JPH0417271A - Secondary battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve a utilization factor of the active material by providing a core member in the center of a battery, and fixing the peripheral part thereof to prevent relaxation of an electrode group. CONSTITUTION:A core member 3 having rigidity is located in the center of an electrode group which consists of spirally wound electrodes, and a mechanism 4 for preventing relaxation of the wound electrode group 5 is comprised in the peripheral part of the wound electrode group 5. Namely, the core member 3 prevents the relaxation of the wound electrode group 5 toward the inside, and an adhesive tape 4 comprised in the peripheral part prevents the relaxation of the wound electrode group toward the outside. Consequently, volume change of the active material 1 can be restricted, and contact between the particles in the active material layer 1 is maintained to prevent isolation and falling of the active material 1 from an electrode substrate 2. Increase of the inner resistance of the electrode can thereby be restricted to maintain a utilization factor of the active material from many sides.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to storage batteries, and particularly to alkaline storage batteries using an alkaline electrolyte such as nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, and nickel-hydrogen batteries, or non-aqueous batteries. The present invention relates to secondary batteries such as lithium secondary batteries that use an electrolytic solution of 100% and an alkali metal such as lithium as a negative electrode active material.

BACKGROUND OF THE INVENTION With recent advances in electronics, application to general electrical equipment such as LSIs and ICs has led to improvements in performance, miniaturization, portability, and cordless technology. As a result, the demand for batteries that power these devices is also increasing. Although there are various types of batteries used, secondary batteries are generally the mainstream for batteries that have moving parts and consume relatively large amounts of power. Among secondary batteries, alkaline storage batteries that use an alkaline electrolyte, such as nickel-cadmium batteries, are superior to conventional lead-acid batteries in terms of weight, high energy density, and ability to withstand overcharging and overdischarging. They are superior to storage batteries, and as a result, demand for small, sealed types is increasing significantly. As demand for these secondary batteries increases, demands for rapid charging and discharging, high capacity, etc. are increasing from the viewpoint of ease of use.

In order to increase the capacity, which enables longer discharge times with one charge, it is necessary to improve the charging density of the electrode active material or the utilization rate of the electrode active material.

In order to improve the packing density of the electrode active material, it is necessary to consider increasing the density of the active material powder, optimizing the active material layer composition, or improving the electrode substrate structure.

In order to improve the utilization rate of electrode active material, active material layer composition,
In addition to chemical approaches such as improving additives to active materials, many proposals have been made from a structural perspective. For example, by winding the electrodes into a spiral electrode group, using multiple rows of adhesive tape to cover and fix the electrodes, and setting the ratio of the adhesive area within a specific range, the variation in the distance between the electrodes can be reduced (especially Publication No. 60-170171).

Furthermore, the separator absorbs the electrolyte and swells, filling the gap between the negative electrode and the separator to ensure sufficient contact (Japanese Patent Application Laid-Open No. 185668/1983). Furthermore, a method of absorbing and retaining electrolyte by disposing a swelling agent in the separator (Japanese Patent Application Laid-Open No.
6-63772), a method for making the electrolyte in a separator into a colloid (Japanese Patent Application Laid-Open No. 152665/1982)
Technologies such as the following have been disclosed.

Problems to be Solved by the Invention An object of the present invention is to provide a secondary battery that can achieve high capacity density. In order to increase the capacity density, it is necessary to increase the capacity density of both the positive electrode and the negative electrode, but since the negative electrode is generally a metal electrode, it has a higher capacity density than the positive electrode, and therefore it is important to increase the capacity density of the positive electrode. The present invention relates to improving the active material usage rate in order to increase the capacity density of the positive electrode by improving the battery structure. In order to concretely explain the content of the invention, a nickel-cadmium battery will be explained below as an example.

Looking at conventional technologies related to these purposes, all of the above-mentioned conventional technologies suppress relaxation between the positive electrode, negative electrode, and electrodes in which a separator is wound or laminated, and changes in electrode thickness, and reduce the electrolytic solution. It seems to work effectively for retention and for reducing contact resistance between the electrode base and the active material layer. However, although it is possible to reduce the variation in the distance between the electrodes by wrapping tape or the like around the spiral electrode, it is difficult to suppress the loosening of the electrode group into the inside of the spiral electrode, and it is difficult to suppress the loosening of the electrode group into the inside of the spiral electrode. Although it is effective for sintered electrodes with strong elasticity, it is not suitable for electrodes with weak elasticity such as paste-type electrodes. Also,
Since the separator and the like are provided with a swelling material layer, when the separator swells, the distance between the positive and negative electrodes increases, and the internal resistance increases.

