JPH01149362A - Nonaqueous solvent secondary battery - Google Patents

Abstract

PURPOSE:To retard gas evolution on the interface between a metal core and a positive mix in charge-discharge by forming a positive electrode by covering a metal core with the positive mix containing an active material through the conductive layer of a metal which constitutes the active material or the conductive resin layer containing the metal. CONSTITUTION:For example, metallic vanadium conductive layers 9 are formed on both sides of a metal core 8, and sheets containing vanadium pentoxide are pressed against both sides of the metal core 8 through the conductive layers 9 to form a positive mix 10 and a positive electrode is obtained. The conductivity on the interface of the metal core 8 and the positive mix 10 is increased and the generation of conductivity detective part is prevented. The current density on the interface on which gas evolved by the reaction of an electrolyte with the metal core is made uniform. Gas evolution caused by uneven current density can be retarded.

Description

DETAILED DESCRIPTION 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 a positive electrode.

[Prior art] In recent years, metal chalcogen compounds have been used as active materials in positive electrode mixtures,
Non-aqueous solvent secondary batteries that use an alkali metal such as lithium as a negative electrode are attracting attention as having high energy. In recent years, nonaqueous solvent secondary batteries have been developed that use chalcogen oxide as a living material, use a positive electrode mixture containing an active material made of this oxide and lithium or a mixture of these oxides as the positive electrode, and use lithium as the negative electrode. is being developed.

Known examples of such batteries include titanium disulfide-lithium batteries, molybdenum disulfide-lithium batteries, manganese dioxide-lithium batteries, and the like.

The positive electrodes of these nonaqueous 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 above-described positive electrode for a non-aqueous solvent secondary battery has not been put into practical use, although the manufacturing process is simple and the manufacturing cost of the battery can be reduced. This is because if a battery is manufactured using the above-mentioned positive electrode, the charge/discharge cycle life of the battery will be shortened and the individual discharge characteristics will not be homogeneous.

That is, in the positive electrode of the non-aqueous solvent secondary battery, if there are poor conductivity, poor crimping, or peeling at the interface between the metal core and the positive electrode mixture, the crimping interface will be damaged during the battery reaction. The current distribution becomes non-uniform and the current density becomes coarser. This coarsening of the current density creates a portion at the interface where a reaction occurs at a voltage higher than the decomposition voltage of the electrolytic solution. For this reason, if a battery reaction is performed while such conductive defects exist, the electrolyte in the positive electrode mixture and the metal core will be mixed in the areas where the reaction is carried out at a voltage higher than the decomposition voltage of the electrolyte. The body reacts and the electrolyte decomposes, producing hydrogen gas, carbon dioxide gas, and other gases. 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 be gradually peeled off 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, and the conduction of electrons between the metal core and the positive electrode mixture decreases significantly. As a result, as the battery is repeatedly charged and discharged, the charge/discharge cycle life decreases even though the positive electrode mixture has sufficient functionality, resulting in a problem that the battery performance becomes non-uniform.

The present invention has been made in order to solve the above-mentioned conventional problems, and the metal core is electrically well coated with a positive electrode mixture so that gas, etc. can be formed at these interfaces during charging and discharging cycles. The present invention aims to provide a non-aqueous solvent secondary battery that suppresses the occurrence of this problem.

[Means for Solving the Problems] The present invention provides a structure in which a metal core is coated with a positive electrode mixture containing an active material via a conductive layer of a metal constituting the active material or a conductive resin layer containing the metal. This is a non-aqueous solvent secondary battery characterized by comprising a positive electrode.

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 positive electrode mixture is manufactured by mixing an active material, a conductive material, and a binder, and has a composition containing lithium as necessary. Examples of the active material used here include chalcogen compounds such as vanadium pentoxide, titanium disulfide, and molybdenum disulfide. Examples of the conductive material include powders such as acetylene black and carbon black. Examples of the binder include polytetrafluoroethylene and polyolefin resin.

