JP2015037068A - Positive electrode for lithium ion battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having a large volume energy density and good load characteristic, and a positive electrode for lithium ion battery which enables the arrangement of the lithium ion secondary battery.SOLUTION: A positive electrode for lithium ion battery comprises: a positive electrode mixture layer including active material particles, a conductive assistant agent, a dispersant and a resin binder. The active material particles include 70-95 mass% of particles having particle diameters of 0.8-35 μm, and 5-30 mass% of particles having particle diameters of 0.001-0.4 μm. The particles having particle diameters of 0.8-35 μm, and the particles having particle diameters of 0.001-0.4 μm account for 90 mass% or more in total. The conductive assistant agent contains a carbon material. In the positive electrode mixture layer, the content of the carbon material is 0.5-7 mass%. The positive electrode mixture layer has a porosity of 5-15 vol.%. A lithium ion secondary battery comprises the positive electrode for lithium ion battery.

Description

  The present invention relates to a lithium ion secondary battery having a large volume energy density and good load characteristics, and a positive electrode for a lithium ion battery that can constitute the lithium ion secondary battery.

  Lithium ion secondary batteries are being rapidly developed as batteries for use in portable electronic devices and hybrid vehicles. In such a lithium ion secondary battery, a carbon material is mainly used as the negative electrode active material, and metal oxides, metal sulfides, various polymers, and the like are used as the positive electrode active material. In particular, lithium composite oxides such as lithium cobaltate, lithium nickelate, and lithium manganate can be used as a positive electrode active material for lithium ion secondary batteries because they can realize high energy density and high voltage batteries. It has been.

  In addition, with the enhancement of functionality of applied devices and the expansion of application fields, lithium ion secondary batteries are required to further improve volume energy density.

  In increasing the volume energy density of the lithium ion secondary battery, for example, the porosity of the positive electrode mixture layer containing the positive electrode active material, the conductive auxiliary agent, the binder, etc. is lowered, and the amount of the positive electrode active material introduced into the layer It is possible to increase

  For example, Patent Document 1 proposes a technique for increasing the density of the positive electrode mixture layer by using a positive electrode active material in which two types of lithium cobaltate particles having different average particle diameters are mixed at a specific ratio. .

JP 2006-286511 A

  However, even with the technique described in Patent Document 1, it is difficult to form a positive electrode mixture layer having a low porosity that can increase the volume energy density of the lithium ion secondary battery to be higher than that of the conventional one.

  Further, when the porosity of the positive electrode mixture layer is lowered, the nonaqueous electrolyte solution does not easily penetrate into the positive electrode mixture layer. Therefore, when the charge / discharge is performed at a particularly large current value, the positive electrode active layer that cannot participate in the battery reaction can be obtained. The problem that the volume of the substance increases and the capacity decreases tends to occur. In this respect, there is room for improvement in the conventional techniques including the technique described in Patent Document 1. Therefore, in order to increase the capacity of the lithium ion secondary battery by lowering the porosity of the positive electrode mixture layer, it is possible to sufficiently extract the capacity even when charging / discharging with a large current value, and to have good load characteristics. It is also required to be able to maintain

  The present invention has been made in view of the above circumstances, and an object thereof is a lithium ion secondary battery having a large volumetric energy density and good load characteristics, and a lithium ion battery that can constitute the lithium ion secondary battery. It is to provide a positive electrode for use.

  The positive electrode for a lithium ion battery of the present invention (hereinafter sometimes simply referred to as “positive electrode”) that has achieved the above object has a positive electrode mixture layer containing active material particles, a conductive auxiliary agent, and a resin binder. As the active material particles, the ratio of particles having a particle diameter of 0.8 to 35 μm is 70 to 95 mass%, and the ratio of particles having a particle diameter of 0.001 to 0.4 μm is 5 to 30 mass. %, And the ratio of the total of the particles having a particle diameter of 0.8 to 35 μm and the particles having a particle diameter of 0.001 to 0.4 μm is 90% by mass or more, and the conductive auxiliary agent As a carbon material, the content of the carbon material in the positive electrode mixture layer is 0.5 to 7% by mass, and the porosity of the positive electrode mixture layer is 5 to 15 vol. % (Volume%).

  The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode for a lithium ion battery of the present invention is used as the positive electrode. is there.

  According to the present invention, it is possible to provide a lithium ion secondary battery having a large volumetric energy density and good load characteristics, and a positive electrode for a lithium ion battery that can constitute the lithium ion secondary battery.

It is a top view which represents typically an example of the lithium ion secondary battery of this invention. It is the sectional view on the AA line of the lithium ion secondary battery of FIG.

  The positive electrode for a lithium ion battery according to the present invention has a positive electrode mixture layer containing substance particles, a conductive auxiliary agent, a dispersant, and a resin binder. For example, the positive electrode mixture layer is formed on one side of a current collector or The structure is formed on both sides.

  In the positive electrode of the present invention, the porosity of the positive electrode mixture layer is 15 vol. % Or less, preferably 13 vol. % Or less. In the present invention, by reducing the porosity of the positive electrode mixture layer in the positive electrode as described above and increasing the amount of active material particles that can be filled in the positive electrode mixture layer, a lithium ion secondary battery having a large volume energy density is obtained. It can be configured.

  However, it is not easy to reduce the porosity of the positive electrode mixture layer as described above, and even if the porosity of the positive electrode mixture layer is simply reduced, as described above, there is no non-existence in the positive electrode mixture layer. Since it becomes difficult for the water electrolyte to penetrate, the load characteristics of the lithium ion secondary battery are impaired.

  Therefore, in the present invention, the particle size and composition of the active material contained in the positive electrode mixture layer and the type and composition of the conductive auxiliary agent contained in the positive electrode mixture layer are adjusted, whereby the porosity as described above is adjusted. Thus, it is possible to form a small positive electrode material mixture layer and to improve the volume energy density of the lithium ion secondary battery, while maintaining good load characteristics.

  However, if the porosity of the positive electrode mixture layer is too small, the amount of the non-aqueous electrolyte solution that can penetrate into the positive electrode mixture layer is very small, which may cause deterioration in battery characteristics. Therefore, the positive electrode of the present invention has a positive electrode mixture layer with a porosity of 5 vol. % Or more, preferably 7 vol. % Or more.

The porosity of the positive electrode mixture layer referred to in this specification excludes all material portions contained in the positive electrode mixture layer when the apparent volume (volume including voids) of the positive electrode mixture layer is 100%. The volume ratio of the part is expressed as a percentage. Specifically, first, the mass of the positive electrode is measured, the mass of the positive electrode mixture layer obtained by subtracting the mass of the positive electrode current collector from that value, and the thickness of the positive electrode current collector from the average thickness of 5 positive electrodes. The density Dc of the positive electrode mixture layer is obtained by dividing the thickness of the positive electrode mixture layer obtained by drawing the area of the positive electrode mixture layer by the volume of the positive electrode mixture layer obtained. Next, the true specific gravity Mc of the positive electrode mixture layer is determined from the true specific gravity and mass ratio of all the materials contained in the positive electrode mixture layer. And the porosity p is calculated | required by a following formula using the density Dc and true specific gravity Mc of the said positive mix layer.
p = {1- (Dc / Mc)} × 100

  In the positive electrode active material particles, the ratio of particles having a particle diameter of 0.8 to 35 μm is 70 to 95 mass%, and the ratio of particles having a particle diameter of 0.001 to 0.4 μm is 5 to 30 mass%. In addition, a particle having a total ratio of 90% by mass or more of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm is used.

  When the active material particles used for the positive electrode have a particle size distribution as described above, a gap formed between particles having a larger particle size (particles having a particle size of 0.8 to 35 μm), Since particles having a smaller particle diameter (particles having a particle diameter of 0.001 to 0.4 μm) are appropriately filled, the porosity of the positive electrode mixture layer can be reduced as described above. Therefore, since the amount of active material particles introduced into the positive electrode mixture layer can be increased, a positive electrode capable of constituting a lithium ion secondary battery having a large volume energy density can be obtained.

  In addition, when the active material particles used for the positive electrode have the particle size distribution as described above, even if the porosity of the positive electrode mixture layer is reduced as described above, lithium that suppresses the deterioration of load characteristics is suppressed. It can be set as the positive electrode which can comprise an ion secondary battery. The reason is not clear, but when the active material particles having the particle size distribution as described above are used for forming the positive electrode mixture layer, the voids formed in the positive electrode mixture layer are considered to be very fine and numerous. Thus, even if the porosity itself is small, it is presumed that the non-aqueous electrolyte can permeate with high uniformity throughout the positive electrode mixture layer.

