JP2011014254A - Manufacturing method of nonaqueous electrolyte secondary battery - Google Patents

Abstract

Provided is a method for producing a non-aqueous electrolyte secondary battery capable of suppressing corrosion of a positive electrode current collector even when a positive electrode active material contains a lithium-containing nickel composite oxide.
The method for producing a non-aqueous electrolyte secondary battery of the present invention includes (i) a step of preparing a positive electrode mixture slurry containing a positive electrode active material, water and a lithium salt, and (ii) the positive electrode mixture. The step of applying the agent slurry to the positive electrode current collector and drying to obtain the positive electrode is included. The positive electrode active material includes a lithium-containing nickel composite oxide. The positive electrode current collector preferably contains aluminum.
[Selection figure] None

Description

  The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery, and more particularly to a method for manufacturing a positive electrode used in a non-aqueous electrolyte secondary battery.

In recent years, in the field of non-aqueous electrolyte secondary batteries, research on lithium ion secondary batteries having high voltage and high energy density has been actively conducted. For example, a lithium-containing cobalt composite oxide (for example, LiCoO ₂ ) exhibiting a high charge / discharge voltage is used as the positive electrode active material in most of the commercially available lithium ion secondary batteries. However, there is a strong demand for higher capacity of the battery, and research and development has been actively conducted on a positive electrode active material having a higher capacity in place of LiCoO ₂ . In particular, research on lithium-containing nickel composite oxide (for example, LiNiO ₂ ) whose main component is nickel has been vigorously conducted.

  The positive electrode active material as described above can be produced, for example, by firing a lithium compound and a compound containing a transition metal such as Co or Ni. At this time, an unreacted lithium compound may remain in the positive electrode active material, for example, as lithium hydroxide (alkali component).

  The positive electrode included in the nonaqueous electrolyte secondary battery can include, for example, a positive electrode current collector and a positive electrode active material layer formed thereon. Such a positive electrode includes, for example, a positive electrode active material, a binder, a conductive agent, and the like dispersed in a dispersion medium such as water to obtain a positive electrode mixture slurry, and the obtained positive electrode mixture slurry is used as a positive electrode current collector. It can be obtained by applying to the body, drying and rolling if necessary. For this reason, especially when using water as a dispersion medium when preparing the positive electrode mixture slurry, the pH of the positive electrode mixture slurry rises to about 9 to 12 if an alkali component remains in the positive electrode active material. When a positive electrode mixture slurry having a high pH is applied to a positive electrode current collector made of, for example, aluminum, the positive electrode current collector is corroded, and hydrogen gas is generated at the interface between the positive electrode current collector and the positive electrode active material layer. The material layer may fall off or rise from the positive electrode current collector.

  Conventionally, in order to solve such problems, it has been proposed to neutralize an alkali component contained in a positive electrode active material using a neutralizing gas such as carbon dioxide gas before preparing a positive electrode mixture slurry. (See Patent Document 1). Specifically, in Patent Document 1, a neutralized gas is brought into contact with a mixed powder of a conductive agent and a positive electrode active material. Since the neutralizing gas is adsorbed on the surface of the conductive agent by bringing the neutralizing gas into contact with not only the positive electrode active material but also the conductive agent, the contact time and the contact probability between the positive electrode active material and the neutralizing gas can be increased. It is disclosed.

JP 2008-226515 A

  In particular, when a lithium-containing nickel composite oxide such as lithium nickelate is used as the positive electrode active material, not only the problem that the positive electrode active material as described above contains an alkali component, but also the lithium-containing nickel composite oxide There is also a problem that lithium hydroxide is produced by hydrolysis with water in the positive electrode mixture slurry. For this reason, when the mixture pace is prepared by dispersing lithium-containing nickel composite oxide in water, the pH of the positive electrode mixture slurry is increased even if the alkali component contained in the positive electrode active material is removed in advance. There is.

  Therefore, an object of the present invention is to provide a method for producing a nonaqueous electrolyte secondary battery that can suppress corrosion of a positive electrode current collector even when the positive electrode active material contains a lithium-containing nickel composite oxide. .

