JP2015176804A - 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.SOLUTION: A lithium ion secondary battery comprises: a positive electrode having a positive electrode mixture layer including active material particles, a conductive assistant agent and a resin binder; a negative electrode; and a nonaqueous electrolyte prepared by dissolving a lithium salt in an organic solvent. Of the active material particles, particles having a particle diameter of 0.8-35 μm account for 70-95 mass%; particles having a particle diameter of 0.001-0.4 μm account for 5-30 mass%; and the particles of 0.8-35 μm in particle diameter and the particles of 0.001-0.4 μm in particle diameter account for 90 mass% or more in total. As the conductive assistant agent, a carbon material is used. 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.%. The organic solvent includes at least one kind of material selected from a nitrile-based solvent and a chain carbonate.

Description

  The present invention relates to a lithium ion secondary battery having a large volumetric energy density and good load characteristics.

  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.

  In addition, 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. 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, the battery design is made so that the capacity can be sufficiently extracted even when charging / discharging with a large current value. It is also required to maintain proper load characteristics.

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

  The lithium ion secondary battery of the present invention capable of achieving the above object is obtained by dissolving a positive electrode having a positive electrode mixture layer containing active material particles, a conductive auxiliary agent and a resin binder, a negative electrode, and a lithium salt in an organic solvent. A lithium ion secondary battery comprising a non-aqueous electrolyte, wherein the proportion of particles having a particle size of 0.8 to 35 μm is 70 to 95 mass% as the active material particles, and the particle size is 0.00. The ratio of particles having a particle diameter of 001 to 0.4 μm is 5 to 30% by mass, and the 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 is 90%. Using particles that are greater than or equal to mass%, using a carbon material as the conductive assistant, setting the content of the carbon material in the positive electrode mixture layer to 0.5 to 7 mass%, and voids in the positive electrode mixture layer The rate is 5-15 vol%, and the organic solvent And it is characterized in that it comprises at least one selected from a nitrile solvent and a chain carbonate.

  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.

  The positive electrode constituting the lithium ion secondary battery of the present invention has a positive electrode mixture layer containing active material particles, a conductive auxiliary agent and a resin binder. For example, the positive electrode mixture layer is used as a current collector. It has a structure formed on one side or both sides.

  In the positive electrode, 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, reducing the porosity of the positive electrode mixture layer as described above is not easy in production, and even if the porosity of the positive electrode mixture layer is simply reduced, as described above, the positive electrode mixture layer Since it becomes difficult for a nonaqueous electrolyte (nonaqueous electrolyte) to permeate therein, 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 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 non-aqueous electrolyte solution that can penetrate into the positive electrode mixture layer becomes very small, and the positive electrode mixture layer cannot hold the required amount of electrolyte solution. There is a risk that battery characteristics may be deteriorated. Therefore, in the present invention, the porosity of the positive electrode mixture layer needs to be 5 vol% or more, preferably 7 vol% or more.

The porosity of the positive electrode mixture layer in the present specification excludes the volume of all materials 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 portion 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

  Further, 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. %, And the total ratio 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.

  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 active material particles constituting the positive electrode, the content of particles having a particle diameter of 0.001 to 0.4 μm in all active material particles is 5 mass% or more, preferably 9 mass% or more, and 30 It is made into the 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 may be reduced as described above. In addition, it is possible to suppress a decrease in load characteristics of the lithium ion secondary battery.

  In the active material particles constituting the positive electrode, 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 95 Not more than mass%, preferably not more than 91 mass%.

  As the active material particles constituting the positive electrode of the present invention, only particles having a particle size of 0.001 to 0.4 μm and particles having a particle size of 0.8 to 35 μm may be used. It may contain particles not corresponding to ˜35 μm and 0.001 to 0.4 μm. However, in the case where particles having particle diameters not corresponding to 0.8 to 35 μm and 0.001 to 0.4 μm are contained, the ratio is desirably 10% by mass or less in all active material particles.

  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 layered lithium transition metal oxide include LiCoO ₂ and a part of Co substituted with Al, Mg, Mn, Ti, or the like, LiNi _1-d Co _d-e Al _e O ₂ ( In addition to 0.1 ≦ d ≦ 0.3, 0.01 ≦ e ≦ 0.2, etc., an oxide containing at least Co, Ni, and Mn (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _5/12 Co _1/6 Mn _5/12 O ₂ , LiNi _3/5 Co _1/5 Mn _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.

