JPH09306546A - Positive electrode plate for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a positive electrode plate for a nonaqueous secondary battery capable of increasing a bulk density to increase discharging capacity, and moreover preventing short-circuiting between electrode plates due to carbon powder. SOLUTION: Ink for a positive electrode mixture is manufactured by kneading lithium-containing double oxide powder (LiCoO powder): composed of the particle diameter mixed powder of powder having a mean particle diameter of 1-10μm, and powder having a mean particle diameter of 20-30μm, a conductive assistant: composed of carbon powder having a mean particle diameter of 0.1-10μm, and a binding agent. The positive electrode mixture ink is applied to a collector, and then dried to form a positive electrode mixture layer. The containing rate of powder, having a mean particle diameter of 1-10μm in lithium- containing double oxide powder, is to be 5-50wt.%, and carbon powder is contained 5-10wt.% to the positive electrode mixture.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a positive electrode plate for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art A positive electrode material made of a material such as manganese or vanadium oxide capable of inserting and removing lithium is used.
A non-aqueous electrolyte secondary battery is known in which metallic lithium is used as a negative electrode material and a non-aqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent is used as an electrolyte. Since this type of battery uses metallic lithium, there is a risk of a short circuit or the like due to generation of dendrites, and it was difficult to put it into practical use. Therefore, a positive electrode material is formed of a positive electrode mixture made of a mixture of a lithium-containing composite oxide, a conductive auxiliary agent made of carbon powder, and a binder, and a material such as graphite capable of inserting and releasing lithium is used for the negative electrode. A rocking chair type battery (lithium ion non-aqueous electrolyte secondary battery) has been proposed in which a material is formed to prevent metallic lithium clusters from existing inside the battery system. In these non-aqueous electrolyte secondary batteries, it is required to increase capacity (energy density) in a small volume.
For that purpose, it is important to increase the packing density of the active material material of the positive electrode material and the negative electrode material. However, in the case of a positive electrode material (positive electrode mixture) mainly composed of an inorganic compound (lithium-containing composite oxide), a large proportion of the positive electrode mixture contains a substance such as a conduction aid that is not directly involved in charging / discharging. Further, since the thickness of the electrode is thin, there is a limit to increase the bulk density of the positive electrode mixture. Therefore, it has been difficult to densely fill the lithium-containing composite oxide.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 4-162357, it has been studied to optimize the average particle diameter and the compounding ratio of the lithium-containing composite oxide and the conductive additive (carbon powder). In the technique disclosed in the publication, the lithium-containing composite oxide has an average particle diameter of 1 μm or more and less than 10 μm, a carbon powder having an average particle diameter of 0.1 μm or more and less than 10 μm as a conductive additive, and an average particle diameter of 0.01 μm or more and 0.08 μm. Two types of carbon powders are used: Then, it has been proposed to specify the weight ratio of the carbon powder to the lithium-containing composite oxide. In this technique, a carbon powder having a small particle diameter forms a conductive network that ensures mutual electrical contact between lithium-containing complex oxides, and a carbon powder having a large particle diameter forms a conductive network and a conductive network and a collector and a conductive network. Ensure electrical contact. Thereby, the content of carbon powder in the positive electrode mixture can be reduced.

[0004]

A positive electrode plate for a non-aqueous electrolyte secondary battery is usually manufactured by applying an ink for a positive electrode mixture to the surface of a current collector such as an aluminum foil having a thickness of several 10 μm and having a thickness of about 100 μm. Form a layer of agent. However, as described above, when a carbon powder having a very small particle size of 0.01 μm or more and less than 0.08 μm is used, the fluidity of the ink for positive electrode mixture becomes low, and the positive electrode mixture having a uniform thickness is obtained. There is a problem that it is difficult to form the layer. Therefore, the bulk density of the positive electrode mixture decreases, and it becomes difficult to increase the capacity. In addition, in the range in which the present inventor has conducted an experiment, the thickness of the layer of the positive electrode mixture could not be made substantially constant, and therefore, the capacity that decreases as described above is the same as that of the conductive additive disclosed in the above publication. It exceeded the capacity increase obtained by the reduction of the compounding ratio.

