KR102301470B1 - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

A nonaqueous electrolyte secondary battery capable of securing good charge/discharge cycle characteristics and suppressing expansion while using a material containing Si and O as constituent elements for a negative electrode active material is provided.
The positive electrode includes a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a binder on one or both sides of a current collector, and the positive electrode mixture layer is a lithium-containing composite oxide containing a specific amount of nickel as a transition metal element. It contains as a positive electrode active material, and contains a vinylidene fluoride-chlorotrifluoroethylene copolymer as a binder, and a negative electrode having a negative electrode mixture layer containing a negative electrode active material on one side or both sides of a current collector; The mixture layer contains a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is 0.5≤x≤1.5) and a graphite carbon material as a negative electrode active material, characterized in that The subject is solved by the nonaqueous electrolyte secondary battery which does.

Description

Nonaqueous electrolyte secondary battery {NONAQUEOUS ELECTROLYTE SECONDARY BATTERY}

The present invention relates to a nonaqueous electrolyte secondary battery having good charge/discharge cycle characteristics and suppressed expansion.

BACKGROUND ART Nonaqueous electrolyte secondary batteries including lithium ion secondary batteries are widely used as power sources for various portable devices because of their high voltage and high capacity. Moreover, the use in power tools, such as a power tool, and medium-sized/large sizes, such as an electric vehicle and an electric bicycle, is also showing expansion in recent years.

In particular, for batteries used in mobile phones, game machines, and the like, which are being miniaturized and multifunctional, higher capacity is required. Among them, as an active material for the negative electrode, more lithium (ions) such as silicon (Si) and tin (Sn) can be occluded and released instead of carbonaceous materials such as graphite employed in conventional lithium ion secondary batteries. The material is attracting attention. In particular, SiO _x having the ultra-fine particles are dispersed in the SiO ₂ structure of Si, has been reported to also combine the characteristics such as excellent high rate characteristics (Patent Documents 1, 2, etc.).

However, since the SiO _x has a large volume expansion and contraction accompanying the charge/discharge reaction, particles are pulverized every charge/discharge cycle of the battery, and the Si deposited on the surface reacts with the non-aqueous electrolyte solvent to increase the irreversible capacity, It is also known that gas is generated in the battery due to this reaction and problems such as the expansion of the battery can occur.

In response to such circumstances, a technique for suppressing the volume change of a negative electrode (negative electrode mixture layer) accompanying a charge/discharge reaction by using _{SiO x together} with a graphite carbon material (Patent Document 3 etc.), and the utilization rate of _{SiO x are limited} to suppress the volume expansion and contraction accompanying the charge/discharge reaction, or use a non-aqueous electrolyte to which a halogen-substituted cyclic carbonate (eg, 4-fluoro-1,3-dioxolan-2-one, etc.) is added By doing so, a technique for improving the charge/discharge cycle characteristics of a battery or suppressing the expansion of a battery can accompanying gas generation has been proposed (Patent Document 4).

Japanese Patent Laid-Open No. 2004-047404 Japanese Patent Laid-Open No. 2005-259697 Japanese Patent Laid-Open No. 2011-233369 Japanese Patent Laid-Open No. 2008-210618

According to the Patent Document 3 or Patent Document 4, technology, it can be satisfactorily achieved the suppression of increase or expansion of the charge-discharge cycle characteristics of the non-aqueous electrolyte secondary battery using an SiO _x to the negative electrode. However, on the other hand, it is also predicted that the charge/discharge cycle characteristics and the level of expansion suppression required for a nonaqueous electrolyte secondary battery will gradually increase in the future, and there is still room for improvement in the techniques of Patent Document 3 and Patent Document 4.

The present invention has been made in view of the above circumstances, and the object thereof is that, while using a material containing Si and O as constituent elements for a negative electrode active material, good charge/discharge cycle characteristics can be ensured, and expansion can be suppressed. An object of the present invention is to provide a non-aqueous electrolyte secondary battery.

The non-aqueous electrolyte secondary battery of the present invention capable of achieving the above object has a positive electrode, a negative electrode, a non-aqueous electrolyte and a separator, wherein the positive electrode includes a positive electrode mixture layer containing a positive electrode active material and a binder, one or both sides of a current collector The positive mix layer contains, as a positive electrode active material, a lithium-containing composite oxide containing nickel as a transition metal element, and contains a vinylidene fluoride-chlorotrifluoroethylene copolymer as a binder, and the transition In the lithium-containing composite oxide containing nickel as a metal element, when the amount of the total transition metal element is 100 (mol%), the proportion a (mol%) of nickel is 30≤a≤100, and the negative electrode is A negative electrode mixture layer containing a negative electrode active material is provided on one side or both surfaces of a current collector, and the negative mixture layer is a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is 0.5 ≤x≤1.5. Hereinafter, the material _{is described as “SiO x} ”) and a graphite carbon material as a negative electrode active material.

ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery which can ensure favorable charge/discharge cycling characteristics and can suppress expansion|swelling can be provided, using the material which contains Si and O as constituent elements for a negative electrode active material.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of the nonaqueous electrolyte secondary battery of this invention, (a) is a top view, (b) is a partial longitudinal sectional view.
FIG. 2 is a perspective view of FIG. 1 ;

The non-aqueous electrolyte secondary battery, for example, but a case of using a SiO _x on the negative electrode active material in terms of high capacity, this in the same cell, because the swelling amount of shrinkage of the SiO _x caused by the charging and discharging size, liable to be a negative electrode is degraded, The charging/discharging cycle characteristic tends to be low.

The non-aqueous electrolyte secondary battery of the present invention, first, the capacity than the SiO _x is but behind, the expansion amount of shrinkage is small graphite carbon material than SiO _x caused by the charge and discharge, as a negative electrode active material in the whole, the negative electrode active material used in combination with SiO _{x It is possible to suppress the decrease in capacity due to reducing the proportion of SiO x} occupied as much as possible while reducing the amount of volume change of the negative electrode mixture layer accompanying charging and discharging, thereby suppressing the deterioration of the negative electrode due to high capacity and repeated charging and discharging. .

By the way, the fall of the charge/discharge cycle characteristic of a nonaqueous electrolyte secondary battery may arise by other than deterioration of a negative electrode. For example, when the volume change of the negative electrode mixture layer is large due to charging and discharging of the battery, the interval between the negative electrode and the positive electrode (the positive electrode mixture layer) opposing it is equal to that of the positive and negative electrodes. Although there is a risk of non-uniformity when viewed over the entire opposing surface, especially in locations where the gap between the negative electrode and the positive electrode is larger than the other portions, the reaction may not occur during charging and discharging, so this affects the charge/discharge cycle characteristics of the battery. damage, and also becomes a cause of the expansion of the battery.

Therefore, the present inventors have _{found that the negative electrode mixture layer containing SiO x} and the graphite carbon material as a negative electrode active material and the expansion and contraction accompanying the charging and discharging of the battery have a good balance, and the interval between the positive electrode and the negative electrode is set on the entire opposing surface thereof. In order to discover the configuration of the positive mix layer that can maintain a high uniformity over the period, studies were repeated. And if it is a positive electrode material layer containing a lithium-containing composite oxide containing a specific amount of nickel as a transition metal element as a positive electrode active material, and containing a vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE) as a binder, a battery It was discovered that the space|interval of a positive electrode and a negative electrode could be maintained in the state with high uniformity over the whole opposing surface even if it repeats charging and discharging, and it came to complete this invention.

The negative electrode according to the nonaqueous electrolyte secondary battery of the present invention has a structure in which a negative electrode mixture layer containing a negative electrode active material is provided on one or both surfaces of a current collector.

In the negative electrode active material, the combined use of SiO _x with the graphite carbon material. Thereby, a high capacity|capacitance of a nonaqueous electrolyte secondary battery can be aimed at, and the outstanding charge/discharge cycling characteristic can also be ensured by combination with a specific positive electrode.

