JPH06290811A - Manufacture of non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To prevent the elusion of iron from a battery can and to provide a good cycle characteristic having no dispersion in a cycle life by manufacturing a battery by carrying out initial charging just after assembling of a battery, and then, carrying out aging and main charging in order. CONSTITUTION:A negative electrode 2, which uses a carbon material as a negative electrode active material, a positive electrode 1, separators 3a, 3b, and a non-aqueous electrolyte are sealed in a battery can 4, and a battery is assembled, and immediately after this, initial charging is carried out, and then, aging, main charging are carried out in order, and consequently, a non-aqueous electrolyte secondary battery is obtained. Although the electric potential of the negative electrode in an uncharged battery just after assembly is high when a carbon material is used for the negative electrode active material, the electric potential of the negative electrode is lowered when initial charging is carried out by a minute charging amount. Then aging is carried out, and the electrolyte sufficiently penetrates the separator without any elusion of iron constituting the battery can, as the electric potential of the negative electrode is lowered. In addition, main charging is carried out after this, and battery action proceeds uniformly, so that a non-aqueous electrolyte secondary battery having a long cycle life is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery using a carbonaceous material as a negative electrode active material.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras and radio-cassettes, there is an increasing demand for rechargeable secondary batteries in place of disposable primary batteries. Most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte. However, since the voltage of this battery is about 1.2V, it is difficult to improve the battery energy density. There is also a drawback that the self-discharge rate at room temperature is as high as 20% or more per month.

Therefore, a non-aqueous electrolyte secondary battery using a non-aqueous solvent as the electrolytic solution and a light metal such as lithium for the negative electrode has been studied. This non-aqueous electrolyte secondary battery has a high energy density of 3 V or more and a low self-discharge rate. However, such a non-aqueous electrolyte secondary battery has a drawback that metallic lithium or the like for the negative electrode grows in a dendrite form and contacts the positive electrode due to repeated charging and discharging, and as a result, a short circuit easily occurs inside the battery. In addition, it is difficult to put it into practical use.

Therefore, a non-aqueous electrolyte secondary battery in which lithium or the like is alloyed with another metal and this alloy is used for the negative electrode has been studied. However, in this case, it is still difficult to put into practical use due to the drawback that this alloy is likely to be formed into particles by repeating charging and discharging.

Therefore, for example, Japanese Patent Laid-Open No. 62-90863.
As disclosed in the publication, a non-aqueous electrolyte secondary battery using a carbonaceous material such as coke as a negative electrode active material has been proposed. Since this non-aqueous electrolyte secondary battery does not have the above-mentioned drawbacks in the negative electrode, it has excellent cycle life characteristics. Then, as the positive electrode active material, Li _X MO ₂ (M represents one kind or more than one kind of transition metal, as suggested by the inventor of the present application in JP-A-63-135099, and 0.05 < x <1.10.)
By using, the battery capacity is improved and a non-aqueous electrolyte secondary battery with high energy density can be obtained.

[0006]

Meanwhile, the non-aqueous electrolyte secondary battery using the carbonaceous material as the negative electrode active material has the advantages of long cycle life and high energy density as described above, but it is mass-produced. In that case, there is an inconvenience that the cycle deterioration degree is different for each product. This variation in the degree of cycle deterioration becomes a particular problem when the battery is used as an assembled battery.

Then, the inventors of the present invention investigated the cause of the variation in the cycle deterioration degree and found the following.

[0008] First, among the manufactured non-aqueous electrolyte secondary batteries, particularly those with severe cycle deterioration, the battery can is corroded and the iron constituting the battery can is eluted in the electrolyte. It is considered that a part of iron eluted from the battery can into the electrolytic solution irreversibly penetrates into the electrode to hinder the battery reaction at the electrode and accelerate cycle deterioration.

Such iron elution from the battery can occurs especially in the aging step performed after the battery is assembled.