  In the positive electrode of the present invention, the content of particles having a particle diameter of 0.001 to 0.4 μm in all active material particles is 5% by mass or more, preferably 9% by mass or more, and 30% by mass or less. Preferably it is 20 mass% or less. When the content of particles having a particle diameter of 0.001 to 0.4 μm in the total amount of the active material particles of the positive electrode is the above value, the porosity of the positive electrode mixture layer can be reduced as described above. At the same time, it is possible to suppress a decrease in load characteristics of the lithium ion secondary battery.

  In the positive electrode of the present invention, the content of particles having a particle diameter of 0.8 to 35 μm in all active material particles is 70% by mass or more, preferably 80% by mass or more, and preferably 95% by mass or less. Is 91 mass% or less.

  The positive electrode of the present invention may contain only particles having a particle diameter of 0.001 to 0.4 μm and particles having a particle diameter of 0.8 to 35 μm as active material particles. You may contain the particle | grains which do not correspond to 8-35 micrometers and 0.001-0.4 micrometers. However, when using particles whose particle diameters do not fall within the range of 0.8 to 35 μm and 0.001 to 0.4 μm, the total active material particles may be 10% by mass or less.

  In order to make the active material particles of the positive electrode have the particle size distribution as described above, for example, first group particles and second group particles having a particle diameter smaller than that of the first group particles may be used. That is, by using the second group particles having a particle size distribution between 0.001 and 0.4 μm and the first group particles having a particle size distribution between 0.8 and 35 μm. The particle size distribution of the positive electrode active material particles can be adjusted as described above. In this case, in all active material particles, the first group particles: 70% by mass or more (preferably 80% by mass or more) 95% by mass or less (preferably 91% by mass or less), the second group particles: 5% by mass or more ( What is necessary is just to use together in the ratio of 30 mass% or less (preferably 20 mass% or less).

  Moreover, you may contain the 3rd group particle which has a particle diameter which does not correspond to a 1st group particle and a 2nd group particle in the range of 10 mass% or less of the whole active material particle.

  The average particle diameter A (μm) of the first group particles is, for example, 1 μm or more, preferably 5 μm or more, and 30 μm or less, preferably 20 μm or less. The average particle diameter B (μm) of the second group particles is, for example, 0.001 μm or more, preferably 0.005 μm or more, and 0.3 μm or less, preferably 0.2 μm or less.

  The average particle size of the various particles (first group particles, second group particles, and transition metal oxide particles described later) referred to in the present specification is the particle diameter of 300 particles observed with a transmission electron microscope (TEM). (When the particles are spherical) or the diameter of the major axis length (when the particles have a shape other than the spherical shape), and the average value obtained by dividing the total value of these particle diameters by the number (300) .

  Further, the particle size distribution of the positive electrode active material particles in this specification is such that when the positive electrode active material particles are a group of particles (that is, an aggregate of active material particles having different particle diameters), For each of the 300 particles in the particle group, each particle diameter was examined by the same method as that for obtaining the average particle diameter, and the number of particles contained in the particle group having a particle diameter of 0.8 to 35 μm and the particle diameter Is a value obtained by a method of obtaining the number of particles contained in a particle group of 0.001 to 0.4 μm and calculating the mass ratio of each particle group. However, for example, when two particle groups are used for the positive electrode active material particles, the range of each particle included in each particle group is known by the same method as the method for measuring the average particle diameter described above. In some cases (that is, the particle size of all the particles contained in one particle group is in the range of 0.8 to 35 μm, and the particle size of all the particles contained in the other particle group is 0.001 to 0.001). When the particle size is in the range of 4 μm), the particle size distribution of the active material of the positive electrode referred to in this specification can be grasped by adjusting the amount of each particle group used.

  Further, the first group particles and the second particles are in such a relationship that the ratio A / B between the average particle diameter A of the first group particles and the average particle diameter B of the second group particles is 40 or more, preferably 50 or more. It is desirable to use group particles.

  If the average particle diameter of the first group particles and the average particle diameter of the second group particles are in the above relationship, the voids in the positive electrode mixture layer can be made finer and more numerous. Thus, the load characteristics of the battery are better maintained.

  The upper limit of the A / B value is not particularly limited as long as the average particle diameter A of the first group particles and the average particle diameter B of the second group particles are within the ranges satisfying the above values, respectively. Usually, it is 2500 or less.

There is no restriction | limiting in particular about the kind of active material particle, The same thing as the particle of the active material currently used with the lithium ion secondary battery known conventionally can be used. Specifically, for example, lithium transition metal oxidation of a layered structure represented by Li _{1 + c} M ¹ O ₂ (−0.1 <c <0.1, M ¹ : Co, Ni, Mn, Al, Mg, etc.) Layered oxide composed of solid solution represented by (1-x) Li ₂ MnO ₃ —xLiMO ₂ (0.2 <x <0.7, M: Co, Ni, Mn, Al, Mg, etc.) LiM ² PO ₄ (M ² : Co, Ni, Mn, Fe, etc.), a lithium transition metal oxide particle having a spinel structure in which LiMn ₂ O ₄ and a part of its elements are substituted with other elements And particles of a transition metal phosphate compound. Specific examples of the lithium transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-d Co _{d e} Al _e O ₂ (0.1 ≦ d ≦ 0.3, 0.01 ≦ e ≦ 0.2). ) And other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiMn _3/5 Ni _1/5 Co _1/5 O ₂ etc.).

  Each of the exemplified active material particles may be used alone or in combination of two or more. That is, for the first group particles and the second group particles, the same particles of the active material particles illustrated above may be used. The first group particles and the second group particles may be the same as those illustrated above. Different types of particles of each active material may be used. Further, the first group particles and the second group particles may each include two or more kinds of particles of the active material particles exemplified above.

  The first group particles are, for example, selected from the commercially available active material particles, those having an average particle diameter A satisfying the above values, or classified as necessary and averaged. What was prepared so that the particle diameter A satisfy | fills the said value A can be used.

  The second group particles can be synthesized by, for example, the following methods.

  When the second group particles are particles of the lithium transition metal oxide having the layered structure or the lithium transition metal oxide having the spinel structure, they can be synthesized by the following hydrothermal synthesis method or melt synthesis method.

  As the hydrothermal synthesis method, for example, an aqueous solution containing a predetermined amount of a lithium-containing compound (such as lithium hydroxide), a transition metal-containing compound (such as nitrate), and an oxidizing agent (such as oxygen) is used. Examples thereof include a method of hydrothermal reaction (more specifically, for example, a method described in JP-A No. 2001-163700) under conditions that cause a state or a supercritical state (temperature: 250 ° C. or higher, pressure: 20 MPa or higher). In this method, an aqueous solution containing a lithium-containing compound, a transition metal-containing oxide, and an oxidizing agent may be subjected to a hydrothermal reaction by mixing water in a subcritical state or a supercritical state. The hydrothermal reaction may be performed by mixing water containing a lithium-containing compound and in a subcritical state or a supercritical state with an aqueous solution containing an oxidizing agent.

  As the melt synthesis method, for example, a transition metal-containing compound (oxide, hydroxide, chloride, nitrate, carbonate, acetate, etc.), lithium hydroxide, and lithium nitrate are mixed in a predetermined composition. And a method of melting reaction at a temperature of about 300 to 550 ° C. (more specifically, for example, a method described in International Publication No. 2011/111364).

  On the other hand, when the second group particles are the above-described transition metal phosphate compound, transition metal oxide particles having an average particle size of 50 nm or less are used as growth nuclei, and the particles and lithium-containing compounds (lithium carbonate, water, A method of mixing a solution (such as an aqueous solution) containing a lithium-containing compound (such as lithium oxide or lithium nitrate) and a phosphorus-containing compound (such as phosphoric acid) and heating the mixture (for example, see JP-A-2008-159495) Method).

  In addition, since the synthesis | combination of the transition metal oxide particle whose average particle diameter is 50 nm or less is easy to synthesize | combine a fine particle, it is preferable to employ | adopt a hydrothermal synthesis method. In addition, when heating the mixture of the transition metal oxide particles and the solution containing the lithium-containing compound and the phosphorus-containing compound, dry heat treatment in an inert atmosphere or a reducing atmosphere, hydrothermal treatment, or After the hydrothermal treatment, it is preferable to perform a drying heat treatment in an inert atmosphere or a reducing atmosphere. The temperature during the drying heat treatment is preferably 500 to 700 ° C. Moreover, it is preferable that the temperature at the time of the said hydrothermal treatment is 150-200 degreeC.