SiO _x may contain the microcrystal or amorphous phase of Si, and in this case, the atomic ratio of Si and O becomes the ratio which included the microcrystal or the amorphous phase of Si of Si. That is, SiO _x includes a structure in which Si (eg, microcrystalline Si) is dispersed in an amorphous SiO _{2 matrix, and the amorphous SiO 2} and Si dispersed therein are combined, and the atomic ratio It is sufficient that x satisfies 0.5≤x≤1.5. For example, in the case of a material in which Si is dispersed in an _{amorphous SiO 2 matrix and a molar ratio of SiO 2} to Si is 1:1, x=1, so it is expressed as SiO as a structural formula. In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed in some cases, but when observed with a transmission electron microscope, the presence of fine Si can be confirmed. have.

And, SiO _x is preferably in the carbon composite material and the composite material and, for example, it is preferable that the surface of the SiO _x coated with carbon material. Since SiO _x has little conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive auxiliary) is used to ensure good mixing and dispersion _{of SiO x and the conductive material in the negative electrode.} , it is necessary to form an excellent conductive network. If the SiO _x to a complex composite with the carbon material, for example, than the case where only a material obtained by mixing a conductive material such as SiO _x and the carbon material, the conductive network is formed preferably at the negative electrode.

As the composite of the SiO _x and the carbon material, as described above, in addition to the SiO _x coating the surface of the carbon material, there may be mentioned assembly (造粒體) such as SiO _x and the carbon material.

In _{addition, by using the composite in which the surface of SiO x} is coated with a carbon material as described above, furthermore, by using a composite with a conductive material (carbon material, etc.), a better conductive network can be formed in the negative electrode, so that the battery has a higher capacity and It becomes possible to realize a nonaqueous electrolyte secondary battery having further excellent characteristics (eg, charge/discharge cycle characteristics). Examples of the composite of SiO _x coated with a carbon material and a carbon material include granules _{obtained by further granulating a mixture of SiO x} coated with a carbon material and a carbon material.

Further, as SiO _x whose surface is coated with a carbon material, one in which the surface of a composite (eg, granulated body) of SiO _{x and a carbon material having a smaller specific resistance value is further coated with a carbon material can be preferably used.} It is possible to form the SiO _x and if the carbon material is dispersed, more favorable conductive network in the interior of the assembly, such as in, the heavy-load discharge characteristics in the non-aqueous electrolyte secondary battery having a negative electrode containing SiO _x as the negative electrode active material Battery characteristics can be further improved.

Examples of the carbon material that can be used in the formation of SiO _x with the complex may be, for example, the low-crystalline carbon, a carbon nanotube, a vapor-phase (氣相) grown carbon material such as carbon fiber as preferred.

Specific examples of the carbon material include a fibrous or coiled carbon material, carbon black (including acetylene black and Ketjen black), artificial graphite, graphitized carbon, and non-graphitized carbon. At least one material selected from A fibrous or coil-shaped carbon material is preferable in terms of easy formation of an electrically conductive network and a large surface area. Carbon black (including acetylene black and Ketjen black), graphitizable carbon and non-graphitizable carbon have high electrical conductivity and high liquid retention _{, and even if SiO x} particles expand and contract, the particles It is preferable in that it has the property of being easy to maintain contact with.

Negative electrode active material, the combination is also the graphite carbon material with SiO _x as the negative electrode active material, however, it is also possible to use a graphite carbon material, a carbon material related to the complex of the SiO _x and the carbon material. Since the graphite carbon materials are, in the same manner as the carbon black, and has a high electrical conductivity, high beam-component, addition, SiO _x particles have the properties of readily maintaining contact and even expansion and shrinkage, the particles, SiO _x It can be preferably used for forming a complex with.

Among the carbon materials exemplified above, fibrous carbon materials are particularly preferable as those used when the composite with _{SiO x is granules.} Carbon material of fiber shape, it is possible to follow the SiO _x caused by the charge and discharge of the cell expansion and shrinkage due to the high shape thereof is fine thread-like and flexible, and, since the bulk density of the size, SiO _x particles and the number of the junction because you can have Examples of the fibrous carbon include polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, and carbon nanotubes, and any of these may be used.

In addition, the fibrous carbon material is, for example, may be formed on the surface of the SiO _x particulate in the gas phase method.

While the specific resistance value of _{SiO x} ^{is usually 10 3} to 10 ⁷ kΩ cm, the specific resistance value of the carbon material exemplified above is usually 10 ^{-5 to} 10 kΩ cm.

In addition, complexes of the SiO _x and the carbon material, the material layer covering the carbon material coating layer of the particle surface or may further have a (I material layer containing a non-graphitizable carbon).

_{When using a composite of SiO x} and a carbon material for the negative electrode, _{the ratio of SiO x and the carbon material is SiO x} : 100 parts by mass of the carbon material from the viewpoint of favorably exhibiting the action by the composite with the carbon material. It is preferable that it is 5 mass parts or more, and it is more preferable that it is 10 mass parts or more. Further, in the composite, if the ratio of the carbon material to be complexed with _{SiO x is too large, it leads to a decrease in the amount of SiO x} in the negative electrode mixture layer, and there is a possibility that the effect of increasing the capacity may become small, so SiO _x : 100 parts by mass , it is preferable that it is 50 mass parts or less, and, as for a carbon material, it is more preferable that it is 40 mass parts or less.

The composite of the SiO _x and the carbon material can be obtained, for example, by the following method.

First, a description will be given of a manufacturing method in the case that the composite SiO _x. A dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, sprayed and dried to prepare composite particles containing a plurality of particles. As a dispersion medium, ethanol etc. can be used, for example. It is suitable to perform spraying of a dispersion liquid in 50-300 degreeC atmosphere normally. In addition to the above methods, the same composite particles can be produced also in the granulation method by a mechanical method using a vibration type or planetary type ball mill, rod mill, or the like.

In addition, SiO _x, and a case of manufacturing an assembly of SiO _x smaller than the specific resistance value of the carbon material, the addition of the carbon material in the dispersed dispersion in SiO _x is the dispersion medium, and using this dispersion liquid, which composite the SiO _x What is necessary is just to set it as a composite particle (granulated body) by the same method as the case. In addition, by the same assembling method according to the mechanical method as described above, it can be produced SiO _x and assembly of the carbon material.

Next, when the surface of the SiO _x particles (SiO _x composite particles or granules of SiO _x and carbon material) is coated with a carbon material to form a composite, for example, the SiO _x particles and a hydrocarbon-based gas are heated in the gas phase. By heating, carbon generated by thermal decomposition of hydrocarbon-based gas is deposited on the surface of the particles. As described above, according to the vapor phase growth (CVD) method, the hydrocarbon-based gas spreads to every corner of the composite particle, and a thin and uniform carbon material containing a conductive carbon material is contained on the surface of the particle or in the voids on the surface. Since a film (carbon material coating layer) can be formed, conductivity can be imparted to the _{SiO x particles with good uniformity with a small amount of the carbon material.}

_{In the production of SiO x} coated with a carbon material, the processing temperature (ambient temperature) of the vapor phase growth (CVD) method varies depending on the type of hydrocarbon-based gas, but is usually 600 to 1200 ° C. Among these, it is preferable that it is 700 degreeC or more, and it is more preferable that it is 800 degreeC or more. This is because the higher the treatment temperature, the less impurities remain and a coating layer containing highly conductive carbon can be formed.

As the liquid source of the hydrocarbon-based gas, toluene, benzene, xylene, mesitylene, etc. can be used, but toluene, which is easy to handle, is particularly preferable. By vaporizing them (for example, bubbling with nitrogen gas), a hydrocarbon-based gas can be obtained. Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, in the vapor phase growth (CVD) method, _{after the surface of the SiO x} particles (SiO _x composite particles, or _{an assembly of SiO x} and carbon material) is covered with a carbon material, petroleum-based pitch, coal-based pitch, thermosetting resin, and naphthalene sulfonic acid After making at least 1 sort(s) of organic compound selected from the group which consists of a condensate of salt and aldehydes adhere to the coating layer containing a carbon material, you may bake the particle|grains to which the said organic compound adhered.

Specifically, preparing a _{dispersion in which SiO x} particles (SiO _x composite particles, or _{an assembly of SiO x} and carbon material) coated with a carbon material and the organic compound are dispersed in a dispersion medium, spraying and drying the dispersion, The particles coated with the organic compound are formed, and the particles coated with the organic compound are fired.

