JPH0433249A - Nonaqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To obtain a nonaqueous solvent secondary battery suppressing the gas generation at the boundary of individual members at the time of charging and discharging by forming a conducting layer made of carbon on the surface of a metal core, and using a positive electrode coated with a positive electrode mix mainly made of spinel type LiMn2O4 on the conducting layer. CONSTITUTION:A solution diluted with a polyacrylic aqueous solution in methanol and acetaylene black are kneaded, then it is coated on a metal core 8 made of stainless steel, and it is dried to form a conducting layer 9. Electrolytic manganese dioxide and lithium carbonate are mixed at a preset ratio and baked, spinel type LiMn2O4 thus obtained and acetylene black serving as a conducting material are mixed, and a binder solution is kneaded with it. The kneaded object is coated on the conducting layer 9 and dried to form a positive electrode mix 10, then a positive electrode 6 is obtained. A positive electrode lead 7 connected to the metal core 8 of the positive electrode 6 is connected to a positive electrode terminal 12.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a non-aqueous solvent secondary battery, and particularly to a non-aqueous solvent secondary battery with an improved structure of the positive electrode.

(Prior Art) In recent years, non-aqueous solvent secondary batteries that use a chalcogen compound as the active material of the positive electrode mixture and an alkali metal such as lithium as the negative electrode have attracted attention as having high energy. Among these, recently, non-aqueous solvent dielectrics using chalcogen oxide as a living substance, a positive electrode consisting of a positive electrode mixture containing an active material consisting of this oxide and a mixture of lithium or its oxide, and a negative electrode consisting of lithium have been developed. The next battery is being developed. Examples of such batteries include titanium disulfide-lithium batteries, molybdenum disulfide-lithium batteries,
Manganese dioxide-lithium batteries and the like are known. The positive electrodes of these non-aqueous solvent secondary batteries have a structure in which a sheet-like positive electrode mixture containing an active material and a binder is bonded to a metal core made of nickel, stainless steel mesh, expanded metal, etc. ing.

(Problems to be Solved by the Invention) However, the positive electrode of the non-aqueous solvent secondary battery described above has not been put into practical use, although the manufacturing process is simple and the manufacturing cost of the battery is low. This is because when a battery is manufactured using the above-mentioned positive electrode, the charge/discharge cycle life of the battery becomes short and the individual discharge characteristics become non-uniform.

That is, in the positive electrode of the non-aqueous solvent secondary battery, if there is a poor conductivity at the crimped interface between the metal core and the positive electrode mixture, the current distribution at the crimped interface will be uneven when a battery reaction occurs. As a result, the current density becomes coarser and denser. The coarsening of the current density creates a portion at the pressure bonding interface where a reaction occurs at a voltage higher than the decomposition voltage of the electrolytic solution. Therefore, if a battery reaction is performed while the conductive defective portion is present, the electrolyte in the positive electrode mixture and the metal core may reacts, decomposition of the electrolyte occurs, 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, causing the positive electrode mixture to gradually peel off from the metal core. Therefore, the contact area at the interface between the metal core and the positive electrode mixture is:
It gradually decreases with repeated charging and discharging, and the electronic conductivity between the metal core and the positive electrode mixture decreases significantly. the result,
Despite the fact that the positive electrode mixture has a sufficient function as the battery is repeatedly charged and discharged, there is a problem in that the charge/discharge cycle life decreases and the battery performance becomes non-uniform.

The present invention has been made in order to solve the above-mentioned conventional problems, and by coating a metal core with a positive electrode mixture through a predetermined conductive layer, the present invention provides a positive electrode that is electrically well coated with the positive electrode mixture. It is an object of the present invention to provide a non-aqueous solvent secondary battery which is equipped with the following and suppresses gas generation at the interfaces of the respective members during charging and discharging.

[Structure of the Invention] (Means for Solving Problem R) The present invention comprises a metal core, a conductive layer formed on the surface of the core and made of a conductive resin containing a carcinoma, and a conductive layer formed on the conductive layer. This is a non-aqueous solvent secondary battery characterized by comprising a positive electrode composed of a positive electrode mixture mainly composed of spinel-type LiMn204 coated thereon.

Examples of the metal core include a wire mesh made of metal such as nickel, iron, nickel-plated iron, and stainless steel, expanded metal, punched metal, and metal foil.

The thickness of the conductive layer made of acetylene black or carbon black is preferably in the range of 3 to 1007 m. The reason for this is that when the thickness of the conductive layer is less than 3#,
As the battery deforms during use, the positive electrode deforms, and the metal core is partially exposed, impairing its function as a conductive layer.
There is a possibility that sufficient conductivity may not be obtained. On the other hand, if the thickness of the conductive layer exceeds 100 mm, the process of forming the conductive layer on the metal core takes time and effort, and there is a risk that the productivity of the battery will decrease.

