JP2013012330A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the output characteristics, particularly the pulse discharge characteristics, of a nonaqueous electrolyte secondary battery without reducing the energy density significantly.SOLUTION: A nonaqueous electrolyte secondary battery comprises: a positive electrode 10 comprising a positive electrode collector (a case 50), a first active material layer 12, and a second active material layer 13; a negative electrode 20 containing a negative electrode active material capable of storing and discharging lithium ions; and an electrolytic solution 31 containing a salt of a lithium ion and an anion. The first active material layer 12 contains a first active material capable of storing and discharging lithium ions, and the second active material layer 13 contains a second active material composed of an organic compound capable of storing and discharging anions, and a conductive assistant. The second active material layer 13 is provided between the positive electrode collector (the case 50) and the first active material layer 12.

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. A lithium secondary battery is characterized by a high voltage of 3 V or more and a high energy density. There is a demand for improving output characteristics, particularly pulse discharge characteristics, which are instantaneous large-current characteristics, while maintaining the high energy density that is characteristic of lithium secondary batteries.

  As an approach for improving output characteristics without greatly reducing the energy density, it has been proposed to add activated carbon to the positive electrode (see, for example, Patent Documents 1 to 5). Activated carbon has an electric double layer capacity due to adsorption or desorption of anions or cations on its surface. Since charging to the electric double layer capacity and discharging from the electric double layer capacity are fast, there is a possibility that both high energy density and high output can be achieved by adding activated carbon to the positive electrode.

  However, activated carbon has a very large surface area and its surface is very active. For this reason, decomposition | disassembly of electrolyte solution tends to advance on the surface of activated carbon while the lithium secondary battery which contains activated carbon in a positive electrode is preserve | saved in a charged state.

  In addition, activated carbon has a very high ability to adsorb trace gas components and moisture in the air. Therefore, in order to use activated carbon as the positive electrode material, it is necessary to remove the adsorbed moisture of the activated carbon by processes such as vacuum drying and heat treatment. This removal process takes a long time. Even after this removal step, it is difficult to completely remove the adsorbed moisture. When a positive electrode of a lithium secondary battery is produced using activated carbon having adsorbed moisture remaining on the surface, gas generation in the battery accompanying charge / discharge, deterioration of charge / discharge cycle characteristics, etc. are likely to occur.

  Patent Document 5 discloses a positive electrode made of activated carbon whose surface is coated with a pseudo-capacitance type organic capacitor material. A conductive polymer is disclosed as a pseudo-capacitance type organic capacitor material.

  However, since the capacitor of Patent Document 5 uses activated carbon, it has the above-described problems. Furthermore, the conductive polymer proposed as a pseudo-capacitance type organic capacitor material has a small number of electrons that can be extracted because the electron conjugation spreads throughout the molecule, and the effect of improving output characteristics is insufficient.

  In Patent Document 6, it is proposed to increase the capacity by using a carbon material capable of occluding anions instead of a part of the conductive material. In this case, although the capacity can be increased by the carbon material capable of occluding anions contributing to the charge / discharge reaction, it cannot be expected to improve the output characteristics of the lithium secondary battery.

  Patent Document 7 proposes a nonaqueous electrolyte secondary battery including a conductive material layer including a conductive material and a binder between a positive electrode mixture and a metal current collector.

  However, the conductive material layer formed between the positive electrode mixture and the metal current collector improves the adhesion between the positive electrode mixture and the current collector, but is expected to improve the output characteristics of the battery. Can not.

JP 2002-260634 A JP 2003-77458 A International Publication No. 02/041420 JP 2008-34215 A JP 2003-92104 A JP-A-5-159773 JP 2002-42888 A

  As described above, efforts have been made to improve the output characteristics of the lithium secondary battery by adding the active material as the second component to the positive electrode together with the active material capable of inserting and extracting lithium ions. However, knowledge about the optimal second active material and electrode structure was insufficient.

  The present invention has been made in view of these problems, and an object of the present invention is to improve the output characteristics, in particular, the pulse discharge characteristics, of a nonaqueous electrolyte secondary battery without greatly reducing the energy density.

That is, the present invention
A positive electrode having a positive electrode current collector, a first active material layer, and a second active material layer;
A negative electrode comprising a negative electrode active material capable of inserting and extracting lithium ions;
An electrolyte containing a salt of lithium ions and anions,
The first active material layer includes a first active material that can occlude and release lithium ions as a main active material,
The second active material layer includes, as a main active material, a second active material that is an organic compound capable of occluding and releasing the anions, and a conductive auxiliary agent.
A non-aqueous electrolyte secondary battery in which the second active material layer is provided between the positive electrode current collector and the first active material layer is provided.

  In the present invention, two types of active materials, a first active material and a second active material, are used in the positive electrode. The first active material layer includes a first active material as a main active material. By using a material that can occlude and release lithium ions as the first active material, a sufficient energy density can be secured. The second active material layer includes a second active material as a main active material. The second active material further includes a conductive additive. The second active material is an organic compound that can occlude and release anions contained in the electrolyte. The second active material layer contains a conductive additive together with the second active material, and the pulse discharge characteristics can be improved by being formed between the first active material layer and the positive electrode current collector. Thus, according to the present invention, it is possible to improve the output characteristics of the nonaqueous electrolyte secondary battery, particularly the pulse discharge characteristics, without greatly reducing the energy density. In addition, the second active material in the present invention has a smaller water adsorption capacity than activated carbon. Therefore, the moisture content inside the battery can be reduced.

