JPH04301363A - Hydrogen storage electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a closed cylindrical battery with a long cycle life further with no short-circuit by binding powder of hydrogen storage alloy or its hydride with polyfluorovinylidene and polytetrafluoro-ethylene. CONSTITUTION:A plate-shaped molded unit of mixture, formed by mixing powder of hydrogen storage alloy or its hydride, powder of polyfluorovinylidene and powder of polytetrafluoroethylene, is vacuum-heated at a melting point or more of the polyfluorovinylidene further at a low temperature less than a melting point of the polytetrafluoroethylene. In this way, sintered grain between a melting matrix of the polyfluorovinylidene and the polytetrafluoroethylene of reinforcing the matrix is produced to firmly bind powder grains of the hydrogen storage alloy or its hydride.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage electrode used in alkaline storage batteries and a method for manufacturing the same.

0002

2. Description of the Related Art Conventionally, hydrogen storage electrodes made of hydrogen storage alloys or hydrides thereof have been used as negative electrodes of alkaline storage batteries because they can electrochemically store and release hydrogen. The most frequently considered battery shape is a closed cylindrical one. In this cylindrical type, the positive electrode plate and the negative electrode plate are wound with a separator in between, and the wound electrode plate group is inserted into the cylindrical cell container, so the hydrogen storage electrode is flexible. It is required that the winding property is good and that the hydrogen storage alloy or its hydride powder (hereinafter collectively referred to as hydrogen alloy powder) does not fall off during winding. Therefore, polytetrafluoroethylene (PTFE), polypropylene (PP), or polyethylene (PE) is used as a binder for alloy powder, and the powder is mixed with alloy powder, and a plate-shaped molded body of the mixture is vacuum-treated. The alloy powder is placed in a heating furnace, and the binder is melted by vacuum heating to bind the alloy powder particles, thereby producing each hydrogen storage electrode plate.

0003

[Problems to be Solved by the Invention] PTFE used in the production of the conventional hydrogen storage alloy described above is excellent in providing excellent windability and durability to electrodes, but its melting temperature is 3.
Since the temperature is very high at around 50° C., the vacuum heating treatment requires a high degree of vacuum on the order of at least 10 −5 Torr, which requires a special vacuum heating furnace. On the other hand, PP and PE have a low melting temperature of about 150°C, so they can be used in a normal vacuum heating furnace, but they are considerably inferior to PTFE in terms of electrode windability and durability, and they are difficult to charge and discharge batteries. This repetition causes the alloy powder to fall off from the electrode, resulting in disadvantages such as a reduction in charge/discharge cycle life and a tendency to cause internal short circuits. Therefore, it is desired to develop a hydrogen storage electrode that uses a normal vacuum heating furnace and has excellent windability and durability.

0004

[Means for Solving the Problems] The present invention provides a hydrogen storage electrode that satisfies the above requirements and a method for manufacturing the same.
The hydrogen storage electrode is made by bonding powder of a hydrogen storage alloy or its hydride with polyvinylidene fluoride and polytetrafluoroethylene. Furthermore, the method for producing the hydrogen storage electrode includes forming a plate-shaped body of a mixture of a hydrogen storage alloy or its hydride powder, polyvinylidene fluoride powder, and polytetrafluoroethylene powder, at a melting point of polyvinylidene fluoride. It is characterized by vacuum heating at a temperature higher than that and lower than the melting point of polytetrafluoroethylene.

[0005]

[Operation] By the above vacuum heating, a molten matrix of the polyvinylidene fluoride (PVdF) and sintered particles of the polytetrafluoroethylene (PTFE) reinforcing the matrix are generated, and the combination of these produces a hydrogen storage alloy. Alternatively, the powder particles of the hydride are strongly bound together, and excellent windability and durability are provided as an electrode. The heating temperature in manufacturing the hydrogen electrode is above the melting point of polyvinylidene fluoride (PVdF) and below the melting point of polytetrafluoroethylene (PTFE), preferably at a low temperature of about 170 to 200°C. , for example, can be processed in a general vacuum heating furnace at a low vacuum on the order of 10-2 Torr, whereby the PVdF is melted by the heating to form a three-dimensional network matrix, while the PTFE is completely melted. Although no bonding occurs, the fine fibers partially sinter each other, reinforcing the PVdF matrix and also acting as a softening agent.
It is easier to manufacture than when using only a binder as a binder, and P
Compared to using P or PE as a binder, the present invention provides an electrode with excellent binding properties and durability, and by using this electrode, an excellent sealed cylindrical battery with improved cycle life and no short circuit can be obtained.

