JP2013251068A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with enhanced output characteristics without largely reducing the energy density.SOLUTION: The nonaqueous electrolyte secondary battery includes: a positive electrode 10 containing a first active material capable of occluding and emitting anions; a negative electrode 20; and an electrolyte containing salt of cation and the anions, where the anions is [(FSO)N].

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, portable electronic devices such as portable audio devices, cellular phones, and laptop computers have become widespread. In addition, hybrid vehicles using an internal combustion engine and an electric driving force in combination are beginning to spread from the viewpoint of energy saving or the reduction of carbon dioxide emissions. With these popularizations, there is an increasing demand for higher performance of power storage devices used as power sources. In particular, research and development on non-aqueous electrolyte secondary batteries represented by lithium secondary batteries has been actively conducted, and while maintaining the high energy density that is characteristic of lithium secondary batteries, output characteristics, especially instantaneous There is a demand for improving the pulse discharge characteristic, which is a large current characteristic.

For example, it has been proposed to use, as an electrode active material, an organic compound that can reversibly cause a redox reaction. The specific gravity of the organic compound is about 1 g / cm ³ , and is lighter than inorganic oxides such as lithium cobaltate that have been conventionally used as an electrode active material. Therefore, by using an organic compound as the electrode active material, an electricity storage device having a high weight energy density can be obtained. If an organic compound that does not contain heavy metals is used as the electrode active material, it is possible to reduce risks such as depletion of rare metal resources, fluctuations in resource prices, and environmental pollution due to leakage of heavy metals.

  As a specific attempt, in a coin-type secondary battery including a non-aqueous electrolyte, it has been proposed to use a polymer having a tetrathiafulvalene skeleton on the main chain as a positive electrode active material and lithium ions as a counter ion. (Patent Document 1). A polymer having a tetrathiafulvalene skeleton on the main chain may have a reaction mechanism in which an anion coordinates as a counter ion during the charge reaction (an anion is occluded), and the anion is released by a discharge reaction to return to a neutral state. It is disclosed. An electrode that performs a stable and reversible charge / discharge reaction using this reaction mechanism has been proposed.

Patent Document 2 discloses an ionic conductive material in which an ionic compound represented by the formula Li ⁺ [(FSO ₂ ) ₂ N] ⁻ is contained in a solution of an aprotic solvent. The anion ([(FSO ₂ ) ₂ N] ⁻ ) exhibits wide stability against redox phenomena, and its conductivity in an aprotic solvent, solvated polymer or mixture thereof is bistrifluoromethanesulfonyl. It is disclosed that it is comparable to or higher than the conductivity of an imide (hereinafter sometimes abbreviated as “TFSI”) anion derivative.

Japanese Patent No. 4558835 Japanese Patent No. 3878206

As described above, efforts have been made to use a polymer having a tetrathiafulvalene skeleton in the main chain as a positive electrode active material as a positive electrode including a positive electrode active material capable of occluding and releasing anions. However, when such a positive electrode active material is used, knowledge about an optimal anion species that improves output characteristics has been insufficient. Further, it has been known that an anion represented by [F (SO ₂ ) ₂ N] ⁻ (hereinafter sometimes referred to as “FSI anion”) exhibits better conductivity than a TFSI anion. Knowledge about the behavior of the FSI anion with respect to the reduction reaction rate was insufficient.

  The present invention has been made in view of these problems, and an object thereof is to provide a nonaqueous electrolyte secondary battery having improved output characteristics without greatly reducing the energy density.

The present invention
A positive electrode comprising a first active material capable of occluding and releasing anions;
A negative electrode,
An electrolyte containing a salt of a cation and the anion;
With
The anion is [(FSO ₂ ) ₂ N] ⁻ ;
A non-aqueous electrolyte secondary battery is provided.

  According to the nonaqueous electrolyte secondary battery of the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having improved output characteristics without greatly reducing the energy density.

It is typical sectional drawing which shows the coin-type battery which is one Embodiment of the nonaqueous electrolyte secondary battery by this invention.

The first aspect of the present invention is:
A positive electrode comprising a first active material capable of occluding and releasing anions;
A negative electrode,
An electrolyte containing a salt of a cation and the anion;
With
The anion is [(FSO ₂ ) ₂ N] ⁻ ;
A non-aqueous electrolyte secondary battery is provided.

In the nonaqueous electrolyte secondary battery according to the first aspect, a positive electrode including a first active material capable of reversibly occluding and releasing anions, and an anion represented by [(FSO ₂ ) ₂ N] ⁻ An electrolyte containing a salt with a cation is used. By the combination of the positive electrode and the electrolyte, the non-aqueous electrolyte secondary battery according to the first aspect can ensure a sufficient energy density. Further, the combination of the positive electrode and the electrolyte can reduce the oxidation-reduction reaction resistance, which contributes to the improvement of the discharge rate characteristic and the pulse discharge characteristic. Thus, according to the first aspect of the present invention, it is possible to provide a nonaqueous electrolyte secondary battery with improved output characteristics without greatly reducing the energy density.

