JP3433039B2 - Alkaline storage battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery having a non-sintered nickel positive electrode, and more specifically, to provide an alkaline storage battery having a large battery capacity and excellent charge / discharge cycle characteristics. The present invention relates to improvement of a conductive agent added to a positive electrode active material.

[0002]

2. Description of the Related Art In recent years,
With the spread of cordless devices, demand for alkaline storage batteries such as nickel-hydride storage batteries, nickel-cadmium storage batteries, and nickel-zinc storage batteries is rapidly increasing.

By the way, nickel hydroxide used as a positive electrode active material of an alkaline storage battery has a low electric conductivity. Therefore, conventionally, in the pores of the sintered body of metallic nickel powder,
A sintered nickel positive electrode obtained by impregnating an active material is widely used. The sintered nickel positive electrode complements the low electrical conductivity of the active material by using a sintered body having a high electrical conductivity for the core body (current collector).

However, in the sintered nickel positive electrode,
Due to the generally low porosity of the sintered body (usually
80% or less), the amount of the active material filled is large, that is, there is no high energy density electrode. Further, since the pore size of the pores of the sintered body is extremely small (usually 10 μm or less), it is necessary to fill the sintered substrate with the active material by repeating a complicated impregnation step several times. The drawback is that it must be done by law.

Under these circumstances, a non-sintered nickel positive electrode has recently been proposed. The non-sintered nickel positive electrode is
Usually, it is prepared by filling a kneaded material (paste) of nickel hydroxide and a binder solution into a conductive substrate having high porosity. In the non-sintered nickel positive electrode, a substrate having a high porosity can be used (a substrate having a porosity of 95% or more can be used), so that the filling amount of the active material can be increased and the active material Easy to fill the substrate.

However, in the non-sintered nickel positive electrode, if the porosity of the substrate is increased and the filling amount of the active material is increased, the electron conductivity is deteriorated and the utilization ratio of the active material is lowered. The decrease in the active material utilization rate appears as a decrease in the positive electrode capacity and the battery capacity.

Therefore, in order to prevent this, in a non-sintered nickel positive electrode, a conductive agent is generally added to the active material.

As a conductive agent, a cobalt compound such as cobalt hydroxide is generally used, but it has the drawbacks of being expensive and having a large specific gravity.

Spherical amorphous carbon such as acetylene black is known as a conductive agent which is inexpensive and has a small specific gravity. However, a conductive agent of this kind cannot provide sufficient electron conductivity and has corrosion resistance. Since it is not good, repeated charge and discharge causes oxidative deterioration and the electron conductivity gradually deteriorates.

[0010] Granular artificial graphite (see Japanese Unexamined Patent Publication No. 7-213316) and carbon fiber (see Japanese Unexamined Patent Publication No. 5-314982) have been proposed as conductive agents capable of obtaining considerably good electron conductivity. However, even with these conductive agents, sufficiently satisfactory electron conductivity cannot be obtained, and when charge and discharge are repeated for a long time, the electron conductivity gradually deteriorates due to oxidative deterioration.

The present invention has been made in view of the above circumstances, and by improving the conductive agent used for the non-sintered nickel positive electrode, the battery capacity (initial discharge capacity) is large and the charge / discharge is further improved. An object is to provide an alkaline storage battery having excellent cycle characteristics.

[0012]

The alkaline storage battery (the battery of the present invention) according to the present invention for achieving the above object comprises nickel hydroxide or nickel oxyhydroxide as an active material and a vapor phase as a conductive agent. A non-sintered nickel positive electrode to which graphitized carbon fibers produced by firing carbon fibers obtained by the growth method are added is provided.

In the battery of the present invention, the graphitized carbon fiber produced by firing the carbon fiber obtained by the vapor phase growth method is used as a conductive agent. The reason for limiting to carbon fiber is that it has a smaller electrical contact resistance between carbon particles than spherical carbon, and also the electron conduction between the active material located at a position distant from the substrate and the substrate. This is because it is advantageous in improving the sex. The reason why it is limited to graphitized carbon is that it has higher electric conductivity and is superior as a conductive agent as compared with non-graphitized carbon. The reason why it is limited to the carbon obtained by the vapor phase growth method is that it is more excellent in corrosion resistance than the carbon obtained by the liquid phase growth method, so that it is less likely to be oxidized and deteriorated even after repeated charge and discharge.

