JP6097637B2 - Secondary battery pack having a protection circuit - Google Patents

Description

  The present invention relates to a secondary battery pack having a protection circuit, and more particularly, to a secondary battery pack with reduced impedance so as to facilitate rapid charging with a large current.

  The secondary battery pack is provided in a state in which charge and discharge are possible with an external device via an external output terminal connected to the positive and negative electrodes of the built-in secondary battery. In addition, in order to protect the secondary battery from abnormal states such as overcharge, overdischarge, excessive current, and abnormal temperature rise, a protection circuit that performs control to stop charging and discharging when an abnormal state occurs is provided. The protection circuit includes a charge / discharge control switch interposed between the external output terminal and the secondary battery, and is configured to control on / off thereof. That is, the protection circuit performs control to turn off the charge / discharge control switch and shut off the charge / discharge path when overcharge, overdischarge, or the like is detected.

  FIG. 6 shows a conventional example of a secondary battery pack having such a protection circuit. This battery pack includes a secondary battery 1 and a protection circuit 2. The protection circuit 2 is inserted between the positive electrode terminal 3 and the negative electrode terminal 4 of the secondary battery 1 and the positive output terminal 5 and the negative output terminal 6 that are external output terminals. A temperature protection element 7 and a charge / discharge control switch 8 which is a part of the protection circuit 2 are inserted in the charge / discharge path on the negative electrode side connecting the negative electrode terminal 4 and the negative electrode output terminal 6. The temperature protection element 7 is used to limit or cut off the current flowing through the charging / discharging path according to a change in the resistance value according to the temperature rise due to heat generation of the secondary battery 1.

  The charge / discharge control switch 8 is configured by connecting a discharge control FET 9a made of a MOSFET and a charge control FET 10a in series. The discharge control FET 9a is connected so that the parasitic diode 9b existing between the drain and the source is in a forward direction with respect to the charging current flowing from the positive electrode output terminal 5 toward the secondary battery 1. The charge control FET 10a is connected such that the parasitic diode 10b is in the forward direction with respect to the discharge current.

  The protection circuit 2 includes a protection IC 11 that constitutes a voltage monitoring unit, and a power supply voltage is supplied to the power supply terminal VDD from the secondary battery 1 via the resistor R1. The reference potential terminal VSS is connected to the secondary battery 1 side of the charge / discharge control switch 8. The overcurrent detection terminal V− is connected to the negative output terminal 6 side of the charge / discharge control switch 8 via a resistor R2.

  Control signals DO and CO from the protection IC 11 are supplied to the gates of the discharge control FET 9a and the charge control FET 10a, respectively. In normal charging and discharging operations, the control signals DO and CO are set to the high level, and the discharge control FET 9a and the charge control FET 10a are controlled to be in the ON state.

  The protection IC 11 detects a voltage between the reference potential terminal VSS and the overcurrent detection terminal V-, and detects a current that equivalently flows in the charge / discharge path from the detected voltage. That is, the current is equivalently detected based on the voltage drop caused by the ON resistance of the discharge control FET 9a and the charge control FET 10a. When a current exceeding the specified value (that is, overcurrent) flows, the discharge control FET 9a or the charge control FET 10a is turned off to cut off the current.

  An improvement that facilitates quick charging of the secondary battery is desired for the secondary battery pack having the above-described configuration. In particular, as the functionality of mobile phones and the like increases, lithium secondary batteries are required to have a higher capacity. Be longer than that. In order to overcome this, it is necessary to reduce the time required for charging by enabling charging with a larger current value. In order to enable charging with a large current, it is necessary to reduce the impedance of the secondary battery pack. As a target for reducing the resistance in order to reduce the impedance of the secondary battery pack, the protection circuit 2, the temperature protection element 7, and the wiring material can be considered.

  For example, in order to reduce the resistance of the protection circuit 2, it is necessary to reduce the on-resistance of the charge / discharge control switch 8. For this purpose, a configuration in which two sets of switch circuits including FETs 9a and 10a are connected in parallel has been considered. However, since the protection circuit 2 detects the overcurrent based on the voltage drop caused by the on-resistance of the charge / discharge control switch 8, the detection level of the overcurrent is increased by reducing the on-resistance, and the cost and mounting area are reduced. Considering the increase, the limit is two sets of switch circuits connected in parallel. As the temperature protection element 7, a PTC element has been conventionally used. However, since the resistance value of the PTC element is approximately 0.005Ω, it is configured by combining a bimetal and a PTC element instead of the PTC element. By using a breaker (about 2.5 mΩ), the resistance is reduced.