That is, in the above non-aqueous electrolyte secondary battery, a negative electrode using a carbon material as a negative electrode active material, a positive electrode using Li _X MO ₂ as a positive electrode active material, a separator and an electrolytic solution made of iron plated with nickel. It is assembled by enclosing it in a battery can. The assembled battery is then charged so that it can be used as a non-aqueous electrolyte secondary battery.

However, in the battery immediately after being assembled, the electrolytic solution enclosed in the battery can does not soak into the separator sufficiently, and if the battery is immediately charged in this state, the battery reaction will proceed unevenly. , Lithium deposits and adversely affects the battery reaction. Therefore, conventionally, the assembled battery is not immediately charged, but is aged for about one month to allow the electrolytic solution to sufficiently soak into the separator before charging.

However, in the case of a battery using a carbon material as a negative electrode, the negative electrode has a high potential of about 3 V in an uncharged state in which the carbon material is not charged. When aging a non-charged battery in which the potential of this negative electrode is high, the iron that composes the battery can undergoes an electrochemical reaction during the aging process, eluting into the electrolytic solution and penetrating into the electrode. It will interfere with the reaction.

Therefore, the present invention has been proposed in view of such a conventional situation, and it is possible to prevent the elution of iron from the battery can, the cycle life does not vary from product to product, and good cycle characteristics are obtained. It is an object of the present invention to provide a method for producing a non-aqueous electrolyte secondary battery that exhibits the above-mentioned effect.

[0014]

In order to achieve the above-mentioned object, a method for producing a non-aqueous electrolyte secondary battery of the present invention comprises a negative electrode using a carbon material as a negative electrode active material, a positive electrode, a separator and a non-aqueous electrolysis. It is characterized in that the liquid is enclosed in a battery can to assemble a battery, and immediately after that, initial charging is performed, and then aging and main charging are sequentially performed.

Further, the amount of electricity charged in the initial charging performed immediately after assembling the battery is 0.5 to 11% of the total amount of electricity charged in the main charging. Furthermore, after assembling the battery, the initial charging is performed within 3 days.

In the present invention, the non-aqueous electrolyte secondary battery comprises
For example, the negative electrode, the positive electrode, the separator and the electrolytic solution are enclosed in a nickel-plated iron battery can for assembly.

The negative electrode active material used for the negative electrode is one that can be doped with lithium and dedoped, and includes pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbon. It is possible to use fired materials of organic polymers (phenolic resins, furan resins, etc.), carbon fibers, activated carbon, and the like.

The positive electrode active material used for the positive electrode is L
A lithium composite oxide represented by i _X MO ₂ (M represents one kind or more than one kind of transition metal, and 0.05 <x <1.10) is used.

As the electrolytic solution, any conventionally known electrolytic solution can be used as long as the electrolytic solution is dissolved in an organic solvent. Therefore, as the organic solvent, esters such as propylene carbonate, ethylene carbonate and γ-butyrolactone, ethers such as diethyl ether, tetrahydrofuran, substituted tetrahydrofuran, dioxolane, pyran and its derivatives, dimethoxyethane and diethoxyethane, and 3 3-substituted-2-oxazolidinones such as methyl-2-oxazolidinone, sulfolane,
Methyl sulfolane, acetonitrile, propionitrile, etc. are mentioned, and these are used individually or in mixture of 2 or more types. Further, as the electrolyte, lithium perchlorate, lithium borofluoride, lithium phosphorus fluoride, lithium chloroaluminate, lithium halide, lithium trifluoromethanesulfonate, or the like can be used.

The battery assembled in this manner is an uncharged battery that has not been charged, has the same potential on both the positive and negative electrodes as shown in FIG. 1, and no voltage is generated between the electrodes. This uncharged battery is then used as a non-aqueous electrolyte secondary battery by aging it so that the separator is sufficiently impregnated with the electrolyte solution and then charging is performed to generate a voltage between the positive electrode and the negative electrode. You can use it.

