collector 22a formed of a 10 μm-thick strip-shaped copper foil and dried. , Compression molding with a roll press machine to form the negative electrode mixture layer 22
b was formed, and the negative electrode 22 was produced. After that, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22a. When the positive electrode 21 and the negative electrode 22 were manufactured, their thicknesses, that is, the amounts of the positive electrode material and the negative electrode material were adjusted so that lithium metal was deposited on the negative electrode 22 during charging.

After each of the positive electrode 21 and the negative electrode 22 was prepared, a separator 23 made of a stretched microporous polyethylene film having a thickness of 25 μm was prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 were laminated in this order. Was spirally wound many times to produce a wound electrode body 20.

After the wound electrode body 20 is manufactured, the wound electrode body 20 is sandwiched between a pair of insulating plates 12 and 13, and the negative electrode lead 2 is formed.
6 was welded to the battery can 11, the positive electrode lead 25 was welded to the safety valve mechanism 15, and the spirally wound electrode body 20 was housed inside the nickel-plated iron battery can 11. After that, the electrolytic solution was injected into the battery can 11. The electrolyte was prepared by dissolving LiPF ₆ as an electrolyte salt in a solvent in which 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate were dissolved at a content of 1.0 mol / dm ³ with respect to the solvent. As the compound having the structure, a compound to which 1,1′-sulfonyldiimidazole shown in Chemical Formula 4 was added was used. At that time, the content of 1,1′-sulfonyldiimidazole was changed with respect to the solvent as shown in Table 1 in Examples 1 and 2.

[0093]

[Table 1]

After injecting the electrolyte into the battery can 11, the battery cover 14 was caulked to the battery can 11 via a gasket 17 coated with asphalt on the surface, whereby the diameters of Examples 1 and 2 were 18 mm and the height was 18 mm. A cylindrical secondary battery having a length of 65 mm was obtained.

For the obtained secondary batteries of Examples 1 and 2, a charge / discharge test was performed at room temperature (23 ° C.), and the charge / discharge cycle characteristics at room temperature were examined. As the charge / discharge cycle characteristics, the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle (charge / discharge capacity retention ratio), that is, (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100 is obtained. Was. At that time, charging was performed at a constant current of 1 A until the battery voltage reached 4.2 V, and then the charging was continued.
The charging was performed at a constant voltage of 2 V until the total charging time reached 4 hours, and the discharging was performed at a constant current of 0.5 A to a final voltage of 2.5 V. Table 1 shows the obtained results.

Further, with respect to the secondary batteries of Examples 1 and 2,
Dismantle those one cycle charge and discharge was later allowed to fully charged again conducted under conditions described above, visually and ⁷ Li nuclear magnetic resonance spectroscopy, examined whether lithium metal in the negative electrode mixture layer 22b is deposited Was. Further, two cycles of charge and discharge were performed under the above-described conditions, and the completely discharged battery was disassembled, and similarly, it was examined whether or not lithium metal had precipitated on the negative electrode mixture layer 22b. As a result, in the fully charged state, the presence of lithium metal was recognized in the negative electrode mixture layer 22b, and in the fully discharged state, the presence of lithium metal was not recognized. That is, it was confirmed that the capacity of the negative electrode 22 was represented by the sum of the capacity component due to precipitation and dissolution of lithium metal and the capacity component due to occlusion and release of lithium.

As Comparative Example 1 for this example, 1,
A secondary battery was fabricated in the same manner as in this example except that 1′-sulfonyldiimidazole was not added. For the secondary battery of Comparative Example 1, the discharge capacity retention at room temperature was determined in the same manner as in the present example. The results are also shown in Table 1.

As can be seen from Table 1, according to Examples 1 and 2 to which 1,1'-sulfonyldiimidazole was added,
A higher value of the discharge capacity retention ratio at room temperature was obtained than in Comparative Example 1 in which no addition was performed. Note that the discharge capacity in the first cycle, that is, the initial discharge capacity, was substantially the same in Examples 1 and 2 and Comparative Example 1. That is, it was found that when 1,1′-sulfonyldiimidazole was added to the electrolyte, the charge / discharge cycle characteristics could be improved while maintaining the discharge capacity high, and the capacity characteristics could be improved.

