JP2017188219A - Positive electrode material for nonaqueous electrolyte secondary battery, positive electrode mixture paste, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for a nonaqueous electrolyte secondary battery, which can keep an energy density and an output characteristic in use for a battery, and which can accelerate the gas generation in an overcharged state and activate a current interrupt device mechanism to prevent the battery overcharge with high accuracy.SOLUTION: A positive electrode material for a nonaqueous electrolyte secondary battery is used, which comprises: a mixture of a positive electrode active material including lithium metal composite oxide particles, and a calcium compound including 0.0015-0.0055 atom% of calcium to a total number of atoms of metal elements other than lithium included in the lithium metal composite oxide particles.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode material for a non-aqueous electrolyte secondary battery, a positive electrode mixture paste, and a non-aqueous electrolyte secondary battery.

  In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. In addition, as a battery for electric vehicles such as hybrid cars, development of a high output secondary battery is strongly desired. As such a secondary battery, there is a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery. A non-aqueous electrolyte secondary battery includes a negative electrode, a positive electrode, and an electrolyte, and a material capable of desorbing and inserting lithium is used as an active material for the negative electrode and the positive electrode.

  Such non-aqueous electrolyte secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using a layered or spinel type lithium metal composite oxide as a positive electrode material are among them. Since a high voltage of 4V class can be obtained, it has been put into practical use as a battery having a high energy density.

Conventionally proposed materials include lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel that is cheaper than cobalt, and lithium nickel. Examples thereof include cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese. Among these, lithium nickel cobalt manganese composite oxide is attracting attention as a material that has good cycle characteristics and can take out high output with low resistance.

  In addition, the demand for higher performance for batteries has been increasing recently, and various characteristics must be improved in a well-balanced manner. The demand for measures such as overcharge prevention is increasing. As an overcharge prevention measure for non-aqueous electrolyte secondary batteries, an overcharge prevention device that generates a gas during overcharge and senses an increase in the internal pressure of the battery, such as CID (Current Interrupt Device), is provided. It is common.

  For example, Patent Document 1 proposes a non-aqueous organic solvent containing a cyclohexene-type compound as a constituent member corresponding to such measures for preventing overcharge of a battery. According to this proposal, if non-aqueous electrolyte containing a specific cyclohexene type compound is used, the storage characteristics will be greatly improved, and gas will be generated at a relatively early stage of overcharge. You can do that.

JP 2003-229169 A

  In order to operate the overcharge prevention device, it is necessary to generate gas at an early stage of overcharge and to generate a sufficient amount of gas for the operation of the device. However, the prior art has a problem that the amount of gas at the early stage of overcharging necessary for operating the overcharge prevention device with high sensitivity is not sufficient.

In view of such problems, the present invention promotes gas generation in an overcharge state while maintaining the energy density and output characteristics when used in a battery, and activates a current interrupt mechanism to perform overcharge with high accuracy. An object of the present invention is to provide a positive electrode material for a non-aqueous electrolyte secondary battery that can be prevented.
It is another object of the present invention to provide a non-aqueous electrolyte secondary battery that has high energy density and output characteristics and can prevent overcharge with high accuracy.

  In order to solve the above-mentioned problems, the present inventor diligently studied the influence on the amount of gas generated in the battery during overcharging, and mixed a calcium compound with the lithium metal composite oxide constituting the positive electrode. Thus, the inventors have found that it is possible to promote the amount of gas generated during overcharge while maintaining battery characteristics, and have completed the present invention.

  That is, the positive electrode material for a non-aqueous electrolyte secondary battery of the present invention has a positive electrode active material composed of lithium metal composite oxide particles and 0 to the total of metal elements other than lithium contained in the lithium metal composite oxide particles. And a mixture of calcium compounds containing calcium of from 0015 to 0.0055 atomic%.

  The calcium compound is preferably calcium sulfate, a hydrate thereof, or a mixture of calcium sulfate and a hydrate thereof.

The lithium metal composite oxide particles have a general formula: Li _{1 + s} Ni _x Co _y Mn _z M _t O ₂ (−0.05 ≦ s ≦ 0.20, x + y + z + t = 1, 0.3 ≦ x ≦ 0. 7, 0.1 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Na, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf 1 or more additional elements selected from Ta and W), and preferably hexagonal lithium metal composite oxide particles having a layered structure.

  The lithium metal composite oxide particles have an average particle diameter of 5 to 15 μm and an index indicating the spread of the particle size distribution [(d90−d10) / average particle diameter] is 0.70 or less, and the tap density Is preferably 1.8 to 2.5 g / ml.

  The method for producing a positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention is based on a positive electrode active material composed of lithium metal composite oxide particles and a total of metal elements other than lithium contained in the lithium metal composite oxide. And a calcium compound containing calcium of 0015 to 0.0055 atomic%.

