JP2010080321A - Positive electrode for nonaqueous electrolyte secondary battery and manufacturing method thereof, and non aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for a nonaqueous electrolyte secondary battery and a manufacturing method thereof wherein cost increase and reduction of productivity can be suppressed while improvement of cycle characteristics and storage characteristics (especially both characteristics at high temperatures) can be improved. <P>SOLUTION: In the positive electrode for the nonaqueous electrolyte secondary battery having a positive electrode current collector 2 and a positive electrode active material layer 1 which is formed on a surface of this positive electrode current collector 1 and contains positive electrode active material particles and a binder, TiO<SB>2</SB>particles 3 are contained in the positive electrode active material layer 1. These TiO<SB>2</SB>particles 3 are eccentrically located in the vicinity of a surface of the positive electrode active material layer 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in a positive electrode for a non-aqueous electrolyte secondary battery such as a lithium ion battery or a polymer battery, and a method for producing the same.

  In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and batteries as drive power sources are required to have higher capacities. A non-aqueous electrolyte secondary battery that performs charge / discharge by moving lithium ions between the positive and negative electrodes along with charge / discharge has a high energy density and a high capacity. Widely used as a drive power source.

  Here, the mobile information terminal has a tendency to further increase power consumption with enhancement of functions such as a video playback function and a game function, and the non-aqueous electrolyte secondary battery, which is a driving power source thereof, plays back and outputs for a long time. For the purpose of improvement and the like, further increase in capacity and performance are strongly desired. In addition, non-aqueous electrolyte secondary batteries are expected to be used not only for the above applications, but also for power tools, assist bicycles, and HEVs. Capacity and high performance are strongly desired.

In view of this, we have developed a battery that can be increased in capacity by increasing the end-of-charge voltage of the battery using lithium cobalt oxide as the positive electrode active material from the current 4.2V to about 4.4V. developed. However, in such a battery, the stability of the crystal structure of the positive electrode is lost, and the electrolytic solution may be decomposed or elements may be eluted from the positive electrode active material. I found out there was.
Therefore, a technique for forming an inorganic oxide layer on the surface of the positive electrode or the negative electrode has been proposed (see Patent Document 1 and Patent Document 2 below). Thus, if an inorganic oxide layer is formed on one electrode surface, decomposition products of the electrode and the electrolytic solution are trapped at high temperatures and the like, and side reactions can be suppressed, so that storage characteristics and cycle characteristics are improved. It is stated that it will be greatly improved.

JP 2003-142078 A JP 2005-327680 A

  However, these prior arts require an additional step of forming an inorganic oxide layer on the surface of the active material layer after forming the positive or negative electrode active material layer, which increases costs and reduces productivity. Had the problem of inviting.

  Therefore, the present invention provides a positive electrode for a non-aqueous electrolyte secondary battery capable of suppressing an increase in cost and a decrease in productivity while improving cycle characteristics and storage characteristics (especially both characteristics at high temperatures) and its production. The purpose is to provide methods.

To achieve the above object, the present invention provides a non-aqueous electrolyte comprising a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector and containing positive electrode active material particles and a binder. In the positive electrode for a secondary battery, the positive electrode active material layer includes inorganic oxide particles, and the inorganic oxide particles are unevenly distributed near the surface of the positive electrode active material layer.
If the inorganic oxide particles are unevenly distributed in the vicinity of the surface of the positive electrode active material layer as in the above configuration, the function as a filter in the surface portion of the positive electrode active material layer is the same as when the inorganic oxide layer is formed on the surface of the positive electrode. Demonstrate. Therefore, a reaction product between the electrode and the electrolytic solution can be trapped and a side reaction itself can be suppressed, so that high temperature characteristics (cycle characteristics and storage characteristics at high temperatures) can be improved. In this case, the vicinity of the surface of the positive electrode active material layer where the inorganic oxide particles are unevenly distributed and the vicinity of the positive electrode current collector of the positive electrode active material layer where the positive electrode active material particles are unevenly distributed are integrally formed. Therefore, the adhesion strength between both parts improves.

