JP3089310B2 - Sealed nickel / metal hydride 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 a sealed nickel-metal hydride storage battery having a negative electrode plate carrying a hydrogen storage alloy and a positive electrode plate containing nickel hydroxide as a main active material.

[0002]

2. Description of the Related Art A hydrogen storage electrode is used as a negative electrode of a sealed nickel-metal hydride alkaline storage battery.

[0003] This hydrogen storage electrode uses a hydrogen storage alloy capable of reversibly storing and releasing hydrogen for the electrode, and converts the electrochemical oxidation-reduction reaction of the hydrogen to the electromotive reaction of the negative electrode of an alkaline storage battery. Use. Hydrogen storage alloys used for hydrogen storage electrodes include LaNi ₅ , TiNi, Ti ₂ Ni and
And intermetallic compounds such as TiMn _2, those with substitution of constituent elements of these intermetallic compounds with other elements are used.
If the composition of these hydrogen storage alloys is different, properties such as hydrogen storage capacity, equilibrium hydrogen pressure, and storage capacity characteristics when charging and discharging are repeated in an alkaline electrolyte change, so the alloy composition is changed. Attempts have been made to improve the performance of hydrogen storage electrodes.

The hydrogen storage electrode is manufactured in a porous form by bonding the powder of the hydrogen storage alloy with an alkali-resistant polymer, sintering at a high temperature, or filling a foam metal. Was.

In a sealed nickel-metal hydride storage battery, a negative electrode composed of these hydrogen storage electrodes and a positive electrode plate in which an active material mainly composed of nickel hydroxide is filled in a sintered nickel substrate or a nickel foam are used. Lamination or winding is performed via a separator made of a gas-permeable alkali-resistant insulator such as a non-woven fabric, and this is housed in a pressure-resistant sealed metal storage battery container.

In this storage battery, a pressure-resistant container is used because the partial pressure of oxygen gas generated from the positive electrode at the time of overcharging is increased to increase the rate of the oxygen gas reduction reaction at the negative electrode. This is to prevent gas from accumulating in the battery.

[0007] The reason for using a metal container for the pressure-resistant storage battery is that a metal-made storage container has a higher pressure resistance even when the container wall is thinner than a synthetic resin container. The inner volume can be increased, the volume of the power generating element can be increased, and the electric capacity of the battery can be increased.Moreover, since metal has higher thermal conductivity than synthetic resin, it can be discharged or overcharged with a large current. In this case, the heat generated in the battery can be easily removed.

In this sealed nickel-metal hydride storage battery, a large amount of gas is generated due to abnormal usage such as overcharging with an abnormally large current, for example, at a rate of 10 minutes. In order to prevent the battery from bursting in case the battery internal pressure rises abnormally due to incomplete processing inside the battery, the battery internal pressure should be several kg / cm ² to about 20 kg / cm ²
A safety valve is used that activates when it reaches ² and releases gas in the battery. As the safety valve, a safety valve made of synthetic resin placed in a hole communicating between the inside and outside of the battery and pressed by a spring, or a safety valve made of synthetic resin having rubber elasticity itself is used.

When a metal battery container is used, the metal battery container may have one polarity of a positive electrode or a negative electrode, and may not have any polarity. At least the other polarity electrode terminal must be electrically insulated. The insulating member also serves as a packing for maintaining the airtightness of the battery container. For this packing member, a synthetic resin suitable for performing its function is used.

[0010]

Some of the above-mentioned sealed nickel-metal hydride batteries explode when charged ones are put into a fire. Such batteries are at risk of being injured by an explosion if the user accidentally throws the battery into a fire. Therefore, a sealed nickel-metal hydride storage battery that does not explode when charged in a fire in a charged state has been demanded.

