JP2013073867A - Positive electrode active material for nonaqueous electrolyte secondary battery and method for manufacturing the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent charge/discharge characteristics with which large current can be easily extracted while suppressing an additive amount of a conductive auxiliary material added to a positive electrode active material layer, in a nonaqueous electrolyte secondary battery.SOLUTION: There is provided a method for manufacturing a positive electrode active material for a nonaqueous electrolyte secondary battery, in which a positive electrode active material is irradiated with an electron beam with an exposure dose of 5 kGy or more and 3,000 kGy or less in a gaseous atmosphere. There are also provided a positive electrode active material for a nonaqueous electrolyte secondary battery, obtained by the manufacturing method, and a nonaqueous electrolyte secondary battery having a positive electrode manufactured using the positive electrode active material for the nonaqueous electrolyte secondary battery.

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery.

With the remarkable spread of portable electronic devices such as digital cameras and laptop computers, demand for lithium ion secondary batteries, which are a type of non-aqueous electrolyte secondary battery, is increasing as a power source. A lithium ion secondary battery has a smaller memory effect than a secondary battery such as a nickel cadmium battery, and thus is particularly suitable for a portable electronic device that performs additional charging such as a mobile phone.
In addition, the lithium ion secondary battery has an advantage that a high voltage is obtained because the lithium ion is small and the energy density is high and a non-aqueous electrolyte is used. Therefore, in addition to portable electronic devices such as notebook computers, research and development for application to next-generation electric industry products such as electric bicycles and electric vehicles are being promoted.

As an outer package of a lithium ion secondary battery, the battery contents are stored in a can type in which the battery contents are stored in a rectangular or cylindrical metal can, and an outer package formed by a flexible film. A laminate type (laminate type) is known. In a can-type lithium ion secondary battery, a laminate in which a positive electrode layer, a separator layer, and a negative electrode layer are sequentially laminated is accommodated in a metal can in a flat shape or in a wound and cylindrical shape. . In a laminate-type lithium ion secondary battery, a stacked body in which a positive electrode layer, a separator layer, and a negative electrode layer are sequentially stacked is stored in an outer package in a flat shape. The positive electrode layer and the negative electrode layer are connected to terminals for taking out a potential difference in each active material as a current, and the exterior body is filled with a non-aqueous electrolyte.
In any type of lithium ion secondary battery, the positive electrode layer and the negative electrode layer are called so-called active materials that can occlude and release lithium ions on a sheet-like current collecting base material (current collector). A laminate in which active material layers containing particles are laminated is used.

As a positive electrode active material for forming a positive electrode layer of a lithium ion secondary battery, a lithium-containing transition metal oxide is known. For example, there are LiCoO ₂ (theoretical capacity 274 mAh / g), LiMn ₂ O ₄ (theoretical capacity 148 mAh / g), LiNiO ₂ (theoretical capacity 274 mAh / g), and a compound in which 2 to 3 transition metal elements are mixed. Can be mentioned. Practical discharge capacities are about 120 to 140 mAh / g for LiCoO ₂ , 110 mAh / g for LiMn ₂ O ₄ , and about 160 to 200 mAh / g for LiNiO ₂ .

Since the positive electrode active material is not very high in electrical conductivity, it is mixed with a conductive auxiliary material such as carbon black or carbon fiber material, and the positive electrode active material is secured by binding with a binder. And a nonaqueous electrolyte solution osmose | permeates between these positive electrode active materials and a conductive support material, and a battery reaction arises because the de-insertion reaction of lithium ion occurs.
The lithium ion deinsertion reaction is a reaction that occurs between the positive electrode active material and the non-aqueous electrolyte, and the conductive auxiliary material does not contribute. Therefore, in order to increase the efficiency of the reaction and improve the charge / discharge characteristics, it is preferable that the addition amount of the conductive auxiliary material is as small as possible within a range in which conduction is ensured. However, particularly in large applications such as hybrid vehicles and electric vehicles, it is necessary to extract a large current, so that the amount of conductive auxiliary material added is very large in order to increase the conductivity of the positive electrode. Further, when the amount of the conductive auxiliary material added increases, the amount of the binder added to bind the conductive auxiliary material and the positive electrode active material inevitably increases.
Thus, since the proportion of the positive electrode active material in the positive electrode active material layer decreases as the addition amount of the conductive auxiliary material and the binder increases, the positive electrode must be made thick in order to extract a large amount of power. In other words, there is a problem that the battery becomes large.

By the way, in the negative electrode, in order to improve the capacity | capacitance characteristic and cycling characteristic of a battery, the method of irradiating an electron beam to a negative electrode active material and activating this negative electrode active material is known (patent document 1).
However, according to the above method, although the performance of the negative electrode is improved, the above-mentioned problem cannot be solved for the positive electrode.

JP 2005-276845 A

  The present invention improves the charge / discharge characteristics of a non-aqueous electrolyte secondary battery and can extract a large current while suppressing the amount of conductive auxiliary material and binder added to the positive electrode active material layer. It aims at providing the positive electrode active material for water electrolyte secondary batteries, its manufacturing method, and the nonaqueous electrolyte secondary battery using the said positive electrode active material for non-aqueous electrolyte secondary batteries.

  The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is a method characterized by irradiating a positive electrode active material with an electron beam at an irradiation dose of 5 kGy to 3000 kGy in a gas atmosphere. .

