JP2014093271A - Nonaqueous electrolytic secondary battery electrode, battery using the same, and method for manufacturing such electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture, by use of an active material mixture, a nonaqueous electrolytic secondary battery electrode which is stable in shape, provided that the active material mixture includes an electrode active material of a transition metal oxide and a binding material dispersed in water.SOLUTION: A method for manufacturing a nonaqueous electrolytic secondary battery electrode comprises the steps of: preparing an active material mixture by dispersing, in water, particles of a transition metal oxide and/or transition metal complex oxide which has an average particle diameter of 1-20 μm, and which lithium ions can be caused to intrude into and can be desorbed from, and particles of a binding material having an average particle diameter of 0.10-0.30 μm; and applying the active material mixture to a current collector, followed by drying.

Description

  The present invention relates to an electrode for a nonaqueous electrolyte secondary battery, a battery using the same, and a method for producing the electrode.

  Lithium ion storage batteries are currently widely used as power sources for mobile devices. Lithium ion storage batteries are expected to be used for large power supplies such as electric vehicles and power storage because they have a higher energy density than existing nickel-cadmium storage batteries and nickel-hydrogen storage batteries. In particular, non-aqueous electrolyte secondary batteries using transition metal composite oxides as active materials are attracting attention because of their good cycle characteristics and high safety (see, for example, Non-Patent Document 1).

In such a non-aqueous electrolyte secondary battery, the positive electrode has a structure in which a positive electrode active material, a conductive material, and a binder (binder) for imparting shape stability to the positive electrode active material are kneaded together. This is a structure in which is formed by attaching to a current collector. The structure of the negative electrode is the same as that of the positive electrode except that the negative electrode active material is used instead of the positive electrode active material.
Organic polymer particles are used as the binder described above. For example, Patent Document 1 discloses polymethyl acrylate particles, acrylate ester-based particles, polyvinylidene fluoride particles, and the like as a binder used for a positive electrode or negative electrode active material. U.S. Patent No. 6,099,077 discloses ethylene / ethyl acrylate copolymer particles. Patent Document 3 discloses a lithium secondary battery using a binder added with PTFE powder.

JP-A-8-7881 JP 2004-172017 A JP-A-6-275277

Takami, Kosugi, Honda "New Rechargeable Battery SCiBTM for Hybrid Vehicles with Excellent Durability and Safety" Toshiba Review Vol.63, No.12, pp.54-57 (2008)

However, in the case of a secondary battery using a transition metal oxide or / and transition metal composite oxide as a positive electrode or negative electrode active material, particles of the positive electrode or negative electrode active material that affect the shape stability of the positive electrode or negative electrode The relationship between the range of the diameter and the range of the particle size of the binder has not been investigated conventionally.
For example, in the example of Patent Document 1, as a positive electrode, a lithium cobaltate active material having a particle diameter of 10 μm, polymethyl acrylate particles having a particle diameter of 2 μm, acrylic ester particles having a particle diameter of 5 μm, and the like are dispersed in isopropyl alcohol. I'm coating things. However, when such organic polymer particles having a large particle diameter are used, the shape stability of the active material may decrease after drying.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-172017) discloses an example in which particles of an ethylene / ethyl acrylate copolymer having a particle diameter of 0.18 to 0.26 μm are dispersed in NMP in a positive electrode lithium cobaltate active material. Is applied and dried, and the peel strength is measured. However, since the particle diameter of the positive electrode active material is not disclosed, it cannot be said that the relationship between the particle diameter range of the positive electrode or negative electrode active material and the particle diameter range of the binder is required.

  In addition, in Patent Document 2, polyvinylidene fluoride or the like is added and dissolved in a solution in which particles are dispersed in Examples. For this reason, an organic solvent capable of dissolving polyvinylidene fluoride and the like is required, and Patent Document 2 uses the NMP. However, when an organic solvent is used as the dispersant, it is necessary to recover the solvent in addition to the cost of the solvent itself, so that the cost is high in terms of equipment.

  In Patent Document 3, in a lithium secondary battery using a positive electrode active material made of a composite oxide containing lithium, cobalt, phosphorus, etc., the particle diameter ratio of the binder to the positive electrode active material is set to 0.02 to 0.02%. It is described that, when used at 20 times, preferably 0.1 to 5 times, irregular voids can be suppressed in the positive electrode, and the occurrence of cracks and defects is suppressed (paragraph [0021]). . However, even if the preferable range of the particle size ratio is defined, all combinations of the active material and the binder having each particle size falling within the range of the particle size ratio do not necessarily give good results. The inventor has confirmed.