  The conductive auxiliary agent for the positive electrode mixture layer of the positive electrode includes graphite such as natural graphite (such as flaky graphite) and artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. Carbon materials such as carbon 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 dispersing agent such as polyvinyl pyrrolidone (PVP) can be used for the positive electrode mixture layer of the positive electrode. 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.

  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 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), and this is applied to one or both sides of the current collector and dried. Manufactured through a calendaring process.

  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.

  However, the positive electrode used in the present invention is not limited to those manufactured by the method described above, 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 10 to 150 μm per one surface of the current collector, for example.

  The lithium ion secondary battery of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte (non-aqueous electrolyte), and there are no particular restrictions on the other configurations and structures, and conventionally known lithium ions Various configurations and structures employed in the secondary battery 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 150 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 nonaqueous electrolyte according to the lithium ion secondary battery of the present invention, a solution in which a lithium salt is dissolved in an organic solvent such as a cyclic carbonate or a chain carbonate is usually used. In order to improve the permeability of the non-aqueous electrolyte to the layer and the diffusibility of lithium ions and further enhance the load characteristics of the battery, the organic solvent of the non-aqueous electrolyte is at least selected from nitrile solvents and chain carbonates It is desirable to contain one kind, and it is more desirable to contain at least a nitrile solvent.

  Nitrile-based solvents have high ion conductivity and are suitable for increasing the diffusibility of lithium ions in the battery. Especially in the case of a positive electrode in which the positive electrode active material layer is thickened to increase the filling amount of the positive electrode active material. Lithium ions can be diffused well to a region in the vicinity of the current collector where lithium ions are difficult to reach during discharge under load. Therefore, it is possible to draw out a sufficient capacity even during high load discharge, and the load characteristics of the lithium ion secondary battery using the positive electrode can be further improved. Specifically, when the non-aqueous electrolyte organic solvent contains a nitrile solvent, even if the thickness of the positive electrode mixture layer on one side of the current collector is as thick as 80 to 150 μm, it is sufficient for high-load discharge. Large capacity can be obtained.

  On the other hand, a nitrile solvent is highly reactive with the negative electrode surface (the active surface of the negative electrode) and may cause deterioration of the negative electrode. Therefore, the nitrile solvent may be used with at least one carbonate selected from cyclic carbonates and chain carbonates. desirable.

  That is, the nonaqueous electrolyte according to the lithium ion secondary battery of the present invention desirably contains at least one selected from a nitrile solvent and a chain carbonate as an organic solvent, and contains at least a nitrile solvent. Is more desirable, and most desirably contains a nitrile solvent and at least one carbonate selected from cyclic carbonates and chain carbonates.

  Specific examples of nitrile solvents include mononitriles such as acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, acrylonitrile; malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1, 5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8- Dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, dinitriles such as 2,4-dimethylglutaronitrile; cyclic nitriles such as benzonitrile; alkoxy-substituted nitriles such as methoxyacetonitrile; One of them May be used alone, or in combination of two or more kinds. Among these, mononitrile is more preferable, and acetonitrile is still more preferable.

  Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate (1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate), vinylene carbonate, and the like. Specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate. The exemplified cyclic carbonate and chain carbonate may contain only one of them, and two or more kinds (two or more of the above exemplified cyclic carbonates, among the above exemplified chain carbonates). Or one or more of the exemplified cyclic carbonates and one or more of the exemplified chain carbonates) may be contained. In the case of containing a nitrile solvent as the organic solvent, among these, it is more preferable to contain a cyclic carbonate, and it is more preferable to contain ethylene carbonate or propylene carbonate.

  The content of the nitrile solvent in the total organic solvent of the non-aqueous electrolyte used in the lithium ion secondary battery is 5 mass from the viewpoint of better ensuring the effect of improving the load characteristics of the non-aqueous secondary battery. % Or more, preferably 10% by mass or more. However, if the amount of the nitrile solvent in the total organic solvent of the non-aqueous electrolyte is too large, there is a high risk of causing the negative electrode to deteriorate due to the reaction with the negative electrode, so the non-aqueous electrolyte used in the lithium ion secondary battery The content of the nitrile solvent in the total organic solvent is preferably 80% by mass or less, and more preferably 40% by mass or less.