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

  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 non-aqueous electrolyte secondary battery 1 which is an embodiment of a non-aqueous electrolyte secondary battery according to the present invention. The coin-type non-aqueous electrolyte secondary battery 1 has a structure in which the inside is sealed by a coin-type case (positive electrode current collector) 50, a sealing plate 51, and a gasket 52. Inside the coin-type non-aqueous electrolyte secondary battery 1, a negative electrode 20 including a negative electrode active material layer 21 and a negative electrode current collector 22, a separator 30, and a positive electrode active material layer 11 are housed. The coin-type case (positive electrode current collector) 50 also has a role as a positive electrode current collector. The positive electrode 10 includes a positive electrode active material layer 11 and a coin-type case (positive electrode current collector) 50 that is a positive electrode current collector. The positive electrode 10 and the negative electrode 20 are opposed to each other with the separator 30 interposed therebetween. The positive electrode active material layer 11, the separator 30, and the negative electrode active material layer 21 are disposed so that the positive electrode active material layer 11 and the negative electrode active material layer 21 are in contact with the separator 30.

  The positive electrode active material layer 11 includes a first active material layer 12 and a second active material layer 13. In the positive electrode active material layer 11, the second active material layer 13 is formed between the first active material layer 12 and the coin-type case (positive electrode current collector) 50. In the present embodiment, one surface of the second active material layer 13 is in contact with the coin-type case (positive electrode current collector) 50 and the other surface is in contact with the first active material layer 12. One surface of the first active material layer 12 is in contact with the second active material layer 13, and the other surface is in contact with the separator 30.

  The positive electrode active material layer 11 includes at least two active materials. One of the two active materials is a first active material that can occlude and release lithium ions. The other of the two active materials is a second active material that is an organic active material capable of occluding and releasing anions. The first active material is included in the first active material layer 12, and the second active material is included in the second active material layer 13. The electrolytic solution 31 contains a salt of lithium ions and anions. An electrode group including the positive electrode 10, the negative electrode 20, and the separator 30 is impregnated with an electrolytic solution 31.

  The reason why the nonaqueous electrolyte secondary battery of the present invention can achieve high capacity and high output (excellent pulse discharge characteristics) includes the following three reasons.

  The first reason is the material characteristics of the two active materials contained in the positive electrode. Of the two types of active materials contained in the positive electrode, one type is a positive electrode active material (first active material) that can occlude and release lithium ions. The first active material is a main active material in the positive electrode. The main active material means an active material that occupies a storage capacity exceeding 50% with respect to the total storage capacity of the nonaqueous electrolyte secondary battery. As the lithium ions move between the positive electrode and the negative electrode along with charge and discharge, the first active material can realize a high voltage of 3 V class and a high capacity. On the other hand, of the two types of active materials contained in the positive electrode, the other type is an organic active material (second active material) that can occlude and release anions. The reaction in which the second active material that is an organic compound occludes and releases anions is faster than the reaction in which the first active material occludes and releases lithium ions. For this reason, the second active material can contribute to high output, particularly excellent pulse discharge characteristics. Furthermore, the second active material that is an organic compound can have a larger capacity than activated carbon. Therefore, when the organic compound is used, a higher capacity can be obtained than when activated carbon is used instead. Therefore, the second active material can contribute to both high capacity and high output.

  The second reason is a synergistic effect by combining two active materials. Here, an important point is that the reaction ions of the first active material are different from the reaction ions of the second active material. Since the first active material can occlude and release lithium ions, the reaction ions of the first active material are lithium ions. On the other hand, since the second active material can occlude and release anions, the reaction ions of the second active material are anions. Thus, the reaction ions of the two active materials are different from each other, so that the reactions of the active materials can proceed smoothly without affecting each other.

  When high output is not required, that is, when charging / discharging is performed at a relatively low speed, an active material having a low reaction rate can sufficiently react, so the active material contributing to charging / discharging does not depend on the reaction rate of the material. . Therefore, since no active material reacts preferentially, as a result, the first active material which is the main active material mainly contributes to charge / discharge. In other words, it is the reaction between the first active material and lithium ions that mainly contributes to charging and discharging. In this case, the anion hardly moves between the positive and negative electrodes and stays in the electrolyte, and mainly lithium ions move between the positive and negative electrodes.

  On the other hand, when high output is required, that is, when charging / discharging is performed at a relatively high speed, both the first active material and the second active material are involved in charging / discharging. In other words, in addition to the reaction between the first active material and lithium ions, the reaction between the second active material and the anion proceeds. In this case, both lithium ions and anions move between the positive and negative electrodes. Specifically, in the discharging process, lithium ions move from the negative electrode toward the positive electrode, and the anions move from the positive electrode toward the negative electrode. In general, the movement speed (mobility) of anions in an electrolyte is equal to or higher than that of lithium ions. Since an anion is added as a reactive ion, the concentration of the reactive ion increases approximately twice, so that a large current can be taken out and a high output can be realized.

  As a comparison with the above description, for example, a case will be described in which two active materials A and B capable of inserting and extracting lithium ions are used for the positive electrode. However, it is assumed that the active material B has a faster charge / discharge reaction than the active material A. In this case, the reaction ions of the active material A and the active material B are both lithium ions. Therefore, when charging / discharging is performed, the reaction between the active material B and lithium ions proceeds rapidly, so that lithium ions are consumed and the reaction of the active material A is suppressed. In addition, since the reactive ions are only lithium ions, the output characteristics are limited by the moving speed of the lithium ions in the electrolyte. Therefore, even if the active material B having reactive ions common to the active material A is added to the active material A, the synergistic effect of A + B cannot be obtained to the maximum.

  Further, in the prior art, it has been proposed to add activated carbon as an active material that is a second component to an active material that can occlude and release lithium ions. However, the reactive ion of activated carbon is both a lithium ion and an anion, and reacts with an anion at a potential higher than the natural potential and reacts with lithium ion at a lower potential. Therefore, the effect of improving the output characteristics by adding activated carbon varies depending on the potential, and may be obtained above a certain potential, and may not be sufficiently obtained below a certain potential. I can say that.

