JPH10284065A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive separator without using a porous film. SOLUTION: In a nonaqueous electrolyte battery composed of a positive electrode, a negative electrode and nonaqueous electrolyte, either one of the electrodes has a conductive active material layer 2 formed on a collector of metal foil, and furthermore, an electronically insulating porous layer 3 is formed on the active material layer 2. The porous layer 3 is made by removing and drying solvent after coating the active material layer 2 on metal foil 1 first and then sprinkling electronically insulating powder bodies on it. Since the electronically insulating porous material layer performs function of a separator in the past, expensive porous film is not required to be used for the separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention aims to provide an inexpensive separator for a non-aqueous electrolyte battery. .

[0002]

2. Description of the Related Art Exhaust gas from automobiles is considered to be one of the major causes of global environmental destruction, and a new exhaust gas regulation bill will be started in California, USA, in 1998. This regulation requires that each automaker make 2% of its total sales from electric vehicles that emit no exhaust gas. One of the main technologies that make up an electric vehicle is a secondary battery, and the performance of the secondary battery determines the basic performance of the vehicle, that is, the acceleration performance and the mileage per charge, so high performance Urgent development of secondary batteries is required.

As for the development of high performance secondary batteries, non-aqueous electrolyte secondary batteries have been studied for a long time, and have only recently entered the practical stage. The nonaqueous electrolyte secondary battery that has entered the practical stage is called a lithium ion secondary battery, and typically, a lithium salt is dissolved in an organic solvent in the electrolyte,
A non-aqueous electrolyte secondary battery in which a so-called organic electrolyte is used, a negative electrode is made of a special carbon material that easily forms a lithium intercalation compound as an active material, and a positive electrode is lithium cobalt oxide (LiCoO ₂ ). It is. Due to the high raw material costs, this battery has a very high manufacturing cost. Therefore, currently used lithium ion secondary batteries are limited to small batteries that use little raw material.

[0004] In the case of a secondary battery for an electric vehicle in which an enormous amount of batteries must be mounted, the price of the electric vehicle can be set to a practicable range unless the raw material costs are sufficiently low. It will be very difficult. The reason why the raw material cost of the lithium ion secondary battery is high is that the positive electrode active material, the negative electrode active material, and the separator are particularly expensive.
Specifically, the positive electrode active material, the negative electrode active material, and the separator account for 70% of the total material cost. For the positive electrode active material, an inexpensive spinel-based lithium manganese composite oxide (L
iMn ₂ O ₄ ) is lithium cobalt oxide (LiCoO)
It is a promising alternative to ₂ ), and has been actively researched and developed, and has recently reached the stage of commercialization. However, the change of the positive electrode active material alone does not lead to a sufficient reduction in manufacturing cost, and it is necessary to replace the negative electrode material and the separator with inexpensive materials.

[0005] Attempts have been made to use extremely general graphite in place of expensive specialty carbon materials as negative electrode materials, and good results have been obtained in combination with special electrolytes.

However, no candidate has been found for the separator at present. In the case of a non-aqueous electrolyte battery, since the resistance of the electrolyte is high, it is necessary to reduce the distance between the positive electrode and the negative electrode as much as possible.
An extremely thin porous membrane of ３０30 microns is used.
The porous membrane used as the separator is required to have a porosity as high as possible from the viewpoint of battery performance, and a certain degree of mechanical strength is required from the viewpoint of assembling the battery. High porosity and mechanical strength are conflicting requirements, and there is no inexpensive material that satisfies both requirements.

[0007]

SUMMARY OF THE INVENTION The present invention aims at producing a nonaqueous electrolyte battery without using an expensive porous membrane as a separator in order to obtain an inexpensive nonaqueous electrolyte battery.

[0008]

In a battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, at least one of the positive electrode and the negative electrode has an electronically insulating porous layer formed on an active material layer. Use the electrode provided. As a method of forming such an electronically insulating porous layer on the active material layer, a paste prepared by wet mixing a solid material constituting the active material layer with a binder and a suitable solvent or liquid is used. Is applied on a metal foil to form a coating film, and in a state where the coating film is not dried, an electronic insulating powder is sprinkled on the coating film, and then the solvent or liquid in the coating film is dried. By removing, an electronically insulating porous layer is formed on the active material layer.

