JP4366792B2 - Battery electrolyte and non-aqueous electrolyte secondary battery - Google Patents

Description

【００５５】
比較例１では、添加剤を含有していないために、電解液のＡｌ酸化分解電位が低く、実際の電池においても、高電位では使用できない。また、リチウム充放電効率も、ＬｉＰＦ₆などの無機リチウム塩に比べると高いものの、十分満足のいく値ではない。
【００５６】
実施例１〜３では、３−（トリフルオロメチル）ピラゾールをそれぞれ１０，３０，５０ｍｍｏｌ／ｄｍ³ 添加したことにより、電解液のＡｌ酸化分解電位が向上し、実際の電池においても４Ｖ以上の高電位で使用可能となった。また、リチウム充放電効率も向上しており、サイクル特性の向上が期待できる。この理由は、まず、添加剤が正極集電体であるアルミニウム表面に安定な吸着層を形成し、アルミニウムの溶解を抑制しているためであると考えている。また、リチウム充放電効率が向上したのは、負極であるリチウム表面にも安定な被膜を形成し、負極上での電流集中や副反応が抑制され、リチウムの消費が少なくなったためと考えている。
【００５７】
そして、実施例４では、酸化分解電位、充放電効率ともに、比較例１と比べると向上しており、３−（トリフルオロメチル）ピラゾールの添加量が５ｍｍｏｌ／ｄｍ³ と少なくても、それなりの効果が認められた。
【００５８】
また、実施例５では、比較例１と比べて、充放電効率のわずかな低下が認められたものの、酸化分解電位の大幅な向上が認められた。これは、３−（トリフルオロメチル）ピラゾールを１００ｍｍｏｌ／ｄｍ³ 添加したことにより、酸化分解電位は向上したものの、添加量が多いために、リチウム表面に抵抗の高い被膜が形成されためであると推定される。
【００５９】
以上のことより、３−（トリフルオロメチル）ピラゾールの添加量は、アルミニウム集電体とリチウム負極のそれぞれの表面に吸着層を形成する量、すなわち、１０〜５０ｍｍｏｌ／ｄｍ³ が適当であると考えている。
【００６０】
また、実施例６〜８及び参考例１は、他のトリフルオロメチル基を有する添加剤を３０ｍｍｏｌ／ｄｍ³ 添加した例である。実施例２と同様の効果が得られることが分かった。
【００６１】
さらに、比較例２は、他のトリフルオロメチル基を有しない１，２，４−トリアゾールを添加した例である。リチウム表面への安定な被膜形成には効果があるので、リチウム充放電効率は向上するものの、アルミニウムの酸化分解電位は実施例ほど向上しなかった。これは、耐酸化性の高いトリフルオロメチル基を持たないためであると考えている。
【００６２】
最後に、実施例９では、比較例２の１，２，４−トリアゾールとトリフルオロメチル基を有する３−（トリフルオロメチル）ピラゾールをそれぞれ１５ｍｍｏｌ／ｄｍ³ 添加した例である。両者を混合することにより、アルミニウムの酸化分解電位と充放電効率のそれぞれの向上が可能である。
【図面の簡単な説明】
【図１】本実施形態の非水電解液二次電池を概略的に示す電池の縦断面図である。
【図２】本実施形態の非水電解液二次電池の概略を示す円筒型電池の説明図であり、２ａは筒型電池の断面斜視図であり、２ｂは電極部分を説明する説明模式図である。
【図３】本実施例の充放電効率試験に用いたセルの縦断面図である。
【符号の説明】
１：正極 ２：負極 ３：非水電解液 ４：正極ケース ５：負極ケース ６：セパレータ ７：ガスケット
１０：円筒型電池 １１：負極合材 １２：負極集電体 １２’：負極リード １３：正極合材 １４：正極集電体 １４’：正極リード １５：電解液 １６：セパレータ １７：正極端子 １８：負極端子部
５０：対極 ６０：作用極 ７０：ポリエチレン製フィルム（セパレータ）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery electrolyte that can be used as a battery electrolyte, and a non-aqueous electrolyte secondary battery that can be used as a battery for electric vehicles and portable electronic devices.