The positive electrode active material is preferably a positive electrode active material made of a light metal-containing transition metal oxide.
The light metal-containing transition metal oxide is from LiM ¹ ₂ O ₄ , LiM ² PO ₄ , LiM ³ VO ₄ and LiM ⁴ O ₂ (wherein M ^{1 to} M ⁴ are each one or more metal elements). It is preferable to include at least one selected from the group consisting of:
M ¹ in the LiM ¹ ₂ O ₄ preferably contains one or more selected from the group consisting of Mn, Al and Mg.
M ² in the LiM ² PO ₄ preferably contains at least one of Mn and Fe.
M ³ in LiM ³ VO ₄ preferably contains one or more selected from the group consisting of Mn, Ni, Co, and Fe.
M ⁴ in LiM ⁴ O ₂ preferably contains one or more selected from the group consisting of Mn, Ni, Co, and Al.

  The positive electrode active material for nonaqueous electrolyte secondary batteries of the present invention is a positive electrode active material obtained by the method for producing a positive electrode material for nonaqueous electrolyte secondary batteries of the present invention.

The non-aqueous electrolyte secondary battery of the present invention is a positive electrode that forms the positive electrode in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting light metal ions, and a non-aqueous electrolyte. The active material is a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention.
The light metal ion is preferably a lithium ion.

According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte secondary battery is controlled while suppressing the amount of conductive auxiliary material and binder added to the positive electrode active material layer. Thus, a positive electrode active material for a non-aqueous electrolyte secondary battery capable of improving the charge / discharge characteristics of the battery and taking out a large current can be obtained.
In addition, if the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is used, the amount of the conductive auxiliary material and binder added to the positive electrode active material layer is suppressed, and the non-aqueous electrolyte secondary battery Charge / discharge characteristics can be improved, and a large current can be taken out.
Moreover, since the non-aqueous electrolyte secondary battery of the present invention uses the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, it has excellent charge / discharge characteristics capable of extracting a large current. Yes.

It is the schematic block diagram which showed an example of the electron beam irradiation apparatus. 2 is a graph showing the particle size distribution of positive electrode ink in Example 1. FIG. It is the graph which showed the relationship between the cycle number in Examples 1-11, and a discharge capacity maintenance factor. 4 is a graph showing the relationship between the number of cycles for each electron beam irradiation dose to the positive electrode active material and the discharge capacity retention rate in Example 1. FIG. It is the graph which showed the relationship between the cycle number in Comparative Examples 1-13, and a discharge capacity maintenance factor. It is the graph which showed the relationship between the cycle number and discharge capacity maintenance factor in Example 1 and Comparative Examples 1, 12, and 13.

[Positive electrode active material for non-aqueous electrolyte secondary battery and method for producing the same]
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is a method characterized by irradiating a positive electrode active material with an electron beam at an irradiation dose of 5 kGy to 3000 kGy in a gas atmosphere. . The positive electrode active material is activated by irradiating the electron beam with the irradiation dose in the above range, the charge / discharge characteristics of the positive electrode are improved, and the addition amount of the conductive auxiliary material and the binder added to the positive electrode active material layer is suppressed. However, a large current can be taken out.

The positive electrode active material can be irradiated with an electron beam by using, for example, an electron beam irradiation apparatus such as a scan method, an area beam method, or a self-shielding method. Of these, a scanning electron beam irradiation apparatus is preferable from the viewpoint of versatility such as the amount of energy irradiation.
Specifically, for example, the electron beam irradiation apparatus 100 illustrated in FIG. The electron beam irradiation apparatus 100 includes a vacuum chamber 101 and a terminal 102 installed in the vacuum chamber 101. In the terminal 102, a filament 103, a repeller 104, and a grid 105 are provided.
An electron beam passage portion 106 made of a material capable of passing the electron beam 110 is provided on a part of the outer wall of the vacuum chamber 101 on the side irradiated with the electron beam 110 from the filament 103. A beam collector 107 is provided outside the electron beam passage 106 side of the vacuum chamber 101, and the inside is adjusted to a gas atmosphere at a predetermined temperature and pressure between the electron beam passage 106 and the beam collector 107. A shield tube 108 capable of transporting the positive electrode active material 111 is provided in the shield tube 108.
In electron beam irradiation using the electron beam irradiation apparatus 100, the inside of the shield tube 108 is adjusted to a gas atmosphere having a predetermined temperature and pressure. Then, while the positive electrode active material 111 is disposed and transported on the belt conveyor 109 in the shield tube 108, the electron beam 110 accelerated under high vacuum is irradiated from the filament 103 toward the beam collector 107. Thereby, the positive electrode active material 111 on the belt conveyor 109 is irradiated with the electron beam 110.

The electron beam applied to the positive electrode active material is preferably accelerated under high vacuum.
The degree of vacuum in the vacuum chamber 101, that is, the degree of vacuum when accelerating the electron beam is preferably 10 ⁻³ Pa or more and 10 ⁻⁵ Pa or less, and more preferably 10 ⁻⁴ Pa or more and 10 ⁻⁶ Pa or less. If the degree of vacuum is equal to or greater than the lower limit, the acceleration of the electron beam is enhanced. If the degree of vacuum is less than or equal to the upper limit value, the electron beam collides more uniformly with the target, and the transition metal-containing oxide is released from the target.
The electron beam applied to the positive electrode active material is preferably accelerated at 50 kV to 300 kV, and more preferably at 100 kV to 300 kV. If the acceleration voltage is equal to or higher than the lower limit, the electron beam is easily accelerated. If the acceleration voltage is equal to or lower than the upper limit value, the electron beam collides more uniformly with the target, and the transition metal-containing oxide is released from the target.

The atmosphere in the shield tube 108, that is, the gas atmosphere in the present invention is preferably a nitrogen gas atmosphere or an argon gas atmosphere from the viewpoint of vapor deposition in an inert gas atmosphere.
The temperature and pressure in the shield tube 108 are not particularly limited, and normal temperature and normal pressure conditions can be adopted.

