JPH09283119A - Negative electrode for nonaqueous electrolyte secondary battery and nonqueous electrolyte secondary battery having this negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode and a secondary battery with high electrolyte retainability and high electronic conductivity, and high load characteristics. SOLUTION: This negative electrode for a nonaqueous electrolyte secondary battery is manufactured by applying slurry containing 100 pts.wt. carbon powder having graphite crystal structure, 1-8 pts.wt. amorphous carbon powder having the mean particle size smaller than the above carbon powder, 1-12 pts.wt. binder solution in terms of solid material, and 0.5-2 pts.wt. thickening agent to both surfaces of a current collector, and drying the slurry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery, which uses a carbon powder having a graphite type crystal structure as a lithium storage material, and a non-aqueous electrolyte secondary battery including the same.

[0002]

2. Description of the Related Art In recent years,
A carbon material having a graphite type crystal structure has been proposed as a new negative electrode material for a non-aqueous electrolyte secondary battery, which replaces a conventional metal material such as lithium metal. When a carbon material is used as the negative electrode material, there is no fear of internal short circuit due to the growth of dendritic electrodeposits, which was a problem when using lithium metal, etc. A water electrolyte secondary battery is obtained.

Conventionally, in a negative electrode using a carbon material having a graphite type crystal structure, a slurry consisting of carbon powder having a graphite type crystal structure, a binder solution and a thickener is applied on both sides of a current collector, It was produced by drying.

However, this negative electrode has a problem that the load characteristics are not good.

Therefore, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery, which uses a carbon material having a graphite type crystal structure as a negative electrode material and has excellent load characteristics, and a non-aqueous electrolyte secondary battery including the same. Is to provide.

[0006]

To achieve the above object, a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention (the electrode of the present invention) comprises 100 parts by weight of carbon powder having a graphite type crystal structure. 1 to 8 parts by weight of amorphous carbon powder having a smaller average particle diameter, and 1 to 12 parts by weight of the binder solution in terms of solid content,
It is prepared by applying a slurry containing 0.5 to 2 parts by weight of a thickener on both sides of a current collector and drying.

The non-aqueous electrolyte secondary battery according to the present invention (the present invention battery) is a non-aqueous electrolyte secondary battery provided with the present electrode.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Carbon powder having a graphite type crystal structure in the present invention means that Lc (size of crystallite in the c-axis direction) is 200 Å or more, and d ₀₀₂ [lattice plane (00
2) The interplanar spacing] is 3.37 Å or less, which is a carbon powder belonging to the hexagonal system. The amorphous carbon powder in the present invention means that Lc is 30 Å or less and d ₀₀₂ is 3.45 Å
The above is the carbon powder. Specific examples thereof include Ketjen Black (KB), carbon black, acetylene black, soot, charcoal, and activated carbon. Examples of the binder solution in the present invention include dispersions in which styrene-butadiene rubber, (meth) acrylic rubber, acrylonitrile rubber, etc. are dispersed in water or a non-aqueous solvent. Examples of the thickener in the present invention include carboxymethyl cellulose (CMC), methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid and salts thereof, oxidized starch, phosphorylated starch, and casein. Specific examples of the negative electrode current collector include copper foil and nickel foil.

The electrode of the present invention comprises 100 parts by weight of carbon powder having a graphite type crystal structure, 1 to 8 parts by weight of amorphous carbon powder having a smaller average particle size, and a binder (solid content) of 1 to 12.
Parts by weight and 0.5 to 2 parts by weight of a thickener. Amorphous carbon powder to carbon powder having a graphite type crystal structure,
If the proportions of the binder and the thickener deviate from the above ranges, the load characteristics will deteriorate.

As the amorphous carbon powder, one having an average particle size smaller than that of the carbon powder having the graphite type crystal structure is used in order to improve the liquid content. The average particle size of the preferred amorphous carbon powder is ½ or less of the average particle size of the carbon powder having the graphite type crystal structure.

The non-aqueous electrolyte is not particularly limited, and conventionally known ones for non-aqueous electrolyte secondary batteries can be used. Specific examples of the solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, and 3-.
Methylsulfolane, 2,4-dimethylsulfolane, 3-
Methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2- Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate and a mixed solvent of two or more of these, and specific examples of the solute include LiP.
F ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ ,
LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ and LiSO
₂ (CF ₂ ) ₃ CF ₃ can be mentioned respectively.

The positive electrode active material is also not particularly limited, and conventionally known materials for non-aqueous electrolyte secondary batteries can be used. Specific examples of the positive electrode active material include LiCoO ₂ ,
LiNiO ₂ , LiMnO ₂ , LiVO ₂ , LiNbO
₂ is mentioned.