[0002]
[Prior art]
With the background of energy problems and environmental problems, there is a need for technologies that make more effective use of electric power. For this purpose, there is a need for an electric storage means that can store a large amount of electricity and efficiently extract the stored electricity. As such electricity storage means, a secondary battery having a large discharge capacity and a high discharge voltage and capable of repeated charge and discharge is optimal.
[0003]
As such a secondary battery, there is a lithium secondary battery that undergoes a charging reaction in which lithium ions are released from the positive electrode and stored in the negative electrode during charging, and a discharging reaction that is released from the negative electrode and stored in the positive electrode during discharging. . A lithium secondary battery has a high energy density and high output density, and a large discharge capacity and a high discharge voltage can be obtained. In particular, lithium ion secondary batteries in which a negative electrode active material made of a carbon material is used for the negative electrode are considered to be practically superior because of their long life and high safety, such as batteries for portable electronic devices and electric vehicles. It is expected to be used for such as.
[0004]
In the lithium ion secondary battery, an electrolytic solution in which, for example, an organic supporting salt is dissolved in an organic solvent is used. Examples of the organic supporting salt used in the electrolyte of such a non-aqueous electrolyte secondary battery include lithium salts (LiSO ₂ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF) of perfluoroalkylsulfonic acid derivatives. ₃ ) ₃ ) and so on. Organic supported salts such as lithium salts of perfluoroalkyl sulfonic acid derivatives are thermally and electrically stable.
[0005]
[Problems to be solved by the invention]
However, a non-aqueous electrolyte secondary battery using an electrolyte in which an organic supporting salt such as a lithium salt of a perfluoroalkylsulfonic acid derivative is dissolved is a non-aqueous electrolyte secondary battery in which an inorganic lithium salt is dissolved in the electrolyte. Compared with, the charge / discharge efficiency is improved, but when used at a high voltage of 4 V or higher, aluminum (Al) used for the positive electrode current collector is eluted, resulting in inferior battery cycle characteristics.
[0006]
Therefore, an object of the present invention is to provide a battery electrolyte that can achieve battery characteristics with good cycle characteristics even when used at a high voltage.
[0007]
Another object of the present invention is to provide a non-aqueous electrolyte secondary battery that has good battery characteristics even when used at a high voltage.
[0008]
[Means for Solving the Problems]
As a result of intensive studies conducted by the present inventors for the purpose of solving the above problems, at least one compound selected from heterocyclic compounds containing nitrogen or oxygen having one or more fluorine atoms in an organic solvent. It was discovered that the inclusion of a battery electrolyte that can achieve battery characteristics with good cycle characteristics even when used at a high voltage, and the following inventions were made.
[0009]
That is, the battery electrolyte solution of the present invention that solves the above problems is a battery electrolyte solution obtained by dissolving at least a lithium salt of a perfluoroalkylsulfonic acid derivative in an organic solvent, and the organic solvent contains one or more. of having a fluorine atom, it contains at least one compound selected from heterocyclic compounds containing nitrogen or oxygen,
The heterocyclic compound, pyrazoles, imidazoles, triazoles, oxazoles, at least one compound selected from the coumarins (excluding coumarins), characterized in der Rukoto.
[0010]
In other words, a positive electrode that causes a problem when a lithium salt of a perfluoroalkylsulfonic acid derivative is contained in an electrolyte by containing a heterocyclic compound having a fluorine atom and containing nitrogen or oxygen in the battery electrolyte. A strong adsorption layer film that is resistant to oxidation of the current collector can be formed on the positive electrode current collector. Specifically, a film is formed by the action of an unshared electron pair present in the oxygen atom and nitrogen atom of the heterocyclic compound, and in this case, the heterocyclic compound used in the battery electrolyte of the present invention is: Since some of the hydrogen atoms are replaced by fluorine atoms, it is difficult to oxidize and decompose.