  The total content of all active material particles in the positive electrode mixture layer is preferably 90 to 98.5% by mass.

  Examples of the conductive auxiliary agent related to the positive electrode mixture layer of the positive electrode of the present invention include natural graphite (such as flake graphite) and graphite such as artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal Carbon materials such as carbon black such as black; carbon fiber; etc. are used.

  The content of the carbon material in the positive electrode mixture layer is 0.5 mass% or more, preferably 0.7 mass% or more, and is 7 mass% or less, preferably 5 mass% or less. The carbon material is generally bulky and acts in a direction that makes it difficult to reduce the porosity of the positive electrode mixture layer, but when the carbon material content is the above value, the porosity of the positive electrode mixture layer Can be reduced as described above, and the conductivity in the positive electrode mixture layer can be ensured satisfactorily.

  In addition, the conductive auxiliary agent includes materials other than carbon materials (conductive fibers such as metal fibers, metal powders such as aluminum powder, conductive whiskers made of carbon fluoride, zinc oxide, potassium titanate, titanium oxide, etc. Or an organic conductive material such as a polyphenylene derivative) may be used together with the carbon material. The total content of the conductive auxiliary in the positive electrode mixture layer is preferably 0.5 to 10% by mass.

  A dispersant such as polyvinyl pyrrolidone (PVP) can be used for the positive electrode mixture layer of the positive electrode of the present invention. As will be described later, the positive electrode mixture layer is usually formed using a positive electrode mixture-containing composition in which active material particles, a conductive auxiliary agent, a resin binder, and the like are dispersed in a solvent. However, by including the dispersing agent of the positive electrode mixture-containing composition, the active material particles and the conductive auxiliary agent can be more favorably dispersed, and a positive electrode material mixture layer having better properties can be formed. Become.

  The content of the dispersant in the positive electrode mixture layer is preferably 0.5 to 50 parts by mass when the amount of the carbon material in the positive electrode mixture layer is 100 parts by mass.

  Examples of the resin binder related to the positive electrode mixture layer of the positive electrode of the present invention include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. .

  The content of the resin binder in the positive electrode mixture layer is preferably 1 to 6% by mass.

  Moreover, it is preferable that the positive mix layer contains the fluorine-type polymer which has multiple pendant groups containing a fluorine separately from the resin binder. If it is a positive electrode which has a positive mix layer containing such a fluorine-type polymer, it will be 4.3-4.6V higher than the end-of-charge voltage of about 4.2V normally employ | adopted with the conventional lithium ion secondary battery. The storage characteristics of the lithium ion secondary battery when it is charged with the end voltage set to the extent and the storage characteristics of the lithium ion secondary battery at a high temperature of about 85 ° C. or less can be improved.

  In the fluorine-based polymer having a plurality of pendant groups containing fluorine, the pendant group is a carboxyl group or a salt thereof or a functional group (A) which is a sulfonic acid group or a salt thereof, and the functional group (A) and the main chain. It is preferably composed of an intervening group (structural portion).

  When the functional group (A) related to the pendant group is a carboxyl group salt, specific examples thereof include a metal salt of a carboxyl group and an ammonium salt of a carboxyl group. In the case of a metal salt of a carboxyl group, an alkali metal salt (monovalent metal salt) such as lithium salt, sodium salt or potassium salt may be used, or an alkaline earth metal salt such as magnesium salt, calcium salt, strontium salt or barium salt. Or a metal salt having a valence of 2 or more. In addition, when the carboxyl group salt related to the pendant group is a divalent or higher metal salt, a ring structure including a plurality of pendant groups is formed in the molecule of the fluorine polymer, or the molecule of the fluorine polymer. A cross-linked structure with a plurality of pendant groups may be formed between them.

  Further, when the functional group (A) related to the pendant group is a salt of a sulfonic acid group, specific examples thereof include a metal salt of a sulfonic acid group and an ammonium salt of a sulfonic acid group. In the case of a metal salt of a sulfonic acid group, it may be an alkali metal salt (monovalent metal salt) such as lithium salt, sodium salt or potassium salt, or an alkaline earth metal salt such as magnesium salt, calcium salt, strontium salt or barium salt. It may be a divalent or higher metal salt. In addition, when the salt of the sulfonic acid group related to the pendant group is a metal salt having a valence of 2 or more, a ring structure including a plurality of pendant groups is formed in the molecule of the fluoropolymer, A cross-linked structure with a plurality of pendant groups may be formed between molecules.

  In at least a part of the pendant groups contained in the fluoropolymer, a group interposed between the functional group (A) and the main chain is a hydrocarbon group; a perfluorocarbon group (in a hydrocarbon group) A group in which all of hydrogen is substituted with fluorine), or is composed of a hydrocarbon group and at least one group selected from the group consisting of an ester group, a carbonate group and an amide group; or a perfluorocarbon And at least one group selected from the group consisting of an ester group, a carbonate group and an amide group. Since these groups are less susceptible to oxidative decomposition than ether groups (ether bonds), the fluorine-based polymer has good oxidation resistance.

  The group interposed between the functional group (A) and the main chain of the pendant group is composed of a hydrocarbon group and at least one group selected from the group consisting of an ester group, a carbonate group, and an amide group. As a more specific structure, for example, the functional group (A) is bonded to a hydrocarbon group, and the hydrocarbon group is connected to the main chain via an ester group, a carbonate group or an amide group. The structure which is combined with is mentioned. Further, the group intervening between the functional group (A) and the main chain of the pendant group is at least one group selected from the group consisting of a perfluorocarbon group, an ester group, a carbonate group, and an amide group. As a more specific structure, for example, the functional group (A) is bonded to a perfluorocarbon group, and this perfluorocarbon group is bonded via an ester group, a carbonate group, or an amide group. And a structure bonded to the main chain.

  Examples of the hydrocarbon group interposed between the functional group (A) related to the pendant group and the main chain include a linear or branched alkylene group (alkylene chain). As will be described later, in the hydrocarbon group (for example, a linear or branched alkylene group), at least a part of the hydrogen needs to be substituted with fluorine. The number of carbon atoms in the hydrocarbon group is preferably 1 to 20, for example.

  The functional group (A) related to the pendant group is directly bonded to the carbon of the hydrocarbon group or perfluorocarbon group in the pendant group. The group interposed between the functional group (A) and the main chain is composed of a hydrocarbon group and at least one group selected from the group consisting of an ester group, a carbonate group and an amide group. In this case, among the carbons of the hydrocarbon group, fluorine is bonded to at least the carbon located at the α-position or β-position of the functional group (A) [that is, the α of the functional group (A) In the carbon located at the position or β-position, at least part of the hydrogen that can be bonded to it is substituted with fluorine (fluorine atom, F).

  On the other hand, the group interposed between the functional group (A) and the main chain is a perfluorocarbon group, or at least one selected from the group consisting of a perfluorocarbon group, an ester group, a carbonate group, and an amide group As described above, since the functional group (A) is directly bonded to the carbon of the perfluorocarbon group, it is located at least at the α-position of the functional group (A). Fluorine is bonded to the carbon to be processed.

  In the pendant group, when the functional group (A) is a carboxyl group or a salt thereof, a highly electron-attracting fluorine is bonded to the α-position or β-position carbon of the carboxyl group or a salt thereof. Since the electron density of oxygen on the carboxyl group or its salt is low, hydrogen (in the case of a carboxyl group) and counter ion (in the case of a salt of a carboxyl group) are likely to dissociate. Therefore, the said fluorine-type polymer which has a carboxyl group or its salt as a functional group (A) shows a favorable ion dissociation property also in an organic solvent.

  Further, in the pendant group, when the functional group (A) is a sulfonic acid group or a salt thereof, a fluorine having a strong electron-withdrawing property is bonded to the carbon located at the α-position or β-position of the sulfonic acid group or the salt As a result, the electron density on the oxygen of the sulfonic acid group or its salt is lowered, so that hydrogen (in the case of a sulfonic acid group) and counter ion (in the case of a salt of a sulfonic acid group) are easily dissociated. Therefore, the said fluorine-type polymer which has a sulfonic acid group or its salt as a functional group (A) shows a favorable ion dissociation property also in an organic solvent.

