JPH04196063A - sealed lead acid battery - Google Patents

Abstract

PURPOSE:To prevent head from running away by arranging a thermal deforma tion member, which is deformed with temperature rise to pressurize a sealed unit lead-acid battery in a laminated direction, between the sealed unit lead-acid battery and a case. CONSTITUTION:A thermal deformation member 5 which is arranged between a unit lead-acid battery 1 located outside in a laminated direction and a case 4 is formed of shape memorizing alloy. The thermal deformation member 5 consists of the base 5a and the reverse section 5b in which a slit 5b1 is formed to separate the reverse section 5b in two for easy reversal and which is protruded from the surface of the base 5a to one direction into a convex form. When the reverse section 5b is heated to a preset temperature depending on the shape memorizing alloy to be used it reverses its direction protruded from the surface of the base 5a in accordance with shape memorization. In this way, as temperature rises in the case 4, the thermal deformation member 5 is deformed to pressurize the unit lead-acid battery 1 to a laminated direction, so that when heat starts running away electrolyte is filled into porosities in a negative plate to restrain the negative plate from absorbing oxygen gas. It is thus possible to restrain heat from running away.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to improvements in sealed lead-acid batteries.

(Prior art) In recent years, sealed lead-acid batteries that use at least one film-pack sealed unit lead-acid battery have been developed as sealed lead-acid batteries used in portable electronic devices that have become smaller and lighter. It is used. FIG. 5 is a partially enlarged view of an example of a film-pack type sealed unit lead-acid battery 1 (hereinafter simply referred to as a unit lead-acid battery) constituting a unit cell of this type of sealed lead-acid battery. This unit lead-acid battery 1 is
It is composed of an electrode plate group 2 as a battery element in which a positive electrode plate and a negative electrode plate are laminated with a separator interposed therebetween, and a bag-like exterior body 3 that houses the electrode plate group 2. The bag-like exterior body 3 is made of a sheet-like or film-like thermoplastic synthetic resin that is acid-resistant and heat-adhesive. Some conventional sealed lead-acid batteries are formed by housing at least one of these unit lead-acid batteries in a rigid case. To obtain a high voltage, the required number of unit lead-acid batteries are connected in series, and each unit lead-acid battery is housed in a polymerized state in a case.

(Problems to be Solved by the Invention) This type of sealed lead-acid battery is used for so-called cyclic charging and discharging applications in which charging and discharging are repeated, for example, as a power source for electronic devices such as portable handheld word processors. However, in sealed lead-acid batteries used for cyclic charging and discharging applications, when charging and discharging are repeated, the positive electrode active material gradually softens, the bonding force between the particles of the positive electrode active material decreases, and the battery capacity decreases. Furthermore, when charging and discharging are repeated, the spongy lead of the negative electrode active material contracts and undergoes a morphological change in which the particles expand. In a battery that is in such a state due to repeated charging and discharging, the positive electrode plate tends to generate oxygen gas during charging, and the negative electrode plate is always in a state of absorbing oxygen gas. Especially when the charge amount is 1
When it exceeds 00%, oxygen gas starts to be generated rapidly. When the oxygen gas generated in this way is absorbed by the negative electrode plate,
The negative electrode plate generates heat and the battery voltage decreases. When charging is further performed and a charging current flows, the absorption of oxygen gas by the negative electrode plate further increases and the temperature rises. In a sealed lead-acid battery, when a heat escape phenomenon occurs in which the charging current is used to generate oxygen gas, the rated capacity ratio of the battery decreases and the charge/discharge characteristics of the battery deteriorate.

(Means for Solving the Problems) The present invention is directed to a sealed lead-acid battery comprising at least one film pack type sealed unit lead-acid battery housed in a rigid case. A thermally deformable member is disposed between the unit lead-acid battery and the case, which deforms when the temperature inside the case rises to a predetermined temperature, pressurizes the unit lead-acid battery in the stacking direction, and returns to its original shape when the temperature drops. Here, the lamination direction is the direction in which cathode plates and anode plates constituting a unit lead-acid battery are laminated, or the direction in which a plurality of unit lead-acid batteries are laminated. Formed from memory alloy or bimetal.