The irradiation dose of the electron beam is 5 kGy or more because the positive electrode active material is activated and a secondary battery having excellent charge / discharge characteristics is obtained. Further, the irradiation dose of the electron beam is 3000 kGy or less because the destruction of the positive electrode active material is suppressed.
In addition, when using the electron beam irradiation apparatus 100, the electron beam irradiation dose (E) is represented by the following formula (i).
E = nk (I / v) (i)
However, in said Formula (i), n is the frequency | count of irradiation of the electron beam 110, k is an eigen constant of the electron beam irradiation apparatus 100, and I is a current value flowing between the filament 103 and the beam collector 107. , V is the conveying speed of the belt conveyor 109.

<Positive electrode active material>
As the positive electrode active material, a material capable of inserting and extracting lithium ions can be used. Examples thereof include light metal-containing transition metal oxides containing light metals, transition metal oxides not containing light metals, and transition metal sulfides. Among these, light metal-containing transition metal oxides are preferable from the viewpoint of producing a secondary battery.
A positive electrode active material may be used individually by 1 type, and may use 2 or more types together.

As the light metal-containing transition metal oxide, LiM ¹ ₂ O ₄ , LiM ² PO ₄ , LiM ³ VO ₄ and LiM ⁴ O ₂ (wherein M ^{1 to} M ⁴ are each one or more of metal elements). One or more lithium-containing transition metal oxides selected from the group consisting of Examples of the metal elements M ^{1 to} M ⁴ include Mn, Al, Mg, Fe, Ni, and Co.

M ¹ in LiM ¹ ₂ O ₄ preferably contains one or more selected from the group consisting of Mn, Al and Mg. _{Specifically, LiMn 2 O 4, LiMn 2} -x Mg x O 4, LiMn 2-x Al x O 4 ( provided that, 0 <x ≦ 0.3), and the like.
M ² in LiM ² PO ₄ preferably contains at least one of Mn and Fe. Specific examples include LiMnPO ₄ and LiFePO ₄ .
M ³ in LiM ³ VO ₄ preferably contains one or more selected from the group consisting of Mn, Ni, Co and Fe. Specific examples include LiMnVO ₄ , LiNiVO ₄ , LiCoVO ₄ , LiFeVO _{4, and the} like.
M ⁴ in LiM ⁴ O ₂ preferably contains one or more selected from the group consisting of Mn, Ni, Co, and Al. _{Specifically, LiMnO 2, LiNiO 2, LiCoO} 2, LiNi 5/9 Co 1/3 Mn 2/9 O 2, LiNi 0.85 Al 0.15 O 2 and the like.
As the lithium-containing transition metal oxide other than _{the, Li 2 MnO 3, Li 2} FeSiO 4 , and the like.
Examples of the transition metal oxide include V ₂ O ₅ and MoO ₃ .
Examples of the transition metal sulfide include TiS ₂ and amorphous MoS ₃ .

As the positive electrode active material, a group consisting of LiMn ₂ O ₄ , LiFePO ₄ , LiMnPO ₄ , LiCoO ₂ , LiNiO ₂ , LiNi _5/9 Co _1/3 Mn _2/9 O ₂ and LiMnVO ₄ from the viewpoint of battery reaction. One or more selected from are particularly preferred.

When irradiating the positive electrode active material with an electron beam, it is easy to sufficiently irradiate the entire positive electrode active material with an electron beam. Therefore, it is preferable to make the positive electrode active materials close to each other. It is more preferable to mold the material into a circular pellet. Thus, when making a positive electrode active material into a pellet, in order to irradiate an electron beam uniformly to the whole positive electrode active material, it is preferable to irradiate an electron beam from the front and back both sides of this pellet.
The diameter of the positive electrode active material pellet is preferably 5 mm to 300 mm, more preferably 10 mm to 150 mm.
The thickness of the positive electrode active material pellet is preferably 0.1 mm or less, more preferably 0.05 mm or less, because the electron beam is easily irradiated uniformly.

By irradiating the positive electrode active material with a predetermined electron beam by the above method, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is obtained.
In the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention described above, the positive electrode active material itself is activated by irradiation with an electron beam having an irradiation dose of 5 kGy to 3000 kGy. Therefore, if the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is used, excellent charge / discharge that can extract a large current while suppressing the amount of conductive auxiliary material and binder added to the positive electrode active material layer A non-aqueous electrolyte secondary battery having characteristics can be manufactured.

[Nonaqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode capable of inserting and extracting light metal ions, a negative electrode capable of inserting and extracting light metal ions, and a non-aqueous electrolyte, and forms the positive electrode. The positive electrode active material is the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention described above. That is, the nonaqueous electrolyte secondary battery of the present invention can employ a known mode except that the positive electrode active material for a nonaqueous electrolyte secondary battery of the present invention is used as the positive electrode active material.

The nonaqueous electrolyte secondary battery of the present invention is preferably a lithium ion secondary battery. That is, it is preferable that the light metal ions occluded and released by the positive electrode and the negative electrode are lithium ions.
As the structure of the non-aqueous electrolyte secondary battery of the present invention, for example, in the case of a lithium ion secondary battery, the battery contents can be encapsulated in a can type in which the battery contents are enclosed in a metal can or a flexible film is molded. Examples include a laminate type (laminated type) in which an object is enclosed.
In a can-type lithium ion secondary battery, for example, a laminate in which a positive electrode layer, a separator layer, and a negative electrode layer are sequentially laminated is flattened or wound into a cylindrical shape in a metal can. Stored. In a laminate-type lithium ion secondary battery, for example, a stacked body in which a positive electrode layer, a separator layer, and a negative electrode layer are sequentially stacked is housed in an outer package in a flat shape. The positive electrode active material layer, the separator layer, and the negative electrode active material layer are entirely filled with a non-aqueous electrolyte.
Further, the positive electrode layer and the negative electrode layer are provided with terminals for taking out a potential difference in each active material as a current.

