JP4114247B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery using a lithium-containing composite oxide as a positive electrode active material.
[0002]
[Prior art]
In recent years, consumer electronic devices have become portable and cordless. Currently, nickel cadmium batteries or sealed small lead-acid batteries play a role as driving power sources for these electronic devices, but as the use of portable and cordless devices becomes established, the high energy density of secondary batteries that serve as driving power sources There is a strong demand for downsizing and weight reduction. In recent years, there has been a demand for a battery that can be charged and discharged at a high rate, as represented by the rapid market expansion of small camcorders.
[0003]
Under such circumstances, a non-aqueous electrolyte secondary battery using lithium cobalt composite oxide showing a high charge / discharge voltage, for example, LiCoO _2, as a positive electrode active material and utilizing insertion / extraction of lithium ions is disclosed. (Japanese Patent Laid-Open No. 63-59507).
[0004]
In order to realize high rate charge / discharge in such a battery, for example, the electrode area is made as large as possible by adopting a spiral structure in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween. ing.
[0005]
As an example of the electrode plate preparation means, in the means shown in JP-A-3-244508, first, 100 parts by weight of LiCoO ₂ powder as a positive electrode active material, 3 parts by weight of acetylene black, 4 parts of graphite powder. Part by weight and 7 parts by weight of a fluororesin binder are mixed and suspended in a carboxymethyl cellulose aqueous solution to form a paste. This paste is applied to both sides of an aluminum foil, dried and rolled to obtain a positive electrode plate.
[0006]
[Problems to be solved by the invention]
Since the positive electrode active material is a lithium compound capable of intercalating and deintercalating lithium ions, the lithium ions are eluted when the positive electrode active material is kneaded with an aqueous solution containing a thickener. The composite oxide of lithium and transition metal is synthesized from a lithium compound and a transition metal compound, and it is difficult to completely remove alkali components such as Na and Ka from these raw materials. In the positive electrode active material synthesized from these materials, an alkali component remains as a synthesis unreacted substance, and the pH of the positive electrode mixture paste is remarkably increased. Therefore, when the positive electrode mixture paste is applied to the aluminum foil as the current collector, the aluminum foil is corroded and hydrogen gas is generated at the interface between the aluminum foil and the positive electrode active material. As a result, the positive electrode active material is detached or lifted from the aluminum foil, and the yield of the positive electrode mixture paste application process is reduced. In addition, the battery characteristics were liable to deteriorate, such as the deterioration of the current collecting characteristics due to the rising of the positive electrode active material and the non-conductive layer formed at the interface between the aluminum and the positive electrode active material due to the corrosion of the aluminum foil.
[0007]
Further, as disclosed in JP-A-8-67991, carbon dioxide gas is passed through the positive electrode mixture paste to adjust the pH of the positive electrode mixture paste to 7 to 11, and then this is applied to the current collector surface. Means for producing a positive electrode plate by coating is known. However, this means is not preferable because the content as a fluororesin binder contained in the positive electrode mixture paste is altered by neutralization with carbon dioxide gas and the function as the binder is lowered.
[0008]
Accordingly, the present invention aims to provide a non-aqueous electrolyte secondary battery that solves such conventional problems, particularly a non-aqueous electrolyte secondary battery that uses a lithium-containing composite oxide as a positive electrode active material. Yes.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an aluminum current collector corroded by a strong alkali, and a positive electrode plate coated with a positive electrode mixture paste mainly composed of a positive electrode active material such as a lithium-containing composite oxide on the surface thereof. In a non-aqueous electrolyte secondary battery in which a separator is interposed between the negative electrode plate and the bipolar plate, 100 to 10,000 ppm of MoO ₃ is added by weight to the positive electrode active material. Therefore, since the positive electrode mixture paste applied to the aluminum current collector corroded by strong alkali contains MoO ₃ , the corrosion of the aluminum current collector can be reduced and the positive electrode mixture paste This improves the coating property and improves the current collecting characteristics.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an aluminum current collector corroded by a strong alkali, and a positive electrode plate coated with a positive electrode mixture paste including a positive electrode active material mainly composed of a composite oxide mainly composed of a lithium transition metal on the surface thereof; In a non-aqueous electrolyte secondary battery in which a negative electrode plate and a separator between the positive electrode plate and the negative electrode plate are interposed, the positive electrode mixture paste contains 100 to 10,000 ppm of MoO ₃ by weight with respect to the positive electrode active material. A non-aqueous electrolyte secondary battery using the added one is obtained.
[0011]
Since the positive electrode mixture paste includes a thickener, a conductive agent, and a binder as a positive electrode active material, an aluminum current collector can be obtained by adding 100 to 10,000 ppm of MoO ₃ by weight with respect to the positive electrode active material. Corrosion is alleviated.
[0012]
The chemical reaction formula when the aluminum foil used for the current collector is corroded by alkali is as follows.
