JP2012252797A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery that enhances an output characteristic, particularly a pulse discharge characteristic without greatly reducing energy density.SOLUTION: A nonaqueous electrolyte secondary battery has a positive electrode containing a first active material capable of occluding and discharging lithium ions and a second active material capable of occluding and discharging anions, a negative electrode containing a negative electrode active material capable of occluding and discharging lithium ions and nonaqueous electrolyte containing lithium ions and anions. The second active material is an organic compound, and the first active material has a particular shape. (a) The second active material has a particular shape or (b) the first active material is coated with a non-redox material, so that the nonaqueous electrolyte comes into direct contact with particles of the (a) first active material or particles comprising the (b) first active material and the non-redox material, and the second active material.

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 the 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.

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

  As described above, although an active material that can occlude and release lithium ions and an active material that is a second component are added to the positive electrode, efforts have been made to improve the output characteristics of the lithium secondary battery. The knowledge about the optimal combination of the first active material and the second active material and the electrode structure was insufficient.

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

That is, the present invention
A positive electrode comprising: a first active material capable of inserting and extracting lithium ions; and a second active material capable of inserting and extracting anions;
A negative electrode comprising a negative electrode active material capable of inserting and extracting lithium ions;
A non-aqueous electrolyte containing a salt of lithium ion and the anion,
The second active material is an organic compound;
The first active material has a particle shape;
(A) the second active material has a particle shape, and the non-aqueous electrolyte is in direct contact with each of the first active material and the second active material,
Or
(B) The surface of the first active material is coated with a non-redox material, and the first active material and the non-active material can be subjected to a redox reaction between the first active material and the lithium ions. The non-aqueous electrolyte is in direct contact with the surface of the particles composed of the redox material, and the non-aqueous electrolyte is in direct contact with the second active material,
A non-aqueous electrolyte secondary battery is provided.

Further, the present invention from another viewpoint,
The first active material particles capable of occluding and releasing lithium ions and the non-aqueous electrolyte containing a salt of lithium ions and anions have no swellability, can occlude and release the anions, and Preparing a mixture comprising a second active material particle, which is an organic compound;
The shape of the particles of the first active material and the second active material is such that a positive electrode active material layer containing the first active material and the second active material as a positive electrode active material is formed on the positive electrode current collector. Forming the mixture while holding;
Impregnating the non-aqueous electrolyte into the positive electrode active material layer;
The manufacturing method of the nonaqueous electrolyte secondary battery containing this is provided.

Furthermore, the present invention from another viewpoint,
A first active material particle capable of occluding and releasing lithium ions and having a surface coated with a non-oxidation-reducing substance; a second anion capable of occluding and releasing anions; and an organic compound. Preparing a mixture comprising an active material;
Forming the mixture such that a positive electrode active material layer containing the first active material and the second active material as a positive electrode active material is formed on a positive electrode current collector;
Impregnating the positive electrode active material layer with a nonaqueous electrolyte containing a salt of lithium ion and the anion;
The manufacturing method of the nonaqueous electrolyte secondary battery containing this 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. A sufficient energy density can be secured by using a material capable of inserting and extracting lithium ions as the first active material. Furthermore, the pulse discharge characteristics can be improved by using an organic compound that can occlude and release anions contained in the electrolyte as the second active material. Further, (a) the second active material has a particle shape, or (b) the surface of the first active material is coated with a non-oxidation / reduction material. Therefore, the non-aqueous electrolyte is in direct contact with each of (a) the particles of the first active material or (b) the particles composed of the first active material and the non-oxidation-reduction material and the second active material. is doing. Thereby, a 1st active material and a 2nd active material can charge / discharge each independently. That is, it is possible to provide a battery having both good output characteristics (pulse discharge characteristics) due to the second active material and high capacity due to the first active material. Further, since the first active material and the second active material can be charged and discharged independently of each other, desired output characteristics (pulse discharge characteristics) can be obtained by arbitrarily changing the composition ratio of both active materials in the positive electrode. Can be designed.

  Thus, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery with improved output characteristics, particularly pulse discharge characteristics, without greatly reducing the energy density. In addition, the second active material that is an organic compound in the present invention has a smaller moisture adsorption capacity than activated carbon. Therefore, the moisture content inside the battery can be reduced.

  According to the production method of the present invention, (a) particles of the first active material or (b) particles composed of the first active material and the non-oxidation / reduction material, and the second active material are non-reactive. A nonaqueous electrolyte secondary battery including a positive electrode having a structure in which a water electrolyte is in direct contact can be efficiently produced.

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 positive electrode in one Embodiment of this invention. It is typical sectional drawing which shows the positive electrode in another embodiment of this invention. 3 is a graph showing charge / discharge characteristics of the battery of Example 1. 6 is a graph showing charge / discharge characteristics of the battery of Example 3. 5 is a graph showing charge / discharge characteristics of the battery of Comparative Example 1.

  Hereinafter, embodiments of the nonaqueous electrolyte secondary battery of the present invention will be described.

(Embodiment 1)
FIG. 1 shows a schematic cross section of a coin-type non-aqueous electrolyte secondary battery 100 which is an embodiment of the non-aqueous electrolyte secondary battery according to the present invention. The battery 100 has a structure in which the inside is sealed by a coin-type case 50, a sealing plate 51, and a gasket 52. Inside battery 100, positive electrode 10 including positive electrode active material layer 11 and positive electrode current collector 12, negative electrode 20 including negative electrode active material layer 21 and negative electrode current collector 22, and separator 30 are housed. 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 a liquid non-aqueous electrolyte 31. The separator 30 has a fine space (micropore), and the electrolyte 31 is held in the fine space.

  FIG. 2 schematically shows a cross-sectional structure of the positive electrode 10. It is assumed that the positive electrode 10 is in a state after being impregnated with the electrolyte 31. The positive electrode 10 includes a positive electrode current collector 12 and a positive electrode active material layer 11 provided on the positive electrode current collector 12.

  The positive electrode active material layer 11 includes at least two types of electrode active materials, that is, a first active material 13 and a second active material 14. The first active material 13 is a positive electrode active material capable of inserting and extracting lithium ions, and has a particle shape. The second active material 14 is made of an organic compound that can occlude and release anions. As shown in FIG. 2, in the first embodiment, the second active material 14 does not have swelling properties with respect to the non-aqueous electrolyte 31 and has a particle shape.