The method for producing the nonaqueous electrolyte secondary battery of the present invention is as follows.
(I) a step of preparing a positive electrode mixture slurry containing a positive electrode active material, water, and a lithium salt; and (ii) applying the positive electrode mixture slurry to a positive electrode current collector and drying the positive electrode mixture slurry. A obtaining step. The positive electrode active material includes a lithium-containing nickel composite oxide. The lithium-containing nickel composite oxide has a hexagonal layered structure, and the proportion of Ni in the metal element contained in the composite oxide is preferably 70 mol% or more. Specifically, the lithium-containing nickel composite oxide has the following general formula (1):
LiαNi _1-x M _x O _{2 + d} (1)
(Wherein M is at least one metal element selected from the group consisting of Co, Mn, Ti, and Al, and 0 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.2, and 0. 99 ≦ α ≦ 1.04.)
It is further preferred that

The lithium salt preferably includes a salt composed of lithium and a conjugate base of a strong acid. The lithium salts include LiF, LiCl, LiBr, LiI, LiBF ₄ , LiPF ₆ , CH ₃ COOLi, Li ₂ SO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiNO _3. More preferably, at least one selected from the group consisting of:
In the step (i), the amount of the lithium salt added to the positive electrode mixture slurry preferably occupies 0.1 to 5% by weight of the positive electrode mixture slurry. The pH of the positive electrode mixture slurry is preferably 7.0 to 12.1.

  The positive electrode current collector preferably contains aluminum.

  In the production method of the present invention, a lithium salt is added to the aqueous dispersion of the positive electrode active material when preparing the positive electrode mixture slurry. Since the lithium salt dissociates into ions in the positive electrode mixture slurry, lithium ions can be present in the positive electrode mixture slurry. Due to the presence of lithium ions in the positive electrode mixture slurry, hydrolysis of the lithium-containing nickel composite oxide is suppressed due to the common ion effect of lithium ions, and generation of lithium hydroxide in the positive electrode mixture slurry is suppressed. can do. Therefore, according to the present invention, an increase in the hydroxide ion concentration in the positive electrode mixture slurry can be suppressed.

  Among various positive electrode current collectors, a positive electrode current collector containing aluminum is easily corroded in an alkaline environment. For this reason, this invention is especially suitable when using the positive electrode electrical power collector containing aluminum.

It is a longitudinal cross-sectional view which shows roughly an example of the nonaqueous electrolyte secondary battery produced with the manufacturing method of this invention.

The method for producing the nonaqueous electrolyte secondary battery of the present invention is as follows.
(I) a step of preparing a positive electrode mixture slurry containing a positive electrode active material, water, and a lithium salt; and (ii) applying the positive electrode mixture slurry to a positive electrode current collector and drying the positive electrode mixture slurry. A obtaining step. The positive electrode active material includes a lithium-containing nickel composite oxide. The present invention is characterized by the step (i).

In the step (i), at least a positive electrode active material, water, and a lithium salt are mixed to prepare a positive electrode mixture slurry. As described above, when the lithium-containing nickel composite oxide is used as the positive electrode active material, the lithium-containing nickel composite oxide is hydrolyzed to produce lithium hydroxide. For example, taking lithium nickelate (LiNiO ₂ ) as an example, the hydrolysis of lithium nickelate is represented by the following formula:
LiNiO ₂ + H ₂ O⇔HNiO ₂ + LiOH (A)
It is represented by As shown on the right side of the formula (A), HNiO ₂ and LiOH are generated by hydrolysis of LiNiO ₂ . LiOH is dissociated into Li ⁺ and OH ^{− in the} positive electrode mixture slurry.