  The positive electrode paste for a non-aqueous electrolyte secondary battery of the present invention contains the positive electrode material for a non-aqueous electrolyte secondary battery.

  The method for producing a positive electrode paste for a non-aqueous electrolyte secondary battery according to the present invention is a method of mixing and kneading the positive electrode material for a non-aqueous electrolyte secondary battery, a conductive material and a binder, and a solvent.

  In the said manufacturing method, 0.0015-0.0055 atomic% of calcium is contained with respect to the sum total of the said positive electrode active material and metal elements other than lithium contained in the lithium metal complex oxide in this positive electrode active material. Calcium compounds can be added individually and mixed and kneaded with other constituent materials.

  The non-aqueous electrolyte secondary battery of the present invention has a positive electrode including the positive electrode material for a non-aqueous electrolyte secondary battery.

  By using the positive electrode material for a non-aqueous electrolyte secondary battery of the present invention, it is possible to obtain a non-aqueous electrolyte secondary that has high battery capacity and high output characteristics and can prevent overcharge with high accuracy.

FIG. 1 is a schematic cross-sectional view of a coin cell type battery used for battery evaluation. FIG. 2 is a schematic explanatory diagram of an impedance evaluation measurement example and an equivalent circuit used for analysis. FIG. 3 is a schematic explanatory view of a laminate type battery used for battery evaluation. FIG. 4 is a schematic explanatory view showing a gas generation amount evaluation method for pressurizing the laminate cell by the hydraulic press machine PA.

  The present invention includes (1) a positive electrode material for a non-aqueous electrolyte secondary battery and a method for producing the same, (2) a positive electrode mixture paste for a non-aqueous electrolyte secondary battery containing the positive electrode material for the non-aqueous electrolyte secondary battery, (3) The present invention relates to a non-aqueous electrolyte secondary battery having a positive electrode including the positive electrode material for the non-aqueous electrolyte secondary battery. Hereinafter, each of the inventions (1) to (3) will be described in detail, but the present invention is not limited to these descriptions.

(1-1) Positive electrode material for non-aqueous electrolyte secondary battery The positive electrode material for a non-aqueous electrolyte secondary battery of the present invention is included in a positive electrode active material composed of lithium metal composite oxide particles and lithium metal composite oxide particles. It includes a mixture of calcium compounds containing 0.0015 to 0.0055 atomic% of calcium with respect to the total of metal elements other than lithium.

(Calcium compound)
The positive electrode material for non-aqueous electrolyte secondary batteries of the present invention (hereinafter sometimes simply referred to as “positive electrode material”) is a lithium metal composite oxide particle (hereinafter sometimes simply referred to as “composite oxide particle”). And a mixture of a positive electrode active material and a calcium compound. That is, the calcium compound is present outside the composite oxide particles, and each is present as a separate particle in a mixed state. Although the detailed mechanism is unknown, the amount of gas generated at the time of overcharge increases by mixing the calcium compound with the positive electrode material. Since the calcium compound is present outside the composite oxide particle, it has less influence on lithium insertion / extraction of the lithium metal composite oxide compared to the case where calcium is added to the composite oxide particle. It is advantageous to obtain excellent battery characteristics such as high charge / discharge capacity (hereinafter also referred to as “battery capacity”) and excellent output characteristics. If calcium is added to the composite oxide particles to increase the amount of gas generated during overcharge, the amount of calcium added increases and the battery characteristics deteriorate.

  The calcium compound is preferably calcium sulfate or a hydrate thereof, or a mixture of calcium sulfate and its hydrate. These compounds are preferable because they do not contain an element that adversely affects the battery characteristics of the positive electrode active material.

  The amount of the calcium compound mixed with the positive electrode active material is 0.0015 to 0.0055 atomic% with respect to the total amount of metal elements other than lithium contained in the composite oxide particles in the amount of calcium contained. As a result, the amount of gas generated during overcharging while maintaining good battery characteristics when a non-aqueous electrolyte secondary battery having a positive electrode containing a positive electrode material (hereinafter simply referred to as “battery”) is obtained. Can be sufficient. If the amount of calcium contained is less than 0.0015 atomic%, the amount of gas generated at the time of overcharging decreases, and it becomes impossible to operate the overcharge prevention device accurately at an early stage of overcharging. On the other hand, when it exceeds 0.0055 atomic%, the amount of the calcium compound in the positive electrode material increases, and the amount of the composite oxide particles relatively decreases, so that the battery characteristics are deteriorated. In order to achieve a higher level of gas generation during overcharge and battery characteristics, it is more preferable to mix a calcium compound having a calcium content of 0.002 to 0.005 atomic%.