  The positive electrode active material layer 11 has a substrate 17. The first active material 13 and the second active material 14 are uniformly dispersed in the substrate 17. When the volume of the substrate 17 is sufficiently smaller than the volumes of the first active material 13 and the second active material 14, the substrate 17 fills a gap around the first active material 13 and the second active material 14. The substrate 17 is typically composed of a binder, a conductive aid, and an electrolyte 31. In the substrate 17, the electrolyte 31 may constitute a gel electrolyte.

  The second active material 14 does not directly cover the surface of the first active material 13. The second active material 14 does not exist so as to cover the surface of the first active material 13, and the first active material 13 and the second active material 14 exist in different particles. The particles of the first active material 13 and the particles of the second active material 14 exist independently of each other. Therefore, the positive electrode 10 according to the first embodiment has a structure in which the non-aqueous electrolyte (specifically, the electrolyte 31) is in direct contact with each of the first active material 13 and the second active material 14. As long as the first active material 13 and the second active material 14 form particles, the region where these particles exist in the positive electrode active material layer 11 is not limited, and these particles may be in contact with each other. .

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

  The first reason is material characteristics of the two active materials contained in the positive electrode. One of the two active materials contained in the positive electrode 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. In addition, a main active material means the active material which occupies 50% or more of electrical storage capacity with respect to the total electrical storage capacity of a nonaqueous electrolyte secondary battery. According to the first active material, a lithium ion moves between the positive electrode and the negative electrode along with charge / discharge, whereby a high voltage of 3V class and a high capacity can be realized. On the other hand, the other one of the two active materials contained in the positive electrode is an organic active material (second active material) that can occlude and release anions.

  In the present invention, as the second active material, although described in detail later, a compound having a radical, a compound having a π-conjugated electron cloud, and the like are preferably used. These compounds are suitable as active material materials for the positive electrode because the oxidation-reduction reaction proceeds at a potential of about 3 to 4 V with respect to lithium. Moreover, the reaction in which these compounds occlude and release anions as the second active material is faster than the reaction in which the first active material occludes and releases lithium ions. Therefore, by using the second active material, it is possible to provide a non-aqueous electrolyte secondary battery having high output, particularly excellent pulse discharge characteristics. Furthermore, since these compounds have a capacity larger than that of activated carbon, when these compounds are used as the second active material, 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 using two kinds of 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 reactive 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 a second component to an active material capable of occluding and releasing 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 the addition of 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 serious adverse effect due to the use of the first active material and the second active material. When activated carbon is added as the second component to the active material capable of occluding and releasing lithium ions as in the above 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.

  As the second active material in the present invention, an organic compound such as a compound having a radical and a compound having a π-conjugated electron cloud is preferably used. The organic compound has a low water adsorption capacity compared to the water adsorption capacity of activated carbon. Therefore, these organic compounds do not have an adverse factor due to the combined use with an active material (first active material) that can occlude and release lithium ions. For this reason, a highly reliable nonaqueous electrolyte secondary battery can be obtained by using a 2nd active material with a 1st active material.

  The fourth reason is that the two active materials can react independently without interfering with each other.

  For example, it is assumed that the active material D covers the entire surface of the active material C in a positive electrode using two types of positive electrode active materials C and D. In such a positive electrode structure, since the contact between the active material C and the electrolyte is inhibited by the active material D, the active material C cannot perform a charge / discharge reaction alone, and sufficient battery performance cannot be obtained. Specifically, the first active material must be charged after the second active material is charged first, or conversely, the first active material is discharged first, and the second active material is discharged first. Mutual inhibition occurs that must be done after a while.

  On the other hand, in the positive electrode according to the present invention, the surface of the first active material is not directly covered with the second active material, and (a) particles of the first active material or (b) non-oxidized with the first active material. It has a structure in which the non-aqueous electrolyte is in direct contact with each of the particles composed of the reducing substance and the second active material. Therefore, said inhibition by using an organic compound as a 2nd active material is suppressed, and a 1st active material can be charged / discharged independently. That is, the first active material that provides a high capacity and the second active material that provides a high output can separate the functions and perform charge / discharge reactions independently of each other, resulting in high capacity and high output (pulse discharge). A non-aqueous electrolyte secondary battery can be obtained.

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

  Hereinafter, constituent materials that can be used for the battery 100 of the first embodiment will be described.

As the 1st active material 13, a well-known thing can be used as a positive electrode active material material of a lithium ion battery. Specifically, a transition metal oxide that may contain lithium can be used as the first active material 13. 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 13. 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 13.

  The average particle diameter of the particles of the first active material 13 is, for example, 0.05 μm to 50 μm. A large contact area between the first active material 13 and the electrolyte 31 can be ensured by adjusting the average particle size of the particles of the first active material 13 to the above range. Furthermore, since the contact area between the first active material 13 and the conductive additive is increased, good electronic conductivity can be ensured. In the present specification, the average particle diameter means a particle diameter corresponding to 50% of the cumulative volume of the particle size distribution measured by a laser diffraction particle size meter (may be expressed as median diameter or D50). .

  As the second active material 14, a compound having a radical, a compound having a π-conjugated electron cloud, or the like is preferably used.

  Examples of the compound having a radical include a compound having a partial structure of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) represented by the following formula (1). These compounds are desirably polymers from the viewpoint of suppressing dissolution in the electrolyte 31. Examples of the polymer include compounds represented by the following formula (2).