[0011]
Moreover, the battery electrolyte of the present invention produces a stable coating on the surface of the lithium-containing metal of the negative electrode when used in a non-aqueous electrolyte secondary battery using a lithium-containing metal for the negative electrode. There is also an advantage that current concentration and side reaction on the negative electrode surface can be prevented.
[0012]
Furthermore, the lithium salt of the perfluoroalkylsulfonic acid derivative is preferably at least one substance selected from LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiC (SO ₂ CF ₃ ) _3. . These lithium salts, in combination with the heterocyclic compound, increase the oxidative decomposition potential of the electrolytic solution and improve the aluminum elution preventing effect.
[0013]
The heterocyclic compound preferably has at least one perfluoroalkyl group.
[0015]
Moreover, it is preferable that the density | concentration which adds these said heterocyclic compounds in an organic solvent is 10-50 mmol / dm < ³ >. If it is less than this, the effect of the present invention will be reduced, and if it is more than this, the original function of the electrolyte may be inhibited.
[0016]
Therefore, according to the battery electrolyte of the present invention, a battery that can achieve battery characteristics with good cycle characteristics even when used at a high voltage can be obtained.
[0017]
The non-aqueous electrolyte secondary battery of the present invention that solves the above problems includes a positive electrode capable of releasing and occluding lithium ions, a negative electrode comprising a lithium-containing metal capable of releasing and occluding lithium ions, and the positive electrode and A non-aqueous electrolyte secondary battery comprising an electrolyte solution that is interposed between the negative electrodes and in which at least a lithium salt of a perfluoroalkylsulfonic acid derivative is dissolved in an organic solvent, wherein the electrolyte solution is the above-described present invention. It is characterized by being the electrolyte solution for batteries . Aluminum is selected as the positive electrode current collector in such a non-aqueous electrolyte secondary battery.
[0018]
In the non-aqueous electrolyte secondary battery of the present invention, since the electrolyte used forms a stable coating on the surface of the positive electrode current collector, the battery performance such as cycle characteristics is extremely excellent even when used at a high voltage.
[0019]
Therefore, according to the non-aqueous electrolyte secondary battery of the present invention, it is possible to drive portable electronic devices, automobiles, etc. with high functions, and battery performance is extremely high such as being able to be used repeatedly over a long period of time. It will be expensive.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(Battery electrolyte)
The battery electrolyte of the present invention is not particularly limited by the type of battery used, and can be used for known types of batteries. The battery may be a primary battery or a secondary battery.
[0021]
The battery electrolyte of this embodiment is a battery electrolyte obtained by dissolving at least a lithium salt of a perfluoroalkylsulfonic acid derivative in an organic solvent, and the organic solvent has one or more fluorine atoms. It contains at least one compound selected from heterocyclic compounds containing nitrogen or oxygen.
[0022]
The lithium salt of a perfluoroalkyl sulfonic acid derivative exhibits the role of an electrolyte in the battery electrolyte. The electrolyte is not limited to the case where a lithium salt of a perfluoroalkylsulfonic acid derivative is used alone. For example, a known inorganic electrolyte salt such as LiPF ₆ or LiBF ₆ can also be used by dissolving in an organic solvent.
[0023]
Furthermore, the lithium salt of a perfluoroalkylsulfonic acid derivative is preferably a trifluorosulfonic acid lithium salt because of its high thermal and electrochemical stability. Among these, it is more preferable to contain at least one selected from LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiC (SO ₂ CF ₃ ) ₃ .
[0024]
The electrolyte is preferably dissolved in an organic solvent so that the concentration in the electrolytic solution is 0.1 to 3.0 mol / dm ³ , particularly 0.5 to 2.0 mol / dm ³ . If the concentration in the electrolyte is less than 0.1 mol / dm ³ , a sufficient current density may not be obtained. If the concentration is greater than 3.0 mol / dm ³ , the viscosity increases and the conductivity of the electrolyte decreases. There is a fear.
