JP3182786B2 - Battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery having an electrode in which an electrode constituting material layer is formed on the surface of a planar current collector.

[0002]

SUMMARY OF THE INVENTION The present invention relates to a battery having an electrode in which an electrode constituting material layer is formed on a planar current collector, wherein the surface roughness of the planar current collector is 0.15 μm in center line average roughness. The battery performance is improved by the above and 3.0 μm or less.

[0003]

2. Description of the Related Art A so-called non-aqueous electrolyte battery using lithium as a negative electrode active material and an organic solvent as an electrolyte has advantages such as low self-discharge, high nominal voltage, and excellent storage stability. Have. A typical example is a lithium-manganese dioxide battery, which has been developed for a long time and has high reliability, and is widely used as a power source for clocks and memory backup.

[0004] However, most of the non-aqueous electrolyte batteries conventionally used are primary batteries, but in recent years, with the spread of video cameras and small audio equipment, portable power sources have been used repeatedly for a long time and economically. The demand for rechargeable batteries is growing, and the development of non-aqueous electrolyte
Commercialization is underway.

Some proposals have been made on the electrode structure of the positive electrode and the negative electrode of a non-aqueous electrolyte secondary battery. For example, in a method of pressing a mixture in which an expanded metal is used as a current collector and a mixture of an active material and a binder powder, it is difficult to reduce the thickness of the electrode, and the productivity is low.

On the other hand, a strip electrode obtained by applying a slurry obtained by dispersing an active material and a binder powder in an organic solvent to a strip-shaped metal foil serving as a current collector and drying the resultant is rolled together with the strip-shaped separator into a roll (or spiral). According to the spirally wound electrode body obtained by winding the electrode, a large-area electrode can be accommodated in a limited space, so that a lightweight and high-capacity nonaqueous electrolyte secondary battery can be obtained. In addition, the metal foil used as a current collector is usually used in a rolled state.

[0007]

However, in the battery assembling process such as the above-described process of manufacturing the wound electrode body,
In some cases, an electrode constituent material made of an active material or the like may fall off from the metal foil serving as a current collector, which adversely affects the productivity of battery manufacturing.

In addition, the active material (or active material carrier) expands and contracts due to repetition of charge and discharge during use of the battery, and the adhesion between the current collector and the electrode constituent material layer is reduced. As a result, there is a disadvantage that the battery performance such as the capacity deterioration and the cycle characteristics is deteriorated.

An object of the present invention is to provide a battery having improved electrode performance by improving the adhesion between a current collector and an electrode constituent material layer in an electrode.

[0010]

Means for Solving the Problems The present invention has been made based on the finding by the present inventors that it is effective that the surface of the current collector of the electrode is roughened to achieve the above object. A battery comprising an electrode in which an electrode constituent material layer is formed on the surface of a planar current collector,
The surface roughness of the current collector on which the electrode constituent material layer is formed is 0.15 μm or more, preferably 0.17 μm or more and 3.0 μm or less, preferably 0.60 μm or less in center line average roughness. There is a feature.

[0011] A winding formed by laminating an electrode provided with an electrode constituting material layer on a flat current collector having the above-mentioned surface roughness and a flat separator, and then winding in a spiral shape. A battery provided with an electrode body is preferred.

It is preferable that the surface roughness of the current collector is determined within the above-mentioned range in consideration of the thickness of the planar current collector used. Further, the current collector having the surface roughness as described above may be used for both or any one of the negative electrode and the positive electrode.

Next, the definition of the surface roughness will be described below. The surface roughness is defined in JIS standard B0601 for the center line average roughness (Ra), the maximum height (Rmax), and the ten-point average roughness (Rz).

FIG. 6 is a cross-sectional view of a surface having irregularities for explaining the definition of the center line roughness (Ra). As shown in the figure, the center line is drawn so that the area surrounded by the unevenness (cross-sectional curve) of the surface and the straight line is equal on both sides of the straight line. With this center line as the x-axis and the vertical direction as the y-axis, the sectional curve is represented by y = f (x). At this time,

[0015]

(Equation 1)

The value obtained from the above equation in units of micrometers (μm) is defined as center line roughness (Ra).