  Examples of the compound having a π-conjugated electron cloud include tetrathiafulvalene represented by the following formula (3) and derivatives thereof, EBDT (2,2′-ethanediylidene-bis-1,3-dithiol) represented by the following formula (4), and the like. Derivatives and the like. From the viewpoint of suppressing dissolution in the electrolyte 31, the compound having a π-conjugated electron cloud may be used as a crystal or a polymer as long as it has a low molecular weight. The polymer having a π-conjugated electron cloud may be, for example, a side-chain polymer including a structure having a π-conjugated electron cloud in the side chain, and a main chain type including a structure having a π-conjugated electron cloud in the main chain. It may be a polymer. The number of structures having a π-conjugated electron cloud contained in one molecule of polymer (in the case of a polymer composed of repeating units containing the structure, the average degree of polymerization of the polymer) is 4 or more, preferably 10 or more. Preferably it is 20 or more. The upper limit of the number of structures having a π-conjugated electron cloud (or average degree of polymerization) contained in one molecule of polymer is not particularly limited, but is preferably 4000 or less from the viewpoint of synthesis controllability. That is, when the polymer is composed of repeating units containing the structure, the number average molecular weight of the polymer is about 800 or more, preferably about 2000 or more, more preferably about 4000 or more, and the upper limit is not particularly limited, 800,000 or less is desirable from the viewpoint of synthesis controllability. In the present specification, the molecular weight of the polymer means a molecular weight in terms of polystyrene obtained from gel permeation chromatography (hereinafter referred to as “GPC”).

  As in the first embodiment, when the second active material is used as particles, it is desirable that the second active material does not have swelling properties with respect to the electrolyte. This is because, when the second active material has swelling properties with respect to the electrolyte, it is difficult for the second active material to maintain the particle shape even after the positive electrode is impregnated with the electrolyte. When the second active material is excessively swollen by the electrolyte, the second active material is widely dispersed inside the pores filled with the electrolyte in the positive electrode. Many directly covered sites occur. If the second active material directly covers the surface of the first active material, the first active material is likely to be inhibited by the second active material. That is, it becomes difficult to charge and discharge the first active material alone, making it difficult to construct a secondary battery having both the high capacity of the first active material and the high output characteristics of the second active material. Become.

  Therefore, the organic compound used as the second active material 14 in Embodiment 1 is more preferably a compound having a π-conjugated electron cloud. This is because a compound having a π-conjugated electron cloud has a relatively small amount of swelling with respect to the electrolyte 31, and conversely, a compound having a radical has a relatively large amount of swelling with respect to the electrolyte 31. .

  The average particle diameter of the particles of the second active material 14 is, for example, 0.03 μm to 20 μm. A large contact area between the second active material 14 and the electrolyte 31 can be secured by adjusting the average particle size of the particles of the second active material 14 to the above range. Furthermore, since the contact area between the second active material 14 and the conductive auxiliary agent also increases, good electron conductivity can be ensured.

  The positive electrode active material layer 11 (specifically, the substrate 17) is, if necessary, a conductive aid for assisting electronic conductivity in the electrode and / or a binder for maintaining the shape of the positive electrode active material layer 11. An agent may be included.

  As the conductive auxiliary agent, various electron conductive materials that do not cause a chemical change at the reaction potential of the electrode can be used. 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 may be a mixture thereof. From the viewpoint that the energy density per unit weight can be increased, it is preferable to use carbon black as a conductive aid. Furthermore, in order to increase the contact area, it is desirable to use carbon black having a large specific surface area as a conductive aid.

  The binder may be either a thermoplastic resin or a thermosetting resin. Examples of the binder include polyolefin resins such as polyethylene and polypropylene; fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), and copolymer resins thereof; Examples thereof include styrene butadiene rubber, polyacrylic acid and copolymer resins thereof.

  The addition amount of the first active material 13 in the positive electrode 10 is preferably 50% or more, more preferably 70% or more, expressed by the storage capacity of the first active material 13 in the total storage capacity of the battery 100. preferable. The amount of the second active material 14 added to the positive electrode 10 is preferably 50% or less, more preferably 30% or less, expressed as the storage capacity of the second active material 14 in the total storage capacity of the battery 100. preferable. When the storage capacity of the first active material 13 is 50% or more of the total storage capacity of the battery 100, that is, when the storage capacity of the second active material 14 is 50% or less of the total storage capacity of the battery 100, A battery 100 that realizes both a high capacity derived from the substance 13 and a high output derived from the second active material 14 can be constructed. Further, when the storage capacity of the first active material 13 is 70% or more of the total storage capacity of the battery 100, that is, when the storage capacity of the second active material 14 is 30% or less of the total storage capacity of the battery 100, A battery 100 that realizes both a higher capacity derived from the one active material 13 and a higher output derived from the second active material 14 can be constructed.

  When the storage capacity of the first active material 13 is smaller than 50% of the total storage capacity of the battery 100, that is, when the storage capacity of the second active material 14 is larger than 50% of the total storage capacity of the battery 100, the second active material 14 Although the high output derived can be realized, it is difficult to realize the high capacity derived from the first active material 13.

  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 foil or mesh made of metal such as aluminum or stainless steel, carbon, or the like. When the positive electrode current collector 12 is a metal foil, an aluminum foil having a thickness of about 5 to 30 μm is preferably used. This is because the aluminum foil is excellent in electrochemical stability in the operating range of the positive electrode 10 and can maintain a sufficient strength even if it is a thin film having a thickness of about 5 to 30 μm. Further, the surface of the metal foil may be roughened by electrolytic etching treatment, blast treatment or the like.

  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 separator 30 is a resin layer made of a resin having no electronic conductivity, and is a microporous film having a large ion permeability and sufficient mechanical strength and electrical insulation. From the viewpoint of excellent organic solvent resistance and hydrophobicity, a polyolefin resin in which polypropylene, polyethylene or the like is used alone or in combination is preferable. Instead of the separator 30, a resin layer having an ion conductivity that swells and contains the electrolyte 31 and functions as a gel electrolyte may be provided.

  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 capable of reversibly occluding and releasing lithium ions is not particularly limited as long as it is a known negative electrode material in a lithium battery. For example, graphite materials such as natural graphite and artificial graphite, and amorphous carbon materials Lithium metal, lithium-containing composite nitride, lithium-containing titanium oxide, silicon, an alloy containing silicon, silicon oxide, tin, an alloy containing tin, and tin oxide. The negative electrode active material may be a mixture of these negative electrode materials. For the negative electrode current collector 22, for example, a material known as a current collector of a negative electrode for a lithium secondary battery, such as copper, nickel, and stainless steel, can be used.

  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 nonaqueous electrolyte 31 is an electrolytic solution containing a nonaqueous solvent and a salt (electrolyte salt) of lithium ions and anions.