  The average particle diameter of the calcium compound is preferably 1 to 500 μm, more preferably 1 to 200 μm, and still more preferably 1 to 100 μm. Here, the volume-based average particle diameter Mv measured by the laser light diffraction scattering method is used as the average particle diameter. By setting the average particle size to 1 to 500 μm, the dispersibility of the calcium compound in the positive electrode material can be improved, and a sufficient gas generation amount can be ensured at an early stage during overcharge. When the average particle size is less than 1 μm, the calcium compound may aggregate and the dispersibility may decrease. On the other hand, if the average particle size exceeds 500 μm, calcium compounds may be ubiquitous and the amount of gas generated in the early stage during overcharge may be reduced.

(composition)
The lithium metal composite oxide particles have a general formula: Li _{1 + s} Ni _x Co _y Mn _z M _t O ₂ (−0.05 ≦ s ≦ 0.20, x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Na, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta And one or more additive elements selected from W) and hexagonal lithium metal composite oxide particles having a layered structure are preferable. A lithium metal composite oxide having a hexagonal structure having a layered structure has an advantage of excellent theoretical capacity density and cycle characteristics as compared with a spinel structure positive electrode active material.

  When the atomic ratio s indicating the excess amount of lithium (Li) is in the range of −0.05 to 0.20, better battery capacity and output characteristics can be obtained. When the excess amount s of Li is less than −0.05, the reaction resistance of the positive electrode in the battery using the obtained positive electrode material (hereinafter sometimes referred to as “positive electrode resistance”) increases, and therefore the output of the battery is high. May be lower. On the other hand, when the excessive amount s of Li exceeds 0.20, when the positive electrode material is used for the positive electrode of the battery, the battery capacity may decrease and the positive electrode resistance may increase. From the viewpoint of further reducing the reaction resistance, s indicating an excessive amount of Li is more preferably set to 0.10 or more.

  Nickel (Ni), cobalt (Co), and manganese (Mn) together with Li constitute a basic skeleton of a hexagonal lithium composite oxide having a layered structure. The atomic ratios x, y, and z indicating these contents are determined in consideration of battery capacity, cycle characteristics, safety, etc. in the non-aqueous electrolyte secondary battery using the obtained positive electrode active material. The value of x is preferably 0.3 to 0.7, more preferably 0.33 to 0.45, and the value of y is preferably 0.1 to 0.4, more preferably 0.25 to 0. .35, and the value of z is preferably 0 to 0.4, more preferably 0.30 to 0.40.

  In the present invention, in addition to Ni, Co, and Mn, additive elements can be contained in the lithium-containing composite oxide within the above range. The additive elements are sodium (Na), magnesium (Mg), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium ( One or more additive elements selected from Hf), tantalum (Ta), and tungsten (W). By appropriately adding the additive element, the battery characteristics can be further improved.

The positive electrode material preferably has an SO ₄ content of 1% by mass or less. Thereby, when a battery is obtained using the positive electrode material, it is possible to suppress a decrease in battery characteristics of the battery.

(Average particle size)
The composite oxide particles preferably have an average particle size of 5 to 15 μm. When the average particle size is less than 5 μm, when the positive electrode is formed, the packing density of the particles may decrease, and the battery capacity per positive electrode volume may decrease. On the other hand, when the average particle size exceeds 15 μm, the specific surface area of the positive electrode active material decreases, and the interface between the battery electrolyte and the composite oxide particles decreases, thereby increasing the reaction resistance of the positive electrode and Output characteristics may deteriorate.

  Therefore, if the composite oxide particles are adjusted so that the average particle diameter is preferably 5 to 15 μm, more preferably 5 to 10 μm, the battery capacity per unit volume in a battery using this positive electrode active material for the positive electrode A battery having excellent output characteristics can be obtained.

(Particle size distribution)
The composite oxide particles preferably have [(d90−d10) / average particle size], which is an index indicating the spread of the particle size distribution, of 0.70 or less, and more preferably 0.65 or less.

  When the particle size distribution is wide, there are many fine particles having a very small particle size with respect to the average particle size and coarse particles having a very large particle size with respect to the average particle size in the positive electrode active material. Become. When the positive electrode is formed using a positive electrode active material in which a large amount of fine particles are present, the cycle characteristics may be deteriorated because the fine particles are selectively deteriorated due to a local reaction of the fine particles. On the other hand, when a positive electrode is formed using a positive electrode active material with a large amount of coarse particles, the reaction area between the electrolyte and the positive electrode active material may not be sufficient, and the battery output may decrease due to an increase in positive electrode resistance. is there.

  Therefore, by setting the particle size distribution of the positive electrode active material to 0.70 or less with the above-mentioned index [(d90-d10) / average particle size], the proportion of fine particles and coarse particles can be reduced. The battery used for the positive electrode has good cycle characteristics and further excellent battery output.

  In addition, in the index [(d90−d10) / average particle size] indicating the spread of the particle size distribution, d10 is a cumulative value of particles in each particle size from the smaller particle size side, and the accumulated volume is the sum of all particles. It means the particle size which becomes 10% of the volume. D90 means a particle size in which particles are similarly accumulated and the accumulated volume is 90% of the total volume of all particles.