  In addition, the content of the chain carbonate in the total organic solvent of the non-aqueous electrolyte used in the lithium ion secondary battery is from the viewpoint of better ensuring the load characteristics improvement effect of the non-aqueous secondary battery due to its use. It is preferably 5% by mass or more, and more preferably 10% by mass or more. However, if the amount of chain carbonate in the total organic solvent of the non-aqueous electrolyte is too large, there is a high risk of causing the deterioration of the negative electrode due to the reaction with the negative electrode, so the non-aqueous electrolyte used in the lithium ion secondary battery, The content of the chain carbonate in the total organic solvent is preferably 95% by mass or less, and more preferably 80% by mass or less.

  Further, when the organic solvent of the non-aqueous electrolyte used for the lithium ion secondary battery contains a nitrile solvent, the carbonate in all organic solvents (at least one selected from cyclic carbonate and chain carbonate) The content of the carbonate) is preferably 10% by mass or more and more preferably 30% by mass or more from the viewpoint of better ensuring the effect of suppressing the reaction between the nitrile solvent and the negative electrode due to its use. preferable. However, if the amount of the carbonate-based solvent in the total organic solvent of the non-aqueous electrolyte is too large, for example, the amount of the nitrile-based solvent is too small, and the effect of improving the load characteristics of the non-aqueous secondary battery due to their use is small There is a risk of becoming. Therefore, the content of the carbonate in the total organic solvent of the nonaqueous electrolyte used for the nonaqueous secondary battery is preferably 80% by mass or less, and more preferably 60% by mass or less.

  As the organic solvent for the nonaqueous electrolyte, a solvent other than these can be used together with the nitrile solvent and the carbonate solvent. Specific examples of the organic solvent that can be used with the nitrile solvent and the carbonate solvent include: chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethoxyethane, diethyl ether, 1, Chain ethers such as 3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as 1,3-dioxane, 1,4-dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfites such as ethylene glycol sulfite; Is mentioned. Further, these compounds may be halogen-substituted products typified by fluorinated products.

Specific examples of the lithium salt of the non-aqueous _{electrolyte, LiClO 4, LiPF 6, LiBOB} , LiAsF 6, inorganic lithium salts such _{LiSbF 6; LiCF 3 SO 3,} LiCF 3 CO 2, Li 2 C 2 F 4 (SO ₃ ) ₂ , LiNC _n F _2n SO ₄ (n ≧ 2), LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ ₂ ) 2), an organic lithium salt such as LiN (R _f OSO ₂ ) ₂ [where R _f is a fluoroalkyl group], etc., and only one of these may be used, or two or more of them may be used in combination May be. Among these, when a compound having a phosphorus atom is used, it becomes easier to release a free fluorine atom, and therefore it is more preferable to use LiPF ₆ .

  The concentration of the lithium salt in the non-aqueous electrolyte (when using a plurality of types of lithium salts, the total concentration; the same shall apply hereinafter) is preferably 0.6 to 1.8 mol / l, and 0.9 to 1 More preferably, it is 6 mol / l.

  Depending on the type of organic solvent used in the non-aqueous electrolyte, the solubility of the specific lithium salt is low, and it may not be possible to ensure the above concentration by using only one type of lithium salt. For this, a plurality of lithium salts may be used in combination so that the total lithium salt concentration satisfies the above value.

  The nonaqueous electrolyte preferably contains vinylene carbonate. Vinylene carbonate has a function of forming a film on the negative electrode surface by charging and discharging a lithium ion secondary battery. And since the reaction derived from the contact between the negative electrode and the nonaqueous electrolyte can be suppressed by the coating derived from vinylene carbonate formed on the negative electrode surface, the deterioration of the negative electrode due to the nitrile solvent can be suppressed more favorably. That is, vinylene carbonate has not only a function as a nonaqueous electrolyte organic solvent but also a function as an additive for suppressing deterioration of the negative electrode. When a carbon material is used as the negative electrode active material (described later), the effect of suppressing the reaction between the negative electrode and the nonaqueous electrolyte component by vinylene carbonate becomes more remarkable. As described above, vinylene carbonate is preferably used in combination with other cyclic carbonates or chain carbonates because a relatively large amount of the vinylene carbonate is consumed by being involved in film formation by charging and discharging the battery as described above. .