  The breaker is configured by superposing a PTC element and a bimetal between a pair of lead terminals opposed in the vertical direction. Due to the deformation of the bimetal according to the temperature, the conduction between the lead terminals is switched between a very low resistance conduction state in which the lead terminals are in direct contact and a high resistance substantial interruption state via the PTC element. By using a breaker, the resistance value does not depend on temperature, and a low resistance can be realized as compared with a PTC element whose resistance value varies depending on the temperature. In rapid charging in which charging is performed with a large current, the heat generation of the cell increases, and therefore a breaker that does not increase resistance due to heat generation is an element that is advantageous for reducing resistance.

  Furthermore, for example, Patent Document 1 discloses an improved technique for reducing the resistance of a wiring material that connects the secondary battery 1, the protection circuit 2, and the temperature protection element 7. That is, a clad material having a two-layer structure in which a weld layer and a base layer are clad is used as the wiring material. The weld layer is a layer for ensuring the ease of resistance welding, and is made of Ni, Ni alloy, or Fe alloy. The base layer is a low resistance layer and is made of Cu or a heat-resistant Cu alloy. Using this wiring material between the electrode of the battery and the external terminal of the battery pack, the weld layer is fixedly connected to the electrode by resistance welding. As a result, the electrical resistance can be reduced to about half compared to a conventional lead material using pure nickel.

JP 11-297300 A

  As in the above-mentioned conventional example, two sets of FETs are connected in parallel, and a breaker is used as a temperature protection element, or as in Patent Document 1, a wiring material is formed by a clad structure of a weld layer and a base layer made of Cu or a heat-resistant Cu alloy. By reducing the resistance, a corresponding effect can be obtained in reducing the impedance of the secondary battery pack. However, it has been found that the following problems need to be solved when a large current is passed through the secondary battery pack having such a reduced impedance.

  That is, charging / discharging between the secondary battery pack and the set device is performed through contact between the contact of the set device and the external output terminal of the secondary battery pack. The external output terminal associated with charging / discharging has a large contact resistance of about 20 mΩ per point. For this reason, it is an important issue to effectively dissipate the heat generated at the contact portion, particularly in a device that uses a large current such as rapid charging. This will be described with reference to a cross-sectional view of the main part of the secondary battery pack shown in FIG. FIG. 1 conceptually shows the structure of a portion where the protection circuit 2 is attached to the secondary battery 1. In FIG. 7, the same elements as those shown in FIG. 6 are denoted by the same reference numerals, and the description thereof is omitted.

  In the secondary battery 1, elements constituting a unit cell are built in the outer can 12, and the upper portion of the outer can 12 is sealed with an upper insulating plate 13. A positive electrode lead tab 14 and a negative electrode lead tab 15 extending from the unit cell penetrate the upper insulating plate 13. The upper end of the positive electrode lead tab 14 is welded to the outer can 12 and is electrically connected to the positive electrode cell terminal 3 on the upper surface of the peripheral edge of the outer can 12. The upper end of the negative electrode lead tab 15 is electrically connected to the negative electrode cell terminal 4 on the upper surface of the insulator 17 through the internal lead 16. A cap frame 18 is attached to the top of the outer can 12 to cover the protection circuit board 19 on which the protection circuit 2 (see FIG. 5) is mounted.