  The average particle diameter, d90 and d10 can be obtained from the volume integrated value measured with a laser light diffraction / scattering particle size analyzer. As the average particle size, the volume-based average particle size Mv is used in the same manner as the calcium compound.

(Crystallite diameter)
The crystallite diameter of the composite oxide particles is preferably 50 to 200 nm, more preferably 120 to 180 nm, and still more preferably 140 to 160 nm. By controlling the crystallite diameter within this range, the crystal structure becomes dense, the lithium is uniformly and sufficiently inserted into and extracted from the crystal showing the charge / discharge reaction of the composite oxide particles, the battery capacity is improved, and The output resistance can be improved by reducing the reaction resistance of the positive electrode. When the crystallite diameter exceeds 200 nm, lithium is not uniformly inserted and extracted, and the battery capacity may be reduced. On the other hand, when the crystallite diameter is less than 50 nm, the crystal structure is not sufficiently developed, and battery characteristics such as battery capacity and output characteristics may not be sufficiently obtained. This crystallite diameter can be obtained by the Scherrer equation from the (003) plane peak of X-ray diffraction.

(Characteristic)
When the positive electrode material is used for the positive electrode of a 2032 type coin battery, for example, a high initial discharge capacity of 150 mAh / g or more and a low positive electrode resistance of 4.0 Ω or less can be obtained, and the positive electrode active for a non-aqueous electrolyte secondary battery can be obtained. It exhibits excellent properties as a substance.

(1-1) Method for Producing Positive Electrode Material for Nonaqueous Electrolyte Secondary Battery The method for producing the positive electrode material of the present invention includes a positive electrode active material composed of lithium metal composite oxide particles and lithium contained in the lithium metal composite oxide. And a calcium compound containing 0.0015 to 0.0055 atomic% of calcium with respect to the total of these metal elements.

  The positive electrode active material composed of lithium metal composite oxide particles and the calcium compound are sufficiently mixed in order to make the calcium compound dispersed uniformly in the positive electrode material.

  For the mixing, a general mixer can be used. For example, the calcium oxide compound and the calcium compound are mixed to such an extent that the complex oxide particles are not destroyed using a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like. Mix well. Thereby, the calcium compound can be uniformly distributed in the lithium metal composite oxide powder.

  The amount of the calcium compound mixed with the positive electrode active material is 0.0015 to 0.0055 atomic%, preferably 0.002 with respect to the total amount of metal elements other than lithium contained in the composite oxide particles in the amount of calcium contained. -0.005 atomic%.

  Moreover, the average particle diameter of the calcium compound to mix becomes like this. Preferably it is 1-500 micrometers, More preferably, it is 1-200 micrometers, More preferably, it is 1-100 micrometers. Here, the volume-based average particle diameter Mv measured by the laser light diffraction scattering method is used as the average particle diameter. Thereby, the dispersibility of the calcium compound in a positive electrode material can further be improved.

The composite oxide particles have a general formula: Li _{1 + s} Ni _x Co _y Mn _z M _t O ₂ (−0.05 ≦ s ≦ 0.20, x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Na, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W It is preferably a hexagonal lithium metal composite oxide particle having a layered structure. Since the powder characteristics and particle structure of the composite oxide particles are inherited up to the positive electrode material, the composition, powder characteristics, particle structure and the like of the composite oxide particles can be the same as those of the positive electrode material described above. . The composite oxide particles are selected according to the positive electrode material to be obtained.

  As a more preferable embodiment of the composite oxide particles, the average particle diameter is 5 to 15 μm and the index indicating the spread of the particle size distribution [(d90−d10) / average particle diameter] is 0 as in the positive electrode material. It is preferable that the tap density is 1.8 to 2.5 g / ml. A more preferable range of the average particle diameter is 5 to 10 μm.

(2-1) Positive electrode mixture paste for non-aqueous electrolyte secondary battery The positive electrode mixture paste for non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes simply referred to as “positive electrode mixture paste”) is the positive electrode. Contains materials. In the positive electrode mixture paste, particulate calcium compounds are dispersed between the composite oxide particles. By producing a positive electrode using such a positive electrode mixture paste, the calcium compound is dispersed between the composite oxide particles even in the positive electrode, and in the finally obtained battery at an early stage of overcharge. It is possible to generate a sufficient amount of gas. Further, since the calcium compound is present between the composite oxide particles, the influence on the composite oxide particles is minimal, and high battery characteristics can be maintained.

  The constituent material of the positive electrode mixture paste other than the positive electrode material is not particularly limited, and a material equivalent to a known positive electrode mixture paste can be used. The positive electrode mixture paste includes, for example, a positive electrode material, a conductive material, and a binder. The positive electrode mixture paste may further contain a solvent. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the positive electrode material paste has a positive electrode material content of 60 to 95 parts by mass and a conductive material content of 1 to 20 masses. And the content of the binder is preferably 1 to 20 parts by mass.