The ratio of the inorganic oxide particles to the total amount of the positive electrode active material layer is desirably 0.1 to 3.0% by mass.
When the ratio is less than 0.1% by mass, the effect of adding the inorganic oxide particles may not be sufficiently exhibited. On the other hand, when the ratio exceeds 3.0% by mass, the positive electrode active This is because the ratio of the positive electrode active material particles in the material layer is relatively reduced, and the energy density is lowered.
It is desirable that the inorganic oxide particles comprise TiO ₂ of the rutile structure.

  A first step of producing a positive electrode slurry containing inorganic oxide particles, positive electrode active material particles, and a binder, and applying the inorganic oxide particle-containing positive electrode slurry to the surface of the positive electrode current collector; And a third step in which the inorganic oxide particle-containing positive electrode slurry is heated and dried while generating thermal convection.

  When the inorganic oxide particle-containing positive electrode slurry is applied to the surface of the positive electrode current collector and then heated, the inorganic oxide particles present on the positive electrode current collector side move in the positive electrode surface direction. For this reason, when the said slurry dries and the positive electrode active material layer is formed, inorganic oxide particles will be unevenly distributed in the surface vicinity of a positive electrode. Thus, the positive electrode active material layer in which the inorganic oxide particles are unevenly distributed in the vicinity of the surface can be produced on the surface of the positive electrode current collector by simply applying and drying the slurry once. Therefore, an increase in cost and a decrease in productivity can be suppressed while improving cycle characteristics and storage characteristics (especially both characteristics at high temperatures).

In the first step, inorganic oxide particles and a dispersion stabilizer are dispersed in a solvent to prepare an inorganic oxide particle dispersion, and positive electrode active material particles and a binder are dispersed in a solvent to obtain a positive electrode slurry. After the production, it is desirable to produce the inorganic oxide particle-containing positive electrode slurry by mixing the inorganic oxide particle dispersion and the positive electrode slurry.
In addition to the step of preparing the positive electrode slurry, if there is a step of preparing an inorganic oxide particle dispersion by dispersing inorganic oxide particles and a dispersion stabilizer in a solvent, It becomes possible to disperse the oxide particles while suppressing aggregation.

As the inorganic oxide particles, those having an average particle diameter of 10 to 500 nm are desirably used.
Since the average particle diameter of the positive electrode active material particles generally used in non-aqueous electrolyte secondary batteries is around 10 μm, when the average particle diameter of the inorganic oxide particles exceeds 500 nm, the inorganic oxide particle-containing positive electrode slurry is dried. Heat convection is less likely to occur. On the other hand, if the average particle size of the inorganic oxide particles is too small, thermal convection tends to occur, but there is a problem that the cost becomes high and the cohesiveness becomes high and it is difficult to prepare the dispersion.
In the present specification, the average particle size of various particles is a value measured by the particle size distribution method.

It is desirable that the viscosity of the positive electrode slurry containing inorganic oxide particles in the second step is 0.6 to 2.0 Pa · s.
When the viscosity of the slurry is less than 0.6 Pa · s, there may be a problem in handling such as a reduced coating thickness of the slurry. On the other hand, when the viscosity of the slurry exceeds 2.0 Pa · s, the migration This may cause a problem that the inorganic oxide particles are less likely to be unevenly distributed near the surface of the positive electrode active material layer.

The drying temperature in the third step is preferably 100 to 150 ° C.
When the drying temperature is less than 100 ° C., there may be a problem that migration hardly occurs. On the other hand, when the drying temperature exceeds 150 ° C., the thermal stability of the binder or the like may be deteriorated.

  A positive electrode current collector, a positive electrode having a positive electrode active material layer formed on the surface of the positive electrode current collector and containing positive electrode active material particles and a binder, a negative electrode, and a separator interposed between the positive and negative electrodes And a non-aqueous electrolyte secondary battery impregnated in the electrode body. The positive electrode active material layer includes inorganic oxide particles, and the inorganic oxide The particles are characterized by being unevenly distributed near the surface of the positive electrode active material layer.

The ratio of the inorganic oxide particles to the total amount of the positive electrode active material layer is preferably 0.1 to 3.0% by mass, and the inorganic oxide particles are preferably made of TiO ₂ having a rutile structure.

  A first step of producing a positive electrode slurry containing inorganic oxide particles, positive electrode active material particles, and a binder, and applying the inorganic oxide particle-containing positive electrode slurry to the surface of the positive electrode current collector; 2 steps, a third step of heating the inorganic oxide particle-containing positive electrode slurry and drying it while generating thermal convection, and an electrode with a separator disposed between the positive electrode and the negative electrode And a fourth step of impregnating the electrode body with a non-aqueous electrolyte after the body is produced.

