JP2015090842A - Nonaqueous electrolyte secondary battery, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolyte secondary battery in which a conductive polymer is used for a positive electrode, and a carbonaceous material is used for a negative electrode, and which enables the efficient suppression of the worsening of a battery performance by stabilizing a capacity-keeping rate; and a method for manufacturing such a nonaqueous electrolyte secondary battery.SOLUTION: The nonaqueous electrolyte secondary battery comprises: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte having ion conductivity and including a support electrolyte. The positive electrode includes a conductive polymer. The negative electrode includes a carbonaceous material which ions can go into and go away from. The support electrolyte of the electrolyte includes a lithium salt, having an ion radius of an anion component of 26 pm or larger.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the same, and more particularly to a non-aqueous electrolyte secondary battery that effectively suppresses deterioration of battery performance by stabilizing the capacity retention rate and a method for manufacturing the same. It is.

  In recent years, with the advancement and development of electronic technology in portable PCs, mobile phones, personal digital assistants (PDAs), secondary batteries that can be repeatedly charged and discharged are widely used as power storage devices for these electronic devices. Yes.

  Among secondary batteries, a secondary battery that uses a lithium-containing transition metal oxide such as lithium manganate or lithium cobaltate as an electrode active material and a carbonaceous material that can insert and desorb lithium ions as a negative electrode. Is widely used as a so-called rocking chair type lithium ion secondary battery in which the lithium ion concentration in the electrolyte does not substantially change during charging and discharging. This rocking chair type secondary battery can reduce the amount of electrolyte compared to the so-called reserve type secondary battery, and can be downsized, and has a high energy density while being small. Therefore, it is widely used as an electricity storage device for the electronic devices described above.

  However, in the lithium ion secondary battery, the electrode and the electrolytic solution are deteriorated due to an electrochemical reaction accompanying charging / discharging, so that the capacity retention rate becomes unstable as the number of cycles increases. Therefore, in general, the life, that is, the cycle characteristics are not good.

  Therefore, in order to improve the above problem, a non-aqueous electrolyte secondary battery using a conductive polymer such as polyaniline having a dopant as a positive electrode active material is also known (Patent Document 1). However, in general, a secondary battery having a conductive polymer as a positive electrode active material is an anion transfer type in which an anion is doped into a positive electrode polymer during charging and the anion is dedoped from the positive electrode polymer during discharge. Such a rocking chair type secondary battery cannot be constructed. Therefore, a non-aqueous electrolyte secondary battery using a conductive polymer as a positive electrode active material basically requires a large amount of electrolyte, resulting in a problem that it cannot contribute to battery size reduction.

  In order to solve such a problem, a conductive polymer having a polymer anion such as polyvinyl sulfonic acid as a dopant is used for the positive electrode to be a cation transfer type so that the ion concentration in the electrolytic solution does not substantially change. A secondary battery is also proposed (see Patent Document 2).

Japanese Patent Laid-Open No. 3-129679 Japanese Patent Laid-Open No. 1-132052

  However, the secondary battery of Patent Document 2 uses a metal such as lithium for the negative electrode. In general, in a lithium ion secondary battery, it is considered desirable to use a carbonaceous material that can insert and desorb lithium ions from the viewpoint of safety and cycle characteristics. Since this is the same in the case of a non-aqueous electrolyte secondary battery using a conductive polymer, this point is regarded as a problem in the secondary battery of Patent Document 2.

  Accordingly, the present inventors have been conducting various researches and experiments on non-aqueous electrolyte secondary batteries using a conductive polymer for the positive electrode and a carbonaceous material for the negative electrode, and in the process, Efforts were made to improve battery performance degradation, which is a problem in water electrolyte secondary batteries.

  The present invention has been made in view of such circumstances, and is a non-aqueous electrolyte secondary battery using a conductive polymer for a positive electrode and a carbonaceous material for a negative electrode, and the battery has a capacity retention rate stabilized. An object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of effectively suppressing deterioration of performance and a method for manufacturing the same.

  In order to achieve the above object, the present invention provides a non-aqueous electrolysis comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing a support salt having ion conductivity. In the liquid secondary battery, the positive electrode includes a conductive polymer, the negative electrode includes a carbonaceous material capable of inserting / extracting ions, and the supporting salt of the electrolytic solution has an ionic radius of 26 pm of an anionic component. A non-aqueous electrolyte secondary battery containing the above lithium salt is a first gist.

Moreover, this invention is a manufacturing method of the nonaqueous electrolyte secondary battery which is said 1st summary, Comprising: The manufacturing method of a nonaqueous electrolyte secondary battery provided with the process of following (I)-(III). This is the second gist.
(I) A step of preparing a positive electrode and a negative electrode, arranging a separator between the two, and producing a laminate composed of the positive electrode, the separator, and the negative electrode.
(II) A step of accommodating at least one of the laminates in a battery container.
(III) A step of injecting an electrolytic solution into the battery container.