The present invention has been made in order to solve the above-mentioned problems.
A negative electrode plate mainly composed of a hydrogen storage alloy, a positive electrode plate mainly composed of nickel hydroxide, a metal storage battery container, and a positive electrode electrically connected to the battery container and the terminal while maintaining the hermeticity of the storage battery container. In a sealed nickel-metal hydride storage battery comprising a thermoplastic synthetic resin packing member that electrically insulates a portion having a negative polarity and a portion having a negative polarity, and a synthetic resin safety valve body, the safety valve body is When made of a thermoplastic synthetic resin, the melting point of the packing member is 270 ° C. or less, and when the safety valve body is a rubber elastic body, the melting point of the packing member is 270 ° C. or less. A sealed nickel-metal hydride storage battery having a rubber-like elastic body having a heat-resistant temperature of 230 ° C. or lower.

[0012]

[Function] The hydrogen storage alloy of a sealed nickel-metal hydride storage battery has a hydrogen equilibrium pressure of about 0.01 at the flat part of the hydrogen equilibrium pressure-hydrogen storage isotherm (PCT characteristic) near room temperature.
Use the one of about -0.5 atm. The equilibrium hydrogen pressure of the hydrogen storage alloy increases as the temperature increases. Therefore, when the battery is charged, the hydrogen stored in the hydrogen storage alloy of the negative electrode is released from the hydrogen storage alloy when the temperature of the battery increases, and the hydrogen partial pressure in the space in the battery is increased. Most of the hydrogen involved in the charge / discharge of the nickel-metal hydride storage battery is stored in a range where the equilibrium hydrogen pressure of the hydrogen storage alloy of the negative electrode exceeds 1 atm at 100 ° C. Therefore,
When the temperature of the battery exceeds 100 ° C., the partial pressure of hydrogen in the battery exceeds 1 atm.

On the other hand, in the positive electrode of the sealed nickel-metal hydride battery, the main charge product is preferably β phase, and γ
Phases are not preferred. The reason is that, when the γ phase is generated, since this crystal has a larger interlayer distance than the β phase, the active material expands, which causes absorption of the electrolytic solution due to swelling of the positive electrode plate and lowering of the mechanical strength of the positive electrode plate. It is in. Therefore, an additive to the positive electrode active material or the electrolytic solution is used or charging conditions are devised so as to suppress generation of the γ phase as a charging product. Therefore, in the sealed nickel-metal hydride storage battery, the main component of the charge product of the positive electrode is β-phase nickel oxyhydroxide.

When the β-phase nickel oxyhydroxide is heated, crystallization water is desorbed at a temperature of about 100-150 ° C. Next, a decomposition reaction of the β-phase nickel oxyhydroxide occurs at 150 to 300 ° C. to generate oxygen gas.
This pyrolysis reaction occurs most actively around 260 ° C.

Now, when the temperature of the nickel-metal hydride storage battery in a charged state is increased while keeping it sealed,
The following happens:

That is, when the temperature of the battery exceeds about 100 ° C., hydrogen gas is actively released from the hydrogen storage alloy of the negative electrode, and the hydrogen partial pressure in the battery increases. When the temperature further rises and exceeds about 150 ° C., oxygen gas starts to be generated from the positive electrode, and the gas in the battery becomes a mixture of oxygen and hydrogen. When the temperature further rises, the amount of generated oxygen increases, and the hydrogen concentration of the mixture of oxygen and hydrogen in the battery enters the explosion limit. When the battery is heated by the flame outside the battery and the battery seal is broken and the internal gas of the battery is ignited, the battery does not explode when the internal gas of the battery is not at the explosion limit. The battery explodes when the gas is at the explosion limit.

The reaction of generating hydrogen gas stored in the hydrogen storage alloy of the negative electrode and the reaction of generating oxygen gas by thermal decomposition of β-nickel oxyhydroxide of the positive electrode are both endothermic reactions. Evaporation of the alkaline electrolyte occurs before the reaction takes place, which is also an endothermic process. Therefore,
When a charged nickel-metal hydride storage battery is heated from the outside by a flame, the temperature of the electrode plate group is slower than that of the portion near the outside of the battery.