FIG. 7 is for explaining the definition of the maximum height (Rmax), and is a sectional view of a surface having irregularities.
As shown in the figure, when the cross-sectional curve is sandwiched by two straight lines parallel to the center line, the interval between the two straight lines is measured in the y-direction of the cross-sectional curve, and the value expressed in units of micrometers is the maximum height. (Rmax).

[0018]

Since the surface of the planar current collector is appropriately roughened, the adhesion between the surface of the current collector and the electrode constituting material layer is improved.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

Experimental Example (Surface Roughening Treatment) First, an experimental example in which the surface of a Ti (titanium) foil used as a current collector is roughened will be described.

A titanium foil having a thickness of 10 μm is converted to 30% by weight of H
₂ Soak in an aqueous solution of SO ₄ (sulfuric acid)
It was kept at 5 ° C. After a certain period of time, the titanium foil was taken out of the above-mentioned aqueous sulfuric acid solution and washed sufficiently with water, and then the surface roughness (Ra and Rmax) of the titanium foil was measured.

Further, the surface roughness of the titanium foil was measured while changing the surface roughening treatment time of dipping the titanium foil in an aqueous sulfuric acid solution. FIG. 3 shows the results of these measurements as the relationship between the acid treatment time for surface roughening with an aqueous sulfuric acid solution and the surface roughness (Ra and Rmax). As shown in FIG. 3, the center line average roughness (Ra) and the maximum height (Rm
ax) both increase.

Next, the relationship between the center line average roughness (Ra) and the maximum height (Rmax) was examined by similarly roughening a 100 μm thick titanium foil. FIG. 4 shows this result.
This is shown together with the case where the above-mentioned titanium foil is 10 μm. From the figure, the relationship of Rmax = 8.3Ra (2) was obtained in the range of 0 ≦ Ra ≦ 4.5 μm.

The surface roughness was measured using a surface roughness / contour measuring instrument SEF-30D manufactured by Kosaka Laboratory Co., Ltd. under the following measurement conditions. Vertical magnification: 5000 times Horizontal magnification: 100 times Reference length: 2.50 mm Cut-off value: 0.8 mm Feeding speed: 0.05 mm / s

Example 1 In Example 1, a negative electrode 1 as shown in FIG. 1 was prepared using the titanium foil obtained in the above experimental example as a current collector, and a non-aqueous solution as shown in FIG. An electrolyte secondary battery was manufactured. First, the negative electrode 1 was obtained as follows. 10μ thickness in the above experimental example
roughened surface 9 with Ra of 0.15 μm obtained from titanium foil of
The titanium foil having a and 9b was used as a negative electrode current collector 9 as shown in FIG.

Ninety parts by weight of pitch coke, which is a carbon material as a negative electrode active material carrier, and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed to prepare a negative electrode mixture (a negative electrode constituent material). This negative electrode mixture was dispersed in N-methylpyrrolidone as a solvent to form a slurry (paste).

This negative electrode mixture slurry was prepared by using the above-mentioned Ra of 0.1.
Both surfaces 9a of the negative electrode current collector 9 made of 15 μm titanium foil,
9b was uniformly applied and dried. Thereafter, the strip-shaped negative electrode 1 having the negative electrode constituent material layers 1a on both surfaces 9a and 9b of the negative electrode current collector 9 as shown in FIG. 1 was obtained by compression molding and cutting. Incidentally, the thickness of the negative electrode 1 was about 170 μm.

Next, the positive electrode 2 was obtained as follows. 91 parts by weight of LiCoO ₂ as a positive electrode active material were mixed with 6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode mixture (positive electrode constituent material). This positive electrode mixture was dispersed in N-methylpyrrolidone to form a slurry (paste). A 20 μm-thick strip-shaped aluminum foil is used as the positive electrode current collector 10,
The positive electrode mixture slurry was uniformly applied to both surfaces of the current collector 10, dried, compression molded and cut to obtain a belt-shaped positive electrode 2. In addition, the thickness of the positive electrode 2 was about 180 μm.

The above-described strip-shaped negative electrode 1, strip-shaped positive electrode 2, and a pair of strip-shaped separators 3a, 3b each made of a microporous polypropylene film having a thickness of 25 μm are laminated in the order of negative electrode 1, separator 3b, positive electrode 2, and separator 3a. From
The spirally wound spirally wound electrode body 15 as shown in FIG. 2 was produced by spirally winding this laminate. Reference numeral 33 denotes a winding core.

