JP7321731B2 - Battery pack, protection circuit - Google Patents

Description

The present technology relates to a battery pack including a protection element that blows a fuse element provided on a charging/discharging current path to cut off the charging/discharging current path, and a protection circuit.

In recent years, lithium ion secondary batteries have been used in many applications, from home appliances such as mobile phones and notebook PCs to power tools and electric vehicles. A lithium-ion secondary battery has a high energy density and is suitable for high output. However, when an excessive current is output, the internal resistance of the battery itself generates heat, and there is a risk of smoke and fire. For this reason, in order to ensure the safety of users and electronic devices, in general, a number of protection circuits such as overcharge protection and overdischarge protection are built into the battery pack, and a PTC (Positive Temperature Coefficient) element is used for charging and discharging. It has a function of interrupting the input/output of the battery pack in a predetermined case by connecting it in series with the current path.

However, since the element resistance of the PTC rises with temperature and the current is limited by the resistance, connecting the PTC increases the direct current resistance of the circuit, making it unsuitable for applications in which a large current flows. In addition, the method of protection by the protection circuit is mainly FET, which controls the conducting current, so that the DC resistance value can be kept low, but semiconductors have the risk of malfunctioning in high temperature environments.

In a battery system such as a lithium-ion secondary battery, a method has been proposed in which a fuse element is connected to the charging/discharging circuit of the battery cell, and the charging/discharging circuit is cut off by blowing the fuse with the heat of the heating resistor. It is For example, in the protection circuit 100 shown in FIG. It includes a control IC 104 that monitors and outputs a control signal to the FET 102 when the battery stack 103 is abnormal, and a fuse 105 that is connected to the charging/discharging path of the battery stack 103 .

In the protection circuit 100, the FET 102 restricts the energization of the heating resistor 101 when the battery stack 103 is normal. When the control IC 104 detects an abnormality such as overcharging or overdischarging of the battery stack 103 , the protection circuit 100 causes the FET 102 to energize the heating resistor 101 . As a result, the protection circuit 100 melts the fuse 105 due to the heat generation of the heating resistor 101 , and cuts off the charging/discharging path of the battery stack 103 .

JP-A-2006-109596

However, the protection circuit 100 requires the FET 102 and the control IC 104 for controlling the FET 102 in order to control the energization of the heating resistor 101, which causes an increase in the number of parts and the number of assembly steps, and also exposes the circuit to a high-temperature environment. If the control IC 104 fails in this case, the fuse 105 may not be fused.

The present technology has been proposed in view of such conventional circumstances. The purpose is to provide a circuit.

In order to solve the above-described problems, a battery pack according to the present technology includes a battery cell, a protection element connected in series with the battery cell, and a heat-sensitive element that controls operation of the protection element. The protection element includes an insulating substrate, a first terminal portion and a second terminal portion which are spaced apart from the insulating substrate and connected to a charging/discharging path of the battery cell, and the first terminal portion. A fuse element provided between the second terminal portion and a heating resistor connected in series with the heat sensitive element and controlled in energization, wherein the heat sensitive element is a thermostat, a thermistor, or It is either a diode, and when the heat-sensitive element is heated to a temperature equal to or higher than a predetermined temperature, the heating resistor is energized to generate heat to a temperature that melts the fuse element.

Further, the protection circuit according to the present technology is configured to energize first and second electrodes connected to an external circuit and a fuse provided in series on a current path extending between the first and second electrodes. and a heat-sensitive element for controlling energization of the heat-generating resistor, wherein the heat-sensitive element is either a thermostat, a thermistor, or a diode, and the heat-sensitive element is heated to a temperature equal to or higher than a predetermined temperature, the heating resistor is energized so as to generate heat to a temperature that melts the fuse.

According to the present technology, by activating the protection element using the heat-sensitive element, it is possible to reliably cut off the charge/discharge current path of the battery cell without the risk of malfunction even when exposed to a high-temperature environment.

FIG. 1 is a circuit diagram showing a configuration example of a battery pack to which the present technology is applied. 2A and 2B are views showing the protection element, FIG. 2A being a plan view with the cover member omitted, and FIG. FIG. 3 is a perspective view showing an example of a fuse element. FIG. 4 is a circuit diagram of a battery pack using a thermostat as a heat-sensitive element, (A) showing the state before the thermostat is heated, and (B) showing the state in which the thermostat is heated and the fuse element is blown. . FIG. 5 is a circuit diagram of a battery pack using a thermistor as a heat sensitive element. FIG. 6 is a circuit diagram of a battery pack using diodes as heat sensitive elements. FIG. 7 is a circuit diagram of a battery pack equipped with a protection IC and a switch for detecting abnormal voltages of battery stacks and battery cells, in addition to heat-sensitive elements. FIG. 8 is a diagram showing the circuit configuration of a conventional battery pack.