[0025]
The organic solvent is not particularly limited as long as it is an organic solvent that is usually used for an electrolyte solution of a non-aqueous electrolyte secondary battery. For example, a carbonate compound, a lactone compound, an ether compound, a sulfolane compound, a dioxolane compound, a ketone Examples thereof include compounds, nitrile compounds, halogenated hydrocarbon compounds and the like.
[0026]
Specifically, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, vinylene carbonate and other carbonates, γ-butyl lactone and other lactones , Ethers such as dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, sulfolanes such as sulfolane and 3-methylsulfolane, dioxolanes such as 1.3-dioxolane, 4-methyl- Ketones such as 2-pentanone, nitriles such as acetonitrile, pyropionitrile, pareronitrile, benzonitrile, 1,2- Halogenated hydrocarbons such as chloroethane, other methyl formate, dimethylformamide, dimethylformamide, dimethyl sulfoxide, etc. are mentioned, and these are used alone or as a mixture of a plurality of organic solvents selected from these. Also good.
[0027]
Among these organic solvents mentioned in the examples, in particular, by using one or more non-aqueous solvents selected from the group consisting of carbonates and ethers, the solubility, dielectric constant and viscosity of the electrolyte are excellent, and the battery Charge / discharge efficiency is also high, which is preferable.
[0028]
A heterocyclic compound containing nitrogen or oxygen having one or more fluorine atoms is one in which one or more hydrogen atoms of the heterocyclic compound containing oxygen or nitrogen are substituted by a substituent containing a fluorine atom. is there. As heterocyclic compound, peak Razoru, imidazoles, triazoles, oxazoles, at least one or more compounds selected from the coumarins (excluding coumarins). That is, pyrazole, imidazole, triazole, Okisazo Le a Doya, 1 or more alkyl groups of the hydrogen atoms of these heterocyclic compounds, a carbonyl group, an amino group, a nitro group, a nitrile group, a phenyl group, such as acrylic group It is a compound substituted with a substituent. When two or more hydrogen atoms are substituted with a substituent, they may be substituted with different substituents.
[0029]
Examples of the substitution containing a fluorine atom include a fluorine atom, an alkyl group in which a hydrogen atom is substituted with a fluorine atom, and a perfluorosulfone group. From the viewpoint of oxidation resistance, it is preferable that all the hydrogen atoms in the substituent are substituted with fluorine atoms. Among these, a perfluorosulfone group is preferable as a substituent for substituting a hydrogen atom of a heterocyclic compound.
[0030]
That is, as the heterocyclic compound containing nitrogen or oxygen having one or more fluorine atoms in the present embodiment, the above compounds can be used alone or a plurality of compounds selected from them can be used.
[0031]
Specific examples include 3- (trifluoromethyl) pyrazole as pyrazoles, 2- (trifluoromethyl) benzimidazole as imidazoles, and 3-amino-1,2,4-triazole and oxazole as triazoles. as a class of 5-etc. (trifluoromethyl) Isookisazo Le and the like.
[0032]
The addition amount of the heterocyclic compound containing one or more fluorine atoms and containing nitrogen or oxygen is effective and preferably added in the range of 10 to 50 mmol / dm ³ . When the addition amount is less than 10 mmol / dm ³ , since the addition amount is small, a uniform adsorption film is not formed on the electrode surface, and a sufficient effect may not be obtained. On the contrary, if the addition amount is more than 50 mmol / dm ³ , the elution of aluminum is suppressed, but an excessive adsorption layer is formed on the electrode surface. Reaction may also occur, and lithium charge / discharge efficiency may decrease. In addition, when a lithium-containing metal is used for the positive electrode current collector made of aluminum and the negative electrode, it is sufficient that there is a sufficient addition amount to adsorb on the surface of the lithium-containing metal. 20-30 mol / dm ^{3 is} added.
(Non-aqueous electrolyte secondary battery)
The shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and can be used as a battery having various shapes such as a coin shape, a cylindrical shape, and a square shape.