  According to a second aspect of the present invention, in the first aspect, the first active material capable of occluding and releasing the anion is a non-aqueous polymer containing a tetrachalcogenofulvalene skeleton in the main chain. An electrolyte secondary battery is provided. A polymer containing a tetrachalcogenofulvalene skeleton in a repeating unit can contribute to high output, particularly excellent pulse discharge characteristics. By including the tetrachalcogenofulvalene skeleton in the main chain of the polymer, the site where the oxidation-reduction reaction occurs without degrading the reversible oxidation-reduction characteristics of the tetrachalcogenofulvalene, the polymer can be polymerized. Contribute. Therefore, it is possible to form a polymer structure in which a portion where no oxidation-reduction reaction is performed is made as small as possible. Thereby, according to the 2nd aspect of this invention, the nonaqueous electrolyte secondary battery which improved the output characteristic can be provided more reliably, without reducing an energy density largely.

  According to a third aspect of the present invention, in the first aspect or the second aspect, the first active material capable of occluding and releasing the anion has a tetrachalcogenofulvalene skeleton in a side chain of the polymer. A non-aqueous electrolyte secondary battery is provided. A polymer containing a tetrachalcogenofulvalene skeleton in a repeating unit can contribute to high output, particularly excellent pulse discharge characteristics. Even when the tetrachalcogenofulvalene skeleton is contained in the side chain of the polymer, the reversible redox property of the tetrachalcogenofulvalene is not impaired. Thereby, according to the 3rd aspect of this invention, the nonaqueous electrolyte secondary battery which improved the output characteristic can be provided more reliably, without reducing an energy density largely.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the positive electrode further includes a second active material capable of occluding and releasing lithium ions. Provide the next battery. Since the positive electrode further includes the second active material, the material characteristics of the second active material are exhibited, so that a high capacity can be realized.

  A fifth aspect of the present invention provides a nonaqueous electrolyte secondary battery according to the fourth aspect, wherein the second active material is a transition metal oxide or a lithium-containing transition metal oxide.

A sixth aspect of the present invention provides the nonaqueous electrolyte secondary battery according to the fifth aspect, wherein the transition metal oxide is V ₂ O ₅ .

  Hereinafter, embodiments of the nonaqueous electrolyte secondary battery of the present invention will be described. FIG. 1 shows a schematic cross section of a coin-type electricity storage device 1 which is an embodiment of a nonaqueous electrolyte secondary battery according to the present invention. The electricity storage device 1 has a structure in which the inside is sealed by a coin-type case 50, a sealing plate 51, and a gasket 52. The electricity storage device 1 contains a positive electrode 10 including a positive electrode active material layer 11 and a positive electrode current collector 12, a negative electrode 20 including a negative electrode active material layer 21 and a negative electrode current collector 22, and a separator 30. . The positive electrode 10 and the negative electrode 20 are opposed to each other with the separator 30 in between, and the positive electrode active material layer 11 and the negative electrode active material layer 21 are disposed in contact with the separator 30. An electrode group including the positive electrode 10, the negative electrode 20, and the separator 30 is impregnated with an electrolytic solution 31. In the present embodiment, a lithium secondary battery will be described as an example of a nonaqueous electrolyte secondary battery.

  The positive electrode active material layer 11 includes at least an organic active material (first active material) that can occlude and release FSI anions as a positive electrode active material.

  As an organic active material that can occlude and release FSI anions, a polymer containing a tetrachalcogenofulvalene skeleton in a repeating unit, which will be described in detail later, can be used.

式（１）中、Ｘ¹、Ｘ²、Ｘ³、およびＸ⁴は、互いに独立して、硫黄原子、酸素原子、セレン原子、またはテルル原子である。Ｒａ、Ｒｂ、Ｒｃ、およびＲｄから選ばれる１つまたは２つは、重合体の主鎖または側鎖の他の部分と結合するための結合手である。Ｒａ、Ｒｂ、Ｒｃ、およびＲｄから選ばれる、残りの３つまたは２つは、互いに独立して、鎖状の脂肪族基、環状の脂肪族基、水素原子、ヒドロキシル基、シアノ基、アミノ基、ニトロ基、ニトロソ基、またはアルキオチオ基である。鎖状の脂肪族基および環状の脂肪族基は、それぞれ、酸素原子、窒素原子、硫黄原子、ケイ素原子、リン原子、ホウ素原子よりなる群から選ばれる少なくとも１種を含んでいてもよい。ＲａとＲｂとは、互いに結合して環を形成していてもよく、また、ＲｃとＲｄとは、互いに結合して環を形成していてもよ
い。 Hereinafter, the polymer containing the tetrachalcogenofulvalene skeleton in the repeating unit will be described in detail. In the polymer, a portion having a tetrachalcogenofulvalene skeleton has a π-conjugated electron cloud and functions as a redox site. The structure of the part is represented by, for example, the following formula (1).

In the formula (1), X ¹ , X ² , X ³ , and X ⁴ are each independently a sulfur atom, an oxygen atom, a selenium atom, or a tellurium atom. One or two selected from Ra, Rb, Rc, and Rd is a bond for bonding to the other part of the main chain or side chain of the polymer. The remaining three or two selected from Ra, Rb, Rc, and Rd are each independently a chained aliphatic group, cyclic aliphatic group, hydrogen atom, hydroxyl group, cyano group, amino group , A nitro group, a nitroso group, or an alkiothio group. Each of the chain-like aliphatic group and the cyclic aliphatic group may contain at least one selected from the group consisting of an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, a phosphorus atom, and a boron atom. Ra and Rb may be bonded to each other to form a ring, and Rc and Rd may be bonded to each other to form a ring.

