JP2018041542A - Method for manufacturing secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the reliability of a secondary battery in a method for manufacturing a secondary battery, in which exposed portions of a plurality of pieces of current collector foil exposed from separators are laser-welded to respective current collectors.SOLUTION: A method for manufacturing a secondary battery 1 comprises: a primary processing step (S21) of performing a laser welding operation to bond a positive electrode exposed portion 210 of a plurality of pieces of positive electrode current collector foil 21 exposed from separators 23 to a current collector 80 with a first power density Q1 at a first scanning speed V1; and a secondary processing step (S22) of further performing a laser welding operation to a bonding portion 231 of the positive electrode exposed portion 210 and the current collector 80, which is formed in the first laser welding step (S21) with a second power density Q2 at a second scanning speed V2. The first power density Q1 is lower than the second power density Q2, and the first scanning speed V1 is smaller than the second scanning speed V2.SELECTED DRAWING: Figure 8

Description

  The present disclosure relates to a method for manufacturing a secondary battery, and more particularly, to a laser welding technique for joining an exposed portion where a plurality of current collector foils are exposed from a separator and a current collector.

  In a manufacturing process of a secondary battery such as a lithium ion secondary battery, laser welding is performed to join the exposed portion where the current collector foils are exposed from the separator and the current collector. Various techniques have been proposed for this laser welding (for example, JP 2000-133241 A (Patent Document 1)).

JP 2000-133241 A

  A large amount of heat (total amount of heat) is required to join the exposed portion to the current collector by laser welding. As a method for applying this amount of heat to the joint, for example, it is conceivable to irradiate laser light having a relatively high power density. However, in this case, there is a possibility that fragments (spatters) of the current collector foil melted by the laser irradiation are scattered and mixed into the secondary battery.

  Conversely, it may be possible to realize a large amount of heat by setting a low scanning speed while irradiating a laser beam having a relatively low power density. However, in this case, although the generation of spatter can be suppressed, voids can be generated inside the joint. This gap can cause poor conduction.

  The present disclosure has been made in order to solve the above-described problems, and an object of the present disclosure is to provide a secondary battery manufacturing method in which a plurality of current collector foils are laser-welded to an exposed portion where a current collector foil is exposed from a separator. It is to provide a technology capable of improving the reliability of the secondary battery.

  In the method for manufacturing a secondary battery according to an aspect of the present disclosure, the secondary battery includes an electrode body and a current collector. The electrode body has an exposed portion in which a plurality of current collector foils are laminated via a separator, and the plurality of current collector foils are exposed from the separator. The current collector electrically connects the exposed portion and the external terminal. The manufacturing method includes first and second steps. The first step is a step of performing laser welding for joining the exposed portion and the current collector at the first power density and the first scanning speed. The second step is a step of further performing laser welding on the joint between the exposed portion and the current collector in the first step at the second power density and the second scanning speed. The first power density is lower than the second power density, and the first scanning speed is slower than the second scanning speed.

  According to the said manufacturing method, generation | occurrence | production of the sputter | spatter at the time of joining an exposed part and an electrical power collector can be suppressed by performing the 1st process with a low power density and a slow scanning speed. However, in the first step, the power density is low, but the scanning speed is low, so the amount of heat (total amount of heat) given to the joint is large, and voids are likely to occur in the joint. On the other hand, in the second step, the exposed portion has already been shortened by the first step and new sputtering is unlikely to occur, so that the power density is increased and the scanning speed is increased. As a result, since the power density is high, the gap generated in the first step by melting deep into the joint can be eliminated. In addition, although the power density is high, the scanning speed is fast, so the amount of heat given to the joint is small, and the generation of new voids is suppressed. Thus, by performing laser welding in two stages, the reliability of the secondary battery can be improved.

  According to the present disclosure, in a method for manufacturing a secondary battery in which an exposed portion where a plurality of current collector foils are exposed from a separator and a current collector are laser-welded, the reliability of the secondary battery can be improved.