Next, such a wound electrode body 15 was housed in a nickel-plated iron battery can 5 as shown in FIG.

At this time, insulating plates 4 a and 4 b are respectively disposed on the upper and lower surfaces of the wound electrode body 15, and a nickel negative electrode lead 11 derived from the negative electrode current collector 9 is welded to the bottom of the battery can 5. At the same time, the aluminum positive electrode lead 12 derived from the positive electrode current collector 10 was welded to the projection 34a of the metal safety valve 34.

A non-aqueous electrolyte obtained by dissolving Li PF ₆ at a ratio of 1 mol / liter in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in an equal volume was injected into the battery can 5.

Thereafter, each of the battery can 5, the safety valve 34 and the metal battery lid 7 whose outer periphery is in close contact with each other is caulked via an insulating sealing gasket 6 coated with asphalt on the surface thereof. 5 was sealed. Thereby, the battery lid 7 and the safety valve 34 were fixed, and the airtightness in the battery can 5 was maintained. At this time, the lower end of the gasket 6 in FIG. 1 contacts the outer peripheral surface of the insulating plate 4a, so that the insulating plate 4a is in close contact with the upper surface of the spirally wound electrode body 15. As described above, a diameter of 14 mm and a height of 4
A 2 mm cylindrical non-aqueous electrolyte secondary battery was produced. This battery is referred to as battery A for convenience.

The above cylindrical non-aqueous electrolyte secondary battery is
In order to form a double safety device, a safety valve 34, a stripper 36, and an intermediate fitting 35 made of an insulating material for integrating the safety valve 34 and the stripper 36 are provided. Although not shown, this safety valve 3 is
Holes are provided in the battery cover 7 at each of the cleavage portions that are cleaved when the battery 4 is deformed.

If the internal pressure of the battery rises for some reason, the safety valve 34 is turned around the projection 34a as shown in FIG.
To disconnect the positive electrode lead 12 and the protruding portion 34a so as to cut off the battery current, or exhaust the gas generated in the battery by breaking the open portion of the safety valve 34. Respectively.

Examples 2, 3, 4, 5, and 6 In Examples 2 to 6, the Ra obtained in each of the above-described experimental examples was used.
Are 0.20, 0.30, 0.50, 1.0 and 3.0μ
m, a cylindrical non-aqueous electrolyte secondary battery B, C, D, E, and F having a diameter of 14 mm and a height of 42 mm was obtained in the same manner as in Example 1, except that the titanium foil of m was used as the negative electrode current collector 9. Produced.

The following batteries were produced as Comparative Examples 1 and 2 for confirming the effects of the present invention.

Comparative Example 1 In Comparative Example 1, a diameter of 14 mm and a height of 42 mm were obtained in the same manner as in Example 1 except that the titanium foil having Ra of 5 μm obtained in the above experimental example was used for the negative electrode current collector 9. Of the non-aqueous electrolyte secondary battery G was manufactured.

Comparative Example 2 In Comparative Example 2, a cylinder having a diameter of 14 mm and a height of 42 mm was formed in the same manner as in Example 1 except that a titanium foil having a Ra of 0.10 μm without roughening was used for the negative electrode current collector 9. A non-aqueous electrolyte secondary battery H was manufactured.

The eight types of batteries A, B, C, D,
For E, F, G and H, a charge / discharge cycle in which the upper limit voltage was 4.1 V, the battery was charged at a constant current of 360 mA for 2 hours, and then discharged to a final voltage of 2.75 V with a constant resistance of 18Ω was repeated.

In each battery, the ratio of the energy density at the 10th charge / discharge cycle to the energy density at the 100th charge / discharge cycle is defined as the energy density retention rate (%).

FIG. 5 shows the relationship between the energy density retention and the center line average roughness (Ra) of the surface of the negative electrode current collector. In addition, the code | symbol AH in a figure shows each battery, and the horizontal axis which shows Ra is a logarithmic scale.

As is clear from FIG. 5, Ra is 0.15 μm.
In the batteries A, B, C, D, E, F, and G using the negative electrode current collector having the roughened surface as described above, the Ra that does not roughen is 0.
The energy density retention is higher than that of the battery H of Comparative Example 2 using the negative electrode current collector having a surface of 10 μm.

