WO2009057893A1

WO2009057893A1 - A safeguard apparatus preventing overcharge for a secondary battery

Info

Publication number: WO2009057893A1
Application number: PCT/KR2008/005643
Authority: WO
Inventors: Hyosung Lee; Jungsik Yun; Suyoung Chang; Seungjun Lee; Jeonkeun Oh
Original assignee: SK Energy Co Ltd
Current assignee: SK Energy Co Ltd
Priority date: 2007-10-30
Filing date: 2008-09-23
Publication date: 2009-05-07
Anticipated expiration: 2010-04-30
Also published as: KR101046192B1; KR20090043717A

Abstract

The present invention relates to a safeguard apparatus preventing overcharge for a secondary battery. The safeguard apparatus preventing overcharge for a secondary battery that is comprised of a plurality of cells 10 which are arranged at regular intervals and respectively comprise a cathode 1, an anode 2 and electrolyte 3, wherein the secondary battery is comprised of a connection part 20 which is formed of a conductive material and disposed at an upper side of each cell 10; and a cut-off unit 200 which is formed of a conductive material and contacted with or separated from the connection unit 20 so as to switch on/off electric connection of the cells 10, is characterised to have a mechanical operating mechanism and is provided between the adjacent cells 10 of the secondary battery so as to convert horizontal force generated by change in volume of each cell 10 into vertical force.

Description

[DESCRIPTION]

[invention Title]

A SAFEGUARD APPARATUS PREVENTING OVERCHARGE FOR A SECONDARY BATTERY

[Technical Field]

The present invention relates to a safeguard apparatus preventing overcharge for a secondary battery.

In generally, a battery can be classified into a primary y) battery incapable of repeating charge/discharge due to an irreversible reaction and a secondary battery capable of repeating charge/discharge due to a reversible reaction. The primary battery includes a dry battery, a mercury battery, a voltaic battery and the like, and the second battery includes

") a lead battery, a lithium-ion battery, a Ni-Cd battery and the like. Among them, the Ni-Cd battery generally includes an anode formed of nickel oxide, a cathode formed of Cd compound, and KOH solution as electrolyte. Since the Ni-Cd battery is light and rechargeable, it is used as a battery of a notebook

Λ⁾ computer. However, when the Ni-Cd battery is charged before it is fully discharged, the charge starting point is erroneously recognized as the fully discharged point, so that a phenomenon called memory effect occurs. The lithium-ion battery was developed to overcome this drawback. The lithium- ion battery includes an anode formed of lithium oxide and a cathode formed of carbon. Since the lithium- ion battery can provide electric power having high voltage and high energy density, it can be formed to be smaller and lighter, and also since it is free from the problem of memory effect, it is widely used a rechargeable battery for various portable electronic instruments such as a notebook computer, PDA, and a cellular phone . As described above, the lithium- ion battery has been used

^'>) widely due to its advantages. Therefore, there have been many efforts to improve the lithium-ion battery. The lithium-ion battery generally uses liquid electrolyte. In order to further increase stability, there has been developed a lithium-ion polymer battery in which a gel-type polymer functions as a

' ,) separator membrane between an anode and a cathode and also serves as electrolyte. That is, because the lithium-ion polymer battery uses solid electrolyte having excellent conductivity, it is possible to fundamentally remove a risk of leakage and explosion of the conventional liquid electrolyte.

'!) Further, in case of a lithium metal polymer battery, a cathode is formed of lithium metal, instead of the carbon. In the following Table 1, the characteristics of the lithium-ion battery, the lithium-ion polymer batter and the lithium metal polymer battery are provided in brief. Tabl e 1

As described in Table 1, the lithium- ion polymer battery has good characteristics over the entire fields, and thus it is most widely used.

[Background Art]

However, the lithium- ion polymer battery has an unsolved problem in the stability. When the lithium-ion polymer battery is overcharged, or its temperature is unusually increased, gas is generated therein, and the battery is swelled due to the generated gas. If the swelling of the battery is continued, a battery pouch may be forcibly opened so as to exhaust the gas, or it may cause the risk of fire or explosion. To solve the problems, there have been many studies in various fields. These studies can be broadly classified into a method of chemically preventing overcharge and a method of electrically preventing overcharge, which are described below.