An isotropic pitch can be used as said pitch, and a phenol resin, a furan resin, furfural resin, etc. can be used as a thermosetting resin. As a condensate of naphthalene sulfonate and aldehydes, a naphthalene sulfonic acid formaldehyde condensate can be used.

_{As a dispersion medium for dispersing the SiO x} particles coated with the carbon material and the organic compound, for example, water or alcohols (such as ethanol) can be used. It is suitable to perform spraying of a dispersion liquid in 50-300 degreeC atmosphere normally. Although 600-1200 degreeC is suitable normally, as for a calcination temperature, 700 degreeC or more is preferable especially, and it is more preferable that it is 800 degreeC or more. This is because the higher the treatment temperature, the less impurities remain, and a coating layer made of a high-quality carbon material with high conductivity can be formed. However, the treatment temperature is required to be below the melting point _{of SiO x .}

Examples of the graphite carbon material used as the negative electrode active material with the SiO _x, for example, graphite, such as scale-like natural graphite; artificial graphite obtained by graphitizing easily graphitized carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB), and carbon fibers at 2800° C. or higher; and the like.

The ratio _{of SiO x in} the total amount of the negative electrode active material is preferably 0.01 mass % or more, more preferably 1 mass % or more, and 3 mass % from the viewpoint of satisfactorily securing the effect of increasing the capacity by using _{SiO x .} More preferably. In addition, from the viewpoint of further avoiding the problem due to the volume change of _{SiO x} accompanying charging and discharging, _{the ratio of SiO x in} the total amount of the negative electrode active material is preferably 20 mass % or less, more preferably 15 mass % or less desirable.

The negative mix layer usually contains a binder. As the binder related to the negative electrode mixture layer, for example, PVDF, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), etc. are preferably used.

Moreover, you may make the negative mix layer contain conductive support agents, such as various carbon blacks, such as acetylene black, and carbon nanotube, as needed.

For the negative electrode, for example, a negative electrode mixture-containing composition is prepared in which a negative electrode active material and a binder, and optionally a conductive support agent are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water (however, The binder may be dissolved in a solvent), this is applied to one side or both sides of the current collector, and after drying, it is manufactured through a step of performing a press treatment such as a calendering treatment if necessary. In addition, the negative electrode is not limited to what was manufactured by the said method, The thing manufactured by another manufacturing method may be sufficient.

It is preferable that the thickness of the negative mix layer is 10-100 micrometers per single side|surface of an electrical power collector. Moreover, as a composition of a negative mix layer, for example, it is preferable that the quantity of a negative electrode active material is 80-95 mass %, It is preferable that the quantity of a binder is 1-20 mass %, When using a conductive support agent, It is preferable that the amount is 1-10 mass %.

As the current collector of the negative electrode, copper or nickel foil, punching metal, net, expanded metal, etc. can be used, but copper foil is usually used. In this negative electrode current collector, when the overall thickness of the negative electrode is made thin 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 preferably 5 µm.

The positive electrode according to the nonaqueous electrolyte secondary battery of the present invention has a structure in which a positive electrode mixture layer containing a positive electrode active material and a binder is provided on one or both surfaces of a current collector.

In the positive electrode active material, as a lithium-containing composite oxide containing nickel (Ni) as a transition metal element, when the total amount of the transition metal element is 100 (mol%), the proportion a (mol%) of nickel is 30≤a Use those with ≤100. The positive electrode active material is, for example, a non-aqueous capacity than LiCoO ₂ as a positive electrode active material of which is a general-purpose electrolyte secondary cell cursor, the non-aqueous electrolyte can be made more high capacity of secondary cells. In addition, the lithium-containing composite oxide containing Ni as the transition metal element has a better balance between the negative electrode mixture layer containing SiO _{x and graphitic carbon material than LiCoO 2} , and the expansion and contraction accompanying charging and discharging of the battery. A mixture layer can be formed.

In the lithium-containing composite oxide containing Ni as the transition metal element, when the total amount of the transition metal element is 100 (mol%), the proportion a (mol%) of nickel is 30≦a≦100, except for Ni It is not necessary to contain the transition metal element of , and may contain it. However, since it is possible to further improve the packing density in the positive mix layer or to increase the thermal stability of the lithium-containing composite oxide, the lithium-containing composite oxide containing Ni as the transition metal element is a transition metal element. It is preferable that the lithium nickel cobalt-manganese composite oxide contains cobalt (Co) and manganese (Mn) in addition to Ni as the Ni.

As the lithium nickel cobalt-manganese composite oxide, one represented by the following general compositional formula (1) is preferable.

Li _1+s M ¹ O ₂ (1)

[In the general composition formula (1), -0.3≤s≤0.3, M ¹ is a group of three or more elements including at least Ni, Co and Mn, and ^{among each element constituting M 1} , Ni, Co and 30<a<65, 5<b<35, 15<c<50 when the ratio (mol%) of Mn is a, b, and c, respectively.]

In the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), Ni is a component contributing to the capacity improvement of the lithium nickel cobalt manganese composite oxide, and the total number of ^{elements in the element group M 1 is 100 mol%} In this case, it is preferable that the ratio a of Ni exceeds 30 mol%, and it is more preferable that it is 50 mol% or more. Further, in the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), the total number of ^{elements in the element group M 1 is 100 mol% from the viewpoint of ensuring satisfactory the effect of containing an element other than Ni.} It is preferable that it is less than 65 mol%, and, as for the ratio a of Ni, it is more preferable that it is 60 mol% or less.

In the lithium nickel cobalt manganese composite oxide represented by the general composition formula (1), Co is also a component contributing to the capacity improvement of the lithium nickel cobalt manganese composite oxide, similarly to Ni, and is also used to improve the packing density in the positive electrode mixture layer. On the other hand, when there is too much, there is a possibility that cost increase or safety fall may be caused. In addition to these reasons, the total number ^{of elements in the element group M 1} in the general composition formula (1) representing the lithium nickel cobalt manganese composite oxide is 100 mol from the viewpoint of ensuring satisfactory the stabilizing action of the average valence of Mn, which will be described later. %, the proportion b of Co is preferably more than 5 mol%, more preferably 20 mol% or more, more preferably less than 35 mol%, and still more preferably 30 mol% or less.

In addition, in the lithium nickel cobalt manganese composite oxide, when ^{the total number of elements in the element group M 1} in the general composition formula (1) is 100 mol%, the ratio c of Mn exceeds 15 mol% It is preferable, and it is more preferable that it is 20 mol% or more, Moreover, it is preferable that it is less than 50 mol%, and it is still more preferable that it is 30 mol% or less. By containing Mn in the same amount as above in the lithium nickel cobalt manganese composite oxide and Mn is always present in the crystal lattice, the thermal stability of the lithium nickel cobalt manganese composite oxide can be improved, and a battery with higher safety can be constructed. becomes

In addition, in the lithium nickel cobalt manganese composite oxide, by containing Co together with Mn, Co acts to suppress the valence fluctuation of Mn accompanying Li doping and de-doping during battery charging and discharging. Therefore, by stabilizing the average valence of Mn to a value near tetravalent, the reversibility of charging and discharging can be further improved. Therefore, by using such a lithium nickel cobalt-manganese composite oxide, it becomes possible to comprise the battery which was further excellent in the charge/discharge cycle characteristic.

In the lithium nickel cobalt manganese composite oxide, the element group M ¹ may consist only of Ni, Co and Mn, but together with these elements, Mg, Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge and At least one element selected from the group consisting of Sn may be included. However, the total ratio d of Mg, Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge and Sn when the total number of elements in the element group M ^{1 is 100 mol% is 5 mol% or less} It is preferable, and it is more preferable that it is 1 mol% or less. Elements other than Ni, Co, and Mn in the element group M ¹ may be uniformly distributed in the lithium nickel cobalt manganese composite oxide, or may be segregated on the particle surface or the like.

The lithium nickel cobalt-manganese composite oxide having the above composition has a high true density of 4.55 to 4.95 g/cm 3 , and becomes a material having a high volumetric energy density. In addition, although the true density of the lithium nickel cobalt manganese composite oxide containing Mn in a certain range varies greatly depending on its composition, in the narrow composition range as described above, the structure is stabilized and uniformity can be increased, so for example g is considered to be a large value close to the true density of LiCoO _2. In addition, the capacity per mass of the lithium nickel cobalt manganese composite oxide can be increased, and a material excellent in reversibility can be obtained.