(Examples 3 to 7) As Examples 3 to 7, lithium ion secondary batteries in which the capacity of the negative electrode 22 was represented by a capacity component due to insertion and extraction of lithium were produced. that time,
Except for using non-graphitizable carbon as a negative electrode material capable of inserting and extracting lithium, and adjusting the thickness of the positive electrode 21 and the negative electrode 22 so that lithium metal does not precipitate on the negative electrode 22 during charging, Same as Examples 1 and 2.
In addition, the content of 1,1'-sulfonyldiimidazole was changed with respect to the solvent as shown in Table 2 in Examples 3 to 7.

[0100]

[Table 2]

The non-graphitizable carbon is obtained by using petroleum pitch as a starting material, and adding an oxygen-containing functional group to the pitch by 10% to 20%.
%, And oxygen baking was performed, followed by baking at 1000 ° C. in an inert gas stream. When X-ray diffraction measurement was performed on the obtained non-graphitizable carbon,
The (002) plane spacing was 0.376 nm, and the true specific gravity was 1.58 g. This non-graphitizable carbon was pulverized into a powder having an average particle size of 10 μm to obtain a negative electrode material.

With respect to the obtained secondary batteries of Examples 3 to 7, high-temperature storage characteristics and high-temperature cycle characteristics were examined. Table 2 shows the results.

As the high-temperature storage characteristics, the discharge capacity retention after storage at 60 ° C. was determined as follows.
First, the battery was charged and discharged at 20 ° C., and the capacity before storage was determined. At that time, charging was performed at a constant current of 1 A and the battery voltage was 4.2 V.
After that, the charging was performed at a constant voltage of 4.2 V until the total charging time reached 4 hours, and the discharging was performed at a constant current of 0.5 A to a final voltage of 2.5 V. Then, after storing at 60 ° C. for 1 week, 4 cycles of charging and discharging were performed at 20 ° C. under the same charging and discharging conditions as when the capacity before storage was determined.
The highest value in the cycle was taken as the capacity after storage. Subsequently, the ratio of the capacity after storage to the capacity before storage, that is, (capacity after storage / capacity before storage) × 100 was calculated as a discharge capacity retention rate after storage at 60 ° C.

The high-temperature cycle characteristic is 60 ° C.
, The discharge capacity retention rate after 100 cycles was determined.
This is because charge / discharge is performed 100 cycles under the same charge / discharge conditions as the high-temperature storage characteristics at 60 ° C. (Electric discharge capacity of eyes) × 100.

As Comparative Example 2 for this embodiment, 1
A secondary battery was fabricated in the same manner as in this example except that 1′-sulfonyldiimidazole was not added.
For the secondary battery of Comparative Example 2, high-temperature storage characteristics and high-temperature cycle characteristics were examined in the same manner as in this example. Table 2 shows the obtained results.

As can be seen from Table 2, according to Examples 3 to 7 in which 1,1′-sulfonyldiimidazole was added,
Higher values were obtained for the discharge capacity retention rate after storage at 60 ° C. or the discharge capacity retention rate after 100 cycles at 60 ° C. as compared to Comparative Example 2 in which no addition was made. In each of Examples 3 to 7 and Comparative Example 2, the capacity before storage in the high-temperature storage characteristics and the discharge capacity in the first cycle in the high-temperature cycle characteristics were almost equal. That is, it was found that when 1,1′-sulfonyldiimidazole was added to the electrolyte, the high-temperature storage characteristics and the high-temperature cycle characteristics could be improved while the discharge capacity was kept high, and the capacity characteristics could be improved.