[0009]

In a conventional non-aqueous electrolyte battery, a porous film-shaped separator is usually sandwiched between a positive electrode and a negative electrode. For example, in a cylindrical non-aqueous electrolyte battery, a battery element as a power generating element has a porous film-like separator (13) between a strip-shaped negative electrode (11) and a strip-shaped positive electrode (12) as shown in FIG. ) Is sandwiched between them and wound up as tightly as possible to create a wound body. In order to wind the wound body firmly, it is necessary to apply a certain amount of tension to the electrode and the separator. If a material having low mechanical strength is used as the separator, sufficient tension cannot be applied to the separator, so that the wound body cannot be wound up firmly. As described above, the separator is required to have a certain level of mechanical strength, and a sufficient porosity is required to sufficiently fulfill the function as a battery separator.
At present, available porous thin film products that meet both requirements are very expensive.

In the battery according to the present invention, at least one of the positive electrode and the negative electrode uses an electrode having an electronically insulating porous layer formed on an active material layer. In the battery according to the present invention, since the porous layer formed on the active material layer functions as a conventional separator, a non-aqueous electrolyte battery can be prepared without using a porous film separator.

[0011]

The present invention will be described in more detail with reference to the following examples.

Example 1 Method for Producing Electrode A solid material used as an active material is mixed with a small amount of a conductive agent (eg, acetylene black or graphite) as necessary, and a solvent (eg, PVDF) is dissolved in a binder (eg, PVDF). N
-Methyl-2-pyrrolidone) to prepare a slurry. Next, this slurry is applied on a metal foil serving as a current collector. FIG. 5 is a view showing a coating apparatus for applying a slurry onto a metal foil. The coating device includes a coating head, a dryer (25), and a powder sprinkler (26). Further, the coating head is a back roll (21),
It comprises a coating roll (22), a knife roll (23) and a paint reservoir (24). In FIG. 5, the metal foil (1) is led to a dryer between the back roll (21) and the coating roll (22).

The prepared slurry is stored in a paint reservoir (2).
Meet 4). The gap between the coating roll (22) and the knife roll (23) is appropriately adjusted, and the back roll (2) is adjusted.
When 1) and the coating roll (22) are rotated in the direction of the arrow, the slurry is first applied to a suitable thickness on the coating roll (22) and then the back roll (2).
The slurry is transferred to the metal foil (1) above 1), and a slurry coating film is applied on the metal foil with an appropriate thickness. The coating film before drying naturally has a solvent in which a binder is dissolved on its surface. Then, the electronic insulating powder (28) is filled in a powder sprinkler (26) installed between the coating head and the dryer, and the electronic insulating powder is uniformly sprinkled on the surface of the coating film. The powder sprinkler (26) is a device in which a vibrator is fixed to a container having a mesh at the bottom. By adjusting the vibration amount of the vibrator, the electronic insulating powder in the container passes through the mesh at the bottom. A certain amount is sprinkled on the surface of the coating film. The electronic insulating powder sprinkled on the surface of the coating film absorbs and wets the solvent in which the binder present on the coating film surface is dissolved. Then dryer (25)
And the solvent is completely removed from the coating film and the electronic insulating powder layer on the coating film surface. After the drying, the electrode is press-molded by a roll press to form an electrode having a cross section shown in FIG.
FIG. 1 is a cross-sectional view in the width direction of an electrode, in which a conductive active material layer (2) is formed on a metal foil current collector (1), and further, on the active material layer. The electrode has a porous layer (3) formed by solidifying the electronic insulating powder.

Preparation of Negative Electrode Acetylene black was added to mesocarbon microbeads that had been graphitized at 2800 ° C. as an anode active material,
Solvent (N-methyl-2-) in which binder (PVDF) is dissolved
Pyrrolidone) to form a slurry. A copper foil having a thickness of 0.01 mm is used for the metal foil, and alumina powder is used as the electronic insulating powder, and a strip-shaped negative electrode (11) is formed according to the above-described electrode forming method. FIG. 2 shows a plan view of the negative electrode (11) and a sectional view in the length direction thereof. An active material layer (2a) having mesocarbon microbeads as an active material is formed on both surfaces of the copper foil current collector (1a),
Further, a porous layer (3) formed by solidifying alumina powder is formed on the active material layer (2a). The strip-shaped negative electrode (11) has a width of 56 mm and a length La = 560.
mm, the active material layer is not formed on one side at one electrode end, and the current collector (1a) is exposed.