When the center line average roughness (Ra) is about 0.3 μm (battery C), the energy density retention rate is the highest, and Ra is about 0.
If it exceeds 3 μm, it gradually decreases. When Ra is 5 μm (battery G), the energy density retention rate is considerably reduced.

From the above, the preferable range of the center line average roughness (Ra) of the surface of the current collector is 0.15 μm ≦ Ra ≦
3.0 μm, more preferably 0.17 μm ≦ Ra ≦ 0.60 μm.

As described above, when the current collector has a moderately rough surface, the area where the electrode constituent material can contact the surface of the current collector increases, and the surface of the current collector and the electrode constituent material layer Therefore, it is considered that the battery performance such as the energy density does not deteriorate even if charging and discharging are repeated.

It is desirable to determine the surface roughness of the current collector within the above-mentioned range, taking the following points into consideration.

That is, if the maximum height (Rmax) of the current collector becomes more than half the thickness t (thickness before roughening) of the current collector by roughening the surface of the current collector, There is a possibility that a hole is formed on the surface of the electric body.

If there is a hole in the current collector, a problem arises when the slurry is applied in the above-described electrode manufacturing process. In addition, problems such as a decrease in the strength of the current collector and a dropout of the electrode constituent material can be considered. Therefore, the following equation (3) holds. Rmax ≦ 0.5t (3)

Here, the thickness t of the current collector is desirably small because electrodes having as large an area as possible must be accommodated in a limited space in order to increase the capacity and weight of the battery. If the thickness of the current collector is t
When the thickness is increased, the amount of the active material (or the active material carrier) provided on the current collector decreases, and the battery capacity decreases.

For the above-mentioned reason, in order to secure the battery capacity, the thickness t of the current collector in the above-mentioned wound electrode body 15 is increased.
Is desirably 50 μm or less. Therefore, Ra ≦ 3.0 μm (4) is obtained from the above equations (2) and (3).

However, since the condition of the equation (4) varies depending on the thickness t of the current collector, it is preferable to determine the condition according to the current collector used.

Example 7 In Example 7, an experimental example in which the surface of an aluminum foil used as a positive electrode current collector was roughened will be described.

The aluminum foil having a thickness of 20 μm is sufficiently ground with sandpaper, immersed in a 20% by weight aqueous hydrochloric acid solution, and after a certain period of time, the aluminum foil is taken out from the above aqueous hydrochloric acid solution and sufficiently washed with water, and the surface of the aluminum foil is washed. 14 mm in diameter in the same manner as in Example 1 except that the roughness was used for the positive electrode current collector and a copper foil having a thickness of 10 μm was used for the negative electrode current collector.
Was manufactured.

Example 8 The same procedure as in Example 7 was repeated except that the aluminum foil having a Ra of 2.00 μm was soaked in an aqueous hydrochloric acid solution for a longer time than the Example 7 and used as a positive electrode current collector. A cylindrical nonaqueous secondary battery J having a height of 42 mm was produced.

Comparative Example 3 In Comparative Example 3, a cylindrical non-aluminum sheet having a diameter of 14 mm and a height of 42 mm was produced in the same manner as in Example 7, except that an aluminum foil having a surface roughness Ra of 0.16 μm was used for the positive electrode current collector. A water secondary battery K was produced.

The above three types of batteries were repeatedly charged at a constant current of 360 mA for 2 hours at an upper limit voltage of 4.1 V, and then discharged repeatedly at a constant resistance of 18Ω to a voltage of 2.75 V throughout.

In each of the batteries I, J, and K, the ratio of the energy density at the tenth charge / discharge cycle to the energy density at the 100th charge (energy density retention) was measured, and was 87%, 93%, and 82%, respectively. Met. As described above, the same effect is obtained even when the positive electrode current collector is roughened.

As described above, according to the nonaqueous electrolyte secondary battery of this embodiment, the center line average roughness (Ra) is 0.15 μm.
By using a metal foil having a roughened surface in the range of m ≦ Ra ≦ 3.00 μm as a current collector, a high-capacity strip electrode can be obtained without deterioration in capacity even when charge and discharge are repeated. .