  When the functional group (A) of the pendant group is a carboxyl group or a salt thereof, the pendant group preferably has, for example, a structural portion represented by the following general formula (1).

In the general formula (1), n is an integer of 1 to 20, and M ¹ is hydrogen, metal, or ammonium. Also, as M ¹ in the case of a metal, as described above, lithium, sodium, alkali metal (monovalent metal), such as potassium; magnesium, calcium, strontium, divalent or more such alkaline earth metals such as barium Of metals.

  When the fluoropolymer contains the pendant group having the structural part represented by the general formula (1), the pendant group is only the structural part represented by the general formula (1). And may be composed of a structural part represented by the general formula (1) and an ester group, a carbonate group or an amide group, or a structural part represented by the general formula (1) In addition, a hydrocarbon group or a perfluorocarbon group (such as an alkylene group which may be fluorine-substituted) may be bonded via an ester group, a carbonate group or an amide group.

  In addition, when the said fluorine-type polymer contains what has the structure part represented by the said General formula (1) as the said pendant group, the one part or all part pendant group is the said General formula (1). What is necessary is just to have the structure part represented. In the case where only a part of the pendant group of the fluoropolymer is a structural portion represented by the general formula (1), the other pendant group includes, for example, a carboxyl group or a salt thereof, a hydrocarbon, It may be a structure composed of a perfluorocarbon group.

  When the functional group (A) of the pendant group is a sulfonic acid group or a salt thereof, the pendant group preferably has, for example, a structural portion represented by the following general formula (2).

In the general formula (2), m is an integer from 1 to 20, ^{M 2} is hydrogen, metal or ammonium. Also, as M ² in the case of a metal, as described above, lithium, sodium, alkali metal (monovalent metal), such as potassium; magnesium, calcium, strontium, divalent or more such alkaline earth metals such as barium Of metals.

  When the fluoropolymer contains the pendant group having a structural portion represented by the general formula (2), the pendant group is represented by the general formula (2). May be composed only of the structural part, and may be composed of the structural part represented by the general formula (2) and an ester group, a carbonate group or an amide group, or represented by the general formula (2). Or a hydrocarbon group or a perfluorocarbon group (such as an alkylene group which may be fluorine-substituted) may be bonded via an ester group, a carbonate group or an amide group. .

  In addition, when the said fluorine-type polymer contains what has the structure part represented by the said General formula (2) as the said pendant group, the one part or all part pendant group is the said General formula (2). What is necessary is just to have the structure part represented. When only a part of the pendant group of the fluorine-based polymer is a structural portion represented by the general formula (2), the other pendant group includes, for example, a sulfonic acid group or a salt thereof, and a hydrocarbon. Or the structure comprised by the perfluorocarbon group may be sufficient.

  One pendant group may contain a plurality of structural parts represented by the general formula (1) and structural parts represented by the general formula (2). Specifically, for example, the pendant group has a hydrocarbon group (for example, an alkylene group) separately from the structural part represented by the general formula (1) and the structural part represented by the general formula (2). In addition, a plurality of structural parts represented by the general formula (1) and structural parts represented by the general formula (2) may be bonded to the hydrocarbon group.

  The fluoropolymer may contain only a pendant group having a carboxyl group, may contain only a pendant group having a carboxyl group salt, or contains only a pendant group having a sulfonic acid group. Alternatively, it may contain only a pendant group having a salt of a sulfonic acid group. The fluorine-based polymer contains a plurality of types of a pendant group having a carboxyl group, a pendant group having a carboxyl group salt, a pendant group having a sulfonic acid group, and a pendant group having a sulfonic acid salt. Also good. Further, when one pendant group contains a plurality of carboxyl groups or sulfonic acid groups or salts thereof [for example, a structural moiety represented by the general formula (1) or the general formula (2) A plurality of structural parts, which may contain any one of a carboxyl group, a salt of a carboxyl group, a sulfonic acid group, and a salt of a sulfonic acid. It may be.

  The fluoropolymer preferably has a primary amino group or a secondary amino group in the molecule. In a lithium ion secondary battery using a composite oxide (lithium transition metal oxide) containing the transition metal as shown above as the active material for the positive electrode, the transition metal ions are eluted from the positive electrode active material as it is charged and discharged. As a result, battery characteristics may be adversely affected. Since primary amino groups and secondary amino groups have a property of forming a complex with a metal salt, the effect of capturing the metal ions can be expected by including a fluorine-based polymer having these groups in the positive electrode mixture layer. . In particular, when a lithium ion secondary battery is charged at a high voltage or placed in a high temperature environment in a charged state, elution of transition metal ions easily occurs. In the positive electrode mixture layer, the storage characteristics of the lithium ion secondary battery under these circumstances can be further improved.

  The fluoropolymer can be produced by using a raw material polymer having a primary amino group or a secondary amino group, forming an amide group from the amino group and introducing the pendant group (in detail) (Not described later), by not using all of the primary amino group or secondary amino group of the raw material polymer for introduction of the pendant group, leaving a part as it is, in the molecule of the fluoropolymer, the primary amino group or It can have a secondary amino group.

  The fluoropolymer can be produced by using a raw material polymer having a carboxyl group, forming an ester group or an amide group from the carboxyl group and introducing a pendant group (details will be described later). In the molecule of the fluorinated polymer, all of the carboxyl groups of the raw polymer are not used for introduction of the pendant group, but a part of the carboxyl group is left as it is and a compound having a plurality of amino groups is reacted with the carboxyl group. Can have a primary amino group or a secondary amino group.

  The main chain of the fluoropolymer is composed only of hydrocarbon groups from the viewpoint of enhancing its oxidation resistance; is composed only of perfluorocarbon groups; hydrocarbon groups, amide groups, ester groups and carbonates Or at least one group selected from the group consisting of groups; or at least one group selected from the group consisting of ester groups, carbonate groups and amide groups. It is preferable. As the hydrocarbon group constituting the main chain, for example, a linear or branched alkylene group (a part of hydrogen of the alkylene group may be substituted with fluorine) is preferable, and the main chain is constituted. As the perfluorocarbon group, for example, a linear or branched perfluoroalkylene group (a group in which all of the hydrogen of the alkylene group, except for the portion substituted with the pendant group, are substituted with fluorine) is preferable. From the viewpoint of cost reduction of the fluorine-based polymer and improvement in characteristics required for specific applications (for example, adsorbability to the positive electrode active material described later), hydrocarbon groups not substituted with fluorine (particularly linear) Or a branched alkylene group) is more preferable.

  Moreover, it is preferable that at least a part of the main chain of the fluoropolymer has a sugar chain structure. The detailed reason is not clear, but since many sugar chains are electrochemically stable, a fluorine-based polymer having a sugar chain structure in a part of the main chain is stable even at a high voltage, for example. Expected to be usable.

  Examples of the sugar chain structure constituting the main chain include a structure derived from chitosan and a structure derived from carboxyl alkyl cellulose. As will be described later, when the main chain of the fluoropolymer is derived from chitosan, the amino group possessed by chitosan can be used for the introduction of the pendant group, and this amino group represents the amide group related to the pendant group. Will be configured. In addition, when the main chain of the fluoropolymer is derived from carboxyalkyl cellulose, a carboxyl group possessed by carboxyalkyl cellulose can be used for introduction of the pendant group, and this carboxyl group is an ester group or amide related to the pendant group. It will constitute the group.

  Moreover, in order to provide various characteristics to the said fluorine-type polymer, groups other than the said pendant group can also be contained. For example, solubility in solvents, compatibility with other polymers, adsorptivity to other substances, and resistance to decomposition in non-aqueous electrolytes (non-aqueous electrolytes used in lithium ion secondary batteries) A group capable of improving the properties and gas generation characteristics may be contained.

  The molecular weight of the fluoropolymer is preferably a number average molecular weight of 500 or more, preferably 5 million or less, more preferably 10,000 or more, and further preferably 30,000 or more. preferable.

  The number average molecular weight of the said fluorine-type polymer as used in this specification is a number average molecular weight (polystyrene conversion value) measured using gel permeation chromatography.