It is a perspective view which shows the secondary battery manufactured using the manufacturing method which concerns on this Embodiment. It is a figure which shows the structure of the electrode body shown in FIG. 1 in detail. It is a top view of the electrode body for demonstrating the structure of the positive electrode side end surface of an electrode body. FIG. 4 is a cross-sectional view of the electrode body taken along line IV-IV ′ in FIG. 3. It is a figure for demonstrating the conventional laser welding result with a low power density and a slow scanning speed. It is a figure for demonstrating the laser welding conditions in this Embodiment. It is a figure for demonstrating the laser welding result in this Embodiment. It is a flowchart which shows the manufacturing method of the secondary battery which concerns on this Embodiment. It is a figure for demonstrating the result of an evaluation test.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Configuration of secondary battery>
FIG. 1 is a perspective view showing a secondary battery 1 manufactured using the method for manufacturing a secondary battery according to the present embodiment. Secondary battery 1 is, for example, a lithium ion secondary battery.

  The secondary battery 1 includes a housing 10, an electrode body 20 and an electrolytic solution 30 accommodated in the housing 10. The housing 10 includes a case main body 11 and a lid body 12 welded to the case main body 11. The lid body 12 is provided with an explosion-proof valve 40, a liquid injection plug 50, a positive electrode external terminal 60, and a negative electrode external terminal 70. In FIG. 1, the inside of the housing 10 is shown through.

  The explosion-proof valve 40 is activated when the internal pressure of the housing 10 rises and reaches a predetermined pressure, thereby preventing the housing 10 from bursting. The injection stopper 50 is used for injecting the electrolytic solution 30 into the housing 10.

  FIG. 2 is a diagram showing the configuration of the electrode body 20 shown in FIG. 1 in more detail. The electrode body 20 includes a positive electrode current collector foil (or positive electrode plate) 21, a negative electrode current collector foil (or negative electrode plate) 22, and a separator 23. The positive electrode current collector foil 21 is, for example, an aluminum alloy foil having a thickness of 15 μm. The negative electrode current collector foil 22 is a copper foil having a thickness of 10 μm, for example. The separator 23 is a porous insulating layer.

  The electrode body 20 is formed in a flat shape by winding a positive electrode current collector foil 21 and a negative electrode current collector foil 22 via a separator 23. More specifically, in the electrode body 20, a part of the positive electrode current collector foil 21 (positive electrode current collector foil exposed portion) 210 is exposed from one end of the separator 23, and the negative electrode current collector foil 22 is exposed from the other end of the separator 23. It is wound so that a part (negative electrode current collector foil exposed part) 220 is exposed.

  A current collecting terminal 81 and an intermediate member 82 are provided on the end face on the positive electrode side of the electrode body 20. Hereinafter, the current collecting terminal 81 and the intermediate member 82 are also collectively referred to as a current collector 80. The positive electrode current collector foil exposed portion 210 is electrically connected to the positive electrode external terminal 60 via the current collector 80. Similarly, a current collector 90 (a current collecting terminal and an intermediate member) is provided on the negative electrode side end face of the electrode body 20. The negative electrode current collector foil exposed portion 220 is electrically connected to the negative electrode external terminal 70 via the current collector 90. The current collectors 80 and 90 are formed using a conductive material such as copper, nickel, or aluminum. Since the configuration of the negative electrode side end surface of the electrode body 20 is basically the same as the configuration of the positive electrode side end surface, the configuration of the positive electrode side end surface of the electrode body 20 will be representatively described below.

  FIG. 3 is a plan view of the electrode body 20 for explaining the configuration of the end face on the positive electrode side of the electrode body 20. FIG. 4 is a cross-sectional view of the electrode body 20 taken along the line IV-IV ′ of FIG. 3.