[0013]
2Al + 3H ₂ O → Al ₂ O ₃ + 3H ₂ ↑ (Reaction Formula 1)
Al ₂ O _3, which is a very thin and dense oxide film, is present on the surface of aluminum foil. In a neutral aqueous solution, this oxide film inhibits the reaction between aluminum metal and water. Such a reaction does not occur. However, this oxide film is different from an alkaline aqueous solution as Al ₂ O ₃ + H ₂ O → 2AlO ₂ ⁻ + 2H ⁺ (Reaction Formula 2)
The oxide film is eluted in the solution as aluminate ions. Subsequently, active aluminum metal appears on the surface and reacts with water to cause the reaction of reaction formula 1.
[0014]
Since MoO ₃ added to the positive electrode mixture paste is a strong oxidizing agent, the following reaction occurs with the aluminum metal appearing on the surface of the aluminum foil.
[0015]
2Al + 3MoO ₃ → Al ₂ O ₃ + 3MoO ₂ (Reaction Formula 3)
When the reaction occurs in Reaction Formula 3, the reaction shown in Reaction Formula 1 between the aluminum metal and water is inhibited, and corrosion of the aluminum foil can be prevented even in an alkaline aqueous solution.
[0016]
For this reason, by adding MoO ₃ to the positive electrode mixture paste, generation of hydrogen gas between the aluminum foil and the positive electrode active material layer is eliminated, and the positive electrode active material does not fall off or rise from the aluminum foil. Wearability improves and the yield of a positive electrode plate also improves. In addition, since the nonconductive layer is not formed at the interface between the aluminum foil and the positive electrode active material layer, the current collection characteristics of the aluminum foil can be improved.
[0017]
In the present invention, MoO ₃ added to the positive electrode mixture paste functions to prevent corrosion of the aluminum foil, and a part of Co in LiCoO ₂ as disclosed in JP-A-8-250119 is used. In the system LiCo _1-x Mo _x O ₂ (0 <x <1) substituted with Mo, the effect of preventing corrosion of the aluminum foil as in the present invention cannot be obtained.
[0018]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a longitudinal section of a cylindrical battery used in this example. In FIG. 1, 1 is a battery case obtained by processing an organic electrolyte resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which a positive electrode plate 5 and a negative electrode plate 6 are wound in a spiral shape a plurality of times via a separator 7. A positive electrode lead 5 a is drawn from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is drawn from the negative electrode plate 6 and connected to the bottom of the battery case 1. Insulating rings 8 are provided above and below the electrode plate group 4, respectively.
[0019]
Hereinafter, the positive electrode plate 5, the negative electrode plate 6, the electrolytic solution, and the like will be described in detail.
The negative electrode plate 6 was prepared by mixing 10 parts by weight of a fluororesin binder with 100 parts by weight of carbon powder obtained by heat-treating coke, and suspending it in an aqueous solution of carboxymethyl cellulose to make a paste. This negative electrode mixture paste was applied to the surface of a copper foil having a thickness of 0.015 mm, dried and then rolled to a thickness of 0.2 mm, and cut into a size of 37 mm in width and 280 mm in length to obtain a negative electrode plate.
[0020]
The positive electrode plate 5 is prepared by mixing 5 parts by weight of acetylene black and 7 parts by weight of a fluororesin binder with 100 parts by weight of LiCoO ₂ powder as a positive electrode active material, and suspending it in an aqueous solution of carboxymethyl cellulose to adjust the pH. It has the paste-like positive electrode mixture made into 10-14. This positive electrode mixture paste was applied to both surfaces of an aluminum foil, dried and then rolled to 0.17 mm by a roll press, cut into a width of 35 mm and a length of 250 mm to obtain a positive electrode plate.
[0021]
A positive electrode lead 5a and a negative electrode lead 6a were attached to the positive electrode plate 5 and the negative electrode plate 6, respectively, wound in a spiral shape via a separator 7, and inserted into a battery case 1 having a diameter of 13.8 mm and a height of 50 mm.
[0022]
For the electrolyte, a solution obtained by dissolving lithium hexafluorophosphate at a ratio of 1 mol / liter in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate, and injecting a predetermined amount thereof into the electrode plate group 4, The battery was sealed and used as a test battery.
[0023]
Hereinafter, the production of the positive electrode plate 5 will be described in detail. A mixture of 100 parts by weight of LiCoO ₂ and 5 parts by weight of acetylene black and 7 parts by weight of a fluororesin binder is suspended in an aqueous solution of carboxymethyl cellulose to form a paste. While adjusting this, 0 to 30000 ppm of MoO ₃ is added to LiCoO ₂ in the positive electrode mixture paste while stirring. This paste was applied on both sides of an aluminum foil having a thickness of 0.02 mm with a multicoater and dried.
[0024]
The obtained electrode plate was rolled to a thickness of 0.17 mm using a roller press and cut into a width of 35 mm and a length of 250 mm to produce a positive electrode plate. Moreover, the coating property of the positive electrode active material was evaluated by the weight per 1 cm ^{3 of} the positive electrode mixture coated on the aluminum foil (hereinafter referred to as coating density), and this was measured by the following method.