  In the first step, inorganic oxide particles and a dispersion stabilizer are dispersed in a solvent to prepare an inorganic oxide particle dispersion, and positive electrode active material particles and a binder are dispersed in a solvent to obtain a positive electrode slurry. After the production, it is desirable to produce the inorganic oxide particle-containing positive electrode slurry by mixing the inorganic oxide particle dispersion and the positive electrode slurry.

  As the inorganic oxide particles, those having an average particle size of 10 to 500 nm are desirably used, and the viscosity of the inorganic oxide particle-containing positive electrode slurry in the second step is 0.6 to 2.0 Pa · s. Desirably, the drying temperature in the third step is preferably 100 to 150 ° C.

  According to the present invention, it is possible to suppress an increase in production cost and a decrease in productivity of a nonaqueous electrolyte secondary battery while improving cycle characteristics and storage characteristics (particularly both characteristics at high temperatures). There is an effect.

  Hereinafter, a positive electrode for a nonaqueous electrolyte secondary battery according to an example of the present invention, a manufacturing method thereof, and the like will be described below. In addition, the nonaqueous electrolyte secondary battery positive electrode and the manufacturing method thereof in the present invention are not limited to those shown in the following embodiments, and can be appropriately changed and implemented without changing the gist thereof.

[Production of positive electrode]
First, lithium cobaltate (average particle size: 10 μm) as a positive electrode active material, acetylene black as a carbon conductive agent, and PVDF as a binder at a mass ratio of 95: 2.5: 2.5 After mixing, these were stirred using TK CONBIMIX made by Tokushu Kika with NMP as a diluent solvent to prepare a positive electrode slurry.

In parallel with this, using NMP as a solvent, TiO ₂ particles having an rutile structure (average particle size 250 nm, CR-EL manufactured by Ishihara Sangyo Co., Ltd.) are set to have a solid content concentration of 30% by mass with respect to NMP. prepared, the PVDF was prepared such that the 3.75 wt% with respect to the TiO ₂ particles, was placed in Kika made Filmics, the mixed dispersion treatment to prepare a TiO ₂ particle dispersion by performing.
Next, the positive electrode slurry and the TiO ₂ particle dispersion were mixed to prepare a TiO ₂ particle-containing positive electrode slurry (viscosity: 1.0 Pa · s). At this time, the solid content ratio of the TiO ₂ particles of TiO ₂ particles containing the positive electrode in the slurry to be 1 mass%, to prepare a mixed ratio of both.

Next, the TiO ₂ particle-containing positive electrode slurry is applied to both surfaces of the positive electrode current collector made of aluminum foil at a coating speed of 1.2 m / min. Further, the first drying chamber (temperature: 115 ° C.) and the second drying are applied. The positive electrode slurry containing TiO ₂ particles was dried in a drying furnace having a furnace length of 4 m having two drying chambers (temperature: 120 ° C.).
Finally, the positive electrode was prepared by rolling the electrode plate prepared as described above so that the packing density of the positive electrode active material was 3.60 g / cc.

(Production of negative electrode)
Carbon material (artificial graphite) which is a negative electrode active material, CMC1380 (manufactured by Daicel Chemical Industries, Ltd.) dissolved in 1% by mass of pure water, and SBR (styrene butadiene rubber) have a solid content mass ratio of 98. 1: After preparing a negative electrode slurry by mixing using TK CONBMIX made by Special Machine, the negative electrode slurry was applied to both sides of the negative electrode current collector made of copper foil, Furthermore, the negative electrode by which the negative electrode active material layer was formed on both surfaces of the negative electrode collector was produced by drying and rolling. The filling density of the negative electrode active material layer is 1.60 g / cc.

(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved at a ratio of 1.0 mol / liter in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7.

[Separator type]
As the separator, a microporous membrane (thickness: 16 μm, porosity of 47%) made of polyethylene (hereinafter sometimes abbreviated as PE) was used.