<Positive electrode>
As the positive electrode, for example, a current collecting base material and a positive electrode active material layer formed on the current collecting base material and including the positive electrode active material for the non-aqueous electrolyte secondary battery of the present invention, the conductive auxiliary material, and the binder And a laminate having the following.

As a material for forming the current collecting base material of the positive electrode, a conductive substance is preferable because it is easy to flow a high current. Specific examples include copper, nickel, stainless steel, iron, and aluminum. Among these, aluminum is preferable from the viewpoint of relatively low cost and metal ionization tendency.
As the current collecting base material of the positive electrode, rolled aluminum foil is preferable. In the rolled aluminum foil, since the aluminum crystals are arranged in the rolling direction, even if stress is applied, the current collecting base material is hardly broken, and the moldability is improved.

A positive electrode active material layer is a layer containing the positive electrode active material for nonaqueous electrolyte secondary batteries of this invention, a conductive support material, and a binder.
As the conductive auxiliary material, a substance that can ensure the conductivity of the current collecting base material and does not cause a chemical reaction during charge and discharge is preferable. Examples thereof include carbon-based materials such as acetylene black, ketjen black, channel black, and furnace black, metal fibers, conductive polymers, carbon fluoride, and metal powder. Of these, acetylene black and ketjen black are particularly preferable.
A conductive auxiliary material may be used individually by 1 type, and may use 2 or more types together.

As the binder, a polymer that is chemically stable with respect to the dispersion solvent described later is preferable. For example, resin polymers such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), aromatic polyamide, rubber polymers such as styrene / butadiene rubber (SBR) and ethylene / propylene rubber, polyvinylidene fluoride ( PVDF) and fluorine-based polymers such as polytetrafluoroethylene. Of these, fluorine-based polymers such as PVDF and polytetrafluoroethylene are preferred from the viewpoint of improving the adhesion between the current collecting base material and the positive electrode active material and the adhesion between the positive electrode active material.
A binder may be used individually by 1 type and may use 2 or more types together.

The content of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention in the positive electrode active material layer (100% by mass) is preferably 1% by mass to 99% by mass, and more preferably 90% by mass to 98% by mass. More preferred. If the content of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is equal to or higher than the lower limit value, excellent charge / discharge characteristics are easily obtained. When the content of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is not more than the upper limit value, an electrode having a high energy density is easily obtained.
The content of the conductive auxiliary material in the positive electrode active material layer (100% by mass) is preferably 0% by mass to 8% by mass, and more preferably 1% by mass to 2% by mass. The higher the content of the conductive auxiliary material, the easier it is to obtain an electrode with a higher energy density. If the content of the conductive auxiliary material is not more than the upper limit value, a low-resistance electrode is easily obtained.
1 mass% or more and 10 mass% or less are preferable, and, as for content of the binder in a positive electrode active material layer (100 mass%), 1 mass% or more and 2 mass% or less are more preferable. If the content of the binder is not less than the lower limit value, an electrode having a high energy density is easily obtained. If the content of the binder is not more than the upper limit value, it is easy to obtain an electrode having good mechanical strength of the positive electrode active material layer and excellent long life.

(Production method of positive electrode)
The positive electrode can be manufactured, for example, by a method having the following coating process, drying process, and pressing process.
Coating step: A step of applying a positive electrode ink containing the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, a conductive auxiliary material, and a binder on the current collecting base material.
Drying step: a step of drying the positive electrode ink coated on the current collecting base material.
Pressing step: a step of pressing the dried positive electrode ink film to form a positive electrode active material layer.

Coating process:
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, a conductive auxiliary material, and a binder are dispersed in a solvent, kneaded to prepare a slurry-like positive electrode ink, and the positive ink is placed on a current collecting substrate. Apply.
In preparing the positive electrode ink, the mixing method and mixing order of the materials are not particularly limited.
As a kneader for kneading each material, a kneader capable of imparting high shear is preferable. Specifically, a blade type stirrer such as a planetary mixer, a kneader, a homogenizer, an ultrasonic homogenizer, or a disperser is preferable, and a planetary mixer is particularly preferable from the viewpoint of kneading.

The positive electrode ink is preferably defoamed after kneading. In particular, from the viewpoint of uniformly removing the gas component in the positive electrode ink, it is particularly preferable to perform deaeration of the planet while evacuating.
Examples of the defoaming device for defoaming the positive ink include a vacuum defoaming device, a centrifugal defoaming device, and a planetary defoaming device.

As a solvent used for the positive electrode ink, water, an aqueous solvent obtained by mixing ethanol, N-methylpyrrolidone (NMP) or the like with water, a cyclic amide solvent such as NMP, N, N-dimethylformamide, or N, N-dimethyl is used. Examples thereof include linear amide solvents such as acetamide and aromatic hydrocarbons such as toluene and xylene.
These solvents may be used alone or in combination of two or more.

The content of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention in the positive electrode ink (100% by mass) is preferably 30% by mass to 70% by mass, and more preferably 40% by mass to 55% by mass. . If content of the positive electrode active material for nonaqueous electrolyte secondary batteries is more than a lower limit, it will be easy to suppress sedimentation of a positive electrode active material. If content of the positive electrode active material for nonaqueous electrolyte secondary batteries is below an upper limit, it will be easy to suppress aggregation of a positive electrode active material.
The content of the conductive auxiliary material in the positive electrode ink is preferably 0.5 parts by mass or more and 20 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. If content of a conductive auxiliary material is more than a lower limit, an electrode with a high energy density will be easy to be obtained. If the content of the conductive auxiliary material is not more than the upper limit value, a low-resistance electrode is easily obtained.
The content of the binder in the positive electrode ink is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. When the content of the binder is equal to or higher than the lower limit value, the adhesion between the positive electrode active materials or between the positive electrode active material and the current collecting base material is improved. If the content of the binder is not more than the upper limit value, it is easy to contain a sufficient amount of the positive electrode active material, and the battery capacity is improved.