  The vinylene carbonate content in the non-aqueous electrolyte may be used within the range of the amount described above as the preferred content of the carbonate in the total organic solvent, but the vinylene carbonate is coated with the charge / discharge of the battery. Since it also has the function of an additive to be formed, it is also preferable to adjust the amount in the total amount of the nonaqueous electrolyte. Specifically, from the viewpoint of ensuring the above-mentioned effect by use better, the content of vinylene carbonate in the non-aqueous electrolyte used for the lithium ion secondary battery is preferably 2% by mass or more, and 4% by mass. % Or more is more preferable. However, if the amount of vinylene carbonate in the non-aqueous electrolyte is too large, the amount of gas generated in the battery increases, and the storage characteristics of the battery may deteriorate. Therefore, the content of vinylene carbonate in the non-aqueous electrolyte used for the lithium ion secondary battery is preferably 15% by mass or less, and more preferably 10% by mass or less.

  In addition, the non-aqueous electrolyte includes 1,3-propane sultone, diphenyl disulfide, biphenyl, fluorobenzene, t-butylbenzene, for the purpose of improving battery safety, charge / discharge cycleability, and high-temperature storage properties. Additives such as halogen-substituted cyclic carbonates (such as 4-fluoro-1,3-dioxolan-2-one), sulfolane, fluoroethylene carbonate, and ethylene sulfite can be appropriately added.

  Furthermore, the lithium ion secondary battery of the present invention is obtained by adding a gelling agent such as a known polymer to the liquid nonaqueous electrolyte (nonaqueous electrolyte) to form a gel (gel electrolyte). It may be used. In the case of using a gel electrolyte, depending on the configuration, it may be disposed between the positive electrode and the negative electrode to have a separator function.

  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 1A
<Preparation of positive electrode>
LiFePO ₄ (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 0.3 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 100% by mass, and the A / B ratio was 57. It was.

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 at a concentration of 1.2 M into a 3: 7 mixed solvent, the laminate film outer package was sealed to produce a lithium ion secondary battery.

Example 1B
A lithium ion secondary battery was produced in the same manner as in Example 1A, except that the organic solvent of the nonaqueous electrolytic solution was changed to a mixed solvent of ethylene carbonate and acetonitrile in a volume ratio of 6: 4.

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 1A 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 1A except that this positive electrode was used.

  Tables 1 and 2 show the configurations of the positive electrode active material and the positive electrode according to the lithium ion secondary batteries of Examples 1A and 1B and Comparative Example 1, respectively. In addition, the following evaluations were performed on the lithium ion secondary batteries of Examples 1A and 1B and Comparative Example 1. The results are shown in Table 3.

<Volume energy density measurement>
The lithium ion secondary batteries of Examples 1A and 1B 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., followed by a voltage of 4.2 V. Constant voltage charging was performed until the current value 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>
For the lithium ion secondary batteries of Examples 1A and 1B 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 reached 1.5 V at 1.5 C. The discharge capacity (1.5 C discharge capacity) was determined. And about each battery, the value which remove | divided 1.5C discharge capacity by 0.2C discharge capacity was represented by percentage, the capacity | capacitance maintenance factor was calculated | required, and the load characteristic was evaluated. It can be said that the higher the capacity retention rate, the better the load characteristics of the battery.

<Charge / discharge cycle characteristics>
The lithium ion secondary batteries of Examples 1A and 1B and Comparative Example 1 were charged at a constant current until the voltage became 4.2 V at a current value of 1 C in an environment of 25 ° C., and the current value was 0 at a voltage of 4.2 V. A constant current-constant voltage charge in which constant voltage charge was performed until 0.05 C and a charge / discharge cycle in which constant current discharge was performed up to 2.5 V at a current value of 1 C were repeated 200 cycles. And about each battery, the value which remove | divided the discharge capacity of the 200th cycle by the discharge capacity (initial discharge capacity) of the 1st cycle was represented by 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 Tables 1 to 3, lithium ion secondary materials of Examples 1A and 1B using positive electrode active materials (particles) having an appropriate particle size distribution and appropriate porosity of the positive electrode mixture layer In the battery, the porosity of the positive electrode mixture layer related to the positive electrode used was very small, a large volume energy density could be secured, and good load characteristics could be maintained. In particular, the lithium ion secondary battery of Example 1B containing a nitrile solvent as the organic solvent for the nonaqueous electrolyte was a battery exhibiting excellent load characteristics. In addition, the lithium ion secondary batteries of Examples 1A and 1B 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 2A
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 556. .