The graphitized carbon fiber preferably contains lithium in the crystal (interlayer etc.). This is because it is considered that the electron conductivity is improved by including lithium in the graphite crystal. As a method of containing lithium in the crystal of graphite, there is a method of using lithium hydroxide or an aqueous solution of potassium hydroxide to which a lithium salt is added as an electrolytic solution, and incorporating lithium into the crystal of the graphitized carbon fiber during charging. Conceivable . Alternatively, a method of adding lithium hydroxide or a lithium salt to an alkaline electrolyte and anodizing the graphitized carbon fiber so that lithium is incorporated into the crystal of the graphitized carbon fiber is also considered.
To be

The graphitized carbon fiber has a bulk density of 0.0
It is preferably from 15 to 0.4 g / cm ³ . If the bulk density is less than 0.015 g / cm ³ , contact between graphitized carbon fibers will be poor, and the bulk density will be 0.4 g / cm 3.
^When it exceeds ³ , it becomes difficult to uniformly mix it with nickel hydroxide, and in any case, it becomes difficult to obtain excellent electron conductivity. Furthermore, the fiber length of the graphitized carbon fiber is preferably 10 μm to 1 mm. Fiber length is 10
If it is less than μm, the contact between the graphitized carbon fibers becomes poor, and it is difficult to obtain electron conductivity. On the other hand, the fiber length is 1m
When it exceeds m, the filling amount of the active material into the substrate is reduced and the battery capacity is reduced. Furthermore, the fiber diameter of the graphitized carbon fiber is preferably 0.1 to 50 μm. When the fiber diameter is less than 0.1 μm, it is too thin to obtain excellent electron conductivity. On the other hand, when the fiber diameter exceeds 50 μm, the filling amount of the active material into the substrate is reduced, and the battery capacity is reduced.

The preferred amount of graphitized carbon fiber added to nickel hydroxide or nickel oxyhydroxide is 1 part by weight per 100 parts by weight of nickel hydroxide or nickel oxyhydroxide.
~ 20 parts by weight. If the added amount is less than 1 part by weight,
If sufficient electron conductivity is not obtained and the addition amount exceeds 20 parts by weight, the filling amount of the active material into the substrate decreases,
Battery capacity decreases.

The present invention is particularly significant when applied to an alkaline storage battery provided with a non-sintered nickel positive electrode using a punching metal as a substrate in which electron conductivity between the active material and the substrate is not sufficiently ensured. is there. This is because the effect of the present invention appears remarkably.

The non-sintered nickel positive electrode of the battery of the present invention uses a conductive agent having high electric conductivity and excellent corrosion resistance, so that it has good electron conductivity over a long period of charge / discharge cycle.

[0019]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible.

(Example 1) [Production of positive electrode] A reaction mixture was prepared by uniformly mixing benzene and iron fine particles (average particle size 20 nm) as a catalyst, and the reaction temperature was set at 1200 ° C. Benzene was pyrolyzed by spraying it in a hydrogen gas stream in the apparatus, and the pyrolysis product was subjected to a gas phase reaction to produce carbon fiber. The supply rate of the mixed solution was 1 cm ³ / sec and the supply rate of hydrogen gas was 10 cm ^3.
It was set to 0 cm ³ / sec. FIG. 1 is a sectional view schematically showing the reaction apparatus S used. A mixed liquid supply pipe 2 is attached to the outer peripheral wall of a cylindrical device body 1 of the reaction device S, a hydrogen gas supply pipe 3 is attached to the bottom wall, and a discharge pipe 4 is attached to the upper wall. A storage tank 5 for storing a mixed liquid of benzene and iron fine particles is connected to the mixed liquid supply pipe 2. Device body 1
When hydrogen gas is caused to flow through the inside of the device in the direction of the arrow and a mixed liquid of benzene and iron fine particles is sprayed into the apparatus main body 1 through the mixed liquid supply pipe 2, carbon becomes fibrous with iron fine particles as nuclei. It is configured to produce carbon fibers grown to. The carbon fibers discharged from the discharge pipe 4 are separated from other components (unreacted benzene, iron fine particles, etc.) and collected.

The carbon fiber obtained as described above was treated at 2900 °
It was fired at C for 1 hour to obtain a graphitized carbon fiber as a conductive agent. When the bulk density of this graphitized carbon fiber was determined,
It was 0.04 g / cm ³ . Next, 8 parts by weight of this graphitized carbon fiber, 72 parts by weight of nickel hydroxide, and 20 parts by weight of a 1% by weight aqueous solution of methylcellulose were kneaded,
A paste was prepared, and this paste was filled into a porous substrate made of 2.4 g of nickel foam metal (size 42 mm × 85 mm), dried, pressure-molded, and weighed 6.4 g.
The non-sintered nickel positive electrode of was produced.

[Preparation of Negative Electrode] Compositional Formula MmNi _3.2 CoA
0.5 parts by weight of polyethylene oxide was added to 100 parts by weight of a hydrogen storage alloy represented by _0.2 Mn _0.6 , and an appropriate amount of water was added to prepare a paste. Iron was used as a substrate in the paste. Pass through a nickel-plated punching metal, pull up, dry, press mold,
A hydrogen storage alloy negative electrode was produced.