Moreover, you may add a thickener to positive electrode ink according to a required viscosity.
As the thickener, polymer materials such as carboxymethyl cellulose (CMC) and polyethylene glycol are preferable.
A thickener may be used individually by 1 type and may use 2 or more types together.

As a coating method of the positive electrode ink, a general wet material coating method can be adopted, and the coating can be performed in accordance with physical properties such as the viscosity of the slurry-like positive electrode ink. Examples thereof include gravure coating, micro gravure coating, die coating, dip coating, slit coating, comma coating, lip coating, and direct coating.
The thickness of the coating film of the positive ink is preferably 0.01 mm or more and 1 mm or less, and more preferably 0.03 mm or more and 0.2 mm or less.

Drying process:
The method of drying the coating film of the positive electrode ink may be any method that can keep the solvent in the positive electrode active material layer, such as warm air drying in a small drying oven, hot air drying, vacuum drying, far infrared drying, Constant temperature and high humidity drying is preferred. These drying methods may be performed singly or in combination of two or more.
In hot air drying, the air volume, the wind contact angle, the distance from the outlet, and the like affect the drying efficiency, so these conditions are selected as appropriate.
Furthermore, when coating and drying are continuously performed by a roll-to-roll method, drying may be performed by a roll support, floating, or the like, or a combination of these may be performed.
The amount of residual solvent in the coated film after drying is preferably as small as possible, preferably 1% by mass or less, and more preferably 0.5% by mass or less.

Pressing process:
In order to improve the energy density per unit area, the coating film is pressed after reheating or while reheating to obtain a positive electrode active material layer. Examples of the pressing method include a metal roll pressing method, a rubber roll pressing method, and a flat plate pressing method.

The bulk density of the positive electrode active material layer after pressing is preferably 1.0 g / cm ² or more and 5.0 g / cm ² or less. If the bulk density of the positive electrode active material layer is 1.0 g / cm ² or more, the binder can be sufficiently present in the vicinity of the current collecting substrate, and the adhesion between the positive electrode active material layer and the current collecting substrate is improved. . When the bulk density of the positive electrode active material layer is 5.0 g / cm ² or less, sufficient voids are obtained in the positive electrode active material layer, and the non-aqueous electrolyte easily penetrates into the positive electrode active material layer, thereby improving battery performance. .

<Negative electrode>
As a negative electrode, the laminated body which has a current collection base material and a negative electrode active material layer formed on a current collection base material and containing a negative electrode active material, a conductive support material, and a binder is mentioned, for example.
Examples of the material for the current collecting base material of the negative electrode include those listed as the materials for the current collecting base material of the positive electrode. Among these, copper is preferable from the viewpoint of being relatively inexpensive and the tendency of metal ionization.
As the current collecting base material for the negative electrode, rolled copper foil is preferable among copper. In the rolled copper foil, since the copper crystals are arranged in the rolling direction, the current collecting base material is not easily broken even when stress is applied, and the moldability is improved. On the other hand, the rolled copper foil has a length restriction due to its production method, and therefore, an electrolytic copper foil is preferred from the viewpoint of no length restriction due to the production process.

The negative electrode active material layer is a layer including a negative electrode active material, a conductive auxiliary material, and a binder.
As the negative electrode active material, amorphous carbon, natural graphite, artificial graphite, mesocarbon micro beads (MCMB), carbon materials such as hard carbon, oxide materials such as Li ₄ Ti ₅ O ₄ , SiO ₂ , lithium metal alloy And lithium metal. Of these, artificial graphite and natural graphite are preferred because they are widely used industrially, are inexpensive and easy to handle.

Examples of the conductive auxiliary material for the negative electrode active material layer include the same conductive auxiliary materials as those described for the positive electrode active material layer, and preferred embodiments are also the same.
Examples of the binder for the negative electrode active material layer include the same materials as those described for the positive electrode active material layer. Of these, fluorine polymers such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene, and rubber polymers such as styrene / butadiene rubber (SBR) and ethylene / propylene rubber are preferable.

1 mass% or more and 99 mass% or less are preferable, and, as for content of the negative electrode active material in a negative electrode active material layer (100 mass%), 90 mass% or more and 98 mass% or less are more preferable. When the content of the negative electrode active material is at least the lower limit value, excellent charge / discharge characteristics are easily obtained. If content of a negative electrode active material is below an upper limit, an electrode with a high energy density will be easy to be obtained.
The content of the conductive auxiliary material in the negative electrode active material layer (100% by mass) is preferably 0% by mass to 8% by mass, and more preferably 1% by mass to 2% by mass. The higher the content of the conductive auxiliary material, the easier it is to obtain an electrode with a higher energy density. If the content of the conductive auxiliary material is not more than the upper limit value, a low-resistance electrode is easily obtained.
The content of the binder in the negative electrode active material layer (100% by mass) is preferably 1% by mass to 10% by mass, and more preferably 1% by mass to 2% by mass. If the content of the binder is not less than the lower limit value, an electrode having a high energy density is easily obtained. If the content of the binder is not more than the upper limit value, it is easy to obtain a low resistance electrode.