Since the synthetic resin packing and the synthetic resin safety valve element of this battery are both located outside the battery itself or in a portion very close to the outside of the battery, these constituent members are used as a battery electrode group. Temperature rises faster than

Therefore, in a sealed nickel-metal hydride storage battery, if the material of the safety valve body is a thermoplastic synthetic resin and the melting point of the synthetic resin packing member is lower than 270 ° C., the battery is placed in a fire. When the battery is turned on, the inside of the battery is heated, the temperature of the electrode group rises to 260 ° C. or more, and oxygen gas is generated from the positive electrode most actively. The packing member is heated earlier than the electrode plate group and reaches 270 ° C., the packing member is melted, and hydrogen gas in the battery is discharged out of the battery.

When the material of the safety valve body is a rubber-like elastic body, in many cases except for a thermoplastic elastomer,
Since the rubber-like elastic body is crosslinked, it does not melt when heated, but deteriorates due to heat. And
In a sealed nickel-metal hydride storage battery, since the internal gas is released from the safety valve at a temperature slightly higher than the heat resistance temperature of the rubber-like elastic body, the melting point of the packing member made of thermoplastic synthetic resin is lower than 270 ° C. If the temperature is high, if the heat-resistant temperature of the rubber-like elastic body of this safety valve body is 230 ° C. or less, oxygen gas is actively released from the positive electrode, and before the composition of the internal gas of the battery reaches the explosion limit, Gas inside the battery is released from the safety valve to the outside of the battery. When the melting point of the packing member is 270 ° C. or more, the internal gas of the battery is released from the packing member when the temperature is raised, even if the heat-resistant temperature of the rubber-like elastic safety valve is higher than 230 ° C.

Therefore, when the temperature inside the battery further rises and a large amount of oxygen gas is generated in the battery, most of the hydrogen gas in the battery has been discharged to the outside. When the composition reaches the explosion limit, the risk of ignition and explosion is significantly reduced.

By this action, the battery of the present invention does not explode even if it is charged into a fire in a charged state, and the hydrogen gas released from the battery simply burns safely outside the battery. That's it.

On the other hand, unlike the construction of the present invention, the material of the safety valve body is a thermoplastic synthetic resin, and the melting point of both the synthetic resin packing member and the synthetic resin safety valve body is 300.
If the temperature is higher than ℃, when the charged battery is heated, a large amount of hydrogen gas is generated from the negative electrode, a large amount of oxygen gas is generated from the positive electrode, and the internal gas of the battery reaches the explosion limit. As a result, the packing made of synthetic resin or the safety valve made of synthetic resin melts and the sealing of the battery is broken.

Also, unlike the construction of the present invention, the material of the safety valve body is a rubber-like elastic body, the melting point of the synthetic resin packing member is higher than 300 ° C., and the heat resistance of the safety valve body made of the rubber-like elastic body is high. Even when the temperature is higher than 230 ° C., when the charged battery is heated, a large amount of hydrogen gas is generated from the negative electrode, and a large amount of oxygen gas is generated from the positive electrode,
After the internal gas of the battery reaches the explosion limit, the sealing of the battery is broken due to deterioration of the synthetic resin packing or melting of the synthetic resin safety valve element.

Therefore, when these batteries different from the configuration of the present invention are thrown into a fire, the gas inside the batteries enters the explosion limit due to heating, and then the seal of the batteries is broken to ignite the gas inside the batteries, Battery explodes.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described by way of preferred embodiments. [Experiment 1] In the experiment, FIG. 1 shows a schematic diagram of a longitudinal sectional structure.
The test was performed using a cylindrical nickel-metal hydride storage battery having a sub shape (diameter 23 mm × height 43 mm).

In FIG. 1, F is a band-shaped negative electrode plate mainly composed of a hydrogen storage alloy, H is a band-shaped sintered positive electrode plate mainly composed of nickel hydroxide as an active material, and G is a sulfonated hydrophilic plate. This is a separator having a thickness of 0.15 mm and made of a nonwoven fabric made of polypropylene containing polystyrene imparted with properties. The negative electrode plate F and the positive electrode plate H are wound via a separator G. I is a battery container which also serves as a negative electrode terminal obtained by plating nickel having a thickness of 0.4 mm on iron. The negative electrode plate F is electrically connected to the battery container I by a negative electrode lead K.