On the other hand, the electrode active material layer of a secondary battery increases in volume by absorbing electrolyte, and also changes in volume during charging and discharging reactions, but in paste-type electrodes, these volume changes are tends to be larger than in the case of Due to this volume change, the active material layer attached to the electrode base is released from the electrode base, and the conductivity between particles of the active material and conductive agent in the active material layer becomes insufficient, resulting in an increase in the active material utilization rate. will decrease. However, in the above conventional technology,
Not enough consideration was given to them.

Means for Solving the Problems The present invention is characterized in that, in order to solve the problems of the prior art described above, a rigid core is disposed at the center of an electrode group in which electrodes are spirally wound, and A mechanism for preventing loosening of the electrode group is provided on the outer periphery of the wound electrode group. The position where the core body is arranged is the space occupied by the winding shaft around which the electrode is wound. If the shape of the core is cylindrical or cylindrical, it can be in uniform contact with the wound electrode group, but other shapes such as a polygonal prism can also be used as long as they meet this purpose. It would be impractical for the dimensions of the core to deviate significantly from the diameter of the winding shaft currently used in conventional winding techniques. This is because if the diameter of the core is too large, the volume occupied by the wound electrode group will be reduced, reducing the filling capacity of the battery.If the diameter of the core is too small, the space occupied by the winding shaft will be reduced. This is because simply inserting the core does not result in uniform contact with the wound electrode group, or problems arise such as the need for a technique to wind the electrode around a thinner winding shaft than before. . More specifically, the diameter of the core is 1 to 5III
11 is suitable, and 2 to 3.5 mm is more preferred. It is sufficient that the length of the core body is equal to the length of the electrode. This is because even if there are more than that, they will not come into contact with the electrode group. Specifically, the mechanism provided on the outer periphery of the wound electrode group to prevent loosening of the wound electrode group is desirably a sheet-like adhesive tape or the like that has strong adhesive strength and is lightweight. A mechanism for preventing loosening of the wound electrode group, such as an adhesive tape, covers part or all of the outer periphery of the wound electrode group. There is a concern that the oxygen absorption of the cadmium electrode will be reduced by covering the entire outer periphery, but experiments conducted by the inventors have revealed that this effect is small. Therefore, it is sufficient that the width of the adhesive tape is about the same as the height of the wound electrode group, and the length needs to be at least the outer circumference of the wound electrode group, but how far beyond that is necessary? It depends on the method of winding the electrode, the tensile strength of the adhesive tape, etc. The thickness of the adhesive tape is preferably as thin as possible so long as it can fulfill the purpose of the present invention. However, a range of 100 to 4011 m is a realistically usable range.

Methods for installing the core body, adhesive tape, etc. according to the present invention on the wound electrode group include a method in which they are installed simultaneously when the electrode group is wound, or a method in which they are installed after winding. The former can be achieved by using the core as a winding shaft, winding the electrode group around it, and placing adhesive tape or the like at the end of the electrode group.

In the latter case, after the electrode group is wound, the core body is inserted into the hole occupied by the winding shaft, and adhesive tape or the like is wound around the wound electrode group. The former is superior to the latter in terms of workability and effectiveness of the invention.

The material used in the present invention is required to be chemically stable with respect to the electrolyte, that is, in the case of a nickel-cadmium battery, it is required to have alkali resistance. Further, even if it is in contact with the wound electrode group, since it is a part where electricity does not need to flow, it does not need to be made of a conductive material, and either a conductive material or a dielectric material can be used. Specifically, any of metals such as nickel and stainless steel, ceramics such as alumina and zirconia, and synthetic resins such as polyvinyl chloride, polytetrafluoroethylene, polyethylene, polystyrene, polypropylene, and polyester can be used.

Function The function of the present invention is related to the suppression of volume change due to charging and discharging of the nickel electrode active material. That is, the charging and discharging reaction of a nickel electrode is generally expressed by: The charging reaction product has a density of 4.6 g/cj, while the discharging reaction product has a density of 4.1 g/CIA. Therefore, the volume of the nickel electrode active material layer changes as the charge/discharge reaction progresses. In addition, the active material that has been photodischarged is not the same as uncharged Ni (OH) z, but contains water and electrolyte in its crystals, and also contains γ-Ni00H (density), which is an overcharged product. 3.
8g/c+J) may accumulate. Therefore, an increase in volume due to charging and discharging of the nickel electrode is inevitable, and a practical issue is how to suppress this to a small range.