[Battery assembly]
A lead terminal is attached to each of the positive and negative electrodes, and a spiral wound electrode is pressed through a separator to produce a flattened electrode body, and then a storage space for an aluminum laminate film as a battery exterior body An electrode body was disposed therein, and a nonaqueous electrolyte solution was poured into the space, and then an aluminum laminate film was welded and sealed to prepare a battery. In this battery, the end-of-charge voltage is specified to be 4.40 V, and the design capacity at this potential is 750 mAh.

(Example)
As an example, the battery shown in the best mode was used.
The battery thus produced is hereinafter referred to as the present invention battery A.

(Comparative Example 1)
A positive electrode and a battery were produced in the same manner as in the above example except that the TiO ₂ particle dispersion was not mixed with the positive electrode slurry (no TiO ₂ particles were present in the positive electrode active material layer).
The battery thus manufactured is hereinafter referred to as a comparative battery Z1.

(Comparative Example 2)
A positive electrode and a battery were produced in the same manner as in Comparative Example 1 except that an inorganic oxide layer was separately formed on the surface of the positive electrode active material layer of the comparative battery Z1.
Here, the inorganic oxide layer was produced as follows.

First, pure water is used as a solvent, and rutile TiO ₂ particles (average particle size 250 nm, CR-EL manufactured by Ishihara Sangyo Co., Ltd.) are prepared so that the solid content concentration is 40% by mass with respect to pure water. SBR was prepared to be 3.75% by mass with respect to the TiO ₂ particles, placed in Special Mechanics Films, and mixed and dispersed to prepare a TiO ₂ particle dispersion. Then, by using the TiO ₂ particle dispersion, on both sides of the positive electrode active material layer of the comparative battery Z1, after applying the TiO ₂ particle dispersion by a gravure coating method, a drying and removing the solvent, the positive electrode An inorganic oxide layer (the thickness of one surface is 2 μm) was formed on both surfaces of the active material layer. In addition, at the time of the coating of the TiO ₂ particle dispersion liquid, the coating treatment was performed on each side so as to cover the entire surface of the positive electrode active material layer.
The battery thus produced is hereinafter referred to as a comparative battery Z2.

(Experiment 1)
The charge storage characteristics (remaining capacity after charge storage) of the present invention battery A and comparative batteries Z1 and Z2 were examined, and the results are shown in Table 1. In addition, the calculation method of charging / discharging conditions and remaining capacity ratio is as follows.

[Charging / discharging conditions]
-Charging conditions After constant current charging with a current of 1.0 It (750 mA) until the battery voltage reaches 4.40 V, the current value becomes 1/20 It (37.5 mA) at a voltage of 4.40 V. Condition to charge.
-Discharge condition The condition that constant current discharge is performed up to a battery voltage of 2.75 V at a current of 1.0 It (750 mA).
The charging / discharging interval is 10 minutes.

[Calculation method of remaining capacity ratio]
Charging / discharging was performed once under the above charging / discharging conditions, and the discharge capacity at this time was defined as the discharge capacity before the storage test. Next, after the battery charged under the above charging conditions was left at 60 ° C. for 5 days, discharging was performed under the same conditions as the above discharging conditions, and the discharging capacity at this time was defined as the first discharging capacity after the storage test. And the remaining capacity ratio was computed from the following (1) Formula using the discharge capacity of the 1st time after this storage test, and the discharge capacity before the said storage test.
Residual capacity ratio (%) =
(First discharge capacity after storage test / Discharge capacity before storage test) × 100 (1)

〔Experimental result〕
As is clear from Table 1, in the comparative battery Z1 in which no TiO ₂ particles are present on the surface of the positive electrode, the remaining capacity ratio is 18.2%, which is very low, whereas the TiO _{2 on} the surface of the positive electrode is very low. In the present invention battery A and the comparative battery Z2 in which particles are present, it can be seen that the remaining capacity ratios are 57.4% and 75.9%, respectively, which are high. From the above, when the inorganic oxide particles (TiO ₂ particles) are unevenly distributed in the vicinity of the surface of the positive electrode active material layer (surface of the electrode), an effect similar to the case where a separate inorganic oxide layer is formed on the surface of the positive electrode active material layer Was found to be obtained.