Therefore, in the present invention, in preparing the positive electrode mixture slurry in the step (i), a lithium salt is added to the aqueous dispersion of the positive electrode active material. Since the lithium salt is dissociated into ions in the positive electrode mixture slurry, lithium ions are present in the positive electrode mixture slurry. Due to the presence of lithium ions in the positive electrode mixture slurry, the reaction that proceeds to the left side of the formula (A) becomes dominant. That is, hydrolysis of the lithium-containing nickel composite oxide is suppressed by the common ion effect of lithium ions. Therefore, an increase in the hydroxide ion concentration in the positive electrode mixture slurry can be suppressed, and as a result, corrosion of the positive electrode current collector can be suppressed during the production of the positive electrode. Moreover, since the corrosion of the positive electrode current collector can be suppressed, the yield at the time of manufacturing the positive electrode can be improved.
Further, since water can be used instead of an organic solvent as a dispersion medium for preparing the positive electrode mixture slurry, discharge of VOC and the like during battery production can be reduced.

Although it is conceivable that carbon dioxide gas is bubbled into the prepared positive electrode mixture slurry, the supply amount of carbon dioxide gas is adjusted according to the temperature of the positive electrode mixture slurry, the atmosphere in which the positive electrode mixture slurry is placed, and the like. Since it is necessary, the process of preparing the positive electrode mixture slurry becomes complicated. On the other hand, in the present invention, the equilibrium reaction represented by the formula (A) is controlled only by adding a lithium salt to the positive electrode mixture slurry. Therefore, an increase in pH of the positive electrode mixture slurry can be suppressed by a simple operation.
Furthermore, when carbon dioxide gas is bubbled through the positive electrode mixture slurry, lithium carbonate is generated. Such lithium carbonate is decomposed when the battery is stored at a high temperature or a charge / discharge cycle is repeated, and carbon dioxide gas is generated in the battery. As described above, when gas is generated in the battery, the internal pressure of the battery rises and a problem may occur.

As the positive electrode active material, the following general formula (1):
LiαNi _1-x M _x O _{2 + d} (1)
(Wherein M is at least one metal element selected from the group consisting of Co, Mn, Ti, and Al, and 0 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.2, and 0. 99 ≦ α ≦ 1.04.)
It is preferable to use a lithium-containing nickel composite oxide represented by Since the composite oxide has a high Ni content, it has a high capacity, but the reactivity between the composite oxide and water as a dispersion medium during slurry preparation is significantly high when the nickel content is high. Become. However, even when such a complex oxide is used, hydrolysis of the complex oxide can be remarkably suppressed according to the present invention.
Furthermore, when a part of nickel contained in the composite oxide is replaced with a metal element other than Ni, it is possible to reduce the change in the crystal structure of the composite oxide. As a result, the charge / discharge cycle life of the composite oxide can be improved.

  The molar ratio x of the element M is more preferably 0 ≦ x ≦ 0.1. Thereby, the effect of this invention can be acquired notably.

The lithium salt preferably includes a salt composed of lithium and a conjugate base of a strong acid. Such a salt has a large dissociation constant. Therefore, lithium ions can be stably present in the positive electrode mixture slurry containing water as a dispersion medium. In the present invention, a strong acid refers to an acid having a pKa (-log ₁₀ Ka; Ka is an acid dissociation constant) in water of 5 or less.

Examples of the salt composed of lithium and a strong acid conjugate base include LiF, LiCl, LiBr, LiI, LiBF ₄ , LiPF ₆ , CH ₃ COOLi, Li ₂ SO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiNO ₃ . The lithium salt preferably includes at least one of the salts.

The amount of the lithium salt added to the positive electrode mixture slurry preferably occupies 0.1 to 5% by weight of the positive electrode mixture slurry. If the amount of the lithium salt is less than 0.1% by weight, the amount of lithium ions present in the positive electrode mixture slurry cannot be sufficiently increased, and thus the pH of the positive electrode mixture slurry is sufficiently increased. May not be suppressed.
When the amount of the lithium salt is more than 5% by weight, a decrease in capacity per unit electrode volume due to the presence of the lithium salt in the positive electrode mixture may not be negligible.

  The weight ratio between the lithium-containing nickel composite oxide and the lithium salt in the positive electrode mixture slurry is preferably 99.9: 0.1 to 95.0: 5.0. The ratio between the number of moles of the lithium-containing nickel composite oxide and the number of moles of lithium contained in the lithium salt is preferably 1: 0.1 to 1: 0.0001.

