JP2001185126A - Lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery capable of normally operating even with a thick electrode by improving contact of active material particles for reduction of internal resistance against electron conduction and reduction of contact resistance between active material and a current collector and to improve the filled rate of active material and energy density in the battery by thickening an electrode. SOLUTION: In a lithium secondary battery interposing electrolyte between electrodes made of active material and enclosing those in a can, the electrodes are formed of active material sintered body of a thickness of more than or equal to 100 μm and a current collector made of one or plural kinds of metal of gold, silver, cupper, platinum, palladium, nickel, titan, chromate, iron, aluminum is provided on the active material sintered body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery and a method of manufacturing the same, and more particularly to a lithium secondary battery in which an electrolyte is sandwiched between electrodes made of an active material and sealed in a can and a method of manufacturing the same.

[0002]

2. Description of the Related Art With the phenomenal development of mobile communication in recent years, a small secondary battery having a high energy density has been desired. One of such high performance secondary batteries is a lithium secondary battery.

In order to further increase the energy density of a lithium secondary battery, it is necessary to fill the active material with a high density. One of the methods for filling the active material with high density is to sinter the active material.

However, when sintering an active material to form an electrode, there is a problem that it is difficult to use a carbon-based material as a conductive agent used in a conventional lithium secondary battery. This is because if a carbon-based conductive agent is added before sintering, the carbon material burns and scatters during sintering or reacts with the active material, which is an oxidizing agent, to inhibit the electrochemical reaction of the active material. is there.

Therefore, a method has been proposed in which a conductive agent such as a carbon material that is not suitable for the sintering process is not used.

For example, in Japanese Patent Application Laid-Open No. 8-148141, the active material is slurried together with a binder, and the thickness after firing on a current collector substrate by a doctor blade method is 20 μm.
A method has been proposed in which an active material layer is formed so as to have a thickness of m or less and then fired to remove the binder.

According to this method, since the electrode can be formed only of the active material, there is no reaction between the active material and the conductive agent, and the process of forming the electrode is not limited. In addition, there is an advantage that the amount of the active material can be increased by adding no conductive agent.

However, most of the lithium transition metal composite oxides serving as active materials exhibit only semiconducting electronic conductivity. Therefore, unless the film thickness is as thin as 20 μm or less, satisfactory charge / discharge behavior cannot be obtained. Becomes When the thickness of the electrode is thin as described above, the volume ratio of members other than the electrode, such as the current collector, occupying in the battery increases, so that even if the packing density of the active material in the electrode is improved, the overall battery is high. An obstacle to energy density.

[0009] On the other hand, various methods for improving the current collection effect have been studied for the current collection from the electrodes.

For example, Japanese Patent Application Laid-Open No. 6-236758 discloses that a current-collecting material made of metal, carbon fiber or graphite fiber is applied to a chemical processing method such as a photography technique and an etching technique or a mechanical processing technique such as a press technique. It has been proposed to use a current collecting core formed by a processing method or the like and having a current collecting protrusion protruding into the positive electrode active material. According to this method, the contact area between the current-collecting material having excellent electron conductivity and the active material increases, and therefore, the emission area of the electrons in the current-collecting core to the positive electrode active material increases. Since a large amount of electrons can be emitted at one time, there is an advantage that a non-uniform oxidation-reduction reaction in the positive electrode and a voltage drop due to internal resistance can be suppressed.

However, in this method, it is necessary to form an active material layer on the surface of the current collecting core. Therefore, if this method is combined with the electrode obtained by sintering the active material, the material of the current collecting core is gold. However, there is a problem that the metal is limited to an inert metal and the cost setting is also limited.

[0012]

According to a first aspect of the present invention, there is provided a lithium secondary battery in which an electrolyte is sandwiched between electrodes made of an active material and sealed in a can. In the battery, the electrode is formed of an active material sintered body having a thickness of 100 μm or more, and gold,
A current collector made of one or more of silver, copper, platinum, palladium, nickel, titanium, chromium, iron, and aluminum is provided.