[0033]
In the present embodiment, a description will be given based on a coin-type non-aqueous electrolyte secondary battery as shown in FIG. The non-aqueous electrolyte secondary battery of the present embodiment is an electrolysis that fills the gap between the positive electrode 1 and the negative electrode 2 joined through the separator 6 inside the positive electrode case 4 and the negative electrode case 5 joined through the gasket 7. And liquid 3. The positive electrode 1 and the positive electrode case 4 and the negative electrode 2 and the negative electrode case 5 are electrically joined to each other.
[0034]
The positive electrode 1 is not particularly limited in its material configuration as long as lithium ions can be released during charging and occluded during discharging, and those having a known material configuration can be used. In particular, it is preferable to use a material obtained by applying a mixture obtained by mixing a positive electrode active material, a conductive material, and a binder to a current collector.
[0035]
The positive electrode active material is not particularly limited by the type of the active material, and a known active material can be used. For example, TiS ₂ , TiS ₃ , MoS ₃ , FeS ₂ , Li _(1-X) MnO ₂ , Li _(1-X) Mn ₂ O ₄ , Li _(1-X) CoO ₂ , Li _(1-X) NiO ₂ , V ₂ O _{3 and the} like. In addition, X in the illustration of this positive electrode active material shows the number of 0-1.
[0036]
Among them, lithium and transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ have excellent active material performance such as excellent electron and lithium ion diffusion performance. Therefore, when such a composite oxide of lithium and transition metal is used for the positive electrode active material, high charge / discharge efficiency and good cycle characteristics can be obtained. In particular, if LiMn ₂ O ₄ is used, it is possible to reduce costs because of its abundant manganese resources.
[0037]
The negative electrode 2 is not particularly limited in its material configuration as long as lithium ions can be occluded during charging and released during discharging, and those having a known material configuration can be used. In particular, it is preferable to use a material obtained by applying a mixture obtained by mixing a negative electrode active material, a conductive material, and a binder to a current collector. The negative electrode active material is not particularly limited by the type of the active material, and a known negative electrode active material can be used. Among them, carbon materials such as natural graphite and artificial graphite with high crystallinity are excellent in the performance of the active material such as lithium ion storage performance and diffusion performance. Therefore, when such a carbon material is used for the negative electrode active material, high charge / discharge efficiency and good cycle characteristics can be obtained. Furthermore, it is more preferable to use a lithium-containing metal as the negative electrode 2 from the viewpoint of battery capacity.
[0038]
As the electrolytic solution 3, an electrolytic solution having the same form as the battery electrolytic solution of the present invention can be used.
[0039]
The positive electrode case 4 and the negative electrode case 5 are not particularly limited, and can be made of known materials and forms.
[0040]
The separator 6 plays a role of electrically insulating the positive electrode 1 and the negative electrode 2 and holding the electrolytic solution 3. For example, a microporous film such as polyethylene may be used. The separator 6 is preferably larger than the positive electrode 1 and the negative electrode 2 in order to ensure insulation between the positive electrode 1 and the negative electrode 2.
[0041]
The gasket 7 ensures electrical insulation between the cases 4 and 5 and the sealing performance in the cases 4 and 5. For example, it can be composed of a chemically and electrically stable polymer for an electrolyte such as polypropylene.
[0042]
A method for producing the non-aqueous battery of the present invention having the above configuration will be described.
[0043]
An example of a method for manufacturing a coin-type battery is described below. As the positive electrode, LiMn ₂ O ₄ as a positive electrode active material, graphite as a conductive material, and polyvinylidene fluoride as a binder are mixed to obtain a positive electrode material. This positive electrode material is dispersed in N-methyl-2-pyrrolidone as a dispersing material to form a slurry. This slurry is applied to a positive electrode current collector made of aluminum, dried and press-molded to obtain an electrode. For the negative electrode, lithium foil is punched into a circle and used.
A positive electrode and a negative electrode are placed inside a case through a polyethylene film as a separator, filled with the above-described battery electrolyte, and then pressed and joined to cases 4 and 5 to produce a coin-type battery. be able to.