Although the true density of the lithium nickel cobalt manganese composite oxide is increased especially when the composition is close to the stoichiometric ratio, specifically, in the general composition formula (1), -0.3≤s≤0.3, By adjusting the value of s in this way, true density and reversibility can be improved. s is more preferably -0.05 or more and 0.05 or less, and in this case, the true density of the lithium nickel cobalt manganese composite oxide can be set to 4.6 g/cm 3 or more, and a higher value.

The lithium nickel cobalt-manganese composite oxide represented by the general composition formula (1) is a Li-containing compound (such as lithium hydroxide), a Ni-containing compound (such as nickel sulfate), a Co-containing compound (such as cobalt sulfate), and a Mn-containing compound (such as manganese sulfate) etc.), and a compound (oxide, hydroxide, sulfate, etc.) containing other elements included in ^{element group M 1 are mixed and calcined.} Further, in order to synthesize a lithium nickel cobalt manganese composite oxide with a higher purity, it is preferable to mix a composite compound (hydroxide, oxide, etc.) containing a plurality of elements included in ^{element group M 1 and a Li-containing compound and calcination.} do.

The firing conditions can be, for example, 800 to 1050° C. for 1 to 24 hours, but preliminary heating is performed by heating to a temperature lower than the firing temperature (for example, 250 to 850° C.) and maintaining at that temperature. After that, it is preferable to raise the temperature to the calcination temperature to advance the reaction. Although there is no restriction|limiting in particular about the time of preheating, Usually, what is necessary is just about 0.5 to 30 hours. In addition, the atmosphere at the time of firing can be an atmosphere containing oxygen (that is, in the atmosphere), a mixed atmosphere of an inert gas (argon, helium, nitrogen, etc.) and oxygen gas, an oxygen gas atmosphere, etc. The concentration (by volume) is preferably 15% or more, and preferably 18% or more.

As the positive electrode active material, only lithium-containing composite oxides containing Ni as the transition metal element [preferably lithium nickel cobalt manganese composite oxides, more preferably those represented by the general composition formula (1) above] may be used, but such The lithium-containing composite oxide may be used in combination with another lithium-containing composite oxide.

For example, it is preferable to use a lithium nickel cobalt manganese composite oxide and a lithium cobalt composite oxide containing a dissimilar metal element other than lithium, nickel, cobalt and manganese as the positive electrode active material.

In this case, in the lithium cobalt composite oxide, the lithium cobalt composite oxide (A) having an average particle diameter A (μm) of more than 10 μm and 30 μm or less, and lithium having an average particle diameter B (μm) of 1 μm or more and 10 μm or less Cobalt composite oxide (B) is used, and the difference "AB" between the average particle diameter A of the lithium cobalt composite oxide (A) and the average particle diameter B of the lithium cobalt composite oxide (B) is 5 (㎛) or more it is preferable Moreover, it is preferable to use the lithium nickel cobalt manganese composite oxide in which the relationship with the average particle diameter B of the lithium cobalt composite oxide (B) is C>B when the average particle diameter is C (μm).

When the lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) as described above and lithium nickel cobalt manganese composite oxide are used together, in the positive electrode mixture layer, lithium cobalt composite oxide (A) or lithium nickel cobalt manganese composite oxide Since the lithium cobalt composite oxide (B) with a small particle diameter can be filled in the gaps between the particles of

In addition, the lithium nickel cobalt manganese composite oxide used as the positive electrode active material _{has higher stability under high voltage than, for example, LiCoO 2} , and the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are the dissimilar metal elements By the action of, for example, stability under a high voltage is higher than that of _{LiCoO 2 .} Therefore, when lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are used for the positive electrode active material in addition to lithium nickel cobalt manganese composite oxide, it may be used in a method of performing constant current-constant voltage charging with a final voltage of 4.3 V or more. , since deterioration of the positive electrode active material is less likely to occur, the charge/discharge cycle characteristics of the nonaqueous electrolyte secondary battery can be further improved.

In addition, the lithium nickel cobalt manganese composite oxide tends to cause gas generation in the battery, particularly when the particle diameter is small. However, by using the lithium cobalt composite oxide (B), which is less likely to cause gas generation in the battery than the lithium nickel cobalt manganese composite oxide, for the positive electrode active material with a small particle diameter that enters the gap between particles of the positive electrode active material with a large particle diameter, yes For example, it is possible to suppress the occurrence of expansion during storage. Therefore, when lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are used for the positive electrode active material in addition to lithium nickel cobalt manganese composite oxide, the storage characteristics of the nonaqueous electrolyte secondary battery are also improved.

As for the average particle diameter A of lithium cobalt composite oxide (A), it is more preferable that it is 17 micrometers or more, and it is still more preferable that it is 24 micrometers or less. Moreover, it is more preferable that it is 5 micrometers or more, and, as for the average particle diameter B of lithium cobalt composite oxide (B), it is still more preferable that it is 10 micrometers or less.

The average particle diameter of the lithium nickel cobalt-manganese composite oxide is preferably 10 µm or more, more preferably 11 µm or more, more preferably 17 µm or less, and still more preferably 16 µm or less.

In addition, the average particle diameter A of the lithium cobalt composite oxide (A), the average particle diameter B of the lithium cobalt composite oxide (B), and the average particle diameter C (μm) of the lithium nickel cobalt manganese composite oxide, A≥C>B It is preferable that the relationship of A > C > B is satisfied, and it is more preferable that the relationship A > C > B is satisfied. In this case, the effect of increasing the charging amount of the positive electrode active material by improving the density of the positive electrode mixture layer, the effect of improving the charge/discharging cycle characteristics accompanying the improvement of the stability of the positive electrode active material, and increasing the particle size of the lithium nickel cobalt manganese composite oxide to some extent The effect of improving the storage characteristics can be more favorably secured.

The average particle diameters of lithium cobalt composite oxide (A), lithium cobalt composite oxide (B) and lithium nickel cobalt manganese composite oxide as used herein were measured using a microtrack particle size distribution measuring device "HRA9320" manufactured by Nigiso Corporation. _{The value (d 50} ) of the 50% diameter in the volume-based integrated fraction when the integral volume is obtained from particles having a small particle size distribution is the median diameter.

Further, in the lithium cobalt composite oxide (A) having the average particle diameter A and the lithium cobalt composite oxide (B) having the average particle diameter B, the ratio of the dissimilar metal element in the total amount of cobalt and the dissimilar metal element is , it is preferable that the lithium cobalt composite oxide (B) is larger than the lithium cobalt composite oxide (A).

The lithium cobalt composite oxide is inferior in stability under high voltage and stability to heat as the particle diameter is small. Therefore, the lithium cobalt composite oxide (B) having a smaller average particle diameter contains a large amount of the above-mentioned dissimilar metal element having an effect of enhancing its stability, thereby enhancing the stability of the battery against charge and discharge and heat, and the non-aqueous electrolyte secondary battery. It becomes possible to ensure further favorable charge/discharge cycle characteristics and storage characteristics.

However, since the dissimilar metal element is a component that cannot contribute to the capacity of the lithium cobalt complex oxide, the capacity of the lithium cobalt complex oxide decreases as the amount in the lithium cobalt complex oxide increases. Therefore, in the lithium cobalt composite oxide (A) having a larger average particle diameter and higher stability, by reducing the content of the dissimilar metal element, the capacity decrease due to the inclusion of the dissimilar metal element is suppressed as much as possible, resulting in stability It becomes possible to further raise the balance of a capacity|capacitance and capacity|capacitance.

The lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are preferably represented by the following general compositional formula (2).

Li _1+y Co _z M ² _1-z O ₂ (2)

[In the general composition formula (2), -0.3≤y≤0.3, 0.95≤z<1.0, and M ² is at least one element selected from the group consisting of Mg, Zr, Al and Ti.]