After all, none of the patent documents suggests a combination of a preferable range of the particle diameter of the active material and a preferable range of the particle diameter of the binder.
In addition, each patent document discusses a combination of a positive electrode active material and a binder, and the transition metal oxide or / and transition metal composite oxide-based negative electrode active material has a particle diameter of the active material. It does not suggest a combination of the preferable range of and the preferable range of the particle diameter of the binder. The transition metal oxide and / or transition metal composite oxide-based negative electrode active material has a residual alkali component in the powder, and when dispersed with water, the liquid becomes alkaline. The negative electrode active material is an insulator. In this respect, the physical properties are different from those of the active materials such as lithium cobaltate listed in the above patent documents.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an electrode for a nonaqueous electrolyte secondary battery that is easy to manufacture and excellent in shape stability, and a battery using the same.

As a result of intensive research by the present inventors, the average particle diameter of the transition metal oxide, which is an active material for electrodes, and the average particle diameter of the binder dispersed in water are each within a certain range. It has been found that an electrode having good shape stability can be produced at low cost. Based on this finding, the present invention has been completed.
An electrode for a non-aqueous electrolyte secondary battery according to the present invention includes an average particle diameter of 1 μm or more and 20 μm or less, a transition metal oxide or / and a transition metal composite oxide capable of inserting / extracting lithium ions, and an average particle An active material mixture containing a binder having a diameter of 0.10 μm or more and 0.30 μm or less is included.

The transition metal may be titanium, and the transition metal composite oxide may be lithium titanate or titanium dioxide having a spinel structure. Further, a part of titanium may be substituted with another element.
The active material mixture may be used for the negative electrode.
The aforementioned binder is made of particles obtained by mixing one or more of tetrafluoroethylene (PTFE), styrene-butadiene copolymer (SBR), acrylate ester, and methacrylate ester. Is preferred.

Furthermore, according to this invention, the nonaqueous electrolyte secondary battery which comprises said nonaqueous electrolyte secondary battery electrode is provided.
The method for producing an electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a transition metal oxide having an average particle diameter of 1 μm or more and 20 μm or less and capable of inserting / extracting lithium ions and / or transition metal composite oxidation. And the active material mixture dispersed in water obtained in the above step and the active material mixture applied to the current collector are coated with the binder and the binder having an average particle size of 0.10 μm or more and 0.30 μm or less. And removing the water.

  There is no problem even if the solid content concentration of the active material slurry is low, but if it is 70% by weight or more, a solid electrode with good dispersion can be obtained. In addition, there is no problem in manufacturing an electrode by a conventional coating method, but if the electrode is formed by pressurization, a stronger electrode can be obtained.

  The electrode for a non-aqueous electrolyte secondary battery according to the present invention comprises a transition metal oxide or / and a transition metal composite oxide having an average particle diameter of 1 μm or more and 20 μm or less capable of inserting / extracting lithium ions. And an aqueous dispersion binder having an average particle diameter of 0.1 μm or more and 0.3 μm or less can be manufactured at low cost and with good shape stability.

Embodiments of the present invention will be described below. The scope of the present invention is defined by the scope of the claims, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.
<Electrode>
The electrode for a nonaqueous electrolyte secondary battery of the present invention is composed of at least an active material mixture and a current collector. The active material mixture includes at least an active material (sometimes referred to as an electrode active material) and a binder (binder), and may include a conductive aid as necessary.

As the active material, a transition metal oxide and / or transition metal composite oxide having an average particle diameter of 1 μm or more and 20 μm or less and capable of inserting / extracting lithium ions is used. For example, although not particularly limited, lithium titanium oxide, titanium oxide, niobium oxide, vanadium oxide, molybdenum oxide, and the like can be given. In particular, the composite oxide containing titanium is stable with respect to the cycle, and spinel type Li ₄ Ti ₅ O ₁₂ , anatase type TiO ₂ , TiO ₂ (B) and the like are preferable.

  A binder having an average particle size of 0.10 μm or more and 0.30 μm or less is used by being dispersed in water. For example, although not particularly limited, it is possible to use at least one selected from the group consisting of polytetrafluoroethylene (PTFE), styrene-butadiene copolymer (SBR), acrylate ester, polyimide, and derivatives thereof. it can. You may add a dispersing agent and a thickener to these.