That is, the present inventors have intensively studied to solve the above problems. In the course of the research, conventional lithium hexafluorophosphate as a supporting salt (electrolyte) for the electrolyte in a non-aqueous electrolyte secondary battery using a conductive polymer for the positive electrode and a carbonaceous material for the negative electrode When a lithium salt such as (LiPF ₆ ) or lithium tetrafluoroborate (LiBF ₄ ) is used instead of a small ion radius of the anion component but a large ion radius of the anion component, a rocking chair type It became a secondary battery and found out that the capacity maintenance rate was stabilized. The reason for the rocking chair type is that the anion component is difficult to move due to the size of the anion component of the lithium salt, so that only the lithium ion that is the cation component moves actively. It can be considered that the anion and cation move as in the reserve type and the difference in fluctuation (up and down movement) in the electrolyte concentration increases (the reserve type element is suppressed), and the rocking chair type is obtained. In addition, with the shift to the rocking chair type, as described above, only small lithium ions actively move, so that charging / discharging is performed smoothly and the capacity maintenance rate is stabilized. .

  The lithium salt capable of stabilizing the capacity retention rate as described above needs to have an ionic radius of an anionic component of at least 26 picometers (pm) as a result of repeated experiments by the present inventors. As a result, the present invention has been reached.

  Thus, the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing a support salt having ion conductivity. A non-aqueous electrolyte secondary battery, wherein the positive electrode includes a conductive polymer, the negative electrode includes a carbonaceous material capable of inserting / extracting ions, and the supporting salt of the electrolyte includes ions of anion components A lithium salt having a radius of 26 pm or more is included. Therefore, deterioration of battery performance can be effectively suppressed by stabilizing the capacity maintenance rate.

  In particular, the supporting salt of the electrolytic solution was selected from the group consisting of lithium trifluoromethanesulfonate (LiTFS), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), and lithium bis (pentafluoroethanesulfonyl) imide (LiBETI). When it is at least one, the capacity retention rate is more stable, and deterioration of battery performance can be effectively suppressed.

  Further, when the conductive polymer constituting the positive electrode is at least one selected from the group consisting of polyaniline, polyaniline derivative, polypyrrole, and polypyrrole derivative, battery performance such as weight energy density can be further improved. It becomes like this.

And when the said positive electrode contains the following (a) component further, the improvement of battery performance, such as a weight energy density, will come to be obtained.
(A) At least one of polycarboxylic acid and polycarboxylic acid metal salt.

  The polycarboxylic acid (a) is selected from the group consisting of polyacrylic acid, polymethacrylic acid, polyvinylbenzoic acid, polyallylbenzoic acid, polymethallylbenzoic acid, polymaleic acid, polyfumaric acid, polyaspartic acid, and polyglutamic acid. If it is at least one, it is possible to obtain a further improvement in weight energy density.

And when it is a manufacturing method of the said nonaqueous electrolyte secondary battery, Comprising: It is a manufacturing method provided with the process of following (I)-(III), non-aqueous with little deterioration of battery performance by stabilization of a capacity | capacitance maintenance factor An electrolyte secondary battery can be obtained efficiently.
(I) A step of preparing a positive electrode and a negative electrode, arranging a separator between the two, and producing a laminate composed of the positive electrode, the separator, and the negative electrode.
(II) A step of accommodating at least one of the laminates in a battery container.
(III) A step of injecting an electrolytic solution into the battery container.

In each non-aqueous-electrolyte secondary battery of Example 1 and Comparative Example 1, it is a graph which made the vertical axis | shaft the capacity | capacitance maintenance factor (%) and made the horizontal axis the cycle frequency (times).

  Hereinafter, embodiments of the present invention will be described in detail. However, the description described below is an example of embodiments of the present invention, and the present invention is not limited to the following contents.

  A nonaqueous electrolyte secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing a support salt having ionic conductivity. A secondary battery, wherein the positive electrode includes a conductive polymer, the negative electrode includes a carbonaceous material capable of inserting / extracting ions, and the electrolyte supporting salt has an ionic radius of 26 pm or more of the anion component It is characterized by including the lithium salt. Here, the “ion radius” refers to the radius when an ion is considered to be spherical, and in the present invention refers to the effective ion radius of Shannon.

  Hereinafter, the respective members and materials used will be described in order.

<About positive electrode>
[Conductive polymer]
As described above, the positive electrode of the nonaqueous electrolyte secondary battery of the present invention contains a conductive polymer. In the present invention, the conductive polymer means that an ionic species is inserted into or desorbed from a polymer in order to compensate for a change in charge generated or lost by an oxidation reaction or reduction reaction of the polymer main chain. A group of polymers in which the conductivity of the polymer itself changes.

  In such a polymer, a state with high conductivity is referred to as a doped state, and a state with low conductivity is referred to as a dedope state. Even if a polymer having conductivity loses conductivity by an oxidation reaction or a reduction reaction and becomes insulative (that is, in a dedoped state), such a polymer is reversibly conductive again by the oxidation-reduction reaction. Therefore, the insulating polymer in such a dedope state is also included in the category of the conductive polymer in the present invention.

  Further, as one of the preferred conductive polymers of the present invention, at least one proton acid selected from the group consisting of inorganic acid anions, fatty acid sulfonate anions, aromatic sulfonate anions, polymer sulfonate anions and polyvinyl sulfate anions is preferable. A polymer having an anion as a dopant. Further, another conductive polymer preferable in the present invention is a polymer in a dedope state obtained by dedoping the conductive polymer.