On the other hand, as is clear from Table 1, when an inorganic oxide layer is formed on the surface of the positive electrode active material layer as in the comparative battery Z2, an additional inorganic oxide layer preparation step is required in addition to the positive electrode active material layer preparation step. On the other hand, when the inorganic oxide particles (TiO ₂ particles) are unevenly distributed on the surface of the positive electrode active material layer by causing migration, only the positive electrode active material layer preparation step is sufficient. Therefore, in the present invention, the number of production steps of the positive electrode and the battery can be reduced, and the battery can be provided efficiently and at low cost.

The battery A of the present invention has a smaller remaining capacity ratio than the comparative battery Z2. It is believed that this is a positive electrode active material layer in Comparative Battery Z2 are completely coated with TiO ₂ particles, the present invention cell A is due to the fact that not completely cover the surface of the positive electrode active material in TiO ₂ particles .

  However, essentially, the effect of unevenly distributing the inorganic oxide particles on the surface of the positive electrode is sufficiently ensured by the present manufacturing process, and the above-described disadvantage is that the inorganic oxide particles are unevenly distributed. It can be solved by slightly increasing the thickness of the portion.

(Experiment 2)
The positive electrode after rolling to produce an electrode section using a JEOL Ltd. cross section polisher (SM-09010), measuring the distribution of JEOL Ltd. EDX (JSM-6500F) in the electrode section inorganic oxide particles (TiO ₂ particles) did. An SEM image and EDS mapping (a diagram showing the distribution state of TiO ₂ particles, where the whitened portions are TiO ₂ particles) are shown in FIGS. 1 and 2, respectively.

As is apparent from FIGS. 1 and 2, TiO ₂ particles were localized near the surface of the positive electrode active material layer (upper part of FIG. 2), the positive electrode current collector vicinity of the positive electrode active material layer (lower part of FIG. 2) It is recognized that there is not much.

The reason for this will be described with reference to FIGS. 3 and 4, 1 is a positive electrode active material layer, 2 is a cathode current collector, 3 TiO ₂ particles, 4 hot air, 5 is a TiO ₂ particle-containing positive electrode active material slurry. First, as shown in FIG. 3, the temperature rise with hot air, TiO ₂ particles 3 of the TiO ₂ particles containing positive electrode slurry 5 is moved in the arrow A direction (front side of the positive electrode from the positive electrode current collector 2 side) ( Resulting in migration). At this time, the migration in the arrow A direction is due to the fact that the average particle size of the TiO ₂ particles 3 is much smaller than the average particle size of the positive electrode active material particles. When the positive electrode slurry 5 containing TiO ₂ particles is dried while such migration occurs, the positive electrode active material layer 1 in which the TiO ₂ particles 3 are unevenly distributed near the surface is formed as shown in FIG. .

[Other matters]
(1) The inorganic oxide particles used in the present invention are not limited to titania, and the type thereof is not limited as long as it has excellent stability in the battery (low reactivity with lithium). For example, alumina, zirconia, magnesia, or the like can be used. Among these, titania and alumina are often used in the paint field, and can be suitably used because they are inexpensive and have a large number of small particle sizes. As titania, titania having a rutile structure is preferably used. This is because titania with anatase structure can insert and release lithium ions, and depending on the environmental atmosphere and potential, it absorbs lithium and expresses electronic conductivity. .

(2) In the above examples, inorganic oxide particles having an average particle diameter of 250 nm are used, but the present invention is not limited to such particles. However, since the average particle size of the positive electrode active material particles generally used in non-aqueous electrolyte secondary batteries is around 10 μm, if the average particle size of the inorganic oxide particles is too large, thermal convection occurs during slurry drying. It becomes difficult. On the other hand, if the average particle size of the inorganic oxide particles is too small, thermal convection is likely to occur, but there is a problem that the cost becomes high and the cohesiveness becomes high and it is difficult to prepare the inorganic oxide particle dispersion. . Accordingly, the average particle size of the inorganic oxide particles is desirably 10 to 500 nm.

(3) The ratio of the inorganic oxide particles to the total amount of the solid content (the ratio of the inorganic oxide particles to the total amount of the positive electrode active material layer) is not limited to 1% by mass, but is 0.1 to 3.0% by mass. It is preferable to regulate to. This is because when the ratio is less than 0.1% by mass, the effect of adding the inorganic oxide particles may not be sufficiently exerted, whereas when the ratio exceeds 3.0% by mass, the positive electrode active material layer in the positive electrode active material layer may not be fully effective. This is because the density of the material decreases and the energy density decreases.

