JPH0521054A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To suppress the gas generation at the boundary surface of respective members upon charging and discharging by covering a metal core body via a predetermined conducting layer with a positive electrode mixture. CONSTITUTION:A generating element 3 is stored in a metal container 1. The generating element 3 is constituted in such a manner that a negative electrode, a separator 5, and a positive electrode are, in this turn, stacked to form a band-like substance followed by spirally winding the band-like substance. The positive electrode 6 is made up in such a way that a metal core body containing a metal cobalt layer is covered with an active substance layer consisted mainly of a lithium containing compound oxide, and is integrated therewith. Since conductivity at the boundary surface between the metal core body and a positive electrode mixture can be enhanced thereby, the occurrence of the conductivity defect points can be prevented. Whereby, gas due to the reaction of the metal core body with an electrolyte is unlikely to be generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous solvent secondary battery, and more particularly to a non-aqueous solvent secondary battery having an improved positive electrode.

[0002]

2. Description of the Related Art In recent years, a non-aqueous solvent secondary battery using a chalcogen compound as an active material of a positive electrode mixture and an alkali metal such as lithium as a negative electrode has been attracting attention as having a high energy density. Among them, recently, a positive electrode using chalcogen oxide, a positive electrode using a composite oxide in which chalcogen oxide holds lithium as an active material, a negative electrode using Lithium as an active material, or holding lithium in a carbonaceous material A non-aqueous solvent secondary battery in which the negative electrode is used is being developed. As such secondary batteries, for example, titanium disulfide-lithium batteries, molybdenum disulfide-lithium batteries, manganese dioxide-lithium batteries and the like are known. The positive electrode of these non-aqueous solvent secondary batteries has a structure in which a sheet-shaped positive electrode mixture containing an active material and a binder is pressure-bonded and integrated to a metal core such as nickel, a stainless steel net, and expanded metal. There is.

[0003]

However, the positive electrode of the above-mentioned non-aqueous solvent secondary battery has not been put into practical use despite its simple manufacturing process and low battery manufacturing cost. This is because when the battery is manufactured using the above-mentioned positive electrode, the charge / discharge cycle life of the battery is shortened and the individual discharge characteristics become non-uniform.

That is, in the positive electrode of the non-aqueous solvent secondary battery described above, if there is a defective conductive portion at the pressure-bonding interface between the metal core and the positive electrode mixture, the current distribution at this pressure-bonding interface during the battery reaction. Becomes non-uniform, and the current density becomes coarse. The roughening of the current density causes a portion in which the reaction is performed at a voltage higher than the decomposition voltage of the electrolytic solution at the pressure bonding interface. For this reason, when the battery reaction is carried out with the presence of the above-mentioned poor conductivity part, the electrolytic solution in the positive electrode mixture reacts with the metal core at the part where the reaction occurs at a voltage higher than the decomposition voltage of the electrolytic solution. As a result, the electrolytic solution is decomposed, and gases such as hydrogen gas and carbon dioxide gas are generated. This gas accumulates little by little at the interface between the metal core and the positive electrode mixture each time the battery is repeatedly charged and discharged, and acts to gradually separate the positive electrode mixture from the metal core. Therefore, the contact area at the interface between the metal core and the positive electrode mixture gradually decreases with repeated charging and discharging,
The electron conductivity between the metal core and the positive electrode mixture is significantly reduced. As a result, there has been a problem that the charge / discharge cycle life is shortened and the battery performance is non-uniform even though the positive electrode mixture has a sufficient function as the battery is repeatedly charged and discharged.

The present invention has been made in order to solve the above problems, and a positive electrode in which a positive electrode mixture is electrically and satisfactorily coated by coating the positive electrode mixture on a metal core through a predetermined conductive layer. It is an object of the present invention to provide a non-aqueous solvent secondary battery in which gas generation at the interface of each member during charge / discharge is suppressed.

[0006]

In order to achieve the above object, a non-aqueous solvent secondary battery of the present invention comprises a metal core body, a conductive layer comprising a thin metal cobalt layer on the surface of the core body, and It is provided with a positive electrode composed of a positive electrode mixture mainly composed of LiCoO ₂ coated on the layer.

Examples of the metal core of the present invention include metal mesh made of metal such as nickel, iron, nickel-plated iron, and stainless steel, expanded metal, punched metal, metal foil and the like. The thickness of the conductive layer made of metallic cobalt is preferably in the range of 3 to 100 μm. The reason is that the thickness of the conductive layer is 3μ.
If it is less than m, the metal core may be partially exposed due to the deformation of the electrode during use of the battery, impairing the function as the conductive layer, and sufficient conductivity may not be obtained.
On the other hand, if the thickness of the conductive layer exceeds 100 μm, the process of forming the conductive layer on the metal core will be troublesome and the productivity of the battery may decrease.