  Specific examples of the conductive polymer include, for example, polyacetylene, polypyrrole, polyaniline, polythiophene, polyfuran, polyselenophene, polyisothianaphthene, polyphenylene sulfide, polyphenylene oxide, polyazulene, and poly (3,4-ethylenedioxythiophene). And various derivatives thereof. Of these, polyaniline, polyaniline derivatives, polypyrrole, and polypyrrole derivatives having a large electrochemical capacity are preferably used, and polyaniline and polyaniline derivatives are more preferably used.

  In the present invention, the polyaniline means a polymer obtained by electrolytic polymerization or chemical oxidative polymerization of aniline, and the polyaniline derivative is obtained by electrolytic polymerization or chemical oxidative polymerization of an aniline derivative, for example. Refers to the polymer produced.

  More specifically, as a derivative of aniline, a substituent such as an alkyl group, an alkenyl group, an alkoxy group, an aryl group, an aryloxy group, an alkylaryl group, an arylalkyl group, or an alkoxyalkyl group is provided at a position other than the 4-position of aniline. What has at least one can be illustrated. Preferable specific examples include, for example, o-substituted anilines such as o-methylaniline, o-ethylaniline, o-phenylaniline, o-methoxyaniline, o-ethoxyaniline, m-methylaniline, m-ethylaniline, m And m-substituted anilines such as -methoxyaniline, m-ethoxyaniline, m-phenylaniline and the like. These may be used alone or in combination of two or more. In the present invention, p-phenylaminoaniline having a substituent at the 4-position can be suitably used as an aniline derivative because polyaniline is obtained by oxidative polymerization.

  Hereinafter, in the present invention, “aniline or a derivative thereof” may be simply referred to as “aniline”, and “at least one of polyaniline and a polyaniline derivative” may be simply referred to as “polyaniline”. Therefore, even when the polymer constituting the conductive polymer is obtained from an aniline derivative, it may be referred to as “conductive polyaniline”.

  Moreover, in the positive electrode which concerns on the nonaqueous electrolyte secondary battery of this invention, it is preferable to have nitrogen further in addition to the said conductive polymer. Here, “having nitrogen” means not only when the molecular structure of the conductive polymer has an N atom, but also when adding a nitrogen source separately to the material. As described above, by containing nitrogen in the positive electrode material, the positive electrode material can more effectively adsorb acid generated in the electrolytic solution. On the other hand, the positive electrode preferably further has at least one (a) of polycarboxylic acid and polycarboxylic acid metal salt.

  In the present invention, the conductive polyaniline can be obtained by electrolytic polymerization of aniline in the presence of a protonic acid or chemical oxidative polymerization using an oxidizing agent in an appropriate solvent, as is well known. However, it can be preferably obtained by oxidative polymerization of aniline with an oxidizing agent in the presence of a protonic acid in an appropriate solvent. As the solvent, water is usually used, but a mixed solvent of a water-soluble organic solvent and water or a mixed solvent of water and a nonpolar organic solvent is also used. In this case, a surfactant or the like may be used in combination.

  For example, the oxidative polymerization of aniline using water as a solvent will be described in more detail. The chemical oxidative polymerization of aniline is performed in water using a chemical oxidant in the presence of a protonic acid. The chemical oxidant used may be either water-soluble or water-insoluble.

  Preferred examples of the oxidizing agent include ammonium peroxodisulfate, hydrogen peroxide, potassium dichromate, potassium permanganate, sodium chlorate, cerium ammonium nitrate, sodium iodate, and iron chloride.

  The amount of oxidant used for the oxidative polymerization of aniline is related to the yield of conductive polyaniline produced, and in order to quantitatively react the aniline used, the number of moles of aniline used (2.5 / n) It is preferable to use a double mole of oxidizing agent. However, n represents the number of electrons required when one molecule of the oxidizing agent itself is reduced. Therefore, for example, in the case of ammonium peroxodisulfate, n is 2 as understood from the following reaction formula.

(NH ₄ ) ₂ S ₂ O ₈ + 2e ⇒ 2NH ₄ ⁺ + 2SO ₄ ²⁻

  However, in order to suppress the polyaniline from becoming a peroxidized state, it is slightly less than (2.5 / n) times the number of moles of aniline to be used (2.5 / n). ) A ratio of 30 to 80% may be used with respect to the molar amount.

  In the production of the conductive polyaniline, the proton acid is doped with the produced polyaniline to make it conductive, and the aniline is salted in water and dissolved in water. The pH of the polymerization reaction system is preferably 1 or less. Used to maintain strong acidity. Accordingly, in the production of the conductive polyaniline, the amount of the protonic acid used is not particularly limited as long as the above object can be achieved, but usually 1.1 to 5 times the number of moles of aniline. Used in a range. However, when the amount of the protonic acid used is too large, the cost for waste liquid treatment is unnecessarily increased in the post-treatment of the aniline oxidative polymerization, so that it is preferably used in the range of 1.1 to 2 moles. It is done. Thus, as the protonic acid, one having strong acidity is preferable, and a protonic acid having an acid dissociation constant pKa value of less than 3.0 is preferably used.