The method of the surface roughening treatment is acid treatment, etching,
A sand brush or the like is used, but the method is not particularly limited. Although the negative electrode current collector is roughened in this embodiment, the positive electrode current collector may be roughened, and the same effect is obtained. Further, as the material of the current collector, titanium is used in this embodiment, but other metal foils such as an Inconel alloy, copper, nickel, and stainless steel can also be used.

Although LiCoO ₂ was used as the positive electrode active material, other oxides of transition metals such as manganese dioxide, vanadium pentoxide, and iron sulfide, chalcogen compounds, and these oxides, chalcogen compounds It is possible to use a composite compound of lithium and lithium (such as a lithium-cobalt composite oxide or a lithium-cobalt-nickel composite oxide).

The negative electrode material may be any material capable of doping and undoping lithium ions, and among them, a carbon material such as pitch coke is preferable. Examples of such carbon materials include coke materials such as petroleum coke and carbon coke, organic polymer fired bodies obtained by firing an organic polymer in a non-oxidizing atmosphere at 500 ° C. or higher, and carbon black such as acetylene black. , Graphite, glassy carbon, activated carbon, carbon fiber, and other organic pyrolytic carbons.

As the non-aqueous electrolyte, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent (non-aqueous solvent) can be used. Here, the organic solvent is not particularly limited, but, for example, propylene carbonate, ethylene carbonate, 1,2-dimethyloxytoshiethane, 1,2-diethoxytoshiethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-
Methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like can be used alone or in combination of two or more. Any known electrolyte can be used as the electrolyte, such as LiClO ₄ , LiAsF ₆ , and LiP.
F ₆ , Li BF ₄ , Li B (C ₆ H ₅ ) ₄ , Li Cl,
_{Li Br, CH 3 SO 3 Li} , CF 3 SO 3 Li and the like.

The non-aqueous electrolyte may be a solid, for example, a polymer complex solid electrolyte.

[0065]

According to the battery of the present invention, since the planar current collector is appropriately roughened in the electrode, the adhesion between the planar current collector and the electrode constituent material layer is improved, Since electrode components can be effectively prevented from dropping and peeling off from the current collector during the electrode manufacturing process and during use of the battery, the productivity of the battery manufacturing can be improved, and the capacity deterioration can be prevented or the cycle characteristics can be improved. And the improvement of the battery performance can be achieved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a negative electrode used in a non-aqueous electrolyte secondary battery of an example according to the present invention.

FIG. 2 is a longitudinal sectional view showing a schematic longitudinal section of a nonaqueous electrolyte secondary battery using the negative electrode shown in FIG.

FIG. 3 is a diagram showing the relationship between the surface roughness (Ra and Rmax) of a metal foil as a current collector obtained in an experimental example of the present embodiment and the acid treatment time for surface roughening.

FIG. 4 is a diagram showing a relationship between a center line average roughness (Ra) and a maximum height (Rmax) obtained in an experimental example of the present embodiment.

FIG. 5 is a diagram showing the relationship between the center line average roughness (Ra) of the surface of the current collector obtained in this example and the energy density retention.

FIG. 6 is a cross-sectional view for explaining the definition of center line average roughness (Ra).

FIG. 7 is a cross-sectional view for explaining the definition of the maximum height (Rmax).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode (electrode) 1a Negative electrode constituent material layer (electrode constituent material layer) 2 Positive electrode (electrode) 3a Strip separator (flat separator) 3b Strip separator 9 Negative current collector (flat current collector) 15 wound electrode body

Claims (3)

(57) [Claims] 1. A carbon material capable of doping and undoping Li.
An electrode in which an electrode constituent material layer is formed on both surfaces of a planar current collector using a negative electrode and a positive electrode using a composite compound with Li
The electrode is formed many times via a band-shaped separator.
In a non-aqueous electrolyte secondary battery including a spirally wound spirally wound electrode body , the surface roughness of the current collector on which the electrode constituent material layer is formed is a center line average roughness. 0.15 μm or more and 3.0 μm
secondary battery, characterized in that m or less. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the composite compound with Li used for the positive electrode is selected from a lithium-cobalt composite oxide and a lithium-cobalt-nickel composite oxide. . 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein said strip separator is a microporous film.