In the general composition formula (2), M ² corresponds to the dissimilar metal element. ^{As described above, the dissimilar metal element M 2} contained in the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) may be any of Mg, Zr, Al, and Ti, and one or two or more of them. However, the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are more preferably Mg and/or Zr because the action of improving the stability and thermal stability under high voltage is better.

Further, in the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B), Co is a component contributing to the capacity improvement, while the dissimilar metal element M ² cannot contribute to the capacity improvement. Therefore, in the general composition formula (2) showing the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B), from the viewpoint of maintaining their capacity high, it is preferable that the amount z of Co be 0.95 or more. do. Further, in the above general formula (2), the amount z of Co is 1.0 less, but from the viewpoint of more satisfactorily secure the above effect due to containing the different metal element M ^2, the amount of the different metal element M ² "1-z" is more preferably 0.005 or more, and therefore, the amount z of Co is still more preferably 0.995 or less.

When the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are those represented by the general composition formula (2), the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) are dissimilar metal elements As M ² , the same element or different elements may be contained, and ^{the amount of the dissimilar metal element M 2} contained in the lithium cobalt composite oxide (A) is “1-z1”, and the lithium cobalt composite oxide ( ^{When the amount of the dissimilar metal element M 2} contained in B) is set to "1-z2", the relationship of (1-z1)<(1-z2) may be satisfied. More specifically, "1-z1" is more preferably 0.01 or more, and still more preferably 0.02 or less. And, as for "1-z2", it is more preferable that it is 0.02 or more, and it is still more preferable that it is 0.03 or less.

Lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B), especially when the composition is close to the stoichiometric ratio, increases the true density and becomes a material having a higher energy volume density. Specifically, in the composition formula, , -0.3≤y≤0.3, and by adjusting the value of y in this way, true density and reversibility at the time of charging and discharging can be improved.

Lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are Li-containing compounds (such as lithium hydroxide), Co-containing compounds (such as cobalt sulfate), and ^{compounds containing a dissimilar metal element M 1} (oxides, hydroxides, sulfate, etc.) and calcining this raw material mixture, for example. In addition, in order to synthesize lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) with higher purity, a composite compound (hydroxide, oxide, etc.) containing ^{Co and a dissimilar metal element M 1 and a Li-containing compound, etc.} It is preferable to mix and calcinate this raw material mixture.

The firing conditions of the raw material mixture for synthesizing the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) can be, for example, from 800 to 1050° C. for 1 to 24 hours, but at a temperature lower than the firing temperature once It is preferable to heat up to (for example, 250-850 degreeC), perform preliminary heating by maintaining at that temperature, and to advance reaction by heating up to calcination temperature after that. Although there is no restriction|limiting in particular about the time of preheating, Usually, what is necessary is just about 0.5 to 30 hours. In addition, the atmosphere at the time of firing can be an atmosphere containing oxygen (that is, in the atmosphere), a mixed atmosphere of an inert gas (argon, helium, nitrogen, etc.) and oxygen gas, an oxygen gas atmosphere, etc. The concentration (by volume) is preferably 15% or more, and preferably 18% or more.

In the nonaqueous electrolyte secondary battery, when lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) are used as the positive electrode active material, the sum of lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) is 100 When it is set as mass %, the content rate of lithium cobalt composite oxide (A) is preferably 50 mass % or more, more preferably 70 mass % or more, and preferably less than 100 mass %, more preferably 90 mass % or less desirable.

Further, in the nonaqueous electrolyte secondary battery, when lithium nickel cobalt manganese composite oxide, lithium cobalt composite oxide (A), and lithium cobalt composite oxide (B) are used, lithium nickel cobalt manganese composite oxide and lithium cobalt composite oxide (A) ) and the lithium cobalt composite oxide (B) are 100 mass %, the content of the lithium nickel cobalt manganese composite oxide is preferably 15 mass % or more, more preferably 20 mass % or more, and 45 mass % % or less, and more preferably 30 mass% or less.

In the positive electrode active material, an active material other than the lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) is added as the transition metal element to a lithium-containing composite oxide [preferably lithium nickel cobalt manganese composite oxide, More preferably, it can also be used together with the thing represented by the said general composition formula (1)]. In this case, for example, an active material different from the lithium-containing composite oxide [preferably lithium nickel cobalt manganese composite oxide, more preferably represented by the general composition formula (1) above] containing Ni as the transition metal element Alternatively, active materials different from lithium nickel cobalt manganese composite oxide, lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) may be used.

Examples of such other active materials include LiCoO _{2 ;} lithium manganese oxides such as LiMnO ₂ and Li ₂ MnO _{3 ;} LiMn ₂ O ₄ , Li _{4 / 3} Ti _{5 / 3} O ₄ Lithium-containing composite oxide, such as a spinel structure; Lithium-containing composite oxides having an olivine structure, such as LiFePO _{4 ;} oxides in which the above oxides are substituted with various elements as a basic composition; etc. can be illustrated, and 1 type, or 2 or more types of these can be used.

However, from a viewpoint of ensuring the effect of this invention favorably, it is preferable that it is 10 mass % or less, and, as for the content rate of the said other active material in positive electrode active material whole quantity, it is more preferable that it is 5 mass % or less.

VDF-CTFE is used for the binder related to the positive mix layer. The positive electrode mixture layer containing the lithium-containing composite oxide containing Ni as the transition metal element as the positive _{electrode active material is a negative electrode mixture layer containing SiO x} and a graphite carbon material as the negative electrode active material, and the expansion accompanying charging and discharging of the battery The balance of shrinkage is favorable compared with the case of the positive mix layer containing _{LiCoO 2 as a positive electrode active material, for example.} However, in addition to the use of such a positive electrode active material, when VDF-CTFE is used for the binder of the positive mixture layer, for example, polyvinylidene fluoride (PVDF), which is commonly used as a binder for the positive mixture layer of a nonaqueous electrolyte secondary battery, is used. Compared with the case, the distance between the positive electrode and the negative electrode can be maintained in a state with higher uniformity over the entire opposing surfaces thereof. This is presumed to be because VDF-CTFE has a higher effect of mitigating this volume change when the positive mix layer absorbs the expansion and contraction of the negative mix layer that occurs accompanying charging and discharging of the battery, compared to PVDF, for example. .

In addition, when the density of the positive electrode mixture layer is increased by using the lithium cobalt composite oxide (A) and lithium cobalt composite oxide (B) as described above and lithium nickel cobalt manganese composite oxide together, the hardness of the positive electrode mixture layer is For example, if the positive electrode and the negative electrode are overlapped with a separator and then wound in a spiral shape to produce a wound electrode body (especially a wound electrode body having a flat cross-section), cracks are likely to occur in the positive electrode mixture layer. However, since VDF-CTFE used as a binder of the positive electrode mixture layer in the present invention is superior to PVDF, for example, in relieving the applied stress, the positive electrode active material is configured as described above, and the density of the positive mixture layer is It is possible to suppress the occurrence of cracks in the positive electrode material layer in the wound electrode body (especially, the wound electrode body having a flat cross section) even when the value is increased.

In addition, when PVDF is used as a binder, defluorination occurs after the battery is formed, which reacts with moisture unavoidably mixed in the battery to generate hydrogen fluoride, which causes corrosion of the positive electrode active material by hydrogen fluoride, such as Co or Mn. Elution of metal ions may occur. In the structure of this invention, generation|occurrence|production of such hydrogen fluoride can also be suppressed, and the effect that battery characteristics, such as charge/discharge cycle characteristic, improves by this can also be anticipated.

The composition of VDF-CTFE used for the positive mix layer is a unit and chlorotriethylene derived from vinylidene fluoride from the viewpoint of further securing the effect of improving the charge/discharge cycle characteristics of the nonaqueous electrolyte secondary battery by the use of VDF-CTFE. When the total of units derived from fluoroethylene is 100 mol%, it is preferable that the ratio of units derived from chlorotrifluoroethylene is 0.5 mol% or more, and it is more preferable that it is 1 mol% or more. However, when the ratio of the units derived from chlorotrifluoroethylene in VDF-CTFE becomes too high, the non-aqueous electrolyte (non-aqueous electrolyte) is absorbed and it becomes easy to swell, and there exists a possibility that the characteristic of a positive electrode may fall. Therefore, in the VDF-CTFE used for the positive mix layer, when the total of units derived from vinylidene fluoride and units derived from chlorotrifluoroethylene is 100 mol%, the ratio of units derived from chlorotrifluoroethylene is , it is preferably 15 mol% or less.