  Examples of such protic acids having an acid dissociation constant pKa value of less than 3.0 include sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, tetrafluoroboric acid, hexafluorophosphoric acid, hydrofluoric acid, hydroiodic acid, and the like. Inorganic acids, aromatic sulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid, and aliphatic sulfonic acids (or alkanesulfonic acids) such as methanesulfonic acid and ethanesulfonic acid are preferably used. A polymer having a sulfonic acid group in the molecule, that is, a polymer sulfonic acid can also be used. Examples of such polymer sulfonic acids include polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, poly (acrylamide t-butyl sulfonic acid), phenol sulfonic acid novolak resin, and perfon represented by Nafion (registered trademark). A fluorosulfonic acid etc. can be mentioned. In the present invention, polyvinyl sulfate can also be used as a protonic acid.

  However, in addition to the above, for example, certain phenols such as picric acid, certain aromatic carboxylic acids such as m-nitrobenzoic acid, certain fats such as dichloroacetic acid, malonic acid, etc. Since the group carboxylic acid also has an acid dissociation constant pKa value of less than 3.0, it is used as a protonic acid in the production of conductive polyaniline.

  Among the various protic acids described above, tetrafluoroboric acid and hexafluorophosphoric acid are protonic acids containing the same anionic species as the base metal salt of the electrolyte salt of the nonaqueous electrolyte solution in the nonaqueous electrolyte secondary battery, For example, in the case of a lithium secondary battery, since it is a protonic acid containing the same anionic species as the lithium salt of the electrolyte salt of the non-aqueous electrolyte in the lithium secondary battery, it is preferably used.

  In addition, conductive polypyrrole can be obtained by using a suitable chemical oxidizing agent in an aqueous solution of pyrrole containing an organic sulfonate such as sodium alkylbenzene sulfonate such as sodium dodecylbenzene sulfonate or sodium anthraquinone sulfonate. Is obtained as a thin film on the anode by electrolytic oxidation polymerization of pyrrole using a stainless steel electrode in an aqueous solution of pyrrole containing sodium alkylbenzenesulfonate or organic sulfonate. be able to. In such a production method, sodium alkylbenzene sulfonate or organic sulfonate acts as an electrolyte, and the alkylbenzene sulfonate anion or organic sulfonate anion functions as a dopant for the generated polypyrrole to impart conductivity to polypyrrole. To do.

  In the present invention, as described above, the conductive polymer may be a polymer doped with a proton acid anion, and the polymer doped with the proton acid anion is dedoped as described above. It may be a polymer in a dedoped state obtained in this way. If necessary, the dedoped polymer may be further reduced.

  Examples of a method for dedoping a conductive polymer include a method of neutralizing a conductive polymer doped with a proton acid anion with an alkali. For example, the conductive polymer doped with protonic acid anions is neutralized with alkali to be dedoped, and the resulting depolymerization is performed. A method of reducing the doped polymer with a reducing agent can be mentioned.

  When the conductive polymer doped with the proton acid anion is neutralized with an alkali, for example, the conductive polymer is put into an alkaline aqueous solution such as an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or aqueous ammonia, What is necessary is just to stir under room temperature or under the heating of about 50-80 degreeC as needed. By conducting the alkali treatment under heating, the dedoping reaction of the conductive polymer can be promoted and dedoping can be performed in a short time.

  On the other hand, as described above, in order to reduce the dedoped polymer, the dedoped polymer is reduced to hydrazine monohydrate aqueous solution, phenylhydrazine / alcohol solution, sodium dithionite aqueous solution, sodium sulfite aqueous solution or the like. What is necessary is just to throw in in an agent solution and to stir under room temperature or the heating of about 50-80 degreeC as needed.

[About at least one of polycarboxylic acid and polycarboxylic acid metal salt (a)]
In the present invention, the polycarboxylic acid refers to a polymer having a carboxyl group in the molecule. As the polycarboxylic acid, for example, polyacrylic acid, polymethacrylic acid, polyvinylbenzoic acid, polyallylbenzoic acid, polymethallylbenzoic acid, polymaleic acid, polyfumaric acid, polyaspartic acid, and polyglutamic acid are preferably used. Acrylic acid and polymethacrylic acid are more preferably used. These may be used alone or in combination of two or more.

  Moreover, the said polycarboxylic acid metal salt says an alkali metal salt and an alkaline-earth metal salt, for example, These are used individually or in combination of 2 or more types. The alkali metal salt is preferably a lithium salt or a sodium salt, and the alkaline earth metal salt is preferably a magnesium salt or a calcium salt.

[About the external shape of the positive electrode]
The positive electrode according to the non-aqueous electrolyte secondary battery of the present invention is usually composed of a composite composed of the conductive polymer and the component (a), and is preferably formed into a porous sheet. Usually, the thickness of the positive electrode is preferably 1 to 500 μm, and more preferably 10 to 300 μm.