  Referring to FIGS. 3 and 4, positive electrode current collector foil exposed portion 210 is collected by sandwiching positive electrode current collector foil exposed portion 210 between current collector terminal 81 and intermediate member 82. Of the collected positive electrode current collector foil exposed portion 210, a portion protruding from the current collector 80 (the current collector terminal 81 and the intermediate member 82) is referred to as a protruding core material portion 211. By irradiating the projecting core part 211 with laser light, the positive electrode current collector foil exposed part 210 and the current collector 80 are joined (laser welding).

  In the protruding core member 211, the foil located at the center in the stacking direction (x direction in the figure) of the positive electrode current collector foil 21 is the highest, and the foil located on the outer side is lower. Considering the dimensional tolerance of the positive electrode current collector foil 21 and the assembly tolerance when the positive electrode current collector foil exposed portion 210 is sandwiched between the current collectors 80, the height H of the central portion of the protruding core member 211 needs to be somewhat high. For example, it can be about 4 mm. The width D of the protruding core member 211 is, for example, about 0.4 mm.

  A large amount of heat is required to weld the protruding core member 211 and the current collector 80 thus configured. As a method for applying this amount of heat to the joint (laser irradiation location), for example, it is conceivable to irradiate laser light having a high power density. However, in this case, there is a possibility that fragments (spatters) of the positive electrode current collector foil 21 melted by the laser irradiation are scattered and mixed into the secondary battery 1.

  On the contrary, it is conceivable to realize a large amount of heat by using a laser beam having a low power density and setting a slow scanning speed.

  FIG. 5 is a diagram for explaining a conventional laser welding result with a low power density and a low scanning speed. By adopting a condition where the power density is low and the scanning speed is low, the occurrence of sputtering can be suppressed.

  On the other hand, a gap 239 may be generated inside the joint 238. The gap 239 is particularly likely to occur between the melted portion (the portion where the protruding core member 211 and the current collector 80 are melted) and the unmelted portion of the protruding core member 211. When the gap 239 is generated, it may cause a conduction failure.

  Further, the joint portion 238 has a deep shape at the center (portion close to the projecting core member 211), and the amount of heat conducted to the projecting core member 211 increases. The effect of this heat may cause the separator 23 to melt and cause defects.

  Therefore, in the present embodiment, laser welding of the protruding core member 211 and the current collector 80 is performed in two stages of primary processing and secondary processing. As a result, as described in detail below, it is possible to realize laser welding with a sufficient bonding strength by reducing the gap 239 while suppressing the occurrence of spatter.

<Laser welding in the present embodiment>
FIG. 6 is a diagram for explaining the laser welding conditions in the present embodiment. FIG. 7 is a diagram for explaining a laser welding result (result after secondary processing) in the present embodiment.

  With reference to FIGS. 6 and 7, the primary processing (corresponding to the “first step” according to the present disclosure) is performed mainly on the protruding core member 211 under a condition where the power density is low and the scanning speed is low. This is done to melt.

As an example, the laser beam output (laser output) is set to 1,200 W, and the spot diameter (diameter) of the laser beam is set to 0.72 mm. From this, the power density Q1 of the laser beam is calculated as 3,000 W / mm ² . The power density is obtained by dividing the laser output by the spot area of the laser beam, and is obtained by laser output (unit: W) / (π × radius ^{2 of the} laser beam spot) (unit: mm ² ). it can. The laser beam scanning speed V1 is set to 300 mm / s.

  In this embodiment, weaving is performed even in the primary processing. The weaving waveform is, for example, zigzag as shown in FIG. The weaving wavelength T is, for example, 0.05 mm, and the amplitude A is, for example, 0.5 mm. The shape of the weaving waveform is not particularly limited, and may be a spiral shape, for example. In the primary processing, since the spot diameter (0.72 mm) is larger than the width D (0.4 mm) of the protruding core member 211, weaving may not be performed.