  The third reason is that there is no harmful effect caused by combining the first active material and the second active material. When activated carbon is added as an active material that is the second component to an active material that can occlude and release lithium ions as in the above-described prior art, the positive electrode has various adverse effects. That is, the surface of activated carbon is very active and highly reactive, and moisture, organic components in the air, etc. are easily adsorbed on the surface, so that complete removal is still difficult even after sufficient vacuum drying. In addition, moisture and organic matter adsorbed on activated carbon can be decomposed on the surface of the active material capable of occluding and releasing lithium ions, which may cause deterioration of reliability such as battery swelling and capacity reduction due to gas generation. There is. The effects of these adverse effects may be noticeable in results such as storage tests and cycle tests. On the other hand, since the organic compound used as the second active material in the present invention has a low moisture adsorptivity, it is a harmful factor caused by combining with an active material (first active material) capable of occluding and releasing lithium ions. Does not have. For this reason, a highly reliable nonaqueous electrolyte secondary battery can be obtained by combining the second active material with the first active material.

  For the above three reasons, the present invention can provide a non-aqueous electrolyte secondary battery having high capacity and high output (excellent pulse discharge characteristics) and having high reliability as a battery.

  Furthermore, the present inventors examined the form of the second active material layer 13 and the form for using the first active material and the second active material together, and found an appropriate form.

  First, the form of the second active material layer 13 will be described below. The second active material layer 13 includes a second active material and a conductive additive. This makes it possible to achieve both high capacity and high output. Since the organic compound used as the second active material has a lower electronic conductivity than a metal or an oxide material, it may not be able to sufficiently exhibit both high capacity and high output characteristics by itself. For example, when an organic compound is present alone as a particle, electron conduction is not efficiently performed within the particle due to its low electron conductivity, and only the organic compound on the surface reacts, and the organic compound present inside the particle is May not contribute to the reaction. In order to achieve both high capacity and high output, all of the second active material needs to contribute to the charge / discharge reaction at high speed and efficiently. When the second active material layer 13 includes a conductive auxiliary agent, the second active material can conduct electrons through the conductive auxiliary agent. Due to the presence of the conductive auxiliary agent that can supplement the electronic conductivity of the second active material, the second active material layer 13 can contribute to both high output and high capacity.

  Furthermore, the second active material that is an organic compound preferably covers at least a part of the surface of the conductive additive. In such a case, the contact area between the second active material and the conductive auxiliary agent is increased, so that electrons are transferred more smoothly between the conductive auxiliary agent and the second active material due to redox. Since the second active material covers the surface of the conductive additive in the second active material layer 13, the oxidation-reduction reaction of the second active material proceeds smoothly, so that the pulse discharge characteristics can be further improved. .

  Next, the form for using a 1st active material and a 2nd active material together is demonstrated below. The second active material is contained in the second active material layer 13 together with the conductive assistant, and the first active material is contained in the first active material layer 12. The second active material layer 13 is formed between the first active material layer 12 and the positive electrode current collector (case 50). As a result, both the function of the first active material and the function of the second active material can be expressed, and both high capacity and high output can be achieved. The reason for this is not clear, but the inventors consider as follows. That is, in order to effectively express the functions of the first active material layer 12 and the second active material layer 13, it is preferable that the contact between adjacent members in the positive electrode 10 is good. Surface contact is more desirable than point contact for efficient contact. Compared to the first active material layer 12, the second active material layer 13 includes a second active material that is an organic compound and a conductive additive, so that better surface contact can be formed between adjacent members. it can.

  By disposing the second active material layer 13 between the first active material layer 12 and the positive electrode current collector (case 50), the second active material layer 13 has electronic conductivity with the first active material layer 12. Good surface contact can be formed with both the positive electrode current collector. Therefore, both the function of the first active material layer 12 and the function of the second active material layer 13 can be sufficiently expressed. Conversely, when the second active material layer 13 is disposed between the first active material layer 12 and the separator 30, one surface of the second active material layer 13 is in contact with the insulating separator 30. In this case, the reaction can proceed in the vicinity of the surface in contact with the first active material layer 12 in the second active material layer 13, but it is efficient in the vicinity of the surface on the separator 30 side in the second active material layer 13. It is inferred that a difficult reaction becomes difficult.

  Generally, a coin-type battery case has a current collector function, and the contact resistance between the case and the electrode adjacent to the case is a factor that affects the battery characteristics, particularly the output characteristics. is there. According to this embodiment, the second active material layer 13 containing the second active material that is an organic active material and a conductive additive is disposed between the first active material layer 12 and the positive electrode current collector. Therefore, the electron conductivity at the interface between the positive electrode active material layer 11 and the coin-type case (positive electrode current collector) 50 that is the positive electrode current collector is improved, and as a result, the electron conductivity of the entire positive electrode 10 is improved. High capacity and high output. The effect of achieving both high capacity and high output by forming the second active material layer 13 between the positive electrode current collector and the first active material layer 12 is particularly great in a coin-type battery.

  Hereinafter, constituent materials that can be used for the coin-type non-aqueous electrolyte secondary battery 1 of the present embodiment will be described.

As the first active material capable of inserting and extracting lithium ions, those known as positive electrode materials for lithium ion batteries can be used. Specifically, a transition metal oxide which may contain lithium can be used as the first active material. 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 first 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 as the first active material.

  A polymer having a tetrachalcogenofulvalene skeleton is preferably used as the second active material that is an organic compound capable of occluding and releasing anions. Typically, the tetrachalcogenofulvalene skeleton is included in the repeating unit of the polymer. In a polymer having a tetrachalcogenofulvalene skeleton, a portion having a tetrachalcogenofulvalene skeleton has a π-conjugated electron cloud and functions as a redox site. The polymer is suitable as an active material for the positive electrode 10 because the oxidation-reduction reaction proceeds at a potential of about 3 to 4 V with respect to lithium.

  The structure of the portion having a tetrachalcogenofulvalene skeleton is represented, for example, by 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 alkylthio 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), compounds in which X ¹ , X ² , X ³ , and X ⁴ are sulfur atoms and Ra, Rb, Rc, and Rd are hydrogen atoms, that is, compounds represented by the following formula (2) are: , Referred to as tetrathiafulvalene (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 anion (PF ₆ ^{− in} the case of formula (3)) 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 anion 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 coin-type non-aqueous electrolyte secondary battery 1 of the present embodiment utilizes such redox characteristics of the tetrathiafulvalene skeleton.