The manufacturing method of a negative electrode active material layer is not specifically limited, For example, it can manufacture by the method similar to the above-mentioned positive electrode active material layer except using a negative electrode active material instead of a positive electrode active material.
The bulk density of the negative electrode active material layer after pressing is preferably 1.0 g / cm ² or more and 3.0 g / cm ² or less. If the bulk density of the negative electrode active material layer is 1.0 g / cm ² or more, the binder can be sufficiently present in the vicinity of the current collecting substrate, and the adhesion between the negative electrode active material layer and the current collecting substrate is improved. . When the bulk density of the negative electrode active material layer is 3.0 g / cm ² or less, sufficient voids are obtained in the negative electrode active material layer, and the nonaqueous electrolyte easily penetrates into the negative electrode active material layer, thereby improving battery performance. .

<Separator>
As a material for forming the separator, a porous sheet-like polymer that transmits light metal ions and does not change in quality by the nonaqueous electrolytic solution is preferable. Specific examples include olefin-based sheet polymers such as polyethylene (PE) and polypropylene (PP), and sheet polymers such as polyimide and polyaramid.

  When the separator is formed of a sheet-like polymer, the thickness varies depending on the application of the non-aqueous electrolyte secondary battery, but is preferably 40 to 60 μm for large industrial applications such as automobiles. The pore diameter is preferably 1 μm or less, and the porosity is preferably 20 to 80%.

Nonwoven fabric can also be used as a material for forming the separator.
Nonwoven fabrics include cotton, rayon, acetate, nylon, polyester, polyolefin resin, polyimide, aramid, and the like. These nonwoven fabrics may be used alone or in combination of two or more.
The bulk density of the nonwoven fabric is not particularly limited. The porosity of the nonwoven fabric is preferably 30 to 90%. The thickness of the nonwoven fabric is preferably 5 to 200 μm. If the thickness of the non-woven fabric is 5 μm or more, the non-aqueous electrolyte can be better retained. If the thickness of the nonwoven fabric is 200 μm or less, the internal resistance becomes smaller.

<Non-aqueous electrolyte>
As the non-aqueous electrolyte, a known non-aqueous electrolyte can be used.
Non-aqueous electrolyte solvents include ether solvents such as diethyl ether and ethylene glycol phenyl ether, amide solvents such as formamide and N-ethylformamide, sulfide solvents such as dimethyl sulfoxide and sulfolane, ethylene carbonate, propylene Examples thereof include carbonate solvents such as carbonate, and organic solvents such as γ-butyrolactone and NMP. Of these, carbonate solvents such as ethylene carbonate and propylene carbonate are preferred. These solvents may be used alone or in combination of two or more.

As an electrolyte contained in the nonaqueous electrolytic solution, a lithium salt is preferable. That is, in the nonaqueous electrolyte secondary battery of the present invention, it is preferable that the light metal ions occluded and released in the positive electrode and the negative electrode are lithium ions.
Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiCl, LiBF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO _{2 and the} like. Among these, LiPF ₆ is preferable from the viewpoint of good withstand voltage characteristics.

<Method for producing non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention can be produced by a known method except that the positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is used.
For example, the positive electrode layer and the negative electrode layer manufactured by the above-described method are laminated via a separator so that the positive electrode layer and the negative electrode layer are not touched, and wound as necessary to form a coin shape, a square shape, A non-aqueous electrolyte secondary battery can be obtained by enclosing it together with a non-aqueous electrolyte in a cylindrical or laminated outer package.
When manufacturing a non-aqueous electrolyte secondary battery, work in a dry room that has an atmosphere with a low dew point (-50 ° C. or lower), a glove box with argon gas in a volume of 95 volume% to 100 volume%, It is essential to prevent moisture from entering the non-aqueous electrolyte secondary battery.

The non-aqueous electrolyte secondary battery of the present invention described above uses the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention activated by irradiation with an electron beam with an irradiation dose of 5 kGy to 3000 kGy. Therefore, it has an excellent charge / discharge characteristic that can extract a large current.
The nonaqueous electrolyte secondary battery of the present invention is not limited to the above-described lithium ion secondary battery. For example, a non-aqueous electrolyte secondary battery in which light metal ions occluded and released by the positive electrode and the negative electrode are sodium ions, calcium ions, and magnesium ions may be used.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Example 1]
<Surface treatment of positive electrode active material>
LiMn ₂ O ₄ (specific gravity 4.2, made by Mitsui Kinzoku, Type-F) was used as the positive electrode active material, and 35 mg of LiMn ₂ O ₄ was applied to the surface of a stainless steel current collector having an area of 2 cm ² at 4 t / cm. The resultant was pressure-bonded at a pressure of ² to produce a pellet having a thickness of about 0.1 mm. Next, both sides of the obtained pellet were irradiated with an electron beam with an irradiation dose of 5 kGy (acceleration voltage 50 kV) using the electron beam irradiation apparatus 100 illustrated in FIG.
Moreover, the pellet which irradiated the electron beam was obtained by the method similar to the above except having changed the irradiation dose into 1000 kGy (acceleration voltage 250 kV) and 3000 kGy (acceleration voltage 300 kV).
In the positive electrode active material having a specific gravity of 3 to 5, the penetration depth of the electron beam is 0.05 mm from the material surface. Therefore, if an electron beam is irradiated on both sides of a 0.1 mm thick pellet, it can be considered that the positive electrode active material in almost the entire area of the pellet is irradiated with an electron beam.
The following was performed in the same manner using three types of pellets with different electron beam irradiation doses.