In the present invention, the amount of the binder contained in the electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 1 part by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the active material. If it is the said range, the adhesiveness of an active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.
The active material may contain a conductive additive as necessary. Although it does not specifically limit as a conductive support material, A carbon material or / and a metal microparticle are preferable. Examples of the carbon material include natural graphite, artificial graphite, vapor-grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. Examples of the metal fine particles include copper, aluminum, nickel, and an alloy containing at least one of these. Further, the fine particles of inorganic material may be plated. These carbon materials and metal fine particles may be used alone or in combination of two or more.

The amount of the conductive additive is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 1 part by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the active material. If it is the said range, the electroconductivity of an electrode will be ensured.
Examples of the current collector used in the electrode for the nonaqueous electrolyte secondary battery of the present invention include copper, aluminum, nickel, titanium, an alloy containing at least one of these, or a polymer having conductivity. Examples of the shape include a foil shape, a mesh shape, a punching shape, an expanded shape, and a foam structure. The porosity of the current collector is defined as “the total volume of the pores existing in the unit volume including the current collector”.

  Here, the mesh shape is a woven or non-woven fabric of metal or conductive polymer fibers. The thickness of the fiber is preferably 50 μm or more and 2000 μm or less. When the thickness is less than 50 μm, the current collector tends to be easily broken. On the other hand, when a fiber thicker than 2000 μm is used, the opening becomes too large to make the porosity described later, and it tends to be difficult to hold the active material mixture by the mesh.

  The punching shape is a plate in which holes such as a circle, a rectangle, or a hexagon are formed, and a metal made of metal is punching metal. Since it is plate-shaped, the porosity corresponds to the hole area ratio (the ratio of the total area of the holes per unit area of the plate in plan view). The hole area ratio is determined by the ratio between the hole diameter and the bone (metal part), the hole shape, and the hole arrangement. The shape of the hole is not particularly limited, but from the viewpoint of increasing the hole area ratio, a round hole zigzag type (open angle of the zigzag type is 60 °, for example) and a square hole parallel type are preferable.

The expanded shape is a staggered cut made on a plate and stretched to form a mesh. Expanded metal is made of metal. The porosity of the expanded metal corresponds to the hole area ratio, which is determined by the hole diameter / bone ratio, the hole shape, and the hole arrangement.
The foam structure has a three-dimensional network structure like a sponge, and the pores are continuous or dispersed. The structure is determined by the pore size and porosity. The shape and diameter of the continuous holes are not particularly limited, but a structure having a high specific surface area is preferable.

The metal used for the current collector of the present invention is only required to be stable at the electrode operating potential. When the operating potential is 0.7 V or less on the basis of lithium, copper and its alloys are preferable, and when 0.7 V or more, aluminum and its alloys are used. Is preferred.
The electrode of the present invention is produced, for example, by supporting an active material mixture in which an active material, a conductive additive, and a binder are dispersed in water on a current collector. After filling and applying the active material mixture to the pores and the outer surface of the current collector, the electrode is prepared by removing water.

  The method for producing the active material mixture is not particularly limited, but since the active material, conductive additive, binder, and water can be uniformly mixed, agitation granulator, ball mill, planetary mixer, jet mill, thin film swirl type It is preferable to use a mixer. The kneading method of the active material mixture is not particularly limited, and after mixing the active material and the conductive aid, it may be prepared by adding a binder dispersed in water, or the active material, the conductive aid, and You may produce by adding water, after mixing a binder.

  The method for supporting the active material mixture on the current collector is not particularly limited. For example, the active material mixture is dispersed on the current collector and pressurized to form an electrode, and then water is removed. Forming a sheet and forming an electrode by pressure bonding to the current collector to remove water, a method of removing the solvent after applying the active material mixture with a doctor blade, die coater, etc., attached to the current collector by spraying A method of removing the solvent later and a method of removing the solvent after impregnating the current collector into the active material mixture are preferable. In particular, a method of forming an electrode by pressure, pressure bonding or the like is preferable. The method for removing water is preferable because it is easy to dry using an oven or a vacuum oven. As the atmosphere, air at room temperature or high temperature, an inert gas, a vacuum state, or the like can be given.