  A positive substrate terminal 20 and a negative substrate terminal 21 are provided on the lower surface of the protection circuit board 19. The positive substrate terminal 20 is connected to the positive cell terminal 3 by the first tab 22, and the negative substrate terminal 21 is connected to the temperature protection element 7 by the second and third tabs 23 and 24. The temperature protection element 7 and the negative electrode cell terminal 4 are connected by a fourth tab 25. The first tab 22 is bent at an angle of 180 degrees, and the upper bent piece is welded to the positive electrode substrate terminal 20 and the lower bent piece is welded to the positive electrode cell terminal 3. Similarly, the second tab 23 is also bent at an angle of 180 degrees, and the upper bent piece is welded to the negative electrode substrate terminal 21 and the lower bent piece is welded to the third tab 24. W indicates a welding point. Although not shown, an insulating tape is attached to the lower portion of the third tab 24 to prevent conduction with the outer can 12. An external output terminal 26 (including the positive and negative output terminals 5 and 6 in FIG. 5) attached to the protective circuit board 19 is exposed on the upper end surface of the cap frame 18.

  When the secondary battery pack is attached to the set device, the device-side contact 27 and the external output terminal 26 are brought into contact with each other. If a large current flows during charging / discharging, heat generation at the contact portion between the external output terminal 26 and the contact 27 tends to be excessive. Even if the impedance of the secondary battery pack is reduced, it is difficult to use the battery in such a way that a large current flows without suppressing the influence of heat generation.

  An example of a conventional measure for solving this problem is shown in FIG. (A) is a front view, (b) is a rear view. In the secondary battery pack shown in FIG. 8, the elements corresponding to the protection circuit board 19 shown in FIG. 7 are composed of a protection circuit board 19a and a connector 19b. That is, the connector 19b including the portion of the external output terminal (reference numeral 26 in FIG. 7) is separated from the protective circuit board 19a by using the flexible board 28. Thereby, the metal heat radiating plate 29 is stuck on the back surface of the connector 19b to improve the heat dissipation. By using the heat radiating plate 29, the temperature rise due to heat generation at the external output terminal is suppressed, but the impedance is increased by the wiring of the flexible substrate 28. In addition, the number of parts increases, leading to an increase in cost.

  On the other hand, the temperature protection element 7 also has a problem of heat generation when a large current is passed. That is, in the configuration of FIG. 7, the positive and negative cell terminals 3, 4, the first and second substrate terminals 20, 22, and the first to fourth tabs 22 to 25 are conventionally provided with conductivity and corrosion resistance. Ni is used in consideration of the above. However, although a large amount of self-heating occurs when a large current flows through the temperature protection element 7, since the thermal conductivity of the Ni wiring is not sufficiently large, the Ni wiring does not sufficiently dissipate heat and is sufficient. There was a risk of fusing in a state where no current could flow.

  In consideration of the above, the present invention improves the efficiency of radiating the heat generated at the external output terminal without increasing the number of parts, suppresses the temperature rise due to energization, and performs rapid charging with a large current. An object is to provide an easy secondary battery pack.

  The present invention also provides a secondary battery pack configured so that heat generated from the temperature protection element is effectively radiated through the protection circuit board and the wiring material between the secondary battery and the temperature protection element. For the purpose.

  The secondary battery pack of the present invention includes a secondary battery having positive and negative cell terminals, a pair of external output terminals for external charge / discharge of the secondary battery, the cell terminals and the external output. A protection circuit inserted in the charge / discharge path between the terminals, a temperature protection element inserted between the cell terminal and the protection circuit, the protection circuit is mounted, and the external output terminal is arranged And a protection circuit board provided with first and second board terminals on the back side. The protection circuit includes a charge / discharge control switch inserted in series in the charge / discharge path, and a current detection unit that detects a current flowing through the charge / discharge path, and the charge / discharge is based on a detection output of the current detection unit. The first substrate terminal is connected to one of the cell terminals, and the second substrate terminal is connected to the other of the cell terminals via the temperature protection element. ing.

  In order to solve the above-described problems, in the secondary battery pack of the present invention, at least one of the first and second substrate terminals has a thickness of Cu or Cu alloy having a thickness in the range of 0.6 mm to 1.0 mm. It is comprised by the system metal member, and is arrange | positioned in the area | region corresponding to at least one part of the planar area | region of the said external output terminal.

  According to the secondary battery pack having the above configuration, the first substrate terminal formed of the Cu-based metal member is arranged corresponding to the planar area of the external output terminal, so that the heat generation at the external output terminal is the first. Heat is effectively radiated from the board terminals. Thus, without increasing the number of parts, the efficiency of dissipating heat generated at the external output terminal can be improved to suppress the temperature rise caused by energization, and quick charging with a large current can be facilitated. In addition, by setting the thickness of the first substrate terminal in the range of 0.6 mm to 1.0 mm, dissolution of the solder layer that joins the first substrate terminal to the protective circuit substrate at the time of resistance welding to the wiring material Can be avoided.