The conductive layer made of a conductive resin containing carbon such as acetylene black or carbon black is formed by, for example, dispersing acetylene black powder in a polyolefin resin solution, applying this dispersion solution to a metal core, and drying it. Ru. Examples of the polyolefin resin used here include polyethylene, polypropylene, polyacrylic acid, and the like. The blending ratio of the polyolefin resin and carbon powder constituting the conductive resin is 3 to 35% by weight, 10 to 50% by weight of the carbon powder, and 10 to 50% by weight of the lyolefin resin solution. If the amount is less than 50% by weight, the conductivity of the conductive resin will decrease, causing an increase in internal resistance and the battery may become inoperable.On the other hand, if the amount of carbon powder exceeds 50% by weight, the conductivity This is because the binding force of the resin decreases and it becomes difficult to uniformly coat the metal core with a conductive layer made of the conductive resin.

In addition, the thickness of the conductive layer made of conductive resin is preferably in the range of 80 to 100 mm, especially from the viewpoint of simplifying the process of coating the metal core with the conductive layer and stabilizing battery performance. .

The spinel type LiMn2O4 is produced, for example, by mixing manganese oxide and lithium salt and heat-treating the mixture.

(Function) According to the present invention, the electrode is composed of a metal core, a conductive layer formed on the surface of the core and made of carbon, and a positive electrode mixture made of spinel-type LiMn2O4 coated on the conductive layer. By using such a positive electrode, the conductivity at the interface between the metal core and the positive electrode mixture can be improved by the conductive layer, and occurrence of poor conductivity can be prevented. Therefore, gas is not generated due to the reaction between the metal core and the electrolytic solution, and the current density at the interface can be made uniform.

As a result, the positive electrode mixture can be electrically connected well to the metal core, making it possible to obtain a non-aqueous solvent secondary battery with stable discharge characteristics and improved charge/discharge cycle life, heavy load characteristics, etc. can.

On the other hand, by coating a metal core with the positive electrode mixture through a conductive layer made of a conductive resin containing carbon, the carbon in the conductive resin can improve the conductivity of the interface, and Due to the binding force of the resin, the coverage between the metal core and the positive electrode mixture can be improved, and the occurrence of poor coverage and peeling can be suppressed. As a result, the current density at the interface can be made uniform, and the occurrence of coating defects and peeling can be prevented, so it is possible to prevent the current density from becoming coarser and denser at the interface, and the gas caused by the coarser current density can be prevented. The occurrence can be suppressed.

Therefore, by preventing the positive electrode mixture from peeling or falling off from the metal core, and by ensuring good electrical connection of the positive electrode mixture to the metal core,
It has stable discharge characteristics and a long charge/discharge cycle life.
A non-aqueous solvent secondary battery with improved heavy load characteristics etc. can be obtained.

(Example) Hereinafter, an example in which the present invention is applied to a cylindrical lithium secondary battery will be described in detail with reference to FIG. 1 and FIGS. 2(a) and 2(b).

Reference numeral 1 in the drawings indicates a bottomed cylindrical metal container that also serves as a negative electrode terminal and has an insulating paper 2 disposed at the bottom.

A cylindrical power generation element 3 is housed within the container 1. This power generation element 3 consists of a negative electrode 4 made of metallic lithium, a separator 5 made of a porous polypropylene thin film impregnated with propylene carbonate, and a positive electrode 6 to be described later, which are laminated in this order to form a strip. It is constructed by winding it into a shape.

The positive electrode 6 has the structure shown in FIGS. 2(a) and 2(b), and is manufactured by the following method.

First, the conductive layer 9 is prepared using a solution 1 prepared by diluting a polyacrylic acid aqueous solution (polyacrylic acid concentration 3 to 35% by weight) with methanol.
00 parts by weight and 10 parts by weight of acetylene glue, the mixture is coated on a metal core 8 made of stainless steel with a thickness of 101 mm, and dried. The positive electrode mixture 1O is a mixture of electrolytic manganese dioxide and lithium carbonate at a predetermined ratio.
20482 parts by weight of spinel type Li Mn obtained by firing at 0° C. for 14 hours and 15 parts by weight of acetylene black as a conductive material are mixed. Subsequently, the binder solution is made of a 3-weight terpolymer elastomer containing BO to 70 mol% of ethylene units, 40 to 30 mol% of propylene units, and 5 mol% or less of dicyclopentadiene units, and having a molecular weight of 103 to 107. part, and the water content is 0.1% by weight.
A binder solution is prepared by dissolving it in a toluene solution adjusted to .

