JP4366790B2 - Battery electrolyte and non-aqueous electrolyte secondary battery - Google Patents

Description

【００７１】
【表２】

【００７２】
比較例１では、本発明の窒素含有環状化合物のリチウム塩を含有していないので、充電時の電流密度が大きい場合に、リチウム充放電効率の低下が大きかった。また、比較例２では、窒素含有環状化合物がリチウム塩でない１，２，３−ベンゾトリアゾールであるので、比較例１と同様に、充電時の電流密度が大きい場合のリチウム充放電効率が低下が大きかった。これは、充電時の電流密度が高くなることで負極の近傍がより還元雰囲気になり、１，２，３−ベンゾトリアゾールが還元されて消費されたためと考えられる。
【００７３】
実施例１では、３ｍｍｏｌ／ｄｍ³ の１，２，３−ベンゾトリアゾールのリチウム塩を添加しているものの添加量が少ないために効果が少なかった。
【００７４】
これに対し、トリアゾール類のリチウム塩を１０〜５０ｍｍｏｌ／ｄｍ³ 添加した実施例２〜３では、効果が発現され、比較例１よりもリチウム充放電効率が高く、充電電流密度が高くても、リチウム充放電効率の低下が少なかった。しかし、実施例４では１，２，３−ベンゾトリアゾールのリチウム塩の溶解度が低いために１，２，３−ベンゾトリアゾールのリチウム塩が電解液中に晶出しており、過剰に添加しても効果のさらなる向上は見られなかった。
【００７５】
また、コイン型電池における安全性評価においては、比較例１では、過充電時の電流密度にかかわらず液漏れを生じた。比較例２では、効果が少なく過充電電流密度が高い場合に液漏れをおこした。
【００７６】
実施例１では効果が現れているが添加量が少ないため過充電電流密度が高い場合に液漏れをおこした。これに対し、実施例２から４ではいずれの電流密度においても液漏れは見られず、安定した効果が見られた。
【００７７】
以上の結果より、窒素含有環状化合物のリチウム塩を電解液に添加することによって、リチウム充放電効率を向上させ、かつ、安全性を向上することができることが明らかとなった。また、安定した効果を発揮するための窒素含有環状化合物のリチウム塩の添加量は、５ｍｍｏｌ／ｄｍ³ より多くすることが好ましい。
【００７８】
また、実施例５、６では、実施例２と同様に、比較例１よりも充放電効率が高く、定電流密度が増加しても、リチウム充放電効率の低下が少なく、安全性評価においても変化がみられなかった。
【００７９】
【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. . Since the lithium secondary battery has both high energy density and high output density, a large discharge capacity and a high discharge voltage can be obtained. Among these, lithium ion secondary batteries using a carbon material or a lithium-containing metal for the negative electrode are expected to have a higher energy density, and are actively researched.
[0004]
However, in a secondary battery using a carbon material for the negative electrode, dendritic lithium is generated on the negative electrode surface during overcharge, and in a secondary battery using a lithium-containing metal for the negative electrode, a dendrite-like lithium is formed on the negative electrode surface during charging. Lithium is generated. This dendrite-like lithium has a very large surface area, and side reactions between the electrolyte and lithium are likely to occur. Therefore, the dendrite-like lithium is consumed in abnormal situations such as when lithium is consumed by the side reaction or when the battery is exposed to high temperatures. Lithium and the electrolyte may react explosively. Further, the cycle characteristics deteriorate due to the release of dendritic lithium from the negative electrode surface. Therefore, development of a lithium secondary battery excellent in safety and reliability is desired. In recent years, attempts have been made to add various substances to the electrolytic solution for the purpose of suppressing the formation of dendritic lithium and improving cycle characteristics and the like.
[0005]
In JP-A-6-349523, benzotriazole or a derivative thereof is added to an electrolytic solution to improve cycle characteristics.
[0006]
[Problems to be solved by the invention]
However, substances such as benzotriazole disclosed in Japanese Patent Application Laid-Open No. 6-349523, for example, reduce benzotriazole even if lithium is deposited on a nickel substrate using an electrolytic solution to which benzotriazole is added. Therefore, as can be seen from the fact that lithium does not precipitate, since the reduction resistance is poor, there is a disadvantage that generation of dendritic lithium cannot be sufficiently suppressed.
[0007]
Therefore, in this invention, it is set as the problem which should be solved to provide the electrolyte solution for batteries which can achieve the battery characteristic excellent in safety | security and reliability.
[0008]
It is another object of the present invention to provide a non-aqueous electrolyte secondary battery having excellent battery characteristics with safety and reliability.