Sectional drawing which shows the principal part which shows the mounting part of the protection circuit board with respect to the secondary battery in the secondary battery pack of embodiment of this invention notionally The top view which shows the part of the protection circuit board in the manufacturing process of the secondary battery pack The top view which shows the part of the secondary battery in the manufacturing process of the secondary battery pack The top view which shows the connection part of the protection circuit board and secondary battery in the manufacturing process of the secondary battery pack The figure which shows the change of the temperature rising characteristic based on the heat dissipation effect by the positive electrode substrate terminal of the secondary battery pack Sectional drawing which shows the process of welding which is a part of manufacturing process of the secondary battery pack The figure which shows the change of the temperature rising characteristic based on the heat dissipation effect by the wiring material with respect to the temperature protection element of the secondary battery pack The block diagram which shows the circuit structural example of the secondary battery pack of a prior art example Sectional drawing which shows the principal part which shows the mounting part of the protection circuit board which comprises the secondary battery pack notionally The structure of the secondary battery pack of another prior art example is shown notionally, (a) is a front view, (b) is a rear view.

  The secondary battery pack of the present invention can take the following aspects based on the above configuration.

  That is, the Cu-based metal member is Sn plated. Thereby, the oxidation of the Cu-based metal that is easily oxidized can be prevented.

  Further, the Cu-based metal member has an electrical resistivity of less than 69.3 nΩm. Preferably, the Cu-based metal member has an electrical resistivity in the range of 1.68 to 63.9 nΩm. Thereby, a sufficient heat dissipation effect is obtained, and application of series welding is facilitated.

  Further, as a wiring material for connecting between the second substrate terminal and the temperature protection element, and between the temperature protection element and the cell terminal, a Cu-based metal layer made of Cu or Cu alloy and a Ni layer are used. A Cu-Ni clad material is used. Thereby, heat generated by energization of the temperature protection element can be effectively radiated.

  The Cu-Ni clad material is joined by resistance welding with the Cu-based metal layer side in contact with the cell terminal and the substrate terminal. With this configuration, both good heat dissipation and suitability for series welding can be achieved.

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

<Embodiment>
A secondary battery pack according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a main part sectional view conceptually showing the structure of the mounting portion of the protection circuit board 19 for the secondary battery 1. The structure of the mounting portion of the protection circuit board 19 is basically the same as that of the conventional example shown in FIG. Therefore, the same elements as those shown in FIG. 7 are denoted by the same reference numerals, and description thereof is omitted. The circuit configuration of the secondary battery pack is the same as that of the conventional example shown in FIG.

  The first feature of the secondary battery pack in the present embodiment is constituted by a Cu-based metal block made of Cu or Cu alloy instead of the positive electrode substrate terminal 20 using Ni in the conventional example shown in FIG. That is, the positive electrode substrate terminal 30 that functions as a heat radiating member is used. The positive electrode substrate terminal 30 is disposed at a position corresponding to the planar area of the external output terminal 26 and is joined to the protection circuit substrate 19 by solder (not shown).

  Since the positive substrate terminal 30 is arranged corresponding to the planar area of the external output terminal 26, heat generated at the contact portion of the external output terminal 26 is efficiently transmitted to the Cu-based metal block of the positive substrate terminal 30. The heat is efficiently radiated from the Cu-based metal block. Thereby, without increasing the number of parts, it is possible to improve the heat dissipation efficiency and sufficiently suppress the temperature rise at the external output terminal 26 due to energization.

  In the configuration of FIG. 1, the size of the positive electrode substrate terminal 30 extends over a region including all of the external output terminals 26, but in order to ensure a heat dissipation effect, the positive electrode substrate terminal 30 has a planar region, What is necessary is just to arrange | position so that it may correspond to at least one part of the planar area | region of the external output terminal 26. FIG. However, although the positive electrode substrate terminal 30 is usually provided corresponding to the positive electrode output terminal of the external output terminals 26, in order to sufficiently obtain the effects of the present embodiment, the positive electrode substrate terminal 30 covers a range including the negative electrode output terminal. It is preferable to be provided.