Further, since the carbon powder having such a very small particle diameter is smaller than the average pore diameter of the pores formed in the commonly used separator, the carbon powder falls off from the surface of the positive electrode when the battery is repeatedly charged and discharged. It was found that the carbon powder formed entered the holes of the separator and caused a short circuit.

If carbon powder having such a very small particle size is not used, these problems can be solved, but as mentioned above, there is a problem that a large amount of conductive auxiliary agent must be added. .

An object of the present invention is to provide a positive electrode plate for a non-aqueous electrolyte secondary battery, which can increase the bulk density of the positive electrode mixture to increase the discharge capacity and can prevent a short circuit between the electrode plates due to carbon powder. It is in.

[0008]

In order to solve the above-mentioned problems, the present invention does not use carbon powder having a small average particle diameter, but has an average particle diameter of 1 to 1 as lithium-containing double oxide powder.
An average particle size of 0.1 was obtained as carbon powder by using a mixed powder of particle sizes of 0 μm powder and powder having an average particle size of 20 to 30 μm.
Powder of 10 μm is used.

As described above, when a carbon powder having an average particle diameter of 0.1 to 10 μm is used as a conduction aid without using a carbon powder having a small average particle diameter (0.01 μm or more and less than 0.08 μm). However, it is necessary to add a large amount of the conductive auxiliary agent, and in a usual structure, it becomes difficult to densely fill the lithium-containing composite oxide, and the capacity cannot be increased. However, the inventors have found that the bulk density of the positive electrode mixture can be relatively easily increased when an appropriate amount of lithium-containing composite oxide powder having an average particle diameter of 20 to 30 μm is used. This is because first, when the particle size of the lithium-containing mixed oxide powder is increased, the fluidity of the positive electrode mixture ink is increased, the thickness of the positive electrode mixture layer can be made uniform, and compression molding of the positive electrode mixture layer by pressing can be performed. It is considered that this is done effectively. However, when only the lithium-containing composite oxide powder having a large particle size is used, the capacity obtained is lower than usual. This is because when only a lithium-containing mixed oxide powder having a large particle size is used, it is possible to move to a lithium site (where lithium can be stable in the crystal) in the crystal structure in which lithium ions are formed in the powder particle. It is considered that this is because the reaction efficiency decreases due to an increase in the migration distance, that is, an increase in diffusion resistance in the solid phase in the lithium insertion reaction of the lithium-containing composite oxide powder itself.

Therefore, the inventor has found that the lithium-containing composite oxide powder having a relatively large average particle diameter (20 to 30 μm) and the relatively small average particle diameter (1 to 10 μm) having good reaction efficiency.
m) It has been found that the bulk density of the positive electrode mixture can be increased and the capacity of the battery can be increased by using the mixed powder having a particle size in which the lithium-containing mixed oxide powder is mixed.

Further, in the present invention, carbon powder having a small particle size is not used as the conductive additive, and the average particle size is 0.1 to 10 μm.
Since only the carbon powder of No. 3 is used, the occurrence of short circuit inside the battery can be reduced.

When a lithium-containing mixed oxide powder having an average particle diameter of less than 1 μm is added, the properties of the positive electrode mixture ink change and it becomes difficult to form a positive electrode mixture layer having a uniform thickness.
When a lithium-containing mixed oxide powder having an average particle size of 10 μm to 20 μm is added, the average particle size of 20 μm
The effect obtained by the above lithium-containing mixed oxide powder is diminished. Further, when a lithium-containing composite oxide powder having an average particle diameter of more than 30 μm is added, the electrochemical characteristics are deteriorated and the capacity of the battery is reduced. Further, secondary processing such as granulation may be required to obtain the lithium-containing composite oxide powder having such a large average particle size, which is not preferable from the viewpoint of increasing the number of manufacturing processes. Further, as the carbon powder, the lower limit of the average particle size is 0.1 μm from the viewpoint of the above-mentioned short circuit prevention.
Should be. Further, if the particles having a particle size of 10 μm or more are used, the characteristics as a conductive additive are deteriorated, so the upper limit of the average particle size should be 10 μm.

The content of the powder having an average particle diameter of 1 to 10 μm in the lithium-containing mixed oxide powder is 5 to 50% by weight,
The carbon powder needs to be contained in an amount of 5 to 10% by weight based on the positive electrode mixture. With such a blending ratio, the bulk density of the positive electrode mixture becomes high and the capacity of the battery becomes high.