(Function) In a normal state, the unit lead-acid battery is restrained by the case and pressurized with a predetermined pressure in the stacking direction, and electrolyte is supplied from the separator to the negative electrode plate. The oxygen gas absorption ability of the negative electrode plate is affected by the amount of electrolyte contained in the negative electrode plate. That is, if the electrolytic solution fills the pores of the active material of the negative electrode plate, oxygen gas absorption by the negative electrode plate can be suppressed. However, pressurization by the case cannot suppress oxygen gas in an overcharged state. Therefore, if the thermally deformable member is arranged as in the invention of claim 1, when the temperature inside the case rises at the stage where the thermal escape phenomenon starts to occur, the thermally deformable member deforms and pressurizes the unit lead-acid battery in the stacking direction. The electrolytic solution contained in the separator can be positively moved into the pores of the negative electrode plate by the pressing force generated by the thermally deformable member.

As a result, according to the present invention, it is possible to replenish the negative electrode plate with the electrolytic solution necessary for suppressing oxygen gas absorption before the thermal escape phenomenon occurs, so that the occurrence of the thermal escape phenomenon can be prevented.

Further, when the thermally deformable member is made of a shape memory alloy or a bimetal as in the invention of claim 2, there is an advantage that it is easy to set the temperature at which the thermally deformable member deforms so as to pressurize the unit lead-acid batteries in the stacking direction. . By the way - when fishing on a boat, the battery temperature at which there is a risk of heat loss occurring is approximately 50℃.
'C.

(Example) An example of the present invention will be described in detail with reference to the drawings. The battery of the present invention is characterized by the structure between the unit lead-acid battery and the case, and the structure of other parts is the same as that of conventional batteries. Therefore, FIG. 1 schematically shows the structure between a unit lead-acid battery and a case at room temperature. In the figure 1.
... is a known film-pack type sealed unit lead-acid battery shown in FIG. It is stored in. The case 4 is made of a synthetic resin case or a metal case, and has sufficient rigidity to be able to pressurize the unit lead-acid batteries in the stacking direction. Reference numeral 5 denotes a thermally deformable member disposed between the unit lead-acid battery 1 and the case 4 located on the outer side in the stacking direction, and in this embodiment, the thermally deformable member 5 is made of a shape memory alloy. FIG. 2 is a front view of the thermally deformable member 5 formed of a shape memory alloy. As shown in the figure, the thermally deformable member 5 has a base portion 5
a and a reversing part 5b, and the reversing part 5b has a slit 5b that divides the reversing part 5b into one part so that reversing can be easily performed.
l is formed. The inverted portion 5b protrudes convexly in one direction from the surface of the base portion 5a. When this reversing portion 5b is heated to a predetermined temperature determined by the shape memory alloy used, it reverses the direction of protrusion from the surface of the base portion 5a based on shape memory. In the battery of this embodiment, the material of the thermally deformable member 5 is selected so that the inversion part 5b is inverted at the temperature (50° C.) at which the thermal escape phenomenon begins to occur.

In this embodiment, in order to secure a space for accommodating the inverted portion 5b before thermal deformation, the case 4 is provided with a stepped portion 4a that comes into contact with the periphery of the base portion 5a of the thermally deformable member 5.

FIG. 3 is a diagram showing the state when the temperature inside the case reaches 50° C. and the thermal escape phenomenon begins to occur when the battery is used. As shown in the figure, the reversing portion 5b reverses the direction of protrusion from the surface of the base portion 5a, and pressurizes the unit lead-acid batteries 1 in the stacking direction (arrow P).

Due to this pressurization, the electrolytic solution contained in the separator in the unit lead-acid battery 1 moves into the pores of the negative electrode plate.

Then, the negative electrode plate comes to sufficiently contain the electrolyte, and absorption of oxygen gas by the negative electrode plate is suppressed.