According to a second aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery in which an electrolyte is sandwiched between electrodes made of an active material and sealed in a can. An active material is formed by sintering such that the thickness after sintering becomes 100 μm or more, and a current collector is formed on the active material sintered body by a sputtering method or a vapor deposition method.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing a configuration example of a lithium secondary battery according to the first aspect of the present invention, taking a coin-type lithium secondary battery as an example. In FIG. 1, 1 is a positive electrode can, 2 is a positive electrode current collector, 3 is a positive electrode, 4 is an insulating packing, 5 is an electrolyte, 6 is a negative electrode, 7 is a negative electrode current collector, and 8 is a negative electrode can.

At least one of the positive electrode 3 and the negative electrode 6 is formed of a sintered body made of a lithium transition metal composite oxide capable of reversibly inserting and removing lithium ions.

The sintered body may be a solid-phase sintered body or a liquid-phase sintered body containing a small amount of a sintering aid that generates a liquid phase during firing. An active material powder that has been bound by cooling the amorphous oxide once the active material powder has been cooled, or an active material powder that has been surface-treated with alkoxysilane to strengthen the bonds between the active material particles. A sintered body may be used. Due to the volume shrinkage due to sintering, the contact area between the active material particles increases, and it is important that sufficient electron conductivity is obtained to carry out the charge / discharge reaction. is not. However, when a material other than the active material is mixed, it is desirable to minimize the addition and increase the energy density.

The thickness of the sintered electrode is 100 μm or more. If the thickness of the sintered body is less than 100 μm due to its brittleness, handling properties are poor. Further, the thickness of the electrode of the lithium secondary battery of the type bound with the current polymer adhesive is 5
Considering that the thickness is about 0 to 100 μm, it is impossible to reduce the thickness of the electrode to less than 100 μm to lower the energy density of the battery as a whole. Specifically, the thickness may be about 1 mm when charging / discharging at a 100 hour rate (0.01 C), or 500 μm or less when charging / discharging at a 10 hour rate (0.1 C). Good. If the thickness is further reduced, charging and discharging with a large current is possible.

Examples of the active material used for the positive electrode 3 and / or the negative electrode 6 include the following lithium transition metal composite oxides. For example, there are lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide, lithium titanium composite oxide, and derivatives thereof.

Here, the active materials used for the positive electrode and / or the negative electrode 6 are not clearly distinguished, and those showing a more noble potential by comparing the charge and discharge potentials of the two kinds of lithium transition metal composite oxides are regarded as positive electrodes. 3 shows a negative electrode with a lower potential.
Can be used to form a battery having an arbitrary voltage.

As for the negative electrode 6, an intercalation compound such as graphite capable of inserting and removing lithium ions, and a metal or alloy capable of dissolving and depositing lithium ions such as metallic lithium and lithium-aluminum alloy can also be used.

To produce the positive electrode 3 and the negative electrode 6,
(1) A slurry is prepared with water or an organic solvent in which an active material and a binder are dissolved, and this slurry is applied on a base film, dried, and then cut to 500 to 800.
(2) a method of sintering at 500 to 800 ° C. after (2) granulating the active material directly or with the addition of a binder, charging the mixture into a mold, press-molding with a press machine, or
(3) The granulated mixture is pressure-formed by a roll press machine and processed into a sheet, and then the sheet is cut to 500 to
A method of sintering at 800 ° C. is used.

Examples of the binder usable here include one or a mixture of two or more of polyacrylic acid, carboxymethyl cellulose, polyvinyl alcohol, diacetyl cellulose, hydroxypropyl cellulose, polybutyral, and the like.

As the base film, for example, a resin film of polyethylene terephthalate, polypropylene, polyethylene, polytetrafluoroethylene or the like is used.