A battery pack and a protection circuit to which the present technology is applied will be described in detail below with reference to the drawings. In addition, the present technology is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present technology. Also, the drawings are schematic, and the ratio of each dimension may differ from the actual one. Specific dimensions and the like should be determined with reference to the following description. In addition, it goes without saying that there are portions with different dimensional relationships and ratios between the drawings.

[Battery pack]
A battery pack to which the present technology is applied can be configured, for example, as a battery pack 10 of lithium-ion secondary batteries, as shown in FIG. The battery pack 10 shown in FIG. 1 includes, for example, a battery stack 15 made up of a plurality of lithium-ion secondary battery cells 15a, a protection element 11 connected in series with the battery stack 15, and the operation of the protection element 11. It has a heat sensitive element 12 that

The protection element 11 cuts off the charging/discharging path of the battery stack 15 when the battery pack 10 becomes abnormal. The heat-sensitive element 12 changes electrical characteristics such as on/off of conduction, resistance value, and output voltage due to heat, and activates the protection element 11 when heated to a temperature equal to or higher than a predetermined temperature. That is, in the battery pack 10 , the operation of the protection element 11 is controlled according to variations in the electrical characteristics of the heat-sensitive element 1 .

The battery stack 15 includes battery cells 15a connected in series and/or in parallel that require control to protect against overvoltage, overcurrent, and the like. It is connected to the charging device 13 so that the charging voltage from the charging device 13 is applied. By connecting the positive terminal 10a and the negative terminal 10b of the battery pack 10 charged by the charging device 13 to an electronic device operated by the battery, the electronic device can be operated.

The battery pack 10 has a charge/discharge control circuit 16 that controls charge/discharge of the battery stack 15 . The charge/discharge control circuit 16 includes two current control elements 17 and 18 connected in series to a current path flowing from the battery stack 15 to the charging device 13, and a control section 19 that controls the operation of these current control elements 17 and 18. Prepare. The current control elements 17 and 18 are composed of, for example, field effect transistors (hereinafter referred to as FETs), and the control section 19 controls the gate voltage to control the charging direction and/or discharging direction of the current path of the battery stack 15. control the conduction and interruption of the When the battery stack 15 is over-discharged or over-charged, the control unit 19 operates by receiving power from the charging device 13, and detects the voltage of each battery cell 15a according to the detection result of a detection circuit (not shown). It controls the operation of the current control elements 17 and 18 so as to cut off the current path.

[Protection element]
Protection element 11 is connected, for example, on a charge/discharge current path between battery stack 15 and charge/discharge control circuit 16 , and its operation is controlled by heat sensitive element 12 . Specifically, as shown in FIGS. 2A and 2B, the protection element 11 includes an insulating substrate 26, first and second electrodes 22 and 23 formed on the insulating substrate 26, and an insulating substrate 26. a heating resistor 24 formed on the surface of the heating resistor 24, an insulating layer 27 covering the heating resistor 24, a heating element lead-out electrode 21 laminated on the insulating layer 27 and connected to the heating resistor 24, a first , a heating element lead-out electrode 21, and a fuse element 20 mounted over the second electrode 23 via connection solder 28. As shown in FIG.

The first and second electrodes 22 and 23 are first and second terminal portions connected to the charging/discharging path of the battery cell 15a, and are formed on the rear surface of the insulating substrate 26, respectively. are connected to external connection electrodes 22a and 23a via castellations. The heating resistor 24 is connected to a heating element power supply electrode 25 and is connected to the heat sensitive element 12 via the heating element power supply electrode 25 . Further, the heating resistor 24 is connected to the fuse element 20 and the charging/discharging path of the battery stack 15 by electrically connecting the heating element lead-out electrode 21 to the fuse element 20 .

[Insulating substrate]
The insulating substrate 26 is made of an insulating material such as alumina, glass ceramics, mullite, or zirconia, and is formed in, for example, a substantially rectangular shape. The insulating substrate 26 may also be made of materials used for printed wiring boards, such as glass epoxy substrates and phenolic substrates.