Further, according to Examples 3 to 6, both high-temperature storage characteristics and high-temperature cycle characteristics can be equal to or higher than Comparative Example 2, and according to Examples 4 to 6, In both cases, values superior to Comparative Example 2 could be obtained. That is, the content of 1,1′-sulfonyldiimidazole is adjusted to 0.01% by mass with respect to the solvent.
It was found that a higher effect can be obtained when the content is at least 20% by mass and less than 20% by mass, and it is further preferable that the content is more than 0.01% by mass and 10% by mass or less.

Examples 8 to 11 As Examples 8 to 11, except that the kind of the electrolyte salt was changed and the content of 1,1′-sulfonyldiimidazole was changed as shown in Table 3. Other than that produced the lithium ion secondary battery similarly to Examples 3-7. LiBF ₄ was used as the electrolyte salt in Examples 8 and 9, and LiPF ₆ was used in Examples 10 and 11.
And LiN (CF ₃ SO ₂ ) ₂ with LiPF ₆ : LiN
A mixture mixed at a molar ratio of (CF ₃ SO ₂ ) ₂ = 9: 1 was used. Further, as Comparative Example 3 for Examples 8 and 9 and Comparative Example 4 for Examples 10 and 11, 1,1′-
A secondary battery was fabricated in the same manner as in this example except that sulfonyldiimidazole was not added. For the secondary batteries of Examples 8 to 11 and Comparative Examples 3 and 4, high-temperature storage characteristics and high-temperature cycle characteristics were examined in the same manner as in Examples 3 to 7. The obtained results are shown in Example 4,
The results are shown in Table 3 together with Comparative Example 5 and Comparative Example 2.

[0109]

[Table 3]

As can be seen from Table 3, Examples 8 to 11
According to the results, as in Examples 3 to 7, a higher height than the comparative example
Thermal storage characteristics and high-temperature cycle characteristics were obtained. In addition,
Pre-storage capacity and high-temperature cycle in high-temperature storage characteristics
The discharge capacity at the first cycle in the characteristics is shown in Examples 8 and 9.
And in Comparative Example 3 or in Examples 10, 11 and
In Comparative Example 4 and Comparative Example 4, the values were almost equal. Sand
And LiBF for the electrolyte salt _FourOr LiN (CF_ThreeS
O_Two)_TwoOr the like, the electrolyte may be 1,1'-sulfonium.
Addition of rudiimidazole keeps discharge capacity high
While improving high-temperature storage characteristics and high-temperature cycle characteristics.
I found out.

The high-temperature storage characteristics and the high-temperature cycle characteristics were determined by using LiPF ₆ and LiN (CF ₃ SO ₂ ) _{2 in the} electrolyte.
Examples 10 and 11 using a mixture of the above are the most excellent, and Examples 4 and 5 using LiPF ₆ as the electrolyte salt are then excellent,
Next, the order of Examples 8 and 9 using LiBF ₄ as the electrolyte salt was followed.

(Examples 12 to 15) The same procedures as in Examples 12 to 15 were carried out except that the type and content of the compound having the NS structure were changed as shown in Table 4.
To 7, a lithium ion secondary battery was produced.
In Examples 12 and 13, N-bismethylthiomethylene-p-toluenesulfonamide shown in Chemical formula 5 was used as the compound having the NS structure. In Examples 14 and 15, 1-p-Trisulfonyl shown in Chemical formula 6 was used. Pyrrole was used. For the secondary batteries of Examples 12 to 15, high-temperature storage characteristics and high-temperature cycle characteristics were examined in the same manner as in Examples 3 to 7.
Table 4 shows the obtained results together with the results of Comparative Example 2.

[0113]

[Table 4]

As can be seen from Table 4, Examples 12 to 15
According to Comparative Example 1, as in Examples 3 to 7, high-temperature storage characteristics and high-temperature cycle characteristics superior to those of Comparative Examples were obtained. The capacity before storage in the high-temperature storage characteristics and the discharge capacity in the first cycle in the high-temperature cycle characteristics were determined in Example 1.
The values were almost equal in any of 2 to 15 and Comparative Example 2. In other words, it has been found that when the electrolyte contains a compound having an NS structure and a molecular weight of less than 500, the high-temperature storage characteristics and the high-temperature cycle characteristics can be improved while maintaining a high discharge capacity.