The salt of lithium ion and anion is not particularly limited as long as it is a salt used in a lithium battery, and examples thereof 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 nonaqueous electrolyte, the positive electrode 10 may contain a solid electrolyte. 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 electrolyte 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. Specific examples of the non-aqueous solvent include at least one selected from the group consisting of cyclic or chain carbonate ester, cyclic or chain ester, cyclic or chain ether, cyclic or chain sulfone, and nitrile. The containing solvent can be used suitably. Specific examples of the cyclic carbonate include ethylene carbonate and propylene carbonate. Specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Specific examples of the cyclic or chain ester include γ-butyrolactone, methyl propionate, butyl propionate and the like. Specific examples of the cyclic or chain ether include 1,4-dioxane, tetrahydrofuran and the like. Specific examples of the cyclic or chain sulfone include dioxolane and sulfolane. Specific examples of nitriles include acetonitrile.

  By including these solvents as components of the non-aqueous solvent, the entire non-aqueous solvent in the electrolyte 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.

(Embodiment 2)
When an organic compound that can be swollen by an electrolyte is used as the second active material, it is desirable to adopt Embodiment 2 described below. In addition, the nonaqueous electrolyte secondary battery of Embodiment 2 differs from Embodiment 1 only in the positive electrode. Therefore, the description other than the positive electrode is omitted, and only the positive electrode is described below.

  FIG. 3 schematically shows a cross-sectional structure of positive electrode 40 in the second embodiment. It is assumed that the positive electrode 40 is in a state after being impregnated with the electrolyte 31. The positive electrode 40 includes a positive electrode current collector 12 and a positive electrode active material layer 41 provided on the positive electrode current collector 12. The positive electrode active material layer 41 includes a first active material 43 and a second active material 44. The first active material 43 is a positive electrode active material that can occlude and release lithium ions, and has a particle shape. The surface of the first active material 43 is coated with a non-oxidation / reduction material (not shown). The particles composed of the first active material 43 and the non-oxidation / reduction material are uniformly dispersed in the substrate 17. The 2nd active material 44 consists of an organic compound which can occlude and discharge | release an anion, and has the swelling property with respect to the electrolyte 31 (refer FIG. 1). The second active material 44 is swollen by the electrolyte 31 and is uniformly dispersed in the substrate 17.

  In the positive electrode 40, the second active material 44 is swollen by the electrolyte 31 and dispersed in the substrate 17, but the surface of the first active material 43 is coated with a non-oxidation-reducing material. Does not directly cover the surface of the first active material 43. A non-aqueous electrolyte (electrolyte 31) is directly applied to the surface of the particles composed of the first active material 43 and the non-oxidation / reduction material so that the first active material 43 and the lithium ions can undergo a redox reaction. Touching. The non-aqueous electrolyte is also in direct contact with the second active material 44. In the second embodiment, the particles composed of the first active material 43 and the non-oxidation / reduction material are composed of only the first active material 43 and the non-oxidation / reduction material.

  When the first active material does not have a coating and the second active material is swellable with respect to the electrolyte, in the positive electrode, the second active material is widely dispersed inside the pores filled with the electrolyte. An obstruction factor arises because the second active material directly covers the surface of the first active material. On the other hand, when the first active material is coated with a non-oxidation / reduction material, the non-oxidation / reduction material prevents direct contact between the first and second active materials. Even if the second active material is swellable with respect to the electrolyte, the positive electrode structure in which the electrolyte is in contact with the surface of the particles composed of the first active material and the non-oxidation-reducing material is obtained. Factors can be suppressed. Therefore, also in the second embodiment, similarly to the first embodiment, the first active material 43 and the second active material 44 can independently perform charge and discharge reactions, and have a high capacity and high output (pulse discharge). ) Can be obtained.

  In this specification, “the second active material does not directly cover the surface of the first active material” means that a small area on the surface of the first active material is directly covered by the second active material. It does not preclude the case. As long as the degree of coating with the second active material is slight, (a) the particles of the first active material or (b) the particles composed of the first active material and the non-oxidation-reducing material are sufficient for the non-aqueous electrolyte. This is because the first active material can carry out a charge / discharge reaction independently.

  Hereinafter, constituent materials that can be used for the positive electrode 40 in the nonaqueous electrolyte secondary battery of Embodiment 2 will be described.

  As the first active material 43, the same material as the first active material 13 in Embodiment 1 can be used. The average particle diameter of the particles composed of the first active material 43 and the non-oxidation / reduction substance is the same as the average particle diameter of the particles of the first active material 13 in the first embodiment.

  The non-oxidation / reduction substance is not particularly limited as long as it does not contribute to the oxidation / reduction reaction in the battery 100. The non-oxidation / reduction substance is a substance that can continue to exist stably in the positive electrode 40 regardless of the usage state of the battery 100. That is, the non-oxidation / reduction substance is “a substance that does not cause an oxidation-reduction reaction in a potential region from the upper limit value to the lower limit value of the charge / discharge voltage of the battery 100”. In other words, the non-redox substance is “a substance that does not cause a redox reaction itself, that is, a substance that does not have a redox potential” and “a redox potential, both of which have a redox potential. It is either “a substance that is not less than the upper limit value or less than the lower limit value of the voltage range”. Specific examples of the non-oxidation / reduction substance include a conductive additive and a non-electron conductor. Examples of the conductive assistant include carbon materials typified by carbon black, and examples of the non-electron conductor include metal oxides typified by titanium oxide, ceramics, and ion conductive ceramics. .

  The non-oxidation / reduction material partially or completely coats the surface of the particles of the first active material 43 to such an extent that the reaction between the first active material 43 and the lithium ions in the electrolyte 31 is allowed. The non-oxidation / reduction material does not interfere with the contact between the first active material 43 and the electrolyte 31 and can prevent the contact between the first active material 43 and the second active material 44. It is preferable that the surface is intermittently and evenly distributed on the surface. Note that, as long as the reaction between the first active material 43 and the lithium ions in the electrolyte 31 is not hindered, the non-oxidation / reduction material may completely cover the surface of the first active material 43.

  The coating amount of the non-oxidation / reduction substance is, for example, 0.1 to 20% by weight with respect to the first active material 43. The thickness of the coating with the non-oxidation / reduction substance is, for example, 1 to 20 nm.