First and second electrodes 22 and 23 are formed on opposite ends of the insulating substrate 26 . The first and second electrodes 22 and 23 are formed of conductive patterns such as Ag and Cu, respectively. The first and second electrodes 22 and 23 are connected to the first and second external connection electrodes 22a and 23a formed on the back surface 26b via castellations from the front surface 26a of the insulating substrate 26. . In the protection element 11, the first and second external connection electrodes 22a and 23a formed on the back surface 26b of the insulating substrate 26 are connected to the connection electrodes provided on the external circuit board on which the protection element 11 is mounted. , the fuse element 20 is incorporated into a portion of the current path formed on the circuit board.

[heating resistor]
The heating resistor 24 is a conductive member that has a relatively high resistance and generates heat when energized, and is made of, for example, nichrome, W, Mo, Ru, or a material containing these. The heat generating resistor 24 is made by mixing the powder of these alloys, compositions, or compounds with a resin binder or the like, making a paste, forming a pattern on the insulating substrate 26 using a screen printing technique, and firing it. It can be formed by, for example,

Heating resistor 24 is thermally connected by overlapping fuse element 20, and melts fuse element 20 when heated by energization. One end of the heating resistor 24 is connected to the heat-sensitive element 12, so that current and heat generation are always regulated. The heating resistor 24 increases the amount of heat generated by an increase in the current due to the energization of the heat-sensitive element 12 and the decrease in electrical resistance, and the fuse element 20 can be fused. As will be described later, the heating resistor 24 is also electrically connected to the fuse element 20 .

[Fuse element]
The protective element 11 is connected to the fuse element 20 by connecting solder 28 across the first electrode 22 and the second electrode 23 . The fuse element 20 conducts between the first and second electrodes 22 and 23 during normal use, and constitutes part of the current path of the external circuit in which the protection element 11 is incorporated. The fuse element 20 is fused due to self-heating (Joule heat) when a current exceeding the rated current is applied, or fused due to the heat generated by the heating resistor 24, thereby disconnecting the first and second electrodes 22 and 23. do.

The fuse element 20 has a predetermined rated current value, and quickly melts due to heat generation of the heating resistor 24 or self-heating when a current exceeding the rated current value is applied. The fuse element 20 is preferably composed mainly of any one selected from nickel, tin, and lead. In addition, in this specification, the main component refers to a component that is 50 wt % or more based on the total mass of the material.

Further, the fuse element 20 may have a laminated structure in which the low-melting-point metal layer 41 and the high-melting-point metal layer 42 are laminated. As the low melting point metal, it is preferable to use solder such as Pb-free solder. As the high melting point metal, it is preferable to use Ag, Cu, or an alloy containing these as main components. By containing the high-melting-point metal and the low-melting-point metal, when the protective element 11 is reflow-mounted, even if the reflow temperature exceeds the melting temperature of the low-melting-point metal layer and the low-melting-point metal melts, the fuse element 20 As a result, it does not lead to melting.

As shown in FIG. 3, the fuse element 20 may have an inner layer of a low melting point metal and an outer layer of a high melting point metal. By using a fusible conductor in which the entire surface of the inner low-melting-point metal layer 41 is covered with the outer high-melting-point metal layer 42, even if a low-melting-point metal having a lower melting point than the reflow temperature is used, the inner layer outflow of the low-melting-point metal to the outside can be suppressed. Also, when cutting by fusion, the melting of the low-melting-point metal of the inner layer causes the high-melting-point metal of the outer layer to be eroded (soldered) and melted quickly.

[Cover member]
Moreover, the protective element 11 has a cover member 34 attached on the surface 26a of the insulating substrate 26 on which the fuse element 20 is provided to protect the inside and prevent the melted fuse element 20 from scattering. The cover member 34 can be made of an insulating member such as various engineering plastics and ceramics. The cover member 34 is connected to the surface 26 a of the insulating substrate 26 with an insulating adhesive or the like, thereby covering the fuse element 20 .

[Heat sensitive element]
The heat-sensitive element 12 may be an electronic component whose electrical characteristics are temperature-dependent. For example, as shown in FIG. 4, a thermostat that opens and closes a circuit according to changes in ambient temperature may be used. The heat-sensitive element 3 is thermally connected to the battery stack 15 by arranging it in close proximity to or in contact with the battery stack 15 , and is heated by the abnormal heat generation of the battery stack 15 . As a result, the heat-sensitive element 12 changes electrical characteristics such as resistance and output voltage.