First, as the method of chemically preventing overcharge, which employs non-aqueous electrolyte or other electrolyte formed of a compound that is decomposed upon the overcharge, instead of the existing electrolyte, there have been disclosed Korean Patent No.0472506 entitled "Rechargeable lithium batteries comprising non-aqueous electrolyte containing polymerizable aromatic additives for overcharge protection" , Korean Patent No.0628629 entitled "Non-aqueous electrolyte for secondary battery and secondary battery comprising the electrolyte", and Korean Patent Publication No .2006-0121173 entitled "Non-aqueous electrolyte solution and lithium secondary battery" .

Second, as the method of electrically preventing overcharge, which is provided with an electric circuit for cutting off the electric power upon occurrence of overheat, overcurrent and overvoltage, or which is configured to allow a fuse to be cut off (by the overheat) , there have been disclosed Korean Patent Publication No .2007-0010755 entitled "Apparatus of stabilizating for storage battery" , Korean Patent No.0729106 entitled "Safety device for preventing overcharge and secondary battery therewith" , Japanese Patent Publication No .1993-326027 entitled "Charge control method for secondary battery", Japanese Patent Publication No .1993-234614 entitled "Cylindrical battery", Japanese Patent No.3778805 entitled "Secondary battery", Japanese Patent No.3622243 entitled "Charge-and-discharge protection instrument of rechargeable battery", Japanese Patent No.3526766 entitled "Method and circuit for inspecting function of overcharging protective circuit", Japanese Patent Publication No.2007-

¹O 028898 entitled "Charge and discharge protection circuit", and Japanese Patent Publication No.2004-088878 entitled "Battery protective circuit". In Korean Patent Publication No.2007- 0010755, if a charged voltage exceeds a predetermined voltage, the electric power is cut off so as to stop the charging. In

!.) Korean Patent No.0729106, there are provided an exothermic device for generating heat at a predetermined temperature or more and a temperature sensitive device, and the temperature sensitive device senses the heat generated from the exothermic device and then reversibly turns on and off the current. In

'?{) Japanese Patent Publication No.1993-326027 , a strain gauge is disposed at one side of the battery so as to detect a change in stress of the battery caused by increase of an internal pressure of the battery resulted from charge of the battery. When the change in stress reaches a predetermined value, the completion of the battery charge is determined so that a control unit finishes the charge. In Japanese Patent Publication No .1993-234614 , an automatic reset thermal switch or a thermal fuse is connected in series with the battery and a zener diode is connected in parallel with the battery so as to improve the overcharge characteristic. In Japanese Patent No.3778805, an additive for generating gas at a predetermined voltage or more by a chemical reaction occurred in the battery- is previously added m the battery, and an opening that is opened by the gas pressure is formed at one side of the battery. When the overcharge is occurred, a large amount of gas that is more than an amount of normally generated gas is generated m the battery and thus an internal pressure is further increased. Therefore, the opening is opened so as to exhaust the gas and heat to the outside. In Japanese Patent No.3622243, Japanese Patent No.3526766, Japanese Patent Publication No .2007-028898 and Japanese Patent Publication No.2004-088878 , an electric circuit for detecting overcurrent and overvoltage is provided at the battery.

However, m case of the method of chemically preventing overcharge, since the electrolyte used therein has lower performance compared to the recent electrolyte, it is necessary to further improve the performance. And in case of the method of electrically preventing overcharge, particularly, Japanese Patent Nos.3622243 and 3526766 and Japanese Patent Publication Nos .2007-028898 and 2004-088878, since the electric circuit has to be separately provided at the battery, the number of parts is increased, and thus it makes the ) assembling process complicated and also the manufacturing cost high. Although the other apparatuses for shutting off the current using overheat, overcurrent and overvoltage has a smaller number of parts than the methods having the electric circuit, they have to ultimately provide an additional circuit at the battery, and thus it is not possible to completely avoid the above-mentioned problems.

[Disclosure] [Technical Problem]

"j Therefore, an object of the present invention is provide a safeguard apparatus preventing overcharge for a secondary battery, which has a mechanical structure for converting horizontal force into vertical force in the battery and a switch disposed in a vertical direction so that the current is () physically cut off by using the swelling of the battery caused by gas generated upon the overcharge.

[Technical Solution]

To achieve the object, the present invention provides a safeguard apparatus preventing overcharge for a secondary battery that is comprised of a plurality of cells 10 which are arranged at regular intervals and respectively comprise a cathode 1, an anode 2 and electrolyte 3, wherein the secondary battery is comprised of a connection part 20 which is formed of a conductive material and disposed at an upper side of each cell 10; and a cut-off unit 200 which is formed of a conductive material and contacted with or separated from the connection unit 20 so as to switch on/off electric connection

) of the cells 10, is characterised to have a mechanical operating mechanism and is provided between the adjacent cells 10 of the secondary battery so as to convert horizontal force generated by change in volume of each cell 10 into vertical force .