The positive electrode plate H is electrically connected to a perforated lid plate E by a positive electrode lead J. The perforated lid plate E is
At the periphery, the upper end of the battery container is sealed by caulking via a synthetic resin packing member A that plays a role of electrical insulation and airtightness. A safety valve body D made of a thermoplastic synthetic resin is placed in a central hole of the perforated lid plate E. The safety valve body D is provided with a cap B serving as a positive electrode terminal via a spring C. Plate E is pressed. The cap B has an exhaust hole B1 and is welded and connected to a perforated lid plate E. Before the safety valve D is melted, the internal pressure of the battery is 10kg.
/ Cm ² , the safety valve body D is lifted, and the gas inside the battery is discharged from the hole at the center of the perforated lid plate E through the exhaust hole B1 to the outside of the battery system. Has become.

The total weight of nickel hydroxide contained in the nickel hydroxide electrode H of the positive electrode is 8.7 g per cell. Therefore, assuming that nickel hydroxide follows a one-electron reaction, the theoretical capacity of one battery positive electrode is about 2.5 A
h. To this electrode was added 0.04 grams of cobalt hydroxide per gram of nickel hydroxide. The theoretical capacity of this positive electrode will be referred to as the rated capacity.

The negative electrode plate C was manufactured as follows.

The composition of the hydrogen storage alloy is LmNi in atomic ratio.
The constituent elements were melted in a vacuum in a high-frequency induction furnace in a metal state so as to obtain _3.8 Co _0.7 Al _0.5 , cast, and then pulverized. Here, Lm is a lanthanum-rich misch metal which is a mixture of rare earth metals containing about 90% by weight of La. This alloy powder was dispersed in an aqueous solution of polyvinyl alcohol which functions as a thickener and a binder to form a paste. The paste was applied to both surfaces of a nickel-plated iron punching metal, dried, pressed, and cut to produce a hydrogen storage electrode. The weight of the hydrogen storage alloy contained in one negative electrode plate of this battery is about 12.5
g.

As an electrolyte, 3.8 ml of a 7 M KOH aqueous solution to which 10 g / l of LiOH and 0.6 M of zinc were added was injected.

Each of the packing member A and the safety valve body D was manufactured using a synthetic resin of various materials to produce 1,000 batteries each having the above-described structure, and these batteries were charged and discharged under the following conditions for formation.

<Electrification Conditions> In the formation, two cycles of charging and discharging are performed under the following conditions.

Charging: The battery is charged for 15 hours at a current rate of 10 hours based on the rated capacity.

Discharge: Discharge is performed at a rate of 5 hours based on the rated capacity until the terminal voltage becomes 1 V.

After charging the battery under the following conditions, the charged battery is suspended and heated from below using a Bunsen burner by the flame of city gas.
An in-fire test was conducted to determine the number of battery explosions.

<Charging Condition Before Putting into Fire> The battery is charged for 15 hours at a current of 10 hours based on the rated capacity,
Leave for a time. The material and melting point of the packing member of the battery used in this experiment, the material and melting point of the safety valve body, and the frequency of explosion due to heating (each 1000
The number of batteries that exploded out of the batteries. unit:
%) Are shown in Table 1.

[0039]

[Table 1] From Table 1, the negative electrode plate mainly composed of a hydrogen storage alloy, the positive electrode plate mainly composed of nickel hydroxide, a metal storage battery container, and the battery container and the terminals of the battery container while maintaining the hermeticity of the storage battery container In a sealed nickel-metal hydride storage battery including a thermoplastic synthetic resin packing member that electrically insulates a portion having a polarity of a positive electrode and a portion having a polarity of a negative electrode, and a synthetic resin safety valve body, When the safety valve body is made of a thermoplastic synthetic resin, if at least one of the packing member and the safety valve body has a melting point of 270 ° C. or less, the charged sealed nickel alloy
When the explosion of the metal hydride storage battery does not occur and the melting points of both the packing member and the safety valve body are higher than 270 ° C., it is understood that the explosion of the battery occurs. [Experiment 2] In place of the thermoplastic safety valve element D and the spring C in the battery used in Experiment 1, as shown in FIG. 2, a safety valve element D ′ made of a synthetic resin having rubber elasticity was used. A battery having the same configuration as that of the battery of Experiment 1 including the value of the operating pressure was manufactured.

