JPH097602A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To provide a nonaqueous electrolyte secondary battery in which a preservation characteristic is improved by forming a positive electrode active layer on the surface of a predetermined metal collector in which layer a compound expressed by a specific formula is used as a main active material to adopt it as a positive electrode plate. CONSTITUTION: A positive electrode active layer containing a compound expressed by a formula as a main active material is formed on a surface of a metal collector containing metal chrome in which aluminum is contained as a main component or containing a chrome component of 10 to 5000ppm as an aluminum alloy to adopt it as a positive electrode plate. As a result, Cr2 O3 having low electric resistance is created by a chrome component during the long-term preservation of a battery, so that increase of polarization of a positive electrode is prevented to make a nonaqueous electrolyte secondary battery having an improved preservation characteristic. In the formula, M is Co, Ni, Fe, Mn or the like and X is 0.05<=X<=1.10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of battery characteristics of a non-aqueous electrolyte secondary battery, particularly storage characteristics thereof.

[0002]

2. Description of the Related Art In recent years, portable electronic devices have become portable.
Cordless use is progressing rapidly. Accordingly, there is an increasing demand for a small, lightweight secondary battery having a high energy density, which serves as a driving power supply. From this point of view, non-aqueous electrolyte secondary batteries, especially lithium secondary batteries, are highly expected as batteries having high voltage and high energy density, and development is urgently needed. From such a situation, a lithium composite transition metal oxide showing a high charge / discharge voltage, for example, a general formula Li _x MO ₂ (where 0.05 ≦ x ≦ 1.10,
A non-aqueous electrolyte secondary battery has been proposed in which M is a positive electrode active material represented by at least one element selected from Co, Ni, Fe, and Mn), and lithium ion insertion and desorption are used. Aluminum (Al) is generally used for the positive electrode current collector of such a battery.

[0003]

These batteries are required to maintain charge / discharge characteristics during storage for a long period of time.
A storage test at high temperature is performed as the acceleration test. For example, a storage test at 60 ° C. for 20 days corresponds to storage at room temperature (20 ° C.) for one year. However, when the above non-aqueous electrolyte secondary battery is charged, when it is stored for a long period of time or subjected to an accelerated test at high temperature, the battery capacity is significantly lower than the level before storage even when recharged after storage. There was a problem.

The present inventor has found that the cause of such characteristic deterioration is due to the following phenomenon. That is, as a result of analyzing the positive electrode plate before performing high temperature storage and after performing high temperature storage in a charged state, it was found that aluminum hydroxide (Al (OH) ₃ ) and oxidation on the surface of the positive electrode current collector of the battery after storage. coating of aluminum _{(Al 2 0 3 · XH 2} O) was formed. This is because a small amount of water present in the electrolytic solution is oxidatively decomposed at the positive electrode and reacts with aluminum which is a current collector, and the above-mentioned Al ₂ O ₃ .XH ₂ O and Al (O
It is considered that this is because the film of H) ₃ was formed. For far larger electric resistance of the Al ₂ 0 ₃ · XH ₂ O and Al (OH) ₃ is compared with Al, the surface resistance of the positive electrode current collector is markedly increased during high temperature storage of the battery after storage It is conceivable that the polarization of the positive electrode increased during the charging, and the battery was not sufficiently charged within the predetermined charging voltage, and the discharge capacity decreased.

The present invention is intended to solve such problems, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent storage characteristics.

[0006]

The present invention has the general formula Li _x M
A non-aqueous electrolyte solution including a positive electrode containing a lithium composite oxide represented by O ₂ as a main active material, a negative electrode plate, and an electrode plate group in which a separator is interposed between the positive and negative electrode plates. The non-aqueous electrolyte secondary battery is characterized in that a positive electrode current collector containing Al as a main component and chromium (Cr) as a metal or an alloy with Al is used in the secondary battery.

The content of Cr in the positive electrode current collector is 10 to 5
000 ppm, preferably 10 to 500 ppm, and C of the surface layer from the surface to a depth of 3 μm
The content of r is 10 to 10,000 ppm, preferably 10
It is good to set it to 0 to 5000 ppm.