The obtained electrode may be used as a negative electrode of a nonaqueous electrolyte secondary battery or may be used as a positive electrode. When used as a positive electrode, lithium ions may be inserted in advance.
<Capacity ratio and area ratio of negative electrode to positive electrode>
As for the ratio of the electric capacity of the positive electrode and the negative electrode in the secondary battery produced using the electrode for nonaqueous electrolyte secondary battery of the present invention, it is desirable to satisfy the following formula (1).

0.7 ≦ B / A ≦ 1.3 (1)
In the above formula (1), A represents the electric capacity per 1 cm ² of the positive electrode, and B represents the electric capacity per 1 cm ² of the negative electrode.
When B / A is less than 0.7, the potential of the negative electrode may become a potential at which the negative electrode current collector reacts with lithium or a lithium deposition potential during overcharging, while B / A is 1.3. If it is larger, a side reaction may occur due to the large amount of the negative electrode active material not involved in the battery reaction.

Although the area ratio of the positive electrode to the negative electrode in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, it is preferable to satisfy the following formula (2).
1 ≦ D / C ≦ 1.2 (2)
However, C shows the area of a positive electrode, D shows the area of a negative electrode. When D / C is less than 1, for example, when B / A = 1 as described above, the capacity of the negative electrode is smaller than that of the positive electrode, so that the potential of the negative electrode may become a lithium deposition potential during overcharge. On the other hand, when D / C is larger than 1.2, the negative electrode in the portion not in contact with the positive electrode is large, and thus the negative electrode active material that does not participate in the battery reaction may cause a side reaction. Although control of the area of a positive electrode and a negative electrode is not specifically limited, For example, in the case of electrode preparation, it can carry out by controlling the coating width.

The area ratio between the separator and the negative electrode used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but preferably satisfies the following formula (3).
1 ≦ F / E ≦ 1.5 (3)
However, E shows the area of a negative electrode and F shows the area of a separator. When F / E is less than 1, the positive electrode and the negative electrode are in contact with each other. When F / E is greater than 1.5, the volume required for the exterior increases, and the capacity density and output density of the battery may decrease.

<Separator>
Examples of the separator used in the nonaqueous electrolyte secondary battery of the present invention include porous materials and nonwoven fabrics. The material of the separator is preferably one that does not dissolve in the organic solvent that constitutes the electrolytic solution. Specifically, a polyolefin polymer such as polyethylene or polypropylene, a polyester polymer such as polyethylene terephthalate, cellulose, or glass. Inorganic materials.

The thickness of the separator is preferably 1 to 500 μm. If it is less than 1 μm, it tends to break due to insufficient mechanical strength of the separator and cause an internal short circuit. On the other hand, when it is thicker than 500 μm, the load resistance of the battery tends to be lowered due to an increase in the internal resistance of the battery and the distance between the positive electrode and the negative electrode. A more preferable thickness is 10 to 300 μm.
<Nonaqueous electrolyte>
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but a polymer is impregnated with an electrolytic solution in which a solute is dissolved in a non-aqueous solvent, or an electrolytic solution in which a solute is dissolved in a non-aqueous solvent. A gel electrolyte or the like can be used.

  The non-aqueous solvent preferably includes a cyclic aprotic solvent and / or a chain aprotic solvent. Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic esters, cyclic sulfones and cyclic ethers. Examples of the chain aprotic solvent include chain carbonates, chain carboxylic acid esters and chain ethers. In addition to the above, a solvent generally used as a solvent for nonaqueous electrolytes such as acetonitrile may be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, sulfolane, dioxolane, propionic acid Methyl and the like can be used. These solvents may be used alone or as a mixture of two or more. However, in view of the ease of dissolving the solute described below and the high conductivity of lithium ions, a mixture of two or more of these solvents. Is preferably used. A gel electrolyte in which an electrolyte is impregnated in a polymer can also be used.

The solute is not particularly limited. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), LiN (SO ₂ CF ₃ ) _2, etc. are dissolved in the solvent. It is preferable because it is easy to do. The concentration of the solute contained in the electrolytic solution is preferably 0.5 mol / L or more and 2.0 mol / L or less. If it is less than 0.5 mol / L, the desired lithium ion conductivity may not be exhibited. On the other hand, if it is higher than 2.0 mol / L, the solute may not be dissolved any more. The non-aqueous electrolyte may contain a trace amount of additives such as a flame retardant and a stabilizer.