As the safety valve element, various kinds of fluorine rubber, olefin thermoplastic elastomer, and nitrile rubber having different materials and different heat resistance temperatures were used. Note that the rubber-like elastic body of the safety valve body excluding the olefin-based thermoplastic elastomer has no melting point because it is crosslinked. And
The olefin-based thermoplastic elastomer uses polypropylene for the hard phase and ethylene propylene rubber for the soft phase, and is not vulcanized and has thermoplasticity.

Using these batteries, an in-fire experiment was performed under the same conditions as in Experiment 1.

The material and melting point of the packing member of the battery used in this experiment, the material and melting point of the safety valve body, and the frequency of explosion due to heating (the number of batteries that exploded out of 1000 batteries used in the experiment) (Unit:%) is shown in Table 2.

[0043]

[Table 2] From Table 2, the negative electrode plate mainly composed of a hydrogen storage alloy, the positive electrode plate mainly composed of nickel hydroxide, a metal storage battery container, and the battery container and terminals of the battery container while maintaining the hermeticity of the storage battery container In a sealed nickel-metal hydride storage battery including a thermoplastic synthetic resin packing member that electrically insulates a portion having a polarity of a positive electrode and a portion having a polarity of a negative electrode, and a synthetic resin safety valve body, When the safety valve element is a rubber elastic body, if the melting point of the packing member is 270 ° C. or less or the heat resistant temperature of the rubber elastic body is 230 ° C. or less, the charged battery is fired. It turns out that there is no explosion when thrown in.

In the experiment 1, a thermoplastic synthetic resin having no rubber-like elasticity was used as the safety valve body D pressed by the spring C. However, instead of this material, the safety valve D used in the experiment 2 was used. When a rubber-like elastic body is used, the same result as in Experiment 2 is obtained.

In Experiments 1 and 2, the case where a cylindrical nickel-metal hydride storage battery was used was described, but a prismatic nickel-metal hydride storage battery was used instead of the cylindrical battery. Even if it is used, the same operation and effect as the above embodiment can be obtained.

Further, in the above embodiment, the case where a hydrogen storage alloy having a specific composition is used for the negative electrode has been described.
In addition, the generation of oxygen gas due to the thermal decomposition of β-nickel oxyhydroxide on the positive electrode, such as alloys in which the mixing ratio of the constituent elements of the above alloys has been changed, alloys containing different elements, or Laves phase alloys, has been actively promoted. If the hydrogen storage alloy releases most of the stored hydrogen at a temperature lower than the temperature at which it occurs, the same operation and effect as in the above embodiment can be obtained.

[0047]

According to the present invention, an explosion does not occur even if a charged sealed nickel-metal hydride storage battery is put into a fire.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cross section of a cylindrical sealed nickel-metal hydride storage battery in which a safety valve body is pressurized by a spring.

FIG. 2 is a schematic view of a vertical section of a cylindrical nickel-metal hydride storage battery having a safety valve body having rubber elasticity itself.

[Explanation of symbols]

 A packing member made of thermoplastic synthetic resin D, D 'safety valve body made of synthetic resin F negative electrode plate G separator H positive electrode plate

Claims (1)

(57) [Claims] 1. A negative electrode plate mainly composed of a hydrogen storage alloy, a positive electrode plate mainly composed of nickel hydroxide, a metal storage battery container, and a battery container and a terminal while maintaining the hermeticity of the storage battery container. A sealed nickel-metal hydride battery comprising a thermoplastic synthetic resin packing member that electrically insulates a portion having the polarity of the positive electrode and a portion having the polarity of the negative electrode, and a safety valve body made of the synthetic resin. When the safety valve body is made of a thermoplastic synthetic resin, the packing portion
When the melting point of the material is 270 ° C. or less and the safety valve body is a rubber elastic body, the melting point of the packing member is 270 ° C.
Or the heat-resistant temperature of the rubber-like elastic body is 23
A sealed nickel-metal hydride storage battery characterized by a temperature of 0 ° C. or lower.