  The amount of the pendant group introduced into the fluoropolymer is preferably 1 mol% or more, more preferably 3 mol% or more, more preferably 5 mol based on the monomer constituting the main chain. % Or more is more preferable. The upper limit of the introduction amount of the pendant group in the fluorine-based polymer is not particularly limited, and may be selected according to solubility in the solvent to be used, restrictions due to ease of synthesis or steric hindrance, cost, and the like. When one pendant group can be introduced per ordinary monomer, the upper limit is 100 mol% of the pendant group with respect to the monomer constituting the main chain. Depending on the case, a plurality of the pendant groups may be introduced per monomer, and in this case, the upper limit of the pendant group introduction amount with respect to the monomer constituting the main chain is 100 mol% or more.

  The amount of the pendant group introduced into the fluoropolymer as used herein is a single amount constituting the main chain, which is determined from the ratio of each element obtained from proton and fluorine 19 nuclear magnetic resonance spectroscopy (NMR) measurements. The molar ratio of the pendant group to the body.

  There is no restriction | limiting in particular about the manufacturing method of the said fluorine-type polymer, You may employ | adopt any method. A typical production method is a method in which a hydroxyl group of polyvinyl alcohol is reacted with a fluorinated dicarboxylic acid anhydride or a fluorinated disulfonic acid anhydride; polyethyleneimine, polyallylamine, an aminated acrylic polymer, a fluorine atom on the amino group of chitosan A method of reacting a fluorinated dicarboxylic acid anhydride or a fluorinated disulfonic acid anhydride; a method of transesterifying an acetyl group of polyvinyl acetate with a fluorinated dicarboxylic acid or a fluorinated disulfonic acid; poly (meth) acrylic acid , A method of reacting a fluorinated product having an amino group and a carboxylic acid by activating the carboxyl group of polymaleic acid or carboxyalkyl cellulose; a method of reacting a fluorinated product having an amino group and a carboxylic acid with polymaleic anhydride; Can be mentioned. In addition, by reacting the carboxyl group or sulfonic acid group of the pendant group introduced into the main chain by such a method with a weak acid salt such as a hydroxide or carbonate containing a metal or ammonium as a counter ion, The fluoropolymer having a pendant group containing a carboxyl group salt or a sulfonic acid group salt can be obtained. Alternatively, a monomer having a pendant group containing a fluorinated carboxylic acid or a salt thereof or a fluorinated sulfonic acid or a salt thereof is prepared in advance, and the fluorine-based polymer can be produced by polymerizing the monomer.

  The fluorine-based polymer is preferably present on the surface of the active material particles. In this case, the lithium ion secondary battery is further improved.

  For example, in a lithium ion secondary battery using a non-aqueous electrolytic solution containing a solvent such as ethylene carbonate and an additive such as vinylene carbonate, a solid electrolyte interface that acts as a protective film on the negative electrode surface by reductive decomposition of the additive ( It is known that a SEI) layer is formed and the decomposition reaction of the non-aqueous electrolyte component due to contact between the negative electrode and the non-aqueous electrolyte can be suppressed. The fluorine-based polymer is also introduced into the positive electrode mixture layer and is present on the surface of the positive electrode active material particles, thereby suppressing contact between the non-aqueous electrolyte of the lithium ion secondary battery and the positive electrode active material particles. As in the case of the SEI layer, it can be expected to suppress the decomposition reaction of the non-aqueous electrolyte component, thereby improving the storage characteristics of the lithium ion secondary battery in a high-voltage charge state and storage characteristics at a high temperature. To do. That is, since the fluorine-based polymer has high ion dissociation properties, it is considered that the insertion or desorption of ions is not inhibited even when it is present on the surface of the active material particles of the positive electrode, but electrons are not transmitted. It is estimated that the oxidative decomposition of the electrolyte component can be suppressed.

  The fluorine-based polymer may be contained in the positive electrode mixture layer, but is preferably present on the surface of the active material particles. In this case, the contact between the active material particles and the non-aqueous electrolyte component Therefore, the storage characteristics of the lithium ion secondary battery are further improved. Further, when the fluorine-based polymer has a primary amino group or a secondary amino group in the molecule, the fluorine-based polymer is present on the surface of the active material particles, so that Since the eluting metal ions can be captured better, it is possible to further enhance the storage characteristics of the lithium ion secondary battery in a high voltage charging state and the storage characteristics at a high temperature.

  The content of the fluorine-based polymer in the positive electrode mixture layer is preferably 0.01 parts by mass or more with respect to 100 parts by mass of all active material particles from the viewpoint of ensuring the above-described effect due to its use. And more preferably 0.05 parts by mass or more. However, if the amount of the fluorinated polymer in the positive electrode mixture layer is too large, the cost is increased and the productivity of the battery is reduced, or the ionic conductivity and the internal resistance are increased, thereby deteriorating the battery characteristics. There is a risk of letting it go. Therefore, the content of the fluorine-based polymer in the positive electrode mixture layer is preferably 0.3 parts by mass or less and more preferably 0.2 parts by mass or less with respect to 100 parts by mass of all active material particles. preferable.

  As the current collector for the positive electrode, the same one as used for the positive electrode of a conventionally known non-aqueous secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  The positive electrode of the present invention is, for example, a paste in which active material particles, a conductive auxiliary agent, a resin binder, and a dispersant as necessary are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). A slurry-like positive electrode mixture-containing composition is prepared (however, a resin binder may be dissolved in a solvent), applied to one or both sides of a current collector, and dried, then necessary. It is manufactured through a process of applying a calendar process accordingly.

  For the preparation of the positive electrode mixture-containing composition, active material particles prepared by previously mixing a plurality of types of particles having different particle diameters (for example, first group particles and second group particles) to have a particle size distribution as described above are used. In addition to use, a plurality of types of particles (for example, first group particles and second group particles) that satisfy the particle size distribution after mixing may be used without being mixed in advance.

  Moreover, what is necessary is just to add the said fluoropolymer to a positive mix mixture containing composition, when making the said positive mix layer contain the said fluoropolymer. Since the fluoropolymer is adsorbed on the surface of the active material particles in the positive electrode mixture-containing composition, most of the fluoropolymer is active in the positive electrode mixture layer formed using the positive electrode mixture-containing composition. It exists on the surface of the substance particle.

  However, the positive electrode of the present invention is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a positive electrode as needed.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode for a lithium ion battery of the present invention may be used for the positive electrode. There is no particular limitation, and various configurations and structures employed in conventionally known lithium ion secondary batteries can be applied.

  For example, a negative electrode having a structure in which a negative electrode active material, a binder, and, if necessary, a negative electrode mixture layer containing a conductive auxiliary agent on one or both sides of the current collector can be used. .

  Examples of the negative electrode active material include graphite [natural graphite such as flaky graphite; artificial graphite obtained by graphitizing graphitized carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB) and carbon fibers at 2800 ° C. or higher. , Etc.], pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, MCMB, carbon fibers, activated carbon, and other carbon materials; metals that can be alloyed with lithium (Si, Sn, etc.) and And materials containing these metals (alloys, oxides, etc.), etc., and one or more of these can be used.

  Moreover, the thing same as what was illustrated previously as what can be used for the positive electrode of this invention can be used for the binder and electroconductive auxiliary agent of a negative electrode.

  As a composition of each component in the negative electrode mixture layer, for example, the content of the negative electrode active material is preferably 80.0 to 99.8% by mass, and the content of the binder is 0.1 to 10% by mass. It is preferable. Moreover, when making a negative mix layer contain a conductive support agent, it is preferable that content of the conductive support in a negative mix layer is 0.1-10 mass%. Furthermore, the thickness of the negative electrode mixture layer (when the positive electrode mixture layer is formed on both sides of the current collector, the thickness per side of the current collector) is preferably 10 to 100 μm.

  The negative electrode is, for example, a paste or slurry in which a negative electrode active material, a binder, and a negative electrode mixture containing a conductive auxiliary agent used as necessary are dispersed in an organic solvent such as NMP or a solvent such as water. The negative electrode mixture-containing composition is prepared, applied to one or both sides of the current collector, dried, and then subjected to a calendaring process as necessary.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a negative electrode as needed.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is 5 μm in order to ensure mechanical strength. Is desirable.

  For the non-aqueous electrolyte solution according to the lithium ion secondary battery of the present invention, a solution in which a lithium salt is dissolved in a non-aqueous solvent is usually used.