In the formula (1), a compound in which X ¹ , X ² , X ³ , and X ⁴ are sulfur atoms, and Ra, Rb, Rc, and Rd are hydrogen atoms is a tetrathiafur represented by the following formula (2) Valene (hereinafter sometimes abbreviated as “TTF”). Hereinafter, taking TTF as an example, a mechanism in which a portion having a tetrachalcogenofulvalene skeleton functions as a redox site and reacts with an anion in an electrolyte will be described.

When TTF is subjected to one-electron oxidation in a state of being dissolved in an electrolytic solution, as shown in the following formula (3), one electron is extracted from one of the two five-membered rings, and a positive 1 Charged to the valence. As a result, one FSI anion ([(FSO ₂ ) ₂ N] ⁻ ) is coordinated to the tetrathiafulvalene skeleton as a counter ion. When one-electron oxidation is further performed from this state, one electron is extracted from the other five-membered ring and is charged to be positively divalent. As a result, another FSI anion ([(FSO ₂ ) ₂ N] ⁻ ) is coordinated to the tetrathiafulvalene skeleton as a counter ion.

  Even in the oxidized state, the cyclic skeleton is stable, and by receiving electrons again, the cyclic skeleton can be reduced to return to an electrically neutral original state. In other words, the oxidation-reduction reaction exemplified in the above formula (3) is reversible. The non-aqueous electrolyte secondary battery of this embodiment can utilize such redox characteristics of the tetrathiafulvalene skeleton.

  For example, when TTF is used for the positive electrode 10 of the electricity storage device 1, the tetrathiafulvalene skeleton moves toward an electrically neutral state in the discharging process. In other words, the reaction in the left direction proceeds in Equation (3). On the contrary, in the charging process, the tetrathiafulvalene skeleton proceeds to a positively charged state, that is, the reaction in the right direction proceeds in Formula (3).

In the formula (1), X ¹ , X ² , X ³ , and X ⁴ are each independently a sulfur atom, a selenium atom, a tellurium atom, or an oxygen atom, and Ra, Rb, Rc, and Rd are hydrogen Compounds that are atoms are collectively referred to as tetrachalcogenofulvalene or its oxygen-containing analogs. These compounds have redox properties similar to TTF. For example, TTF Chemistry: Fundamentals and Applications of Tetrathiafulvalene, Journal of the American Chemical Society, 97th Edition. , Part 10, 1975, p. 2921-2922, and Chemical Communications, 1997, p. 1925-1926.

  In addition, a compound in which a functional group is bonded to a tetrachalcogenofulvalene skeleton, that is, a compound in which Ra, Rb, Rc, and Rd in the formula (1) have various structures is the same redox as tetrachalcogenofulvalene. Has characteristics. This has been reported, for example, in TTF Chemistry: Fundamentals and Applications of Tetrathiafulvalene, along with methods for synthesizing these compounds. Thus, an important structure for obtaining good redox characteristics is the structure of the tetrachalcogenofulvalene skeleton itself. Accordingly, Ra, Rb, Rc, and Rd in the formula (1) are not particularly limited as long as they are structures that do not contribute to the oxidation-reduction of the tetrachalcogenofulvalene skeleton.

  The organic active material that can be used in the present embodiment is, for example, a polymer including a tetrachalcogenofulvalene skeleton as exemplified in Formula (1) in a repeating unit. A molecule including a tetrachalcogenofulvalene skeleton has a lower solubility in an organic solvent as the molecular weight is increased. Therefore, when an organic solvent is contained in the electrolytic solution, the polymer containing the tetrachalcogenofulvalene skeleton is used as the first active material, thereby suppressing dissolution of the first active material in the electrolytic solution, Deterioration of characteristics can be suppressed.

  It is desirable that the polymer has a large molecular weight. Specifically, it is desirable to have four or more tetrachalcogenofulvalene skeletons represented by the formula (1) in one molecule. That is, the degree of polymerization of the polymer (n in formula (4) described later or the sum of n and m in formula (6) described later) is preferably 4 or more. Thereby, an organic active material that is hardly soluble in an organic solvent can be realized. More desirably, the degree of polymerization of the polymer is 10 or more, and more desirably 20 or more. The upper limit of the polymerization degree of the polymer is not particularly limited. From the viewpoint of production cost, yield, etc., the degree of polymerization of the polymer is, for example, 300 or less, and desirably 150 or less.

式（４）中、Ｘは酸素原子、硫黄原子、セレン原子、またはテルル原子である。Ｒ⁵およびＲ⁶は、互いに独立して、鎖状飽和炭化水素基、鎖状不飽和炭化水素基、環状飽和炭化水素基、環状不飽和炭化水素基、フェニル基、水素原子、ヒドロキシル基、シアノ基、アミノ基、ニトロ基、またはニトロソ基である。鎖状飽和炭化水素基、鎖状不飽和炭化水素基、環状飽和炭化水素基、および環状不飽和炭化水素基は、それぞれ、酸素原子、窒素原子、硫黄原子、およびケイ素原子からなる群から選ばれる少なくとも１種を含んでいてもよい。Ｒ⁹は、リンカーを表し、典型的にはアセチレン骨格およびチオフェン骨格の少なくとも１種を含む、鎖状不飽和炭化水素基または環状不飽和炭化水素基であり、酸素原子、窒素原子、硫黄原子、およびケイ素原子からなる群から選ばれる少なくとも１種を含んでいてもよい。ｎは、モノマー単位の繰り返し数を表わす整数である。 The tetrachalcogenofulvalene skeleton may be contained in the main chain of the polymer, may be contained in the side chain, or may be contained in both the main chain and the side chain. . When the polymer contains a tetrachalcogenofulvalene skeleton in the main chain, the structure of the polymer is represented, for example, by the following formula (4).