An example of using a thermostat 12a as the heat-sensitive element 12 will be described. The thermostat 12a is mounted on an insulating substrate (not shown) and has one end connected to the open end of the battery stack 15 as shown in FIG. , and the other end is connected to the heating resistor 24 of the protection element 11 . The thermostat 12 a always opens the energization path from the battery stack 15 to the heat generating resistor 24 .

In the battery pack 10, when the thermostat 12a is heated due to abnormal heat generation of the battery stack 15 or the like, the thermostat 12a is displaced so as to close the energization path from the battery stack 15 to the heating resistor 24, and the fuse is closed. Electric power of the battery stack 15 sufficient to melt the element 20 is applied to the heating resistor 24 .

As the heat sensitive element 12, in addition to the thermostat 12a, as shown in FIG. 5, a negative characteristic thermistor 12b (NTC thermistor, CTR thermistor) whose resistance value decreases as the ambient temperature rises can be used. As the heat-sensitive element 12, a diode 12c whose voltage changes when the temperature exceeds the threshold value can be used as shown in FIG. In addition, as the heat-sensitive element 12, a Peltier element, a thermocouple, a bimetal, a temperature sensor, etc. may be used.

Also, the heat-sensitive element 12 is thermally connected by being provided close to or in contact with the exterior of the battery cell 15a. Alternatively, the heat sensitive element 12 may be provided in contact with the exterior of the battery pack 10 . Further, a sheet-like or grease-like thermally conductive material may be interposed between the heat sensitive element 12 and the exterior of the battery cell 15a or the exterior of the battery pack 10 . Moreover, the battery pack 10 may be provided with one heat sensitive element 12 for the battery stack 15, or may be provided with a heat sensitive element 12 for each battery cell 15a. Alternatively, one thermal sensitive element 12 may be provided for a plurality of battery cells 15a.

[Protection circuit]
Such a protection element 11 has a circuit configuration as shown in FIGS. 1 and 4A. That is, the protection element 11 blows the fuse element 20 by energizing the fuse element 20 connected in series between the first and second electrodes 22 and 23 and the connection point of the fuse element 20 to generate heat. It is a circuit configuration including a heating resistor 24 . In the protective element 11 , an electric path is formed to the heat sensitive element 12 (thermostat 12 a ), the heating element feeding electrode 25 , the heating resistor 24 , and the fuse element 20 to the heating resistor 24 . Electricity supply to the heating resistor is controlled.

In the protection element 11 shown in FIG. 1, the first electrode 22 is connected to one open end side of the battery stack 15 via the first external connection electrode 22a, and the second electrode 23 is connected to the second external connection electrode 22a. The fuse element 20 is connected to the positive terminal 10a side of the battery pack 10 via the connection electrode 23a, so that the fuse element 20 is placed on the charge/discharge current path of the battery pack 10 via the first and second external connection electrodes 22a and 23a. connected in series.

The protection element 11 is connected to one open end of the battery stack 15 where the heating element feeding electrode 25 energizes the heating resistor 24, and the heat sensitive element 12 (thermostat 12a) regulates the energization of the heating resistor 24. It is Therefore, the fuse element 20 does not melt due to the heat generated by the heating resistor 24, and the charging/discharging current path of the battery pack 10 can be energized.

When the battery pack 10 needs to cut off the current path of the battery pack 10 due to abnormal heat generation due to overvoltage of the battery cells 15a or abnormal overheating due to fire or the like, the heat sensitive element 12 (thermostat 12a) is activated. is heated, and when it exceeds a predetermined threshold value, the energization path to the heating resistor 24 is closed. As a result, electricity is supplied from the battery stack 15 to the heating resistor 24 . As a result, the heating resistor 24 of the protective element 11 is heated to a high temperature, and the fuse element 20 incorporated in the current path of the battery pack 10 is melted. The melted conductor of the fuse element 20 is attracted to the heating element extraction electrode 21 and the first and second electrodes 22 and 23 with high wettability, thereby melting the fuse element 20 . Therefore, the battery pack 10 can fuse the first electrode 22 to the heating element lead-out electrode 21 to the second electrode 23 (FIG. 4(B)) to cut off the current path of the battery stack 15 .

Such a battery pack 10 can cut off the charging/discharging current path of the battery stack 15 by activating the protective element with the heat-sensitive element 12 . Therefore, the charging/discharging current path of the battery stack 15 is cut off without the risk of malfunction even when exposed to a high-temperature environment, regardless of the switch operation of the current control elements 17 and 18 and the control IC that controls the protective element. be able to.