  In addition, this Embodiment is not necessarily restricted to the structure which acquires the heat dissipation effect through the positive electrode substrate terminal 30. FIG. That is, as shown in FIG. 1, the configuration is not limited to the configuration in which the positive electrode substrate terminal 30 is arranged corresponding to the planar area of the external output terminal 26. Instead of this, even if the negative electrode substrate terminal 31 is arranged corresponding to the planar area of the external output terminal 26 and heat is radiated through the negative electrode substrate terminal 31, a corresponding effect can be obtained. .

  The thickness of the Cu-based metal block is set in the range of 0.6 mm to 1.0 mm. This thickness range is set to prevent the solder for fixing the Cu-based metal block from melting due to heat generated by resistance welding when the first tab 32 is resistance-welded to the positive electrode substrate terminal 30. It is. Further, Sn plating for preventing oxidation is applied to the Cu-based metal block of the positive electrode substrate terminal 30. As the first tab 32 that connects between the positive electrode substrate terminal 30 and the positive electrode cell terminal 3, a Cu—Ni clad material made of a Cu-based metal layer made of Cu or a Cu alloy and an Ni layer is used.

  The second feature of the present embodiment is that the second and third tabs 33 and 34 that connect the negative electrode substrate terminal 31 and the temperature protection element 7, and the connection between the temperature protection element 7 and the negative electrode terminal 4 are connected. The fourth tab 35 is formed of the same Cu—Ni clad material as that of the first tab 32. The negative electrode substrate terminal 31 is formed of the same Cu-based metal block as the positive electrode substrate terminal 30.

  As described above, when a Cu-Ni clad material is used as a tab that is a wiring material, the Cu-based metal layer has a low resistance. Can be easily. Moreover, compared with the case where a tab is formed only with a Cu-based metal layer, it is possible to avoid the occurrence of problems associated with the welding of wiring materials, as will be described later.

  In the above configuration, the first tab 32 is bonded to the positive substrate terminal 30 and the positive cell terminal 3, the second tab 33 is bonded to the negative substrate terminal 31 and the third tab 34, and the fourth tab 35 is bonded to the negative cell terminal 4. Joining is performed by resistance welding. This is because resistance welding is easy to work and the welding apparatus is simple, which is advantageous in reducing manufacturing costs. Further, as indicated by a welding point W in FIG. 1, series welding is adopted as resistance welding. Accordingly, in the present embodiment, the materials of the positive and negative electrode substrate terminals 30 and 32 and the first to fourth tabs 32 to 35 are selected so as to be suitable for series welding as will be described later.

  The process of attaching the protective circuit board 19 to the upper end portion of the secondary battery 1 by resistance welding is performed, for example, as shown in FIGS. 2A to 2C (a part of the process is shown). 2A is a plan view showing a state in which the protection circuit board 19 is turned upside down from the state shown in FIG. FIG. 2B is a plan view of the secondary battery 1. FIG. 2C is a plan view showing a state in which the secondary battery 1 and the protection circuit board 19 are connected to each other.

  First, as shown in FIG. 2A, the third tab 34 and the fourth tab 35 are connected to the temperature protection element 7, and one end of the second tab 33 is welded to one end of the third tab 34. Next, the upper end surface (corresponding to the lower end surface in FIG. 1) of the protection circuit board 19 in the upside down state and the temperature protection element 7 are aligned and the other end of the second tab 33 is connected to the negative electrode substrate terminal 31. Place on top and weld. Also, one end of the first tab 32 is disposed on the positive electrode substrate terminal 30 and welded. As shown in FIG. 2B, the positive cell terminal 3 and the negative cell terminal 4 are arranged on the upper end surface of the secondary battery 1.

  The upper end surface of the secondary battery 1 and the upper end surface of the protection circuit board 19 are aligned as shown in FIG. 2C, the other end of the first tab 32 is disposed on the positive electrode terminal 3, and the fourth tab 35 Are placed on the negative electrode terminal 4 and welded to each other. Next, the first tab 32 and the second tab 33 are bent by 180 degrees at the center (as indicated by the alternate long and short dash line), so that the protective circuit board 19 is placed at the top of the outer can 12 as shown in FIG. It is assumed that it is attached to. Thereafter, although not illustrated, the cap frame 18 and the outer can 12 are integrated by injecting an integrally molded resin into the space between the cap frame 18 and the outer can 12, and the secondary battery 1 is completed.

  As described above, according to the present embodiment, the positive electrode substrate terminal 30 is formed of a Cu-based metal block in order to obtain good heat dissipation efficiency. Moreover, the thickness is set in the range of 0.6 mm to 1.0 mm. The reason for this configuration will be described below.

  Compared to the conventional positive electrode substrate terminal 20 using Ni, the positive electrode substrate terminal 30 using Cu-based metal has higher conductivity and thermal conductivity. That is, the thermal conductivity (300 K) of Ni is 90.9 W / (m · K), whereas the thermal conductivity of brass (C2680, Cu—Pb—Fe—Zn alloy) is 117 w / (m・ K). Therefore, a sufficiently high heat dissipation effect can be obtained as compared with the case where Ni is used.

In order to verify this heat dissipation effect, the change in the surface temperature of the first tab 32 when a large current was passed was measured. The measurement was performed for the example of the present embodiment and the conventional example, and the positive electrode substrate terminal and the first tab of the example and the conventional example were set as follows.
[Conventional example]
Positive electrode substrate terminal 20: Ni block (thickness 0.4 mm)
First tab 22: Ni material (thickness 0.1 mm)
[Example]
Positive electrode substrate terminal 30: Cu-based metal block (uses pure Cu: thickness 0.4mm)
1st tab 32: Cu-Ni clad material (thickness 0.1 mm)
FIG. 3 shows the results of measuring the change in the surface temperature of the tub with respect to the energization time when a current of 3A was passed through the positive electrode substrate terminal at room temperature of 25 ° C. As shown in FIG. 3, the temperatures reached on the surface of the tab material are as follows.

Conventional example: 45.5 ° C (Δ20.5 ° C)
Example: 37.5 ° C. (Δ12.5 ° C.)
Thus, according to the configuration of the example, it is possible to suppress the temperature of about 8 ° C. Therefore, it can be seen that the use of the Cu-based metal block has a great effect of suppressing the temperature rise near the contact portion.

  However, because of the high conductivity, a large amount of energy is required for resistance welding when the first tab 32 is joined, and heat generation is increased. Therefore, there arises a problem that the solder fixing the positive electrode substrate terminal 30 to the protection circuit substrate 19 is melted. In order to solve this problem, it has been found effective to sufficiently increase the thickness of the Cu-based metal block.

  In practice, the thickness of the Cu-based metal block is set to 0.6 mm to 1.0 mm in the present embodiment, compared to 0.4 mm or less in the case of the positive electrode substrate terminal 20 using conventional Ni. . Thus, it was confirmed that it is possible to appropriately perform resistance welding and to avoid melting due to heat generation of the solder fixing the Cu-based metal block. Further, if the thickness of the Cu-based metal block is 1.0 mm or less, the height of the solder-mounted component can be kept within a range that can be stored in the battery pack.

  As the Cu-based metal block constituting the positive electrode substrate terminal 30, any Cu and Cu alloy whose conductivity and thermal conductivity are in a range suitable for heat dissipation and resistance welding can be used. If it is a normal Cu-based metal, the thermal conductivity is in a range where a desirable discharge effect can be obtained.

  On the other hand, as described below, it is desirable to use a material in an appropriate range from the viewpoint of resistance welding as described below. As general resistance welding, there are two kinds of methods, that is, series welding and direct welding. In the case of the secondary battery pack having the above configuration, the first, second, and fourth tabs 32, 33, and 35 are welded to the positive and negative cell terminals 3 and 4 and the positive and negative electrode substrate terminals 30 and 31, respectively. Is used.

  The state of resistance welding is shown in FIG. 4 by taking the joining of the first tab 32 to the positive electrode substrate terminal 30 as an example. The positive substrate terminal 30 is joined to the protective circuit board 19 by solder 36. This resistance welding is performed by series welding using a pair of welding rods 37. This is because direct welding is inappropriate in this configuration. That is, in the case of direct welding, it is necessary to press the electrode rod 37 in the opposite direction against the lower surface of the positive electrode substrate terminal 30 and the upper surface of the first tab 32, and energize, but as shown in FIG. The electrode rod 37 cannot be pressed against the lower surface of the positive substrate terminal 30.

  At the time of series welding, a welding point W is formed between the positive electrode substrate terminal 30 and the first tab 32 by the effective current Ie flowing through the positive electrode substrate terminal 30 as indicated by an arrow in FIG. Appropriate heat generation is required at the location where the welding point W is to be formed. If the electrical conductivity of the positive electrode substrate terminal 30 is too high, the welding energy required for this will be excessive. As a result, heat generation at the contact point of the welding rod 37 with respect to the first tab 32 also increases, and the welding rod 37 is bitten (attached).

  The positive electrode substrate terminal 30 can be welded even when pure copper having a conductivity of 100% is used. Therefore, using a Cu-based metal having an electrical resistivity of less than 69.3 nΩm, it is possible to reduce the resistance for rapid charging as compared with an electrode using Ni. In consideration of application of series welding and a heat dissipation effect, it is preferable to use a Cu-based metal having an electrical resistivity in the range of 1.68 to 63.9 nΩm. 1.68 nΩm corresponds to the electrical resistivity of pure copper, and 63.9 nΩm corresponds to the electrical resistivity of brass. Furthermore, it is desirable that the electrical resistivity be about 63.9 nΩm in order to avoid the problem of mass production due to the biting of the welding rod during series welding. By appropriately lowering the electrical conductivity, welding is possible even with low welding energy, and biting of the welding rod can be easily avoided.

Examples of suitable Cu-based metal blocks include the following alloys.
(1) Brass (C2680, Cu—Pb—Fe—Zn alloy)
Electrical conductivity: about 27%, thermal conductivity: 117 w / m · k
(2) Bronze alloy (MF202, Cu—Sn—Ni—P alloy)
Conductivity: about 32%, thermal conductivity: 155 w / m · k
Compared to the Ni block of the conventional example, which is pure Ni: 99.9% or more, conductivity: about 22%, and thermal conductivity: 90.9 w / m · k, these materials ensure weldability. However, it can be seen that the heat conduction is good and the cost can be reduced.

  Further, since the Cu-based metal block is easily oxidized, it is desirable to perform plating for preventing oxidation, and Sn plating and Ni plating were examined as plating materials. As a result, Ni plating has a high melting point, and it is understood that Sn plating with a low melting point is optimal because the Ni layer at the welding point W cannot be scattered with the energy of resistance welding when using the series welding method. It was.

  As described above, the first to fourth tabs 32 to 35 are adapted to a large current as a low resistance by using a Cu—Ni clad material. As the Cu-Ni cladding material, for example, the ratio of the thickness of the Cu layer (or Cu alloy layer) and the Ni layer is about Cu: Ni = 3: 1, and the thickness of the entire cladding material is about t = 0.1 mm. By using this, good characteristics can be obtained.

  The tabs of the Cu—Ni clad material are resistance welded with the Cu-based metal layer in contact with the positive and negative electrode cell terminals 3 and 4 and the positive and negative electrode substrate terminals 30 and 31. The reason is to avoid the occurrence of burning of the Cu material in the welding process, as will be described below.

  That is, in series welding, not only the effective current Ie flowing through the positive electrode substrate terminal 30 indicated by the arrow in FIG. 4 but also the reactive current In that does not contribute to welding flows through the Cu—Ni cladding material of the first tab 32. When the Ni layer is brought into contact with the positive electrode substrate terminal 30, the electrode rod 37 comes into contact with the Cu layer, and the reactive current In becomes large. Therefore, the heat generation between the electrode rod 37 and the Cu layer causes the Cu layer to contact the Cu layer. Burning occurs or unnecessary welds are formed, and the Cu layer adheres to the electrode rod 37 and peels off. On the other hand, the reactive current In of the surface layer is suppressed by bringing the Cu-based metal layer into contact with the positive electrode substrate terminal 30 and thus the electrode rod 37 is in contact with the Ni layer. Bonding can be reduced.