As the binder related to the positive mixture layer, only VDF-CTFE may be used, and a binder different from VDF-CTFE (for example, like a fluororesin other than VDF-CTFE such as PVDF, it is universal in the positive mixture layer of a nonaqueous electrolyte secondary battery) binder) may be used in combination. However, from the viewpoint of further ensuring the above-mentioned effects by the use of VDF-CTFE, the amount of the binder other than VDF-CTFE in the total amount of the binder in the positive mix layer is preferably 50% by mass or less.

A conductive support agent is normally contained in a positive mix layer. Examples of the conductive aid related to the positive mix layer include graphites such as natural graphite (scaly graphite and the like) and artificial graphite; carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; carbon fiber; It is preferable to use carbon materials, such as conductive fibers, such as a metal fiber; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; etc. can also be used.

It is preferable that the thickness of the positive mix layer is 10-100 micrometers per single side|surface of an electrical power collector, for example. Moreover, as a composition of a positive mix layer, for example, it is preferable that the quantity of a positive electrode active material is 60-95 mass %, It is preferable that the quantity of a binder is 1-15 mass %, It is preferable that the quantity of a conductive support agent is 3-20 It is preferable that it is mass %.

The current collector of the positive electrode is the same as that used for the positive electrode of a conventionally known nonaqueous electrolyte secondary battery, for example, a punching metal made of aluminum (including an aluminum alloy. , expanded metal, etc. can be used, but an aluminum foil having a thickness of 10 to 30 µm is preferable.

The nonaqueous electrolyte secondary battery of the present invention has a positive electrode, a negative electrode, a nonaqueous electrolyte and a separator, the negative electrode is the above negative electrode, and the positive electrode is the above positive electrode. Various configurations and structures employed in known nonaqueous electrolyte secondary batteries can be applied.

For the separator related to the nonaqueous electrolyte secondary battery of the present invention, a separator used in a normal nonaqueous electrolyte secondary battery, for example, a polyolefin microporous membrane such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or PP, or may be a laminate of a microporous film made of PE and a microporous film made of PP.

Moreover, you may use the laminated-type separator which formed the heat resistant porous layer containing a heat resistant inorganic filler on the surface of the said microporous film. When such a laminated separator is used, the shrinkage of the separator is suppressed even when the temperature inside the battery rises, and short circuit due to contact between the positive electrode and the negative electrode can be suppressed, so that a non-aqueous electrolyte secondary battery with higher safety can be obtained. .

As the inorganic filler to be contained in the heat-resistant porous layer, boehmite, alumina, silica and the like are preferable, and one or two or more of them can be used.

Moreover, it is preferable to make the heat resistant porous layer contain the binder for binding said inorganic fillers, or adhere|attaching a heat resistant porous layer and a microporous film. Examples of the binder include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymer, fluorine-based rubber, styrene-butadiene rubber ( SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy It is preferable to use resin etc., and 1 type, or 2 or more types of these can be used.

It is preferable that the thickness of a separator (the separator which consists of a microporous film made from polyolefin, and the said laminated|stacked separator) is 10-30 micrometers, for example. Moreover, in the case of the said laminated-type separator, it is preferable that the thickness of a heat resistant porous layer is 3-8 micrometers, for example.

For the non-aqueous electrolyte according to the non-aqueous electrolyte secondary battery of the present invention, for example, a solution (non-aqueous electrolyte) in which a lithium salt is dissolved in an organic solvent can be used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li + ions and does not easily cause side reactions such as decomposition in the voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , 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], etc. may be used. have.

The organic solvent used for the nonaqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause side reactions such as decomposition in the voltage range used as the battery. For example, Cyclic carbonates, such as ethylene carbonate, a propylene carbonate, and a butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile, and methoxypropionitrile; sulfurous acid esters such as ethylene glycol sulfite; etc. are mentioned, These can also be used in mixture of 2 or more types. In addition, in order to obtain a battery with better characteristics, it is preferable to use it in a combination that can obtain high electrical conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, for the purpose of improving the safety of these non-aqueous electrolytes, such as improvement of charge/discharge cycle characteristics, high-temperature storability and overcharge prevention, acid anhydride, sulfonic acid ester, dinitrile, vinylene carbonate, 1,3-propane sultone, di Additives (including derivatives thereof) such as phenyldisulfide, cyclohexylbenzene, biphenyl, fluorobenzene and t-butylbenzene may be appropriately added.

It is preferable to set it as 0.5-1.5 mol/l, and, as for the density|concentration in the non-aqueous electrolyte solution of this lithium salt, it is more preferable to set it as 0.9-1.25 mol/l.

Moreover, you may use for the nonaqueous electrolyte secondary battery of this invention what was made into a gel form (gel-form electrolyte) by adding a gelatinizer, such as a well-known polymer, to the said nonaqueous electrolyte solution.

As a form of the nonaqueous electrolyte secondary battery of this invention, the cylindrical shape (a square cylinder, cylindrical shape, etc.) etc. which used a steel can, an aluminum can, etc. as an outer can are mentioned. Moreover, it can also be set as the soft package battery which used the laminate film which vapor-deposited the metal as an exterior body.

Since the nonaqueous electrolyte secondary battery of the present invention has high capacity and excellent charge/discharge cycle characteristics, it can be preferably used for applications requiring such characteristics, and various uses to which conventionally known nonaqueous electrolyte secondary batteries are applied. can also be used for

[Example]

Hereinafter, the present invention will be described in detail based on Examples. However, the following examples are not intended to limit the present invention.

Example 1

<Synthesis of lithium composite oxide>

A mixed aqueous solution containing nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate at a concentration of 3.78 mol/dm 3 , 0.25 mol/dm 3 , 0.08 mol/dm 3 , and 0.08 mol/dm 3 was prepared. Next, aqueous ammonia whose pH has been adjusted to about 12 by addition of sodium hydroxide is placed in a reaction vessel, and while this is vigorously stirred, the mixed aqueous solution and ammonia water having a concentration of 25% by mass are each added to 23 cm 3 It was dripped using the metering pump at the rate of /min, 6.6 cm<3>/min, and the coprecipitation compound (spherical coprecipitation compound) of Ni and Co and Mn and Mg was synthesize|combined. In addition, at this time, the temperature of the reaction solution is maintained at 50° C., and an aqueous sodium hydroxide solution having a concentration of 3 mol/dm 3 is added dropwise at the same time so that the pH of the reaction solution is maintained around 12, and nitrogen gas is added 1d Bubbling at a flow rate of m 3 /min.

The coprecipitation compound was washed with water, filtered and dried to obtain a hydroxide. This hydroxide, LiOH·H ₂ O, BaSO ₄ and Al(OH) ₃ are dispersed in ethanol so as to be 1:1:0.01:0.01 in a molar ratio to form a slurry, and then mixed in a planetary ball mill for 40 minutes. , to obtain a mixture obtained by drying at room temperature. Next, the mixture is placed in an alumina crucible, heated to 600° C. in a dry air flow of 2 dm 3 /min, held at that temperature for 2 hours to perform preliminary heating, and further heated to 900° C. and calcined for 12 hours, A lithium-containing composite oxide was synthesized.

The obtained lithium-containing composite oxide was washed with water, then heat-treated in the air (oxygen concentration was about 20 vol%) at 700°C for 12 hours, and then pulverized with a mortar to obtain powder. The lithium-containing composite oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium-containing composite oxide was performed as follows by using an Inductive Coupled Plasma (ICP) method. First, 0.2 g of the lithium-containing composite oxide was collected and placed in a 100 mL container. Then, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were sequentially added and dissolved by heating, and after cooling, the composition was further diluted 25 times and analyzed by ICP ("ICP-757" manufactured by JARRELASH) (calibration curve method (檢量 wire method)). As a result of deriving the composition of the lithium-containing composite oxide from the obtained results, it was found that the composition was represented by _{Li 1.0} Ni _0.89 Co _0.05 Mn _0.02 Mg _0.02 Ba _0.01 Al _0.01 O _{2 .} Moreover, the average particle diameter of the said lithium nickel cobalt-manganese composite oxide was 15 micrometers.