[0008]

Function: Cr present on the surface layer of the positive electrode current collector according to the present invention
Components are oxidized when stored in a state in which the battery is charged to Cr ₂ 0 _3. Electrical resistance of the material Al ₂ 0 ₃ · XH ₂
Since it is smaller than the resistance of O and Al (OH) ₃ ,
The increase in surface resistance of the positive electrode current collector during storage of the battery is suppressed. As a result, it is possible to suppress an increase in the polarization of the positive electrode when the battery is charged after storage, and it is possible to charge an amount of electricity that is almost the same as before storage even after storage at high temperature, and it is possible to prevent the discharge capacity from decreasing. This improving effect is due to the action of the Cr component existing in the surface layer of the current collector, and a further effect can be obtained by forming the surface layer having a higher Cr concentration than the inner layer of the current collector.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings.

Example 1 A positive electrode current collector material containing metallic Cr in Al was prepared by melting metallic Cr powder in Al.
Was added to the above. That is, Al is melted in an inert gas such as nitrogen or argon, and the melting temperature at this time is 670 ° C. which is 660 ° C. or higher at which Al melts and 690 ° C. or lower at which alloying with Cr starts.
Al is made into a liquid state at a predetermined weight ratio (10, 50, 100, 500, 100) of fine metal Cr powder to Al.
0 and 5000 ppm), and further stirred for 30 minutes to uniformly disperse Cr. These Al to which Cr was added was cooled, then rolled into a foil having a thickness of about 10 to 30 μm, and used as a positive electrode current collector. A positive electrode paste containing a positive electrode composition was applied to both surfaces of this positive electrode current collector and dried to a thickness of O.D. It was rolled to 2 mm and cut into a size of 36 mm in width and 250 mm in length to obtain a positive electrode plate 5. This positive electrode paste is LiCoO2 powder 1 which is the positive electrode active material.
A mixture of 3 parts by weight of acetylene black, 4 parts by weight of graphite powder, and 7 parts by weight of a fluororesin binder in 100 parts by weight was suspended in an aqueous solution of carboxymethyl cellulose to prepare a paste. did.

FIG. 1 shows a vertical sectional view of a cylindrical battery used in the experiment of this embodiment. In FIG. 1, 1 is a battery case formed by processing a 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 spirally wound through a polypropylene separator 7 and housed in a battery case 1 having a diameter of 13.8 mm and a height of 50 mm. Has been done. One end of the positive electrode lead 5a made of Al connected to the positive electrode plate 5 is connected to the sealing plate 2, and the negative electrode lead 6a made of stainless steel connected to the negative electrode plate 6 is inside the battery case 1. Connected to the bottom. 8
Are insulating rings provided on the upper and lower portions of the electrode plate group 4, respectively.

The negative electrode plate 6 was prepared by mixing 100 parts by weight of carbon powder obtained by heat-treating coke with 10 parts by weight of a fluororesin binder and suspending it in an aqueous solution of carboxymethyl cellulose. The strike-shaped negative electrode composition was applied to the surface of a copper foil having a thickness of 15 μm, dried and rolled to a thickness of 0.2 mm, and cut into a width of 37 mm and a length of 280 mm to obtain a negative electrode plate.

For the electrolytic solution, a solvent prepared by mixing ethylene carbonate and diethyl carbonate in equal volumes is used, and lithium hexafluorophosphate (Li
A solution of PF ₆ ) dissolved at a rate of 1 mol / l was used to inject into the electrode plate group 4, and then the battery was sealed and sealed to obtain the battery of Example 1.

[Embodiment 2] Next, an embodiment of a positive electrode current collector containing Cr as an Al alloy in Al will be described. Al is melted by the same method and conditions as in Example 1 except that the melting temperature is 800 ° C. This melting temperature is C
The temperature is arbitrarily set in the range of 690 ° C. or higher at which an alloy with r is started to be formed. When the melting temperature is set high, the handling becomes difficult, and the power consumption increases, so the temperature is set to 800 ° C. In this embodiment, Cr metal powder is used in a weight ratio of 10, 50, 100, 500, 1000, to Al.
5000 ppm was added. Cool these, 10-3
Roll to a thickness of 0 μm. A paste containing the above-mentioned active material was applied to both surfaces thereof to form a positive electrode plate 5. A battery was constructed in the same manner as in Example 1 using the positive electrode plate obtained by the above method.

Example 3 Next, C was formed on the surface of the Al current collector.
An example of forming a layer having a high r concentration will be described. First, Cr was dispersed in Al under the same method and conditions as in Example 1 10
A foil with a thickness of about 30 μm was prepared. Next, in order to diffuse Cr existing in Al to the surface of this foil and form a layer having a high Cr concentration on the surface, 200 to 350 is used.
The heat treatment was performed in the temperature range of ° C for 3 hours or more. The reason for setting this temperature range is that if the temperature is not higher than 200 ° C, the diffusion of metallic Cr does not occur, and if the temperature is higher than 350 ° C, Al softens, the malleability and ductility become remarkably strong, and the strength as a current collector cannot be secured. This is because. When the Cr concentration added to Al and the Cr concentration at a depth of 3 μm from the surface of the foil were examined by this heat treatment step, the results shown in FIG. 4 were obtained. The heat-treated foil was used as a positive electrode current collector, and a paste containing the same positive electrode composition as in Example 1 was applied to both surfaces of the positive electrode current collector to obtain a positive electrode plate 5. A battery was constructed in the same manner as in Example 1 using the positive electrode plate obtained by the above method.

[Comparative example] 10% of Al containing no Cr added
A positive electrode current collector was obtained by rolling to a thickness of 30 μm, and a battery was prepared in the same manner as in Example 1.

Examples 1, 2, and 3 thus prepared
And the battery of the comparative example at 20 ° C. and the end-of-charge voltage 4.1.
V, discharge end voltage 3.0 V, charge / discharge current 100 mA were charged and discharged to confirm the discharge capacity before storage. Then, it was stored in a charged state at 60 ° C. for 20 days. After charging and discharging the stored battery at 100 mA for 5 cycles,
A high rate discharge test was performed at 500 mA, and the capacity retention rate after storage was calculated from (Equation 1).

[0018]

[Equation 1]

Test results of the batteries of Example 1 and Comparative Example,
The capacity retention rate after storage with respect to the Cr content rate is shown in FIG. From this result, A containing metal Cr according to the present invention
The battery using 1 as the positive electrode current collector (● in FIG. 2) maintains the capacity after storage compared to the battery using Al containing no Cr in the positive electrode current collector (○ in FIG. 2) in the comparative example. It is recognized that the rate is improving.

In Example 1, the Cr content is 10 to 10.
It can be seen that the capacity retention rate after storage is significantly improved in the range of 500 ppm. Further, when it exceeds 500 ppm, the improvement effect tends to decrease, but when the Cr content is 5000 ppm or less, a higher capacity retention rate than that of the comparative example is obtained, and the effect of the present invention is recognized. But,
When excessive Cr is contained, electric resistance increases, polarization increases, and the absolute value of charge / discharge capacity before storage decreases. In addition, the amount of unoxidized Cr remaining after storage increases, and the electrical resistance of this unoxidized Cr is large,
The polarization during charging and discharging increases and the charging and discharging capacity decreases,
The improvement effect decreases. Therefore, the improvement effect cannot be expected when the excess Cr of 5000 ppm or more is contained. From the above results, the Cr content is 10 to 5000 p.
It was effective in the range of pm, and particularly remarkable in the range of 10 to 500 ppm.

Test results of the batteries of Example 2 and Comparative Example,
The capacity retention rate after storage with respect to the Cr content rate is shown in FIG. From FIG. 3, the same effect as in Example 1 was observed. That is, when the Cr content is in the range of 10 to 500 ppm, the capacity retention rate after storage is significantly improved. If the content exceeds 500 ppm, the improvement effect tends to decrease, but 50
When the content is within 00 ppm, a higher capacity retention rate than that of the comparative example is obtained, and the effect of the present invention is recognized. However, if the Cr content is 5000 ppm or more, the improvement effect cannot be expected for the same reason as in Example 1. From the above results, it was found that the Cr content is effective in the range of 10 to 5000 ppm, and particularly remarkable in the range of 10 to 500 ppm.

In the second embodiment, an example in which Cr metal powder is used is shown, but the same effect was obtained even if the alloy CrAl ₇ powder was added.

Test results of the batteries of Example 3 and Comparative Example,
FIG. 5 shows the capacity retention rate after storage with respect to the Cr content rate at a depth of 3 μm. As shown in FIG. 5, the Cr content in the surface layer portion of the positive electrode current collector having a depth of 3 μm was 100 to 500.
When it is in the range of 0 ppm, a remarkable improvement effect of improving the capacity retention rate after storage is observed. If the content exceeds 5000 ppm, the improvement effect tends to decrease, but 10,000
When the Cr content is within ppm, a higher capacity retention rate is obtained than in the comparative example, and the effect of the present invention is recognized. However, if it exceeds 10000 ppm, the improvement effect cannot be expected for the same reason as in Example 1. From the above results, it was found that the Cr content is effective in the range of 10 to 10,000 ppm, and particularly remarkable in the range of 100 to 500 ppm.