^"> Preferably, the safeguard apparatus 100 applies the vertical force to the cut-off unit 200, when the volume of the cell 10 is increased, so that the electric connection is cut off.

Preferably, the safeguard apparatus 100a comprises a rod

:) 111 formed with at least one groove 112 at a middle portion thereof; at least a pair of fixing parts 116 that are respectively provided at faced surfaces of adjacent cells 10; at least a pair of bars 113 that are connected with the fixing parts 116 to be engaged in the groove 112 when the cell 10 is in a normal state and to be disengaged from the groove 112 when the cell 10 is in a swelled state; an elastic part 114 that is disposed between a lower end of the rod 111 and a bottom surface of a battery; and a connection stick 115 that connects an upper end of the rod 111 and a cut-off unit 200. In this case, the rod 111 and the connection stick 115 is independently manufactured and then assembled, and also integrally formed with each other.

Preferably, the safeguard apparatus 100 returns the cutoff unit 200 to its initial position, when the volume of the cell 10 is reduced, so that the electric connection between the cells is restored.

Preferably, the safeguard apparatus 100b comprises a cam 121 that is formed to be rotated around a fixing shaft 122 and have a long axis and a short axis orthogonal to each other; at least a pair of sliding surfaces 125 that are respectively provided at faced surfaces of adjacent cells 10 and contacted with an external circumferential surface of the cam 121; and a connection stick 123 that is contacted with an upper external circumferential surface of the cam 121, formed with a sliding part 124 formed at a lower end thereof to be rounded, and connected with a cut-off unit 200.

In this case, the cam 121 has a long axis and a short axis, and one of the long axis and the short axis, which is contacted with the connection stick 123 when the electric connection is cut off, is provided with an additional weight, or the cam 121 has a long axis and a short axis, and one of the long axis and the short axis, which is contacted with the F; connection stick 123 when the electric connection is cut off, is provided with an elastic means for connecting a bottom surface of the battery and the axis.

Preferably, the safeguard apparatus 100c comprises at least a pair of fixing parts 135 that are respectively

10 provided at faced surfaces of adjacent cells 10; at least a pair of upper links 131 of which one ends are respectively hinged to the fixing parts 135 and the other ends are hinged to each other so that hinged portions are directed upward or downward; and a connection stick 133 that connects a cut-off

';; unit 200 and a hinge shaft on which the upper links 131 are hinged to each other. Preferably, the safeguard apparatus 100c further comprises an elastic part that connects a bottom surface of the battery and a hinge shaft on which the upper links 131 are hinged to each other. Preferably, the safeguard i) apparatus according to claim 9, wherein the safeguard apparatus 100c further comprises at least a pair of lower links 132 of which one ends are respectively hinged to the fixing parts 135 and the other ends are hinged to each other so that hinged portions are directed upward or downward; and an elastic part 134 that connects a bottom surface of the battery and a hinge shaft on which the lower links 132 are hinged to each other.

Preferably, the safeguard apparatus 100 moves vertically upward the cut-off unit 200 when the volume of the cell 10 is increased .

Preferably, the safeguard apparatus 100 moves vertically downward the cut-off unit 200 when the volume of the cell 10 is increased. At this time, a surface of the cell 10 is formed C) of a material having a low compressive strength, or the cutoff unit 200 is formed of a material having a low flexural strength .

Further, a pair of connection units 20 and a cut-off unit

200 that are provided at a pair of cells 10 are formed to be

) separated from each other so that the cut-off unit 200 is moved vertically upward or downward, or one end of the cut-off unit 200 is connected with one of the connection units 20 and the other end of the cut-off unit 200 is connected with the other connection unit 20 so that one end of the cut-off unit

^) 200 is contacted with or separated from the connection unit 20 to switch on/off electric connection.

[Advantageous Effects]

According to the present invention, since the current can be efficiently cut off when the secondary battery is overcharged, it is possible to completely remove the risk of fire, explosion and the like caused by gas and overheat generated upon the overcharge. Particularly, in the present invention, the current can be facilely cut off using the simple mechanical structure and the swelling of the battery caused by gas generated upon the overcharge, it is possible to improve the reliability of cutting off the current. Furthermore, since the mechanical structure has a simple structure converting the horizontal force into the vertical force, it is easy and facile to design and manufacture it, and also the manufacturing cost is not so high.

[Description of Drawings]

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, m which:

Fig 1 is a schematic view of a structure of a general lithium- ion battery.