The positive electrode current collector 2 and the negative electrode current collector 7 are arranged for current collection from the positive electrode 3 and contact with the positive electrode can 1, current collection from the negative electrode 6 and contact with the negative electrode can 8, and have a thickness of 1 μm. It is composed of one or more of gold, silver, copper, platinum, palladium, nickel, titanium, chromium, iron and aluminum having the following thicknesses. These current collectors are formed by a sputtering method or an evaporation method.

The thickness of the current collectors 2 and 7 is at most 5000
If there is, it will fully exhibit the current collection function. Increasing the thickness of the current collectors 2 and 7 increases the volume ratio and the weight ratio of the current collectors 2 and 7 in the battery, which hinders an increase in energy density. In the current lithium secondary battery,
Considering that the current is collected using a metal foil having a thickness of 20 μm, it is desirable to make the thickness of the current collectors 2 and 7 smaller than this in order to improve the energy density.

The electrolyte 5 may be an organic electrolyte in which a required electrolyte salt is dissolved in an organic solvent, a solid polymer electrolyte in which an electrolyte salt is dissolved in an ion conductive polymer material, or a gel electrolyte in which these are combined. An inorganic solid electrolyte made of an inorganic material can be used.

When an organic electrolyte is used as the electrolyte 5, a separator for separating the positive electrode 3 and the negative electrode 6 is required.

Examples of the organic solvent used for the organic electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, sulfolane,
There is one or a mixture of two or more solvents selected from 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and methylethyl carbonate.

Examples of the ion conductive polymer material include polyethylene oxide and polypropylene oxide.

As the electrolyte salt, for example, LiClO ₄ ,
LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF
₃ SO ₂ ) _{2 and the} like.

As the inorganic solid electrolyte, for example, Li _{1.3
Al 0.3 Ti 1.7 (PO 4)} 3, Li 3.6 Ge 0.6 V 0.4 O 4 oxide crystalline solid electrolyte such as, 40Li ₂ O-35B ₂
O ₃ -25LiNbO ₃ oxide-based amorphous solid electrolytes such as, mention may be made of sulfide-based amorphous solid electrolytes such as _{1Li 3 PO 4 -63Li 2 S-} 36SiS 2.

As the separator, for example, a nonwoven fabric made of polyolefin fiber or a microporous film made of polyolefin can be used. Here, examples of the polyolefin include polyethylene and polypropylene.

The positive electrode can 1 and the negative electrode can 8 are used for connection to external equipment and for shutting off the inside of the battery from the outside air. For example, nickel, stainless steel, titanium, aluminum or the like is used.

The insulating packing 4 is used to block the inside of the battery from the outside air and to prevent a short circuit between the positive electrode can 1 and the negative electrode can 8, and is made of, for example, polyethylene, polypropylene, styrene-butadiene copolymer or the like.

[0036]

Example 1 10 wt% of polyvinyl alcohol as a binder with respect to 100 wt% of Li _1.1 Mn _1.9 O ₄ powder
In addition, 30 wt% of water was further added and mixed to prepare a slurry. After this slurry was spray-dried, the obtained powder was filled in a 20 mmφ mold and press-molded under a pressure of ² t / cm ² . Put the molded body in the firing furnace, 7
It baked at 50 degreeC over 10 hours. The sintered body is 18mmφ
The electrode thickness after firing is 500
μm.

Gold was sputtered on one side of the active material sintered body to form a current collector having a thickness of 5000 °.

[0038]

Example 2 A positive electrode was produced in the same manner as in Example 1 except that the thickness of the electrode after firing was 1.0 mm.

[0039]

Example 3 A positive electrode was produced in the same manner as in Example 1 except that the thickness after firing was 100 μm.

[0040]

Comparative Example 1 10 wt% of polyvinyl alcohol was used as a binder with respect to 100 wt% of Li _1.1 Mn _1.9 O ₄ powder.
In addition, 30 wt% of water was further added and mixed to prepare a slurry. Using this slurry, an active material layer was formed on a current collector made of a gold foil having a thickness of 20 μm by a doctor blade method so that the thickness after firing became 500 μm. Further, this was fired at 400 ° C. to remove the binder and form an electrode.