[Preparation of Alkaline Storage Battery] The positive electrode and the negative electrode described above were superposed with a separator interposed therebetween and spirally wound to manufacture a spirally wound electrode body. Then, this spiral electrode body was inserted into an AA size battery can, and 2.4 g of an 8 mol / liter potassium hydroxide aqueous solution was injected as an alkaline electrolyte, which was then sealed to form a sealed alkaline storage battery X (main Invention battery) was produced.

Example 2 As the alkaline electrolyte, 7 mol / liter of potassium hydroxide and 1 mol of lithium hydroxide were used.
A sealed alkaline storage battery Y (battery of the present invention) was produced in the same manner as in Example 1 except that an alkaline aqueous solution containing mol / liter was used.

(Comparative Example 1) A sealed type was prepared in the same manner as in Example 1 except that 8 parts by weight of acetylene black was used as the conductive agent instead of 8 parts by weight of the graphitized carbon fiber in the production of the positive electrode. An alkaline storage battery A (comparative battery) was produced.

(Comparative Example 2) The same as Example 1 except that 8 parts by weight of artificial graphite (Lonza SFG75) was used as the conductive agent in place of 8 parts by weight of the graphitized carbon fiber in the production of the positive electrode. Then, a sealed alkaline storage battery B (comparative battery) was produced.

Comparative Example 3 In the same manner as in Example 1 except that 8 parts by weight of uncalcined carbon fiber was used as a conductive agent instead of 8 parts by weight of graphitized carbon fiber in the production of the positive electrode. Thus, a sealed alkaline storage battery C (comparative battery) was produced.

(Comparative Example 4) In the production of a positive electrode, a conductive agent was obtained by a liquid phase growth method instead of 8 parts by weight of graphitized carbon fiber produced by firing carbon fiber obtained by a vapor phase growth method. A sealed alkaline storage battery D (comparative battery) was produced in the same manner as in Example 1 except that 8 parts by weight of graphitized carbon fiber produced by firing carbon fiber was used. The graphitized carbon fiber produced by firing the carbon fiber obtained by the above liquid phase growth method is a commercially available graphitized carbon fiber produced by carbonizing / graphitizing the carbon fiber produced by the liquid phase growth method. Of non-woven fabric (product code "Melvlon F-104" manufactured by Petka Co., Ltd.) in a mortar with an average fiber length of 300 μm
What was crushed to an average fiber diameter of 7 μm was used.

<Battery Capacity and Charging / Discharging Cycle Characteristics of Each Battery> The process of charging the batteries X and Y of the present invention and the comparative batteries A, B, C and D for 1.2 hours at 1 A and then discharging to 1 V at 1 A. Was performed as a cycle, and the battery capacity (first cycle discharge capacity) and charge / discharge cycle characteristics of each battery were examined. The results are shown in Figure 2. Figure 2
3 is a graph showing charge / discharge cycle characteristics of each battery, with the horizontal axis representing the charge / discharge cycle and the vertical axis representing the discharge capacity in each charge / discharge cycle.

As shown in FIG. 2, the batteries X and Y of the present invention are
Compared to the comparative batteries A, B, C, D, the battery capacity is large and the charge / discharge cycle characteristics are excellent. Comparative battery A has a small battery capacity and poor charge / discharge cycle characteristics.
This is because the acetylene black used as the conductive agent has low electric conductivity and poor corrosion resistance. Comparative battery B,
Battery capacity of C and D is not so small, but the charge and discharge cycle characteristics are not good because the corrosion resistance of the conductive agent used is not good. The battery capacity of the battery Y of the present invention is larger than that of the battery X of the present invention because the graphitized carbon fiber containing lithium having an extremely high conductivity is used as the conductive agent.
It is thought to be because .

(Example 3) In Example 1 (conductive agent: conductive agent of the present invention), except that 1.2 g of punching metal was used as the porous substrate instead of foam metal in the production of the positive electrode. Similarly, a sealed alkaline storage battery E
(Invention battery) was produced (weight of non-sintered nickel positive electrode: 5.2 g).

Comparative Example 5 Comparative Example 2 (conductive agent: Lo) except that 1.2 g of punching metal was used as the porous substrate in place of the foam metal in the production of the positive electrode.
nka SFG75), a sealed alkaline storage battery F (comparative battery) was produced (weight of non-sintered nickel positive electrode: 5.2 g).