  Examples of the solvent for the non-aqueous electrolyte include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ -Butyrolactone (γ-BL), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), Dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative Aprotic organic solvents such as conductors, diethyl ether, and 1,3-propane sultone can be used alone or as a mixed solvent in which two or more are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, From lithium salts such as LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] There may be mentioned at least one selected. The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  In addition, non-aqueous electrolytes used in lithium ion secondary batteries include acid anhydrides and sulfonic acids for the purpose of further improving charge / discharge cycle characteristics and further improving safety such as high-temperature storage and prevention of overcharge. Esters, dinitriles, 1,3-propane sultone, diphenyl disulfide, biphenyl, cyclohexylbenzene, fluorobenzene, t-butylbenzene, vinylene carbonate (VC) and derivatives thereof, halogen-substituted cyclic carbonates [4-fluoro-1, Additives (including their derivatives) such as 3-dioxolan-2-one (FEC) etc. can also be added as appropriate.

  Further, a gelling agent made of a polymer or the like may be added to the nonaqueous electrolytic solution and used as a gel (gel electrolyte).

  The separator according to the lithium ion secondary battery of the present invention has a property that the pores are blocked at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower) (ie, shutdown function). It is preferable to have a separator used in a normal lithium ion secondary battery, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP). The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be. The thickness of the separator is preferably 10 to 30 μm, for example.

  A laminated separator in which a heat-resistant layer containing a heat-resistant inorganic filler such as silica, alumina or boehmite is formed on one or both sides of the polyolefin microporous film as described above may be used.

  In the lithium ion secondary battery according to the present invention, the positive electrode according to the present invention and the negative electrode are laminated electrode bodies laminated via the separator, or laminated via the separator, and then spirally wound. Used as a formed wound electrode body.

  In the lithium ion secondary battery of the present invention, for example, a laminated electrode body or a wound electrode body is loaded into the exterior body, and a nonaqueous electrolyte is injected into the exterior body so that the electrode body is immersed in the nonaqueous electrolyte. Then, it is manufactured by sealing the opening of the exterior body. As the exterior body, it is possible to use a tubular exterior body (such as a rectangular tube or a cylindrical body) made of steel, aluminum, or aluminum alloy, or an exterior body composed of a laminated film on which metal is deposited.

  Since the lithium ion secondary battery of the present invention has a large volumetric energy density and good load characteristics, it is used in applications where conventional lithium ion secondary batteries are used, including applications requiring such characteristics. It can be applied to the same application.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
The average particle size A is 1 [mu] m LiFePO ₄ (first group particles), and mixed average particle diameter B of 0.009 LiFePO ₄ (second group particles) at a ratio of 80:20 (mass ratio) positive An active material was obtained. The obtained positive electrode active material has a ratio of particles having a particle diameter of 0.8 to 35 μm of 80% by mass and a ratio of particles having a particle diameter of 0.001 to 0.4 μm of 20% by mass. The ratio of the total amount of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm in the total amount was 100 mass%, and the A / B ratio was 111.

Mixture (positive electrode active material): 89.6 parts by mass, acetylene black (conductive auxiliary agent): 5.48 parts by mass, PVDF (binder): 4.67 parts by mass, and PVP (dispersant): 0.8. 25 parts by mass was dispersed in NMP as a solvent to prepare a positive electrode mixture-containing composition. This positive electrode mixture-containing composition was applied to one surface of an aluminum foil having a thickness of 15 μm serving as a current collector in an amount of 20 mg / cm ² after drying, dried, pressed, and then subjected to 30 A positive electrode was produced by cutting into a size of × 30 mm. The positive electrode mixture layer of the obtained positive electrode had a thickness of 67.4 μm.

<Production of negative electrode>
Scale-like graphite (manufactured by Hitachi Chemical Co., Ltd.): 98 parts by mass, CMC: 1 part by mass and SBR: 1 part by mass are dispersed in water to prepare a negative electrode mixture-containing composition, and this negative electrode mixture-containing composition Was applied to one side of a copper foil having a thickness of 8 μm to be a current collector, dried and pressed, and then cut into a size of 35 × 35 mm to produce a negative electrode. The negative electrode mixture layer of the obtained negative electrode had a thickness of 80 μm.

<Battery assembly>
The positive electrode and the negative electrode are laminated via a separator (PE microporous film having a thickness of 16 μm) and inserted into a laminate film exterior, and a non-aqueous electrolyte (volume ratio of ethylene carbonate and diethyl carbonate) After injecting LiPF ₆ in a 3: 7 mixed solvent at a concentration of 1.2 M), the laminate film outer package is sealed, and the appearance shown in FIG. 1 is the lithium ion having the structure shown in FIG. A secondary battery was produced.

  Here, FIG. 1 and FIG. 2 will be described. FIG. 1 is a plan view schematically showing a nonaqueous electrolyte secondary battery, and FIG. 2 is a cross-sectional view taken along line AA of FIG. The nonaqueous electrolyte secondary battery 1 includes a laminated electrode body constituted by laminating a positive electrode 5 and a negative electrode 6 with a separator 7 in a laminated film outer package 2 constituted by two laminated films, and nonaqueous electrolysis. The laminate film exterior body 2 is sealed by heat-sealing the upper and lower laminate films at the outer peripheral portion thereof. In FIG. 2, each layer constituting the laminate film outer package 2 and each layer of the positive electrode 5 and the negative electrode 6 are not shown separately in order to prevent the drawing from becoming complicated.

  The positive electrode 5 is connected to the positive electrode external terminal 3 in the battery 1 through a lead body. Although not shown, the negative electrode 6 is also connected to the negative electrode external terminal 4 in the battery 1 through a lead body. doing. The positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out to the outside of the laminate film exterior body 2 so that they can be connected to an external device or the like.

Comparative Example 1
LiFePO ₄ (positive electrode active material) having an average particle diameter of 1 μm: 90 parts by mass, acetylene black: 5.0 parts by mass, PVDF: 4.7 parts by mass, and PVP: 0.3 parts by mass in NMP as a solvent To prepare a positive electrode mixture-containing composition. A positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing composition was used, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

  Table 1 shows the configurations of the positive electrodes according to the lithium ion secondary batteries of Example 1 and Comparative Example 1. Further, the following evaluations were performed on the lithium ion secondary batteries of Example 1 and Comparative Example 1. The results are shown in Table 2.

<Volume energy density measurement>
The lithium ion secondary batteries of Example 1 and Comparative Example 1 were charged at a constant current until the voltage reached 4.2 V at a current value of 0.2 C in an environment of 25 ° C., and then the current value at a voltage of 4.2 V. The battery was charged at a constant voltage until the temperature reached 0.05C. About each battery after constant current-constant voltage charge, it discharged until it became 2.5V with the electric current value of 0.2C in the environment of 25 degreeC, and discharge capacity (0.2C discharge capacity) was calculated | required. And about each battery, the obtained discharge capacity was remove | divided by the volume of the positive mix layer, and the volume energy density of the positive electrode was computed.

<Evaluation of load characteristics>
About the lithium ion secondary battery of Example 1 and Comparative Example 1, constant current-constant voltage charging was performed under the same conditions as in volume energy density measurement, and discharging was performed until the current value of 1C reached 2.5 V. The discharge capacity (1C discharge capacity) was determined. And about each battery, the value which remove | divided 1C discharge capacity by 0.2C discharge capacity was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required. It can be said that the higher the capacity retention rate, the better the load characteristics of the battery.

<Charge / discharge cycle characteristics at 25 ° C.>
About the lithium ion secondary battery of Example 1 and Comparative Example 1, constant current charging was performed until the current value reached 0.05 V at a voltage value of 4.2 V until the current value reached 0.05 C at a current value of 1 C. A series of operations for performing constant current-constant voltage charging and constant current discharging up to 2.5 V at a current value of 1 C was set as one cycle, and this was repeated 200 cycles. And about each battery, the value which divided | segmented 1C discharge capacity of 200th cycle by 1C discharge capacity (initial 1C discharge capacity) calculated | required at the time of load characteristic evaluation was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required. It can be said that the higher the capacity retention rate, the better the charge / discharge cycle characteristics of the battery.

  As shown in Table 1 and Table 2, as the positive electrode active material (particles), the lithium ion secondary battery of Example 1 in which an appropriate particle size distribution was used and the porosity of the positive electrode mixture layer was appropriate The porosity of the positive electrode mixture layer related to the positive electrode used was very small, good load characteristics could be maintained, and a large volume energy density could be secured. The lithium ion secondary battery of Example 1 also had good charge / discharge cycle characteristics. On the other hand, the battery of Comparative Example 1 using an active material containing only particles having a large particle size as the positive electrode active material (particles) does not have a sufficiently small porosity of the positive electrode mixture layer, and thus has a volume energy. The density was small.