  Specific examples of the organic compound having swelling properties with respect to the electrolyte 31 used as the second active material 44 in the second embodiment include the compounds having the radicals described in the first embodiment. . This is because, as described above, relatively many compounds having radicals have swelling properties with respect to the electrolyte 31.

  As in the second embodiment, when the surface of the first active material is coated with a non-redox material, the second active material can be swollen by a compound that can maintain the particle shape without being swollen by the electrolyte and the electrolyte. Any of the compounds to be used may be used. Specifically, the compound having a radical exemplified in Embodiment 1 and the compound having a π-conjugated electron cloud can be suitably used as the second active material regardless of the presence or absence of swelling with respect to the electrolyte. .

  A positive electrode similar to the positive electrode 10 in Embodiment 1 when a first active material having a coating with a non-oxidation / reduction material is used and a compound capable of maintaining the particle shape without being swollen by an electrolyte is used as the second active material. A structure is obtained. That is, the positive electrode structure in which the first active material and the second active material each have the shape of a particle, and the electrolyte is in direct contact with the surface of the particle composed of the first active material and the non-redox material Is obtained. In this case, the average particle diameter of the second active material particles is the same as that in the first embodiment. Such a positive electrode can be manufactured by a manufacturing method similar to that of the positive electrode 10 in Embodiment 1.

  The positive electrode active material layer 41 may include a conductive auxiliary agent that assists electronic conductivity in the electrode and / or a binder for maintaining the shape of the positive electrode active material layer 41 as necessary. Preferred materials for the conductive assistant and the binder are the same as those in the first embodiment. Preferred addition amounts of the first active material 43 and the second active material 44 in the positive electrode 40 are also the same as those in the first embodiment. A preferable material for the positive electrode current collector 12 is the same as that in the first embodiment.

  As a manufacturing method of the nonaqueous electrolyte secondary battery 100, a known manufacturing method can be adopted. The positive electrode 10 in Embodiment 1 can be manufactured as follows, for example. First, the particles of the first active material 13 that can occlude and release lithium ions and the nonaqueous electrolyte 31 containing a salt of lithium ions and anions have no swellability and can occlude and release anions. And a mixture containing particles of the second active material 14, which is an organic compound. Next, the first active material 13 and the second active material 14 are formed so that the positive electrode active material layer 11 including the first active material 13 and the second active material 14 as the positive electrode active material is formed on the positive electrode current collector 12. The mixture is molded while maintaining the shape of the particles. The positive electrode 10 is obtained by impregnating the positive electrode active material layer 11 with the nonaqueous electrolyte 31. As a method of forming the positive electrode active material layer 11 by forming the above mixture, either a dry method or a wet method may be used. In the dry method, for example, the positive electrode active material layer 11 is formed by uniformly kneading the mixture and then pressing the mixture onto the positive electrode current collector 12. In the wet method, for example, a paste in which the particles of the first active material 13 and the particles of the second active material 14 are dispersed in a solvent that does not dissolve the second active material 14 (for example, water) is prepared as the mixture. . The paste is applied onto the positive electrode current collector 12 to form a coating film, and the coating film is dried, whereby the positive electrode active material layer 11 is formed.

  In the case of using particles of the first active material 43 whose surface is coated with a non-oxidation / reduction substance, for example, the positive electrode can be produced as follows. First, lithium ions can be occluded and released, and particles of the first active material 43 whose surface is coated with a non-oxidation reducing substance, anions can be occluded and released, and an organic compound can be used. A mixture containing a second active material is prepared. Next, the mixture is formed such that a positive electrode active material layer including the first active material 43 and the second active material as a positive electrode active material is formed on the positive electrode current collector 12. A positive electrode is obtained by impregnating the positive electrode active material layer with a non-aqueous electrolyte 31 containing a salt of lithium ions and anions. For example, when the second active material 44 having swellability with respect to the nonaqueous electrolyte 31 is used, the positive electrode active material layer 41 in the second embodiment is formed, and the positive electrode 40 is obtained. When the second active material 14 that does not swell with respect to the nonaqueous electrolyte 31 is used, a layer similar to the positive electrode active material layer 11 in the first embodiment is formed, and a structure similar to that of the positive electrode 10 is obtained. .

  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, 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 this specification, “the second active material has no swellability with respect to the electrolyte” means that the second active material can maintain the particle shape in the positive electrode of the non-aqueous electrolyte secondary battery. means. Whether or not the second active material has swelling properties with respect to a liquid non-aqueous electrolyte (electrolytic solution) can be confirmed, for example, by the following method. That is, the particles of the second active material are introduced into a large excess of the electrolytic solution, and the particle size distribution measurement is performed on the mixed solution. If it is confirmed that the shape of the particles is maintained, it can be determined that the second active material does not have swelling properties with respect to the electrolytic solution. If the presence of the particles is not confirmed, it can be determined that the second active material has swelling properties with respect to the electrolytic solution.

  Moreover, you may confirm whether the 2nd active material has swelling property with the following method. Specifically, when the volume swelling ratio of the second active material after assembly based on the pre-assembly of the nonaqueous electrolyte secondary battery (the state in which the electrolyte is not impregnated) is 0% or more and less than 20%, It can be determined that “it does not have swelling”. On the contrary, when the volume swelling ratio of the second active material after assembly with respect to the pre-assembly of the non-aqueous electrolyte secondary battery is 20% or more, it can be determined that it has “swellability”. However, as can be understood from technical common sense, a compound having a volume swelling ratio that is high enough to dissolve in the electrolyte in the battery is not suitable as the second active material in the present invention. This is because such a compound elutes from the positive electrode and is no longer functioning as a positive electrode active material. It is assumed that the second active material is held in the positive electrode in the battery. Although the upper limit of the volume swelling rate of a 2nd active material is not specifically limited, For example, it is 200% or less.

  The volume swelling rate of the second active material is represented by the following formula (5).

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to a following example.

  In Examples 1 to 3 and Comparative Example 1, various positive electrodes including a first active material capable of occluding and releasing lithium ions and a second active material composed of an organic compound capable of occluding and releasing anions A coin-type nonaqueous electrolyte secondary battery shown in FIG. 1 was produced using these positive electrodes.