Comparative Example 6 Comparative Example 3 (conducting agent: unfired carbon fiber) except that 1.2 g of punching metal was used as the porous substrate in place of the foam metal in the production of the positive electrode. In the same manner as above, a sealed alkaline storage battery G (comparative battery) was produced (weight of non-sintered nickel positive electrode: 5.2 g).

<Battery Capacity and Charge / Discharge Cycle Characteristics of Each Battery> The battery E and comparative batteries F and G of the present invention were subjected to a charge / discharge cycle test under the same conditions as above, and the battery capacity and charge / discharge cycle characteristics of each battery were determined. Examined. The results are shown in FIG. 3, which has the same coordinate system as in FIG.

From the comparison between FIG. 2 and FIG. 3, the battery E of the present invention has a slightly smaller battery capacity than the corresponding battery X of the present invention, whereas the comparative batteries F and G show the corresponding comparative battery B. , C, the battery capacity is much smaller, and the charge / discharge cycle characteristics are not so good. From this fact, it can be seen that the present invention is particularly significant when applied to an alkaline storage battery having a non-sintered nickel positive electrode using a punching metal as a porous substrate.

<Relationship between Bulk Density of Graphitized Carbon Fiber and High Rate Discharge Characteristic> In the production of a positive electrode, various bulks shown in Table 1 produced by firing carbon fiber obtained by a vapor phase growth method as a conductive agent. In the same manner as in Example 1 except that the high density graphitized carbon fiber was used, the sealed alkaline storage batteries H, I,
J, K, L, M, N, O, P and Q were produced. The alkaline storage battery K is the same battery as the battery X of the present invention.

[0037]

[Table 1]

Each battery was charged at 100 mA for 16 hours and then discharged at 100 mA to 1 V to obtain a discharge capacity C1. Then, each battery was charged at 100 mA for 16 hours and then discharged to 2000 V at 1 V. The discharge capacity C2 was determined. The discharge rate R defined by the following formula was determined from the discharge capacity C1 and the discharge capacity C2. The higher the discharge rate R, the better the high rate discharge characteristics. The results are shown in Fig. 4. FIG. 4 shows the relationship between the bulk density of the graphitized carbon fiber and the high rate discharge characteristics, the vertical axis represents the discharge rate R (%) and the horizontal axis represents the bulk density (g / cm) of the graphitized carbon fiber used in each battery. ³ is a graph showing the above. The horizontal axis is a common logarithmic scale.

Discharge rate R (%) = C2 / C1 × 100

As shown in FIG. 4, the bulk density is 0.015 to 0.015.
0.4 g / cm ³ alkaline storage batteries I, J, K, L,
The discharge rates R of M, N and O are larger than those of other alkaline storage batteries. From this fact, in order to obtain an alkaline storage battery excellent in high rate discharge characteristics, the bulk density is 0.015 to
It can be seen that it is preferable to use 0.4 g / cm ³ of graphitized carbon fiber.

Although nickel hydroxide was used as the active material of the non-sintered nickel positive electrode in the above examples, a discharge-start alkaline storage battery using nickel oxyhydroxide as the positive electrode active material (first discharge without charging) It has been separately confirmed that the same excellent effects as described above can be obtained by applying the present invention in the case of the alkaline storage battery).

[0042]

The present invention provides an alkaline storage battery having a large battery capacity and excellent charge / discharge cycle characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reaction device for producing carbon fibers by a vapor growth method.

FIG. 2 is a graph showing charge / discharge cycle characteristics of the battery of the present invention and the comparative battery.

FIG. 3 is a graph showing charge / discharge cycle characteristics of a battery of the present invention and a comparative battery.

FIG. 4 is a graph showing the relationship between the bulk density of graphitized carbon fibers and high rate discharge characteristics.

[Explanation of symbols] S reactor 1 device body 2 Mixed liquid supply pipe 3 Hydrogen gas supply pipe 4 discharge pipe 5 storage tanks

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Mutsumi Yano 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Kozo Nogami 2-5- Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 In Sanyo Electric Co., Ltd. (72) Inventor Ichiro Yonezu 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (56) Reference JP-A-5-314982 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/62 H01M 4/24-4 / 32 H01M 10/26

Claims (3)

(57) [Claims] 1. Non-sintering in which nickel hydroxide or nickel oxyhydroxide as an active material is added with graphitized carbon fiber produced by firing carbon fiber obtained by a vapor phase growth method as a conductive agent. An alkaline storage battery comprising a nickel positive electrode, a negative electrode, and an alkaline electrolyte. 2. The alkaline electrolyte is lithium hydroxide or
The alkaline storage according to claim 1, wherein a lithium salt is added.
battery. 3. The bulk density of the graphitized carbon fiber is 0.015.
~ 0.4g / cm ³ Alka according to claim 1 or 2.
Rechargeable battery.