In formula (4), X is an oxygen atom, a sulfur atom, a selenium atom, or a tellurium atom. R ⁵ and R ⁶ are each independently a chain saturated hydrocarbon group, a chain unsaturated hydrocarbon group, a cyclic saturated hydrocarbon group, a cyclic unsaturated hydrocarbon group, a phenyl group, a hydrogen atom, a hydroxyl group, cyano Group, amino group, nitro group, or nitroso group. The chain saturated hydrocarbon group, the chain unsaturated hydrocarbon group, the cyclic saturated hydrocarbon group, and the cyclic unsaturated hydrocarbon group are each selected from the group consisting of an oxygen atom, a nitrogen atom, a sulfur atom, and a silicon atom. At least one kind may be included. R ⁹ represents a linker, and is typically a chain unsaturated hydrocarbon group or a cyclic unsaturated hydrocarbon group containing at least one of an acetylene skeleton and a thiophene skeleton, and includes an oxygen atom, a nitrogen atom, a sulfur atom, And at least one selected from the group consisting of silicon atoms. n is an integer representing the number of repeating monomer units.

Formula (4) is an alternating copolymer in which repeating units including a tetrachalcogenofulvalene skeleton and repeating units not including a tetrachalcogenofulvalene skeleton (R ⁹ in Formula (4)) are alternately arranged. However, the order of the coupling is not particularly limited. That is, a polymer having a repeating unit containing a tetrachalcogenofulvalene skeleton and a repeating unit not containing a tetrachalcogenofulvalene skeleton in the main chain includes a block copolymer, an alternating copolymer, and a random copolymer. Any of copolymers may be used. In the case of a block copolymer, a unit in which repeating units including a tetrachalcogenofulvalene skeleton are directly bonded continuously and a unit in which repeating units not including a tetrachalcogenofulvalene skeleton are continuously bonded alternately It has an ordered structure. In addition, the random copolymer has a structure in which repeating units including a tetrachalcogenofulvalene skeleton and repeating units not including a tetrachalcogenofulvalene skeleton are randomly arranged.

For example, a polymer in which X in formula (4) is a sulfur atom, R ⁵ and R ⁶ are phenyl groups, and R ⁹ is a diethynylbenzene group is represented by the structural formula shown in formula (5). It is a polymer. The polymer represented by the formula (5) is an alternating copolymer of 4,4′-diphenyltetrathiafulvalene and 1,3-diethynylbenzene. N in the formula (5) is an integer representing the number of repeating monomer units.

ただし、式（６）中、Ｒ¹⁰およびＲ¹²は、重合体の主鎖を構成する３価の基であり、互いに独立して、炭素原子、酸素原子、窒素原子および硫黄原子からなる群から選ばれる少なくとも１つと、炭素数１〜１０の飽和脂肪族基および炭素数２〜１０の不飽和脂肪族基からなる群から選ばれる少なくとも１つの置換基または少なくとも１つの水素原子とを含む。Ｌ¹は、Ｒ¹²と結合した、エステル基、エーテル基、カルボニル基、シアノ基、ニトロ基、ニトロキシル基、アルキル基、フェニル基、アルキルチオ基、スルホン基、またはスルホキシド基を含む１価の基である。Ｒ¹¹は、Ｒ¹⁰およびＭ¹と結合した２価の基であり、炭素数１〜４の置換基を有していてもよい、アルキレン、アルケニレン、アリーレン、エステル、アミド、およびエーテルからなる群から選ばれる少なくとも１種を含む。Ｍ¹は、Ｒ¹¹と結合した、式（１）で表すことのできる１価の基である。ｎおよびｍは、各モノマー単位の繰り返し数を表わす整数である。 When the polymer contains a tetrachalcogenofulvalene skeleton in the side chain, the structure of the polymer is represented, for example, by a structure in which two repeating units are bonded to each other in * as shown in the following formula (6). As in the above description, the order in which two repeating units are combined is not particularly limited.

However, in formula (6), R ¹⁰ and R ¹² are trivalent groups constituting the main chain of the polymer, and are independently of each other from the group consisting of carbon atom, oxygen atom, nitrogen atom and sulfur atom. And at least one selected from at least one substituent selected from the group consisting of a saturated aliphatic group having 1 to 10 carbon atoms and an unsaturated aliphatic group having 2 to 10 carbon atoms, or at least one hydrogen atom. L ¹ is a monovalent group including an ester group, an ether group, a carbonyl group, a cyano group, a nitro group, a nitroxyl group, an alkyl group, a phenyl group, an alkylthio group, a sulfone group, or a sulfoxide group bonded to R ^12. is there. R ¹¹ is a divalent group bonded to R ¹⁰ and M ^1, and a group consisting of alkylene, alkenylene, arylene, ester, amide, and ether, which may have a substituent having 1 to 4 carbon atoms. It contains at least one selected from M ¹ is a monovalent group that can be represented by the formula (1) bonded to R ¹¹ . n and m are integers representing the number of repetitions of each monomer unit.