  The thickness of the positive electrode is obtained by measuring the positive electrode using a dial gauge (manufactured by Ozaki Mfg. Co., Ltd.) whose tip shape is a flat plate having a diameter of 5 mm, and obtaining the average of 10 measured values with respect to the surface of the electrode. . When a positive electrode (porous layer) is provided on the current collector and is composited, the thickness of the composite is measured in the same manner as described above, the average of the measured values is obtained, and the thickness of the current collector is subtracted. Thus, the thickness of the positive electrode can be obtained.

[Production of positive electrode]
The positive electrode according to the nonaqueous electrolyte secondary battery of the present invention is produced, for example, as follows. For example, the component (a) is dissolved or dispersed in water, and a conductive polymer powder and, if necessary, a conductive aid such as conductive carbon black are added thereto, and this is sufficiently dispersed. A paste having a solution viscosity of about 0.1 to 50 Pa · s is prepared. After coating this on the current collector, the positive electrode active material containing the conductive polymer, the component (a), and, if necessary, a conductive auxiliary agent on the current collector by evaporating water A sheet electrode can be obtained as a composite (porous sheet) having layers.

  The conductive auxiliary agent is excellent in conductivity, is effective for reducing electrical resistance between battery active materials, and is a conductive material whose properties do not change depending on the potential applied during battery discharge. desirable. Usually, conductive carbon black, for example, acetylene black, ketjen black and the like, and fibrous carbon materials such as carbon fiber and carbon nanotube are used.

  In the positive electrode forming material according to the nonaqueous electrolyte secondary battery of the present invention, the component (a) is usually 1 to 100 parts by weight, preferably 2 to 70 parts by weight with respect to 100 parts by weight of the conductive polymer. Parts, most preferably in the range of 5 to 40 parts by weight. That is, if the amount of the component (a) with respect to the conductive polymer is too small, a non-aqueous electrolyte secondary battery excellent in weight energy density tends not to be obtained. Conversely, the amount of the component (a) If there is too much, the weight of the positive electrode due to the increase in the weight of the member other than the positive electrode active material tends to make it impossible to obtain a non-aqueous electrolyte secondary battery with a high energy density when considering the weight of the entire battery. Because there is.

<About negative electrode>
The negative electrode according to the non-aqueous electrolyte secondary battery of the present invention is a known carbon that is made of a material containing a carbonaceous material that can insert and desorb ions and is used as a negative electrode active material of a lithium ion secondary battery. Quality material can be used. Specific examples include calcined bodies such as coke, pitch, phenol resin, polyimide, and cellulose, artificial graphite, and natural graphite. Among these, artificial graphite and natural graphite are preferable. These may be used alone or in combination of two or more.

  The carbonaceous material is preferably used as a main component of the negative electrode material. Here, the main component means a component indicating the majority of the whole, and includes the case where the whole consists of only the main component.

<Current collector>
Examples of the material for the current collector include metal foils such as nickel, aluminum, stainless steel, and copper, and meshes. Note that the positive electrode current collector and the negative electrode current collector may be formed of the same material or different materials.

<About electrolyte>
The electrolytic solution is obtained by dissolving a supporting salt (electrolyte) in a solvent. In the present invention, the supporting salt of the electrolytic solution contains a lithium salt having an ionic radius of 26 pm or more of the anion component, and the ratio of the specific lithium salt to the entire supporting salt is 80 to 100% by weight. Is preferred. That is, it is optimal from the viewpoint of stabilizing the capacity retention rate that is the effect of the present invention that all of the supporting salt is the specific lithium salt, but the ratio of the specific lithium salt is within the above range. This is because the effects are sufficiently recognized. In addition, the ionic radius of the anion component of the specific lithium salt in the present invention indicates the effective ionic radius of Shannon as described above.

  And the ionic radius of the anion component of the specific lithium salt is preferably in the range of 32 to 36 pm. That is, if the ionic radius of the anionic component is too small, stabilization of the capacity retention rate, which is the effect of the present invention, cannot be obtained. Conversely, if the ionic radius of the anionic component is too large, This is because the solubility of the supporting salt becomes poor.

  Specific examples of the specific lithium salt include lithium trifluoromethanesulfonate (LiTFS) (27.0 pm), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) (32.5 pm), lithium bis (pentafluoroethanesulfonyl). ) Imido (LiBETI) (36.2 pm or more). These may be used alone or in combination of two or more. In addition, the numerical value in said () shows the ion radius (an effective ion radius of Shannon) of the anion component in lithium salt.

  Here, in order to clarify the ionic radius of the anion component in the specific lithium salt, the chemical structural formula of lithium trifluoromethanesulfonate is shown in the following formula (1), and the chemical structural formula of lithium bis (trifluoromethanesulfonyl) imide is The chemical structural formula of lithium bis (pentafluoroethanesulfonyl) imide is shown in the following formula (3).

  On the other hand, the chemical structural formula of lithium hexafluorophosphate (25.4 pm), which is mentioned as a lithium salt having an ionic radius of an anion component of less than 26 pm, is shown in the following formula (4), and tetrafluoroboric acid The chemical structural formula of lithium (22.9 pm) is shown in the following formula (5). By comparing with the above formulas (1) to (3), it is clear that the ionic radii of formulas (4) and (5) are small.