In the above examples, the compound having the NS structure was described with specific examples, but the above-mentioned effects are considered to be caused by the NS structure. Therefore, the same result can be obtained even when a compound having another NS structure is used.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and can be variously modified. For example, in the above embodiments and examples, a battery using lithium as an electrode reactive species has been described.
The present invention can be applied to a case where another light metal or an alloy containing a light metal is used, and the same effect can be obtained. In that case, a negative electrode material, a positive electrode material, a non-aqueous solvent, an electrolyte salt or the like capable of inserting and extracting a light metal is selected according to the light metal. However, it is preferable to use lithium or an alloy containing lithium as the light metal because voltage compatibility with lithium ion secondary batteries currently in practical use is high. When an alloy containing lithium is used as the light metal, a substance capable of forming an alloy with lithium exists in the electrolyte, and an alloy may be formed at the time of deposition. Possible substances are present and may form an alloy upon precipitation.

In the above embodiments and examples, the gel electrolyte which is one kind of the electrolyte or the solid electrolyte has been described. However, the present invention is similarly applicable to other electrolytes. Can be. Other electrolytes include:
For example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, an inorganic solid electrolyte made of ionic conductive ceramics, ionic conductive glass or ionic crystal, or a mixture of these inorganic solid electrolyte and electrolyte Or a mixture of these inorganic solid electrolytes and a gel electrolyte or an organic solid electrolyte.

Further, in the above embodiments and examples, a cylindrical secondary battery having a wound structure has been described. However, the present invention relates to an elliptical or polygonal secondary battery having a wound structure. Alternatively, the present invention can be similarly applied to a secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. In addition, the present invention can be applied to a secondary battery such as a coin type, a button type, and a card type.

In the above embodiments and examples, the case where the electrolyte of the present invention is used for a secondary battery has been described. However, the present invention can be applied to other batteries such as a primary battery. Further, it can be used for other electrochemical devices such as a capacitor, a capacitor or an electrochromic device.

[0120]

As described above, the electrolyte according to any one of the first to ninth aspects includes a compound having an NS structure in which nitrogen and sulfur are bonded and having a molecular weight of less than 500. Therefore, thermal stability and oxidative stability can be improved while maintaining high conductivity.

Further, according to the battery according to any one of claims 10 to 26, since the electrolyte of the present invention is used, it is possible to improve the stability while keeping the conductivity of the electrolyte high. Can be. Therefore, a high discharge capacity can be obtained, and cycle characteristics, high-temperature characteristics, storage stability, and the like can be further improved, and excellent battery characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a part of a wound electrode body in the secondary battery shown in FIG.

[Explanation of symbols]

11 ... battery can, 12, 13 ... insulating plate, 14 ... battery lid, 1
Reference numeral 5: safety valve mechanism, 15a: disk plate, 16: thermal resistance element, 17: gasket, 20: wound electrode body, 21: positive electrode, 21a: positive electrode current collector, 21b: positive electrode mixture layer, 22:
Negative electrode, 22a: negative electrode current collector, 22b: negative electrode mixture layer, 23
... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead

Claims (26)