At this time, the potential of the negative electrode is high in the uncharged battery that has not been charged yet and has been assembled. Therefore, when aging is performed on an uncharged battery in which the potential of the negative electrode is high, iron constituting the battery can causes an electrochemical reaction during the aging and is eluted into the electrolytic solution. Then, a part of the eluted iron irreversibly penetrates into the electrode to hinder the battery reaction at the electrode.

Therefore, in the present invention, an uncharged battery immediately after assembly is initially charged by a small amount of charge electricity,
Aging is performed after this initial charging.

When the assembled uncharged battery is initially charged for a short time i, for example, the potential of the negative electrode decreases as shown in FIG. If aging is performed after lowering the potential of the negative electrode in this manner, the potential of the negative electrode is low, so iron is not eluted from the battery can during aging,
The electrolyte can be sufficiently impregnated in the separator.

When main charging is performed after aging,
The battery reaction proceeds uniformly at the electrodes, and a non-aqueous electrolyte secondary battery having a long cycle life can be obtained.

The amount of electricity charged during the initial charging is 0.5 to 1 of the total amount of electricity charged during the main charging performed after aging.
It is preferably 1%. If the amount of electricity charged during the initial charge is less than 0.5% of the total amount of electricity charged during the main charge, the effect of the initial charge cannot be sufficiently obtained, and the amount of electricity charged during the main charge is insufficient. In the case of more than 11%, lithium is deposited on the negative electrode because the electrolyte is not sufficiently impregnated in the separator at the time of initial charging, which causes cycle deterioration of the battery.

Further, it is desirable that the initial charging be performed within 3 days after the uncharged battery is assembled. If the period from the battery assembly to the initial charge exceeds 3 days, the uncharged battery immediately after being assembled has a high negative electrode potential, and iron elutes from the battery can during this period. This may cause cycle deterioration of the battery.

The non-aqueous electrolyte secondary battery manufactured by the manufacturing method of the present invention may have a cylindrical shape, a coin shape or a button shape. The present invention exerts the same effects regardless of which shape the battery is manufactured.

[0028]

In the present invention, the negative electrode using the carbon material as the negative electrode active material, the positive electrode, the separator, and the non-aqueous electrolyte are enclosed in a battery can to assemble an uncharged battery, and immediately after that, initial charging is performed and then aging is performed. A non-aqueous electrolyte secondary battery is manufactured by sequentially performing main charging.

When a carbon material is used as the negative electrode active material, the potential of the negative electrode of the uncharged battery immediately after assembly is high, but the potential of the negative electrode decreases when the initial charge is performed by a small amount of charge. When aging is performed after this, the potential of the negative electrode is lowered, so that the electrolytic solution sufficiently penetrates into the separator without elution of the iron forming the battery can. Then, when main charging is further performed thereafter, the battery reaction proceeds uniformly, and a non-aqueous electrolyte secondary battery having a long cycle life can be obtained.

[0030]

EXAMPLES The present invention will be described below based on specific experimental results.

Example 1 FIG. 2 shows a non-aqueous electrolyte secondary battery of this example. This non-aqueous electrolyte secondary battery was prepared as follows.

First, the positive electrode plate 1 was manufactured as follows. LiCoO ₂ was obtained by mixing 1 mol of lithium carbonate and 1 mol of cobalt carbonate and firing in air at a temperature of 900 ° C. for 5 hours. This LiCoO ₂ was pulverized with a bowl mill to obtain a positive electrode compound powder. 91 parts by weight of this positive electrode compound powder, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added as a dispersant to the mixture to prepare a positive electrode mixture paste. It was Then, the positive electrode mixture paste was uniformly applied to both surfaces of a current collector made of an aluminum foil having a thickness of 30 μm, dried, and then roller pressed to obtain a positive electrode plate 1. The positive electrode plate 1 has a width of 35 mm, a length of 300 mm and a thickness of 0.18.
It was a plate-shaped body of mm. An aluminum lead wire 7 was attached to the end of the positive electrode plate 1 by welding.