[0009]
[Means for Solving the Problems]
As a result of diligent research, the present inventors have found that by adding a lithium salt of a nitrogen-containing cyclic substance to the electrolyte, it is possible to suppress the generation of dendritic lithium, and the following Invented.
[0010]
That is, the battery electrolyte of the present invention that solves the above problems is a battery in which a supporting salt is dissolved in an organic solvent for a non-aqueous electrolyte battery using a positive electrode and a negative electrode capable of occluding and releasing lithium ions. The supporting salt contains a lithium salt of a nitrogen-containing cyclic compound.
[0011]
In other words, the battery electrolyte of the present invention contains a lithium salt of a nitrogen-containing cyclic compound having excellent reduction resistance in the battery electrolyte so that the lithium salt of the nitrogen-containing cyclic compound is reduced on the negative electrode surface. Forms a highly stable film and suppresses current concentration and side reactions on the negative electrode, so that dendrite formation is suppressed and cycle characteristics are improved, and at the same time, the reaction area between lithium and electrolyte is reduced and safety is improved. Will improve.
[0013]
  The lithium salt of the nitrogen-containing cyclic compound takes into account the high effect of suppressing dendrite formation.ShiA lithium salt of at least one compound selected from 1,2,3-benzotriazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, pyrazole and imidazole.
[0014]
  The organic solvent contains 5 to 100 mmol / dm of lithium salt of the nitrogen-containing cyclic compound.^ThreeAddedTheIf the amount is less than this, the effect of the present invention is reduced, and if the amount is more than this, the additive is only crystallized (or does not dissolve) in the battery electrolyte, and the effect is not improved.
[0015]
Therefore, according to the battery electrolyte of the present invention, a battery capable of achieving battery characteristics excellent in safety and reliability can be obtained.
[0016]
Further, the non-aqueous electrolyte secondary battery of the present invention that solves the above-mentioned problems is a positive and negative electrodes capable of releasing and occluding lithium ions, and a supporting salt dissolved in an organic solvent interposed between the positive and negative electrodes. A nonaqueous electrolyte secondary battery comprising the nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution is the above-described battery electrolyte solution of the present invention.
[0017]
In the non-aqueous electrolyte secondary battery of the present invention, since the non-aqueous electrolyte used forms a stable film with excellent reduction resistance on the surface of the negative electrode, the battery performance is excellent in safety and reliability. Can be achieved.
[0018]
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.
[0019]
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.
[0020]
The battery electrolyte of this embodiment is a battery electrolyte obtained by dissolving a supporting salt in an organic solvent for a non-aqueous electrolyte battery using a positive electrode and a negative electrode capable of occluding and releasing lithium ions. The supporting salt contains a lithium salt of a nitrogen-containing cyclic compound.
[0021]
The lithium salt of the nitrogen-containing cyclic compound exhibits the action of the supporting salt in the battery electrolyte solution of the present embodiment.
[0022]
  The nitrogen-containing cyclic compound in the lithium salt of the nitrogen-containing cyclic compound is1, 2,3-benzotriazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, pyrazole, imidazoleThe
[0023]
The lithium salt of the nitrogen-containing cyclic compound is at least one compound selected from substances obtained by substituting lithium for the imide hydrogen of the nitrogen-containing cyclic compound. The lithium salt of the nitrogen-containing cyclic compound may be a mixture of a plurality of compounds.
[0024]
  The concentration of the lithium salt of the nitrogen-containing cyclic compound added to the electrolyte isAnd5-100 mmol / dm^Three And goodPreferably, 10-50 mmol / dm^ThreeIt is. If the amount is less than this, the effect of the present invention is lowered, and if it is more than this, the additive is crystallized in the battery electrolyte, and the improvement in the effect is small. That is, the effect of the present invention can be sufficiently obtained if there is an addition amount sufficient to adsorb on the active sites on the negative electrode surface. Note that crystals that crystallize in the electrolyte by adding an excessive amount of the lithium salt of the nitrogen-containing cyclic compound are electrolyzed when the lithium salt of the nitrogen-containing cyclic compound is consumed in the electrolyte and the concentration decreases. Since it can be replenished in the solution, it functions to keep the lithium salt concentration of the nitrogen-containing cyclic compound in the electrolyte at a certain level or higher.
[0025]
Lithium salts of triazoles can be synthesized by a dehydrogenation reaction of triazoles with lithium metal.