  For example, when TTF is used for the positive electrode of the electricity storage device, the tetrathiafulvalene skeleton moves toward an electrically neutral state in the discharge 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 (TTF Chemistry: Fundamentals and Applications of Tetrathiafulvalene), Journal of the American Chemical Society (Journal of the Chemical Society 97) , 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 is reported, for example, in TTF Chemistry: Fundamentals and Applications of Tetrahiafulvalene, together with methods for synthesizing these compounds, in TTF Chemistry: Fundamentals and Applications of Tetrahiafulvalene. 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 have a structure that does not significantly affect the redox of the tetrachalcogenofulvalene skeleton.

  The solubility of an organic compound in an organic solvent decreases as the molecular weight increases. Therefore, by using a polymer containing a tetrachalcogenofulvalene skeleton in the repeating unit as the second active material, the dissolution of the second active material in the electrolyte containing the organic solvent is suppressed, and the cycle characteristics are deteriorated. Can be suppressed.

  The polymer having a tetrachalcogenofulvalene skeleton preferably has a large molecular weight. Specifically, it is preferable to have four or more tetrachalcogenofulvalene skeletons represented by formula (1) in one molecule. That is, the degree of polymerization (number average degree of polymerization) of the polymer, specifically, n in formula (4) described later or the sum of n and m in formula (6) described below is 4 or more. Is preferred. Thereby, the 2nd active material which is hard to melt | dissolve in an organic solvent is realizable. More preferably, the degree of polymerization of the polymer is 10 or more, and more preferably 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, preferably 150 or less.

  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 block copolymer, units in which repeating units including a tetrachalcogenofulvalene skeleton are directly bonded continuously and units in which repeating units not including a tetrachalcogenofulvalene skeleton are directly bonded are alternately arranged. It has the structure. 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 Formula (5) is an integer representing the number of repeating monomer units.

  When the polymer contains a tetrachalcogenofulvalene skeleton in the side chain, the structure of the polymer is represented by, for example, a structure in which two repeating units are bonded to each other with the symbol * 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.

  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 chained aliphatic group, cyclic aliphatic group, hydrogen atom, hydroxyl group, cyano group, amino group, nitro group, nitroso group, or alkylthio 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 second active material layer 13 includes a conductive additive in addition to the second active material. 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. Although the shape of a conductive support agent is not specifically limited, For example, it is a particulate form. Although the shape of the 2nd active material which coat | covered at least one part of the conductive support agent is not specifically limited, For example, it is a film | membrane form.

  The first active material layer 12 may include a conductive auxiliary agent that assists electronic conductivity in the positive electrode 10 as necessary. As a conductive support agent, the same material as the conductive support agent contained in the second active material layer 13 can be used.

  Furthermore, the first active material layer 12 and the second active material layer 13 may contain a binder for maintaining the shape of the positive electrode active material layer 11 as necessary. The binder may be either a thermoplastic resin or a thermosetting resin. The binder is, for example, a polyolefin resin typified by polyethylene or polypropylene; a fluororesin typified by polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), or a co-polymer of them. Combined resin: styrene butadiene rubber, polyacrylic acid and copolymer resin thereof, etc., and a mixture thereof may be used.

  The main active material in the first active material layer 12 is the first active material. That is, the first active material in the first active material layer 12 occupies a capacity exceeding 50% with respect to the capacity of the first active material layer 12. The first active material layer 12 may substantially contain only the first active material as the active material, or may contain an active material other than the first active material, for example, the second active material. . The first active material layer 12 may contain only the first active material as the active material.

  The main active material in the second active material layer 13 is the second active material. That is, the second active material in the second active material layer 13 occupies a capacity exceeding 50% with respect to the capacity of the second active material layer 13. The second active material layer 13 may substantially contain only the second active material as the active material, or may contain an active material other than the second active material, such as the first active material. The second active material layer 13 may contain only the second active material as the active material.

  The capacity | capacitance of the 1st active material layer 12 with respect to the total capacity | capacitance of the positive electrode active material layer 11 is 50 to 90%, for example. The capacity of the second active material layer 13 with respect to the total capacity of the positive electrode active material layer 11 is, for example, 10 to 50%. However, even if the capacity of the second active material layer 13 is very small, the effect of improving the charge / discharge characteristics by the second active material can be obtained.

  As the coin-type case (positive electrode current collector) 50, a known material can be used for the case of the coin-type battery. The coin-type case (positive electrode current collector) 50 is made of, for example, a metal such as aluminum or stainless steel or a metal mixture.

  In the present embodiment, the coin-type case (positive electrode current collector) 50 itself serves as the positive electrode current collector. However, the positive electrode current collector may be separately provided on the coin-type case (positive electrode current collector) 50. In this case, the positive electrode current collector may be welded or disposed on the coin-type case (positive electrode current collector) 50. As the positive electrode current collector, a known material can be used as the positive electrode current collector of the nonaqueous electrolyte secondary battery. The positive electrode current collector is, for example, a foil or mesh made of a metal such as aluminum or stainless steel, carbon, or the like. When a metal foil or metal mesh is used as the positive electrode current collector, good electrical contact can be maintained by welding the positive electrode current collector to the case 50.

  Further, like the coin-type nonaqueous electrolyte secondary battery 2 shown in FIG. 2, the coin-type case (positive electrode current collector) 50, that is, the coin-type case (positive electrode current collector) 50 and the second active material layer. 13 may be provided with a conductive auxiliary layer 14. By providing the conductive auxiliary layer 14, the electron conductivity between the second active material layer 13 and the coin-type case (positive electrode current collector) 50 in the positive electrode 15 is increased, and the coin-type non-aqueous electrolyte secondary battery 2 is improved. The output characteristics can be improved. The provision of the conductive auxiliary layer 14 is particularly preferable when the coin-type case (positive electrode current collector) 50 itself is used as the positive electrode current collector.