The conductive layer of the metal constituting the active material is formed on the surface of the metal core by electroplating, for example, in an electrolytic solution containing ions of the metal, using the metal core as an anode. The thickness of such a metal conductive layer is 3 to 50. lol
It is desirable to keep it within the range of . The reason for this is that if the thickness of the conductive layer is less than 3p, the positive electrode will deform as the battery deforms during use, and the metal core will be partially exposed, which will not only impair its function as a conductive resin layer, but also Otherwise, proper conductivity may not be obtained. On the other hand, if the thickness of the conductive layer exceeds 50 mm, it is not preferable because the step of providing the metal layer on the metal core requires time and effort and reduces the production capacity of the battery.

The conductive resin layer is formed, for example, by dispersing metal powder constituting the active material in a solution of a polyolefin resin, applying this dispersed solution to a metal core, and drying it. Examples of polyolefin resins used here include:
Other examples include polyethylene, polypropylene, and polyacrylic acid.

The blending ratio of the resin such as polyolefin resin constituting the conductive resin layer and the metal constituting the active material is 3 to 35%.
It is desirable that the metal content be in the range of 10 to 50% with respect to the polyolefin resin solution having a concentration of % by weight. The reason for this is that if the amount of metal is less than 10%, the conductivity of the resin layer will decrease, causing an increase in internal resistance and the battery may not work. If the amount of metal exceeds 50%, the resin layer This results in a decrease in the binding strength of the layer and makes it difficult to uniformly form the resin layer on the metal core.

The thickness of the conductive resin layer is preferably in the range of 5p or more, and particularly preferably in the range of 80 to 1004p. The reason for this is that if the thickness of the conductive resin layer is less than 5p, the conductive resin layer will be too thin and the metal core will be partially exposed, which will not only impair its function as a conductive resin layer, but also prevent sufficient conductivity. There is a risk that you will not be able to have sex. In particular, from the viewpoint of the process of providing a conductive resin layer on a metal core and the stabilization of battery performance, the thickness of the conductive resin layer was set to 880-1ft.
It is preferable to keep it within the range of .

[Function] According to the present invention, a metal core of a non-aqueous solvent secondary battery is coated with a positive electrode mixture containing an active material through a conductive layer of metal constituting the active material, thereby forming a positive electrode. The conductivity of the interface between the core and the positive electrode mixture is improved, and the occurrence of poor conductivity can be prevented. Therefore, the current density at the interface where the metal core and the electrolyte react to generate gas can be made uniform. As a result, it is possible to obtain a non-aqueous solvent secondary battery that has stable discharge characteristics and has improved charge/discharge cycle life, heavy load discharge characteristics, etc. due to good electrical connection to the metal core.

On the other hand, by coating the metal core with the positive electrode mixture via a conductive resin layer containing a metal constituting the active material of the positive electrode mixture, the metal in the resin layer improves the conductivity of the interface. Moreover, due to the binding force of the resin, the coating properties of the metal core and the positive electrode mixture can be improved, and the occurrence of poor coating and peeling parts can be suppressed. Therefore, the current density at the interface where the metal core and the electrolytic solution react to generate gas can be made uniform, and the presence of defective coatings and peeling spots is suppressed, so that the defective coating and peeling spots at the interface are suppressed. It is possible to prevent the current density from becoming denser at the interface due to the difference in electrical resistance between the coated portion and the well-coated portion, and it is possible to suppress gas generation due to the denser current density. As a result, by preventing the positive electrode mixture from peeling off or falling off from the metal core and by providing good electrical connection to the metal core, it has stable discharge characteristics and improves charge/discharge cycle life, heavy load discharge characteristics, etc. A non-aqueous solvent secondary battery can be obtained.

[Example] Hereinafter, an example in which the present invention is applied to a cylindrical vanadium pentoxide-lithium secondary battery will be described in detail with reference to FIG. 1.