[0026]
For example, 1 mol / dm in tetrahydrofuran^ThreeOf benzotriazole is slowly dropped into a tetrahydrofuran bath. When an equivalent amount of lithium metal is added little by little in the tetrahydrofuran bath and allowed to act gently with benzotriazole with stirring, a yellowish white benzotriazole lithium salt precipitates. The obtained precipitate was filtered and dried, and then purified by recrystallization from a mixed solvent of methanol and acetone. This was vacuum dried at 150 ° C. for 24 hours to obtain a lithium salt of benzotriazole.
[0027]
Similarly, lithium salts of other triazoles can be synthesized.
[0028]
As the supporting salt, the lithium salt of the nitrogen-containing cyclic compound of the present invention can be used alone, but it is preferable to use another known supporting salt in consideration of improving the battery characteristics.
[0029]
The supporting salt that can be used in combination with the lithium salt of the aforementioned nitrogen-containing cyclic compound in the battery electrolyte of this embodiment is LiPF.₆, LiBF_FourLiClO_Four, LiCF_ThreeSO_ThreeInorganic lithium salt such as LiN (SO₂C_xF_{2x + 1}) (SO₂C_yF_{2y + 1}) Is an organic lithium salt. Here, x and y represent an integer of 1 to 4, and x + y is 3 to 8. Specifically, LiN (SO₂CF_Three) (SO₂C₂F₆), LiN (SO₂CF_Three) (SO₂C_ThreeF₇), LiN (SO₂CF_Three) (SO₂C_FourF₉), LiN (SO₂C₂F₆) (SO₂C₂F₆), LiN (SO₂C₂F₆) (SO₂C_ThreeF₇), LiN (SO₂C₂F₆) (SO₂C_FourF₆) Etc. Among them, LiN (SO₂CF_Three) (SO₂C_FourF₉), LiN (SO₂C₂F₆) (SO₂C₂F₆) Or the like is preferably used for the supporting salt because of its excellent electrical characteristics. Moreover, since an organic lithium salt may destroy aluminum which is a positive electrode current collector at a high potential of 4 V or higher, LiPF is used as an additive for suppressing this.₆Etc. may be added as a supporting salt.
[0030]
The supporting salt has a concentration in the electrolyte of 0.1 to 3.0 mol / dm.^ThreeIn particular, 0.5 to 2.0 mol / dm^ThreeIt is preferable to use an organic solvent. The concentration in the electrolyte is 0.1 mol / dm^ThreeIf it is smaller, sufficient current density may not be obtained, and it may be 3.0 mol / dm.^ThreeIf it is larger, the viscosity is increased and the conductivity of the electrolytic solution may be lowered.
[0031]
The organic solvent is not particularly limited as long as it is an organic solvent used as an electrolyte in a normal nonaqueous electrolyte secondary battery. For example, a carbonate compound, a lactone compound, an ether compound, a sulfolane compound, a dioxolane compound, A ketone compound, a nitrile compound, a halogenated hydrocarbon compound, etc. can be mentioned.
[0032]
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. 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 of the supporting salt, the dielectric constant and the viscosity are excellent, and the battery The charge / discharge efficiency is also preferable.
(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, TiS₂TiS_Three, MoS_Three, FeS₂, Li_(1-X)MnO₂, Li_(1-X)Mn₂O_Four, Li_(1-X)CoO₂, Li_(1-X)NiO₂, V₂O_ThreeEtc. In addition, X in the illustration of a positive electrode active material shows the number of 0-1.
[0036]
Among them, LiCoO₂LiNiO₂, LiMn₂O_FourSuch lithium and transition metal composite oxides 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, LiMn₂O_FourCan be used 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 active material performance 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, the electrolyte solution 3 such as polypropylene can be composed of a chemically and electrically stable polymer.
[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 the coin battery shown in FIG. 1 will be described below. As the positive electrode 1, LiMn as a positive electrode active material₂O_FourAnd 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 a positive electrode 1.
[0044]
The negative electrode 2 is prepared by mixing a graphite material as a negative electrode active material and polyvinylidene fluoride as a binder. This negative electrode material is dispersed in N-methyl-2-pyrrolidone as a dispersant to form a slurry. This slurry is applied to a copper negative electrode current collector, dried, and press-molded to form negative electrode 2.
[0045]
The positive electrode 1 and the negative electrode 2 are placed in cases 4 and 5 through a polyethylene separator 6 and filled with the battery electrolyte, and then the cases 4 and 5 are pressed and joined to form a coin type. A battery can be fabricated.
[0046]
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.
[0047]
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.
[0048]
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.
[0049]
A negative electrode lead 12 ′ is welded to the end portion of the negative electrode current collector 12 of the wound body, and a nickel negative electrode terminal 18 is welded to the case 21 through 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 via 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.