<Preparation of positive electrode ink>
In a kneading machine Hibismix kettle manufactured by Primics, the positive electrode active material pellets, Denka black (HS100, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive auxiliary material, and polyvinylidene fluoride (PVDF) (#) as a binder (# 7200, manufactured by Kureha Co., Ltd.) at a ratio of positive electrode active material: conductive auxiliary material: binder (mass ratio) = 100: 2: 3, kneaded for 120 minutes, and then N-methyl-2-pyrrolidone ( NMP) (manufactured by Mitsubishi Chemical Co., Ltd.) was added so that the solid content was 80% by mass, and the mixture was stirred with a blade at a rotation speed of 102 rpm to prepare a powder-liquid lump in a funicular state. Next, the mass was kneaded in the Hibismix at a rotation speed of 102 rpm for 30 minutes, and then NMP was added in small portions about 5 times so that the solid content was 65% by mass to prepare 500 g of positive electrode ink.

<Manufacture of positive electrode>
Aluminum foil (Nippon Foil Co., Ltd., thickness 15 μm) is used as a current collecting base material, and the positive electrode ink is spread over the current collecting base material with a YA-C applicator having a slit clearance of 100 μm over a width of 10 cm and a length of 40 cm. After coating and drying in an oven at 80 ° C. for 45 minutes, the four corners are attached to a hydraulic metal roll with cello tape (registered trademark) (manufactured by Nichiban Co., Ltd.) and subjected to pressure molding at a linear pressure of 98000 N / cm, A positive electrode was obtained.

<Preparation of negative electrode ink>
A natural graphite (manufactured by Hitachi Chemical Co., Ltd., SMG), which is a negative electrode active material, and artificial graphite (manufactured by TIMCAL, SFG-6), which is a conductive auxiliary material, are added to a kneader Hibismix kettle manufactured by Primix. : Conductive auxiliary material (mass ratio) = 91: 7, and after kneading for 120 minutes, NMP (manufactured by Mitsubishi Chemical Corporation) is added so that the solid content is 65% by mass, and the rotational speed is 40 rpm. Stir with a blade. Thereafter, PVDF (# 7200, manufactured by Kureha Co.), which is a binder, was further added so that the total amount of the negative electrode active material and the conductive auxiliary material and the mass ratio of the binder was 98: 2, and the solid content was NMP was added so that it might become 50 mass%, and it stirred at 30 rpm for 30 minutes, and prepared 500 g of negative electrode inks.

<Manufacture of negative electrode>
A copper foil (made by Mitsui Kinzoku Co., Ltd., thickness 12 μm) is used as a current collecting base material, and the negative ink is spread over the current collecting base material by a YA-C applicator having a slit clearance of 100 μm over a width of 11 cm and a length of 40 cm. After coating and drying in an oven at 80 ° C. for 45 minutes, the four corners are attached to a hydraulic metal roll with cello tape (registered trademark) (manufactured by Nichiban Co., Ltd.) and subjected to pressure molding at a linear pressure of 300 N / cm, A negative electrode was obtained.

[Examples 2 to 11]
A positive electrode and a negative electrode were obtained in the same manner as in Example 1 except that the positive electrode active material used was changed as shown in Table 1.
Incidentally, LiFePO ₄ was _{used, LiMnPO 4, LiMnVO 4, LiNiVO} 4, LiCoVO 4, LiFeVO 4, LiCoO 2, LiNiO 2, LiNi 0.85 Al 0.15 O 2 and _LiNi 5/9 _Co 1/3 _{Mn 2 /} The specific gravity of ₉ O ₂ is in the range of 3-5.

[Comparative Examples 1 to 11]
The positive electrode active material to be used was changed as shown in Table 1, and a positive electrode and a negative electrode were obtained in the same manner as in Example 1 except that the positive electrode active material was not irradiated with an electron beam.

[Comparative Example 12]
A positive electrode and a negative electrode were obtained in the same manner as in Example 1 except that the irradiation dose was 3 kGy (acceleration voltage 30 kV) in the electron beam irradiation of the positive electrode material.

[Comparative Example 13]
A positive electrode and a negative electrode were obtained in the same manner as in Example 1 except that the irradiation dose was 3500 kGy (acceleration voltage 320 kV) in the electron beam irradiation of the positive electrode material.

In each example, the particle size distribution was measured for each of the prepared positive electrode inks, and the pore distribution was measured for each of the manufactured positive electrode electrodes. Moreover, the coin cell was manufactured using the manufactured positive electrode and negative electrode, and the charge / discharge characteristic was evaluated. Each measuring method and evaluation method are shown below.
[Measurement of particle size distribution]
About the prepared positive electrode ink, using a Multisizer 4 (manufactured by Beckman Coulter, Inc.), a constant minute current is passed, and the volume of the particle is obtained from the resistance value of the electrode when the particle flows in an aperture having a diameter of 50 μm. Was measured.
For the particle size distribution, the measurement was repeated three times, the accuracy was confirmed to be 95% or more, and the average value of the measured values was taken.

[Measurement of pore distribution]
A 5 cm × 5 cm square sample was cut out from the produced positive electrode, and the porosity of pores in the positive electrode active material layer in the range of 30 nm to 10 μm was measured using a mercury intrusion porosimeter.

[Evaluation of charge / discharge characteristics]
A positive electrode obtained in each example was punched into a disk shape having a diameter of 15 mm, and a negative electrode was punched into a disk shape having a diameter of 16.5 mm to prepare a coin cell, and charge / discharge characteristics were evaluated.
As a separator of the coin cell, a polypropylene porous film having a thickness of 25 μm is used, and as a non-aqueous electrolyte, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and lithium hexafluorophosphate ( A liquid (manufactured by Kishida Chemical Co., Ltd.) in which LiPF ₆ ) was mixed at a mass ratio of 1: 1: 1: 1 was used.
Using the produced coin cell, after charging to 4.5V at a constant current (0.2C), discharging to 3.0V at a constant current (2C) and measuring the discharge capacity was performed 2000 cycles. The maintenance rate was measured. The discharge capacity retention rate (%) was defined as the ratio of the discharge capacity after each cycle to the discharge capacity after one cycle. The discharge capacity retention rate was measured by preparing five coin cells for each positive electrode and measuring the average value thereof.