  According to the primary processing, the projecting core member 211 is melted at a low power density Q1 and a slow scanning speed V1, so that the projecting core member 211 and the current collector 80 are joined to form the joint 231. The occurrence of spatter at the time can be suppressed. When the state during the primary processing was actually confirmed by visual observation, no spatter scattering was confirmed. Moreover, when the circumference | surroundings (within the range of distance 100mm) of the junction part 231 were confirmed after the primary process, it was confirmed that the sputter | spatter with a diameter of 50 micrometers or more has not scattered.

  Further, according to the primary processing, since the scanning speed V1 is slow even if the power density Q1 is low, the amount of heat (total amount of heat) is sufficiently large, and most of the protruding core material portion 211 is melted to be high. H can be lowered (for example, 1 mm or less).

  On the other hand, since the amount of heat is large, voids (not shown) may be generated in the joint portion 231 after the primary processing, as described with reference to FIG. When the cross section of the joint portion 231 after the primary processing was confirmed, it was confirmed that the void ratio was 70%.

  Therefore, in the present embodiment, secondary processing is performed following primary processing. The secondary processing (corresponding to the “second step” according to the present disclosure) has a power density Q2 higher than the power density Q1 and a scanning speed V1 mainly for the purpose of eliminating voids generated in the primary processing. It is performed at a faster scanning speed V2. The power density Q2 in the secondary processing is preferably set to a power density that causes keyhole welding.

In the present embodiment, the laser output is set to 500 W, and the spot diameter of the laser light is set to 0.040 mm. From this, the power density Q2 of the laser beam is calculated as 400,000 W / mm ² . The laser beam scanning speed V1 is set to 1,800 mm / s. It should be noted that these specific numerical values are merely examples.

  In addition, weaving is also performed in the secondary processing. The weaving waveform is equivalent to that during the primary processing. By performing the weaving process, a sufficient width can be secured in the joint portions 231 and 232 even when the spot diameter of the laser beam is small.

  In the secondary processing, although the power density Q2 is high, most of the protruding core member 211 is already melted by the primary processing, so that almost no spattering occurs. Actually, spatter scattering during the secondary processing was not visually confirmed. Further, it was confirmed that spatter having a diameter of 50 μm or more was not scattered around the joint portion 232 after the secondary processing.

  According to the secondary processing, most of the voids generated in the primary processing can be lifted and disappeared by the heat generated by the laser irradiation penetrating deeper into the joint portion 232. In the secondary processing, the power density Q2 is high, but the scanning speed V2 is also high, so that the amount of heat given to the joint 232 is small compared to the primary processing. Furthermore, the amount of heat conducted downward from the keyhole tip is small. Therefore, generation of new voids due to secondary processing can be suppressed. When the cross sections of the joint portions 231 and 232 after the secondary processing were confirmed, it was confirmed that the voids were completely eliminated (that is, the void ratio was 0%). Therefore, according to the present embodiment, it is possible to prevent the occurrence of poor conduction.

  Since the joining part 232 has a shape in which both ends are deeply melted, the joining area between the protruding core part 211 and the current collector 80 is increased. Therefore, high bonding strength can be realized. Further, the fact that both ends of the joint portion 232 are deeply melted means that the ratio of the current collector 80 melted is relatively high and the ratio of the protruding core member 211 melted compared to the welding result shown in FIG. Is relatively low. Therefore, the influence of heat conducted to the constituent elements such as the separator 23 via the protruding core part 211 is reduced, and the occurrence of defects can be suppressed.

<Production flow of secondary battery>
FIG. 8 is a flowchart for explaining a method for manufacturing secondary battery 1 according to the present embodiment. In step (hereinafter abbreviated as “S”) 1, the positive electrode current collector foil exposed portion 210 of the electrode body 20 is sandwiched between the current collector terminal 81 and the intermediate member 82 (current collector 80) to form the protruding core material portion 211. Is done.

  In S21, primary processing for performing laser welding for joining the protruding core member 211 and the current collector 80 is performed. Furthermore, in S <b> 22, secondary processing is performed in which laser welding is further performed on the joint portion 231 between the protruding core member 211 and the current collector 80 by primary processing. Since these steps have been described in detail with reference to FIGS. 6 and 7, the description thereof will not be repeated.