Fig. 2 is a schematic view of a safeguard apparatus preventing overcharge for a secondary battery according to the present invention.

Fig 3 is a view of a safeguard apparatus preventing overcharge for a secondary battery according to a first embodiment of the present invention.

Fig. 4 is a view of a safeguard apparatus preventing overcharge for a secondary battery according to a second embodiment of the present invention.

Fig. 5 is a view of a safeguard apparatus preventing overcharge for a secondary battery according to a third embodiment of the present invention.

[Detailed Description of Main Elements]

1 : cathode 2 : anode

3 : electrolyte 4 : wire

10: cell 20: connection unit

100: safeguard apparatus 200: cut-off unit

100a: first embodiment

111: rod 112 : groove

113: bar 114: elastic part

115 : connection stick 116 : fixing part

100b: second embodiment

121: cam 122: fixing shaft

123 : connection stick 124 : sliding part

125: sliding surface

100c : third embodiment

131: upper link 132: lower link

133: connection stick 134 : elastic part 135 : fixing part

[Best Mode]

Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings .

Fig. 1 conceptionally shows a structure of a general lithium- ion battery. The lithium-ion battery has the same structure as a lithium-ion polymer battery, except phase (liquid/solid) of electrolyte. Materials of electrodes and electrolyte may be slightly different from those in Fig. 1 according to batteries. As shown in Fig. 1, the lithium- ion battery generally includes a cathode (negative electrode) 1 formed of carbon, an anode (positive electrode) 2 formed of a lithium compound, electrolyte 3 interposed between the cathode 1 and the anode 2, and a wire 4 for connecting the cathode 1 and the anode 2. Lithium ions in the electrolyte 3 are moved to the cathode 1 upon charge of the battery and moved to the anode 2 upon discharge of the battery, and a chemical reaction occurs while each electrode emits or absorbs surplus electrons in each electrode. In this process, the electrons are moved through the wire 4 and thus electric energy is generated.

Of course, the lithium- ion battery may be comprised of the single cathode 1, the single anode 2, the single electrolyte 3 and the single wire 4. However, the lithium-ion battery is generally comprised of a plurality of cells 10 that respectively include the single cathode 1, anode 2, electrolyte 3 and wire 4 and are connected with each other. That is, the plurality of cells 10 is received in a pack of the lithium-ion battery.

Fig. 2 conceptionally shows a safeguard apparatus preventing overcharge for a secondary battery according to the present invention. As described above, the battery is comprised of the plurality of cells 10 connected with each other. Therefore, the cells 10 are connected with each other by a connection unit 20. In the present invention, a part of the connection unit 20 is cut out and then a cut-off unit 200 is disposed at a position of the cut-out part of the connection unit 20 so as to be moved up and down. When the cut-off unit 200 connects the separated connection units 20, the cells 10 are connected with each other so that the charge and discharge are normally performed.

A safeguard apparatus 100 preventing overcharge for a secondary battery according to the present invention is provided between the cells 10. As described above, when the battery is overcharged, the cells 10 are swelled by gas generated in each cell 10. Thus, a volume of each cell 10 is increased, and the safeguard apparatus 100 receives a pressure applied in a horizontal direction by the cells 10 having the increased volume. The safeguard apparatus 100 is a mechanical structure for converting horizontal force into vertical force, and thus the horizontal force applied by the swelling of the cells 10 is converted into the vertical force. As shown in Fig, 2, since the safeguard apparatus 100 is connected with the cut-off unit 200, the safeguard apparatus 100 pushes up the cut-off unit 200. As the cut-off unit 200 is pushed up, the electrical connection between the separated connection units

'0 20 is cut off, and current does not flow any longer. Therefore, since the charge of the battery is stopped, the overcharge is prevented.

It is possible to maintain the status that the cut-off unit 200 is pushed up. But it is preferable that, if the gas is exhausted from each cell 10 and the volume of each cell 10 is reduced, the safeguard apparatus 100 is returned to its original position and the cut-off unit 200 connects again the separated connection units 20 so as to turn on the current.

Fig. 2C is a schematic view of Figs. 2A and 2B, in which

O the connection unit 20 and the cut-off unit 200 are symbolized. The connection unit 20 serves as an electric wire, and the cut-off unit 200 serves as an electric switch. That is, if the connection unit 20 and the cut-off unit 200 can function as the electric wire and the electric switch, respectively, they may be formed into any shapes .