This electrode is very fragile and may be peeled off from the current collector if not handled with care. The stripped electrode was powdery. Therefore,
This electrode can only maintain its shape by being supported by a current collector made of strong metal foil, etc.
The shape cannot be maintained on the thin film current collector formed by the sputtering method or the like shown in the embodiment.

[0042]

To [Comparative Example 2] Li _1.1 Mn _1.9 O ₄ powder 100 wt%, 10 wt% polyvinyl alcohol as a binder
In addition, 30 wt% of water was further added and mixed to prepare a slurry. Using this slurry, an active material layer was formed on a current collector made of a gold foil having a thickness of 20 μm by a doctor blade method so that the thickness after firing became 1.0 mm. Further, this was fired at 400 ° C. to remove the binder and form an electrode.

Note that this electrode is very brittle, and may be peeled off from the current collector if not handled with care. The stripped electrode was powdery. Therefore,
This electrode can only maintain its shape by being supported by a current collector made of strong metal foil, etc.
The shape of the thin film current collector formed by the sputtering method or the like described in the examples cannot be maintained.

[0044]

Comparative Example 3 A positive electrode was produced in the same manner as in Example 1, except that the current collector was not formed by the sputtering method.

[0045]

Comparative Example 4 A positive electrode was produced in the same manner as in Example 2, except that the current collector was not formed by the sputtering method.

[0046]

Comparative Example 5 10% by weight of polyvinyl alcohol as a binder with respect to 100% by weight of Li _1.1 Mn _1.9 O ₄ powder
In addition, 30 wt% of water was further added and mixed to prepare a slurry. Using this slurry, an active material layer was formed on a current collector made of a gold foil having a thickness of 20 μm by a doctor blade method so that the thickness after firing became 20 μm.
Further, this was fired at 400 ° C. to remove the binder and form an electrode.

This electrode is very fragile and may be peeled off from the current collector if not handled with care. The stripped electrode was powdery.

[0048]

Comparative Example 6 10 wt% of polyvinyl alcohol was used as a binder with respect to 100 wt% of Li _1.1 Mn _1.9 O ₄ powder.
In addition, 30 wt% of water was further added and mixed to prepare a slurry. Using this slurry, an active material layer is formed on a PET film having a thickness of 25 μm by a doctor blade method so that the volume after sintering becomes 50 μm in consideration of the fact that the volume after firing becomes 75%. Formed. The formed tape was peeled off from the PET film, punched out with a 20 mmφ mold, and the punched out piece was placed in a firing furnace, and 750 mm.
Calcination was carried out at 10 ° C. for 10 hours. The sintered body was shrunk to a size of 18 mmφ, and the thickness after firing was 50 μm.

An attempt was made to form a current collector by sputtering gold on one side of the active material sintered body, but the sintered body was broken during handling. Therefore, this electrode
The shape can only be maintained by being supported by a current collector made of a strong metal foil or the like, and it is difficult to maintain the shape with a thin-film current collector formed by a sputtering method or the like shown in Examples. Things.

[0050]

[Electrochemical Evaluation] The electrodes shown in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5 were used as positive electrodes, and negative electrodes were used as negative electrodes. Is metal lithium, and propylene carbonate: diethyl carbonate = 1 mol / l of LiClO ₄ is dissolved in the electrolyte.
A 1: 1 solution was used, a polypropylene microporous membrane was used as a separator, and current collection on the negative electrode side was performed by directly attaching metallic lithium to a negative electrode can, and a coin cell for electrochemical capacity evaluation was assembled.