(4) The viscosity of the positive electrode slurry containing inorganic oxide particles is not limited to 1.0 Pa · s, but is preferably 0.6 to 2.0 Pa · s. When the viscosity of the slurry is less than 0.6 Pa · s, this may cause a handling problem such as a decrease in the coating thickness of the slurry, while the viscosity of the slurry exceeds 2.0 Pa · s. This is because migration is difficult to occur, and it may be difficult to make the inorganic oxide particles unevenly distributed near the surface of the positive electrode active material layer.

(5) Although the drying temperature of the said inorganic oxide particle containing positive electrode slurry is not limited to 115 degreeC and 120 degreeC, it is desirable that it is 100-150 degreeC. This may cause a problem that migration is less likely to occur when the drying temperature is less than 100 ° C., and may cause a problem that the thermal stability of the binder and the like decreases when the drying temperature exceeds 150 ° C. Because there is.

(6) The positive electrode active material is not limited to the above lithium cobaltate, but is a nickel-cobalt-manganese lithium composite oxide, a nickel-manganese-aluminum lithium composite oxide, or a nickel-cobalt-aluminum composite oxide. Lithium composite oxide containing nickel such as spinel type lithium manganate, olivine type lithium phosphate and the like may be used.

(7) The negative electrode active material is not limited to the above artificial graphite, and may be any material that can insert and desorb lithium ions, such as graphite, coke, tin oxide, metallic lithium, silicon, and mixtures thereof. The kind is not ask | required.

(8) The binder used for the negative electrode is not limited to SBR (styrene butadiene rubber), but it is preferable to use a latex-based binder. Specific examples include styrene-butadiene latex, acrylonitrile-butadiene latex, acrylic ester latex, vinyl acetate latex, methyl methacrylate-butadiene latex, and carboxyl-modified products thereof.

(9) The lithium salt of the electrolytic solution is not limited to the above LiPF ₆ , but LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiPF _6-X ( C _n F _{2n + 1} ) _X [where 1 <x <6, n = 1 or 2], etc., or a mixture of two or more of these may be used. The concentration of the lithium salt is not particularly limited, but is preferably regulated to 0.8 to 1.8 mol per liter of the electrolyte. The solvent of the electrolytic solution is not limited to ethylene carbonate (EC) or diethyl carbonate (DEC), but propylene carbonate (PC), γ-butyrolactone (GBL), ethyl methyl carbonate (EMC), dimethyl carbonate. A carbonate-based solvent such as (DMC) is preferable, and a combination of a cyclic carbonate and a chain carbonate is more preferable.

(10) The present invention is not limited to a liquid battery, but can be applied to a gel polymer battery. Examples of the polymer material in this case include polyether solid polymer, polycarbonate solid polymer, polyacrylonitrile solid polymer, oxetane polymer, epoxy polymer, a copolymer composed of two or more of these, or a crosslinked polymer. A molecule or PVDF is exemplified, and a solid electrolyte in which this polymer material, a lithium salt, and an electrolyte are combined into a gel can be used.

  The present invention can be expected to be developed not only for driving power sources for mobile information terminals such as mobile phones, notebook personal computers, and PDAs, but also for high power driving power sources such as HEVs and electric tools.

It is a SEM image of the electrode cross section of the positive electrode for nonaqueous electrolyte secondary batteries of this invention. It is EDS mapping of the electrode cross section of the positive electrode for nonaqueous electrolyte secondary batteries of this invention. It is explanatory drawing which shows the heating state at the time of producing the positive electrode for nonaqueous electrolyte secondary batteries of this invention. It is explanatory drawing of the positive electrode for nonaqueous electrolyte secondary batteries of this invention.