The core body in the present invention has a function of preventing the wound electrode group from relaxing inward. Further, an adhesive tape or the like provided on the outer periphery of the wound electrode group prevents the wound electrode group from loosening outward. As a result, it becomes possible to suppress a change in the volume of the active material layer, maintain contact between particles in the active material layer, and prevent the active material layer from separating or falling off from the electrode base. This suppresses an increase in the internal resistance of the nickel electrode and makes it possible to maintain a wide range of active material utilization. Furthermore, by preventing the active material layer from falling off, the life characteristics of the battery are also improved.

The effects of the present invention are particularly remarkable in paste-type nickel electrodes in which the volume occupancy of the active material is increasing. This is because in a paste-type nickel electrode, the function of suppressing the volume increase of the active material by the electrode base is small, and the present invention complements this function.

Although the above description relates to a nickel-cadmium battery, the present invention is applicable to other secondary batteries in which repeated volume changes of the active material due to charging and discharging are unavoidable, such as nickel-zinc batteries, nickel-iron batteries, and nickel-hydrogen batteries. , lithium secondary batteries, etc.

Examples Example (1) A cylindrical battery according to the present invention was produced and its battery performance was measured. The test nickel electrode was made with the following materials and preparation: 80 wt% nickel hydroxide as an active material, 10 wt% nickel fiber as a conductive material, 5 wt% metal cobalt as an activator for the active material, and 5 wt% PTFE as a binder. Added to the machine and mixed.

Water was added to the mixture to give a moisture content of 20-t%. PTFE dispersion (Daikin Industries, Polyflon Dispersion D-1) was used. The resulting paste-like crosstalk material is used as an electrode substrate 6
It was attached to both sides of a 0-mesh nickel wire mesh. It was dried at 80°C and bonded using a press to obtain a nickel electrode. The active material filling capacity density of this nickel electrode is 655 mA
h/cd was obtained. A schematic cross-sectional view of the nickel electrode is shown in FIG. As shown in the figure, an active material layer 1 and an electrode base 2
It has a three-layer structure with active material layers on both sides of the electrode base. The thickness of the electrode was 0.6 mm, and the electrode substrate was 0.2 mm. This electrode base is plate-shaped and flexible, and is suitable for a wound electrode.

The sample cadmium electrode was produced as follows. Cadmium oxide 85-t% and Ni powder 10-t% as conductive material
t% and 5wt% of PTFE as a binder were added into a Laikai machine and kneaded. PTFE is PTFE dispersion (Daikin Industries, Polyflon Dispersion D-1
) was used. The paste was attached to a 40-mesh wire mesh. Thereafter, it was dried at 140°C to obtain a measurement electrode. A schematic cross-sectional view of a cylindrical battery produced using these is shown in FIG. The core 3 was filled in the center of the wound battery 5.

The core is made of PTFE and has a diameter of 3+s+s and a length of 40mm+.
A cylindrical one was used. Further, in order to prevent the wound electrode group from loosening, adhesive tape 4 was placed around the outer periphery of the wound electrode group. It was filled into a battery case 6 of battery size AA type. The adhesive tape used was made of polypropylene and had a width of 40 mm and a thickness of 0.1 mm.

For comparison, a battery of Comparative Example 1 was prepared with the core removed. To the above battery, 300 g/It of potassium hydroxide and 1
5g/j! An electrolytic solution containing lithium hydroxide hydrate was injected into the battery, and the battery was charged and discharged at 25°C. The charging rate is 0. 15 by IC
After charging for h, discharge at a discharge rate of 0.2 C, and the battery voltage becomes 1
．． The discharge capacity was determined using Ov as the final voltage. The results obtained are shown in FIG. In the figure, the active material utilization rate of the battery according to the present invention is 85% in the first cycle and 9% in the second cycle.
0%, and 93% after the third cycle, indicating stable battery performance. On the other hand, the battery 8 of Comparative Example 1 had a low utilization rate (about 85% utilization rate) from the first cycle.

Therefore, it became clear that the battery according to the present invention has a higher discharge capacity than a conventional battery such as Comparative Example 1.

Example (2) A schematic cross-sectional view of the produced cylindrical battery is shown in FIG. The core body 9 has an outer diameter of 3III11, an inner diameter of 1.5 mm, and a length of 40 mm.
A man made cylindrical acrylic resin tube was used. A piece of polypropylene with a width of 40 mm and a thickness of 0.05 mm was provided on the outer periphery. The battery size was AA type. Other Ni poles and C
A battery was prepared using an electrode prepared under the same conditions as in Example 1 for the d-electrode. The results are shown in FIG. As shown in the figure, the active material utilization rate 10 of the battery of the present invention is stable at about 96%.