Since the electrode of the present invention contains a predetermined amount of amorphous carbon powder having an average particle size smaller than that of carbon powder having a graphite type crystal structure and high electric conductivity, it has high liquid content and high electron conductivity. Therefore, the electrode of the present invention and the battery of the present invention have excellent load characteristics. In addition, even if the amount of the binder of the negative electrode is made larger than usual in order to improve the adhesion of the negative electrode mixture layer to the current collector,
Since the negative electrode has high liquid content and electron conductivity, the load characteristics are unlikely to deteriorate.

Typical examples of the application target of the present invention are negative electrodes for lithium secondary batteries and lithium secondary batteries, but the present invention is widely applied to negative electrodes for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries. Obviously, it is a possible invention.

[0015]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications can be made without departing from the scope of the invention. Is possible.

(Experiment 1) The relationship between the ratio of the amorphous carbon powder to the carbon powder having a graphite type crystal structure and the load characteristics was investigated.

[Production of Positive Electrode] LiCoO ₂ powder having an average particle diameter of 5 μm as a positive electrode active material and artificial graphite powder as a conductive agent were mixed at a weight ratio of 9: 1. This mixture and P
5% by weight of VdF (polyvinylidene fluoride) NMP (N
-Methyl-2-pyrrolidone) was kneaded at a weight ratio of 95: 5 to prepare a slurry. This slurry was applied on both sides of an aluminum foil as a positive electrode current collector by the doctor blade method, and vacuum dried at 150 ° C. for 2 hours to prepare an electrode plate having a positive electrode mixture layer with a thickness of 50 μm on each side. . This electrode plate was rolled and slit to produce a strip-shaped positive electrode having a thickness of 0.100 mm, a width of 40 mm and a length of 280 mm.

[Preparation of Negative Electrode] 100 parts by weight of graphite powder (Lc>1000Å; d ₀₀₂ = 3.35Å) having an average particle size of 20 μm and SBR (styrene-butadiene rubber) dispersion (resin solid content: 5 parts by weight) Is added to water and mixed, and further, Ketjen black (Lc = 12Å; d ₀₀₂ = 3.50Å) having an average particle diameter of 0.1 μm is added in an amount of X parts by weight (X =
0, 0.5, 1, 3, 5, 8, 10 or 15) and 1 part by weight of carboxymethyl cellulose, and kneaded to obtain 8
A seed slurry was prepared. Each of these slurries was applied to both sides of a copper foil as a negative electrode current collector by the doctor blade method, and dried in vacuum at 150 ° C. for 2 hours to form an electrode plate having a negative electrode mixture layer with a thickness of 50 μm on each side. It was made. These electrode plates are rolled and slit to a thickness of 0.100m.
A strip-shaped negative electrode having m, a width of 42 mm, and a length of 300 mm was produced.

[Preparation of Non-Aqueous Electrolyte Solution] LiPF ₆ (lithium hexafluorophosphate) was added to 1 M (mol / liter) in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 2: 3. It melt | dissolved and prepared the nonaqueous electrolytic solution.

[Production of Lithium Secondary Battery] Cylindrical (AA size) lithium secondary batteries A1 to A4, B1 to B1 having a positive electrode capacity smaller than the negative electrode capacity, using the above positive electrode, negative electrode and non-aqueous electrolyte solution. B4 was produced. A polypropylene microporous membrane having ion permeability was used as the separator.

FIG. 1 is a cross-sectional view schematically showing the manufactured lithium secondary battery. The illustrated non-aqueous electrolyte secondary battery A is shown in FIG.
Is composed of a positive electrode 1, a negative electrode 2, a separator 3 which separates these electrodes 1 and 2 from each other, a positive electrode lead 4, a negative electrode lead 5, a positive electrode lid 6, a negative electrode can 7 and the like.

The positive electrode 1 and the negative electrode 2 are wound in a spiral shape with a separator 3 interposed therebetween and are housed in a negative electrode can (battery can) 7 as a spiral electrode body. The positive electrode 1 is connected via a positive electrode lead 4. Is connected to the positive electrode lid 6 and the negative electrode 2 is connected to the negative electrode can 7 via the negative electrode lead 5 so that the chemical energy generated inside the battery A can be extracted from both terminals as electric energy to the outside. The separator 3 includes
Non-aqueous electrolyte is injected before sealing.

<Load Characteristics of Each Battery> Each battery is stored at room temperature (2
At 5 ° C), the battery was charged to 4.1V at 1C and then discharged to 2.75V at 2C to obtain the discharge capacity. The results are shown in FIG. FIG. 2 shows the relationship between the ratio of the amorphous carbon powder to the graphite powder and the load characteristics, with the vertical axis indicating the discharge capacity (m
3 is a graph showing Ah) with the horizontal axis representing the number of parts by weight of Ketjenblack.