For example, in Figs. 2A, 2B and 3 to 5 , the connection unit 20 is formed into a conductive plate, but it is possible that the connection unit 20 is formed into a line and arranged

) on a surface of each cell 10. In Figs. 2A, 2B and 3 to 5 , the cut-off unit 200 is fixedly and vertically connected with the safeguard apparatus 100 and completely separated from the connection units 20 (case i) . If the safeguard apparatus 100 applies the vertical force to the cut-off unit 200, the cut-

0 off unit 200 is moved up. However, as shown in Fig. 2C, the cut-off unit 200 may be formed into a switch used in a general electric circuit (case ii) . In other words, one end of the cut-off unit 200 is hinged to or integrally formed with one of the connection units 20, and the other end of the cut-off unit i 200 is contacted with or separated from the other connection unit 20. At this time, the safeguard apparatus 100 may be fixed connected with the cut-off unit 200. But it is preferable that the safeguard apparatus 100 is just contacted with the cut-off unit 200 and slid upward so as to push up the

Λ) cut-off unit 200.

Alternatively, when the volume of the cell 10 is increased, the safeguard apparatus 100 pulls down the cut-off unit 200 to cut off the current. In this case, if the cut-off unit 200 is completely separated from the connection units 20 (case i) , the cut-off unit 200 and the connection unit 20 can have the same structure as the case that the cut-off unit 200 is pushed up, and if the cut-off unit 200 is formed into the switch used m a general electric circuit (case ii) , the cutoff unit 200 is formed to be spread downward when the external force is not applied, or one end of the cut-off unit 200 is hinged to one of the connection units 20.

(The structure that the safeguard apparatus 100 is moved up or down when the volume of the cell 10 is increased will be ; fully described m the embodiments.)

As described above, the present invention is not limited to the connection unit 20 and the cut-off unit 200 in Figs. 2A and 2B. If the connection unit 20 can serve as the electric wire and the cut-off unit 200 can serve as the electric switch ) that physically turn on/off the current, they may be formed into any shapes.

Figs. 3 to 5 exaggeratmgly show the safeguard apparatus of the present invention so as to facilely grasp its operation principle . ■^>( Embodiment 1

Fig. 3 is a view of a safeguard apparatus preventing overcharge for a secondary battery according to a first embodiment of the present invention, wherein Fig. 3A shows a normal state and Fig. 3B shows an overcharge state. The safeguard apparatus 100a includes a rod 111 formed with at least one groove 112 at a middle portion thereof; at least a pair of fixing parts 116 that are respectively provided at faced surfaces of adjacent cells 10; at least a pair of bars ) 113 that are connected with the fixing parts 116 to be engaged m the groove 112 when the cell 10 is in a normal state and to be disengaged from the groove 112 when the cell 10 is in a swelled state; an elastic part 114 that is disposed between a lower end of the rod 111 and a bottom surface of a battery; ϋ and a connection stick 115 that connects an upper end of the rod 111 and a cut-off unit 200.

As shown m a left perspective view of Fig. 3A, the bar 113 is normally engaged in the groove 112. That is, a size of a hole formed by the pair of bars 113 is equal to or greater i ) than a size of the groove 112, but smaller than a cross- section area of the rod 111 so that the bar 113 can be engaged in the groove 112.

However, if the cell 10 is swelled due to the overcharge and the volume is increased, the bars 113 are pushed and moved

'" inside as shown in the right side of Fig. 3B. Then, as shown in the left side of Fig. 3B, the hole size formed by the pair of bars 113 becomes larger than the cross-sectional area of the rod 111, and thus the rod 111 can be freely moved through the hole formed by the pair of bars 113. The lower end of the rod 111 and the bottom surface of a battery (i.e., the bottom surface on which the cells 10 are fixed) are connected to each other by the elastic part 114, and the elastic part 114 is disposed to be normally in a compressed state as shown in Fig. 3A. Therefore, if the bar 113 is disengaged from the groove 112 and thus the rod 111 can be freely moved, the rod 111 is pushed up by an elastic force of the elastic part 114.

At this time, since the rod 111 is connected with the cut-off unit 200 via the connection stick 115, if the rod 111 is pushed up by the elastic part 114, the cut-off unit 200 is also moved upward and thus the electrical connection between the connection units 20 that electrically connects each cell 10 is cut off. Therefore, the charge is not performed any longer, and it is possible to remove the risk of fire and explosion and the like due to the overcharge of the battery.

In Fig.3, one pair of bars 113 are provided, however, several pairs of bars 113 may be provided. Of course, if several pairs of bars are provided, a plurality of grooves 112 corresponding to the number of bars 113 have to be provided.