  The conductive auxiliary layer 14 includes a conductive auxiliary agent that assists electronic conductivity in the positive electrode 10. 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 conductive auxiliary layer 14 may contain a binder for maintaining the shape. As a binder, the thing similar to the material mentioned above as a binder which the positive electrode active material layer 11 may contain can be used.

  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 can be 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, for example, a foil or mesh made of a metal such as copper, nickel, or stainless steel. 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, the separator 30 is preferably made of 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 is a nonaqueous electrolyte containing a nonaqueous solvent and a salt (electrolyte salt) of lithium ions and anions. The salt of a lithium ion and an anion will not be specifically limited if it can be used in a lithium battery, For example, the salt of a lithium ion and the following anion is mentioned. 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.

The nonaqueous electrolyte may contain a solid electrolyte in addition to a salt of lithium ions and anions. Examples of solid electrolytes include Li ₂ S—SiS ₂ , Li ₂ S—B ₂ S ₅ , Li ₂ S—P ₂ S ₅ —GeS ₂ , sodium / alumina (Al ₂ O ₃ ), amorphous or low phase transition temperature. (Tg) polyether, amorphous vinylidene fluoride-6-fluorinated propylene copolymer, heterogeneous polymer blend polyethylene oxide and the like.

  When the electrolyte salt is a liquid, the electrolyte salt itself may be used as the electrolytic solution 31. When the electrolyte is a solid, it is necessary to dissolve it in a non-aqueous solvent to obtain the electrolytic solution 31.

  As the non-aqueous solvent, a known non-aqueous solvent that can be used in a non-aqueous secondary battery or a non-aqueous 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 preferable. This is because propylene carbonate has a freezing point of −49 ° C., which is lower than that of ethylene carbonate, so that the nonaqueous electrolyte secondary battery can be operated even at a low temperature.

  Moreover, the solvent containing cyclic ester can also be used suitably as a non-aqueous solvent. 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 non-aqueous solvent, the electrolytic solution 31 can have a very high dielectric constant as a whole. 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 coin-type non-aqueous electrolyte secondary battery 1 can be manufactured by stacking a separately prepared second active material layer 13 and first active material layer 12 on a coin-type case (positive electrode current collector) 50 in this order. it can. Further, the coin-type nonaqueous electrolyte secondary battery 1 is manufactured by forming the second active material layer 13 directly on the coin-type case (positive electrode current collector) 50 and superimposing the first active material layer 12 thereon. You can also.

  The coin-type non-aqueous electrolyte secondary battery 2 has the same method as the coin-type non-aqueous electrolyte secondary battery 1 on the conductive active material layer 14 formed on the positive electrode current collector (case 50). It can be produced by stacking the positive electrode active material layer 11. The conductive auxiliary layer 14 can be formed, for example, by pressing a mixture containing a conductive auxiliary and a binder. In addition, the conductive auxiliary layer 14 formed on the positive electrode current collector is prepared by applying a paste-like mixture containing a conductive auxiliary agent, a binder and a solvent on the positive electrode current collector and drying it. May be.

  The first active material layer 12 can be produced by a normal method such as pressing and molding a mixture containing the first active material. The mixture may contain a conductive aid, a binder, and the like as necessary. Moreover, the 1st active material layer 12 can also be produced by preparing the paste-form mixture containing a 1st active material and a solvent, apply | coating this on a suitable support body, and making it dry.

  The second active material layer 13 may be produced by either a dry method or a wet method. In the dry process, for example, the second active material layer 13 is obtained by pressing and molding a mixture containing a particulate second active material and a particulate conductive additive. In the wet process, for example, a second active material is dissolved in a solvent to prepare a solution in which the second active material is uniformly dispersed at a molecular level, and a conductive auxiliary agent is added thereto, and the second active material and the conductive auxiliary agent are added. A paste-like mixture is prepared. The second active material layer 13 formed on the positive electrode current collector is obtained by drying the coating film formed by applying the paste-like mixture on the positive electrode current collector. From the viewpoint of forming the second active material layer 13 in which the second active material widely covers the surface of the conductive additive, it is preferable to employ a wet method.

  As described above, the non-aqueous electrolyte secondary battery of the present invention, in particular, the coin-type non-aqueous electrolyte secondary batteries 1 and 2 can be easily manufactured without greatly changing the conventional manufacturing method.

  According to the above embodiment, a highly reliable nonaqueous 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, this embodiment can realize high output 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 this embodiment is the most effective approach for high output.

  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 unit]
As a polymer containing a tetrachalcogenofulvalene skeleton as a repeating unit, a copolymer compound represented by the following formula (8) (hereinafter referred to as copolymer compound [11c]) was synthesized.

  Second unit (redox site in side chain) for unit number n of first unit (unit having redox site in side chain) constituting copolymer compound [11c] to be co-synthesized represented by formula (8) The unit ratio m / n of the number of units m) is approximately 1. The copolymer compound [11c] has three steps: synthesis of a tetrathiafulvalene derivative to be contained in the side chain, synthesis of a copolymer main chain compound, and coupling of tetrathiafulvalene to the copolymer main chain compound. Synthesized. Hereinafter, these will be described in order.

The synthesis of the tetrathiafulvalene derivative was performed by the route shown in the following formula (9). 5 g of tetrathiafulvalene [9a] (manufactured by Aldrich) was added to the flask, and 80 mL of tetrahydrofuran (manufactured by Aldrich) was further added. After cooling this to −78 ° C., 20 mL of an n-hexane-tetrahydrofuran solution of lithium diisopropylamide (manufactured by Kanto Chemical Co., Ltd., concentration 1 mol / L) was added dropwise over 10 minutes, and then 7.3 g of paraformaldehyde (Kanto Chemical Co., Ltd.). The reaction was allowed to proceed by stirring for 15 hours. The solution after the reaction was poured into 900 mL of water, extracted with 1 L of diethyl ether (manufactured by Kanto Chemical Co., Ltd.) twice, washed with 500 mL of saturated ammonium chloride aqueous solution and 500 mL of saturated saline, and then dried over anhydrous sodium sulfate. Went. After removing the desiccant, 6.7 g of the crude product obtained by concentration under reduced pressure was purified on a silica gel column to obtain 1.7 g of a purified product. It was confirmed by ¹ H-NMR and IR that the purified product was the tetrathiafulvalene derivative [9c] shown on the right side of the formula (9).