Example 1
In Example 1, the second active material does not have swellability with respect to the electrolyte, the first active material and the second active material each have a particle shape, and the surface of the first active material is non-oxidized and reduced. A positive electrode coated with the material was prepared. As the first active material, lithium iron phosphate (LiFePO ₄ ) (average particle size 9 μm, carbon amount 2 wt%, manufactured by TATUNG FINE CHEMICALS) was used. As the second active material, bisethylenedithiotetrathiafulvalene (BEDT-TTF) represented by the following formula (6), which is a compound having a π-conjugated electron cloud and a tetrathiafulvalene derivative (average particle diameter after grinding: 10 μm, Aldrich) Used).

  In order to confirm that the second active material (BEDT-TTF) does not have swelling property with respect to the electrolyte, the swelling property was evaluated. In the evaluation of swelling, first, 0.1 mL of a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1 was added to 2 mg of the second active material pulverized in a mortar, The presence or absence of swelling of the second active material particles therein was visually observed. As a result, swelling of the BEDT-TTF powder was not confirmed. Further, the mixed solvent was added to the solution in an excess amount, that is, until the total volume became 10 mL, and diluted, and particle size distribution measurement (SALD-7000, manufactured by Shimadzu Corporation) was performed. As a result, BEDT-TTF particles of about 10 μm were confirmed. Therefore, it was confirmed that the BEDT-TTF powder did not swell with respect to the electrolyte and could exist as particles.

[Production of positive electrode]
50 mg of lithium iron phosphate subjected to carbon coating treatment, 50 mg of BEDT-TTF, and 128 mg of acetylene black as a conductive assistant were weighed and kneaded in a mortar. Further, 27 mg of polytetrafluoroethylene was added as a binder and kneaded in a mortar. The mixture obtained in this manner was pressure-bonded with a rolling roller onto a stainless mesh (Niraco Co., 30 mesh) as a current collector, vacuum-dried, and punched into a disk shape having a diameter of 16 mm. A positive electrode was produced. The application weight of the active material in this positive electrode was 7.3 mg for lithium iron phosphate and 5.6 mg for BEDT-TTF.

In order to confirm the distribution of the positive electrode active material in the prepared positive electrode, the cross section of the positive electrode of Example 1 was measured twice by an electron beam microanalyzer (EPMA) and Auger electron spectroscopy. Specifically, the first measurement was performed immediately after producing the positive electrode, and the second measurement was performed after the produced positive electrode was immersed in an electrolyte solvent. As a solvent for immersing the positive electrode, a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1 was used. The positive electrode was immersed in this mixed solvent and subjected to vacuum impregnation, and then the mixed solvent was removed by vacuum drying treatment, and then the second measurement was performed. As a result, in any of the two measurements, there was no change in the distribution of the positive electrode active material in the positive electrode, and LiFePO ₄ and BEDT-TTF were both present as particles of about 10 μm. Therefore, in the positive electrode of Example 1, the second active material did not cover the surface of the first active material, and both the first active material and the second active material were present as particles.

[Production of non-aqueous electrolyte secondary battery]
A coin-type non-aqueous electrolyte secondary battery shown in FIG. 1 was produced using the positive electrode of Example 1. Lithium metal (thickness 0.3 mm) was used as the negative electrode. As the non-aqueous solvent, a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 3 was used. An electrolyte was prepared by dissolving lithium hexafluorophosphate as an electrolyte salt in the mixed solvent so as to have a concentration of 1.25 mol / L.

  This electrolyte 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 battery of Example 1 was obtained.

[Evaluation of battery charge / discharge characteristics]
By performing a charge / discharge test on the battery of Example 1, the charge / discharge characteristics were evaluated. The charge / discharge test was performed by placing the battery in a constant temperature bath environment at 25 ° C. and performing constant current charge / discharge at a current value of 10 hours (0.1 CmA) with respect to the battery capacity. The voltage range for charging and discharging was set so as to include the redox potentials of the first active material and the second active material. That is, in the present Example 1, the charge upper limit voltage was 3.7 V, and the discharge lower limit voltage was 3.0 V. A charge / discharge curve for the third cycle was obtained after confirming that the charge / discharge operation could be stably performed by repeating the charge / discharge test for 3 cycles. In addition, the rest time until the start of discharge after the end of charging and the rest time until the start of charging after the end of discharging were both 30 minutes. The charge / discharge curve of the third cycle is shown in FIG. The horizontal axis of FIG. 4 is the value obtained by dividing the discharge capacity of the battery, that is, the amount of discharge electricity by the total weight of the first active material and the second active material in the positive electrode. In FIG. 4, the high voltage curve is the transition of the battery voltage during charging, and the low voltage curve is the transition of the battery voltage during discharging. The same applies to FIGS. 5 and 6 described later.

  As shown in FIG. 4, the battery of Example 1 showed reversible charge / discharge with a capacity of 90 mAh / g. That is, it was confirmed that both the first active material and the second active material contributed to charging / discharging with the designed capacity. Further, as shown by the discharge curve in FIG. 4, the battery of Example 1 has a flat portion of the discharge voltage in three stages of 3.15V, 3.3V, and 3.4V. This discharge behavior indicates that the first active material was first discharged at 3.4V, and then the second active material was discharged in two stages of 3.3V and 3.15V. That is, both the first active material and the second active material were discharged at a discharge voltage specific to each active material.

  As described above, in the battery of Example 1, the first active material and the second active material were able to discharge the designed capacity at the designed voltage independently of each other.

(Example 2)
In Example 2, a positive electrode was produced in which the second active material did not have swelling properties with respect to the electrolyte, and the first active material and the second active material each had a particle shape. As the first active material, vanadium pentoxide (V ₂ O ₅ ) (average particle diameter after grinding: 10 μm, manufactured by Aldrich) was used. As the second active material, the same BEDT-TTF as the second active material in Example 1 was used.

[Production of positive electrode]
A positive electrode of Example 2 was produced in the same manner as in Example 1 except that vanadium pentoxide was used as the first active material. In order to measure the distribution of the positive electrode active material, the cross section of the positive electrode of Example 2 was measured twice by EPMA and Auger electron spectroscopy in the same manner as in Example 1. As a result, in any of the two measurements, there was no change in the distribution of the positive electrode active material in the positive electrode, and V ₂ O ₅ and BEDT-TTF were both present as particles of about 10 μm. Thus, in the positive electrode of Example 2, the second active material did not cover the surface of the first active material, and both the first active material and the second active material were present as particles.