Preparation of Positive Electrode Commercially available manganese dioxide (MnO 2) and lithium carbonate (L
i2CO3) is mixed well at a ratio of 1 mol: 0.27 mol, and calcined in air at 800 ° C. for about 12 hours to synthesize a spinel-type lithium manganese composite oxide. This spinel-type lithium manganese composite oxide has an average particle size of 0.01.
A powder of about 0 mm is added, graphite is added thereto as a conductive agent, and the mixture is wet-mixed with a solvent (N-methyl-2-pyrrolidone) in which a binder (PVDF) is dissolved to form a slurry.
An aluminum foil having a thickness of 0.02 mm is used as the metal foil, and an alumina powder is used as the electronic insulating powder, and a strip-shaped positive electrode (12) is formed according to the above-described electrode forming method. FIG. 3 shows a plan view of the positive electrode (12) and a cross-sectional view in the length direction thereof. Aluminum foil current collector (1
An active material layer (2c) using a lithium manganese composite oxide as an active material is formed on both surfaces of (c), and a porous layer formed by solidifying alumina powder on the active material layer (2c) (3) is formed. Strip-shaped positive electrode (1
2) The width is 55 mm and the length Lc is 520 mm. An exposed portion of the current collector (1c) is provided at one electrode end, and a positive electrode lead (5) made of aluminum is welded thereto to expose the current collector. As for the portion, an insulating adhesive tape (40) having a width of 58 mm is protruded and adhered to the direction from which the positive electrode lead is taken out as shown in the plan view of FIG.

Preparation of Lithium Ion Secondary Battery The strip-shaped negative electrode (11) and the strip-shaped positive electrode (12) prepared as described above are superposed and spirally wound to form an electrode element as shown in FIG. At the time of winding, the positive electrode starts to be wound from the side where the positive electrode lead (5) is attached, and the negative electrode starts from the side opposite to the exposed portion of the current collector. Therefore, as shown in FIG. ) Is located at the center of the wound body, and a negative electrode current collector (1a) is arranged on the outermost periphery of the wound body. As shown in FIG. 4 in which the arrangement of the electrodes is further enlarged, the negative electrode active material layer (2a) and the positive electrode active material layer (2c) are formed of a porous layer (3) formed by solidifying alumina powder. ). That is, it can be seen that the porous layer (3) functions as a separator in a conventional battery.

Next, as shown in FIG.
An insulating sheet (7) is placed on the bottom of a 8.0 mm metal can (4), the battery element is housed in the metal can (4), and an insulating sheet (7) is placed on the top of the battery element. The gasket (8) is inserted into the opening of the metal can. The positive electrode lead (5) protruding from the electrode element is welded to a closing lid (9) having an explosion-proof function. Then, an electrolytic solution (1 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate) was placed in the metal can.
5.2 g of an electrolyte solution in which 1 liter of LiPF6 is dissolved). After injecting the electrolytic solution, as shown in FIG. 6, a closing lid (9) to which the positive electrode lead (5) is welded is set inside the gasket (8), and the positive external terminal (10) is closed with the closing lid ( 9) Overlap the battery can to make the outer diameter of the battery can about 0.5m
m, and finally the edges of the metal can were caulked and sealed to form a lithium ion secondary battery having an outer diameter of 17.5 mm and a height of 65 mm with the battery structure shown in FIG. In the final completed battery, the electrode end of the negative electrode (exposed current collector) arranged at the outermost periphery of the wound battery element is in contact with the inner wall of the battery can and is electrically connected. The can is the negative electrode external terminal.