In the present invention, since only the carbon powder of 0.1 to 10 μm is used, the conductivity is expected to decrease, but by specifying the blending ratio of the two kinds of lithium-containing composite oxides, It was possible to prevent the conductivity from decreasing. This is because the amount of the powder having an average particle diameter of 20 to 30 μm becomes more than half, so by adding a relatively small amount of the lithium-containing composite oxide powder, it is possible to form a conductive network between the lithium-containing composite oxide powders. It is considered that this is because electrical contact can be achieved between the conductive networks and between the conductive networks and the current collector.

The lithium-containing complex oxide referred to here is a complex oxide containing lithium, such as LiCoO ₂ and L.
iNiO ₂ , LiCo _0.97 Sn _0.03 O ₂ , LiCo _0.96
It can be used _{Al 0.05 O 2, LiCo 0.98 In} 0.06 O 2 and the like. As the carbon powder, graphite, amorphous carbon or the like can be used. Further, as the binder, a fluororesin such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) can be used. Further, the positive electrode plate may be impregnated with an electrolyte (non-aqueous electrolytic solution). The non-aqueous electrolyte is formed by dissolving a lithium salt in an organic solvent. As lithium salts,
LiClO ₄ , LiBF ₄ , LiAsF ₆ , CF ₃ SO
₃ Li, LiPF ₆ or the like can be used. As the organic solvent, propylene carbonate, ethylene carbonate, dimethyl carbonate, tetrohydrofuran, or a mixture thereof can be used.

The powder having the range of each average particle size is a powder having one peak of particle distribution within the range and the average value of the particle size falls within the range. For example, powder having an average particle size of 1 to 10 μm means a particle size of 1 to 1
The powder has one particle distribution peak in the range of 0 μm, and the average particle diameter falls within the range of 1 to 10 μm.

To make a non-aqueous electrolyte secondary battery using the positive electrode plate of the present invention, the positive electrode plate and the negative electrode plate of the present invention may be laminated with an electrolyte layer containing a non-aqueous electrolytic solution interposed therebetween. In this case, as the negative electrode plate, metallic lithium or graphite that absorbs and releases lithium ions can be used as the negative electrode material.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Positive electrode plates for non-aqueous electrolyte secondary batteries of Examples and Comparative Examples used for the test were manufactured as follows. First, a lithium-containing composite oxide powder made of lithium cobalt oxide (LiCoO ₂ ) having an average particle size and weight ratio shown in Table 1, a conductive additive made of carbon powder, and a binder made of polyvinylidene fluoride (PVDF). , N-methyl-
Ink for a positive electrode mixture was prepared by kneading with a dispersion solvent composed of 2-pyrrolidone (NMP). The weight ratios (% by weight) shown in Table 1 are respective weight ratios with respect to the positive electrode mixture layer (the positive electrode mixture ink from which the dispersion solvent has been removed) to be formed later. Further, as the carbon powder having an average particle diameter of 0.1 μm or more, carbon powder made of graphite was used, and
The carbon powder of acetylene black was used as the carbon powder of 05 μm. Next, the ink for the positive electrode mixture was coated with a thickness of 20 μm.
After being applied to the positive electrode current collector made of aluminum foil with a bar coater, it is dried at 100 ° C. and then pressed,
Each positive electrode plate was completed by forming a positive electrode material mixture layer having a thickness of about 90 μm. The pressing was performed at a pressure within the range in which the maximum packing density of each electrode plate was obtained and the positive electrode material mixture layer was not peeled or stretched.

[0019]

[Table 1] Next, the bulk density (g / cm ³ ) of the positive electrode mixture layer of each positive electrode plate was measured. The bulk density is substantially the weight density of the positive electrode mixture layer, and was calculated from the formula (weight of positive electrode plate-weight of current collector) / (volume of positive electrode mixture layer). The volume of the positive electrode mixture layer was calculated by the formula (area of positive electrode plate) × (thickness of positive electrode plate−thickness of current collector). Table 2 shows the measurement results. From Table 2, it can be seen that the positive electrode plates of Examples 1 to 7 have high bulk density.
On the other hand, it can be seen that the positive electrode plates of Comparative Examples 1, 3, 6, 7 have a low bulk density. This is because the positive electrode plates of Comparative Examples 1 and 3 used LiCoO ₂ powder having a small average particle size, and Comparative Example 6
This is because the positive electrode plate of No. 7 used carbon powder (acetylene black) having a small average particle size, so the fluidity of the positive electrode mixture ink was high, and the positive electrode mixture layer with a uniform thickness could not be formed.