As shown in FIG. 2, the batteries A1 to A4 have a larger discharge capacity at 2C than the batteries B1 to B4 and are excellent in load characteristics. From this fact, it is understood that when the ratio of the amorphous carbon powder to 100 parts by weight of the graphite powder is 1 to 8 parts by weight, a lithium secondary battery having excellent load characteristics can be obtained. It is considered that the batteries A1 to A4 were excellent in load characteristics because the negative electrode had a high liquid content and a sufficient electron passage was formed between the graphite particles and between the graphite particles and the current collector. Further, the reason why the load characteristics of the batteries B1 and B2 were not good is considered to be that the liquid content of the negative electrode was low, and that sufficient electron passages were not formed between the graphite particles and between the graphite particles and the current collector. To be The reason why the load characteristics of the batteries B3 and B4 were not good is supposed to be that the non-aqueous electrolyte (solvent) was decomposed on the surface of the particles of the amorphous carbon due to the excessive addition of the amorphous carbon.

(Experiment 2) The relationship between the ratio of the binder to the carbon powder having a graphite type crystal structure and the load characteristics was investigated.

Graphite powder having an average particle size of 20 μm (Lc> 10)
00Å; d ₀₀₂ = 3.35Å) 100 parts by weight and SBR
(Styrene-butadiene rubber) dispersion (solid content: 0.5, 1, 5, 10, 12, 13 or 15 parts by weight) was added to water and mixed, and the average particle diameter was 0.1 μm.
Ketjen Black (Lc = 12Å; d ₀₀₂ = 3.5
0 Å) 5 parts by weight and 1 part by weight of carboxymethyl cellulose were added and kneaded to prepare 7 kinds of slurries. Each of these slurries was applied to both sides of a copper foil as a negative electrode current collector by the doctor blade method, and dried in vacuum at 150 ° C. for 2 hours to form an electrode plate having a negative electrode mixture layer with a thickness of 50 μm on each side. It was made. These electrode plates are rolled and slit to have a thickness of 0.100 mm, a width of 42 mm, and a length of 300 mm.
A strip-shaped negative electrode was prepared. Lithium secondary batteries A5 to A were prepared in the same manner as in Experiment 1 except that these negative electrodes were used.
8, B5 to B7 were produced, charged and discharged under the same conditions as in Experiment 1, and the discharge capacity was obtained. However, the battery A6 has the same specifications as the battery A3. The results are shown in FIG. FIG. 3 is a graph showing the relationship between the ratio of the binder to the graphite powder and the load characteristic, the discharge capacity (mAh) at 2 C on the vertical axis, and the number of parts by weight of the binder on the horizontal axis.

As shown in FIG. 3, the batteries A5 to A8 have a large discharge capacity at 2C and excellent load characteristics as compared with the batteries B5 to B7. From this fact, it is understood that when the ratio of the binder to 100 parts by weight of graphite powder is 1 to 12 parts by weight, a lithium secondary battery having excellent load characteristics can be obtained. The reason why the load characteristic of the battery B5 was not good is considered that the graphite powder was not used uniformly because the binding property between the negative electrode mixture and the current collector was insufficient. Battery B
The reason why the load characteristics of 6 and B7 are not good is considered to be that the charge and discharge at the negative electrode did not occur uniformly because the sufficient electron passage was not formed due to the presence of the excessive binder.

(Experiment 3) The relationship between the ratio of the thickening agent to the carbon powder having the graphite type crystal structure and the load characteristic was investigated.

Graphite powder having an average particle size of 20 μm (Lc> 10)
00Å; d ₀₀₂ = 3.35Å) 100 parts by weight and SBR
(Styrene-butadiene rubber) dispersion (solid content: 5 parts by weight) was added to water and mixed, and Ketjen black (Lc = 12Å; d) having an average particle diameter of 0.1 μm.
₀₀₂ = 3.50Å) 5 parts by weight and carboxymethyl cellulose Z parts by weight (Z = 0.25, 0.5, 1, 1.5,
2, 2.5 or 3) was added and kneaded to prepare 7 kinds of slurries. Each of these slurries was applied to both sides of a copper foil as a negative electrode current collector by a doctor blade method, and vacuum dried at 150 ° C. for 2 hours to give a thickness of 50 on each side.
An electrode plate having a negative electrode mixture layer of μm was prepared. These electrode plates are rolled and slit to a thickness of 0.100 mm and a width of 42
A band-shaped negative electrode having a length of 300 mm and a length of 300 mm was produced. Lithium secondary batteries A9 to A12 and B8 to B10 were produced in the same manner as in Experiment 1 except that these negative electrodes were used, charged and discharged under the same conditions as in Experiment 1, and the discharge capacity was obtained. However, the battery A10 has the same specifications as the battery A3. FIG. 4 shows the results. FIG. 4 shows the relationship between the ratio of the thickener to the graphite powder and the load characteristics, with the vertical axis representing the discharge capacity (mA) at 2C.
3 is a graph showing h) in which the abscissa represents the number of parts by weight of the thickener.