Performance test of prototype battery The prototype battery was charged at a charging voltage of 4.2 V, charged at a charging current of 1000 mA for 2.5 hours, and discharged at a discharging current of 50 mA.
The charge / discharge was repeated by a method of performing the operation at 0 mA to a final voltage of 2.7 V, and a cycle test was performed. In order to compare the performance with the prototype battery, a commercially available lithium ion secondary battery of the same size as the prototype battery was purchased, and this battery was also subjected to a cycle test under the same conditions as the prototype battery. The test results are as shown in Table 1. In addition, it was confirmed that the purchased commercially available lithium ion secondary battery uses lithium cobalt oxide as a positive electrode active material and a porous film made of polypropylene as a separator. As shown in Table 1, the lithium-ion secondary battery prototyped according to the present invention was superior to a commercially available lithium-ion secondary battery in discharge capacity and cycle characteristics.

According to the present invention, an inexpensive spinel-based lithium manganese composite oxide (LiMn ₂ O ₄ ) is used for the positive electrode active material, and an expensive porous film is used for the separator. However, it can be seen that a lithium-ion secondary battery having a characteristic that is equal to or higher than that of a conventional lithium cobalt oxide as a positive electrode active material and has sufficiently satisfactory characteristics can be produced.

In the above embodiment, a lithium ion secondary battery using a spinel-based lithium manganese composite oxide as a positive electrode active material has been described. However, the present invention can of course be applied to other non-aqueous electrolyte batteries. It is. In forming the electronically insulating porous layer on the active material layer, alumina powder was used as the electronically insulating powder. However, the present invention is not limited to this, and other electronically insulating inorganic materials may be used. (Oxides, carbonates, etc.) and organic materials (polyethylene, P
VDF) can be used, and an ion conductive material (for example, β-alumina) may be used as long as it is electronically insulating.

[0021]

In the battery according to the present invention, the electronically insulating porous layer formed on the active material layer has the function of a separator and is joined to the surface of the electrode. It does not break, tear or stretch. In addition, the electronically insulating porous layer formed on the active material layer forms a coating film by applying a slurry comprising a solid material, a binder, and a solvent constituting the active material layer on a metal foil, Since it can be formed by a method of sprinkling an electronically insulating powder on the coating film and then drying and removing the solvent, it can be formed at extremely low cost. Therefore, the manufacturing cost can be greatly reduced as compared with a conventional nonaqueous electrolyte secondary battery using an expensive commercially available porous film as a separator. As a result, an inexpensive and high-performance nonaqueous electrolyte battery that can be used for a wide range of applications can be provided, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electrode.

FIG. 2 is a plan view and a cross-sectional view of a strip-shaped negative electrode.

FIG. 3 is a plan view and a cross-sectional view of a belt-shaped positive electrode.

FIG. 4 is a cross-sectional view of a wound battery element.

FIG. 5 is a schematic diagram of an electrode coating apparatus.

FIG. 6 is a sectional view of a battery.

FIG. 7 is a schematic view of a conventional wound battery element.

[Explanation of symbols]

1 is a metal foil, 2 is an active material layer, 3 is an insulator porous layer, 4 is a metal can, 5 is a positive electrode lead, 6 is a negative electrode lead, 7 is an insulating sheet 8 is a gasket, 9 is an explosion-proof valve (blocking lid) ) 10 is a positive electrode external terminal, 11 is a negative electrode, 12 is a positive electrode, 13 is a separator, 21 is a back roll, 22 is a coating roll, 23 is a knife roll, 24 is a paint pool, 25 is a dryer, and 26 is powder sprinkling. Machine, 27 is paint, 28 is powder,
40 is an insulating tape.

Claims (2)

[Claims] 1. A battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode has a conductive active material layer formed on a current collector of a metal foil. A non-aqueous electrolyte battery, comprising an electrode having an electronically insulating porous layer formed on the active material layer. 2. A process for producing an electrode having an electronically insulating porous layer formed on an active material layer, wherein a solid material constituting the active material layer is wet-mixed with a binder or a suitable solvent or liquid together with a binder. Applying the paste thus prepared on a metal foil to form a coating film, and sprinkling an electronic insulating powder on the coating film, and then drying and removing the solvent or liquid in the coating film. A method for producing an electrode for a battery, comprising: