JPH08329984A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To prevent break of a negative electrode at the time of charging and discharging, to enlarge the capacity of a battery, and to facilitate the manufacture of the battery by using the positive electrode active material which includes lithium in a positive electrode, and using a metal which can not be combined with lithium as a negative electrode. CONSTITUTION: In the positive electrode, the lithium included positive electrode active material such as charcogers material containing lithium is used. As a negative electrode, a metal such as nickel, copper, molybdenum, or the alloy thereof, which can not be combined with lithium, is used. Since these metals are used for the negative electrode, deterioration of strength of the negative electrode material due to charging and discharging is prevented, and the quantity of the positive electrode active material is increased by the volume of the negative electrode active material at the excessive quantity to enlarge the capacity of the battery. Surface treatment such as polishing of these metal for negative electrode is easier in comparison with the metal lithium, and since the metal lithium is not used for the negative electrode, an equipment for storing the metal lithium in the high dry atmosphere is unnecessary.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention realizes an excellent battery capacity in which a positive electrode has a positive electrode active material containing lithium and a negative electrode is made of a metal that does not alloy with lithium within a certain charge / discharge cycle when a secondary battery is manufactured. The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art A negative electrode using lithium as a negative electrode active material, a positive electrode using a metal oxide, sulfide or chloride, or a carbon compound of halogen, etc. as a positive electrode active material, propylene carbonate, ethylene carbonate, dimethoxyethane, etc. Lithium perchlorate in an organic solvent, a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution (ion conductor) in which an inorganic salt such as lithium borofluoride is dissolved, compared to other secondary batteries,
It has advantages such as high voltage and high energy density. Therefore, non-aqueous electrolyte secondary batteries using lithium as a negative electrode active material have been attracting attention as electronic devices have been downsized.

[0003]

However, metallic lithium and lithium alloys have a high reactivity, and this high reactivity hinders the practical application of a non-aqueous electrolyte secondary battery using lithium as a negative electrode active material. There is. That is, a non-aqueous electrolyte secondary battery using metallic lithium or a lithium alloy as a negative electrode active material is likely to form a non-uniform coating film of carbonate or nitride on the surface of the non-aqueous electrolyte secondary battery. It hinders dissolution and precipitation.

Therefore, dendritic deposits called dendrites are formed on the surface of the negative electrode as the charge / discharge cycle progresses. This dendrite causes an internal short circuit, has low reversibility, and reduces battery capacity. Further, dendrites are generated in the current concentrating portion where dissolution and precipitation of lithium easily occur, leading to a decrease in the strength of the negative electrode, resulting in breakage of the negative electrode.

Such a phenomenon reduces the battery capacity with charge / discharge cycles. As a means for preventing the decrease in the battery capacity, a method of adding a negative electrode active material in excess of several times (usually three times) the electric capacity of the positive electrode is considered. Further, as a means for preventing the breakage of the negative electrode, a method in which lithium is pressure-bonded onto a current collector of a metal foil that does not alloy with lithium has been considered.

However, the excessive amount of the negative electrode active material and the current collector occupy a useless volume in the battery,
It was reducing the battery capacity. Furthermore, since lithium and lithium alloys easily react with water, a high dry atmosphere was required during storage of these and production of a non-aqueous electrolyte secondary battery using them as a negative electrode active material.

[0007]

Means for Solving the Problems In the non-aqueous electrolyte secondary battery, the present inventors have stated that the positive electrode has a positive electrode active material containing lithium at the time of making the secondary battery, so that lithium is not used in the negative electrode. The inventors have found that a battery having a battery capacity superior to that of a battery using lithium for the negative electrode can be obtained, and completed the present invention.

That is, according to the present invention, a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode has a positive electrode active material containing lithium when the secondary battery is prepared, and the negative electrode does not alloy with lithium. A non-aqueous electrolyte secondary battery comprising a metal is provided. The negative electrode that can be used in the present invention is made of a metal that does not alloy with lithium, and specific examples thereof include simple metals selected from nickel, copper, and molybdenum, or alloys selected from a plurality of these metals. The thickness of the negative electrode is usually 70 μm. Further, the negative electrode may be formed on a negative electrode current collector made of a metal such as aluminum or copper, if necessary. The shape of the negative electrode and the negative electrode current collector is not particularly limited, and examples thereof include a sheet shape.

This metal that does not form an alloy with lithium is easily subjected to surface processing (polishing, etc.) which is difficult with metallic lithium.
Therefore, the non-aqueous electrolyte secondary battery using the negative electrode in which the surface of a metal that does not alloy with lithium is used is more likely to make the dissolution and precipitation of lithium more uniform than when using lithium for the negative electrode. In addition, when a material that is easily alloyed is used as the negative electrode, strength deterioration of the negative electrode due to absorption and desorption of lithium is a problem, and the metal that is difficult to alloy with lithium is used as the negative electrode to prevent breakage of the negative electrode. Is possible.

Furthermore, since metallic lithium is not used for the negative electrode, equipment for storing lithium in a highly dry atmosphere is not required, which facilitates battery production. The positive electrode that can be used in the present invention comprises, for example, a mixture of a positive electrode active material, a conductive agent and a binder. The thickness of the positive electrode is usually 40 μm. Further, the positive electrode may be formed on a positive electrode current collector made of a metal such as aluminum or copper, if necessary. The shape of the positive electrode current collector is not particularly limited, and examples thereof include a sheet shape. The method for forming the positive electrode may be, for example, a method in which the sheet-shaped current collector is coated with the mixture and then pressed, but is not limited to this method.

As the positive electrode active material, one containing lithium as an active material at the time of making a secondary battery is used. For example, a chalcogenide containing lithium and the like can be mentioned. Specific examples thereof include chalcogen compounds such as LiCoO ₂ , LiNiO ₂ , and LiMnO ₂ , but the invention is not limited thereto. The conductive agent has a function of supplementing the conductivity of the positive electrode, and acetylene black or the like can be used, but is not limited thereto.

The binder has a function of adhering the positive electrode active material and the conductive agent, and is made of Teflon resin, ethylene-propylene-
Examples thereof include, but are not limited to, a diene terpolymer. As the electrolyte that can be used in the present invention, a solid electrolyte or an electrolyte (electrolyte solution) dissolved in a non-aqueous solvent can be used.

Examples of the solid electrolyte include polyethylene oxide (PEO) and the like. In addition, examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, and tetrahydrofuran, and these can be used alone or in combination of two or more.

As the electrolyte dissolved in the non-aqueous solvent, for example, lithium perchlorate, lithium borofluoride,
Examples thereof include lithium arsenic hexafluoride and lithium phosphorus hexafluoride, which may be used alone or in combination of two or more. A particularly preferable ionic conductor is an electrolytic solution prepared by dissolving lithium arsenic hexafluoride in a non-aqueous solvent composed of a mixed solution of ethylene carbonate and dimethyl carbonate at a ratio of 1: 1 (volume ratio) to a concentration of 1 mol / liter. .

In the non-aqueous electrolyte secondary battery of the present invention, a separator may be provided between the positive electrode and the negative electrode to retain the ionic conductor and prevent a short circuit between the positive electrode and the negative electrode.
The material of the separator is not particularly limited as long as it is an insulator that is not dissolved in the electrolytic solution and is easily processed. Specific examples thereof include porous polypropylene and porous polyethylene.

The shape of the non-aqueous electrolyte secondary battery of the present invention may be any of cylindrical type, prismatic type, button type, sheet type and the like.
In particular, a cylindrical shape or a rectangular shape in which a sheet-shaped electrode is wound or folded is preferable, but the present invention is not limited to this. The method for forming the non-aqueous electrolyte secondary battery is not particularly limited, and the non-aqueous electrolyte secondary battery can be manufactured by a known method. For example, the non-aqueous electrolyte secondary battery of the present invention includes the cylindrical non-aqueous electrolyte secondary battery shown in FIG. Briefly explaining the method of forming the secondary battery of FIG. 1, a sheet composed of the positive electrode 1 having the positive electrode lead 4, the separator 3 and the negative electrode 2 having the negative electrode lead 5 is wound around the center pin 11 and placed in the negative electrode can 7. Install. Here, the negative electrode lead 5 is connected to the negative electrode can 7 via the insulator 10.
By sealing this negative electrode can 7 with a positive electrode lid 6 having a safety valve 8 and a gasket 9, the cylindrical battery of FIG. 1 is formed. The positive electrode lead 4 is connected to the positive electrode lid 6 via the insulator 10.

[0017]

The non-aqueous electrolyte secondary battery of the present invention is characterized in that the positive electrode has a positive electrode active material containing lithium and the negative electrode is made of a metal that does not alloy with lithium when the secondary battery is prepared. The strength of the negative electrode material does not deteriorate due to discharge, and the negative electrode is prevented from breaking. Further, since the positive electrode active material can be increased by the volume occupied by the excess negative electrode in the conventional non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having the same volume and a large battery capacity can be obtained.

Furthermore, since metallic lithium is not used, equipment for a highly dry atmosphere, which is required for storing lithium and for manufacturing batteries, is not required.

[0019]

【Example】

Example 1 LiCoO _{2 as} a positive electrode active material, acetylene black as a conductive agent, and Teflon resin as a binder were mixed at a weight ratio of 6: 1: 1. The positive electrode 1 was prepared by applying the mixture onto an aluminum sheet (area 25 × 400 mm ² ) having a thickness of 20 μm that functions as a current collector and pressing the mixture. Further, the positive electrode lead 4 was arranged on the positive electrode 1.

The negative electrode 2 was a nickel sheet (area 30 × 400 mm ² ) having a thickness of 10 μm, and the negative electrode lead 5 was arranged on the sheet. The ionic conductor (electrolyte solution) is prepared by dissolving lithium arsenic hexafluoride in a non-aqueous solvent consisting of a mixed solution of ethylene carbonate and dimethyl carbonate at a ratio of 1: 1 (volume ratio) to a concentration of 1 mol / liter. It was adjusted.

Next, the positive electrode 1 and the negative electrode 2 were put together through a polypropylene porous separator 3 and the separator 3 was impregnated with an electrolytic solution to obtain a sheet-shaped secondary battery. The obtained sheet-shaped battery was wound, housed in the negative electrode can 7, and the negative electrode lead 5 was connected to the negative electrode can 7 via the insulator 10. Next, by sealing this negative electrode can 7 with a positive electrode lid 6 having a safety valve 8 and a gasket 9,
A cylindrical non-aqueous electrolyte secondary battery having a volume of 8 cc as shown in FIG. 1 was prepared. The positive electrode lead 4 was connected to the positive electrode lid 6 via the insulator 10.

The positive electrode volume, the positive electrode current collector volume, the negative electrode volume and other volumes of the cylindrical non-aqueous electrolyte secondary battery of this Example 1 (here, other volumes are separator, safety valve,
Table 1 shows the volume of the gasket and the like) together with the positive electrode capacity and the negative electrode capacity. The battery life of the obtained battery was evaluated by a charge / discharge cycle test. The conditions were constant current discharge with a charge / discharge current of 450 mA and a voltage range of 4.2 to 3.0V.

As a result, the discharge capacity of the battery was 700
mAh was 520 mAh after 30 cycles and 390 mAh after 60 cycles. The results are shown in Table 2. (Comparative Example 1) As the negative electrode, metal lithium (area: 30 x 400 mm ² ) having a thickness of 72 µm stored in a glove box replaced with argon gas was used, and the negative electrode capacity was set to 3 times the positive electrode capacity. The volume and the negative electrode volume were determined. Other conditions were the same as in Example 1 to prepare a non-aqueous electrolyte secondary battery. Table 1 shows the positive electrode volume and the negative electrode volume of the secondary battery of Comparative Example 1 together with the positive electrode capacity and the negative electrode capacity. The other volumes were the same as in Example 1.

The battery life of the obtained battery was evaluated by a charge / discharge cycle test. As a result, the discharge capacity of the battery was 540 mAh at the beginning and 510 mA after 30 cycles.
h, 20 mAh after 60 cycles and a significant decrease after 60 cycles. Table 2 shows the charge / discharge capacity of each cycle. Comparative Example 2 The negative electrode has a thickness of 10 μm as a negative electrode current collector.
Using a nickel sheet (area: 30 × 400 mm ² ) on which lithium was pressure-bonded, the positive electrode volume and the negative electrode volume were adjusted so that the negative electrode capacity was 3 times the positive electrode capacity, excluding the volume of the negative electrode current collector nickel sheet. The volume was determined. Other conditions were the same as in Example 1 to prepare a non-aqueous electrolyte secondary battery. Table 1 shows the positive electrode volume, the negative electrode volume, and the negative electrode current collector volume of the secondary battery of Comparative Example 2 together with the positive electrode capacity and the negative electrode capacity. The other volumes were the same as in Example 1.

The battery life of the obtained battery was evaluated by a charge / discharge cycle test. As a result, the discharge capacity of the battery showed a low value at the initial value of 450 mAh, but it was 420 mAh after 30 cycles and 400 mAh after 60 cycles.
The amount of change due to the progress of the cycle was small. Table 2 shows the discharge capacity of each cycle. (Comparative Example 3) The negative electrode has a thickness of 3 which is easily alloyed with lithium.
A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that 0 μm aluminum (area: 30 × 400 mm ² ) was used. The positive electrode volume, the positive electrode current collector volume, the negative electrode volume and other volumes, the positive electrode capacity and the negative electrode capacity of the secondary battery of Comparative Example 3 were the same as in Example 1.

The battery life of the obtained battery was evaluated by a charge / discharge cycle test. As a result, the discharge capacity of the battery was 500 mAh initially and 450 mA after 30 cycles.
h, 20 mAh after 60 cycles, 6 as in Comparative Example 1
It dropped significantly after 0 cycles. Table 2 shows the charge / discharge capacity of each cycle.

[0027]

[Table 1]

In Example 1 and Comparative Examples 1 to 3,
The area of the positive electrode, the negative electrode, and the separator and the electrolytic solution volume were the same.

[0029]

[Table 2]

When these four types of batteries were disassembled after completion of the charge / discharge test, breakage of the negative electrode was confirmed in the batteries of Comparative Examples 1 and 3. From these results, the non-aqueous electrolyte secondary battery (Comparative Example 1) using lithium having no current collector as a negative electrode and the non-aqueous electrolyte secondary battery having a negative electrode of a metal that is easily alloyed with lithium (Comparative Example 3) were obtained. It was found that the charge / discharge characteristics were poor.

In Example 1, the initial discharge capacity was about 1.6 times that of Comparative Example 2, and about 1.2 times after 30 cycles,
After 60 cycles, the discharge capacity was almost the same. Therefore, it was found that the non-aqueous electrolyte secondary battery of the present invention (Example 1) exhibited excellent battery capacity without impairing charge / discharge cycle characteristics, as compared with the conventional non-aqueous electrolyte secondary battery.

[0032]

The non-aqueous electrolyte secondary battery of the present invention is characterized in that the positive electrode has a positive electrode active material containing lithium and the negative electrode is made of a metal that does not alloy with lithium when the secondary battery is prepared. In addition, the strength of the negative electrode material does not deteriorate due to charge / discharge, and the negative electrode can be prevented from breaking. Further, since the positive electrode active material can be increased by the volume occupied by the excessive amount of the negative electrode active material in the conventional non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having the same volume as the conventional one and a large battery capacity can be obtained. be able to.

Furthermore, since metallic lithium is not used, equipment for a high dry atmosphere required for storing lithium and for manufacturing batteries is not required. Therefore, it is possible to provide a non-aqueous electrolyte secondary battery that realizes an excellent battery capacity within a certain charge / discharge cycle and is easy to manufacture.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode lead 5 Negative electrode lead 6 Positive electrode lid 7 Negative electrode can 8 Safety valve 9 Gasket 10 Insulator 11 Center pin

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Watanabe 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Masami Tsutsumi, 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor Tsutomu Miyashita 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (3)

[Claims] 1. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode of the secondary battery has a positive electrode active material containing lithium, and the negative electrode is made of a metal that does not alloy with lithium. Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal that does not alloy with lithium is selected from one or more of nickel, copper and molybdenum. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a chalcogen compound containing lithium.