Example 2
83. LiMn _1/3 Ni _1/3 Co _1/3 O ₂ (first group particles) having an average particle diameter A of 5 μm and LiFePO ₄ (second group particles) having an average particle diameter B of 0.009 μm. It mixed by the ratio (mass ratio) of 3: 16.7, and the positive electrode active material was obtained. In the obtained positive electrode active material, the ratio of particles having a particle diameter of 0.8 to 35 μm is 83.3 mass%, and the ratio of particles having a particle diameter of 0.001 to 0.4 μm is 16.7 mass%. The total ratio of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm in the total amount of the positive electrode active material was 100% by mass, and A / B was 555. .

  The positive electrode active material: 90.1 parts by mass, acetylene black: 4.76 parts by mass, PVDF: 4.92 parts by mass, and PVP: 0.22 parts by mass were dispersed in NMP as a solvent to form a positive electrode composite. An agent-containing composition was prepared. A positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing composition was used, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2
83. LiMn _1/3 Ni _1/3 Co _1/3 O ₂ (first group particles) having an average particle diameter A of 5 μm and LiFePO ₄ (second group particles) having an average particle diameter B of 0.5 μm. It mixed by the ratio (mass ratio) of 3: 16.7, and the positive electrode active material was obtained. The obtained positive electrode active material had a ratio of particles having a particle diameter of 0.8 to 35 μm of 83.3% by mass and a ratio of particles having a particle diameter of 0.001 to 0.4 μm of 0% by mass. The total ratio of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm in the total amount of the active material was 83.3 mass%, and A / B was 10. .

  A positive electrode was produced in the same manner as in Example 2 except that the positive electrode active material was used, and a lithium ion secondary battery was produced in the same manner as in Example 2 except that this positive electrode was used.

Comparative Example 3
83. LiMn _1/3 Ni _1/3 Co _1/3 O ₂ (first group particles) having an average particle diameter A of 17 μm and LiFePO ₄ (second group particles) having an average particle diameter B of 0.5 μm. It mixed by the ratio (mass ratio) of 3: 16.7, and the positive electrode active material was obtained. The obtained positive electrode active material had a ratio of particles having a particle diameter of 0.8 to 35 μm of 83.3% by mass and a ratio of particles having a particle diameter of 0.001 to 0.4 μm of 0% by mass. The total ratio of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm in the total amount of the active material was 83.3 mass%, and A / B was 34. .

  A positive electrode was produced in the same manner as in Example 2 except that the positive electrode active material was used, and a lithium ion secondary battery was produced in the same manner as in Example 2 except that this positive electrode was used.

Comparative Example 4
LiMn _1/3 Ni _1/3 Co _1/3 O ₂ (first group particles) having an average particle diameter A of 5 μm and LiFePO ₄ (second group particles) having an average particle diameter B of 0.009 μm are 60: A positive electrode active material was obtained by mixing at a ratio (mass ratio) of 40. The obtained positive electrode active material has a ratio of particles having a particle diameter of 0.8 to 35 μm of 60% by mass and a ratio of particles having a particle diameter of 0.001 to 0.4 μm of 40% by mass. The total ratio of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm in the total amount was 100% by mass, and A / B was 555.

  The positive electrode active material: 87 parts by mass, acetylene black: 7.62 parts by mass, PVDF: 5.10 parts by mass, and PVP: 0.28 parts by mass are dispersed in NMP as a solvent to contain a positive electrode mixture. A composition was prepared. A positive electrode was produced in the same manner as in Example 2 except that this positive electrode mixture-containing composition was used, and a lithium ion secondary battery was produced in the same manner as in Example 2 except that this positive electrode was used.

  About the lithium ion secondary battery of Example 2 and Comparative Examples 2-4, volume energy density measurement, load characteristic evaluation, and charging / discharging cycle characteristic evaluation were performed like the lithium ion secondary battery of Example 1, etc.

  Table 3 shows the configurations of the positive electrodes according to the lithium ion secondary batteries of Example 2 and Comparative Examples 2 to 4. Table 4 shows the results of the above evaluations on the lithium ion secondary batteries of Example 2 and Comparative Examples 2 to 4.

  As shown in Tables 3 and 4, the lithium ion secondary battery of Example 2 using an active material (particle) of the positive electrode having an appropriate particle size distribution and having an appropriate porosity of the positive electrode mixture layer is The volume energy density was large, and the load characteristics and charge / discharge cycle characteristics were good.

  On the other hand, in the lithium ion secondary batteries of Comparative Example 2 and Comparative Example 3 using particles having a particle diameter larger than 0.001 to 0.4 μm as the active material (particles) of the positive electrode, The porosity was not small and the volume energy density was small. In addition, the use of a conductive auxiliary using a positive electrode active material (particles) in which the ratio of particles having a particle size of 0.8 to 35 μm and particles having a particle size of 0.001 to 0.4 μm was inappropriate The battery of Comparative Example 4 in which the amount was too large was not low in the porosity of the positive electrode mixture layer, had a low volumetric energy density, and was inferior in charge / discharge cycle characteristics.

Example 3
LiCoO ₂ (first group particles) having an average particle diameter A of 17 μm and LiCoO ₂ (second group particles) having an average particle diameter B of 0.3 μm in a ratio (mass ratio) of 91.8: 8.2. A positive electrode active material was obtained by mixing. In the obtained positive electrode active material, the ratio of particles having a particle diameter of 0.8 to 35 μm is 91.8% by mass, and the ratio of particles having a particle diameter of 0.001 to 0.4 μm is 8.2% by mass. The total ratio of particles having a particle diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm in the total amount of the positive electrode active material was 57% by mass, and A / B was 555. .

  The positive electrode active material: 96.7 parts by mass, acetylene black: 2.0 parts by mass, PVDF: 1.27 parts by mass, and PVP: 0.03 parts by mass were dispersed in NMP as a solvent to form a positive electrode composite. An agent-containing composition was prepared. A positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing composition was used, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 5
LiCoO ₂ (positive electrode active material) having an average particle diameter of 17 μm: 96.72 parts by mass, acetylene black: 2.0 parts by mass, PVDF: 1.25 parts by mass, and PVP: 0.03 parts by mass are solvents. A positive electrode mixture-containing composition was prepared by dispersing in NMP. A positive electrode was produced in the same manner as in Example 1 except that this positive electrode mixture-containing composition was used, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

  The lithium ion secondary batteries of Example 3 and Comparative Example 5 were subjected to volume energy density measurement, load characteristic evaluation, and charge / discharge cycle characteristic evaluation by the following methods.

<Volume energy density measurement>
The lithium ion secondary batteries of Example 3 and Comparative Example 5 were charged at a constant current until the voltage reached 4.4 V at a current value of 0.2 C in an environment of 25 ° C., and then the current value at a voltage of 4.4 V. The battery was charged at a constant voltage until the temperature reached 0.05C. About each battery after constant current-constant voltage charge, it discharged until it became 3.0V with the electric current value of 0.2C in the environment of 25 degreeC, and discharge capacity (0.2C discharge capacity) was calculated | required. For each battery, the obtained discharge capacity was divided by the volume of the battery to calculate the volume energy density.

<Evaluation of load characteristics>
About the lithium ion secondary battery of Example 3 and Comparative Example 5, constant current-constant voltage charging was performed under the same conditions as in the volume energy density measurement, and discharging was performed until the current value of 1C reached 3.0 V. The discharge capacity (1C discharge capacity) was determined. And about each battery, the value which remove | divided 1C discharge capacity by 0.2C discharge capacity was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required.

<Charge / discharge cycle characteristics at 25 ° C.>
About the lithium ion secondary battery of Example 3 and Comparative Example 5, constant current charging was performed until the current value reached 4.4 C at a current value of 1 C, and constant voltage charging was performed until the current value reached 0.05 C at a voltage of 4.4 V. A series of operations for performing constant current-constant voltage charging and constant current discharging up to 3.0 V at a current value of 1 C was set as one cycle, and this was repeated 200 cycles. And about each battery, the value which divided | segmented 1C discharge capacity of 200th cycle by 1C discharge capacity (initial 1C discharge capacity) calculated | required at the time of load characteristic evaluation was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required.

  Table 5 shows configurations of positive electrodes according to the lithium ion secondary batteries of Example 3 and Comparative Example 5. Table 6 shows the results of the above evaluations on the lithium ion secondary batteries of Example 3 and Comparative Example 5.