[Production of non-aqueous electrolyte secondary battery]
A battery of Example 2 was produced in the same manner as in Example 1 except that the positive electrode of Example 2 was used.

[Evaluation of battery charge / discharge characteristics]
A charge / discharge test was performed on the battery of Example 2 in the same manner as in Example 1. In addition, the charge upper limit voltage was 3.7V, and the discharge lower limit voltage was 3.0V. As a result of the test, the battery of Example 2 showed reversible charge / discharge with a capacity of 90 mAh / g. From this, both the first active material and the second active material contributed to charge / discharge with the designed capacity. Further, the battery of Example 2 had a flat portion of discharge voltage of two stages of 3.2V and 3.3V. The first active material and the second active material each have a two-stage average discharge potential, and the average discharge potentials of both active materials are close to each other. Therefore, the first and second active materials are both 3.3V and 3.2V. It is thought that the discharge occurred in two stages. This means that both the first active material and the second active material were discharged at an average discharge potential unique to each active material.

  As described above, in the battery of Example 2, the first active material and the second active material were able to discharge the designed capacity at the designed voltage independently of each other.

(Example 3)
In Example 3, a positive electrode is produced in which the second active material has swelling properties with respect to the electrolyte, the first active material has a particle shape, and the surface of the first active material is coated with a non-oxidation / reduction material. did. As the first active material, lithium iron phosphate (LiFePO ₄ ) having the same carbon coating treatment as the first active material in Example 1 was used. As the second active material, a radical polymer (a number average molecular weight of about 100,000, an average particle diameter after pulverization of about 10 μm) represented by the following formula (2), which is a compound having a radical, was used. The radical polymer was synthesized according to the literature (Chemical Physics Letters, 2002, Vol. 359, p.351-354).

  Swellability evaluation was performed on the second active material (the radical polymer) in the same manner as in Example 1. As a result of visual observation, the radical polymer powder absorbed the solvent and had swelling properties. Furthermore, as a result of particle size distribution measurement by adding an excessive amount of the mixed solvent, the radical polymer is not present in the solvent as particles, and the radical polymer is dispersed at the molecular level with respect to the excessive excessive amount of solvent. It was confirmed that As described above, it was confirmed that the radical polymer powder can exist in a state swollen with respect to the electrolyte in the battery.

[Production of positive electrode]
A positive electrode of Example 3 was produced in the same manner as in Example 1 except that a radical polymer was used as the second active material. In order to measure the distribution of the positive electrode active material, the measurement by EPMA and Auger electron spectroscopy was performed twice on the cross section of the positive electrode of Example 3 in the same manner as in Example 1. In the first measurement (immediately after producing the electrode), both LiFePO ₄ and the radical polymer were present as particles of about 10 μm. However, in the second measurement (after solvent immersion), the radical polymer was not present as particles and was uniformly dispersed throughout the positive electrode. From this, it is considered that the radical polymer swelled by the immersion of the solvent and uniformly spread into the pores filled with the solvent in the positive electrode. In the positive electrode of Example 3, the first active material was present as particles, and the second active material was not present as particles and swelled and widely distributed in the positive electrode.

[Production of non-aqueous electrolyte secondary battery]
A battery of Example 3 was produced in the same manner as in Example 1 except that the positive electrode of Example 3 was used.

[Evaluation of battery charge / discharge characteristics]
A charge / discharge test was performed on the battery of Example 3 in the same manner as in Example 1. In addition, the charge upper limit voltage was set to 3.8V, and the discharge minimum voltage was set to 3.0V. The charge / discharge curve obtained by the charge / discharge test is shown in FIG.

  As shown in FIG. 5, the battery of Example 3 exhibited reversible charge / discharge with a capacity of 110 mAh / g. It was confirmed that both the first active material and the second active material contributed to charging and discharging with the designed capacity. Further, as shown by the discharge curve in FIG. 5, the battery of Example 3 had a flat portion of the discharge voltage of two stages of 3.6V and 3.4V. This discharge behavior indicates that the second active material was first discharged at 3.6V and then the first active material was discharged at 3.4V. Thus, both the first active material and the second active material were discharged at a discharge voltage specific to each active material.

  As described above, in the battery of Example 3, the first active material and the second active material were able to discharge the designed capacity at the designed voltage independently of each other.

(Comparative Example 1)
In Comparative Example 1, a positive electrode is produced in which the second active material has swelling properties with respect to the electrolyte, the first active material has a particle shape, and the surface of the first active material is not coated with a non-oxidation / reduction material. did. As the first active material, lithium cobaltate (LiCoO ₂ ) (average particle size: 10 μm, manufactured by Nichia Corporation) whose particle surface was not coated with a redox material was used. As the second active material, the same radical polymer represented by the formula (2) as in Example 3 was used.

[Production of positive electrode]
A positive electrode of Comparative Example 1 was produced in the same manner as in Example 3 except that lithium cobaltate was used as the first active material. In order to measure the distribution of the positive electrode active material, the cross section of the positive electrode of Comparative Example 1 was measured twice by the same method as in Example 1 using an electron beam microanalyzer (EPMA) and Auger electron spectroscopy. As a result, in the first measurement (immediately after electrode preparation), both LiCoO ₂ and the radical polymer existed as particles of about 10 μm. However, in the second measurement (after solvent immersion), the radical polymer was not present as particles and was uniformly dispersed throughout the positive electrode. From this, it is considered that the radical polymer swelled by immersion in the solvent and spread uniformly into the pores filled with the solvent in the positive electrode. As described above, in the positive electrode of Comparative Example 1, the first active material was present as particles, and the second active material was not present as particles and swelled and widely distributed in the positive electrode.

[Production of non-aqueous electrolyte secondary battery]
A battery of Comparative Example 1 was obtained in the same manner as in Example 1 except that the positive electrode of Comparative Example 1 was used.

[Evaluation of battery charge / discharge characteristics]
A charge / discharge test was performed on the battery of Comparative Example 1 in the same manner as in Example 1. In addition, the charge upper limit voltage was 4.3 V, and the discharge lower limit voltage was 3.0 V. The charge / discharge curve obtained by the charge / discharge test is shown in FIG.