[Claims] 1. The method according to claim 1, wherein the molecular weight is less than 500 and nitrogen (N)
An electrolyte comprising: a compound having an NS structure in which sulfur and sulfur (S) are bonded. 2. The electrolyte according to claim 1, wherein the compound having an NS structure has a molecular structure in which nitrogen and SO ₂ shown in Chemical Formula 1 are bonded. Embedded image 3. The compound having the NS structure is 1,
2. The composition according to claim 1, comprising at least one member of the group consisting of 1'-sulfonyldiimidazole, N-bismethylthiomethylene-p-toluenesulfonamide, 1-p-trisulfonylpyrrole, and derivatives thereof. An electrolyte as described. 4. The method according to claim 1, wherein the content of the compound having an NS structure, including an electrolyte salt and a solvent, is in the range of 0.01% by mass or more and less than 20% by mass with respect to the solvent. The electrolyte according to claim 1. 5. The electrolyte according to claim 1, further comprising an electrolyte salt and a solvent, wherein the electrolyte salt contains LiPF ₆ . 6. The electrolyte according to claim 1, further comprising an electrolyte salt and a solvent, wherein the electrolyte salt contains LiBF ₄ . 7. The electrolyte according to claim 1, further comprising an electrolyte salt and a solvent, wherein the electrolyte salt contains LiClO ₄ . 8. The electrolyte according to claim 1, further comprising an electrolyte salt and a solvent, wherein the electrolyte salt contains LiN (CF ₃ SO ₂ ) ₂ . 9. The electrolyte according to claim 1, further comprising an electrolyte salt and a solvent, wherein the electrolyte salt contains LiN (C ₂ F ₅ SO ₂ ) ₂ . 10. A battery provided with an electrolyte together with a positive electrode and a negative electrode, wherein the electrolyte has a molecular weight of less than 500 and nitrogen (N)
A battery comprising a compound having an NS structure in which sulfur and sulfur (S) are combined. 11. A battery provided with an electrolyte together with a positive electrode and a negative electrode, wherein the capacity of the negative electrode is represented by the sum of a capacity component due to occlusion and desorption of light metal and a capacity component due to deposition and dissolution of light metal. The electrolyte has a molecular weight of less than 500 and nitrogen (N)
A battery comprising a compound having an NS structure in which sulfur and sulfur (S) are combined. 12. The compound having the NS structure is represented by the following chemical formula 2.
Nitrogen and SO shown in _TwoHas a structure in which
The battery according to claim 10 or 11, wherein the battery is a battery. Embedded image 13. The compound having the NS structure is 1,
11. The composition according to claim 10, comprising at least one member selected from the group consisting of 1'-sulfonyldiimidazole, N-bismethylthiomethylene-p-toluenesulfonamide, 1-p-trisulfonylpyrrole, and derivatives thereof. Or the battery according to claim 11. 14. The electrolyte according to claim 1, further comprising an electrolyte salt and a solvent, wherein the content of the compound is in the range of 0.01% by mass to less than 20% by mass based on the solvent. The battery according to claim 10 or 11. 15. The electrolyte further comprises an electrolyte salt and a solvent, the electrolyte salt, according to claim 10 or claim 11 battery, wherein the containing LiPF _6. 16. The battery according to claim 10, wherein the electrolyte further includes an electrolyte salt and a solvent, and the electrolyte salt contains LiBF ₄ . 17. The battery according to claim 10, wherein the electrolyte further includes an electrolyte salt and a solvent, and the electrolyte salt contains LiClO ₄ . 18. The electrolyte further includes an electrolyte salt and a solvent, wherein the electrolyte salt is LiN (CF ₃ SO ₂ ) _2.
11. The method according to claim 10, wherein
The battery according to 1. 19. The electrolyte further includes an electrolyte salt and a solvent, wherein the electrolyte salt is LiN (C ₂ F ₅ SO ₂ ).
The battery according to claim 10, wherein the battery contains ₂ . 20. The battery according to claim 10, wherein the negative electrode includes a negative electrode material capable of inserting and extracting light metal. 21. The battery according to claim 10, wherein the negative electrode contains a carbon material. 22. The battery according to claim 10, wherein the negative electrode includes at least one member selected from the group consisting of graphite, graphitizable carbon, and non-graphitizable carbon. 23. The battery according to claim 10, wherein the negative electrode contains graphite. 24. The negative electrode according to claim 10, wherein the negative electrode includes at least one selected from the group consisting of metals, semiconductors, alloys, and compounds capable of forming an alloy or a compound with the light metal. Item 12. The battery according to Item 11. 25. The negative electrode comprises tin (Sn), lead (P)
b), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium ( Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr) and yttrium (Y). The battery according to claim 10 or 11, wherein: 26. The battery according to claim 10, wherein the light metal includes lithium (Li).