  As shown in Table 5 and Table 6, as the positive electrode active material (particles), the lithium ion secondary battery of Example 3 using an appropriate particle size distribution and having an appropriate porosity of the positive electrode mixture layer is used. The porosity of the positive electrode mixture layer related to the positive electrode used was very small, good load characteristics could be maintained, and a large volume energy density could be secured. Moreover, the lithium ion secondary battery of Example 3 also had good charge / discharge cycle characteristics. On the other hand, the battery of Comparative Example 5 using an active material containing only particles having a large particle size as the positive electrode active material (particles) does not have a sufficiently small porosity of the positive electrode mixture layer, and thus has a volume energy. The density was small. Further, the battery of Comparative Example 5 was inferior in charge / discharge cycle characteristics.

Example 4
In a 100 ml three-necked reaction flask equipped with a magnetic stirrer, heating oil bath, dropping device, condenser and nitrogen inlet, 0.39 g of polyvinyl alcohol (“PVA203” manufactured by Kuraray Co., Ltd.) and dimethylacetamide (Wako Pure Chemical Industries, Ltd.) 20 ml of Kogyo Co., Ltd. was added, and the oil bath was heated to 100 ° C. with stirring to dissolve the polyvinyl alcohol. A solution prepared by mixing 3.1 g of hexafluoroglutaric acid anhydride with 4 ml of pyridine was dropped into a three-necked reaction flask which was allowed to cool to room temperature after removing the oil bath, and stirring was continued for 1 hour after completion of the dropping. Thereafter, 70 μl of water was added to the three-necked reaction flask and stirred for 20 minutes. Further, 0.76 g of lithium hydroxide monohydrate was added and dissolved, and then a 1N lithium hydroxide aqueous solution was added to the equivalent amount.

  The solution in the three-necked reaction flask thus obtained was added dropwise to 300 ml of tetrahydrofuran (manufactured by Wako Pure Chemical Industries, Ltd.) and precipitated. The recovered precipitate was washed with tetrahydrofuran and dissolved by adding 10 ml of ethanol. The process was repeated. The finally obtained precipitate was dissolved in water and then freeze-dried to obtain a fluoropolymer. The yield was 40%.

  The obtained fluoropolymer has a main chain derived from the main chain of polyvinyl alcohol, a structural part represented by the general formula (1), wherein n is 3 and M is Li, It has a pendant group containing an ester group between the main chain. Furthermore, the amount of pendant groups introduced into the fluoropolymer was about 55 mol% with respect to the vinyl alcohol unit constituting the main chain. The number average molecular weight of the fluoropolymer was about 50,000.

  The same mixture as that prepared in Example 3 was used as the positive electrode active material. This mixture: 96.62 parts by mass, the fluoropolymer: 0.1 parts by mass, acetylene black: 2.0 parts by mass, PVDF: A positive electrode mixture-containing composition was prepared by dispersing 1.25 parts by mass and PVP: 0.03 parts by mass in NMP as a solvent. A positive electrode was produced in the same manner as in Example 3 except that this positive electrode mixture-containing composition was used, and a lithium ion secondary battery was produced in the same manner as in Example 3 except that this positive electrode was used.

  For the lithium ion secondary battery of Example 4, volume energy density measurement, load characteristic evaluation, and charge / discharge cycle characteristic evaluation were performed in the same manner as the lithium ion secondary battery of Example 3 and the like.

  The lithium ion secondary batteries of Example 3 and Example 4 were evaluated for charge / discharge cycle characteristics at 45 ° C. by the following method. For each of the batteries described above, a series of operations for performing constant current-constant voltage charging and constant current discharging under the same conditions as in Example 2 except that the environmental temperature was changed to 45 ° C. was repeated for 100 cycles. And about each battery, the value which remove | divided 1C discharge capacity of 100th cycle by 1C discharge capacity (initial 1C discharge capacity) calculated | required at the time of load characteristic evaluation was represented by percentage, and the capacity | capacitance maintenance factor was calculated | required.

  The configuration of the positive electrode according to the lithium ion secondary battery of Example 4 is shown in Table 7 together with the configuration of the positive electrode according to the lithium ion secondary battery of Example 3. Moreover, about the lithium ion secondary battery of Example 4, the result of said each evaluation is shown in Table 8 with the evaluation result in the lithium ion secondary battery of Example 3. FIG.

  As shown in Table 7 and Table 8, the lithium ion secondary battery of Example 3 and the lithium ion secondary battery of Example 4 have the same configuration except for the presence or absence of the fluoropolymer in the positive electrode mixture layer. Thus, the porosity, volume energy density, load characteristics, and charge / discharge cycle characteristics at 25 ° C. of the positive electrode mixture layer were substantially the same. However, the charge / discharge cycle characteristics at 45 ° C. were much better in the battery of Example 4 using the fluorine-based polymer than in the battery of Example 3 not using this.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Laminate film exterior body 5 Positive electrode 6 Negative electrode 7 Separator

Claims (13)

A positive electrode for a lithium ion battery having a positive electrode mixture layer containing active material particles, a conductive auxiliary agent and a resin binder,
As the active material particles, the ratio of particles having a particle diameter of 0.8 to 35 μm is 70 to 95 mass%, the ratio of particles having a particle diameter of 0.001 to 0.4 μm is 5 to 30 mass%, The ratio of the total particle size of particles having a particle size of 0.8 to 35 μm and particles having a particle size of 0.001 to 0.4 μm is 90% by mass or more,
Carbon material is contained as the conductive auxiliary agent, and the content of the carbon material in the positive electrode mixture layer is 0.5 to 7% by mass,
The positive electrode mixture layer has a porosity of 5 to 15 vol. %, A positive electrode for a lithium ion battery. As the active material particles, first group particles and second group particles having an average particle diameter smaller than that of the first group particles are used.
2. The lithium according to claim 1, wherein the average particle diameter A (μm) of the first group particles is 1 to 30 μm, and the average particle diameter B (μm) of the second group particles is 0.003 to 0.3 μm. Positive electrode for ion battery.   3. The positive electrode for a lithium ion battery according to claim 2, wherein the ratio A / B between the average particle diameter A of the first group particles and the average particle diameter B of the second group particles is 40 or more.   The positive electrode for a lithium ion battery according to claim 2 or 3, wherein the content of the second group particles in all active material particles is 9 to 20% by mass.   5. The positive electrode for a lithium ion battery according to claim 2, wherein the average particle diameter A of the first group particles is 5 to 20 μm.   6. The positive electrode for a lithium ion battery according to claim 2, wherein the second group particles have an average particle diameter B of 0.005 to 0.2 μm.   The positive electrode mixture layer has a porosity of 7 to 13 vol. The positive electrode for a lithium ion battery according to any one of claims 1 to 6.   The positive electrode for a lithium ion battery according to claim 1, wherein the positive electrode mixture layer further contains a dispersant.   The lithium ion battery according to claim 1, wherein the active material particles include lithium transition metal oxide particles having a layered structure or a spinel structure, or particles of a phosphate transition metal compound having an olivine structure. Positive electrode. The positive electrode mixture layer further contains a fluorine-based polymer having a plurality of pendant groups containing fluorine,
The positive electrode for a lithium ion battery according to any one of claims 1 to 9, wherein the content of the fluoropolymer with respect to 100 parts by mass of all active material particles is 0.01 to 0.3 parts by mass.   The positive electrode for a lithium ion battery according to claim 10, wherein the fluoropolymer is present on the surface of the active material particles. The pendant group of the fluoropolymer is composed of a functional group (A) which is a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, and a group interposed between the functional group (A) and the main chain. Configured,
At least a part of the pendant group is a group interposed between the functional group (A) and the main chain is a hydrocarbon group; a perfluorocarbon group; a hydrocarbon group and an ester group Or at least one group selected from the group consisting of carbonate groups and amide groups; or at least one group selected from the group consisting of perfluorocarbon groups and ester groups, carbonate groups and amide groups It consists of a group and
The functional group (A) is directly bonded to the carbon of the hydrocarbon group or the perfluorocarbon group, and the group interposed between the functional group (A) and the main chain is a hydrocarbon group. Or a hydrocarbon group and at least one group selected from the group consisting of an ester group, a carbonate group and an amide group, at least of the carbons of the hydrocarbon group, The positive electrode for a lithium ion battery according to claim 10 or 11, wherein fluorine is bonded to carbon at the α-position or β-position of the functional group (A).   A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode for a lithium ion battery according to claim 1 is used as the positive electrode.

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