The synthesis of the copolymer main chain compound was carried out by the route shown in the following formula (10). As a monomer raw material, 21 g of methacryloyl chloride [10a] (manufactured by Aldrich) and 40 g of methyl methacrylate [10b] (manufactured by Aldrich) are mixed in 90 g of toluene (manufactured by Aldrich), and 4 g of polymerization initiator is used. Azoisobutyronitrile (Aldrich) was added. The reaction was allowed to proceed by stirring the mixture at 100 ° C. for 4 hours. Hexane was added to the solution after the reaction to perform reprecipitation, thereby obtaining 57 g of a precipitated product. It was confirmed by ¹ H-NMR, IR and GPC that the product was a copolymer main chain compound [10c] shown on the right side of the formula (10).

The copolymer main chain compound [10c] includes a unit having a Cl group (first unit) and a unit having a methoxy group (second unit). As a result of ¹ H-NMR measurement in a chloroform solvent, the peak derived from the methyl group directly bonded to the main chain of the copolymer main chain compound [10c] is around 0.5 to 2.2 ppm, the second unit. The peak derived from the methoxy group possessed by was observed at around 3.6 ppm. In addition, the component ratio m / n of the 2nd unit with respect to the 1st unit in a copolymer principal chain compound [10c] is computable from the ratio of the integrated value of these peaks. In the IR measurement, each of the carbonyl group (C═O) and Cl group (C—Cl) of the first unit and the carbonyl group (C═O) of the second unit appeared as different absorption peaks. As a result of measurement by GPC, the degree of polymerization (number average degree of polymerization) of the copolymer main-chain compound [10c] exceeded 20.

Coupling of the tetrathiafulvalene derivative [9c] to the copolymer main chain compound [10c] was performed by the route shown in the following formula (11). Under an Ar gas stream, 1.0 g of tetrathiafulvalene derivative [9c] and 26 mL of tetrahydrofuran were placed in a reaction vessel and stirred at room temperature. To the reaction solution, 0.17 g of NaH (60 wt% in mineral oil) (manufactured by Aldrich) was added dropwise, and the mixture was stirred at 40 ° C. for 1 hour, with 8.58 g of tetrahydrofuran containing 0.58 g of the copolymer main chain compound [ 10c] was added. The reaction was allowed to proceed by stirring the resulting mixture at 70 ° C. overnight. Hexane was added to the solution thus obtained, and 0.2 g of a precipitated product was obtained by reprecipitation. It was confirmed by ¹ H-NMR, IR and GPC that the product was a copolymer compound [11c] shown on the right side of the formula (11). As a result of ¹ H-NMR measurement, the peak derived from the methylene group bonding the main chain of the copolymer compound [11c] and the tetrathiafulvalene group is around 4.8 ppm, and the peak derived from the tetrathiafulvalene group is It was observed at around 6.8 to 7.0 ppm. The copolymer compound [11c] consists of a unit having a tetrathiafulvalene group (first unit) and a unit having a methoxy group (second unit). ^From the ratio of the integrated value of each peak obtained by ¹ H-NMR measurement, the constituent ratio m / n of the second unit to the first unit in the copolymer compound [11c] was calculated by the same method as described above. The composition ratio m / n was approximately 1. The weight average molecular weight of the copolymer compound [11c] was approximately 28,000. As a result of elemental sulfur analysis, the sulfur content of the copolymer compound [11c] was 30.2 wt%. When the theoretical capacity of the copolymer compound [11c] was calculated from the sulfur content, it was 125 mAh / g.

Example 1
In Example 1, a coin-type non-aqueous electrolyte secondary battery shown in FIG. 1 having a second active material layer formed between a positive electrode current collector and a first active material layer was produced. In the first active material layer, vanadium oxide (V ₂ O ₅ ) was used as the first active material. In the second active material layer, the copolymer compound [11c] synthesized above was used as the second active material, and acetylene black was used as the conductive assistant. A second active material layer was prepared so that the second active material covered at least part of the surface of the conductive additive. Lithium metal was used as the negative electrode.

[Production of positive electrode]
First, the 1st active material layer containing a 1st active material was produced. 1800 mg of V ₂ O ₅ (manufactured by Aldrich) and 100 mg of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive assistant were weighed and kneaded in a mortar. Furthermore, a dispersion containing 100 mg of PTFE (made by Daikin Industries) was added as a binder, and the mixture was kneaded and dried in a mortar. A part of the mixture thus obtained was compression molded at a pressure of 10 MPa using a 16 mmφ powder compression molding machine to produce a pellet having a thickness of 0.6 mm. In order to remove residual moisture in the pellet, the pellet was dried with hot air at 200 ° C. The first active material layer thus obtained was evaluated using a mercury porosimeter. The first active material layer had a porous structure with a porosity of 46%. The weight of the first active material (V ₂ O ₅ ) in the first active material layer was 360 mg.

  Next, a second active material layer was produced. 150 mg of the copolymer compound [11c] was dissolved in 3 g of N-methylpyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.). As a result of measuring the obtained solution by laser diffraction particle size distribution (manufactured by Shimadzu Corporation), it was confirmed that particles were not present. Therefore, the copolymer compound [11c] was completely dissolved in the solution. To this solution, 150 mg of acetylene black was further mixed as a conductive additive to prepare a paste-like mixture. The paste mixture was applied onto the positive electrode current collector (coin-type battery case) so as to have a diameter of 16 mm by spin coating. The obtained coating film was vacuum dried at 120 ° C. for 1 hour to remove the solvent in the coating film. Thereby, a laminate including the positive electrode current collector and the second active material layer was obtained. The supported weight of the second active material (copolymer compound [11c]) calculated from the weight increase of the positive electrode current collector was 3.0 mg.