  The measurement results of the particle size distribution of the positive electrode ink and the pore distribution of the positive electrode active material layer and the evaluation results of the charge / discharge characteristics in Examples 1 to 11 and Comparative Examples 1 to 13 are shown in Tables 1 and 2 and FIGS. . The results of the discharge capacity retention rates in the examples of FIGS. 3 and 6 are the results when the irradiation dose of the electron beam to the positive electrode active material is 1000 kGy (acceleration voltage 250 kV). The results of FIGS. 2 to 6 are data in one coin cell before averaging.

  As shown in Table 1, Table 2 and FIG. 2, in Examples 1 to 11 and Comparative Examples 1 to 13, the particle size distribution of the positive ink when the same type of positive electrode active material is used is that of electron beam irradiation. It is almost the same regardless of the presence or absence and the irradiation dose, and it is considered that the solid content was dispersed to the same extent in the positive electrode ink. In addition, the pore distribution in the positive electrode active material layer is almost the same regardless of the presence or absence of electron beam irradiation and the difference in irradiation dose, and the impregnation of the non-aqueous electrolyte into the positive electrode active material layer of the positive electrode is the same. It is thought to be about.

Moreover, as shown in Table 1 and FIGS. 3, 4, and 6, in Examples 1 to 11 using the positive electrode active material irradiated with the electron beam under the irradiation dose of 5 kGy or more and 3000 kGy or less, the discharge capacity was maintained even after 2000 cycles. The rate exceeded 90%, and excellent charge / discharge characteristics were obtained. In other words, the positive electrodes in these examples can easily take out a large current. This is because the positive electrode active material is activated by electron beam irradiation, and the reaction at the interface between the positive electrode active material and the non-aqueous electrolyte and between the positive electrode active material and the conductive auxiliary material proceeds more rapidly. Conceivable.
On the other hand, as shown in Table 2 and FIGS. 5 and 6, in Comparative Examples 1 to 11 using the positive electrode active material not irradiated with the electron beam, the discharge capacity retention rate after 2000 cycles is less than 80%, which is the same. Charge / discharge characteristics were inferior to Examples 1 to 11 using various types of positive electrode active materials.
Moreover, in Comparative Example 12 using LiMn ₂ O ₄ irradiated with an electron beam under the condition of an irradiation dose of 3 kGy as a positive electrode active material, the discharge capacity retention rate after 2000 cycles is LiMn ₂ O ₄ not irradiated with an electron beam. And comparable to that of Comparative Example 1 in which no electron beam irradiation effect was observed.
Moreover, in Comparative Example 13 using LiMn ₂ O ₄ irradiated with an electron beam under the condition of an irradiation dose of 3500 kGy as the positive electrode active material, although the discharge capacity maintenance rate after 2000 cycles is slightly improved, the irradiation dose is 5 kGy or more and 3000 kGy. the following LiMn ₂ O ₄ lower than that of example 1 using irradiated with electron beam under conditions, charge and discharge characteristics was poor. This is presumably because a part of the positive electrode active material was deactivated by the excessive electron beam irradiation.

  By using the positive electrode active material obtained by the production method of the present invention, a positive electrode having excellent charge / discharge characteristics that can easily take out a large current while reducing the amount of conductive auxiliary material and binder added to the positive electrode active material layer An electrode can be manufactured. Therefore, the material cost can be reduced, the manufacturing process of the positive electrode can be simplified, and it can greatly contribute to the cost reduction of the non-aqueous electrolyte secondary battery.

DESCRIPTION OF SYMBOLS 100 Electron beam irradiation apparatus 101 Vacuum chamber 102 Terminal 103 Filament 104 Repeller 105 Grid 106 Electron beam passage part 107 Beam collector 108 Shield pipe 109 Belt conveyor 110 Electron beam 111 Positive electrode active material

Claims (10)

  A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material is irradiated with an electron beam at an irradiation dose of 5 kGy to 3000 kGy in a gas atmosphere.   The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 1 whose said positive electrode active material is a positive electrode active material which consists of a light metal containing transition metal oxide. The light metal-containing transition metal oxide is LiM ¹ ₂ O ₄ , LiM ² PO ₄ , LiM ³ VO _4, and LiM ⁴ O ₂ (where M ^{1 to} M ⁴ are each one or more metal elements). The manufacturing method of the positive electrode active material for non-aqueous-electrolyte secondary batteries of Claim 2 containing 1 or more types chosen from the group which consists of. The ^LiM ₁ ^{M 1} in 2 _{O 4} is, Mn, containing at least one member selected from the group consisting of Al, Mg, method for producing a cathode active material for nonaqueous electrolyte secondary battery according to claim 3. The ^{LiM M 2} in 2 PO ₄ comprises at least one of Mn and Fe, the manufacturing method of the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 3. The ^LiM 3 ^{M 3} in VO ₄ is, Mn, Ni, containing at least one member selected from the group consisting of Co and Fe, the manufacturing method of the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 3. The ^{LiM 4} _{O 2} ^M 4 in the, Mn, Ni, containing at least one member selected from the group consisting of Co and Al, the manufacturing method of the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 3.   The positive electrode active material for nonaqueous electrolyte secondary batteries obtained by the manufacturing method of the positive electrode material for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-7. In a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of occluding and releasing light metal ions, and a non-aqueous electrolyte,
The positive electrode active material which forms the said positive electrode is the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 8, The nonaqueous electrolyte secondary battery characterized by the above-mentioned.   The non-aqueous electrolyte secondary battery according to claim 9, wherein the light metal ion is lithium ion.

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