[0044]
FIG. 2 is a conceptual diagram of a cylindrical nonaqueous electrolyte secondary battery in the present embodiment, FIG. 2a is a schematic cross-sectional perspective view of the battery, and FIG. 2b is an explanatory schematic diagram showing an electrode portion. The manufacturing method for the cylindrical nonaqueous electrolyte secondary battery shown in FIG. 2 will be further described.
[0045]
Cylindrical non-aqueous electrolyte secondary battery 10 has the same positive electrode and negative electrode manufactured in a coin type as a sheet shape, both are stacked via a separator, and wound into a spiral shape many times as a wound body. , And stored in a predetermined cylindrical case.
[0046]
That is, as shown in FIG. 2b, the electrode structure is such that the negative electrode mixture 11 formed on the negative electrode current collector 12 and the positive electrode mixture 13 formed on the positive electrode current collector 14 face each other. The separator 16 and the electrolytic solution 15 are wound between them to form a wound body, which is housed in the battery can shown in FIG. 2a via an insulating plate.
[0047]
A negative electrode lead 12 ′ is welded to the end of the negative electrode current collector 12 of the wound body, and a negative electrode terminal 18 made of nickel is welded to the case 21 via a thin plate 22 for current interruption. On the other hand, a positive electrode lead 17 ′ welded to the positive electrode current collector 14 is attached with an aluminum positive electrode terminal 17 at an end thereof, and is fixed as a battery lid through a current blocking thin plate 22. As a result, the bottom portion of the case 21 becomes the negative electrode terminal portion 18, and the lid portion of the case becomes the positive electrode terminal portion 17. The wound body housed in the case 21 is filled with the non-aqueous electrolyte 15 described above, sealed with a gasket 23, and provided with a safety lid 24. The cylindrical non-aqueous electrolyte has a diameter of 18 mm and a height of 65 mm. A secondary battery can be formed.
[0048]
The cylindrical battery was prepared in the same manner as described above by preparing a positive electrode, a negative electrode, and an electrolytic solution, using a 25 μm-thick microporous polyethylene film as a separator, and laminating the positive electrode and the negative electrode in order. After that, the wound body is formed by winding it many times in a spiral mold. Next, an insulator was inserted into the bottom of the battery can, and the wound body was stored. Then, the negative electrode and the positive electrode terminal are connected to the bottom and lid of the battery can, and the non-aqueous electrolyte is injected into the battery can prepared as described above and sealed to form a cylindrical non-aqueous electrolyte secondary. A battery can be produced.
[0049]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.
(Example 1)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 10 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. What dissolved pyrazole was used as electrolyte solution.
(Example 2)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 30 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. What dissolved pyrazole was used as electrolyte solution.
(Example 3)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 50 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. What dissolved pyrazole was used as electrolyte solution.
(Example 4)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and further 5 mmol / dm ³ of 3- (trifluoromethyl) as an additive. What dissolved pyrazole was used as electrolyte solution.
(Example 5)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 100 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. What dissolved pyrazole was used as electrolyte solution.
(Example 6)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 30 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. What dissolved benzimidazole was used as electrolyte solution.
(Example 7)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 30 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. What dissolved -1,2,4-triazole was used as electrolyte solution.
(Example 8)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 30 mmol / dm ³ of 5- (trifluoromethyl) is added as an additive. What dissolved isoxazole was used as electrolyte solution.
( Reference Example 1 )
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 30 mmol / dm ³ of 6- (trifluoromethyl) is added as an additive. What dissolved the coumarin was used as electrolyte solution.
(Example 9 )
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 15 mmol / dm ³ of 3- (trifluoromethyl) is added as an additive. A solution in which pyrazole and 15 mmol / dm ³ of 1,2,4-triazole were dissolved was used as an electrolytic solution.
(Comparative Example 1)
A solution obtained by dissolving 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ as an electrolyte in an equal volume mixed solvent of ethylene carbonate and dimethoxyethane was used as an electrolytic solution.
(Comparative Example 2)
In an equal volume mixed solvent of ethylene carbonate and dimethoxyethane, 1.0 mol / dm ³ of LiN (SO ₃ CF ₃ ) ₂ is dissolved as an electrolyte, and 30 mmol / dm ³ of 1,2,4-triazole as an additive. A solution in which was dissolved was used as an electrolytic solution.