式（７）中、Ｒ²¹は、２価の基であり、置換基を有していてもよい炭素数１〜４のアルキレン；置換基を有していてもよい炭素数１〜４のアルケニレン；置換基を有していてもよいアリーレン；エステル；アミド；およびエーテルからなる群から選ばれる少なくとも１種を含む。Ｒ²⁰およびＲ²²は、互いに独立して、炭素数１〜４の飽和脂肪族基、フェニル基、または水素原子である。Ｒ²⁵、Ｒ²⁶、およびＲ²⁷は、互いに独立して、鎖状の脂肪族基、環状の脂肪族基、水素原子、ヒドロキシル基、シアノ基、アミノ基、ニトロ基、ニトロソ基、またはアルキオチオ基であり、Ｒ²⁵とＲ²⁶とは互いに結合して環を形成していてもよい。Ｌ¹は、エステル基、エーテル基、カルボニル基、シアノ基、ニトロ基、ニトロキシル基、アルキル基、フェニル基、アルキルチオ基、スルホン基、またはスルホキシド基を含む１価の基である。ｎおよびｍは、各モノマー単位の繰り返し数を表わす整数である。 For example, when X is a sulfur atom, a polymer having a structure represented by the following formula (7) is exemplified.

In formula (7), R ²¹ is a divalent group, optionally having 1 to 4 carbon atoms which may have a substituent; alkenylene having 1 to 4 carbon atoms which may have a substituent. An arylene which may have a substituent; an ester; an amide; and at least one selected from the group consisting of ethers. R ²⁰ and R ²² are each independently a saturated aliphatic group having 1 to 4 carbon atoms, a phenyl group, or a hydrogen atom. R ²⁵ , R ²⁶ , and R ²⁷ are each independently a chain aliphatic group, cyclic aliphatic group, hydrogen atom, hydroxyl group, cyano group, amino group, nitro group, nitroso group, or alkylothio group R ²⁵ and R ²⁶ may be bonded to each other to form a ring. L ¹ is a monovalent group including an ester group, an ether group, a carbonyl group, a cyano group, a nitro group, a nitroxyl group, an alkyl group, a phenyl group, an alkylthio group, a sulfone group, or a sulfoxide group. n and m are integers representing the number of repetitions of each monomer unit.

For example, L ¹ in formula (7) is a monovalent group containing an ester group, R ²¹ is a divalent ester group, R ²⁰ and R ²² are methyl groups, R ²⁵ , R ²⁶ , and The polymer in which R ²⁷ is a hydrogen atom has a structure represented by the following formula (8). In formula (8), n and m are integers representing the number of repetitions of each monomer unit.

The positive electrode active material layer 11 may further include a positive electrode active material capable of inserting and extracting lithium ions as the second active material. A well-known thing can be used for a 2nd active material as a positive electrode active material of a lithium ion battery. Specifically, a transition metal oxide which may contain lithium can be used. In other words, a transition metal oxide, a lithium-containing transition metal oxide, or the like can be used. Specifically, an oxide of cobalt, an oxide of nickel, an oxide of manganese, an oxide of vanadium represented by vanadium pentoxide (V ₂ O ₅ ), and a mixture or composite oxide thereof Is used as the second active material. A composite oxide containing lithium and a transition metal, such as lithium cobaltate (LiCoO ₂ ), is best known as a positive electrode active material. Further, transition metal silicates, transition metal phosphates typified by lithium iron phosphate (LiFePO ₄ ), and the like can also be used.

  When two or more positive electrode active materials are mixed, that is, when a second active material is included, it is desirable to use an active material having an overlapping potential region with the first active material as the second active material. By overlapping the potential regions of the first active material and the second active material, the output characteristics of the positive electrode as a whole can be improved. For example, a polymer containing a tetrachalcogenofulvalene skeleton that can be used as the first active material in a repeating unit can occlude and release anions at about 3 to 4 V with respect to lithium. Therefore, for example, when this polymer is used as the first active material, the lower limit of the potential range capable of inserting and extracting lithium ions as the second active material is preferably 2.5 V or more, more preferably 3 V or more. A positive electrode active material having an upper limit of the potential range of preferably 4.3 V or less, more preferably 4 V or less is preferably used.

Specifically, the following materials are more preferable as the positive electrode active material capable of inserting and extracting lithium ions. Among the transition metal oxides, manganese oxide and vanadium oxide typified by vanadium pentoxide (V ₂ O ₅ ) are more desirable. Of the transition metal silicates and transition metal phosphates, lithium iron phosphate (LiFePO ₄ ) is more desirable. Vanadium pentoxide (V ₂ O ₅ ) has a reduction potential of 3.4 V to 3.2 V based on lithium. Lithium iron phosphate (LiFePO ₄ ) has a reduction potential around 3.4 V on the basis of lithium. Lithium manganese phosphate and lithium cobaltate have a reduction potential around 4.1 V on the basis of lithium. Lithium manganate and lithium nickelate have a reduction potential around 4.0 V on the basis of lithium. Lithium nickel manganese cobalt composite oxide (LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ) has a reduction potential in the vicinity of 3.7 V on the basis of lithium.