The negative electrode plate 2 was manufactured as follows. The negative electrode active material was a pitch coke having a diameter of 12.7 in a vibration mill.
Obtained by grinding for 2 minutes with a mm stainless steel ball. The true density of this pitch coke is 2.03
The interplanar spacing of the (002) plane determined by g / cm ³ according to the Japan Society for the Promotion of Science by X-ray diffraction measurement was 3.64Å, and the crystal thickness Lc in the C-axis direction was 40Å. Next, 90 parts by weight of this granular pitch coke and 10 parts by weight of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added as a dispersant to the mixture to prepare a negative electrode mixture paste. Then, as shown in FIG. 3, the negative electrode mixture paste is uniformly applied to both surfaces of the copper foil current collector 5 having a thickness of 10 μm to form active material layers 6a and 6b, and after drying,
The negative electrode plate 2 was obtained by performing roller pressing.
The negative electrode plate 2 has a width of 35 mm, a length of 300 mm,
It was a plate-shaped body having a thickness of 0.2 mm. Also, this negative electrode plate 2
A nickel lead wire (not shown) was attached to the end of each by welding.

Using the positive electrode plate 1, the negative electrode plate 2, and a pair of polypropylene thin plate-shaped separators 3a and 3b, the negative electrode plate 2, the separator 3a, the positive electrode plate 1 and the separator 3b are laminated in this order, These were spirally wound. Then, the wound body was housed in a nickel-plated iron battery can 4. In this case, the above-mentioned lead wire was welded to the battery can 4 and the battery lid 9. As the electrolytic solution, a mixed solution of propylene carbonate in which 1 mol / l of lithium hexafluorophosphate was dissolved and diethyl carbonate was used. Then, after injecting this mixed solution into the battery can 4, the polypropylene gasket 8 and the battery lid 9 are attached to the battery can 4.
The battery can 4 is inserted into the upper part and the upper part of the battery can 4 is caulked to seal the battery.
1000 mm cylindrical uncharged battery with a height of 8 mm and a height of 45 mm
The cell was assembled.

The thus-assembled uncharged battery was subjected to constant current charging (initial charging) at a charging current of 1000 mA for 5 seconds, and then left to stand in an environment of a temperature of 60 ° C. for 15 hours for aging. . The uncharged battery left at 60 ° C. for 15 hours was accelerated aging, which is equivalent to leaving the uncharged battery at room temperature for one month. Subsequently, charging current 100 mA, final voltage 4.25.
Main charging was performed with V to manufacture a non-aqueous electrolyte secondary battery. Table 2 shows the amount of electricity charged for the initial charging and the total amount of electricity charged for the main charging of the uncharged battery.

Examples 2 to 7 Non-aqueous electrolyte secondary batteries were prepared in the same manner as in Example 1 except that the charging time of the initial charge applied to uncharged batteries was changed as shown in Table 1. did.

[0037]

[Table 1]

Table 2 shows the amount of electricity charged in the initial charging and the total amount of electricity charged in the main charging performed on the uncharged battery.

Comparative Example 1 An uncharged battery assembled in the same manner as in Example 1 was aged by leaving it for 15 hours in an environment of a temperature of 60 ° C. without performing initial charging. Then, main charging was performed at a charging current of 100 mA and a final voltage of 4.25 V to produce a non-aqueous electrolyte secondary battery.

With respect to the various non-aqueous electrolyte secondary batteries thus produced, the charging current was 100 mA and the final voltage was 4.
After charging at 2V, a charging / discharging cycle of discharging a constant current of 100mA and a constant voltage of 2.5V was repeated 100 times.
The capacity at the cycle was measured to determine the capacity retention rate (capacity at 100 cycle / 10 capacity at 10th cycle × 100). The results are shown in Table 2 together with the amount of electricity charged in the initial charge and the total amount of electricity charged in the main charge. The charging voltage of 4.2 V in the charge / discharge cycle is set according to the recommended voltage of this non-aqueous electrolyte secondary battery.