The fixing part 116 serves only to fix the bar 113. As shown in Fig. 3, the fixing part 116 can be formed into a wide plate so as to be deformed along the deformation of the cell 10. Alternatively, the fixing part 116 may be formed to have a narrow surface area as shown in Fig. 5. In case that several pairs of the bars 113 are provided, if the fixing part 116 is formed to have a wide surface area as shown in Fig. 3, only- one pair of fixing parts 116 can be provided. However, if the fixing part 116 is formed to have the narrow surface area as shown in Fig. 5, several pairs of fixing parts 116 may be provided to be correspondent to the bars 113.

The rod 111 can have any cross-sectional shape, such as a polygon, a circle, an oval and the like, only if the groove 112 engaged or disengaged with the bar 113 can be formed. Further, the rod 111 and the connection stick 115 may be independently manufactured and then assembled, and also they may be integrally formed with each other.

Embodiment 2

Fig. 4 is a view of a safeguard apparatus preventing overcharge for a secondary battery according to a second embodiment of the present invention, wherein Fig. 4A shows a normal state and Fig. 4B shows an overcharge state. As shown in drawings, the safeguard apparatus 100b includes a cam 121 that is formed to be rotated around a fixing shaft 122 and have a long axis and a short axis orthogonal to each other,- at least a pair of sliding surfaces 125 that are respectively provided at faced surfaces of adjacent cells 10 and contacted with an external circumferential surface of the cam 121; a connection stick 123 that is contacted with an upper external circumferential surface of the cam 121, formed with a sliding part 124 formed at a lower end thereof to be rounded, and ) connected with a cut-off unit 200.

The cam 121 is formed to have a large diameter in one direction and a small diameter orthogonal to the large diameter. As shown in Fig. 4A, both ends of the long axis of the cam 121 are contacted with the sliding surfaces 125 in the ;; normal state, and thus the sliding part 124 formed at the lower end of the connection stick 123 is contacted with an end of the short axis of the cam 121.

When the cell 10 is swelled by the overcharge and its volume is increased, a distance between the cells 10 is

> decreased as shown in Fig. 4B. As the distance between the cells 10 is decreased, the cam 121 is slid and rotated along the sliding surfaces 125. Thus, the sliding part 124 of the connection stick 123 becomes contacted with the end of the long axis of the cam 121, the connection stick 123 is

Λ) gradually moved upward and the cut-off unit 200 is pushed up, thereby cutting off the electrical connection between the connection units 20.

At this time, the long axis of the cam 121 is naturally directed downward due to characteristic of its own shape, if there is not any object that restricts the cam 121. That is, if the gas is exhausted from each cell 10 and the volume of the cell 10 is reduced, the distance between the cells 10 becomes wide again and the cam 121 is returned from the state of Fig. 4B to the state of Fig. 4A.

In case of the first embodiment (Fig. 3, 100a), although the distance between the cells 10 becomes wide again, it is impossible to be automatically returned to the initial state. Only when the cut-off unit 200 is pushed down by external force, the state of Fig. 3B can be returned to the Fig. 3A. However, in case of the second embodiment (100b) , the states of Figs. 4A and 4B can be irreversibly changed.

Preferably, in order to facilely return to the initial state in the second embodiment (100b) , an additional weight is further provided at the long axis of the cam 121, or the long axis of the cam 121 is connected with the bottom surface through an elastic means like a spring.

Embodiment 3

Fig. 5 is a view of a safeguard apparatus preventing overcharge for a secondary battery according to a third embodiment of the present invention, wherein Fig. 5A shows a normal state and Fig. 5B shows an overcharge state. As shown in drawings, the safeguard apparatus 100c includes at least a pair of fixing parts 135 that are respectively provided at faced surfaces of adjacent cells 10; at least a pair of upper links 131 of which one ends are respectively hinged to the fixing parts 135 and the other ends are hinged to each other so chat hinged portions are directed upward or downward; and a

; connection stick 133 that connects a cut-off unit 200 and a hinge shaft on which the upper links 131 are hinged to each other. The safeguard apparatus 100c further includes at least a pair of lower links 132 of which one ends are respectively hinged to the fixing parts 135 and the other ends are hinged

>) to each other so that hinged portions are directed upward or downward; and an elastic part 134 that connects a bottom surface of the battery and a hinge shaft on which the lower links 132 are hinged to each other, whereby it is possible to facilely return to an initial position. Fig. 5 shows the third i embodiment 100c that the hinged portions of the upper links 131 are directed upward and the hinged portions of the lower links 132 are directed downward, and also the lower links 132 and the elastic part 134 are provided so as to improve returning performance. Furthermore, although not shown in the

.⁾ drawing, the elastic part 134 may be directly connected with the hinge shaft of the upper links 131.