  The positive electrode active material layer 11 may further include a conductive auxiliary agent for assisting electronic conductivity in the electrode and / or a binder for maintaining the shape of the positive electrode active material layer 11 as necessary. . Examples of the conductive assistant include carbon materials such as carbon black, graphite, and carbon fiber, metal fibers, metal powders, conductive whiskers, and conductive metal oxides, and a mixture thereof may be used. . The binder may be either a thermoplastic resin or a thermosetting resin. The binder is, for example, a polyolefin resin typified by polyethylene and polypropylene; a fluororesin typified by polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), and their co-polymerization Combined resin: styrene butadiene rubber, polyacrylic acid and copolymer resin thereof, etc., and a mixture thereof may be used.

  As the positive electrode current collector 12, a known material can be used as the positive electrode current collector of the non-aqueous electrolyte secondary battery. The positive electrode current collector 12 is, for example, a metal foil or a metal mesh made of a metal such as aluminum, carbon, or stainless steel. When a metal foil or a metal mesh is used as the positive electrode current collector 12, good electrical contact can be maintained by welding the positive electrode current collector 12 to the case 50. When the positive electrode active material layer 11 maintains a self-supporting shape such as a pellet and a film, a configuration in which the positive electrode active material layer 11 is directly in contact with the case 50 without using the positive electrode current collector 12 is adopted. May be.

  The negative electrode active material layer 21 includes a negative electrode active material. As the negative electrode active material, a known negative electrode active material capable of reversibly occluding and releasing lithium ions is used. The negative electrode active material includes, for example, graphite materials represented by natural graphite and artificial graphite, amorphous carbon material, lithium metal, lithium-aluminum alloy, lithium-containing composite nitride, lithium-containing titanium oxide, silicon and silicon. An alloy, silicon oxide, tin, an alloy containing tin, tin oxide, and the like may be used. As the negative electrode current collector 22, a known material can be used as the negative electrode current collector of the nonaqueous electrolyte secondary battery. The negative electrode current collector 22 is a metal foil or mesh made of a metal such as copper, nickel, or stainless steel, for example. When the negative electrode active material layer 21 maintains a self-supporting shape such as a pellet and a film, the negative electrode active material layer 21 is directly brought into contact with the sealing plate 51 without using the negative electrode current collector 22. It may be adopted.

  In addition to the negative electrode active material, the negative electrode active material layer 21 may contain a conductive additive and / or a binder as necessary. As a conductive support agent and a binder, the same material as the conductive support agent and binder which can be used in the positive electrode active material layer 11 can be used.

  The separator 30 is a resin layer made of a resin that does not have electronic conductivity, and is a microporous film that has a large ion permeability, a predetermined mechanical strength, and electrical insulation. From the viewpoint of excellent organic solvent resistance and hydrophobicity, it is desirable that the separator 30 be polypropylene, polyethylene, or a polyolefin resin that combines these. Instead of the separator 30, a resin layer having an ionic conductivity that swells and contains an electrolyte and functions as a gel electrolyte may be provided.

The electrolytic solution 31 includes Li ⁺ [(FSO ₂ ) ₂ N] ⁻ , which is a salt of a cation (lithium ion in the present embodiment) and an anion ([(FSO ₂ ) ₂ N] ^{− in the} present embodiment). Contains electrolyte. The electrolytic solution 31 may further contain a salt that can be used in a lithium battery in addition to Li ⁺ [(FSO ₂ ) ₂ N] ⁻ . Examples of the salt that can be added in addition to Li ⁺ [(FSO ₂ ) ₂ N] ⁻ include salts of lithium ions and the following anions. That is, as anions, halide anions, perchlorate anions, trifluoromethanesulfonate anions, tetrafluoroborate anions (BF ₄ ⁻ ), hexafluorophosphate anions (PF ₆ ⁻ ), bis (trifluoromethanesulfonyl) ) Imide anion, bis (perfluoroethylsulfonyl) imide anion, and the like. Two or more of these may be used in combination as a salt of lithium ions and anions.

  As the solvent for dissolving the electrolyte, a known nonaqueous solvent that can be used in a nonaqueous secondary battery or a nonaqueous electric double layer capacitor can be used. As a specific non-aqueous solvent, a solvent containing a cyclic carbonate can be suitably used. This is because cyclic carbonates have a very high dielectric constant, as typified by ethylene carbonate and propylene carbonate. Among the cyclic carbonates, propylene carbonate is desirable. This is because propylene carbonate has a freezing point of −49 ° C., which is lower than that of ethylene carbonate, so that the electricity storage device can be operated even at a low temperature.

  Moreover, as the non-aqueous solvent, a solvent containing a cyclic ester can also be suitably used. This is because the cyclic ester has a very high dielectric constant as represented by γ-butyrolactone.

  By including these solvents as components of the nonaqueous solvent, the entire nonaqueous solvent in the electrolytic solution 31 can have a very high dielectric constant. As the non-aqueous solvent, only one of these solvents may be used, or two or more may be mixed and used. In addition to the components listed above, examples of the non-aqueous solvent include a chain carbonate ester, a chain ester, and a cyclic or chain ether. Specific examples include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dioxolane, sulfolane and the like.

  The reason why the nonaqueous electrolyte secondary battery of this embodiment can achieve high output (excellent pulse discharge characteristics) is as follows.