One of the conductive layers made of metallic cobalt is formed by dispersing powder of metallic cobalt in a polyolefin resin solution, coating the dispersed solution on a metal core, and drying. Examples of the polyolefin resin used here include polyethylene, polypropylene,
Examples thereof include polyacrylic acid. The compounding ratio of the polyolefin-based resin and the metallic cobalt powder constituting the conductive resin is such that the amount of the metallic cobalt powder is 10 to 5 with respect to the polyolefin-based resin solution having a concentration of 3 to 35% by weight.
The range is 0% by weight. If the cobalt powder content is less than 10% by weight, the conductivity of the conductive resin may be lowered and the internal resistance may be increased to cause the battery to stop operating. However, when the cobalt powder content exceeds 50% by weight, the binding force of the conductive resin is reduced and it becomes difficult to uniformly coat the conductive layer made of the conductive resin on the metal core. Further, the thickness of the conductive layer, particularly from the viewpoint of simplifying the coating step of the conductive layer on the metal core and stabilizing the battery performance,
It is more desirable to set it in the range of 80 to 100 μm.

[0009]

According to the present invention, it comprises a metal core, a conductive layer made of metal cobalt formed on the surface of the metal core, and a positive electrode mixture made of LiCoO ₂ coated on the conductive layer. Since the conductivity at the interface between the metal core body and the positive electrode mixture can be improved by using the positive electrode thus prepared, the occurrence of defective conductivity can be prevented. For this reason,
The current density at the interface can be made uniform without generating gas due to the reaction between the metal core and the electrolytic solution. As a result, the positive electrode mixture can be electrically and satisfactorily connected to the metal core, so that a non-aqueous solvent secondary battery having stable discharge characteristics and improved charge / discharge cycle life and heavy load characteristics can be obtained. it can.

On the other hand, by coating the positive electrode mixture on the metal core through the conductive layer made of metallic cobalt, the thin layer of metallic cobalt can improve the conductivity of the interface,
In addition, metallic cobalt and lithium-doped cobalt oxide (LiCoO ₂ ) have a binding force between the two and can improve the coverage of the metal core body and the positive electrode mixture, so that a defective coating portion or a peeled portion can be formed. Can be suppressed. As a result, the current density at the interface can be made uniform, and the occurrence of coating defects and peeling points can be prevented. Therefore, the current density at the interface can be prevented from becoming dense and dense, and the gas accompanying the current density becoming dense can be prevented. Occurrence can be suppressed.

Therefore, peeling of the positive electrode mixture from the metal core,
(EN) A non-aqueous solvent secondary battery having stable discharge characteristics and improved charge / discharge cycle life, heavy load characteristics, etc. by preventing falling and electrically connecting a positive electrode mixture to a metal core. You can

[0012]

EXAMPLE An example in which the present invention is applied to a cylindrical lithium secondary battery will be described in detail below with reference to the drawings.

(Embodiment) FIG. 1 is a sectional view of a cylindrical lithium secondary battery which is an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a bottomed cylindrical metal container having an insulating paper 2 arranged at the bottom and also serving as a negative electrode terminal. In this container 1, a cylindrical power generating element 3 is housed. The power generation element 3 has a negative electrode 4 made of a carbon agent containing metallic lithium, a separator 5 obtained by impregnating a porous polypropylene thin film with propylene carbonate, and a positive electrode 6 in this order to form a strip, and the strip is formed. It is configured by spirally winding. Furthermore, the metal core 8 of the positive electrode 6 (see FIG. 2)
The positive electrode lead 7 connected to is connected to the positive electrode terminal 12.
Similarly, the negative electrode lead 13 connected to the negative electrode 4 is connected to the metal container 1, sealed with the sealing plate 11, the opening of the metal container 1 is bent inward, and the sealing port is formed. A cylindrical lithium secondary battery can be obtained.