Example 1 Reference numeral 1 in the figure is a bottomed cylindrical metal container that also serves as a negative electrode terminal and has an insulating plate 2 disposed at the bottom.

Inside this container I, a cylindrical power generation element 8 is housed. 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 B (described later), which are laminated in this order to form a band-like object, and this band-like object is formed into a spiral shape. It is constructed by winding.

The positive electrode 6 is manufactured by the following method.

First, a titanium foil lead terminal 7 is attached to one end along the longitudinal direction.
A conductive layer 9 of metal vanadium is formed on both sides of the metal core 8 by electroplating the plate metal core 8 made of nickel, which is provided by spot welding, in an electrolytic solution containing metal vanadium ions as an anode. Form. Next, a well-mixed mixture of vanadium pentoxide powder and phosphorus pentoxide powder was melted at 800°C, and the melt was poured onto a copper plate cooled with dry ice, and rapidly cooled to form an amorphous material. This was ground to a particle size of 184 mm to obtain an active material, and this active material was mixed with 0.5 g of polytetrafluoroethylene powder and formed into a sheet with a thickness of 0.4 M using a roll forming method. Thereafter, this sheet-like material was crimped and integrated with the conductive layers 9 on both sides of the metal core 8 to form a positive electrode mixture 10, thereby manufacturing the positive electrode 6 (as shown in FIGS. 2(a) and 2(b)). . In other words, the positive electrode 6 is the lead terminal 7
The structure is such that both surfaces of the metal core 8 to which the electrodes are connected are coated with a positive electrode mixture lO via a conductive layer 9.

An insulating sealing plate 11 is provided in the vicinity of the opening of the container l in a fluid-tight manner by caulking, and a positive electrode terminal 12 is fitted into the sealing plate 11. The lead terminal 7 is connected to this positive electrode terminal 12 by spot welding. Note that the negative electrode 4 has a lead terminal 13 made of nickel foil.
is crimped, and the lead terminal 13 is connected to the inner surface of the container l by spot welding.

Comparative Example A non-aqueous solvent secondary battery was assembled with the same structure as in Example 1, except that a positive electrode was used in which a positive electrode mixture was directly coated on a metal core without intervening a conductive resin layer.

Therefore, the nonaqueous solvent secondary batteries of Example 1 and Comparative Example were charged for 7 hours at a room temperature of 20° C. with a current of 150 mA, and then discharged until a discharge voltage of t, OV was shown. A characteristic evaluation test of discharge capacity retention rate was conducted in which battery capacity was measured as a cycle. As a result, a characteristic diagram shown in FIG. 3 was obtained. In addition, A in the figure shows the characteristic line of the non-aqueous solvent secondary battery of Example 1, and B shows the characteristic line of the non-aqueous solvent secondary battery of the comparative example. As is clear from FIG. 3, the secondary battery of Example 1 has excellent discharge characteristics in which the discharge capacity retention rate decreases moderately as the number of cycles increases. On the other hand, in the secondary type battery of the comparative example, the discharge capacity retention rate decreases significantly as the number of cycles increases. In particular, when the number of cycles approaches 100, the discharge capacity retention rate decreases extremely.

In addition, heavy load discharge was performed with a load of 750 mA for the non-aqueous solvent secondary batteries of Example 1 and Comparative Example. As a result, a characteristic diagram of the relationship between discharge time and battery voltage shown in FIG. 4 was obtained. In the figure, A indicates the characteristic line of the non-aqueous solvent secondary battery of Example 1, and B indicates the characteristic line of the non-aqueous solvent secondary battery of the comparative example. As is clear from FIG. 4, the secondary battery of Example 1 has a longer discharge time until the discharge voltage suddenly decreases than the secondary battery of the comparative example, and the discharge characteristics under heavy loads are significantly improved. It can be seen that this has been improved. In particular, the battery of Comparative Example had a rapid voltage drop when the discharge time exceeded 25 minutes, whereas the battery of Example 1 did not experience a sudden voltage drop even after 45 minutes, and had stable battery characteristics. It shows.