  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 1A 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.

Example 2B
A lithium ion secondary battery was produced in the same manner as in Example 2A, except that the organic solvent of the non-aqueous electrolyte was changed to a mixed solvent of ethylene carbonate and acetonitrile in a volume ratio of 6: 4.

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 2A except that the positive electrode active material was used, and a lithium ion secondary battery was produced in the same manner as in Example 2A 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 2A except that the positive electrode active material was used, and a lithium ion secondary battery was produced in the same manner as in Example 2A 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 556.

  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 2A 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 2A except that this positive electrode was used.

  For the lithium ion secondary batteries of Examples 2A and 2B and Comparative Examples 2 to 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 1A. .

  Tables 4 and 5 show configurations of the positive electrode active material and the positive electrode according to the lithium ion secondary batteries of Examples 2A and 2B and Comparative Examples 2 to 4, respectively. Table 6 shows the results of the above evaluations on the lithium ion secondary batteries of Examples 2A and 2B and Comparative Examples 2 to 4.

  As shown in Tables 4 to 6, the lithium ion secondary of Examples 2A and 2B using an active material (particle) of the positive electrode having an appropriate particle size distribution and an appropriate porosity of the positive electrode mixture layer The battery had a large volumetric energy density and good load characteristics and charge / discharge cycle characteristics. In particular, the lithium ion secondary battery of Example 2B containing a nitrile solvent as the organic solvent for the nonaqueous electrolyte was a battery exhibiting excellent load characteristics.

  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 diameter of 0.8 to 35 μm and particles having a particle diameter of 0.001 to 0.4 μm was inappropriate was used. 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 3A
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 100% by mass, and A / B was 57. .

  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 1A 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 1A except that this positive electrode was used.

Example 3B
A lithium ion secondary battery was produced in the same manner as in Example 3A, except that the organic solvent of the non-aqueous electrolyte was changed to a mixed solvent of ethylene carbonate and acetonitrile in a volume ratio of 6: 4.

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 1A except that this positive electrode was used.

  For the lithium ion secondary batteries of Examples 3A and 3B and Comparative Example 5, 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 1A.

  Tables 7 and 8 show configurations of the positive electrode active material and the positive electrode according to the lithium ion secondary batteries of Examples 3A and 3B and Comparative Example 5, respectively. Table 9 shows the results of the above evaluations on the lithium ion secondary batteries of Examples 3A and 3B and Comparative Example 5.

  As shown in Table 7 to Table 9, lithium ion secondary materials of Examples 3A and 3B in which positive electrode active materials (particles) having an appropriate particle size distribution were used and the porosity of the positive electrode mixture layer was appropriate The battery had a large volumetric energy density and good load characteristics and charge / discharge cycle characteristics. In particular, the lithium ion secondary battery of Example 3B containing a nitrile solvent as the organic solvent for the nonaqueous electrolyte was a battery that exhibited excellent load 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 4A
A positive electrode was prepared in the same manner as in Example 3A except that the coating amount after drying of the positive electrode mixture-containing composition was 30 mg / cm ² and the thickness of the positive electrode mixture layer after the press treatment was 101 μm. A negative electrode was prepared in the same manner as in Example 1A, except that the coating amount after drying of the negative electrode mixture-containing composition was 1.5 times that in Example 1A so that the thickness of the negative electrode mixture layer after the press treatment was 120 μm. Was made. A lithium ion secondary battery was produced in the same manner as in Example 3A except that these positive electrode and negative electrode were used.

Example 4B
A lithium ion secondary battery was produced in the same manner as in Example 4A, except that the organic solvent of the non-aqueous electrolyte was changed to a mixed solvent of ethylene carbonate and acetonitrile in a volume ratio of 6: 4.

Comparative Example 6
A positive electrode was produced in the same manner as in Comparative Example 5 except that the coating amount after drying of the positive electrode mixture-containing composition was 30 mg / cm ² and the thickness of the positive electrode mixture layer after the press treatment was 101 μm. A lithium ion secondary battery was produced in the same manner as in Example 4A except that was used.