The positive electrode includes at least an organic active material capable of inserting and extracting an anion represented by [(FSO ₂ ) ₂ N] ⁻ as an active material. This organic active material is, for example, a polymer containing the above-described tetrachalcogenofulvalene skeleton in a repeating unit. A polymer containing a tetrachalcogenofulvalene skeleton in a repeating unit is suitable as an active material for a positive electrode because the oxidation-reduction reaction proceeds at a potential of about 3 to 4 V with respect to lithium. When high output is required, that is, when charging / discharging is performed at a relatively high speed, the anion in the electrolyte moves at a high speed, and the anion moves (diffuses) in the vicinity of the active material in the positive electrode. There is a need. In addition, the redox reaction of the tetrachalcogenofulvalene skeleton needs to be fast. The oxidation rate of the tetrachalcogenofulvalene skeleton is governed by the oxidation rate of the tetrachalcogenofulvalene skeleton and the formation rate and stability of the ion pair formed by the tetrachalcogenofulvalene skeleton and the anion. It is guessed. In this embodiment, the anion in the electrolytic solution is an FSI anion. In this case, the oxidant becomes an ion pair formed by the tetrachalcogenofulvalene skeleton and the FSI anion. Since this ion pair formation is a stable and relatively fast reaction, a high-speed oxidation reaction can be realized. The reduction reaction is the reverse reaction.

  For the above reasons, the nonaqueous electrolyte secondary battery of this embodiment has a high capacity and a high output (excellent pulse discharge characteristics). That is, according to the above embodiment, a highly reliable non-aqueous electrolyte secondary battery in which high capacity and high output (excellent pulse discharge characteristics) are compatible can be provided.

  Conventionally, in a cylindrical battery and a square battery, a structural approach such as optimization of electrode thickness and length has been performed for the purpose of increasing output. On the other hand, according to the present invention, high output can be realized by an approach from the material side. For this reason, when the exterior case is simple and the shape thereof cannot be changed, for example, in the case of a coin-type battery, it can be said that the present invention is the most effective approach for high output.

  In the above embodiment, the lithium secondary battery has been described as the nonaqueous electrolyte secondary battery, but the present invention is not limited to this. For example, the combination of the positive electrode and the electrolyte in the nonaqueous electrolyte secondary battery of the present invention can be applied to a sodium ion secondary battery or the like.

  Examples of the present invention will be described below. In addition, this invention is not limited to an Example.

[Synthesis of polymer containing tetrachalcogenofulvalene skeleton in repeating units]
The synthesis of the polymer containing the tetrachalcogenofulvalene skeleton was carried out in two stages: a precursor synthesis step and a polymer synthesis step.

First, a precursor synthesis step was performed. 1.43 g (24 mmol) of isopropylamine was dissolved in 16 mL of tetrahydrofuran (THF). To this solution, 0.6 mL (n-butyllithium: 1.56 mmol) of n-butyllithium in hexane (concentration: 2.6 mol / L) was added dropwise at -78 ° C. After stirring the solution for 10 minutes, 0.10 g (0.43 mmol) of the compound 9a shown on the left side of the formula (9), that is, dimethyltetrathiafulvalene was added at −78 ° C. It changed to a colored suspension. After stirring for another 10 minutes, 3.10 g of C ₆ F ₁₃ I (7.0 mmol) was added at −78 ° C. to turn the suspension into a dark green solution. After this, the dark green solution changed to a red solution by continuing stirring for a while. Furthermore, after stirring at -78 degreeC for 1 hour, when the thin layer chromatography (TLC) was performed, the spot derived from a raw material disappeared and the new spot was confirmed. The reaction solution was gradually warmed to room temperature and further stirred for 4 hours. Water was added to the reaction solution, extraction with ether was performed, and the ether layer was separated. After drying the water in the ether solution, the solvent was removed to obtain a dark red solid. Column operation (silica, chloroform) was performed on this dark red solid, and the dark red band portion was recovered and the solvent was removed to obtain a dark red viscous solid. Hexane was added to the viscous solid and dried to obtain an orange powder product. ^{By 1} H-NMR (CDCL ₃ ) and IR measurement (KBr method), it was confirmed that this product was the compound 9b shown on the right side of the formula (9), that is, diiododimethyltetrathiafulvalene. The yield was 0.14 g (yield 67%).

Subsequently, the synthesis | combining process of the polymer was performed. 0.12 g (0.25 mmol) of the compound 9b obtained above and 2 mL of triethylamine were dissolved in 10 mL (0.12 g, 0.25 mmol) of N-methylpyrrolidone. This solution was bubbled with nitrogen for 10 minutes, then 0.060 g (0.05 mmol) of Pd (PPh ₃ ) ₄ , 0.020 g (0.10 mmol) of CuI, and 0.049 g of 1,3-diethynylbenzene. (0.39 mmol) was added and stirred at 100 ° C. The color of the solution changed from dark red to dark red-orange. The mixed solution was stirred at 100 ° C. for 24 hours. Thereafter, the reaction solution was poured into water to obtain a black-red solid. The solid was washed with stirring in the order of methanol and acetone, then isolated with a Kiriyama funnel and air dried to obtain a dark brown product. ^{According to 1} H-NMR (CDCL ₃ ) and IR measurement (KBr method), this product is compound 10b shown on the right side of formula (10), that is, poly- (2,6-dimethyltetrathiafulvalene)-(2, 6-diethynylbenzene) copolymer was confirmed. In formula (10), n is an integer representing the number of repeating monomer units. The yield was 0.07 g (yield 79%). Moreover, as a result of measuring by gel permeation chromatography (GPC), the molecular weight of this polymer 10b was 36484 in polystyrene conversion.