  In S <b> 30, the electrode body 20 is disposed inside the housing 10. More specifically, the electrode body 20 is accommodated in the housing 10 in a state where the positive electrode external terminal 60 and the negative electrode external terminal 70 provided on the lid body 12 and the electrode body 20 are electrically connected. In S <b> 40, laser light is irradiated to the opening edge portion of the case body 11 and the outer peripheral edge portion of the lid body 12, and the case body 11 and the lid body 12 are welded.

  In S <b> 50, a nozzle (not shown) is inserted into the liquid filling plug 50, and the electrolytic solution 30 is injected into the housing 10. In S <b> 60, the explosion-proof valve 40 is formed on the lid body 12.

  In S70, the secondary battery 1 is charged (initial charge). In S80, so-called aging is performed in which the secondary battery 1 is left for a predetermined period. In addition, the manufacturing method of the secondary battery 1 is not limited to this, The other step may be included.

<Evaluation test results>
In order to confirm the effect of the manufacturing method of the secondary battery 1 according to the present embodiment, the present inventors conducted an evaluation test together with the manufacturing method of the secondary battery according to the comparative example.

  FIG. 9 is a diagram for explaining the results of the evaluation test. FIG. 9 shows laser welding conditions for secondary processing performed after the primary processing is performed under the same laser welding conditions as described in FIG. In the secondary processing, weaving (wavelength T = 0.05 mm, amplitude A = 0.5 mm) is performed.

  In Comparative Examples 1 to 3, the power density is low and the scanning speed is low. When the cross section of the welded part in Comparative Examples 1 and 2 was confirmed, the amount of voids was increased as compared with that after the primary processing. In the cross section of the welded portion of Comparative Example 3, it was confirmed that although the void amount was reduced as compared with that after the primary processing, it was not completely lost but remained in a part.

  In Comparative Example 4, the power density is excessively high and the scanning speed is high. In such a case, many spotters were confirmed to be scattered.

  On the other hand, in Examples 1 to 3, the power density is moderately high and the scanning speed is also moderately high. In such a case, it was confirmed that no spatter was scattered and no gap was generated.

  As described above, according to the present embodiment, the protruding core member 211 can be melted while suppressing generation of spatter by primary processing with a low power density Q1 and a low scanning speed V1. Although voids may occur after primary processing, secondary processing with high power density Q2 and high scanning speed V2 eliminates voids generated in primary processing while suppressing generation of new voids. Can do. As a result, the bonding strength can be further improved. Furthermore, by performing the weaving process, it is possible to ensure a sufficient bonding width. Therefore, the reliability of the secondary battery 1 can be improved.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 1 Secondary battery, 10 Housing | casing, 11 Case main body, 12 Lid body, 20 Electrode body, 21 Positive electrode current collection foil, 22 Negative electrode current collection foil, 23 Separator, 30 Electrolyte, 40 Explosion-proof valve, 50 Injection stopper, 60 Positive electrode external terminal, 70 Negative electrode external terminal, 80, 90 Current collector, 81 Current collector terminal, 82 Intermediate member, 210 Positive electrode current collector foil exposed portion, 211 Projecting core material portion, 220 Negative electrode current collector foil exposed portion, 231, 232 , 238 joint, 239 gap.

Claims (1)

A method for manufacturing a secondary battery, comprising:
The secondary battery is
A plurality of current collector foils are laminated via a separator, and the electrode body having an exposed portion where the current collector foils are exposed from the separator;
A current collector for electrically connecting the exposed portion and the external terminal;
The manufacturing method includes:
A first step of performing laser welding for joining the exposed portion and the current collector at a first power density and a first scanning speed;
A second step of further performing laser welding on the joint between the exposed portion and the current collector in the first step at a second power density and a second scanning speed,
The first power density is lower than the second power density;
The method for manufacturing a secondary battery, wherein the first scanning speed is slower than the second scanning speed.