Based on these results, the storage characteristics of the batteries using the Cr-containing positive electrode current collectors of the present invention shown in Examples 1 to 3 were improved for the following reasons. When aluminum containing Cr is used for the positive electrode current collector according to the present invention, oxides of Cr are formed on the surface of the positive electrode current collector after storage, and oxides or hydroxides of aluminum are detected. There wasn't. From this result, Cr in the present invention
Is preferentially caused to undergo an oxidation reaction with a slight amount of water present in the electrolytic solution. Therefore, aluminum oxide or aluminum hydroxide is not generated on the positive electrode current collector, and the polarization at the time of high-rate discharge becomes small, which allows the battery to be stored in a charged state at a high temperature even before storage. It is considered that the same high capacity maintenance ratio as in the above could be maintained.

Although a carbonaceous material is used for the negative electrode in this embodiment, the effect of the present invention works on the surface of the positive electrode plate, so that another negative electrode material capable of inserting and extracting lithium, such as a metal compound ( Iron oxide, tungsten oxide, etc.), inorganic layered compounds (BC ₂ N, LiN _3, etc.), organic polymer compounds (polyacetylene, polythiophene, etc.)
Similar effects were obtained by using lithium metal, lithium alloy, or the like.

In this embodiment, Li is used as the positive electrode active material.
CoO₂The effect of the present invention was evaluated by the battery using
But LiNiO₂, LiMnO₂, And LiCo_0.9M
n_0.1O ₂, LiNi_0.9Mn_0.1O₂, LiCo_0.8Ni
_0.1Mn_0.1O₂Etc. were used as the positive electrode active material.
It was confirmed that the same effect as in the above example was applied to the battery.
Was. In either case, as a positive electrode active material for battery construction,
For convenience, Li, which is a substance in an almost completely discharged state_xMO
₂(M: at least one of Co, Ni, Fe, and Mn
One element, x = 1) was used, but these positive electrode active materials
Is the value of x when Li is released by the charging reaction after the battery is constructed.
Decrease and the discharge reaction releases Li to increase the value of x.
It will be in the added state. There is a possibility that the x value during that time may change.
The width of the present invention is 0.05 ≦ x ≦ 1.10.
General formula Li_xMO₂(However, 0.05 ≦ x ≦ 1.10, M is C
an element of at least one of o, Ni, Fe, and Mn
The effect when applied to a battery using the positive electrode active material represented by
It can be said that there is.

Although a mixed solvent of ethylene carbonate and diethylene carbonate was used as the electrolytic solution in this embodiment, other non-aqueous solvents such as cyclic ester such as propylene carbonate and cyclic ether such as tetrahydrofuran are used. Similar effects were obtained by using a chain ether such as dimethoxyethane, a non-aqueous solvent such as chain ester such as methyl propionate, or a multi-component mixed solvent thereof.

[0028]

As is apparent from the above description, according to the present invention, the positive electrode current collector containing aluminum as the main component contains 10 to 5000 ppm of the chromium component as metallic chromium or an alloy with aluminum, and thus is preserved. It is possible to provide a non-aqueous electrolyte secondary battery having excellent discharge characteristics after that and excellent in long-term reliability.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the capacity retention rate of the batteries of Example 1 and Comparative Example after storage.

FIG. 3 is a diagram showing the capacity retention rate of the batteries of Example 2 and Comparative Example after storage.

FIG. 4 is a diagram showing the Cr concentration at a depth of 3 μm with respect to the added Cr concentration.

FIG. 5 is a diagram showing the capacity retention rate of the batteries of Example 3 and Comparative Example after storage.

[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 (2)

[Claims] 1. The general formula Li _x MO on the surface of a metal current collector.
₂ (however, 0.05 ≦ x ≦ 1.10, M is Co, Ni, F
a positive electrode plate having a positive electrode active material layer containing a compound represented by at least one of e and Mn) as a main active material, a negative electrode plate, and a separator interposed between these positive and negative electrode plates. In a non-aqueous electrolyte secondary battery including a battery, the metal current collector contains aluminum as a main component, and a chromium component of 10 as a metal chromium or an alloy with aluminum.
A non-aqueous liquid electrolyte secondary battery characterized by containing up to 5,000 ppm. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the surface layer from the surface of the metal current collector to a depth of 3 μm contains a chromium component in an amount of 10 to 10000 ppm.