<Synthesis of lithium cobalt composite oxide (A)>

Co(OH) ₂ and Mg(OH) ₂ , Al(OH) ₃ and Li ₂ CO ₃ are mixed in a molar ratio of 1.97:0.02:0.01:1.02, and the mixture is mixed in the air (oxygen concentration is about 20 vol%). , to synthesize lithium cobalt composite oxide (A) by heat treatment at 950° C. for 12 hours, and then pulverized in a mortar to obtain powder. The lithium cobalt composite oxide (A) after pulverization was stored in a desiccator.

As a result of analyzing the composition of the lithium cobalt composite oxide (A) using the ICP method, Li _{1 . 0} Co _{0 . 985} Mg _{0 . 01} Al _{0 .} That the composition represented by ₀₀₅ O ₂ it was found. Moreover, the average particle diameter of the said lithium cobalt composite oxide (A) was 20 micrometers.

<Synthesis of lithium cobalt composite oxide (B)>

Co(OH) ₂ and Mg(OH) ₂ and Al(OH) ₃ and ZrO ₂ and Li ₂ CO ₃ were mixed in a molar ratio of 1.946:0.03:0.02:0.004:1.02, and the mixture was mixed in the atmosphere (oxygen concentration about 20 vol%) and heat treatment at 950° C. for 12 hours to synthesize lithium cobalt composite oxide (B), and then pulverized in a mortar to obtain powder. The lithium cobalt composite oxide (B) after pulverization was stored in a desiccator.

As a result of analyzing the composition of the lithium cobalt composite oxide (B) using the ICP method, Li _{1 . 0} Co _{0 . 973} Mg _{0 . 015} Al _{0 . 01} Zr _{0 .} That the composition represented by ₀₀₂ O ₂ it was found. Moreover, the average particle diameter of the said lithium cobalt composite oxide (B) was 8 micrometers.

<Production of positive electrode>

A mixture of the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) in a mass ratio of 80:20: 74 parts by mass, the lithium nickel cobalt-manganese composite oxide: 18 parts by mass, and the binder VDF- NMP solution containing CTFE at a concentration of 3% by mass: 20 parts by mass, and artificial graphite as a conductive aid: 1.5 parts by mass and Ketjen Black: 1.5 parts by mass, kneaded using a twin-screw kneader, and NMP was further added to increase the viscosity adjusted to prepare a positive electrode mixture-containing paste.

The positive mixture-containing paste was applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, followed by vacuum drying at 120° C. for 12 hours to form positive mixture layers on both surfaces of the aluminum foil. Then, the press process was performed, the thickness and density of the positive mix layer were adjusted, the nickel lead body was welded to the exposed part of aluminum foil, and the 54-mm strip|belt-shaped positive electrode was produced. The total thickness of the positive mix layer in the obtained positive electrode was 145 micrometers, and the density of the positive mix layer was 3.85 g/cm<3>.

<Production of negative electrode>

A negative electrode active material having an average particle diameter d is ₅₀ and the SiO 8㎛ the surface a composite coating of the carbon material (a 10% by mass amount of the carbon material in the composite material), an average particle diameter of D50% is 16㎛ graphite, SiO Water is added to a mixture in an amount such that the amount of the composite coated with a carbon material is 3.75 mass %: 97.5 parts by mass, SBR as a binder: 1.5 parts by mass, and carboxymethylcellulose as a thickener: 1 part by mass The mixture was mixed to prepare a negative electrode mixture-containing paste.

The negative mixture-containing paste was applied to both surfaces of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum dried at 120° C. for 12 hours to form negative electrode mixture layers on both surfaces of the copper foil. Thereafter, a press treatment was performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel lead body was welded to the exposed portion of the copper foil to prepare a band-shaped negative electrode having a width of 55 mm. The total thickness of the negative electrode mixture layer in the obtained negative electrode was 136 µm.

<Assembly of the battery>

Next, the negative electrode and the positive electrode are overlapped through a separator made of microporous polyethylene film (thickness 18 μm, porosity 50%) and wound in a roll shape, and then a terminal is welded to the positive electrode, It was inserted into the aluminum alloy outer can of thickness 49mm, width 42mm, and height 61mm (494261 type), and the cover was welded and attached. Thereafter, a non-aqueous electrolyte solution prepared by further dissolving _{LiPF 6} to 1 mol% in a solution in which 3% by mass of vinylene carbonate was dissolved at EC:DEC=3:7 (volume ratio) at the injection port of the cover. was poured into the container and sealed to obtain a prismatic nonaqueous secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG. 2 .

Here, the battery shown in Figs. 1 and 2 is described. Fig. 1 (a) is a plan view, (b) is a partial cross-sectional view thereof, and as shown in Fig. 1 (b), the positive electrode 1 and the negative electrode ( 2) is wound in a vortex shape with a separator 3 interposed therebetween, pressurized to form a flat shape to obtain a flat wound electrode body 6, and a non-aqueous electrolyte solution and are accepted together. However, in FIG. 1, in order to avoid complication, the metal foil, nonaqueous electrolyte, etc. used as an electrical power collector used in preparation of the positive electrode 1 and the negative electrode 2 are not shown.

The battery case 4 is made of an aluminum alloy and constitutes an exterior body of the battery, and the battery case 4 also serves as a positive electrode terminal. Then, an insulator 5 made of a PE sheet is disposed at the bottom of the battery case 4, and from the flat wound electrode body 6 comprising the positive electrode 1, the negative electrode 2 and the separator 3, A positive electrode lead body 7 and a negative electrode lead body 8 connected to one end of each of the positive electrode 1 and the negative electrode 2 are drawn out. Further, to the aluminum alloy sealing cover plate 9 that seals the opening of the battery case 4, a stainless steel terminal 11 is attached via an insulating packing 10 made of polypropylene, and this terminal ( To 11), a lead plate 13 made of stainless steel is attached with an insulator 12 interposed therebetween.

And this cover plate 9 is inserted into the opening part of the battery case 4, and by welding the junction part of both, the opening part of the battery case 4 is sealed, and the inside of a battery is sealed. Further, in the battery of FIG. 1 , a non-aqueous electrolyte injection port 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte injection port 14, for example, by laser welding or the like. It is sealed, and the sealing property of a battery is ensured. In addition, the cover plate 9 is provided with a cleavage vent 15 as a mechanism for discharging internal gas to the outside when the temperature of the battery rises.

In the battery of Example 1, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the cover plate 9, and the negative electrode lead body 8 is connected to the lead. It is welded to the plate 13 and conducts the negative electrode lead 8 and the terminal 11 through the lead plate 13 so that the terminal 11 functions as a negative electrode terminal. Depending on the material or the like, the government may be the opposite.

FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1, and FIG. 2 is shown for the purpose of showing that the battery is a prismatic battery. In FIG. 1, the battery is schematically shown, and the battery Among the constituent members of , only specific ones are shown. Also in Fig. 1, the portion on the inner peripheral side of the electrode body is not formed as a cross-section.

Example 2

<Synthesis of lithium nickel cobalt manganese composite oxide>

Ammonia water whose pH has been adjusted to about 12 by the addition of sodium hydroxide is placed in a reaction vessel, and while this is vigorously stirred, nickel sulfate, cobalt sulfate and manganese sulfate are each added to 2.0 mol/dm 3 and 0.8 mol/d m 3 , a mixed aqueous solution containing at a concentration of 1.2 mol/dm 3 and ammonia water having a concentration of 25 mass % are respectively dropped at a rate of 23 cm 3 /min and 6.6 cm 3 /min using a metering pump, Ni and Co and Mn co-precipitation compounds (spherical co-precipitation compounds) were synthesized. At this time, the temperature of the reaction solution is maintained at 50° C., and an aqueous sodium hydroxide solution having a concentration of 6.4 mol/dm 3 is added dropwise at the same time so that the pH of the reaction solution is maintained around 12, and nitrogen gas is added 1d Bubbling at a flow rate of m 3 /min.