  A positive electrode was obtained by laminating the first active material layer on the second active material layer.

[Production of coin-type battery]
A coin-type battery was produced using the positive electrode. The positive electrode was disposed so that the first active material layer was in contact with the separator holding the electrolytic solution, and the second active material layer was positioned on the coin-type battery case side that is the current collector. Lithium metal (thickness 0.3 mm) was used as the negative electrode. As an electrolyte, lithium borofluoride as an electrolyte in a solvent in which propylene carbonate (PC), γ-butyrolactone (GBL), and dimethoxyethane (DME) were mixed at a volume ratio of 2: 1: 2, the concentration was 1 mol / L. An electrolyte solution was prepared by dissolving the solution.

  The electrolyte solution was impregnated into a polypropylene nonwoven fabric (thickness: 80 μm), a positive electrode, and a negative electrode as a separator. Thereafter, the positive electrode, the separator, and the negative electrode were stacked in this order so that the configuration shown in FIG. 1 was obtained. The opening of the coin-type battery 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.

(Example 2)
In Example 2, a coin-type non-aqueous electrolyte secondary battery in which only the positive electrode current collector was different from that in Example 1 was produced.

  A metal mesh (SUS, 30 mesh, manufactured by Nilaco) punched to 15 mmφ was attached onto a coin-type battery case by spot welding to obtain a positive electrode current collector. A positive electrode was produced in the same manner as in Example 1 except that this positive electrode current collector was used. The weight of the second active material (copolymer compound [11c]) supported on the positive electrode current collector was 3.1 mg. A coin-type nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the positive electrode was used.

(Example 3)
In Example 3, a coin-type non-aqueous electrolyte secondary battery different from Example 1 was produced only in that a conductive auxiliary layer was formed between the positive electrode current collector and the second active material layer.

  A paste-like mixture was prepared by mixing 20 mg of natural graphite, 1 mg of carboxymethylcellulose as a binder, and a dispersion containing 1 mg of PTFE (manufactured by Daikin Industries). The paste mixture was applied onto the coin-type battery case by spin coating. The obtained coating film was dried to form a conductive auxiliary layer having a thickness of 30 μm. A second active material layer was formed on the conductive auxiliary layer formed on the case in the same manner as in Example 1. The weight of the second active material (copolymer compound [11c]) supported on the positive electrode current collector having the conductive auxiliary layer was 3.2 mg. A positive electrode was obtained by laminating the first active material layer on the second active material layer in the same manner as in Example 1. A coin-type nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the positive electrode was used.

(Comparative Example 1)
In Comparative Example 1, a positive electrode including only the first active material layer as a positive electrode active material layer was produced, and a coin-type nonaqueous electrolyte secondary battery was produced.

  First, a positive electrode current collector having a conductive auxiliary layer was obtained in the same manner as in Example 3. A first active material layer was produced in the same manner as in Example 1.

  A positive electrode was obtained by directly laminating the first active material layer on the conductive auxiliary layer. A coin-type nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the positive electrode was used.

(Comparative Example 2)
In Comparative Example 2, a coin-type nonaqueous electrolyte secondary battery including a second active material layer formed between the separator and the first active material layer was produced.

  First, the laminated body in which the 2nd active material layer was formed in the single side | surface of a separator was produced. A paste-like mixture containing the second active material and the conductive assistant was prepared in the same manner as in Example 1. Using the bar coater, the paste-like mixture was applied only to one side of a polypropylene nonwoven fabric (thickness 80 μm). The obtained coating film was vacuum dried at 120 ° C. for 1 hour to remove the solvent in the coating film. The obtained laminated body was punched out to 16 mmφ to obtain a laminated body of a separator and a second active material layer. The supported weight of the second active material (copolymer compound [11c]) calculated from the increase in weight of the separator was 3.0 mg.

  Next, a first active material layer was produced in the same manner as in Example 1. Furthermore, a positive electrode current collector having a conductive auxiliary layer was obtained in the same manner as in Example 3.

  A first active material layer was laminated on the conductive auxiliary layer. A laminate of the separator and the second active material layer was laminated on the first active material layer so that the second active material layer was in contact with the first active material layer. Thereby, the laminated body of the positive electrode and the separator was obtained.

  An electrolytic solution was prepared in the same manner as in Example 1. Lithium metal (thickness 0.3 mm) was used as the negative electrode. The electrolyte solution was impregnated into a laminate of the positive electrode and the separator and the negative electrode. Thereafter, as shown in FIG. 1, the laminate of the positive electrode and the separator and the negative electrode were stacked so that the positive electrode, the separator, and the negative electrode were laminated in this order. The opening of the coin-type battery case was closed with a sealing plate fitted with a gasket, and the case was crimped and sealed with a press. Thus, a coin-type non-aqueous electrolyte secondary battery of Comparative Example 2 was obtained.

[Evaluation of battery charge / discharge characteristics]
For each of the batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2, charge / discharge capacity evaluation and output (pulse discharge characteristics) evaluation were performed.

  The battery was first discharged and then charged to evaluate the charge / discharge capacity. The charge / discharge capacity was evaluated by placing the battery in a constant temperature bath environment at 25 ° C. The charge / discharge test was performed by performing constant current charge / discharge at a current value of 20 hours (0.05 CmA) with respect to the battery capacity. In addition, the voltage range was set such that the charge upper limit voltage was 3.9 V and the discharge lower limit voltage was 2.8 V. The pause time from the end of charging to the start of discharging was 30 minutes. The discharge capacity thus obtained was defined as the charge / discharge capacity of the battery.

  In the output (pulse discharge characteristics) evaluation, the closed circuit voltage after 1 second is measured after the above-described charge / discharge capacity evaluation, that is, when the battery is discharged for 1 second at a current value of 10 mA from the fully charged state of the battery. did. The output evaluation was performed by placing the battery in a -20 ° C. thermostatic chamber environment. The discharge lower limit voltage of the battery in output (pulse discharge characteristics) evaluation was 1V.