  As the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.

  The binder (binder) plays a role of holding the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. Polyacrylic acid or the like can be used.

  If necessary, a positive electrode material, a conductive material, and activated carbon may be dispersed and a solvent that dissolves the binder (binder) may be added to the positive electrode mixture paste. Specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used as the solvent. Activated carbon can be added to the positive electrode mixture paste in order to increase the electric double layer capacity.

(2-2) Method for Producing Positive Electrode Mixture Paste for Nonaqueous Electrolyte Secondary Battery The positive electrode mixture paste is a mixture of a powdered positive electrode material and, if necessary, a conductive material and a binder, and further activated carbon and viscosity. A positive electrode mixture paste can be prepared by adding a solvent for adjustment or the like and kneading it.

  The production of the positive electrode mixture paste is to obtain the positive electrode material in advance and then mix and knead with the other constituent materials. The composite oxide particles and the calcium compound are added separately and mixed with the other constituent materials. It is also possible to knead. Here, the order of adding the composite oxide particles and the calcium compound is not limited as long as they are mixed and kneaded. This also forms a positive electrode material that is a mixture of composite oxide particles and calcium compound during kneading of the paste, and a positive electrode mixture paste in which particulate calcium compound is dispersed between the composite oxide particles is obtained. . Therefore, the positive electrode mixture paste of the present invention includes those obtained by individually adding the composite oxide particles and the calcium compound, mixing with other constituent materials, and kneading.

  For the production of the positive electrode mixture paste, any kneading apparatus used in the production of a positive electrode mixture paste of a general non-aqueous electrolyte secondary battery may be used. Examples of the kneading apparatus include a blade planetary kneading machine, a container rotating type planetary kneading machine, a homogenizer, and a roll mill. The kneading apparatus may be selected according to the amount to be kneaded and the required viscosity.

  Further, the kneading time is not particularly limited, but it may be kneaded until each constituent material is uniformly dispersed in the positive electrode mixture paste with the required viscosity. It can be determined by testing.

(3) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and the like, and is composed of the same components as a general non-aqueous electrolyte secondary battery. The The embodiment described below is merely an example, and a battery to which the positive electrode material of the present invention is applied is based on the embodiment described in the present specification, based on the knowledge of those skilled in the art. It can be implemented in a form that has been changed or improved. Moreover, the use of the battery is not particularly limited.

(3-a) Positive electrode Using the positive electrode mixture paste containing the positive electrode material, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.

  The positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

(3-b) Negative electrode The negative electrode is made of metal lithium, lithium alloy, or the like, or a negative electrode active material capable of occluding and desorbing lithium ions, mixed with a binder, and added with an appropriate solvent to form a paste. The composite material is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

  As the negative electrode active material, for example, organic compound fired bodies such as natural graphite, artificial graphite and phenol resin, and powdery bodies of carbon materials such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as polyvinylidene fluoride (PVDF) can be used as in the case of the positive electrode, and N-methyl-2 is used as a solvent for dispersing these active materials and the binder. An organic solvent such as pyrrolidone (NMP) can be used.

(3-c) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains an electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.

(3-d) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in admixture of two or more. be able to.

  The nonaqueous electrolytic solution contains, for example, cyclohexylbenzene as a gas generation amount enhancer during overcharge.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used. Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(3-e) Shape and Configuration of Battery The nonaqueous electrolyte secondary battery of the present invention composed of the positive electrode, the negative electrode, the separator, and the nonaqueous electrolytic solution that have been described above includes various types such as a cylindrical shape and a laminated shape. It can be made into a shape.

  In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. Connect between the positive electrode terminal and between the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead, etc., and seal the battery case to complete the nonaqueous electrolyte secondary battery. .

(3-f) Characteristics The non-aqueous electrolyte secondary battery using the positive electrode material of the present invention has a high capacity and high output, is excellent in gas generation responsiveness during overcharge, and has high reliability. is there. The battery using the positive electrode active material obtained in the preferred embodiment is, for example, as high as 145 mAh / g or more when used in the positive electrode of a 2032 type coin battery, and 150 mAh / g or more when obtained in the preferred embodiment. An initial discharge capacity and a low positive electrode resistance of 4.0Ω or less are obtained, and a high capacity and a high output are obtained.

  This non-aqueous electrolyte secondary battery is suitable for the power source of small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require a high capacity.

  Further, as batteries for electric vehicles increase in size, it becomes difficult to ensure reliability, and expensive protection circuits are indispensable. On the other hand, the non-aqueous electrolyte secondary battery of the present invention not only makes it easy to ensure reliability, but also simplifies an expensive protection circuit and can reduce costs. Therefore, it is also suitable as a power source for electric vehicles. Furthermore, since it is possible to reduce the size and increase the output, it is suitable as a power source for an electric vehicle subject to restrictions on the mounting space.