Next, each of the above positive electrode plates was placed in a non-aqueous electrolyte prepared by dissolving 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1. , And a metallic lithium counter electrode having a capacity exceeding the theoretical capacity of the positive electrode plate, respectively,
The positive electrode plate and the counter electrode were charged for 5 hours at a rate of 2.5 to 4.2 V with respect to the counter electrode (metal lithium), and then discharged for 5 hours to measure the discharge capacity of each positive electrode plate. Then, the discharge capacity per unit weight in the positive electrode mixture layer of each positive electrode plate and the discharge capacity per unit volume in the positive electrode mixture layer of each positive electrode plate were obtained. Table 2 shows the measurement results. From Table 2, it can be seen that the discharge capacity per unit weight and the discharge capacity per unit volume can be increased by using the positive electrode plates of Examples 1 to 7. On the other hand, it can be seen that the discharge capacity per unit weight and the discharge capacity per unit volume are reduced particularly when the positive electrode plates of Comparative Examples 2 and 4 are used. This is because the positive electrode plates of Comparative Examples 2 and 4 used the lithium cobalt oxide powder having a large particle size, and thus the reaction efficiency was lowered. Further, in the positive electrode plate of Comparative Example 5, since the carbon powder having a large particle diameter was used, the utilization ratio of the active material was lowered and the capacity was lowered. Further, in the positive electrode plate of Comparative Example 6, a carbon powder having a small particle size (acetylene black) was used to increase the capacity of the battery.
It turns out that it does not reach the positive electrode plates of Examples 1 to 7.

Next, the above positive electrode plates and a known negative electrode plate using graphite as a negative electrode material are wound so as to be laminated via a separator sold by Polyplastics Co., Ltd. under the trade name of Celgard 2500, and an electrode plate group is wound. Each made. Next, each electrode plate group is housed in a battery can, and then the nonaqueous electrolytic solution used in the above-mentioned test is poured into the battery can to impregnate the electrode plate and the separator with the electrolytic solution to form a lithium ion battery. I made 1000 each. Then, a voltage of 300 V is applied between the terminals of each lithium ion battery for 0.5 seconds,
The occurrence rate of the short-circuited product was examined with a current of 0.5 mA or more flowing as the short-circuited product. Table 2 shows the measurement results.
From Table 2, it can be seen that the batteries using the positive electrode plates of Comparative Examples 6 and 7 using the carbon powder (acetylene black) having a small particle size are more likely to cause a short circuit than the batteries using other positive electrode plates.

[0022]

[Table 2] Next, the average particle diameter of the LiCoO ₂ powder was 5 μm (1-10
(in the range of μm), the content ratio of the powder is changed, and the other positive electrode plates are made in the same manner as in Example 1 and the bulk density of each positive electrode plate is measured. The relationship with density was investigated. FIG. 1 shows the measurement result. From this figure, it can be seen that the bulk density decreases when the content ratio of the powder having the average particle diameter of 5 μm exceeds 50% by weight.

Next, the average particle diameter of these particles is 5 μm (1-10
The batteries were assembled using the positive electrode plates with different powder content ratios (in the range of μm), the discharge capacity per unit weight in the positive electrode mixture layer of each battery was measured, and the average particle diameter was 5 μm.
The relationship between the content ratio of the m powder and the discharge capacity per unit weight was investigated. The assembling of the battery and the measurement of the discharge capacity per unit weight were performed by the same method as the above-mentioned test. FIG.
Indicates the measurement result. From this figure, the average particle size is 5μ
It can be seen that when the content ratio of the powder of m is less than 5% by weight, the utilization factor of the active material is reduced and the discharge capacity per unit weight is reduced. From the above, it is found that the content ratio of the powder having an average particle diameter of 5 μm (within the range of 1 to 10 μm) in the lithium-containing mixed oxide powder is preferably 5 to 50% by weight.