[0050]
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.
[0051]
【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.
[0052]
Example 1
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeFurther, 1,2,3-benzotriazole lithium salt is added as a lithium salt of a nitrogen-containing cyclic compound at 3 mmol / dm.^ThreeThus, using the dissolved one as a non-aqueous electrolyte, a coin-type battery for safety evaluation and a cell for measuring lithium charge / discharge efficiency were prepared by the following methods.
[0053]
<How to make a coin-type battery for safety evaluation>
A method for manufacturing a coin-type battery will be described below. As the positive electrode 1, LiMn₂O_Four90 parts by weight, 6 parts by weight of graphite and 4 parts by weight of polyvinylidene fluoride are mixed to obtain a positive electrode material. This positive electrode material is dispersed in N-methyl-2-pyrrolidone to form a slurry. This slurry was applied to an aluminum positive electrode current collector, dried, and press-molded to obtain positive electrode 1. The negative electrode 2 is made by mixing 92 parts by weight of a graphite material and 8 parts by weight of polyvinylidene fluoride to form a negative electrode material. This negative electrode material is dispersed in N-methyl-2-pyrrolidone to form a slurry. This slurry was applied to a copper negative electrode current collector, dried, and press-molded to obtain negative electrode 2.
[0054]
The positive and negative electrodes 1 and 2 are joined via a polyethylene separator 6 having a thickness of 25 μm and welded to the positive electrode case 4 and the negative electrode case 5, respectively. The positive electrode case 4 and the negative electrode case 5 were joined via a gasket 7 and filled with the non-aqueous electrolyte 3 therein. This coin type battery was used as a coin type battery for safety evaluation.
[0055]
<Production method of lithium charge / discharge efficiency measurement cell>
The coin-type cell of 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 a non-aqueous electrolyte solution was contained through a polyethylene film 70 having a thickness of 40 μm to obtain a lithium charge / discharge efficiency measurement cell.
[0056]
(Example 2)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeFurther, a lithium salt of 1,2,3-benzotriazole as a lithium salt of a nitrogen-containing cyclic compound was added at 10 mmol / dm.^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0057]
(Example 3)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeFurther, a lithium salt of 1,2,3-benzotriazole as a lithium salt of a nitrogen-containing cyclic compound is 50 mmol / dm.^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0058]
(Example 4)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeFurther, a lithium salt of 1,2,3-benzotriazole as a lithium salt of a nitrogen-containing cyclic compound was added at 100 mmol / dm.^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0059]
(Example 5)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeAnd a lithium salt of 1,2,4-benzotriazole as a lithium salt of a nitrogen-containing cyclic compound is 50 mmol / dm.^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0060]
(Example 6)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeAnd a lithium salt of 3-amino-1,2,4-benzotriazole as a lithium salt of a nitrogen-containing cyclic compound is 50 mmol / dm.^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0061]
(Comparative Example 1)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0062]
(Comparative Example 2)
An equal volume mixed solvent of ethylene carbonate and dimethoxyethane as an organic solvent and LiPF as a supporting salt₆1 mol / dm^ThreeIn addition, 1,2,3-benzotriazole was dissolved at a concentration of 50 mmol / dm.^Three1 was prepared in the same manner as in Example 1, and the lithium charge / discharge efficiency measurement cell shown in FIG. 3 was prepared by the same production method as in Example 1. .
[0063]
(Method for synthesizing lithium salt of triazole)
1 mol / dm of benzotriazole in tetrahydrofuran^ThreeDissolve to a concentration of When an equivalent amount of metallic lithium is added little by little to this tetrahydrofuran solution and gently reacted with benzotriazole with stirring, a yellowish white lithium salt of benzotriazole precipitates. The resulting precipitate was filtered and dried, and then purified by recrystallization from a mixed solvent of methanol and acetone. This was vacuum dried at 150 ° C. for 24 hours to obtain a lithium salt of benzotriazole.
[0064]
Similarly, lithium salts of other triazoles can be synthesized.
[0065]
(Safety evaluation test)
The test batteries of each Example and each Comparative Example were charged with a charging current density of 0.5 mA / cm.²And 2.5 mA / cm²Then, the battery is overcharged to 200% of the battery capacity, the lithium metal is deposited on the negative electrode, and then stored in a high-temperature bath at 200 ° C., and the appearance change is observed.