The protection element 11 constitutes a part of the current path to the heating resistor 24 by connecting the fuse element 20 to the heating resistor 24 . Therefore, when the fuse element 20 is melted and the connection with the external circuit is cut off, the protective element 11 cuts off the current path to the heating resistor 24, so that heat generation can be stopped.

[Switch circuit]
As shown in FIG. 7, the battery pack 10 detects the voltage of the entire battery stack 15 and/or the abnormal voltage of each battery cell 15a in addition to the heat sensitive element 12, and activates the protective element 11 by operating the switch. A switch circuit 50 may be provided. The switch circuit 50 has a protection IC 51 that monitors the voltage of the entire battery stack 15 and/or the voltage of each battery cell 15a, and a switch S52 that is operated by the protection IC 51 .

The switch S52 is, for example, an FET, and is connected to one open end of the battery stack 15 or the battery cell 15a and to the heating resistor 24 of the protection element 11 to switch the heat sensitive element 12 (thermistor in FIG. 7). 12b). Also, the switch S52 is controlled to be switched between an ON state and an OFF state by the protection IC 51 .

The protection IC 51 is connected to, for example, the battery stack 15 and both open ends of each battery cell 15a, constantly monitors the voltage of the entire battery stack 15 and/or the voltage of each battery cell 15a, and switches on the switch S52 when an abnormal voltage occurs. The heating resistor 24 is energized. Specifically, the Protection IC 51 detects whether or not there is an overvoltage based on the voltage across the battery stack 15 and/or the battery cell 15a. For example, the protection IC 51 detects that the voltage of the battery stack 15 or the battery cell 15a is overvoltage when the battery cell voltage exceeds a preset threshold during charging. When the protection IC 51 detects overvoltage, the protection IC 51 controls the switch S52 from the off state to the on state. As a result, the protection element 11 is activated and the fuse element 20 is fused to cut off the charging/discharging current path of the battery stack 15 .

[others]
In the protection circuit described above, the heat sensitive element 12 is provided in parallel with the charging/discharging path of the battery stack 15, but the heat sensitive element 12 is provided on a path electrically independent of the charging/discharging path of the battery stack 15. The power may be supplied from a power supply provided separately. Moreover, the battery pack of the present invention is not limited to the battery pack 10 for lithium-ion secondary batteries, and can be applied to various uses that require interruption of the current path in the event of abnormal overheating.

Reference Signs List 10 battery pack 11 protection element 12 heat sensitive element 12a CTR thermistor 13 charger 15 battery stack 16 charge/discharge control circuit 17 current control element 18 current control element 19 control section 20 fuse element 21 Heating element extraction electrode 22 First electrode 22a First external connection electrode 23 Second electrode 23a Second external connection electrode 24 Heating resistor 25 Heating element feeding electrode 26 Insulating substrate 27 Insulation layer, 28 connecting solder

Claims (6)

a battery cell;
a protective element connected in series with the battery cell;
Having a heat-sensitive element that controls the operation of the protection element,
The above protective element is
an insulating substrate;
a first terminal portion and a second terminal portion that are spaced apart from each other on the insulating substrate and connected to the charging/discharging path of the battery cell;
a fuse element provided between the first terminal portion and the second terminal portion;
A heating resistor connected in series with the heat-sensitive element and whose energization is controlled,
the thermal sensitive element is either a thermostat, a thermistor, or a diode;
The battery pack is energized so that when the heat sensitive element is heated to a temperature equal to or higher than a predetermined temperature, the heating resistor generates heat to a temperature that melts the fuse element. 2. The battery pack according to claim 1 , wherein the heat sensitive element is arranged near or in contact with the battery cell and is thermally connected with the battery cell. 3. The battery pack according to claim 1 , wherein the heating resistor and the heat sensitive element are connected in parallel with the charge/discharge path of the battery cell. first and second electrodes connected to an external circuit;
a fuse provided in series on a current path extending between the first and second electrodes;
a heating resistor that melts the fuse when energized;
and a heat-sensitive element that controls energization of the heating resistor,
the thermal sensitive element is either a thermostat, a thermistor, or a diode;
A protection circuit energized so that when the heat-sensitive element is heated to a temperature equal to or higher than a predetermined temperature, the heating resistor generates heat to a temperature that melts the fuse. 5. A protection circuit according to claim 4 , wherein said heat sensitive element is connected to an open end of said external circuit. 6. The protection circuit according to claim 4, wherein the heating resistor and the heat-sensitive element are connected in parallel with the charge/discharge path of the battery cell.

Images