As shown in the drawing, the fixing part 135 is provided on a surface of the cell 10. In the embodiment 100c of Fig. 5, the fixing part 135 has a small surface. However, it may have a large surface like in the first embodiment (Fig. 3, 100a) .

The fixing part 135 is provided on the surface of each cell 10, and one end of each upper link 131 is hinged to each fixing part 135. The other ends of the upper links 131 are hinged to each other. Since the cut-off unit 200 and the hinge shaft on which the upper links 131 are hinged to each other are connected through the connection stick 133, if the volume of the cell 10 is increased and the distance between the cells 10 is reduced, the upper links 131 are folded and thus the cut-off unit 200 is moved upward.

If gas m the cell 10 is exhausted and the volume of the cell 10 is reduced in the status that electric power is cut off, the distance between the cells 10 becomes wide again. Therefore, an angle between the upper links 131 is also increased, and the cut-off unit 200 is moved downward so as to connect again the connection units 20, thereby restoring the electric connection.

In order to facilely restore the electric connection, an elastic part may be interposed between the bottom surface of the battery and the hinge shaft on which the upper links 131 are hinged to each other. In this case, the hinge shaft of the upper links 131 has the same displacement as the cut-off 200. Therefore, if the cut-off unit 200 is moved upward, the elastic part is stretched and the hinge shaft the upper links 131 receives restoring force that is directed downward by the elastic force, so that the upper link 131 and the cut-off unit 200 can be facilely returned to their initial positions.

If the elastic part is not connected to the hinge shaft of the upper links 131, the lower links 132 are provided at the fixing parts 135 to be directed downward in the same manner of the upper links 131, and then the elastic part is disposed at the hinge shaft of the lower links 132, thereby obtaining the same effect as shown in Fig. 5.

In the above-mentioned three embodiments, if the safeguard apparatus 100 receives the horizontal force due to the reduced distance between the cells, the safeguard apparatus 100 converts the horizontal force into the vertical upward force so that the cut-off unit 200 is pushed up. However, the safeguard apparatus 100 may convert the horizontal force into the vertical downward force so that the cut-off unit 200 is pushed down so as to cut off the electric connection. Of course, it needs a precondition that the cutoff unit 200 should be not fitted tightly between the cells 10 when the volume of the cells is increased. In case that the electric connection is cut off by the downward movement of the cut-off unit 200, it is preferable that the surface of the cell 10 is formed of a soft material so that the movement of the cut-off unit 200 is not obstructed, or the cut-off unit 200 is formed of a flexible material so as to be easily movable through the narrowed distance.

In order to move down the cut-off unit 200, for example, the second embodiment 100b has the initial position of the cam 121 that the long axis is directed longitudinally and the short axis is directed transversely. In this case, an additional weight or spring is further provided at the short axis. And in case of the third embodiment 100c of Fig. 5, the elastic part 134 is connected to the hinge shaft of the upper links 131, and the connection stick 133 is connected to the hinge shaft of the lower links 132. Besides these constructions, any other configuration for moving down the cut-off unit 200 may be employed in the spirit and scope of inc invent ion .

''hose ski Med in the art will appreciate that the concept, i OPS and specific embodiments disclosed in the ¹ ørcqoi nq description may be readily utilized as a basis ¹Gf nodi ry.nq or designing other embodiments for carrying o.! the same purposes of the present invention. Those ski ' OO r the art will also appreciate that such GOu v«'o^rM omood i men t s do not depart from the spirit and hcoDo o^f lie 'nvent ion as set forth in the appended claims. [industrial Applicability]

Claims

[CLAIMS]

[Claim l]

A safeguard apparatus preventing overcharge for a secondary battery that is comprised of a plurality of cells 10 which are arranged at regular intervals and respectively comprise a cathode 1, an anode 2 and electrolyte 3, wherein the secondary battery is comprised of a connection part 20 which is formed of a conductive material and disposed at an upper side of each cell 10; and a cut-offO unit 200 which is formed of a conductive material and contacted with or separated from the connection unit 20 so as to switch on/off electric connection of the cells 10, is characterised to have a mechanical operating mechanism and is provided between the adjacent cells 10 of the secondary ) battery so as to convert horizontal force generated by change m volume of each cell 10 into vertical force. [Claim 2]