[0006]

[Example] Next, an example of the present invention will be described. Commercially available misch metal (Mm), Ni, Co, Mn, and Al were weighed and mixed at a constant composition ratio, and the mixture was heated and melted by an arc melting method. As an example, if the alloy composition is M
mNi3.8Co0.4Mn0.4Al0.4 was selected as a hydrogen storage alloy for a negative electrode. The alloy solidified material is crushed into a powder of 250 mesh or less, and 30 wt. of carbonyl nickel powder is added to this alloy powder as a conductive agent. %, 7wt of PVdF powder as a binder
．． % and PTFE 60% dispersion 0.3wt.
% and further as a thickener, for example, 1% CMC aqueous solution 50w
t. % and stirred to form a paste mixture. This paste-like mixture was applied to a perforated plate made of nickel-plated iron, dried at 80° C. for about 1 hour, and then pressed to a thickness of about 0.5 mm. This was heated in a vacuum heating furnace at a vacuum degree of 1×10 −2 Torr and 200° C. for 1 hour to produce a hydrogen storage electrode of the present invention.

For comparison, 7wt. PVdF powder was used as a binder. A hydrogen storage electrode was manufactured by the same manufacturing method as in the above example except that only % was used. Hereinafter, this will be referred to as comparison electrode A. Furthermore, for comparison, PTFE was used as a binder.
Powder 5wt. Using only % and following traditional manufacturing methods,
A conventional hydrogen storage electrode was manufactured by heat treatment at 350° C. for about 1 hour under a high vacuum of 1×10 −5 Torr in a special high vacuum heating furnace. Hereinafter, this will be referred to as comparison electrode B. Furthermore, for comparison, PP powder 7wt. % in a normal vacuum heating furnace using a conventional method.
A conventional hydrogen storage electrode was manufactured by heat treatment at 150° C. for about 1 hour under a low vacuum. Below, this is used as reference electrode C.
It is called. Furthermore, for comparison, PE powder 7wt. %, a conventional hydrogen storage electrode was manufactured by a conventional method through heat treatment at 150° C. for about 1 hour in a conventional vacuum heating furnace under a low vacuum of 1×10 −2 Torr. Hereinafter, this will be referred to as comparison electrode D.

Durability Test First, a durability test was conducted on these electrodes. In this test, each of these electrodes was used as a negative electrode, and a known sintered nickel electrode was used as a positive electrode, which were combined through a separator.
Using potassium hydroxide aqueous solution as the electrolyte, negative electrode regulated test cells were manufactured, and for each test cell,
A charge/discharge test was conducted. The cell charging/discharging conditions are as follows:
After charging at 1C for 1.5 hours (150% charge), it was discharged at 1C to a cell voltage of 1.0V. The life span was defined as the point at which the negative electrode capacity reached 60% of the initial capacity. The test results are shown in Table 1 below.

[0009]

[Table 1]

As is clear from Table 1 above, the electrode of the present invention has the same durability as Comparative Electrode B using PTFE as the electrode. This is advantageous in that such highly durable electrodes can be manufactured easily and at low cost using a normal vacuum heating furnace, without using a high-vacuum heating furnace that requires high vacuum. It means that. or,
As is clear from Table 1, the electrode of the present invention has superior durability compared to electrodes similarly manufactured using each of PVdF, PP, and PE alone as a binder.

Windability Test Next, a windability test was conducted on these electrodes. That is,
Each of these electrodes was used as a negative electrode, and a known sintered nickel electrode was used as a positive electrode, and they were laminated and wound through a nylon separator, and after inserting the wound electrode plate group into a cylindrical metal cell case, the presence or absence of short circuits was checked. . 100 test samples were conducted for each electrode. The results are shown in Table 2 below.

0012

[Table 2]

As is clear from Table 2, the electrode of the present invention and P
No short circuit was observed with comparison electrode B using only TFE. On the other hand, short circuits were observed to occur by 3% in comparison electrode A and by 5% in comparison electrodes C and D.

[0014]

Effects of the Invention As described above, the hydrogen storage electrode of the present invention has a hydrogen alloy or its hydride powder bonded together with polyvinylidene fluoride and polytetrafluoroethylene. In terms of charge/discharge cycle life and winding properties, that is, short circuit prevention during winding, PP
, PE alone as a binder. Further, according to the method for manufacturing an electrode of the present invention, when heat treatment is performed at a temperature higher than the melting point of polyvinylidene fluoride and lower than the melting point of polytetrafluoroethylene, preferably at a low temperature of about 170 to 200°C, the molten The combination of a matrix of polyvinylidene fluoride with partial sintering of fine fibers of polytetrafluoroethylene results in an electrode with the above-mentioned excellent properties, compared to conventional polytetrafluoroethylene alone as a binder. It has the effect that a special vacuum heating furnace required in some cases is not required, and it can be manufactured easily and economically using a general vacuum heating furnace.

Claims (3)

[Claims] 1. A hydrogen storage electrode comprising a powder of a hydrogen storage alloy or its hydride bound by polyvinylidene fluoride and polytetrafluoroethylene. 2. A plate-shaped molded body of a mixture of a hydrogen storage alloy or its hydride powder mixed with polyvinylidene fluoride powder and polytetrafluoroethylene powder at a temperature higher than the melting point of polyvinylidene fluoride and a polytetrafluoroethylene powder. A hydrogen storage electrode and a method for producing the same, characterized by vacuum heating at a low temperature below the melting point of fluoroethylene. 3. The method of claim 2, wherein said mixture is heated at about 170-200° C. under a vacuum on the order of 10 −2 Torr.