  The pH of the positive electrode mixture slurry after adding the lithium salt is preferably 7.0 to 12.1. When the pH of the positive electrode mixture slurry is higher than 12.1, corrosion of the current collector made of aluminum foil cannot be ignored, and the positive electrode mixture may frequently fall off after the electrode is manufactured. Similarly, when the pH of the positive electrode mixture slurry is smaller than 7.0, corrosion of the current collector made of aluminum foil may occur, and the positive electrode mixture may fall off after the electrode is manufactured.

  As a material constituting the positive electrode current collector, a material known in the art can be used. Examples of such a material include stainless steel, aluminum, and titanium.

Among these, the present invention is particularly effective when the positive electrode current collector contains aluminum. As described above, when the positive electrode mixture slurry having a high pH is applied to the positive electrode current collector containing aluminum, the positive electrode current collector may be corroded. However, according to the present invention, an increase in the pH of the positive electrode mixture slurry can be suppressed. Therefore, according to the present invention, corrosion of the positive electrode current collector when the positive electrode mixture paste is applied to the positive electrode current collector containing aluminum can be suppressed.
Examples of the positive electrode current collector containing aluminum include aluminum foil and aluminum alloy foil.

  In addition, the thickness of a positive electrode electrical power collector should just be in the range of 1-500 micrometers.

  The positive electrode mixture slurry may contain a binder, a conductive agent, and the like in addition to the positive electrode active material, water, and lithium salt.

  As a binder used for the positive electrode, sodium salt of carboxymethyl cellulose, polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer Etc.

  Conductive agents used for the positive electrode include natural graphite (such as flake graphite), graphite such as artificial graphite and expanded graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black. , Conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives.

  In the step (ii), the positive electrode mixture slurry is applied to the positive electrode current collector and dried to form a positive electrode active material layer on the positive electrode current collector. Application | coating and drying of a positive mix slurry can be performed using a well-known method in the said field | area.

The application of the positive electrode mixture slurry to the positive electrode current collector can be performed by, for example, a doctor blade method.
Drying of the positive electrode mixture slurry can be performed at 50 to 130 ° C.

  Further, if necessary, the positive electrode active material layer may be rolled so that the positive electrode active material layer has a predetermined density.

  The thickness of the positive electrode active material layer may be in the range of 50 to 130 μm per one surface of the positive electrode current collector, although it depends on the type and size of the battery to be produced.

In the method for producing a non-aqueous electrolyte secondary battery of the present invention,
(Iii) producing a negative electrode;
(Iv) a step of producing an electrode group using the obtained positive electrode and negative electrode, and (v) a step of producing a non-aqueous electrolyte secondary battery using the obtained electrode group. A secondary battery can be manufactured.

FIG. 1 shows an example of a nonaqueous electrolyte secondary battery produced by the production method of the present invention.
A battery 10 in FIG. 1 includes a battery case 11, a wound electrode group 12, a nonaqueous electrolyte (not shown), and a sealing plate 20 that seals an opening of the battery case 11. The electrode group 12 includes the positive electrode 13 and the negative electrode 14 produced as described above, and the separator 15 disposed between the positive electrode 13 and the negative electrode 14.

The electrode group 12 is accommodated in the battery case 11. An upper insulating plate 16 is disposed above the electrode group 12, and a lower insulating plate 17 is disposed below the electrode group 12.
One end of a positive electrode lead 18 is connected to the positive electrode 13. The other end of the positive electrode lead 18 is connected to the lower part of the sealing plate 20. One end of a negative electrode lead 19 is connected to the negative electrode 14. The other end of the negative electrode lead 19 is connected to the inner bottom surface of the battery case 11.

  The opening of the battery case 11 is sealed by caulking the opening end of the battery case 11 to the peripheral edge of the sealing plate 20 via the insulating gasket 21.

Hereinafter, a method for producing the nonaqueous electrolyte secondary battery shown in FIG. 1 will be described.
In the step (iii), the negative electrode 14 is produced. The negative electrode 14 can be obtained, for example, by applying a negative electrode mixture slurry to a negative electrode current collector and drying it.
As a material which comprises a negative electrode collector, a well-known material can be included in the said field | area. As such a material, copper, nickel, stainless steel, or the like can be used.
The thickness of the negative electrode current collector may be in the range of 1 to 500 μm.