  Next, effects of the second feature of the present embodiment will be described. According to the second feature, the second tab 33 and the third tab 34 that connect the negative electrode substrate terminal 31 and the temperature protection element 7, and the fourth that connects the temperature protection element 7 and the negative cell terminal 4. The tab 35 is formed of a Cu—Ni clad material. Thereby, the heat generated by the temperature protection element 7 can be effectively radiated.

  The result of the experiment for demonstrating this effect is demonstrated with reference to FIG. In FIG. 5, the horizontal axis represents the current flowing through the breaker used as the temperature protection element 7, and the vertical axis represents the maximum temperature reached for each current value. The experiment was performed for a case where a Cu—Ni clad material was used as a wiring material and a case where conventional Ni was used. In each case, the temperature at the breakers, the tabs, and the FETs 9a and 10a in the protection circuit 2 (see FIG. 6) was measured. From FIG. 5, it can be seen that when the wiring material of the Cu—Ni clad material is used, the temperature rise in each part is reduced as compared with the case of using the Ni wiring material.

  The secondary battery pack of the present invention improves the efficiency of dissipating heat generated at the external output terminal without increasing the number of parts, suppresses the temperature rise caused by energization, and facilitates rapid charging with a large current. Therefore, it is useful as a battery pack used for a device such as a mobile phone that is required to be rapidly rechargeable.

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Protection circuit 3 Positive electrode terminal 4 Negative electrode terminal 5 Positive output terminal 6 Negative output terminal 7 Temperature protection element 8 Charge / discharge control switch 9a Discharge control FET
9b Parasitic diode 10a Charge control FET
10b Parasitic diode 11 Protection IC
12 Outer can 13 Upper insulating plate 14 Positive electrode lead tab 15 Negative electrode lead tab 16 Internal lead 17 Insulator 18 Cap frame 19 Protection circuit board 20, 30 Positive circuit board terminals 21, 31 Negative circuit board terminals 22-25 First to fourth tabs 26 External output Terminal 27 Contact 28 on device side Flexible substrate 29 Heat radiation plate 32 to 35 First to fourth tabs 36 Solder 37 Welding rod W Welding point

Claims (6)

A secondary battery having positive and negative cell terminals;
A pair of external output terminals for charging and discharging from the outside to the secondary battery;
A protection circuit inserted in a charge / discharge path between the cell terminal and the external output terminal;
A temperature protection element inserted between the cell terminal and the protection circuit;
A protection circuit board on which the protection circuit is mounted, the external output terminal is disposed, and first and second board terminals are provided on the back side of the protection circuit board;
The protection circuit includes a charge / discharge control switch inserted in series in the charge / discharge path, and a current detection unit that detects a current flowing through the charge / discharge path, and the charge / discharge is based on a detection output of the current detection unit. Configured to control the on / off of the control switch,
In the secondary battery pack, wherein the first substrate terminal is connected to one of the cell terminals, and the second substrate terminal is connected to the other of the cell terminals via the temperature protection element,
At least one of the first and second substrate terminals is made of a Cu-based metal member made of Cu or Cu alloy having a thickness in the range of 0.6 mm to 1.0 mm, and at least one of the planar regions of the external output terminals. A secondary battery pack, which is disposed in a region corresponding to the portion.   The secondary battery pack according to claim 1, wherein the Cu-based metal member is Sn plated.   The secondary battery pack according to claim 1, wherein the Cu-based metal member has an electrical resistivity of less than 69.3 nΩm.   The secondary battery pack according to claim 3, wherein the Cu-based metal member has an electrical resistivity in a range of 1.68 to 63.9 nΩm.   As a wiring material for connecting between the second substrate terminal and the temperature protection element and between the temperature protection element and the cell terminal, Cu— consisting of a Cu-based metal layer made of Cu or Cu alloy and a Ni layer. The secondary battery pack according to any one of claims 1 to 4, wherein a Ni clad material is used.   The secondary battery pack according to claim 5, wherein the Cu—Ni clad material is bonded by resistance welding with the Cu-based metal layer side being brought into contact with the cell terminal and the substrate terminal.

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