In order to confirm the effects of the present invention, six 500 mA unit lead-acid batteries were made and housed in a case, and a thermally deformable member was placed between the unit lead-acid batteries and the case in the same way as the batteries in the example. A battery A of the invention and a conventional battery B having the same cell group as this battery A but without a thermally deformable member were manufactured. Then, each battery was repeatedly discharged and charged under the following conditions to examine the charging and discharging characteristics of Battery A of the present invention.

Discharge: 0.17CA, time: 4hr Charging: 0.
3CA, cut voltage: 2.45V/cell (charging at 120% of discharge amount), liquid temperature: 25°C. Figure 4 shows the charge/discharge characteristics of each battery measured under the above conditions. The horizontal axis represents the number of times, and the rated capacity ratio is represented on the vertical axis. In the figure, curve A is the characteristic curve of battery A of the present invention, and curve B is the characteristic curve of conventional battery B. This figure shows that conventional battery B has a rated capacity ratio of 75 after about 340 charging and discharging cycles, while battery A of the present invention only reaches a rated capacity ratio of 75 even after about 500 charging and discharging cycles. It can be seen that it does not decrease. As described above, according to the battery of the present invention, the charging and discharging characteristics can be significantly improved.

In the battery of the above embodiment, the thermally deformable member is formed using a shape memory alloy, but the thermally deformable member may also be formed of other thermally deformable materials such as bimetals that change shape depending on temperature differences. Of course it's good. Furthermore, the shape of the thermally deformable member is not limited to the example, and may be any shape as long as it can press the unit lead-acid battery in the stacking direction with a greater force after thermally deformed than before thermally deformed. good.

In addition, in the battery of this example, a thermally deformable member was placed between one side of the cell group and the case, but thermally deformable members were placed on both sides of the cell group and the unit lead-acid battery was pressurized from both sides in the stacking direction. Of course, it is okay to do so.

(Effects of the present invention) According to the invention of claim 1, when the temperature inside the case rises to a temperature at which a heat escape phenomenon begins to occur, the thermally deformable member deforms and pressurizes the unit lead-acid batteries in the stacking direction. When the escape phenomenon starts to occur, the electrolytic solution can be filled into the pores of the negative electrode plate, and oxygen gas absorption by the negative electrode plate can be suppressed. Therefore, according to the present invention, it is possible to suppress the thermal escape state and improve the charging and discharging characteristics of the battery.

Further, according to the second aspect of the invention, since the thermally deformable member is formed from a shape memory alloy or a bimetal, the temperature at which the thermally deformable member deforms so as to pressurize the unit lead-acid battery in the stacking direction can be accurately set.

Therefore, it becomes possible to suppress the thermal escape state more reliably and improve the charging and discharging characteristics of the battery.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure between a unit lead-acid battery and a case in a normal state of a battery according to an embodiment of the present invention, and FIG.
The figure is a front view of the thermally deformable member used in the embodiment of Fig. 1;
FIG. 3 is a schematic diagram showing the structure between the unit lead-acid battery of the embodiment of FIG. 1 and the case when the temperature inside the case increases, and FIG. FIG. 5, which is a diagram showing the measurement of the charging and discharging characteristics of the battery, is an enlarged partially cutaway view of a film pack type unit lead-acid battery. DESCRIPTION OF SYMBOLS 1... Film pack type unit lead-acid battery, 2... Plate group, 3... Bag-like exterior body, 4... Case, 5... Heat deformable member ElmB, Betsunin

Claims (2)

[Claims] (1) In a sealed lead-acid battery in which at least one film-pack type sealed unit lead-acid battery is housed in a rigid case, between the sealed unit lead-acid battery and the case, the inside of the case A sealed lead-acid battery, characterized in that a thermally deformable member is disposed that deforms when the temperature of the unit rises to a predetermined temperature to pressurize the sealed unit lead-acid battery in the stacking direction, and returns to its original shape when the temperature falls. (2) The sealed lead-acid battery according to claim 1, wherein the thermally deformable member is formed of a shape memory alloy or a bimetal.