The negative electrode mixture slurry can be prepared, for example, by mixing a negative electrode active material, a dispersion medium, and, if necessary, a conductive agent and a binder.
As the negative electrode active material, materials known in the art can be used. Examples of such materials include graphites such as natural graphite (such as flake graphite), artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, silicon Examples thereof include simple substances, silicon oxides, silicon nitrides, silicon alloys, tin simple substances, tin oxides, tin nitrides, and tin alloys.
As the binder and the conductive agent used for the negative electrode, the same materials as the binder and the conductive agent used for the positive electrode can be used.
In addition, the dispersion medium used when preparing the negative electrode mixture slurry is appropriately selected according to the type of the negative electrode active material, the type of the binder, and the like. As the dispersion medium, for example, water, N-methyl-2-pyrrolidone, or the like can be used.

  The thickness of the negative electrode active material layer may be in the range of 50 to 100 μm per one side of the negative electrode current collector, although it depends on the type and size of the battery to be produced.

  In the step (iv), the wound electrode group 12 can be obtained by winding the positive electrode 13, the negative electrode 14, and the separator 15 disposed therebetween in a spiral shape.

In the step (v), a non-aqueous electrolyte secondary battery is manufactured using the obtained electrode group 12. Specifically, one end of the positive electrode lead 18 is connected to the positive electrode 13 included in the electrode group 12, and one end of the negative electrode lead 19 is connected to the negative electrode 14. At this time, the positive electrode lead 18 protrudes from one end face of the electrode group 12 in the winding axis direction, and the negative electrode lead 19 protrudes from the other end face of the electrode group 12 in the winding axis direction.
The electrode group 12 is accommodated in the battery case 11 with the upper insulating plate 16 disposed above the electrode group 12 and the lower insulating plate 17 disposed below the electrode group 12. The other end of the positive electrode lead 18 is connected to the lower part of the sealing plate 20, and the other end of the negative electrode lead 19 is connected to the inner bottom surface of the battery case 11.
A nonaqueous electrolyte is injected into the battery case 11, and the opening end of the battery case 11 is then sealed by crimping the opening end of the battery case 11 to the peripheral edge of the sealing plate 20 via an insulating gasket. In this way, the nonaqueous electrolyte secondary battery 10 can be manufactured.

  As a material constituting the separator 15, a material known in the art can be used. Examples of such a material include polyethylene, polypropylene, a mixture of polyethylene and polypropylene, or a copolymer of ethylene and propylene.

  Nonaqueous electrolytes can include, for example, nonaqueous solvents and solutes dissolved therein. As the non-aqueous solvent, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like can be used.

Examples of the solute include LiPF ₆ , LiBF ₄ , LiCl ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₂ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , imides and the like can be used.

  Examples of the constituent material of the positive electrode lead 18 include metal aluminum and aluminum alloy. Examples of the constituent material of the negative electrode lead 19 include nickel. The constituent material of the battery case 11 is appropriately selected from materials known in the art depending on the type of battery to be manufactured.

  The battery manufactured by the manufacturing method of the present invention is not limited to the cylindrical battery as shown in FIG. The battery produced by the production method of the present invention may be, for example, a coin type, a sheet type, or a square type. The battery may be a large battery used for an electric vehicle or the like. Furthermore, the electrode group included in the battery produced by the production method of the present invention may be a wound type or a laminated type.

Example 1
A positive electrode mixture slurry was prepared as follows. LiNi _0.8 Co _0.2 O ₂ was used as the positive electrode active material. LiF was used as the lithium salt. As the binder, sodium salt of carboxymethyl cellulose was used, and as the conductive agent, acetylene black was used.

  A positive electrode mixture slurry was prepared by mixing 47 parts by weight of a positive electrode active material, 1 part by weight of a binder, 1 part by weight of a conductive agent, 50 parts by weight of water, and 1 part by weight of a lithium salt. The amount of the lithium salt was 1% by weight of the positive electrode mixture slurry.