[0066]
(Lithium charge / discharge efficiency measurement test)
For the test cells of each Example and each Comparative Example, first, 0.5 mA / cm from the working electrode.²With a constant current density of 7.5 C / cm²Of lithium was eluted (discharged). Next, the current density is 0.5 mA / cm from the counter electrode to the working electrode.²2.5 mA / cm²A charge amount of 7.5 C / cm at a constant current density for the two types²Of lithium was deposited (charged).
[0067]
After repeating this charge and discharge 20 cycles, 0.5 mA / cm²The electrochemically active lithium capacity remaining on the working electrode was measured at a constant current density and a final voltage of 1V.
[0068]
Lithium charge / discharge efficiency was measured using the following equation.
[0069]
Lithium charge / discharge efficiency (%) = 100 × (1-1 / FOM)
FOM = (total charge capacity when charge and discharge are repeated) / {(charged lithium capacity) − (remaining electrochemically active lithium capacity)}
(result)
The lithium charge / discharge efficiency measurement results of Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 1, and the safety evaluation results are shown in Table 2.
[0070]
[Table 1]

[0071]
[Table 2]

[0072]
In Comparative Example 1, since the lithium salt of the nitrogen-containing cyclic compound of the present invention was not contained, the lithium charge / discharge efficiency was greatly reduced when the current density during charging was large. In Comparative Example 2, since the nitrogen-containing cyclic compound is 1,2,3-benzotriazole which is not a lithium salt, the lithium charge / discharge efficiency is reduced when the current density during charging is large, as in Comparative Example 1. It was big. This is presumably because the current density at the time of charging was increased, so that the vicinity of the negative electrode became more reducing atmosphere, and 1,2,3-benzotriazole was reduced and consumed.
[0073]
In Example 1, 3 mmol / dm^ThreeHowever, since the addition amount of the 1,2,3-benzotriazole lithium salt was small, the effect was small.
[0074]
On the other hand, the lithium salt of triazoles is 10 to 50 mmol / dm.^ThreeIn the added Examples 2 to 3, the effects were exhibited, the lithium charge / discharge efficiency was higher than that of Comparative Example 1, and the decrease in the lithium charge / discharge efficiency was small even when the charge current density was high. However, in Example 4, since the solubility of 1,2,3-benzotriazole lithium salt is low, the lithium salt of 1,2,3-benzotriazole crystallizes in the electrolyte, and even if added excessively, There was no further improvement in effect.
[0075]
Further, in the safety evaluation of the coin-type battery, in Comparative Example 1, liquid leakage occurred regardless of the current density during overcharge. In Comparative Example 2, liquid leakage occurred when the effect was small and the overcharge current density was high.
[0076]
In Example 1, although the effect appeared, since the addition amount was small, liquid leakage was caused when the overcharge current density was high. On the other hand, in Examples 2 to 4, no liquid leakage was observed at any current density, and a stable effect was observed.
[0077]
From the above results, it was revealed that the lithium charge / discharge efficiency can be improved and the safety can be improved by adding a lithium salt of a nitrogen-containing cyclic compound to the electrolytic solution. Moreover, the addition amount of the lithium salt of the nitrogen-containing cyclic compound for exhibiting a stable effect is 5 mmol / dm.^ThreeMore is preferable.
[0078]
In Examples 5 and 6, as in Example 2, the charge / discharge efficiency is higher than in Comparative Example 1, and even if the constant current density is increased, the decrease in lithium charge / discharge efficiency is small, and the safety evaluation is also performed. There was no change.
[0079]
[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
DESCRIPTION OF SYMBOLS 10: Cylindrical battery 11: Negative electrode compound 12: Negative electrode collector 12 ': Negative electrode lead 13: Positive electrode compound 14: Positive electrode collector 14': Positive electrode lead 15: Electrolytic solution 16: Separator 17: Positive electrode terminal 18: Negative terminal
50: Counter electrode 60: Working electrode 70: Polyethylene film (separator)

Claims (2)

A battery electrolyte comprising a support salt dissolved in an organic solvent for a non-aqueous electrolyte battery using a positive electrode and a negative electrode capable of occluding and releasing lithium ions,
The supporting salt contains a lithium salt of a nitrogen-containing cyclic compound ,
The lithium salt of the nitrogen-containing cyclic compound is at least one selected from 1,2,3-benzotriazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, pyrazole, and imidazole. A lithium salt of the compound,
5 to 100 mmol / dm ³ of a lithium salt of the nitrogen-containing cyclic compound is added to the organic solvent .   A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of releasing and occluding lithium ions, and a non-aqueous electrolyte solution that is interposed between the positive electrode and the negative electrode and has a supporting salt dissolved in an organic solvent. And
  The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte is the battery electrolyte according to claim 1.

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