[0050]
[Measurement of Al oxidation decomposition potential of electrolyte]
In order to see the electrochemical relationship between the positive electrode current collector made of aluminum and the lithium trifluoromethylsulfonate electrolyte, each of the Examples , Reference Examples, and Comparative Examples was made with an aluminum foil as a working electrode and a counter electrode as a lithium foil. Was inserted into a cell containing the electrolyte solution and cyclic voltammetry (CV measurement) was performed. In the CV measurement, the electric potential is scanned, and the current generated in the aluminum foil at that time is observed. Measurement was performed at a measurement temperature of 25 ° C. and a sweep rate of 10 mV / s in a voltage range of 2 to 5 V, and the time when a current of 1 mA / cm ² or more flowed was defined as the oxidation decomposition potential of Al by the electrolytic solution.
[0051]
[Preparation of lithium charge / discharge efficiency measurement cell]
The coin-type cell shown in FIG. 3 is used for the lithium charge / discharge efficiency measurement. For the working electrode 60, a lithium foil having a thickness of 100 μm was punched to a diameter of 15 mm, and for the counter electrode 50, a lithium foil having a thickness of 400 μm was punched to a diameter of 15 mm. These lithium foils were pressure-bonded to the case , and test cells were prepared by impregnating the electrolytic solutions of the Examples , Reference Examples, and Comparative Examples through a polyethylene film 70 having a thickness of 40 μm.
[0052]
[Lithium charge / discharge efficiency measurement]
First, a constant current density of 0.6 mA / cm ² from the working electrode, eluted (discharging) of lithium charge amount 7.5C / cm ^2. Next, lithium with a constant current density and a charge amount of 7.5 C / cm ² was deposited (discharged) from the counter electrode to the working electrode. After repeating this charge and discharge 20 cycles, the electrochemically active lithium capacity remaining on the working electrode was measured with a constant current density of 0.6 mA / cm ² and a final voltage of 1 V. Lithium charge / discharge efficiency was measured using the following equation.
[0053]
Lithium charge / discharge efficiency (%) = 100 × (1-1 / FOM)
FOM = (total charge capacity when charge / discharge is repeated) / {(charged lithium capacity) − (remaining electrochemically active lithium capacity)}
[Test results]
Table 1 shows the Al oxidation decomposition potential side measurement results and lithium charge / discharge efficiency measurement results of the electrolyte solutions of Examples 1 to 9, Reference Example 1 and Comparative Examples 1 and 2.
[0054]
[Table 1]

[0055]
In Comparative Example 1, since no additive is contained, the Al oxidation decomposition potential of the electrolytic solution is low, and even an actual battery cannot be used at a high potential. Moreover, although the lithium charge / discharge efficiency is higher than that of an inorganic lithium salt such as LiPF ₆ , it is not a sufficiently satisfactory value.
[0056]
In Examples 1 to 3, by adding 10, 30, 50 mmol / dm ^{3 of} 3- (trifluoromethyl) pyrazole, respectively, the Al oxidation decomposition potential of the electrolytic solution was improved, and even in an actual battery, a high voltage of 4 V or higher. Usable with potential. Moreover, the lithium charge / discharge efficiency is also improved, and an improvement in cycle characteristics can be expected. The reason for this is considered to be that, first, the additive forms a stable adsorption layer on the aluminum surface, which is the positive electrode current collector, and suppresses dissolution of aluminum. In addition, the lithium charge / discharge efficiency was improved because a stable film was formed on the negative electrode lithium surface, current concentration and side reactions on the negative electrode were suppressed, and lithium consumption was reduced. .
[0057]
In Example 4, both the oxidative decomposition potential and the charge / discharge efficiency are improved as compared with Comparative Example 1. Even if the amount of 3- (trifluoromethyl) pyrazole added is as small as 5 mmol / dm ³ , it is appropriate. The effect was recognized.