<< Comparative Example 1 >>
A positive electrode mixture slurry was prepared in the same manner as in Example 1 except that no lithium salt was added.

  The pH of the positive electrode mixture slurry prepared in Example 1 and the slurry prepared in Comparative Example 1 were measured. As a result, the pH of the positive electrode mixture slurry prepared in Example 1 was 10.6, and the pH of the positive electrode mixture slurry prepared in Comparative Example 1 was 12.7. From these results, it can be seen that the addition of a lithium salt to the positive electrode mixture slurry in which the lithium-containing nickel composite oxide, which is the positive electrode active material, is dispersed in water can suppress an increase in the pH of the positive electrode mixture slurry. . In addition to the LiF, it was confirmed that the same result was obtained as long as it was a lithium salt that can dissociate into ions in the positive electrode mixture slurry and release lithium ions.

Example 2
(Battery 1)
A battery as shown in FIG. 1 was produced.
The positive electrode mixture slurry prepared in Example 1 was applied to both sides of an aluminum positive electrode current collector (thickness: 20 μm), dried and rolled to produce a positive electrode. The thickness of the positive electrode was 140 μm.

  A negative electrode was produced as follows. As the negative electrode active material, artificial graphite (KS-6 manufactured by Timcal Japan) was used. As the binder, an emulsion of carboxymethyl cellulose and styrene butadiene latex was used.

  A negative electrode mixture slurry is prepared by mixing 48 parts by weight of a negative electrode active material, 1 part by weight of carboxymethyl cellulose as a binder and 1 part by weight of an emulsion of styrene butadiene latex, and 50 parts by weight of water as a dispersion medium. did.

  The obtained negative electrode mixture slurry was applied to both sides of a copper negative electrode current collector (thickness: 10 μm), dried and rolled to obtain a negative electrode. The thickness of the negative electrode was 130 μm.

  The positive electrode and negative electrode obtained as described above and a polyethylene separator (thickness: 20 μm) disposed between them were wound in a spiral shape to produce a wound electrode group. One end of an aluminum positive electrode lead was connected to the positive electrode of the electrode group, and one end of a nickel negative electrode lead was connected to the negative electrode.

  The electrode group was accommodated in a nickel-plated iron battery case with an upper insulating plate disposed at the top and a lower insulating plate disposed at the bottom. The other end of the positive electrode lead was welded to the bottom of the sealing plate, and the other end of the negative electrode lead was welded to the inner bottom surface of the battery case.

A non-aqueous electrolyte was poured into the battery case, and then the battery case was sealed by caulking the opening end of the battery case to the peripheral edge of the sealing plate via a polyethylene insulating gasket. The nonaqueous electrolyte secondary battery produced in this manner was designated as battery 1.
The non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1.25 mol / L in a mixed solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 3. . The nominal capacity of the fabricated battery was set to about 2000 mAh when calculated using the weight of the positive electrode active material.

(Battery 2)
A battery 2 was produced in the same manner as the battery 1 except that the amount of the lithium salt added to the positive electrode mixture slurry was 0.1% by weight. The weight ratio of the positive electrode active material (LiNi _0.8 Co _0.2 O ₂ ) to the lithium salt (LiF) was 47: 0.1.

(Battery 3)
A battery 3 was produced in the same manner as the battery 1 except that the amount of the lithium salt added to the positive electrode mixture slurry was 5% by weight. The weight ratio of the positive electrode active material (LiNi _0.8 Co _0.2 O ₂ ) to the lithium salt (LiF) was 47: 5.

(Battery 4)
A battery 4 was produced in the same manner as the battery 1 except that the amount of the lithium salt added to the positive electrode mixture slurry was 0.08% by weight. The weight ratio of the positive electrode active material (LiNi _0.8 Co _0.2 O ₂ ) to the lithium salt (LiF) was 47: 0.08.

(Battery 5)
A battery 5 was produced in the same manner as the battery 1 except that the amount of the lithium salt added to the positive electrode mixture slurry was 5.2% by weight. The weight ratio of the positive electrode active material (LiNi _0.8 Co _0.2 O ₂ ) to the lithium salt (LiF) was 47: 5.2.