The current collection on the positive electrode side was performed by the sputtering method of the first, second, and third embodiments.
The contact was performed by contacting the gold current collector of Å with the positive electrode can, and Comparative Example 1, Comparative Example 2, and Comparative Example 5 had a thickness of 20 μm.
The cell was assembled in such a manner that the contact was performed by contacting the gold foil and the positive electrode can with each other, and that the comparative examples 3 and 4 were performed by directly contacting the sintered body electrode and the positive electrode can.

In order to prevent the sintered body of the positive electrode from cracking when the coin cell is swaged, conductive rubber was previously heat-sealed inside the positive electrode can and integrated with the positive electrode can.

The evaluation of Comparative Example 6 was abandoned because the shape of the positive electrode could not be maintained.

Using this coin cell, 3.0 to 4.3
The charge / discharge capacity was measured between V.

FIG. 2 shows the results of charge / discharge measurement at a 10-hour rate of Example 1 in which gold was sputtered on a sintered electrode having a thickness of 500 μm. FIG. 3 shows the results of the charge / discharge measurement at a rate of 100 hours of Example 2, and FIG. 5 of Example 3 in which gold was sputtered onto a sintered electrode having a reduced thickness of 100 μm.
FIG. 4 shows the results of the charge / discharge measurement at the time rate.

In Example 1, a charge capacity of 115 mAh / g and a discharge capacity of 110 mAh / g were obtained. In Example 2, a charge capacity of 100 mAh / g and a discharge capacity of 99 mAh / g were obtained.
Example 3 has a charge capacity of 102 mAh / g and a discharge capacity of 100 mAh / g.
mAh / g was obtained.

On the other hand, since the active material is not sintered and its shape is difficult to maintain, the current collector is made of metal foil.
The thickness of the electrode without sputtering is 500μ
Comparative Example 1 having a thickness of m and Comparative Example 2 having an electrode thickness of 1.0 mm did not operate at any of the 10-hour rate and the 100-hour rate.

Examples 1 and 2 except that the current collector was not formed by the sputtering method.
Comparative Example 3, in which the thickness of the electrode was 500 μm, and Comparative Example 4, in which the electrode thickness was 1.0 mm, did not operate at either the 10-hour rate or the 100-hour rate.

Since the active material was not sintered and its shape was difficult to maintain, the comparative example 5 in which the current collector was made of metal foil and the electrode was not subjected to sputtering and the thickness of the electrode was 20 μm was 10 hours. As a result, a charge capacity of 112 mAh / g and a discharge capacity of 105 mAh / g were obtained.

As can be seen from the comparison between the results of Example 1 shown in FIG. 2 and the results of Example 2 shown in FIG. 3 with the results of Comparative Examples 1, 2, 3, and 4. By sintering the active material to form an electrode, and further forming a current collector on the electrode by a sputtering method, 500 μm
It can operate even with a thick electrode such as m or 1 mm.

The theoretical capacity of Li _1.1 Mn _1.9 O ₄ is 110 m
Since it is Ah / g, it can be seen that an active material utilization rate of 90% or more was obtained in the example, although there was some error.

This is because the sintering of the active material improves the contact between the active materials. Therefore, the internal resistance is reduced by increasing the number of electron conduction paths. It is presumed that the contact resistance was reduced because the current collector formed by the sputtering method had a sufficiently large contact area.

It has been confirmed that a similar effect can be obtained by forming a current collector by a vapor deposition method.

Further, both Example 1 and Comparative Example 5
Although the charge / discharge can be performed at a time rate, the former has a positive electrode thickness of 500 μm and a current collector film thickness of 5000 °, the latter electrode has a thickness of 20 μm and a current collector film thickness of 20 μm, and the former has a sintered body. There is a contraction of the volume due to, while the latter does not, so there is a large difference in energy density. For example, in Example 1, about 0.4 cc of the positive electrode contained 1.14 mg of the active material. On the other hand, when Comparative Example 5 was laminated, the thickness of the positive electrode of Example 1 was 5
If the thickness is approximately the same as 00 μm, it is necessary to sandwich the separator between the seven electrodes and the current collector and the negative electrode, and thus the 30 μm thick separator used in this example and the comparative example is used. Is 490 μm by using seven sheets, and the positive electrode active material contained therein is 0.47 mg. That is, Example 1 was compared with Comparative Example 5 in the same volume.
2.3 times the amount of the active material.