  The present invention can be used not only as a power source for an electric vehicle driven purely by electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The performance (gas generation amount, initial discharge capacity, positive electrode resistance) of the positive electrode material obtained by the present embodiment, the positive electrode mixture paste using this positive electrode material, and the non-aqueous electrolyte secondary battery was measured.

  A coin-type battery B as shown in FIG. 1 and a laminate cell C as shown in FIG. 3 are prepared, charge / discharge capacity and positive electrode resistance are measured with a coin-type battery, and the thickness of the battery during overcharge is measured with a laminate cell. As a result, the amount of gas generated was evaluated.

(Manufacture and evaluation method of coin-type battery)
The positive electrode active material, acetylene black, and polytetrafluoroethylene resin (PTFE) were mixed by a dry method so that the mixing ratio was 75: 16.7: 8.3 in a mass ratio, and extended into a sheet shape. The thickness of the sheet was adjusted so that the mass when the electrode was punched out to have a diameter of 9 mm was about 10 mg. The obtained sheet was punched out to a diameter of 9 mm and used as a positive electrode (evaluation electrode) 1.

For the negative electrode, a negative electrode active material made of graphite and PVDF as a binder were dissolved in an NMP solution at a mass ratio of 92.5: 7.5 to obtain a negative electrode mixture paste. The obtained negative electrode mixture paste was applied to a copper foil with a comma coater so that the basis weight was 11.8 mg / cm ² and dried at 120 ° C. After drying, a load was applied through a roll press to produce a negative electrode sheet with improved electrode density. The obtained negative electrode sheet was punched out with a diameter of 14 mm and used as the negative electrode 2.

The produced positive electrode 1 was dried at 120 ° C. for 12 hours in a vacuum dryer. Then, using the positive electrode 1 and the negative electrode 2, a 2032 type coin-type battery B was produced in a glove box in an Ar atmosphere in which the dew point was controlled at -80 ° C. The electrolyte is a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) 3: 7 (manufactured by Toyama Pharmaceutical Co., Ltd.) using 1M LiPF ₆ as a supporting electrolyte, and 2% by mass of cyclohexylbenzene added. Was used. As the separator 3, a polyethylene porous film having a film thickness of 25 μm was used. The coin-type battery B has a gasket 4 and is assembled into a coin-type battery B with a wave washer 5, a positive electrode can 6, and a negative electrode can 7.

[Initial discharge capacity]
The battery capacity was evaluated by the initial discharge capacity. The produced coin-type battery is allowed to stand for about 24 hours after assembling, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 4.3 V with a current density of 4 mA / cm ² in a constant temperature bath at 25 ° C. The initial discharge capacity was determined by measuring the discharge capacity when the battery was discharged to 3.0 V after charging for 1 hour and then discharging to 3.0 V. A multi-channel voltage / current generator was used to measure the charge / discharge capacity.

[Positive electrode resistance]
Output characteristics were evaluated by positive electrode resistance. The positive electrode resistance was measured by an alternating current impedance method using a coin-type battery B charged at a charging potential of 4.1V. For the measurement, a Nyquist plot shown in FIG. 2 is obtained by using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron). Since the plot is expressed as the sum of the characteristic curves indicating the solution resistance, the negative electrode resistance and the capacity, and the positive electrode resistance and the capacity, fitting calculation was performed using an equivalent circuit, and the value of the positive electrode resistance was evaluated.

(Manufacturing and evaluation method of laminate cell)
The positive electrode active material and the conductive material acetylene black were mixed and dispersed, and the binder PVDF and the solvent NMP were added and kneaded to obtain a positive electrode mixture paste. The mixing ratio of the positive electrode material, the conductive material, and the binder was 85: 10: 5 by mass ratio. On the aluminum current collector foil (thickness: 0.02 mm), the positive electrode mixture paste was applied and dried, leaving a conductive portion connected to the outside, and a positive electrode active material layer having a positive electrode active material weight of 7 mg / cm ² was formed. The formed positive electrode sheet 8 was produced.

Also, carbon powder (acetylene black) was pasted as a negative electrode active material on a copper current collector foil (thickness 0.02 mm), and a negative electrode active material layer having a negative electrode active material weight of 5 mg / cm ² was formed in the same manner. A negative electrode sheet 9 was produced.

  A laminated sheet was formed between the produced positive electrode sheet 8 and negative electrode sheet 9 with a separator 10 made of a polypropylene microporous film (thickness 20.7 μm, porosity density 43.9%) interposed therebetween. Then, this laminated sheet is sandwiched between two aluminum laminate sheets 11 (thickness 0.55 mm), and the three sides of the aluminum laminate sheet are heat-sealed and sealed, and a laminate cell C configured as shown in FIG. Assembled.