  Next, as the solvent constituting the electrolytic solution, for example, at least one nonaqueous solvent such as carbonates, nitriles, amides, ethers, that is, an organic solvent is used. Specific examples of such an organic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, propionitrile, N, N'-dimethylacetamide, N-methyl-2- Examples include pyrrolidone, dimethoxyethane, diethoxyethane, and γ-butyrolactone. These may be used alone or in combination of two or more.

  The concentration of the specific lithium salt in the electrolytic solution is preferably in the range of 0.5 to 2 mol / L, more preferably in the range of 1 to 2 mol / L. That is, if the concentration of the specific lithium salt is too low, there is a problem in that the capacity retention rate, which is the effect of the present invention, is not stabilized, and a desired weight energy density cannot be obtained. This is because if the concentration of the lithium salt is too high, the viscosity of the electrolytic solution becomes too high, and a lot of time is required in the electrolytic solution injection process at the time of production, so that the production efficiency is lowered.

In addition, in the non-aqueous electrolyte secondary battery of the present invention, the ion radius of the anion component together with the specific lithium salt, if necessary, as long as the stability of the capacity maintenance rate that is the function and effect is not impaired. The present invention does not preclude the use of a slight amount of a lithium salt having a pH of less than 26 pm or a conventionally known supporting salt such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, etc.

  Further, when a separator is used in the non-aqueous electrolyte secondary battery of the present invention, the separator can prevent an electrical short circuit between the positive electrode and the negative electrode arranged to face each other, Any insulating porous sheet that is electrochemically stable, has a large ion permeability, and has a certain degree of mechanical strength may be used. Accordingly, for example, a porous film made of a resin such as paper, nonwoven fabric, polypropylene, polyethylene, or polyimide is preferably used, and these may be used alone or in combination of two or more.

<About the manufacturing method of a nonaqueous electrolyte secondary battery>
The method for producing a non-aqueous electrolyte secondary battery of the present invention using the above material comprises the following steps (I) to (III). Hereinafter, this manufacturing method will be described in detail.
(I) A step of preparing a positive electrode and a negative electrode, arranging a separator between the two, and producing a laminate composed of the positive electrode, the separator, and the negative electrode.
(II) A step of accommodating at least one of the laminates in a battery container.
(III) A step of injecting an electrolytic solution into the battery container.

  Specifically, lamination is performed so that a separator is disposed between the positive electrode and the negative electrode described above, thereby producing a laminate. Next, this laminate is placed in a battery container such as an aluminum laminate package and then dried in a vacuum. Next, an electrolytic solution is poured into the vacuum-dried battery container. Finally, the package that is the battery container is sealed to complete the nonaqueous electrolyte secondary battery of the present invention.

<About non-aqueous electrolyte secondary batteries>
The non-aqueous electrolyte secondary battery of the present invention is formed into various shapes such as a film type, a sheet type, a square type, a cylindrical type, and a button type in addition to the laminate cell.

  Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded.

  First, prior to the production of non-aqueous electrolyte secondary batteries as examples and comparative examples, the following materials and components were prepared, produced, and prepared.

[Preparation of Conductive Polymer 1]
As the conductive polymer 1, a conductive polyaniline powder having tetrafluoroboric acid as a dopant was prepared as follows.

  That is, first, 84.0 g (0.402 mol) of 42 wt% aqueous tetrafluoroboric acid solution (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade) was added to a glass beaker having a capacity of 138 g of ion-exchanged water. While stirring with a magnetic stirrer, 10.0 g (0.107 mol) of aniline was added thereto. When aniline was added to the tetrafluoroboric acid aqueous solution, the aniline was dispersed as oily droplets in the tetrafluoroboric acid aqueous solution, but then dissolved in water within a few minutes, and the uniform and transparent aniline aqueous solution. Became. The aniline aqueous solution thus obtained was cooled to −4 ° C. or lower using a low-temperature thermostatic bath.

  Next, 11.63 g (0.134 mol) of manganese dioxide powder (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade 1) as an oxidizing agent is added little by little to the aniline aqueous solution, and the temperature of the mixture in the beaker is −1. The temperature was not exceeded. Thus, by adding an oxidizing agent to the aniline aqueous solution, the aniline aqueous solution immediately turned black-green. Thereafter, when stirring was continued for a while, a black-green solid started to be formed.

  Thus, after adding an oxidizing agent over 80 minutes, it stirred for further 100 minutes, cooling the reaction mixture containing the produced | generated reaction product. Then, using a Buchner funnel and a suction bottle, the obtained solid was No. The powder was obtained by suction filtration with 2 filter papers. The powder was stirred and washed in an aqueous solution of about 2 mol / L tetrafluoroboric acid using a magnetic stirrer. Then, the mixture was washed with stirring several times with acetone and filtered under reduced pressure. The obtained powder was vacuum-dried at room temperature (25 ° C.) for 10 hours to obtain 12.5 g of conductive polyaniline (conductive polymer 1) having tetrafluoroboric acid as a dopant. The conductive polyaniline was a bright green powder.