<Nonaqueous electrolyte secondary battery>
The positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery of the present invention may be in the form in which the same electrode is formed on both sides of the current collector, and the positive electrode is formed on one side of the current collector and the negative electrode is formed on one side. In other words, in the case of a bipolar type, in order to prevent a liquid junction between the positive electrode and the negative electrode through the current collector, the conductive material and / or the insulating material is interposed between the positive electrode and the negative electrode. Has been placed. In the case of a bipolar electrode, a separator is disposed between the positive electrode side and the negative electrode side of the adjacent bipolar electrode, and the positive electrode and An insulating material is disposed around the negative electrode.

  The nonaqueous electrolyte secondary battery of the present invention may be one obtained by winding or laminating a separator disposed between the positive electrode side and the negative electrode side. The positive electrode, the negative electrode, and the separator are impregnated with a nonaqueous electrolyte that is responsible for lithium ion conduction. In the case of using a gel-like nonaqueous electrolyte, the electrolyte may be impregnated in the positive electrode and the negative electrode, or may be in a state only between the positive electrode and the negative electrode. If the positive electrode and the negative electrode are not in direct contact with the gel electrolyte, it is not necessary to use a separator.

The amount of the nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, but is preferably 0.1 mL or more per 1 Ah of battery capacity. If it is less than 0.1 mL, the conduction of lithium ions accompanying the electrode reaction may not catch up, and the desired battery performance may not be exhibited.
The nonaqueous electrolyte may be added to the positive electrode, the negative electrode, and the separator in advance, or may be added after winding or laminating a separator disposed between the positive electrode side and the negative electrode side. When using a gel-like non-aqueous electrolyte, it may be gelled after impregnation with a monomer, or may be placed between the positive electrode and the negative electrode after gelling in advance.

  The non-aqueous electrolyte secondary battery of the present invention may be wound or laminated with a laminate film after the laminate is wound, or may be rectangular, elliptical, cylindrical, coin-shaped, button-shaped, or sheet-shaped. It may be packaged with a metal can. The exterior may be provided with a mechanism for releasing the generated gas or the like. Further, a mechanism for injecting an additive for recovering the function of the deteriorated nonaqueous electrolyte secondary battery from the outside of the battery may be provided. The number of stacked layers can be stacked until a desired battery capacity is exhibited. In the case of stacking, pressure may be applied in the stacking direction of the electrodes. Pressure may be applied inside the cell or may be applied from the outside of the exterior.

  The nonaqueous electrolyte secondary battery of the present invention can be made into a secondary battery module by connecting a plurality of nonaqueous electrolyte secondary batteries. The module of the present invention can be manufactured by connecting in series or in parallel as appropriate depending on the desired size, capacity, and voltage. Further, a control circuit may be attached to the secondary battery module in order to confirm the state of charge of each battery and improve safety.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples, In the range which does not change the summary, it can change suitably.
(1) Manufacture of electrodes The active materials for electrodes (Li ₄ Ti ₅ O ₁₂ and TiO ₂ (B)) are each 100 parts by weight, the conductive auxiliary material (acetylene black) is 6.8 parts by weight, An active material mixture was prepared by mixing 6.8 parts by weight in terms of solid content of the water-dispersed binder (binder).

The active material for electrodes (Li ₄ Ti ₅ O ₁₂ ) can be found in the literature ("Zero-Strain Insertion Material of Li [Li1 / 3Ti5 / 3] O4 for Rechargeable Lithium Cells" J. Electrochem. Soc., Volume 142, Issue 5, pp. 1431-1435 (1995)). That is, first, titanium dioxide and lithium hydroxide are mixed so that the molar ratio of titanium and lithium is 5: 4, and then this mixture is heated at 800 ° C. for 12 hours in a nitrogen atmosphere. it can.

The active material for electrodes TiO ₂ (B) is the literature (Minoru Inaba, “TiO2 (B) as a promising high potential negative electrode for large-size lithium-ion batteries”, Journal of power sources, 189, 580 (2009)). It was produced by the method described in 1. That is, potassium carbonate and anatase TiO ₂ were mixed at a molar ratio of 1: 4, and K ₂ Ti ₄ O ₉ was obtained by firing twice at 1000 ° C. for 24 hours in air, and then in 1M hydrogen chloride solution. Ion exchange was performed by soaking for 3 days, and it was prepared by dehydration and drying at 500 ° C. for 30 minutes.