Example (3) A cylindrical core was used as the winding axis of the electrode group, and after the electrode group was wound, the portion of the core protruding longer than the electrode group was cut. A cylindrical battery was produced by filling the electrode group into a battery case. The battery size was AA type. A cylindrical polyvinyl chloride core with an outer diameter of 3 mm and a length of 40 mm was used. The width of polypropylene is 40 mm around the outer periphery of the electrode group.
, and a thickness of 0.07III11. Other Ni
A battery was prepared using electrodes prepared under the same conditions as in Example 1 for the electrode and Cd electrode. The results are shown in FIG. As shown in the figure, the active material utilization rate 11 of the battery of the present invention is 97
It stabilizes at about %.

Example (4) Adhesive tape is adhered to the end of the separator, a positive electrode and a negative electrode are interposed on both sides, and when winding the electrode group, the adhesive tape is simultaneously applied to the outer periphery of the electrode group.
0n+m and thickness 0.05mm+. The battery size was AA type. The core has an outer diameter of 3 mm, an inner diameter of 2.0 mm,
A cylindrical stainless steel tube with a length of 40+wm was used. A battery was made using electrodes prepared under the same conditions as in Example 1, except for the Ni electrode and Cd electrode. The results are shown in the 7th section.
As shown in the figure. As shown in the figure, the active material utilization rate 12 of the battery of the present invention is stable at about 95%.

Effects of the Invention According to the present invention, the core body is provided in the center of the battery and the outer periphery thereof is fixed to prevent the electrode group from loosening, so that the adhesion of the battery group is not impaired. Since the contact resistance between the active material of the positive electrode and negative electrode and the electrode base, between the active material particles, and between the active material and the conductive agent can be reduced, the conductive network of the electrode base and the conductive network of the conductive agent can be effectively utilized. This improves charge/discharge efficiency and improves battery performance. As shown in the above examples, the present invention is effective in secondary batteries using high capacity paste electrodes, and is particularly effective on both sides of planar electrode substrates such as wire mesh, expanded metal, perforated plates, etc. This is noticeable in a three-layer structure electrode in which a material layer is formed.

The present invention is applicable not only to nickel-cadmium batteries, but also to other secondary batteries, such as nickel-zinc, nickel-iron, and nickel-hydrogen, in which the volume of the active material inevitably changes repeatedly due to charging and discharging. It is also effective.

[Brief explanation of the drawing]

Figures 1 and 3 are cross-sectional schematic diagrams of a cylindrical battery according to the present invention, Figure 2 is a comparative characteristic diagram of the active material utilization rate of the present invention and the conventional technology, and Figure 4 is a schematic diagram of a three-layer structure electrode. 5.6.7 are cycle characteristic diagrams of the active material utilization rate according to the present invention. DESCRIPTION OF SYMBOLS 1... Active material layer, 2... Electrode base, 3... Core body,
4... Adhesive tape, 5... Spiral electrode, 6... Battery case, 7... Present invention, 9... Core body, 10, 11.
12...This invention. Fig. 1 Fig. 2 Agent Patent Attorney Kunihiko Wakabayashi Number of cycles Fig. 3 Fig. 4 Fig. 2 Aishi base activity IplJ@Utilization rate C%) Fig. 7 Quantity rate (z)

Claims (1)

[Claims] 1. A positive electrode comprising an active material, a conductive material, a binder, etc.;
A secondary battery consisting of a negative electrode containing cadmium, iron, zinc, hydrogen, lithium, etc. as an active material and a separator holding an electrolyte, and comprising a wound electrode group formed by winding the positive electrode, separator, and negative electrode. A secondary battery, characterized in that a rigid core is disposed at the center of the wound electrode group, and a mechanism for preventing loosening of the wound electrode group is provided on the outer periphery of the wound electrode group. battery. 2. The secondary battery according to claim 1, wherein the rigid core has a columnar or cylindrical shape. 3. The secondary battery according to claim 1 or 2, wherein the mechanism for preventing loosening of the wound electrode group is an adhesive tape and is arranged around the wound electrode group. 4. Claims 1 to 4, wherein the mechanism for preventing loosening of the wound electrode group covers at least a part of the outer periphery of the wound electrode group.
The secondary battery according to any one of the items. 5.A positive electrode, a separator,
and a negative electrode, and an adhesive tape is adhered around the wound electrode group when the electrode group is wound. Manufacturing method for secondary batteries.