Thereafter, LiPF ₆ (1 mol / L) and cyclohexylbenzene (2% by mass) as an overcharge gas generating additive were dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 3: 3: 4). 260 μl of an electrolyte solution manufactured by Ube Industries Co., Ltd. was injected, and the remaining side was heat-sealed to prepare a laminate cell C for gas generation test for evaluating the gas generation amount shown in FIG. The size of the produced laminate cell 4 is 60 mm long and 90 mm wide.

[Gas generation test]
The produced laminate cell C was stored for 12 hours in a constant temperature bath (Cosmo Pier) manufactured by Hitachi Appliances, Ltd. set at 25 ° C. After storing for 12 hours, using a charging / discharging device (Hokuto Denko Co., Ltd .: HJ1001SD8) while being housed in a thermostatic chamber, a constant current mode of 0.2 C in the range of 3.0 to 4.3 V The battery was charged and discharged three times. After charging and discharging, the battery was charged in a constant current mode of 1 C up to 4.6 V, and then left in a constant temperature bath for 72 hours to generate gas in the laminate cell C. At this time, the laminate cell C was sandwiched and held between a pair of plate-like members (made of stainless steel), and an exposed portion was formed by exposing a width of 1 cm from the end of the laminate cell from the pair of plate-like members.

[Evaluation of gas generation]
After the gas generation test has been completed, the gas generation tested laminate cell (hereinafter referred to as “tested laminate cell”) CA is taken out of the thermostatic bath and marked with an oil-based magic at a width of 1 cm from the end of the tested laminate cell CA. went.

Thereafter, as shown in the schematic explanatory diagram of the gas generation amount evaluation method in FIG. 4, the tested laminate cell CA is placed on the table T of the manual hydraulic press machine PA (manufactured by NPA Corporation: model number TB-50H). Then, on the tested laminate cell CA, the pressure member PP is left with a width of 1 cm from the end (the portion from the marked portion to the end of the tested laminate cell CA, the non-pressurized portion L ₁ ). A rectangular holding plate (made of stainless steel) was placed.

Further, Non-pressing L _1, arranged rectangular measuring plate (stainless steel) as the mounting member MP, the upper surface to the dial gauge of the one end portion in the measurement plate (portion that is placed on the non-pressing portion) Ga (made by CITIZEN: 2A-104) was installed.

Then, by pressing the pressure member PP manually hydraulic press PA 4 times the pressure of 4kN the post-test laminate cell CA, the gas in the post-test laminate cell CA is in the non-pressure portion L ₁ collected. Non pressure portion L ₁ is bulge by collected gas, one end of the mounting member MP is moved upward.

  Finally, the value of the dial gauge Ga was read, the amount of movement of one end of the mounting member MP was measured, and the amount of generated gas was evaluated.

Example 1
Hexagonal lithium metal composite oxide particles having a layered structure represented by Li _1.04 Ni _0.34 Co _0.33 Mn _0.33 O ₂ obtained by a known technique were used as a positive electrode active material. . The lithium metal composite oxide particles have an average particle size Mv of 5.8 μm, an index indicating the spread of the particle size distribution [(d90−d10) / average particle size] is 0.62, and the tap density is It was 1.9 g / ml. The tap density was measured with a shaking specific gravity measuring instrument (KRS-409, manufactured by Kuramochi Scientific Instruments).

Next, a positive electrode active material, acetylene black, and PTFE were mixed in a dry manner to obtain a positive electrode mixture. During mixing, calcium sulfate dihydrate containing 0.002 atomic% of calcium with respect to the total of metal elements other than lithium contained in the positive electrode active material (lithium metal composite oxide particles) was added. The average particle diameter of the added calcium sulfate dihydrate was 95 μm. A positive electrode material was formed in the positive electrode mixture by adding and mixing calcium sulfate dihydrate. The positive electrode mixture was stretched into a sheet shape, punched out so that the diameter of the electrode was 9 mm, and used as the positive electrode (evaluation electrode) 1 to produce a coin-type battery B. The laminate cell C was the same as the coin-type battery B When the positive electrode active material was used and the positive electrode active material and acetylene black were mixed, a positive electrode material was formed by adding the same amount of calcium sulfate dihydrate as in the coin-type battery B. Thereafter, PVDF as a binder and NMP as a solvent were added and kneaded to obtain a positive electrode mixture paste, and then a laminate cell C was produced.

  Using the obtained coin-type battery B and laminate cell C, the initial discharge capacity, the positive electrode resistance, and the gas generation amount were measured, and the positive electrode material was evaluated. The initial discharge capacity was 150.5 mAh / g, and the positive electrode resistance due to impedance was 2.3Ω. Further, the amount of gas generated (the thickness of the battery swollen by gas generation) was 2.5 mm.