100 parts by weight of this binder solution is kneaded with 97 parts by weight of the mixture of LiMn2o4 and acetylene black. Next, this mixed material is applied onto the conductive layer 9 and dried to prepare a positive electrode mixture IO. In this way, the positive electrode 6 was manufactured. Furthermore, the positive electrode wire 7 connected to the metal core 8 of the positive electrode 6 is connected to the positive electrode terminal 12 . Similarly, the negative electrode gate 13 connected to the negative electrode 4 is connected to the metal container 1, and the sealing plate 1 is connected to the metal container 1.
The cylindrical lithium secondary battery of the embodiment of the present invention shown in FIG. 1 is completed by sealing the metal container 1 with the metal container 1 and bending the opening inward to seal it.

(Comparative Example) A cylindrical lithium secondary battery having the same structure as the example was assembled, except that a positive electrode formed by directly coating a metal core with a positive electrode mixture without intervening a conductive layer was used.

The lithium secondary batteries of this example and comparative example were charged at a room temperature of 20° C. with a current of 150 mA for 7 hours, and then 2. Characteristic evaluation of the discharge capacity was performed using the process of discharging until the discharge voltage of OV was shown as one cycle. As a result, a characteristic diagram shown in FIG. 3 was obtained. Note that A in the figure shows the characteristic line of the secondary battery of the fifth example, and B shows the characteristic line of the secondary battery of the comparative example. As is clear from FIG. 3, it can be seen that the secondary battery A of this example has excellent discharge characteristics, with a gradual decrease in discharge capacity as the number of cycles increases. On the other hand, it can be seen that in secondary battery B of Comparative Example, the discharge capacity decreases significantly as the number of cycles increases. In particular, when the number of cycles approaches 100, the discharge capacity decreases extremely.

In addition, for the secondary batteries of this example and comparative example, 750
Heavy load discharge was performed with a load of mA. As a result, the fourth
A characteristic diagram of the relationship between discharge connection time and battery terminal voltage shown in the figure was obtained. Note that A in the figure shows the characteristic line of the secondary battery of the present example, and B shows the characteristic line of the secondary battery of the comparative example. As is clear from FIG. 4, the secondary battery of this example has a longer discharge connection time until the discharge terminal voltage rapidly decreases than the secondary battery of the comparative example, and has poor discharge characteristics under heavy loads. It can be seen that it has been significantly improved. In particular, the secondary battery of the comparative example has a rapid voltage drop when the discharge time exceeds 25 minutes, whereas the secondary battery of the example does not have a sudden voltage drop even after 45 minutes and remains stable. This shows the battery characteristics.

Further, the above-described discharge capacity characteristic evaluation test was performed for 50 cycles on 100 secondary batteries of the present example and the comparative example, and the battery capacity distribution at that time was examined. The results are shown in Table 1 below. Note that X in Table 1 below is the average value of the battery capacity of 100 secondary batteries of the present example and comparative example, and δ represents the standard deviation obtained from each of the above-mentioned capacity values.

Table 1 As is clear 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 individual battery is improved and uniform. It can be seen that the battery performance has been stabilized.

[Effects of the Invention] As detailed above, according to the present invention, by coating the metal core with the positive electrode mixture through a predetermined conductive layer, the positive electrode mixture is electrically connected to the metal core. A non-aqueous solvent secondary battery equipped with a well-coated cathode that suppresses gas generation at the interface of each member during charging and discharging, which in turn stabilizes battery capacity and improves charge-discharge cycle life and heavy-load discharge characteristics. We can provide batteries.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a non-aqueous solvent secondary battery showing an example of the present invention, FIG. 2(a) is a front view showing a positive electrode used in the battery of the present invention, and FIG. A-A cross-sectional view of , 3rd
The figure is a characteristic diagram showing the relationship between the number of charge/discharge cycles and the discharge capacity of Example A of the present invention and Comparative Example B, and Figure 4 is a characteristic diagram showing the relationship between the number of charge/discharge cycles and discharge capacity of Example A of the present invention.
and FIG. 9 is a characteristic diagram showing the relationship between discharge connection time and battery terminal voltage of Comparative Example B. 1... Container, 3... Power generation element, 4...
Negative electrode, 5... Separator, 6... Positive electrode, 8... Metal core, 9... Conductive layer,
IO...Positive electrode mixture. $1 figure

Claims (1)

[Claims] A metal core, a conductive layer formed on the surface of the core and containing carbon, and a spinel type L coated on the conductive layer.
1. A non-aqueous solvent secondary battery comprising a positive electrode composed of a positive electrode mixture mainly composed of iMn_2O_4.