By the way, as shown in the front view of FIG. 2A and the sectional view of FIG. 2B, the positive electrode 6 is provided with conductive layers 9 on both sides of the metal core body 8, and the positive electrode mixture is provided on the outside thereof. 10 is provided. The positive electrode 6 having such a structure is manufactured by the following method. First, the conductive layer 9 is composed of 100 parts by weight of a solution of a polyacrylic acid aqueous solution (polyacrylic acid concentration: 3 to 35% by weight) diluted with methanol, and 10 parts by weight of metallic cobalt powder adjusted to have a particle size of 0.1 to 15 μm. And are kneaded, applied to a metal core body 8 made of stainless steel having a thickness of 10 μm, and dried to prepare the metal core body 8. The positive electrode mixture 10 is
LiC obtained by firing a mixture of cobalt oxide and lithium carbonate at a predetermined ratio for 12 hours at 800 ° C.
90 parts by weight of oO ₂ and 7 parts by weight of acetylene black as a conductive agent are mixed. Subsequently, the binder solution was prepared by dissolving 3 parts by weight of a terpolymer containing 60 to 70 mol% of ethylene units, 40 to 30 mol% of propylene units and 5 mol% or less of dicyclopentadiene units in toluene and binding it. Use the drug solution. 100 parts by weight of this binder solution is kneaded with 97 parts by weight of a mixture of LiCoO ₂ and acetylene black. Next, the kneaded material is applied onto the conductive layer and dried to prepare the positive electrode mixture 10. In this way, the positive electrode 6 is manufactured.

(Comparative Example) As a comparative example of the present invention, a cylindrical lithium having the same structure as that of the above-described example except that a positive electrode constituted by directly coating a positive electrode material mixture on a metal core without a conductive layer was used. The secondary battery was assembled.

Next, the lithium secondary batteries of this example and the comparative example were tested at room temperature of 20 ° C. with a current of 90 mA.
Characteristic evaluation of the discharge capacity was performed with one cycle of a process of performing charging for a time and then discharging until a discharge voltage of 2.9 V was exhibited. As a result, the characteristic diagram shown in FIG. 3 was obtained. In the figure, A indicates the characteristic line of the secondary battery of this example, and B indicates the characteristic line of the secondary battery of the comparative example. As is clear from FIG. 3, the secondary battery A of this example has excellent discharge characteristics in which the decrease in discharge capacity with the increase in the number of cycles is gradual. On the other hand, in the secondary battery B of the comparative example, it can be seen that the discharge capacity significantly decreases with the increase in the number of cycles. Particularly, when the number of cycles is around 80, the discharge capacity is extremely reduced.

Further, the secondary batteries of this example and comparative example were subjected to heavy load discharge with a load of 230 mA. As a result, the characteristic diagram of the relationship between the discharge connection time and the battery terminal voltage shown in FIG. 4 was obtained. In the figure, A indicates the characteristic line of the secondary battery of this example, and B indicates the characteristic line of the secondary battery of the comparative example. As is clear from FIG. 4, the secondary battery of the present example has a longer discharge connection time until the discharge terminal voltage sharply decreases, as compared with the secondary battery of the comparative example, and has a discharge characteristic under heavy load. It can be seen that it has been greatly improved. In particular, the secondary battery of the comparative example drastically lowers the voltage when the discharge time exceeds 60 minutes, whereas the secondary battery of the embodiment does not undergo a drastic voltage drop even after 90 minutes, and is stable. The battery characteristics are shown.

Further, the above-mentioned discharge capacity characteristic evaluation test was performed for 40 cycles for 100 secondary batteries of each of the present embodiment and comparative example, and the battery capacity distribution at that time was examined. The results are shown in Table 1 below.

[0019]

[Table 1]

As is apparent from Table 1 above, the secondary battery of this example has less variation in battery capacity than the secondary battery of the comparative example, and the performance of each battery is improved and uniformized. Therefore, it can be seen that the battery performance is stabilized.

[0021]

As described above, according to the present invention,
Since the metal core is coated with the positive electrode mixture through the predetermined conductive layer to provide a positive electrode in which the positive electrode mixture is electrically excellently coated on the metal core, each of the above It is possible to provide a non-aqueous solvent secondary battery that can suppress the generation of gas at the interface of members and, in addition, can stabilize the battery capacity and have improved charge / discharge cycle life and heavy load discharge characteristics.

[Brief description of drawings]

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

2A is a front view of the positive electrode of the non-aqueous solvent secondary battery of FIG. 1, and FIG. 2B is a cross-sectional view taken along line I-I of FIG.

FIG. 3 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity in Examples and Comparative Examples.

FIG. 4 is a characteristic diagram showing the relationship between discharge connection time and battery terminal voltage in Examples and Comparative Examples.

Claims (1)

Claim: What is claimed is: 1. An active material layer comprising a lithium-containing composite oxide as a main component is provided on a metal core having a metal cobalt layer,
A non-aqueous solvent secondary battery characterized by using the integrated one as a positive electrode.