  Table 1 summarizes the results of charge / discharge capacity evaluation and output evaluation.

The thicknesses of the first active material layers used in Examples 1 to 3 and Comparative Examples 1 and 2 were equal, and the capacity of the second active material layer used in Examples 1 to 3 and Comparative Example 2 was very small. The batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2 all had reversible and equal charge / discharge capacities derived from the first active material V ₂ O ₅ . As a result of output evaluation, compared with the battery in Comparative Example 1 in which the second active material was not added, the batteries in Examples 1 to 3 had a closed circuit voltage when discharging for 1 second at a current value of 10 mA. it was high. This indicates that the second active material reacted smoothly during high-speed discharge and the voltage drop was reduced. That is, the batteries in Examples 1 to 3 had better output characteristics than the battery in Comparative Example 1. As described above, in Examples 1 to 3, the amount of the added second active material was small, and the output of the battery despite the fact that the second active material contributed very little to the charge / discharge capacity of the battery. The characteristics were greatly improved.

  The battery of Example 3 having a conductive auxiliary layer on the positive electrode current collector exhibited better output characteristics than the battery of Example 1 having no conductive auxiliary layer on the positive electrode current collector.

  The battery of Example 1 having the second active material layer on the positive electrode current collector exhibited better output characteristics than the battery of Comparative Example 1 having the conductive auxiliary layer on the positive electrode current collector. The effect of improving the output characteristics is considered greater when the second active material layer is formed on the positive electrode current collector than when the conductive auxiliary layer is formed on the positive electrode current collector. Moreover, it is thought that the 2nd active material layer formed on the positive electrode electrical power collector can also play the role of a conductive auxiliary layer.

  When the second active material layer is removed from the positive electrode produced in Example 1 (when the conductive auxiliary layer is removed from the positive electrode produced in Comparative Example 1), the resistance is so high that current cannot be taken out in the charge / discharge test. became.

  In addition, from comparison between Example 3 and Comparative Example 1, it is effective for high output to form a conductive auxiliary layer on the positive electrode current collector and further form a second active material thereon. confirmed.

  Further, from the comparison between Example 2 and Comparative Example 1, using a coin-type case with a metal mesh attached as a positive electrode current collector and further forming a second active material on the metal mesh can increase the output. It was confirmed to be effective.

  The batteries of Examples 1 to 3 had a higher output than the batteries of Comparative Examples 1 and 2 because the second active material was an organic compound and the second active material layer was a positive electrode. This is considered to be due to a synergistic effect with that provided between the current collector and the first active material layer. That is, it is considered that the charge / discharge reaction proceeded at a high speed because the second active material was an organic compound. Furthermore, since the second active material layer is provided between the positive electrode current collector and the first active material layer, the contact resistance at the interface between the positive electrode current collector and the positive electrode active material layer is reduced, It is thought that the electronic conductivity of the positive electrode as a whole was improved.

  The battery of Example 2 had a higher closed circuit voltage during pulse discharge than the battery of Comparative Example 2. That is, the battery of Example 2 was superior to the battery of Comparative Example 2 in high output characteristics. In the battery of Example 2, the second active material layer was disposed between the positive electrode current collector and the first active material layer. In the battery of Comparative Example 2, since the second active material layer was formed on the separator, the effect of reducing the contact resistance was not obtained, and it was considered that the high output characteristics of the second active material layer could not be sufficiently exhibited. It is done.

  As described above, according to the present invention, it is possible to improve the output characteristics, particularly the pulse discharge characteristics, of the nonaqueous electrolyte secondary battery without greatly reducing the energy density.

  The nonaqueous electrolyte secondary battery of the present invention is not limited to the embodiment as a coin-type battery, and various embodiments such as a cylindrical battery and a prismatic battery can be adopted.

  The nonaqueous electrolyte secondary battery of the present invention has high output, high capacity, and excellent repeatability. In particular, since the non-aqueous electrolyte secondary battery of the present invention is excellent in pulse discharge characteristics, it can be suitably used in various portable devices, transportation devices, uninterruptible power supplies and the like that require a large current instantaneously.

DESCRIPTION OF SYMBOLS 1, 2 Coin type non-aqueous electrolyte secondary battery 10,15 Positive electrode 11 Positive electrode active material layer 12 First active material layer 13 Second active material layer 14 Conductive auxiliary layer 20 Negative electrode 21 Negative electrode active material layer 22 Negative electrode current collector 30 Separator 31 Electrolytic solution (electrolyte)
50 Coin type case (positive electrode current collector)
51 Sealing plate 52 Gasket

Claims (8)

A positive electrode having a positive electrode current collector, a first active material layer, and a second active material layer;
A negative electrode comprising a negative electrode active material capable of inserting and extracting lithium ions;
An electrolyte containing a salt of lithium ions and anions,
The first active material layer includes a first active material that can occlude and release lithium ions as a main active material,
The second active material layer includes, as a main active material, a second active material that is an organic compound capable of occluding and releasing the anions, and a conductive auxiliary agent.
The non-aqueous electrolyte secondary battery, wherein the second active material layer is provided between the positive electrode current collector and the first active material layer.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the second active material covers the surface of the conductive additive. The positive electrode further has a conductive auxiliary layer composed of a carbon material and a binder,
The nonaqueous electrolyte secondary battery according to claim 1, wherein the conductive auxiliary layer is provided between the positive electrode current collector and the second active material layer.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the second active material is a polymer having a tetrachalcogenofulvalene skeleton.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the first active material is a transition metal oxide that may contain lithium. The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal oxide is V ₂ O ₅ . The non-aqueous electrolyte secondary battery according to claim 1, wherein the transition metal oxide is LiFePO ₄ . The first active material layer includes only the first active material as an active material,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the second active material layer includes only the second active material as an active material.

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