Explanation of symbols

1: Positive electrode active material layer 2: Positive electrode current collector 3: TiO ₂ particles 4: Hot air 5: TiO ₂ particle-containing positive electrode active material slurry

Claims (16)

In a positive electrode for a nonaqueous electrolyte secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer formed on a surface of the positive electrode current collector and including positive electrode active material particles and a binder.
The positive electrode active material layer includes inorganic oxide particles, and the inorganic oxide particles are unevenly distributed near the surface of the positive electrode active material layer. .   The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1, wherein the ratio of the inorganic oxide particles to the total amount of the positive electrode active material layer is 0.1 to 3.0% by mass. The inorganic oxide particles are made of TiO ₂ of the rutile structure, according to claim 1 or 2 for a non-aqueous electrolyte secondary battery positive electrode according to. A first step of preparing an inorganic oxide particle-containing positive electrode slurry containing inorganic oxide particles, positive electrode active material particles, and a binder;
A second step of applying the inorganic oxide particle-containing positive electrode slurry to the surface of the positive electrode current collector;
A third step in which the inorganic oxide particle-containing positive electrode slurry is heated and dried while causing thermal convection;
The manufacturing method of the positive electrode for nonaqueous electrolyte secondary batteries characterized by having.   In the first step, inorganic oxide particles and a dispersion stabilizer are dispersed in a solvent to prepare an inorganic oxide particle dispersion, and positive electrode active material particles and a binder are dispersed in a solvent to obtain a positive electrode slurry. The manufacturing method of the positive electrode for nonaqueous electrolyte secondary batteries of Claim 4 which mixes the said inorganic oxide particle dispersion liquid and the said positive electrode slurry after preparation, and produces the said inorganic oxide particle containing positive electrode slurry.   The method for producing a positive electrode for a nonaqueous electrolyte secondary battery according to claim 4 or 5, wherein particles having an average particle diameter of 10 to 500 nm are used as the inorganic oxide particles.   The production of a positive electrode for a nonaqueous electrolyte secondary battery according to any one of claims 4 to 6, wherein the viscosity of the positive electrode slurry containing inorganic oxide particles in the second step is 0.6 to 2.0 Pa · s. Method.   The manufacturing method of the positive electrode for nonaqueous electrolyte secondary batteries of any one of Claims 4-7 whose drying temperature in the said 3rd step is 100-150 degreeC. A positive electrode current collector, a positive electrode having a positive electrode active material layer formed on the surface of the positive electrode current collector and containing positive electrode active material particles and a binder, a negative electrode, and a separator interposed between the positive and negative electrodes A non-aqueous electrolyte secondary battery comprising an electrode body and a non-aqueous electrolyte impregnated in the electrode body,
The non-aqueous electrolyte secondary battery, wherein the positive electrode active material layer includes inorganic oxide particles, and the inorganic oxide particles are unevenly distributed near the surface of the positive electrode active material layer.   The nonaqueous electrolyte secondary battery according to claim 9, wherein a ratio of the inorganic oxide particles to the total amount of the positive electrode active material layer is 0.1 to 3.0% by mass. The nonaqueous electrolyte secondary battery according to claim 9 or 10, wherein the inorganic oxide particles are made of TiO ₂ having a rutile structure. A first step of preparing an inorganic oxide particle-containing positive electrode slurry containing inorganic oxide particles, positive electrode active material particles, and a binder;
A second step of applying the inorganic oxide particle-containing positive electrode slurry to the surface of the positive electrode current collector;
A third step of heating the inorganic oxide particle-containing positive electrode slurry to produce a positive electrode by drying while generating thermal convection; and
A fourth step in which a separator is disposed between the positive electrode and the negative electrode to produce an electrode body, and then the electrode body is impregnated with a nonaqueous electrolyte;
A method for producing a nonaqueous electrolyte secondary battery, comprising:   In the first step, inorganic oxide particles and a dispersion stabilizer are dispersed in a solvent to prepare an inorganic oxide particle dispersion, and positive electrode active material particles and a binder are dispersed in a solvent to obtain a positive electrode slurry. The manufacturing method of the nonaqueous electrolyte secondary battery according to claim 12, wherein the inorganic oxide particle dispersion liquid and the positive electrode slurry are mixed to prepare the inorganic oxide particle-containing positive electrode slurry.   The method for producing a non-aqueous electrolyte secondary battery according to claim 12 or 13, wherein the inorganic oxide particles have an average particle diameter of 10 to 500 nm.   The manufacturing method of the nonaqueous electrolyte secondary battery according to any one of claims 12 to 14, wherein the viscosity of the positive electrode slurry containing inorganic oxide particles in the second step is 0.6 to 2.0 Pa · s.   The method for producing a nonaqueous electrolyte secondary battery according to any one of claims 12 to 15, wherein the drying temperature in the third step is 100 to 150 ° C.