[0041]

[Table 2]

As can be seen from Table 2, the batteries of Examples 1 to 7 all have a higher capacity retention rate than the battery of Comparative Example 1 and are excellent in cycle characteristics. It is effective to prevent the elution of iron from the battery can during aging and to manufacture a non-aqueous electrolyte secondary battery with excellent cycle characteristics by performing initial charging in advance before aging the rechargeable battery. It can be seen that it is.

However, Examples 2 to 6 and Example 1,
As can be seen by comparing Example 7, when the charged electricity amount at the time of initial charging is too small (Example 1) or too large (Example 7), the capacity retention rate is not sufficiently improved. I can't hope. That is, from this, it is understood that, in order to efficiently improve the cycle characteristics by the initial charging, the amount of charged electricity is 0.5 to 11% of the total amount of charged electricity in the main charging.

Experimental Example 1 In this experimental example, the timing of initial charging of the assembled uncharged battery was examined.

The uncharged battery assembled in the same manner as in Example 1 was left at room temperature for the period shown in Table 3. Subsequently, main charging was performed at a charging current of 100 mA and a final voltage of 4.25 V to produce a non-aqueous electrolyte secondary battery.

With respect to the various non-aqueous electrolyte secondary batteries thus produced, the charging current was 100 mA and the final voltage was 4.
After charging at 2 V, a charge / discharge cycle of discharging at a current of 100 mA and discharging at a constant voltage of 2.5 V was repeated 100 times, and the capacity at each cycle was measured. The relationship between the number of cycles and the capacity is shown in FIG. 4, and the capacity and capacity retention rate (100th cycle capacity / 10th cycle capacity × 100) are shown in Table 3.

[0047]

[Table 3]

As can be seen from FIG. 4 and Table 3, in the non-aqueous electrolyte secondary battery, the longer the period of time when the battery is left uncharged, the lower the capacity retention rate, and the time when the battery is left for more than 3 days. Has a capacity retention rate of 86.9%. From this, it is preferable that the initial charge of the uncharged battery is preferably performed without leaving the uncharged battery for more than 3 days.

[0049]

As is apparent from the above description, in the method for producing a non-aqueous electrolyte secondary battery of the present invention, a negative electrode containing a carbon material as a negative electrode active material, a positive electrode, a separator and a non-aqueous electrolyte solution are used. Assemble the battery by enclosing it in a battery can, perform initial charging immediately after that, and then perform aging and main charging in sequence, so the cycle life does not vary from product to product. It is possible to obtain a battery.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a potential change between electrodes due to charging of a non-aqueous electrolyte secondary battery.

FIG. 2 is a partially cutaway side view showing a structural example of a non-aqueous electrolyte secondary battery manufactured by applying the present invention.

FIG. 3 is a main part schematic perspective view showing a state in which a negative electrode plate is partially cut away.

FIG. 4 is a characteristic diagram showing a relationship between a leaving time and a capacity of an uncharged battery in a non-aqueous electrolyte secondary battery.

[Explanation of symbols]

 1 ... ・ Positive electrode plate 2 ・ ・ ・ ・ Negative electrode plate 3a, 3b ・ ・ ・ Separator 4 ・ ・ ・ ・ Battery can 7 ・ ・ ・ ・ ・ Positive electrode lead 8 ・ ・... Gasket 9 ... Battery lid

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[Procedure amendment]

[Submission date] October 19, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Method for manufacturing non-aqueous electrolyte secondary battery

Claims (3)

[Claims] 1. A battery is assembled by enclosing a negative electrode using a carbon material as a negative electrode active material, a positive electrode, a separator and a non-aqueous electrolyte in a battery can, and immediately after that, initial charging is performed, and then aging and main charging are performed. A method for manufacturing a non-aqueous electrolyte secondary battery, which is performed sequentially. 2. The amount of electricity charged during initial charging immediately after the battery is assembled is 0.5 of the total amount of electricity charged during main charging.
It is -11%, The manufacturing method of the non-aqueous electrolyte secondary battery of Claim 1 characterized by the above-mentioned. 3. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein initial charging is performed within 3 days after the battery is assembled.