(Conductivity of conductive polymer 1)
After pulverizing 130 mg of the above conductive polyaniline powder in a smoked mortar, vacuum pressure molding was performed for 10 minutes under a pressure of 75 MPa using a KBr tablet molding machine for infrared spectrum measurement, and conductive polyaniline having a diameter of 13 mm and a thickness of 720 μm. Got the disc. The conductivity of the disk measured by the 4-terminal method conductivity measurement by the Van der Pau method was 19.5 S / cm.

(Preparation of conductive polymer 1 in a dedope state)
The conductive polyaniline powder in the doped state obtained above is placed in a 2 mol / L aqueous sodium hydroxide solution and stirred in a 3 L separable flask for 30 minutes, and the tetrafluoroboric acid as a dopant is removed by a neutralization reaction. Doped. The dedoped polyaniline was washed with water until the filtrate became neutral, then stirred and washed in acetone, and filtered under reduced pressure using a Buchner funnel and a suction bottle to obtain a dedoped polyaniline powder on No. 2 filter paper. . This was vacuum-dried at room temperature for 10 hours to obtain a brown undoped polyaniline powder.

(Preparation of Conductive Polymer 1 in Reduced Dedoped State)
Next, this dedope polyaniline powder was put into a methanol solution of phenylhydrazine and subjected to reduction treatment for 30 minutes with stirring. The color of the polyaniline powder changed from brown to gray by reduction. After the reaction, it was washed with methanol, washed with acetone, filtered, and vacuum dried at room temperature to obtain polyaniline in a reduced and dedoped state.

(Conductivity of conductive polymer 1 in a reduced and dedoped state)
After pulverizing 130 mg of the above polyaniline powder in the reduced dedope state in a smoked mortar, vacuum reduced pressure molding was performed for 10 minutes under a pressure of 75 MPa using a KBr tablet molding machine for infrared spectrum measurement, and a reduced dedope having a thickness of 720 μm. A polyaniline disk in state was obtained. The electric conductivity of the disk measured by the 4-terminal conductivity measurement by the Van der Pau method was 5.8 × 10 ⁻³ S / cm. Thus, it can be said that the polyaniline compound is an active material compound whose conductivity is changed by ion insertion / extraction.

[Preparation of at least one of polycarboxylic acid and polycarboxylic acid metal salt (a)]
4.4 g of polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 1,000,000) was added to 95.6 g of ion-exchanged water, and allowed to stand overnight to swell. Then, it processed for 1 minute and melt | dissolved using the ultrasonic homogenizer, and 100 g of viscous polyacrylic acid aqueous solution with a 4.4 weight% density | concentration was obtained. Next, 0.73 g of lithium hydroxide powder is added to 100 g of the resulting polyacrylic acid aqueous solution so that half of the amount of carboxyl groups of polyacrylic acid is lithium-chlorinated, thereby preparing a polylithic acid half-lithium salt aqueous solution. And prepared.

[Production of positive electrode]
4 g of the prepared conductive polymer 1 powder in the reduced and dedope state and 0.5 g of conductive carbon black (Denka Black, Denki Kagaku Kogyo Co., Ltd.) powder were mixed, and then mixed with the 4.4 wt% poly In addition to 20.4 g of an aqueous solution of a half lithium salt of acrylic acid, the mixture was well kneaded with a spatula. This is subjected to ultrasonic treatment for 1 minute with an ultrasonic homogenizer, and then mildly dispersed by applying a high shear force using Fillmix 40-40 (manufactured by Primix) to produce a paste having fluidity. Obtained. This paste was further defoamed using a vacuum suction bell and a rotary pump.

  Using a tabletop automatic coating device (manufactured by Tester Sangyo Co., Ltd.), using a doctor blade type applicator with a micrometer, the solution coating thickness is adjusted to 360 μm, and the defoamed paste is applied at a coating speed of 10 mm / second. It apply | coated on the etching aluminum foil (The Hosen company make, 30CB) for electric double layer capacitors. Subsequently, after leaving at room temperature (25 degreeC) for 45 minutes, it dried on the hotplate with a temperature of 100 degreeC. Then, using a vacuum press (Kitagawa Seiki Co., Ltd., KVHC), sandwiched between 15 cm square stainless steel plates and pressed at a temperature of 140 ° C. and a pressure of 1.5 MPa for 5 minutes to 2.7 cm × 2.7 cm. By cutting, a porous polyaniline sheet electrode (positive electrode) was produced.

[Preparation of separator]
As the separator, a polypropylene porous membrane (Celgard 2400, manufactured by Celgard) having a thickness of 25 μm, a porosity of 38%, and an air permeability of 620 seconds / 100 cm ³ was cut into 3.5 cm × 3.5 cm.

[Preparation of negative electrode]
As the negative electrode containing a carbonaceous material, a negative electrode sheet (0.8 mAh / cm ² manufactured by Piotrek Co., Ltd.) containing natural spherical graphite as an active material was cut to 2.9 cm × 2.9 cm.

[Preparation of electrolyte solution i]
As an electrolytic solution i, lithium bis (pentafluoroethanesulfonyl) imide (LiBETI) (ionic radius of anionic component: 36.2 pm or more) is 1 mol / liter in a solvent containing ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1. A solution dissolved at a concentration of L was prepared.