Example 1
In Example 1, a positive electrode was produced using the polymer 10b synthesized above as an organic active material capable of occluding and releasing anions. Lithium metal was used as the negative electrode. In this example, the coin-type non-aqueous electrolyte secondary battery shown in FIG. 1 was produced.

[Preparation of positive electrode]
60 mg of the polymer 10b synthesized above and 160 mg of acetylene black as a conductive assistant were weighed and put in a mortar and kneaded. Furthermore, 40 mg of polytetrafluoroethylene was added as a binder and kneaded in a mortar. The mixture thus obtained was pressed onto a current collector stainless mesh (made by Nilaco, 30 mesh) with a rolling roller, vacuum-dried, and punched into a disk shape having a diameter of 16 mm to produce a positive electrode. . The coating weight of the active material in this positive electrode was 9.2 mg for the polymer 10b.

[Production of electricity storage device]
The positive electrode produced above was used, and lithium metal (0.3 mm thickness) was used as the negative electrode. Propylene carbonate (PC) was used as a solvent for dissolving the electrolyte, and lithium bisfluorosulfonylimide (LiFSI) was dissolved in the solvent so that the concentration was 1.00 mol / L. Produced.

  This electrolytic solution was impregnated into a porous polyethylene sheet (thickness 20 μm) as a separator, a positive electrode, and a negative electrode. The separator, the positive electrode, and the negative electrode were housed in a coin-type battery case so as to have the configuration shown in FIG. The opening of the case was closed with a sealing plate fitted with a gasket, and the case was crimped and sealed with a press. Thus, the coin-type non-aqueous electrolyte secondary battery of Example 1 was obtained.

(Comparative Example 1)
In Comparative Example 1, except that propylene carbonate (PC) was used as the electrolytic solution, and lithium bistrifluoromethanesulfonylimide (LiTFSI) as the electrolyte was dissolved so as to have a concentration of 1.00 mol / L, A coin-type nonaqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as Example 1.

(Comparative Example 2)
In Comparative Example 2, except that the electrolyte solution was propylene carbonate (PC) and lithium hexafluorophosphate (LiPF ₆ ) dissolved in the electrolyte so as to have a concentration of 1.00 mol / L. In the same manner as in Example 1, a coin-type nonaqueous electrolyte secondary battery of Comparative Example 2 was produced.

[Evaluation of battery charge / discharge characteristics]
For each coin-type non-aqueous electrolyte secondary battery obtained in Example 1 and Comparative Examples 1 and 2, resistance measurement by AC impedance was performed. All these tests were performed by placing the batteries in a thermostatic chamber environment at 25 ° C.

  In the AC impedance measurement, the charge / discharge test was repeated three times, and after confirming that the charge / discharge operation could be performed stably, the measurement was performed in the third discharge state. The results are shown in Table 1.

  As shown in Table 1, when the LiFSI salt described in Example 1 was used as the electrolyte salt, the reaction resistance of the positive electrode was the lowest value of the reaction resistance compared to the batteries of Comparative Examples 1 and 2. The reaction resistance obtained from the AC impedance measurement indicates the resistance of the redox reaction of the polymer 10b that is the positive electrode active material. This is considered to be derived from the fact that the reaction of the polymer 10b is the fastest in the system using the LiFSI salt. The low reaction resistance is equivalent to the fact that the pulse characteristics for instantaneously extracting a large current are improved and the output characteristics are improved, which means that good output characteristics can be obtained by using LiFSI salt. Yes.

  The excellent output characteristics were obtained because of the ion pair formation with the FSI anion in the case where a compound that forms an ion pair with an anion in the oxidation state represented by the polymer 10b is used as the active material in the positive electrode. This is thought to be due to the smooth progress.

  The nonaqueous electrolyte secondary battery of the present invention has high output, high capacity, and excellent repeatability. In particular, since the nonaqueous electrolyte secondary battery of the present invention has excellent output characteristics, it is suitably used in various portable devices, transportation equipment, uninterruptible power supplies, etc. that require a large current instantaneously or for a longer period of time. be able to.

DESCRIPTION OF SYMBOLS 1 Coin type electrical storage device 10 Positive electrode 11 Positive electrode active material layer 12 Positive electrode current collector 20 Negative electrode 21 Negative electrode active material layer 22 Negative electrode current collector 30 Separator 31 Electrolytic solution 50 Coin-shaped case 51 Sealing plate 52 Gasket

Claims (6)

A positive electrode comprising a first active material capable of occluding and releasing anions;
A negative electrode,
An electrolyte containing a salt of a cation and the anion;
With
The anion is [(FSO ₂ ) ₂ N] ⁻ ;
Non-aqueous electrolyte secondary battery. The first active material capable of occluding and releasing the anion is a polymer containing a tetrachalcogenofulvalene skeleton in the main chain.
The nonaqueous electrolyte secondary battery according to claim 1. The first active material capable of occluding and releasing the anion is a polymer containing a tetrachalcogenofulvalene skeleton in the side chain.
The nonaqueous electrolyte secondary battery according to claim 1 or 2. The positive electrode further includes a second active material capable of inserting and extracting lithium ions;
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3. The second active material is a transition metal oxide or a lithium-containing transition metal oxide.
The nonaqueous electrolyte secondary battery according to claim 4. The transition metal oxide is V ₂ O ₅ ;
The nonaqueous electrolyte secondary battery according to claim 5.

Images