[0025]
A positive electrode mixture paste is applied to an aluminum foil, and the positive electrode plate after drying is cut out to a certain area and its weight and thickness are measured. The weight of the aluminum foil contained in the cut-out positive electrode plate was calculated from the specific gravity, cut-out area, and thickness of the aluminum foil, and this was subtracted from the measured weight to obtain the weight of the positive electrode mixture. The volume of the aluminum foil is subtracted from the volume of the positive electrode plate to calculate the positive electrode mixture volume. From these, the weight per 1 cm ^{3 of the} positive electrode mixture was calculated as the coating density.
[0026]
When the aluminum foil is corroded, hydrogen gas is generated at the interface between the aluminum foil and the positive electrode active material layer, thereby raising the positive electrode active material. As a result, the apparent volume of the positive electrode active material layer increases and the weight per unit area decreases. Thus, when a coating property falls, a coating density will reduce.
[0027]
The relationship between the coating density measured by the coating density measuring method and the amount of MoO ₃ added to the positive electrode mixture paste is shown by circles in FIG. A positive electrode plate produced using a positive electrode mixture paste to which MoO ₃ is added has an increased coating density, and an improvement in coating properties is observed.
[0028]
This is because the MoO ₃ added to the positive electrode mixture paste protected the oxide film on the surface of the aluminum foil, thereby reducing the alkali corrosion of the aluminum foil.
[0029]
Further, the impedance of the battery of this example using each positive electrode plate produced by the above means was measured by an alternating current (1 kHz) impedance measurement method. The relationship between the impedance of the battery and the amount of MoO ₃ added to the paste is indicated by a circle in FIG. As is clear from FIG. 3, the impedance of the battery produced according to the present invention is reduced. This is because the alkaline corrosion of the aluminum foil is reduced and the current collecting characteristics as an electrode are improved.
[0030]
Even when the addition amount of MoO ₃ exceeds 10,000 ppm, the coating property was improved as compared with the conventional example in which no addition of MoO ₃ was observed, but the impedance of the battery gradually increased when the addition amount of MoO ₃ exceeded 10,000 ppm. Increased. This is because the conductivity of the positive electrode plate was lowered because MoO ₃ as an insulator was added to the positive electrode active material. Further, if the amount of MoO ₃ added is increased, the weight of the battery active material itself is decreased, which is not preferable because the discharge capacity of the battery is decreased. For this reason, it is desirable that the amount of MoO ₃ added in the present invention is 100 to 10,000 ppm.
[0031]
In the above examples, LiCoO ₂ was used as the positive electrode active material, but the same effect was obtained with lithium-containing composite oxides such as LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ .
[0032]
Moreover, in the said Example, although evaluation was performed using carboxymethylcellulose as a thickener, the same effect was acquired even if it used MC and PVA which are other thickeners.
[0033]
Furthermore, in the said Example, although evaluation was performed using a cylindrical battery, the same effect was acquired even if battery shapes, such as a square, differed.
[0034]
Furthermore, although the carbon material was used for the negative electrode in the above examples, the same effect was obtained even when lithium metal or a lithium alloy was used as the negative electrode.
[0035]
Furthermore, although lithium hexafluorophosphate was used as the electrolyte in the above examples, similar effects were obtained with other lithium salts such as lithium perchlorate and lithium tetrafluoroborate.
[0036]
Furthermore, in the above examples, the salt concentration of the electrolyte was 1 mol / liter, but the same effect was obtained even when other concentrations were used.
[0037]
Further, in the above examples, a mixed solvent of ethylene carbonate and diethyl carbonate was used as the electrolytic solution, but other non-aqueous solvents, for example, cyclic esters such as propylene carbonate, cyclic ethers such as tetrahydrofuran, and chain ethers such as dimethoxyethane. The same effect was obtained even when a non-aqueous solvent such as a chain ester such as methyl propionate or a multi-component mixed solvent was used.
[0038]
【The invention's effect】
As described above, the present invention is a non-aqueous electrolysis having a positive electrode plate in which a positive electrode active material layer mainly composed of a lithium-containing composite oxide is formed on an aluminum current collector that is corrosive to a strong alkali. In the liquid secondary battery, the positive electrode plate can reduce corrosion of the aluminum foil by adding 100 to 10000 ppm by weight of MoO ₃ with respect to the positive electrode active material. The current collecting characteristics of the foil can be improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a cylindrical battery in one embodiment of the present invention. FIG. 2 is a diagram showing the correlation between the amount of MoO ₃ added to the positive electrode synthesis paste and the coating density. Of the relationship between the amount of MoO ₃ added to the battery and the impedance of the battery [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6a Negative electrode lead 7 Separator 8 Insulation ring

Claims (3)

Non-aqueous electrolysis using a positive electrode plate comprising a positive electrode active material that reversibly reacts with lithium as a main constituent, and a positive electrode mixture paste showing alkalinity applied to an aluminum current collector corrosive to alkali A non-aqueous electrolyte secondary battery in which 100 to 10,000 ppm of MoO ₃ is added by weight to the positive electrode active material.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material that reversibly reacts with lithium is a lithium composite oxide. The non-aqueous electrolyte secondary battery according to claim 2, wherein the lithium-containing composite oxide is any one of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ .

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