  In the lithium ion secondary batteries of Examples 4A and 4B and Comparative Example 6, the thicknesses of the mixture layers of the positive electrode and the negative electrode were the same as those of the positive and negative electrodes of the lithium ion secondary batteries of Examples 3A and 3B and Comparative Example 5, respectively. The battery is adjusted to be 1.5 times the thickness of the mixture layer.

  For the lithium ion secondary batteries of Examples 4A and 4B and Comparative Example 6, 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 3A.

  Table 10 shows the configurations of the positive electrodes according to the lithium ion secondary batteries of Examples 4A and 4B and Comparative Example 6. Table 11 shows the results of the above evaluations on the lithium ion secondary batteries of Examples 4A and 4B and Comparative Example 6.

  The lithium ion secondary batteries of Example 4A and Comparative Example 6 have the same configurations of the positive electrode mixture layer and the negative electrode mixture layer as the lithium ion secondary batteries of Example 3A and Comparative Example 5, respectively. By increasing the thickness of the agent layer by 1.5 times, the non-aqueous electrolyte hardly penetrates to the bottom of the mixture layer. As shown in Table 11, the lithium ion secondary batteries of Example 3A and Comparative Example 5 As compared with, load characteristics and charge / discharge cycle characteristics deteriorated.

  On the other hand, the lithium ion secondary battery of Example 4B containing a nitrile solvent as an organic solvent for the nonaqueous electrolyte exhibits excellent load characteristics and charge / discharge cycle characteristics even when the thickness of the mixture layer is increased. It was possible to effectively suppress deterioration in characteristics when the thickness of the positive electrode mixture layer or the negative electrode mixture layer was increased.

Claims (16)

A lithium ion secondary battery comprising a positive electrode having a positive electrode mixture layer containing active material particles, a conductive auxiliary agent and a resin binder, a negative electrode, and a nonaqueous electrolyte obtained by dissolving a lithium salt in an organic solvent. And
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%, Using the particles having a ratio of 90% by mass or more of the total of the particles having a particle size of 0.8 to 35 μm and the particles having a particle size of 0.001 to 0.4 μm,
As the conductive auxiliary agent, a carbon material is used,
The content of the carbon material in the positive electrode mixture layer is 0.5 to 7% by mass,
The porosity of the positive electrode mixture layer is 5 to 15 vol%,
The lithium ion secondary battery, wherein the organic solvent contains at least one selected from a nitrile solvent and a chain carbonate.   The lithium ion secondary battery according to claim 1, wherein the organic solvent includes a nitrile solvent and at least one carbonate selected from a cyclic carbonate and a chain carbonate.   3. The lithium ion secondary battery according to claim 2, wherein the content of the nitrile solvent in the total organic solvent of the nonaqueous electrolyte is 5 to 80 mass%.   The lithium ion secondary battery according to claim 2 or 3, comprising mononitrile as the nitrile solvent of the non-aqueous electrolyte.   5. The lithium ion solution according to claim 4, wherein the nitrile solvent of the non-aqueous electrolyte includes at least one mononitrile selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile. Next 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.
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. A lithium ion secondary battery according to any one of the above.   The lithium ion secondary battery according to claim 6, wherein a ratio A / B between an average particle diameter A of the first group particles and an average particle diameter B of the second group particles is 40 or more.   The lithium ion secondary battery according to claim 6 or 7, wherein the content of the second group particles in all active material particles is 9 to 20% by mass.   The lithium ion secondary battery according to any one of claims 6 to 8, wherein an average particle diameter A of the first group particles is 5 to 20 µm.   The lithium ion secondary battery according to any one of claims 6 to 9, wherein an average particle diameter B of the second group particles is 0.005 to 0.2 µm.   The lithium ion secondary battery according to claim 1, wherein a porosity of the positive electrode mixture layer is 7 to 13 vol%.   The lithium ion secondary battery according to claim 1, wherein the positive electrode mixture layer further contains a dispersant.   The lithium ion secondary particle according to any one of claims 1 to 12, 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. Next battery.   The lithium ion secondary battery according to any one of claims 1 to 13, wherein a content of the nitrile solvent in a total organic solvent of the nonaqueous electrolyte is 5 to 80% by mass.   The lithium ion secondary battery according to any one of claims 1 to 14, wherein the nitrile solvent of the non-aqueous electrolyte includes mononitrile.   16. The lithium ion solution according to claim 15, wherein the nitrile solvent of the non-aqueous electrolyte includes at least one mononitrile selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile. Next battery.