The average particle diameter (D50) of the electrode active material (Li ₄ Ti ₅ O ₁₂ ) and the electrode active material TiO ₂ (B) was measured by a laser diffraction scattering particle size distribution analyzer.
As water dispersion binder, polytetrafluoroethylene (PTFE), 1: 1 mixture of PTFE and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene-butadiene copolymer (SBR), acrylic ester Each particle of polymer was used.

The average particle size (D50) of each water-dispersed binder was measured with a laser diffraction / scattering particle size distribution analyzer.
First, the electrode active material and the conductive additive were mixed using an automatic mortar. Transfer the mixed powder to a stainless steel bowl, add a water dispersion binder (solid content concentration of about 50%), pre-mix using an alumina pestle, and then add water to adjust the solid content concentration to 75%. The active material mixture was prepared by mixing until

  The above-mentioned active material mixture was dispersed on an aluminum expanded metal (aperture 1 mm × 2 mm, thickness 0.1 mm), molded by pressing from above, and then vacuum dried at 170 ° C. to produce an electrode. After drying, the thickness of the electrode containing aluminum expanded metal was 0.5 mm. In the examples, this electrode was used as a negative electrode for a battery.

As shown in Table 1, each electrode was classified by the type of electrode active material, the particle size of the electrode active material, the type of binder, and the particle size of binder (Examples 1 to 12, Comparative Example 1). ~ 4).
(2) State of electrode The state of these electrodes (Examples 1-12, Comparative Examples 1-4) was observed visually. The results are shown in Table 1. The presence or absence of the fall was determined by lifting the electrode and holding it for 5 minutes.

(3) Production of Counter Electrode (Positive Electrode) Li _1.1 Al _0.1 Mn _1.8 O _{4 as} an active material for positive electrode is described in literature (“Lithium Aluminum Manganese Oxide Having Spinel-Framework Structure for Long-Life Lithium-Ion Batteries”). "Electrochemical and Solid-State Letters Volume 9, Issue 12, Pages A557 (2006)).

  That is, an aqueous dispersion of manganese dioxide, lithium carbonate, aluminum hydroxide, and boric acid was prepared, and a mixed powder was prepared by a spray drying method. At this time, the amounts of manganese dioxide, lithium carbonate and aluminum hydroxide were adjusted so that the molar ratio of lithium, aluminum and manganese was 1.1: 0.1: 1.8. Next, the mixed powder was heated at 900 ° C. for 12 hours in an air atmosphere, and then again heated at 650 ° C. for 24 hours. Finally, the powder was washed with water at 95 ° C. and dried to prepare a positive electrode active material.

  100 parts by weight of this positive electrode active material, 6.8 parts by weight of conductive additive (acetylene black), and PTFE binder (manufactured by Daikin Industries) (solid content concentration 50 wt%) mixed with 6.8 parts by weight of solid content Thus, an active material mixture was prepared. The production method of the active material mixture was performed in the same manner as the above-described electrode. That is, first, the electrode active material and the conductive additive were mixed using an automatic mortar. Transfer the mixed powder to a stainless steel bowl, add a water dispersion binder (solid content concentration of about 50%), pre-mix using an alumina pestle, and then add water to adjust the solid content concentration to 75%. The active material mixture was prepared by mixing until This active material mixture was dispersed on an aluminum expanded metal (aperture 1 mm × 2 mm, thickness 0.1 mm), molded by pressing from above, and then vacuum dried at 170 ° C. to produce an electrode.

(4) Production of non-aqueous electrolyte secondary battery Li ₄ Ti ₅ O ₁₂ / Li _1.1 Al _0.1 Mn _1.8 O ₄ non-aqueous electrolyte secondary battery or TiO ₂ (B) / Li _1.1 Al _{A 0.1} Mn _1.8 O ₄ nonaqueous electrolyte secondary battery was fabricated as follows.
First, the obtained positive electrode / separator / obtained negative electrode were laminated in this order. A negative electrode concerns on Examples 1-12 and Comparative Examples 1-4, respectively. As the separator, two cellulose nonwoven fabrics (thickness 25 μm, area 20 cm ² ) were used. Next, an aluminum tab serving as a lead electrode was vibration welded to the positive electrode and the negative electrode, and then placed in a bag-shaped aluminum laminate sheet.