[0065]

As described above, according to the lithium secondary battery of the first aspect, the electrodes are formed of an active material sintered body having a thickness of 100 μm or more, and gold and silver are formed on the active material sintered body. ,copper,
A current collector made of one or more of the metals platinum, palladium, nickel, titanium, chromium, iron, and aluminum provided good contact between the active material particles and an internal resistance to electron conduction. Is reduced, and the contact resistance between the active material and the current collector is reduced, so that a lithium secondary battery that can normally operate even with an electrode having a thickness far exceeding 20 μm can be provided. Further, by increasing the thickness of the electrode, the filling rate of the active material in the battery can be increased, and the energy density can be improved.

According to the method of manufacturing a lithium secondary battery according to the second aspect, the electrode is formed by sintering the active material so that the thickness after sintering becomes 100 μm or more. Since the current collector is formed on the body by the sputtering method or the vapor deposition method, the contact between the active material particles is improved, the internal resistance to electron conduction is reduced, and the current collector is formed by the sputtering method or the vapor deposition method. This reduces the contact resistance between the active material and the current collector,
It is possible to provide a lithium secondary battery that operates normally even with an electrode having a thickness far exceeding 20 μm. Further, by increasing the thickness of the electrode, the filling rate of the active material in the battery can be increased, and the energy density can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a coin-type lithium secondary battery according to the present invention.

FIG. 2 is a voltage-electricity characteristic diagram of Example 1 of a lithium secondary battery according to the present invention.

FIG. 3 is a voltage-electricity characteristic diagram of Example 2 of the lithium secondary battery according to the present invention.

FIG. 4 is a voltage-electricity characteristic diagram of Example 3 of the lithium secondary battery of the present invention.

[Explanation of symbols]

1: positive electrode can, 2: positive electrode current collector, 3: positive electrode, 4: insulating packing, 5: electrolyte, 6: negative electrode, 7: negative electrode current collector, 8:
Negative electrode can

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yoko Mishima 3-5-chome, Seika-cho, Soraku-gun, Kyoto Prefecture Inside the Central Research Laboratory, Kyocera Corporation (72) Inventor Shinji Magome 3-chome, Seika-cho, Soraku-gun, Kyoto 5 Kyocera Corporation Central Research Laboratory (72) Inventor Makoto Osaki 3-chome, Soka-cho, Soraku-gun, Kyoto Prefecture 5-5-2 Kyocera Corporation Central Research Laboratory (72) Inventor Ei Higuchi Seika-cho, Soraku-gun, Kyoto Prefecture 3-5-5 Kyocera Corporation Central Research Laboratory F-term (Reference) 5H017 AA03 AS02 BB04 BB08 CC01 EE01 EE04 EE05 HH03 5H029 AJ03 AJ06 AK03 AL03 AL07 AL12 AM03 AM04 AM05 AM07 AM12 AM16 BJ03 CJ02 CJ24 DJ02 DJ07EJ01

Claims (2)

[Claims] 1. A lithium secondary battery in which an electrolyte is sandwiched between electrodes made of an active material and sealed in a can, wherein the electrodes are formed of an active material sintered body having a thickness of 100 μm or more. Lithium secondary battery having a current collector made of one or more of gold, silver, copper, platinum, palladium, nickel, titanium, chromium, iron, and aluminum on the body . 2. A method for manufacturing a lithium secondary battery in which an electrolyte is sandwiched between electrodes made of an active material and sealed in a can, wherein the active material is fired so that the thickness after sintering the electrode becomes 100 μm or more. And forming a current collector on the active material sintered body by a sputtering method or a vapor deposition method.