(Example 2)
Coin-type battery B and laminate cell C were prepared in the same manner as in Example 1 except that calcium sulfate dihydrate was added so that the calcium content was 0.005 atomic%, and the positive electrode material was evaluated.
The initial discharge capacity was 154.5 mAh / g, the positive electrode resistance due to impedance was 3.1Ω, and the amount of gas generated was 2.4 mm.

(Comparative Example 1)
A coin-type battery B and a laminate cell C were produced in the same manner as in Example 1 except that calcium sulfate dihydrate was not added, and the positive electrode material was evaluated.
The initial discharge capacity was 159 mAh / g, the positive electrode resistance due to impedance was 3.3Ω, and the amount of gas generated was 1.4 mm.

(Comparative Example 2)
Coin-type battery B and laminate cell C were prepared in the same manner as in Example 1 except that calcium sulfate dihydrate was added so that the calcium content was 0.001 atomic%, and the positive electrode material was evaluated.
The initial discharge capacity was 159.6 mAh / g, the positive electrode resistance due to impedance was 3.2Ω, and the amount of gas generated was 1.6 mm.

(Comparative Example 3)
Coin-type battery B and laminate cell C were prepared in the same manner as in Example 1 except that calcium sulfate dihydrate was added so that the calcium content was 0.006 atomic%, and the positive electrode material was evaluated.
The initial discharge capacity was 145.1 mAh / g, the positive electrode resistance due to impedance was 2.3Ω, and the amount of gas generated was 2.6 mm.

(Evaluation)
In Examples, it was confirmed that the initial discharge capacity and the positive electrode resistance were good, and the amount of gas generated during overcharge was large. On the other hand, Comparative Example 1 in which the calcium compound is not added and Comparative Example 2 in which the amount is small even when added are preferable from the viewpoint of securing reliability against current interruption during overcharging because the amount of gas generated during overcharging is small. I understand that there is no. In Comparative Example 3 in which the amount of calcium added is large, the initial discharge capacity is greatly reduced, which is not preferable because the battery characteristics are inhibited.

B Coin-type battery 1 Positive electrode (Evaluation electrode)
2 Negative electrode 3 Separator 4 Gasket 5 Wave washer 6 Positive electrode can 7 Negative electrode can C Laminate cell 8 Positive electrode sheet 9 Negative electrode sheet 10 Separator 11 Aluminum laminate sheet CA Tested laminate cell PA Manual hydraulic press UPA Non-pressurized part PP Pressurized member MP Placement member Ga Dial gauge T Table

Claims (9)

  A positive electrode active material comprising lithium metal composite oxide particles, and a calcium compound containing 0.0015 to 0.0055 atomic% of calcium with respect to the total of metal elements other than lithium contained in the lithium metal composite oxide particles; A positive electrode material for a non-aqueous electrolyte secondary battery, comprising a mixture of 2. The positive electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the calcium compound is calcium sulfate, a hydrate thereof, or a mixture of calcium sulfate and a hydrate thereof. The lithium metal composite oxide particles have a general formula: Li _{1 + s} Ni _x Co _y Mn _z M _t O ₂ (−0.05 ≦ s ≦ 0.20, x + y + z + t = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.4, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, M is Na, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta The non-aqueous electrolyte secondary material according to claim 1, wherein the non-aqueous electrolyte secondary particle is a hexagonal lithium metal composite oxide particle having a layered structure. Positive electrode material for batteries.   The lithium metal composite oxide particles have an average particle diameter of 5 to 15 μm and an index indicating the spread of the particle size distribution [(d90−d10) / average particle diameter] is 0.70 or less, and the tap density The positive electrode material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein is 1.8 to 2.5 g / ml.   A positive electrode active material comprising lithium metal composite oxide particles, and a calcium compound containing 0.0015 to 0.0055 atomic% of calcium relative to the total of metal elements other than lithium contained in the lithium metal composite oxide. It mixes, The manufacturing method of the positive electrode material for nonaqueous electrolyte secondary batteries in any one of Claims 1-4 characterized by the above-mentioned.   A positive electrode paste for a non-aqueous electrolyte secondary battery, comprising the positive electrode material for a non-aqueous electrolyte secondary battery according to claim 1.   The non-aqueous electrolyte secondary battery positive electrode material according to any one of claims 1 to 4, a conductive material, a binder, and a solvent are mixed and kneaded. A method for producing a positive electrode paste for an aqueous electrolyte secondary battery.   The method for producing a positive electrode paste for a non-aqueous electrolyte secondary battery according to claim 7, wherein the positive electrode active material and the calcium compound are individually added, mixed with other constituent materials, and kneaded. It has a positive electrode containing the positive electrode material for nonaqueous electrolyte secondary batteries in any one of Claims 1-4, The nonaqueous electrolyte secondary battery characterized by the above-mentioned.

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