[Evaluation]
Each manufactured battery was charged with a charging current of 400 mA until the battery voltage reached 4.2 V, and then further charged with a constant voltage of 4.2 V for 3 hours. Next, the charged battery was discharged at a discharge current of 400 mA, and the discharge capacity (discharge capacity of 400 mA) at this time was determined. The results are shown in Table 1.
Moreover, it charged similarly to the above, the battery after charge was discharged with the discharge current 4000mA, and the discharge capacity at this time (discharge capacity in 4000mA) was calculated | required. The ratio of the discharge capacity at 4000 mA to the discharge capacity of 400 mA was defined as the discharge rate characteristic.
Furthermore, the internal resistance of each battery was measured using the AC impedance method (measurement frequency 1 kHz).

  The results of the evaluation are shown in Table 1. In Table 1, the discharge rate characteristic is expressed as a percentage value.

As shown in Table 1, the discharge capacity decreased as the proportion of the lithium salt in the positive electrode mixture slurry increased. This is presumably because the proportion of the active material per unit weight of the electrode decreases as the amount of lithium salt added increases.
The internal resistance of the battery was slightly higher when 0.1% by weight of lithium salt was added (Battery 2). This is presumably because when the amount of lithium salt added is small, corrosion of the aluminum foil as the current collector proceeds to some extent, and the electronic conductivity between the current collector and the active material is reduced.
The discharge rate characteristics were somewhat degraded regardless of whether the amount of lithium salt added was small or large. In the battery 2 in which the addition amount of the lithium salt is small, it is considered that the discharge rate characteristics are deteriorated because the internal resistance is increased as described above. On the other hand, in the battery 5 in which the amount of lithium salt added is large, the lithium salt is present in a solid state in the positive electrode active material layer, and thus diffusion of lithium ions to the nonaqueous electrolyte is inhibited. As a result, it is considered that the discharge rate characteristics have deteriorated.

  According to the present invention, an increase in pH of a positive electrode mixture slurry prepared by dispersing a positive electrode active material such as a lithium-containing nickel composite oxide in water can be suppressed. Therefore, the production method of the present invention can suppress the corrosion of the positive electrode current collector during the production of the positive electrode. As a result, the yield of the positive electrode can be improved.

DESCRIPTION OF SYMBOLS 10 Battery 11 Battery case 12 Electrode group 13 Positive electrode 14 Negative electrode 15 Separator 16 Upper insulating plate 17 Lower insulating plate 18 Positive electrode lead 19 Negative electrode lead 20 Sealing plate 21 Insulating gasket

Claims (7)

(I) a step of preparing a positive electrode mixture slurry containing a positive electrode active material, water, and a lithium salt; and (ii) applying the positive electrode mixture slurry to a positive electrode current collector and drying the positive electrode mixture slurry. Including a step of obtaining
The manufacturing method of the nonaqueous electrolyte secondary battery in which the said positive electrode active material contains lithium containing nickel complex oxide. The lithium-containing nickel composite oxide has the following general formula (1):
LiαNi _1-x M _x O _{2 + d} (1)
(Wherein M is at least one metal element selected from the group consisting of Co, Mn, Ti, and Al, and 0 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.2, and 0. 99 ≦ α ≦ 1.04.)
The nonaqueous electrolyte secondary battery of Claim 1 represented by these.   The method for producing a nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode current collector contains aluminum.   The manufacturing method of the nonaqueous electrolyte secondary battery in any one of Claims 1-3 in which the said lithium salt contains the salt which consists of lithium and the conjugate base of a strong acid. The lithium salt is LiF, LiCl, LiBr, LiI, LiBF ₄ , LiPF ₆ , CH ₃ COOLi, Li ₂ SO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiNO _3. The manufacturing method of the nonaqueous electrolyte secondary battery of Claim 4 containing at least 1 sort (s) selected from the group which consists of.   The manufacturing method of the nonaqueous electrolyte secondary battery in any one of Claims 1-5 in which the quantity of the said lithium salt occupies 0.1 to 5 weight% of the said positive mix slurry.   The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode mixture slurry has a pH of 7.0 to 12.1.

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