[0058]
Further, in Example 5, although a slight decrease in charge / discharge efficiency was observed as compared with Comparative Example 1, a significant improvement in oxidative decomposition potential was observed. This is because, by adding 100 mmol / dm ^{3 of} 3- (trifluoromethyl) pyrazole, the oxidative decomposition potential is improved, but since the amount of addition is large, a highly resistive film is formed on the lithium surface. Presumed.
[0059]
From the above, the addition amount of 3- (trifluoromethyl) pyrazole is appropriate to be an amount that forms an adsorption layer on the surfaces of the aluminum current collector and the lithium negative electrode, that is, 10 to 50 mmol / dm ^3. thinking.
[0060]
Examples 6 to 8 and Reference Example 1 are examples in which 30 mmol / dm ^{3 of another} additive having a trifluoromethyl group was added. It turned out that the same effect as Example 2 is acquired.
[0061]
Further, Comparative Example 2 is an example in which 1,2,4-triazole having no other trifluoromethyl group is added. Since stable film formation on the lithium surface is effective, lithium charge / discharge efficiency is improved, but the oxidative decomposition potential of aluminum is not improved as much as in the examples. This is considered to be because it does not have a trifluoromethyl group with high oxidation resistance.
[0062]
Finally, Example 9 is an example in which 15 mmol / dm ³ of 1,2,4-triazole of Comparative Example 2 and 3- (trifluoromethyl) pyrazole having a trifluoromethyl group are added. By mixing both, the oxidative decomposition potential and charge / discharge efficiency of aluminum can be improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a battery schematically showing a nonaqueous electrolyte secondary battery according to an embodiment.
FIG. 2 is an explanatory view of a cylindrical battery showing an outline of the nonaqueous electrolyte secondary battery of the present embodiment, 2a is a cross-sectional perspective view of the cylindrical battery, and 2b is an explanatory schematic diagram illustrating an electrode portion. It is.
FIG. 3 is a longitudinal sectional view of a cell used in a charge / discharge efficiency test of the present example.
[Explanation of symbols]
1: Positive electrode 2: Negative electrode 3: Non-aqueous electrolyte 4: Positive electrode case 5: Negative electrode case 6: Separator 7: Gasket 10: Cylindrical battery 11: Negative electrode mixture 12: Negative electrode current collector 12 ′: Negative electrode lead 13: Positive electrode Compound 14: Positive electrode current collector 14 ': Positive electrode lead 15: Electrolytic solution 16: Separator 17: Positive electrode terminal 18: Negative electrode terminal part 50: Counter electrode 60: Working electrode 70: Polyethylene film (separator)

Claims (6)

A battery electrolyte comprising at least a lithium salt of a perfluoroalkylsulfonic acid derivative dissolved in an organic solvent,
The organic solvent contains at least one compound selected from heterocyclic compounds containing nitrogen or oxygen having one or more fluorine atoms ,
The heterocyclic compound, pyrazoles, imidazoles, triazoles, oxazoles, at least one compound selected from the coumarins (excluding coumarins) battery electrolyte, characterized in der Rukoto . The lithium salt of the perfluoroalkylsulfonic acid derivative is at least one substance selected from LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiC (SO ₂ CF ₃ ) _3. Battery electrolyte.   The battery electrolyte according to claim 1, wherein the heterocyclic compound has at least one perfluoroalkyl group.   The organic solvent contains 10 to 50 mmol / dm of the heterocyclic compound. ^Three The electrolyte solution for a battery according to claim 1, which is added.   A positive electrode capable of releasing and occluding lithium ions, a negative electrode made of a lithium-containing metal capable of releasing and occluding lithium ions, and a lithium perfluoroalkylsulfonic acid derivative in an organic solvent interposed between the positive electrode and the negative electrode A non-aqueous electrolyte secondary battery comprising an electrolyte obtained by dissolving a salt,
  The non-aqueous electrolyte secondary battery, wherein the electrolyte solution is the battery electrolyte solution according to any one of claims 1 to 4.   The non-aqueous electrolyte battery according to claim 5, wherein the positive electrode has a current collector made of aluminum.

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