[Preparation of electrolyte ii]
A concentration of 1 mol / L of lithium hexafluorophosphate (LiPF ₆ ) (ionic radius of anion component: 25.4 pm) in a solvent containing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 as the electrolytic solution ii What was dissolved in was prepared.

[Example 1]
<Production of laminate cell>
A laminate was assembled using a positive electrode, a negative electrode, and a separator. Specifically, the laminate was obtained such that two separators were disposed between the positive electrode and the negative electrode described above. After putting the laminate in an aluminum laminate package, it was vacuum dried at 80 ° C. for 2 hours in a vacuum dryer. Next, 0.3 mL of the prepared electrolytic solution i was injected into the vacuum-dried package. Finally, the package was sealed to obtain the nonaqueous electrolyte secondary battery of Example 1. In addition, the liquid injection to the package was performed in a glove box in an ultrahigh purity argon gas atmosphere. The dew point in the glove box was −90 ° C. or lower. In this way, a laminate cell (non-aqueous electrolyte secondary battery) was obtained.

[Comparative Example 1]
Instead of the electrolytic solution i, the prepared electrolytic solution ii was used. Other than that, a laminate cell (non-aqueous electrolyte secondary battery) was produced in the same manner as in Example 1 using the same materials as in Example 1.

  Regarding the non-aqueous electrolyte secondary batteries of Examples and Comparative Examples thus obtained, the capacity retention rate was measured according to the following criteria. The results are also shown in Table 1 below.

≪Measurement of capacity maintenance ratio≫
The nonaqueous electrolyte secondary battery is placed in a constant temperature bath at 25 ° C., and measurement is performed in a constant current / constant voltage charge / constant current discharge mode using a battery charge / discharge device (Hokuto Denko, SD8). It was. The end-of-charge voltage is 3.8V, and after the voltage reaches 3.8V by constant current charging, the constant voltage charging of 3.8V is set to 20% of the current value during constant current charging. The obtained capacity was defined as the charge capacity. Then, constant current discharge was performed to the discharge end voltage 2.0V, and these were made into 1 charge / discharge cycle.
In general, since it is considered that the charge capacity starts to stabilize after the 5th cycle of the charge / discharge cycle, the charge capacity at the 5th cycle is set as a reference (100%), and the charge capacity after the 5th cycle is the same. [Capacity maintenance rate (%)] was measured.

  The result of Table 1 is shown in the graph of FIG. As is apparent from Table 1 and the graph, it can be seen that the nonaqueous electrolyte secondary battery of Example 1 is stable with little decrease in capacity retention rate over time. On the other hand, the non-aqueous electrolyte secondary battery of Comparative Example 1 has a large capacity maintenance rate variation difference (vertical movement) for each cycle and is not stable. It can be seen that it is greatly reduced compared to 1.

  The nonaqueous electrolyte secondary battery of the present invention can be suitably used as a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery. The non-aqueous electrolyte secondary battery of the present invention can be used for the same applications as conventional secondary batteries. For example, portable electronic devices such as portable PCs, cellular phones, and personal digital assistants (PDAs), Widely used in driving power sources for hybrid electric vehicles, electric vehicles, fuel cell vehicles and the like.

Claims (7)

  A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte containing a supporting salt having ionic conductivity, wherein the positive electrode is conductive A non-aqueous solution comprising a polymer, wherein the negative electrode includes a carbonaceous material capable of inserting / extracting ions, and the supporting salt of the electrolytic solution includes a lithium salt having an ionic radius of 26 pm or more of the anionic component. Electrolyte secondary battery.   The lithium salt is at least one selected from the group consisting of lithium trifluoromethanesulfonate (LiTFS), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), and lithium bis (pentafluoroethanesulfonyl) imide (LiBETI). The nonaqueous electrolyte secondary battery according to claim 1.   The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the concentration of the lithium salt in the electrolyte is in the range of 0.5 to 2 mol / L.   The non-aqueous electrolyte 2 according to any one of claims 1 to 3, wherein the conductive polymer constituting the positive electrode is at least one selected from the group consisting of polyaniline, polyaniline derivatives, polypyrrole, and polypyrrole derivatives. Next battery. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the positive electrode further includes the following component (a).
(A) At least one of polycarboxylic acid and polycarboxylic acid metal salt.   The polycarboxylic acid of (a) was selected from the group consisting of polyacrylic acid, polymethacrylic acid, polyvinylbenzoic acid, polyallylbenzoic acid, polymethallylbenzoic acid, polymaleic acid, polyfumaric acid, polyaspartic acid, and polyglutamic acid. The nonaqueous electrolyte secondary battery according to claim 5, wherein the number is at least one. A method for producing a nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, comprising the following steps (I) to (III): Battery manufacturing method.
(I) A step of preparing a positive electrode and a negative electrode, arranging a separator between the two, and producing a laminate composed of the positive electrode, the separator, and the negative electrode.
(II) A step of accommodating at least one of the laminates in a battery container.
(III) A step of injecting an electrolytic solution into the battery container.

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