  As shown in FIG. 6, the battery of Comparative Example 1 showed reversible charging / discharging with a capacity of 120 mAh / g. Both the first active material and the second active material contributed to charging and discharging with the designed capacity. In the charging curve in FIG. 6, a charging voltage of 3.6 V derived from the second active material, then a charging voltage of 4 V or more derived from the first active material is confirmed, and a capacity as designed is confirmed. Therefore, it is considered that the charging reaction of the first active material and the second active material both proceed. However, as shown by the discharge curve in FIG. 6, the flat portion of the discharge voltage of the battery of Comparative Example 1 is only about one stage of 3.6V. Although a discharge voltage of 3.6 V derived from the second active material was confirmed, but a discharge voltage near 4 V derived from the first active material was not confirmed, the discharge reaction of the first active material was allowed to occur in the second active material. It is inferred that the substance is inhibiting. It is considered that this is because the second active material directly covers the surface of the first active material. That is, since the first active material can be discharged only after the second active material is discharged, it is considered that the discharge voltage of the first active material has been pulled down to the discharge voltage of the second active material.

  As described above, in the battery of Comparative Example 1, the first active material and the second active material cannot be discharged at a discharge voltage specific to each active material, unlike the first to third embodiments. Inhibitory factors were caused by the combination of seed active materials. In the battery of Comparative Example 1, although the charging voltage is present in two stages of 3.6 V and 4 V, the discharging voltage is present only in one stage of approximately 3.6 V, so that the charging energy is largely lost.

  The batteries in Examples 1 to 3 have a discharge capacity that combines the design capacity of the first active material and the design capacity of the second active material, and the discharge potentials derived from the first active material and the second active material, respectively. Both active materials were able to charge and discharge independently of each other. That is, by including a second active material that reacts quickly with anions, it is possible to obtain excellent characteristics in pulse discharge, and it is excellent in high capacity characteristics by including a high-capacity first active material that can react with Li. The characteristics could be obtained. Moreover, the battery which has a desired voltage characteristic, a capacity | capacitance characteristic, and a pulse discharge characteristic can be arbitrarily designed by selecting each material and mixture ratio of a 1st active material and a 2nd active material arbitrarily.

  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.

10, 40 Positive electrode 11, 41 Positive electrode active material layer 12 Positive electrode current collector 13, 43 First active material 14, 44 Second active material 17 Substrate 20 Negative electrode 21 Negative electrode active material layer 22 Negative electrode current collector 30 Separator 31 Nonaqueous electrolyte 50 coin-type case 51 sealing plate 52 gasket 100 coin-type non-aqueous electrolyte secondary battery

Claims (15)

A positive electrode comprising: a first active material capable of inserting and extracting lithium ions; and a second active material capable of inserting and extracting anions;
A negative electrode comprising a negative electrode active material capable of inserting and extracting lithium ions;
A non-aqueous electrolyte containing a salt of lithium ion and the anion,
The second active material is an organic compound;
The first active material has a particle shape;
(A) the second active material has a particle shape, and the non-aqueous electrolyte is in direct contact with each of the first active material and the second active material,
Or
(B) The surface of the first active material is coated with a non-redox material, and the first active material and the non-active material can be subjected to a redox reaction between the first active material and the lithium ions. The non-aqueous electrolyte is in direct contact with the surface of the particles composed of the redox material, and the non-aqueous electrolyte is in direct contact with the second active material,
Non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the second active material does not directly cover the surface of the first active material.   3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the second active material does not have swelling properties with respect to the non-aqueous electrolyte and has a particle shape. The volume swelling ratio of the second active material after assembly based on the pre-assembly of the non-aqueous electrolyte secondary battery is less than 20%,
The nonaqueous electrolyte secondary battery according to claim 1, wherein the second active material has a particle shape.   The non-aqueous electrolyte secondary battery according to claim 3 or 4, wherein the second active material is a compound having a π-conjugated electron cloud.   In the case of (b), the non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the second active material has swelling properties with respect to the non-aqueous electrolyte.   3. The non-aqueous solution according to claim 1, wherein in the case of (b), the volume swell ratio of the second active material after assembly is 20% or more after the assembly of the non-aqueous electrolyte secondary battery. Electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-oxidation / reduction substance is a carbon material.   The non-aqueous electrolyte secondary battery according to any one of claims 1, 2, 6 to 8, wherein the second active material is a compound having a radical.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 9, wherein the first active material is a transition metal oxide that may contain lithium. The non-aqueous electrolyte secondary battery according to claim 10, wherein the transition metal oxide is LiFePO ₄ . The non-aqueous electrolyte secondary battery according to claim 10, wherein the transition metal oxide is V ₂ O ₅ . The non-aqueous electrolyte includes a non-aqueous solvent and the salt dissolved in the non-aqueous solvent,
The non-aqueous solvent contains at least one selected from the group consisting of cyclic or chain carbonates, cyclic or chain esters, cyclic or chain ethers, cyclic or chain sulfones, and nitriles. The nonaqueous electrolyte secondary battery according to any one of -12. The first active material particles capable of occluding and releasing lithium ions and the non-aqueous electrolyte containing a salt of lithium ions and anions have no swellability, can occlude and release the anions, and Preparing a mixture comprising a second active material particle, which is an organic compound;
The shape of the particles of the first active material and the second active material is such that a positive electrode active material layer containing the first active material and the second active material as a positive electrode active material is formed on the positive electrode current collector. Forming the mixture while holding;
Impregnating the non-aqueous electrolyte into the positive electrode active material layer;
The manufacturing method of the nonaqueous electrolyte secondary battery containing this. A first active material particle capable of occluding and releasing lithium ions and having a surface coated with a non-oxidation-reducing substance; a second anion capable of occluding and releasing anions; and an organic compound. Preparing a mixture comprising an active material;
Forming the mixture such that a positive electrode active material layer containing the first active material and the second active material as a positive electrode active material is formed on a positive electrode current collector;
Impregnating the positive electrode active material layer with a nonaqueous electrolyte containing a salt of lithium ion and the anion;
The manufacturing method of the nonaqueous electrolyte secondary battery containing this.

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