Furthermore, 1 each of the non-aqueous solvent secondary batteries of Example 1 and Comparative Example
For 00 batteries, the battery capacity distribution was investigated after 50 cycles of the above-described discharge capacity retention rate characteristic evaluation test. 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 non-aqueous solvent secondary batteries of Example 1 and Comparative Example, and δ represents the standard deviation obtained from each of the above capacity values. .

Table 1 As is clear from Table 1 above, the secondary battery of Example 1 has less variation in battery capacity than the secondary battery of Comparative Example, and the performance of each individual battery is improved and made uniform. It can be seen that the present invention stabilizes the battery performance.

Example 2 First, a conductive resin layer solution was prepared by dispersing metal vanadium powder 30 times over a methanol solution of polyacrylic acid with a concentration of 30wt%, and a titanium foil was attached to one end along the longitudinal direction of the solution. The lead terminals were applied to both sides of a plate-shaped metal core made of stainless steel provided by spot welding, and dried to form a conductive resin layer. Continuing, the above-mentioned Example 1
A positive electrode was manufactured by pressing a sheet similar to the above onto the conductive resin layers on both sides of the metal core and drying to form a positive electrode mixture. Example 1 except for using such a positive electrode
A non-aqueous solvent secondary battery similar to the above was assembled.

Therefore, the discharge capacity retention rate, heavy load discharge, and battery capacity distribution of the non-aqueous solvent secondary battery of Example 2 were investigated in the same manner as in Example 1. The results confirmed that it had the same excellent properties as Example 1.

In the above embodiment, propylene carbonate in which IMo's LiC No. 04 was dissolved was used as the non-aqueous electrolyte with which the separator was impregnated, but the present invention is not limited thereto. For example, aprotic solvents such as 1,2 dimethoxyethane, ethylene carbonate, and tetrahydrofuran are used, and LiC, i'04 is used as the electrolyte, but in addition, LiA, 7704, LiBF4, LiPF6゜LiAs
Fb and the like can also be used in the same manner.

Further, in the above embodiment, an example was explained in which the present invention was applied to a cylindrical non-aqueous solvent secondary battery, but the present invention is not limited thereto. For example, it can be similarly applied to non-aqueous solvent secondary batteries of button type, flat type, square type, etc.

[Effects of the Invention] As detailed above, according to the present invention, the metal core is electrically well coated with the positive electrode mixture to prevent gas etc. from being generated at the interface during charging and discharging cycles. It is possible to provide a non-aqueous solvent secondary battery that suppresses this, thereby achieving stabilization of battery capacity and improving charge/discharge cycle life and heavy discharge characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a non-aqueous solvent secondary battery showing an embodiment of the present invention, FIG. 2(a) is a front view of the positive electrode of the non-aqueous solvent secondary battery shown in FIG. b) is a cross-sectional view taken along the line A-A in Fig. 3 (a), and Fig. 3 shows the relationship between the number of charge/discharge cycles and the discharge capacity retention rate of the non-aqueous solvent secondary batteries of the present example and comparative example. The characteristic diagram, FIG. 4, is a characteristic diagram showing the relationship between heavy load discharge time and battery voltage in the non-aqueous solvent secondary batteries of the present example and the comparative example. DESCRIPTION OF SYMBOLS 1... Container, 3... Power generation element, 4... Negative electrode, 5...
... Separator, 6... Positive electrode, 8... Metal core, 9
... Conductive layer, 10... Positive electrode mixture. Applicant's agent Patent attorney Takehiko Suzue

Claims (2)

[Claims] (1) A positive electrode having a structure in which a metal core is coated with a positive electrode mixture containing an active material via a conductive layer of a metal constituting the active material or a conductive resin layer containing the metal. Non-aqueous solvent secondary battery. (2) The non-aqueous solvent secondary battery according to claim 1, wherein the active material of the positive electrode mixture is vanadium pentoxide.