Next, the average particle diameter in the positive electrode mixture is 0.4 μm.
A unit weight of the positive electrode mixture layer of each battery was prepared by using each positive electrode plate formed in the same manner as in Example 1 except that the content of carbon powder (within the range of 0.1 to 10 μm) was changed. Discharge capacity is measured, average particle size 0.4
The relationship between the content of the carbon powder of μm and the discharge capacity per unit weight was investigated. The assembling of the battery and the measurement of the discharge capacity per unit weight were performed by the same method as the above-mentioned test.
FIG. 3 shows the measurement results. From this figure, it can be seen that when the content of the carbon powder is less than 5% by weight, the conductivity in the positive electrode mixture is lowered, the utilization factor of the active material is lowered, and the capacity is lowered. When the content of carbon powder exceeds 10% by weight, Li
It can be seen that the theoretical filling capacity becomes lower and the capacity lowers because the amount of CoO ₂ powder decreases. From the above, it can be seen that the content of carbon powder having an average particle diameter of 0.4 μm (within the range of 0.1 to 10 μm) in the positive electrode mixture is preferably 5 to 10% by weight.

Although LiCoO ₂ powder was used as the lithium-containing mixed oxide powder in the above-mentioned embodiment, LiCoO ₂ powder was used.
Other lithium-containing composite oxide powders such as _0.97 Sn _0.03 O ₂ powder can be used. Even if LiCo _0.97 Sn _0.03 O ₂ powder is used, the same effect as in this embodiment can be obtained.

[0026]

According to the present invention, the bulk density of the positive electrode mixture can be increased without using a carbon powder having a small average particle size (0.01 μm or more and less than 0.08 μm), and lithium-containing double oxides can be used. It is possible to prevent the reaction efficiency of the product powder from decreasing. By using the positive electrode plate of the present invention, the discharge capacity per unit weight and the discharge capacity per unit volume of the non-aqueous electrolyte secondary battery can be increased. Further, according to the present invention, since carbon powder having a small average particle diameter is not used, it is possible to prevent a short circuit between the electrode plates.

[Brief description of drawings]

FIG. 1 Average particle size 5 μm (within the range of 1 to 10 μm)
It is a figure which shows the relationship between the content rate of the powder of, and a bulk density.

FIG. 2 Average particle size 5 μm (within the range of 1 to 10 μm)
FIG. 3 is a diagram showing the relationship between the powder content ratio and the discharge capacity per unit weight.

FIG. 3 is a diagram showing the relationship between the content of carbon powder having an average particle size of 0.4 μm (within the range of 0.1 to 10 μm) and the discharge capacity per unit weight.

Claims (2)

[Claims] 1. A non-aqueous electrolyte in which a layer of a positive electrode mixture containing an active material material made of lithium-containing double oxide powder, a conductive auxiliary agent made of carbon powder, and a binder is formed on a current collector. In the positive electrode plate for a secondary battery, the lithium-containing composite oxide powder has an average particle diameter of 1 to 1
The average particle diameter of the lithium-containing mixed oxide powder 1 to 1 is used by using a mixed powder of particle diameters of 0 μm powder and powder having an average particle diameter of 20 to 30 μm.
The content ratio of the powder of 10 μm is 5 to 50% by weight, powder having an average particle diameter of 0.1 to 10 μm is used as the carbon powder, and the carbon powder is 5 to 10% by weight with respect to the positive electrode mixture.
A positive electrode plate for a non-aqueous electrolyte secondary battery, characterized in that it is contained. 2. A positive electrode plate having a positive electrode mixture layer formed on a current collector, the positive electrode mixture layer containing an active material material made of lithium-containing double oxide powder, a conductive auxiliary agent made of carbon powder, and a binder. A non-aqueous electrolyte secondary battery in which a negative electrode plate is laminated via an electrolyte layer containing a non-aqueous electrolyte solution, wherein the lithium-containing composite oxide powder has an average particle diameter of 1 to 1.
The average particle diameter of the lithium-containing mixed oxide powder 1 to 1 is used by using a mixed powder of particle diameters of 0 μm powder and powder having an average particle diameter of 20 to 30 μm.
The content ratio of the powder of 10 μm is 5 to 50% by weight, powder having an average particle diameter of 0.1 to 10 μm is used as the carbon powder, and the carbon powder is 5 to 10% by weight with respect to the positive electrode mixture.
A non-aqueous electrolyte secondary battery characterized by being contained.