As shown in FIG. 4, the batteries A9 to A12 are
Compared with batteries B8 to B10, the discharge capacity at 2C is large and the load characteristics are excellent. From this fact, graphite powder 1
It can be seen that when the ratio of the thickener to 00 parts by weight is 0.5 to 2 parts by weight, a lithium secondary battery having excellent load characteristics can be obtained. The reason why the load characteristic of the battery B8 was not good is considered to be that a homogeneous and smooth negative electrode could not be obtained due to insufficient viscosity of the slurry, and as a result, charge / discharge at the negative electrode did not occur uniformly. The reason why the load characteristics of the batteries B9 and B10 were not good is considered to be that the charge and discharge at the negative electrode did not occur uniformly because a sufficient electron path was not formed due to the presence of the excessive binder.

(Experiment 4) A suitable average particle diameter of amorphous carbon was investigated.

Graphite powder having an average particle size of 20 μm (Lc> 10)
00Å; d ₀₀₂ = 3.35Å) 100 parts by weight and SBR
(Styrene-butadiene rubber) dispersion (solid content: 5 parts by weight) was added to water and mixed, and further ketjen having an average particle diameter D μm (D = 0.1, 1, 8, 10, 12 or 15). Black (Lc = 12Å; d ₀₀₂ = 3.50
Å) 5 parts by weight and 1 part by weight of carboxymethyl cellulose were added and kneaded to prepare 6 kinds of slurries. Each of these slurries was applied to both sides of a copper foil as a negative electrode current collector by a doctor blade method, and dried in vacuum at 150 ° C. for 2 hours to obtain an electrode plate having a negative electrode mixture layer with a thickness of 50 μm on each side. It was made. These electrode plates are rolled and slit to have a thickness of 0.100 mm, a width of 42 mm, and a length of 300 mm.
A strip-shaped negative electrode was prepared. Lithium secondary batteries A13 to A were manufactured in the same manner as in Experiment 1 except that these negative electrodes were used.
Sample No. 18 was produced and charged and discharged under the same conditions as in Experiment 1 to obtain the discharge capacity. However, the battery A13 has the same specifications as the battery A3. Results are shown in FIG. FIG. 5 is a graph showing the relationship between the average particle size of Ketjen black and the load characteristics, with the vertical axis representing the discharge capacity at 2 C (mAh) and the horizontal axis representing the average particle size of Ketjen black (μm). Is.

As shown in FIG. 5, batteries A13 to A16 are used.
Has a larger discharge capacity at 2C than the batteries A17 and A18 and is excellent in load characteristics. From this fact, it is understood that the average particle size of the amorphous carbon powder is preferably 1/2 or less of the average particle size of the graphite powder in order to obtain a lithium secondary battery having excellent load characteristics. It is inferred that the reason why the load characteristics of the batteries A17 and A18 were relatively poor was that graphite was not fully utilized for charging / discharging because a sufficient electron passage was not formed.

[0034]

EFFECT OF THE INVENTION The electrode of the present invention has high liquid content and electron conductivity. Therefore, the electrode of the present invention and the battery of the present invention have excellent load characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lithium secondary battery manufactured in an example.

FIG. 2 is a graph showing the relationship between the ratio of amorphous carbon powder to graphite powder and load characteristics.

FIG. 3 is a graph showing a relationship between a ratio of a binder to graphite powder and a load characteristic.

FIG. 4 is a graph showing the relationship between the ratio of a thickener to graphite powder and load characteristics.

FIG. 5 is a graph showing the relationship between the average particle size of amorphous carbon powder and load characteristics.

[Explanation of symbols]

 A lithium secondary battery (non-aqueous electrolyte secondary battery) 1 positive electrode 2 negative electrode 3 separator

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Noma 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 in Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. 100 parts by weight of a carbon powder having a graphite type crystal structure, and an amorphous carbon powder having an average particle size smaller than 1 part by weight
A slurry containing 8 parts by weight, a binder solution of 1 to 12 parts by weight in terms of solid content, and a thickener of 0.5 to 2 parts by weight is applied to both sides of a current collector and dried. The produced negative electrode for a non-aqueous electrolyte secondary battery. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the average particle size of the amorphous carbon powder is 1/2 or less of the average particle size of the carbon powder having the graphite type crystal structure. . 3. A non-aqueous electrolyte secondary battery comprising the negative electrode for non-aqueous electrolyte secondary battery according to claim 1.