The safeguard apparatus according to claim 1, wherein the safeguard apparatus 100 applies the vertical force to the cut-!) off unit 200, when the volume of the cell 10 is increased, so that the electric connection is cut off. [Claim 3]

The safeguard apparatus according to claim 2, wherein the safeguard apparatus 100a comprises: a rod 111 formed with at least one groove 112 at a middle portion thereof; at least a pair of fixing parts 116 that are respectively provided at faced surfaces of adjacent cells 10; at least a pair of bars 113 that are connected with the fixing parts 116 to be engaged in the groove 112 when the cell 10 is in a normal state and to be disengaged from the groove 112 when the cell 10 is in a swelled state,- an elastic part 114 that is disposed between a lower end ) of the rod 111 and a bottom surface of a battery; and a connection stick 115 that connects an upper end of the rod 111 and a cut-off unit 200.

[Claim 4]

The safeguard apparatus according to claim 3, wherein the rod 111 and the connection stick 115 is independently manufactured and then assembled, and also integrally formed with each other.

[Claim 5]

The safeguard apparatus according to claim 2, wherein the O safeguard apparatus 100 returns the cut-off unit 200 to its initial position, when the volume of the cell 10 is reduced, so that the electric connection between the cells is restored.

[Claim 6]

The safeguard apparatus according to claim 5, wherein the safeguard apparatus 100b comprises: a cam 121 that is formed to be rotated around a fixing shaft 122 and have a long axis and a short axis orthogonal to each other; at least a pair of sliding surfaces 125 that are respectively provided at faced surfaces of adjacent cells 10 and contacted with an external circumferential surface of the cam 121; and a connection stick 123 that is contacted with an upper v) external circumferential surface of the cam 121, formed with a sliding part 124 formed at a lower end thereof to be rounded, and connected with a cut-off unit 200. [Claim 7]

The safeguard apparatus according to claim 6, wherein the ) cam 121 has a long axis and a short axis, and one of the long axis and the short axis, which is contacted with the connection stick 123 when the electric connection is cut off, is provided with an additional weight.

[Claim 8]

O The safeguard apparatus according to claim 6, wherein the cam 121 has a long axis and a short axis, and one of the long axis and the short axis, which is contacted with the connection stick 123 when the electric connection is cut off, is provided with an elastic means for connecting a bottom surface of the battery and the axis. [Claim 9]

The safeguard apparatus according to claim 5, wherein the safeguard apparatus 100c comprises:

1 at least a pair of fixing parts 135 that are respectively- provided at faced surfaces of adjacent cells 10; at least a pair of upper links 131 of which one ends are respectively hinged to the fixing parts 135 and the other ends are hinged to each other so that hinged portions are directed J) upward or downward; and a connection stick 133 that connects a cut-off unit 200 and a hinge shaft on which the upper links 131 are hinged to each other .

[Claim IO] j The safeguard apparatus according to claim 9, wherein the safeguard apparatus 100c further comprises an elastic part that connects a bottom surface of the battery and a hinge shaft on which the upper links 131 are hinged to each other.

[Claim 11]

! The safeguard apparatus according to claim 9, wherein the safeguard apparatus 100c further comprises: at least a pair of lower links 132 of which one ends are respectively hinged to the fixing parts 135 and the other ends are hinged to each other so that hinged portions are directed upward or downward; and an elastic part 134 that connects a bottom surface of the battery and a hinge shaft on which the lower links 132 are hinged to each other. [Claim 12]

The safeguard apparatus according to any one of claims 1 to 11, wherein the safeguard apparatus 100 moves vertically upward the cut-off unit 200 when the volume of the cell 10 is increased . [Claim 13]

The safeguard apparatus according to any one of claims 1 to 11, wherein the safeguard apparatus 100 moves vertically- downward the cut-off unit 200 when the volume of the cell 10 is increased. [Claim 14]

The safeguard apparatus according to claim 13, wherein a surface of the cell 10 is formed of a material having a low compressive strength. [Claim 15]

The safeguard apparatus according to claim 13, wherein the cut-off unit 200 is formed of a material having a low flexural strength .

[Claim 16]

The safeguard apparatus according to any one of claims 1 to 11, wherein a pair of connection units 20 and a cut-off unit 200 that are provided at a pair of cells 10 are formed to be separated from each other so that the cut-off unit 200 is moved vertically upward or downward, or one end of the cut-off unit 200 is connected with one of the connection units 20 and the other end of the cut-off unit 200 is connected with the other connection unit 20 so that one end of the cut-off unit 200 is contacted with or separated from the connection unit 20 to switch on/off electric connection.