After 1 mL of a non-aqueous electrolyte (propylene carbonate / ethyl methyl carbonate = 3/7 vol%, LiPF ₆ 1 mol / L) was placed in the bag, the non-aqueous electrolyte was sealed by pulling out the outlet of the bag and the electrode. A secondary battery was produced.
(5) Capacity maintenance rate measurement Current value (1 / 8C rate) when charging or discharging is completed in 8 hours with a voltage of 1.5 to 3 V in a state where the manufactured nonaqueous electrolyte secondary battery is sandwiched between metal plates from the outside of the exterior. The charge / discharge cycle test was conducted. A charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko) was used for the cycle, and the number of cycles was 20 cycles.

(6) Overall results Table 1 shows the electrode states and capacity retention ratios for the manufactured electrodes (Examples 1 to 12, Comparative Examples 1 to 4).

As shown in Example 3 and Comparative Example 1, when the average particle diameter of the electrode active material exceeds 20 μm, the active material falls from the current collector even if the same binder is used. Further, as shown in Comparative Example 2, even when the average particle diameter of the binder particles exceeds 0.30 μm, the active material falls from the current collector.
As shown in Example 5 and Comparative Example 3, when the average particle diameter of the electrode active material is less than 1 μm, the active material falls from the current collector even if the same binder is used.

As shown in Example 6 and Comparative Example 4, when the average particle diameter of the binder is less than 0.10 μm, the active material falls from the current collector even when the same electrode active material is used.
In the non-aqueous electrolyte secondary battery using the electrode in which the active material for the electrode did not fall, the ratio of the discharge capacity at the 20th cycle to the discharge capacity at the 1st cycle (capacity maintenance ratio) in all 20 cycle measurements. The result was as good as 90% or more.

From these things, in order to provide the favorable adhesiveness and shape stability of a collector and the active material mixture for electrodes, the active material for electrodes whose average particle diameter is 1-20 micrometers, and an average particle diameter are It can be seen that it is optimal to combine the binders of 0.10 to 0.30 μm.
In addition, regarding the ratio b / a between the average particle diameter a of the electrode active material and the average particle diameter b of the binder, “the electrode state is good within a certain range, and good if it is out of the range. It is not possible to apply a criterion such as “not good” or “good if it is below a certain threshold, not good if it exceeds that threshold”. As can be seen from the calculation, for example, the ratio b / a of Comparative Example 4 is 0.013, the ratio b / a of Example 1 is 0.028, and the ratio b / a of Comparative Example 2 is 0.057. The ratio b / a in Example 7 is 0.17, and it can be seen that the above-mentioned criterion cannot be applied. Therefore, the present inventor has determined that the range of the average particle diameter a of the electrode active material and the average of the binder are larger than the ratio b / a of the average particle diameter a of the electrode active material and the average particle diameter b of the binder. Paying attention to the range of the particle diameter b, each preferred range is defined.

Claims (10)

  Binding with transition metal oxide and / or transition metal composite oxide having an average particle size of 1 μm or more and 20 μm or less and capable of insertion / extraction of lithium ions, and an average particle size of 0.10 μm or more and 0.30 μm or less The electrode for nonaqueous electrolyte secondary batteries containing the active material mixture containing material.   The electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the transition metal is titanium.   The electrode for a nonaqueous electrolyte secondary battery according to claim 2, wherein the transition metal composite oxide is lithium titanate having a spinel structure.   The electrode for a nonaqueous electrolyte secondary battery according to claim 2, wherein the transition metal oxide is titanium dioxide.   The electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the active material mixture is used for a negative electrode.   6. The binder according to claim 1, wherein the binder is made of particles obtained by mixing one or more of tetrafluoroethylene, styrene-butadiene rubber, acrylate ester, and methacrylate ester. 2. An electrode for a nonaqueous electrolyte secondary battery according to item 1.   The nonaqueous electrolyte secondary battery using the electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-6. Binding with transition metal oxide and / or transition metal composite oxide having an average particle size of 1 μm or more and 20 μm or less and capable of insertion / extraction of lithium ions, and an average particle size of 0.10 μm or more and 0.30 μm or less A step of dispersing the material in water to obtain an active material mixture;
Applying the active material mixture obtained in the step to a current collector to remove water, and a method for producing an electrode for a non-aqueous electrolyte secondary battery.   The method for producing an electrode for a non-aqueous electrolyte secondary battery according to claim 8, wherein the solid content concentration of the active material mixture is 70% or more.   The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries of Claim 8 or Claim 9 which pressurizes and shape | molds the said active material mixture and produces the said electrode.