The coprecipitation compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Co, and Mn in a molar ratio of 5:2:3. After 0.196 mol of this hydroxide and 0.204 mol of LiOH·H ₂ O were dispersed in ethanol to form a slurry, the mixture was mixed in a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. Next, the mixture is placed in an alumina crucible, heated to 600° C. in a dry air flow of 2 dm 3 /min, held at that temperature for 2 hours to perform preliminary heating, and further heated to 900° C. and calcined for 12 hours, A lithium nickel cobalt manganese composite oxide was synthesized.

The lithium nickel cobalt manganese composite oxide described above was washed with water, then heat-treated in the air (oxygen concentration is about 20 vol%) at 850°C for 12 hours, and then pulverized in a mortar to obtain powder. The lithium nickel cobalt manganese composite oxide after pulverization was stored in a desiccator.

The composition analysis of the lithium nickel cobalt manganese composite oxide was performed as follows using the ICP method. First, 0.2 g of the lithium nickel cobalt manganese composite oxide was collected and placed in a 100 mL container. Then, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were sequentially added and dissolved by heating, and after cooling, the composition was further diluted 25 times and analyzed by ICP ("ICP-757" manufactured by JARRELASH) (calibration curve method). From the obtained results, as a result of deriving the composition of the lithium nickel cobalt manganese composite oxide, Li _{1 . 02} Ni _{0 . 5} Co _{0 . 2} Mn _{0 .} That the composition represented by ₃ O ₂ it was found. Moreover, the average particle diameter of the said lithium nickel cobalt-manganese composite oxide was 15 micrometers.

A positive electrode was produced in the same manner as in Example 1 except that nickel-cobalt-manganese composite oxide was used as described above, and a nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 1

Except having changed the binder to PVDF, it carried out similarly to Example 1, and produced the positive electrode, except having used this positive electrode, it carried out similarly to Example 1, and produced the nonaqueous electrolyte secondary battery.

Comparative Example 2

Except having changed the binder to PVDF, it carried out similarly to Example 2, and produced the positive electrode, except having used this positive electrode, it carried out similarly to Example 1, and produced the nonaqueous electrolyte secondary battery.

Each of the following evaluations was performed about the nonaqueous electrolyte secondary battery of an Example and a comparative example.

<Battery capacity>

For each battery of Examples and Comparative Examples, after initial charging and discharging, at room temperature (25° C.), charging at a constant current of 1 C until reaching 4.35 V, and then charging at a constant voltage of 4.35 V constant current-constant voltage charging ( Total charge time: 2.5 hours), followed by constant current discharge at 0.2 C (discharge termination voltage: 3.0 V), and the obtained discharge capacity (mAh) was taken as the battery capacity.

<Charging/discharging cycle characteristics>

For each battery of Examples and Comparative Examples, after the initial charge/discharge, a series of charging and discharging operations under the same conditions as those for measuring the battery capacity were performed as 1 cycle, and charging and discharging were repeated 1000 cycles, 200th cycle, 400th cycle, 600th cycle The capacity retention rate was calculated|required by measuring the discharge capacity at the cycle, 800th cycle, and 1000th cycle, and expressing the value obtained by dividing each discharge capacity by the discharge capacity obtained at the 1st cycle as a percentage. It means that the charge/discharge cycle characteristic of a battery is favorable, so that the value of this capacity retention ratio is large.

<60°C storage test (cell expansion)>

Each of the batteries of Examples and Comparative Examples was charged under the same conditions as in the measurement of battery capacity after initial charge/discharge. After charging, the thickness T ₁ of the battery outer can is measured in advance. After that, the battery is stored for a predetermined time in a constant temperature bath set at 60° C., taken out from the constant temperature bath, left at room temperature for 1 minute, and then the battery exterior The thickness T _{2 of the} can was measured. In addition, the thickness of the battery outer can in this test means the thickness between the wide light surfaces of the side part of an outer can. The thickness measurement of the battery outer can was measured in increments of 1/100 mm using a Nogisu ("CD-15CX" manufactured by Mitsutoyo Corporation), making the central portion of the wide light surface a measurement object. In addition, the number of days of storage in the thermostat is 1 day, 10 days, 20 days, 40 days, 60 days, and 80 days, and for each different battery, the thickness T ₂ of the battery outer can after each storage day is measured. did.

The battery expansion was evaluated from the ratio of changes in the thickness of the outer can T ₁ and T _{2 before and after storage to the thickness T 1} of the outer can before storage at 60°C. That is, the battery expansion (%) was calculated|required by the following formula.

Cell expansion (%)=100×(T ₂ -T ₁ )/(T ₁ )

Each of the above evaluation results is shown in Tables 1 and 2.

As shown in Tables 1 and 2, SiO _x and a graphite carbon material are used for the negative electrode active material, a lithium-containing composite oxide containing Ni as a transition metal is used for the positive electrode active material, and VDF is used for the binder related to the positive electrode mixture layer. -The batteries of Examples 1 and 2 using CTFE have a higher capacity retention rate at each cycle number in the evaluation of charge/discharge cycles than those of Comparative Examples 1 and 2 using PVDF as a binder related to the positive electrode mixture layer. The charging/discharging cycle characteristics are good, and in the evaluation of the storage characteristics, especially when the storage days are long, the expansion amount is small and the storage characteristics are good.

1: positive electrode 2: negative electrode
3: separator

Claims (8)

A nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator, comprising:
The positive electrode has a positive electrode mixture layer containing a positive electrode active material and a binder on one side or both sides of the current collector,
The positive mix layer contains, as a positive electrode active material, a lithium cobalt composite oxide containing a dissimilar metal element other than lithium, nickel, cobalt, and manganese, together with a lithium-containing composite oxide, and also vinylidene fluoride-chlorotrifluoroethylene air It contains the coal as a binder,
In the lithium-containing composite oxide, when the total amount of transition metal elements is 100 mol%, the proportion a (mol%) of nickel is 30≤a≤100,
The lithium-containing composite oxide has an average particle diameter of 10 µm or more and 17 µm or less,
The lithium cobalt composite oxide includes a lithium cobalt composite oxide (A) having an average particle diameter A (μm) of more than 10 μm and 30 μm or less, and a lithium cobalt composite oxide having an average particle diameter B (μm) of 1 μm or more and 10 μm or less (B) ) is used to satisfy the relationship of AB≥5,
When the average particle diameter of the lithium-containing composite oxide used as the positive electrode active material is C (μm), C>B,
The negative electrode has a negative electrode mixture layer containing a negative electrode active material on one side or both sides of the current collector,
The negative electrode mixture layer contains SiO _x (however, the atomic ratio x of O to Si is 0.5≤x≤1.5) and a graphite carbon material as a negative electrode active material,
_{A ratio of SiO x in} the total amount of the negative electrode active material is 0.01% by mass or more and 20% by mass or less. The method of claim 1,
The lithium-containing composite oxide has the following general composition formula (1)
Li _1+s M ¹ O ₂ (1)
[In the general composition formula (1), -0.3≤s≤0.3, M ¹ is a group of three or more elements including at least Ni, Co, and Mn, and ^{among each element constituting M 1} , Ni, Co and A nonaqueous electrolyte secondary battery represented by 30<a<65, 5<b<35, 15<c<50] when the ratio (mol%) of Mn is a, b, and c, respectively. The method of claim 1,
The average particle diameter A (μm) of the lithium cobalt composite oxide (A), the average particle diameter B (μm) of the lithium cobalt composite oxide (B), and the average particle diameter C (μm) of the lithium-containing composite oxide, A≥ A nonaqueous electrolyte secondary battery satisfying the relationship C>B. 4. The method according to any one of claims 1 to 3,
When the total of the lithium cobalt composite oxide (A) and the lithium cobalt composite oxide (B) used in the positive mix layer is 100 mass %, the content of the lithium cobalt composite oxide (A) is 50 mass % or more. 4. The method according to any one of claims 1 to 3,
When the total of the lithium cobalt composite oxide (A), the lithium cobalt composite oxide (B), and the lithium-containing composite oxide used in the positive mix layer is 100% by mass, the content of the lithium-containing composite oxide is 15% by mass or more and 45% by mass The following nonaqueous electrolyte secondary batteries. delete delete delete

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