Manufacturing method of sealed secondary battery

Abstract

To provide a manufacturing method of a sealed type battery capable of reducing a generation ratio of a liquid leakage in a heat cooling cycle.SOLUTION: A sealed type battery comprises a gasket interposed to between a sealing board and an external terminal. A manufacturing method of the sealed type battery contains: a step of providing a temperature difference of 10°C or larger between the gasket and both the sealing board and the external terminal as a circumference member of the gasket; and a step of caulking the sealing board, the gasket, and the external terminal.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a sealed secondary battery. [Background technology]

[0002] In recent years, lithium ion batteries, nickel metal hydride batteries, and other secondary batteries have been widely used as vehicle batteries or power sources for personal computers and mobile terminals. In particular, lithium ion secondary batteries, which are lightweight and have a high energy density, are preferably used as high-output power sources for vehicles.

[0003] In this type of secondary battery, a sealed battery is widely known in which a wound electrode body, in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a nonaqueous electrolyte are housed inside a battery case, and an electrode terminal connected to the electrode body is drawn out to the upper end (lid) of the battery case and is fixed by crimping via a gasket. For example, Patent Document 1 discloses a sealed battery in which an external terminal (17) is crimped to a sealing plate (13) via a gasket (20).

[0004] Moreover, gaskets are used to prevent electrolyte leakage from a predetermined space provided inside a sealed secondary battery. Patent Document 2 discloses an internal gasket with convex portions formed on both sides to more effectively prevent electrolyte leakage. One to three convex portions are formed on each side, and the convex portions are sufficiently compressed to suppress the penetration of electrolyte. In the gasket of the prior art, the compression force is increased to prevent electrolyte leakage from the gap between the gasket and the surrounding members. This configuration is said to be effective against the rise in internal pressure of a sealed secondary battery at high temperatures. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-119210 A [Patent Document 2] Japanese Patent Application Publication No. 11-283588 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, a cold-heat cycle test may be performed on sealed batteries as described above, in which low and high temperature conditions are repeated multiple times to check the durability before shipping. The present inventors have found that when moving from high to low temperatures during a cold-heat cycle test (temperature cycle test), the amount of thermal contraction of the gasket is greater than the amount of thermal contraction of the surrounding parts, which may temporarily reduce the contact surface pressure of the gasket and lead to leakage. On the other hand, if the load during gasket assembly is increased too much to prevent leakage, the gasket and surrounding parts may break in terms of durability. For this reason, simply increasing the load during gasket assembly is not an appropriate method for preventing leakage.

[0007] Therefore, a typical objective of the technology disclosed herein is to provide a method for manufacturing a sealed battery that reduces the incidence of leakage during thermal cycles without increasing the load during gasket assembly above a certain level. [Means for solving the problem]

[0008] One embodiment of a manufacturing method for a sealed battery disclosed herein is a manufacturing method for a sealed battery comprising an electrode body, a battery case that houses the electrode body, a sealing plate that seals an opening of the battery case, an external terminal provided on the outside of the sealing plate, an internal terminal connected to the electrode body, a conductive member that connects the external terminal and the internal terminal, and a gasket interposed between the sealing plate and the conductive member, the method including a step of establishing a temperature difference of 10°C or more between the gasket, the sealing plate, and the external terminal, and a step of crimping the external terminal to the periphery of the opening of the sealing plate while interposing the gasket between the sealing plate and the conductive member. In a battery obtained by this method for manufacturing a sealed battery, a temporary decrease in contact pressure between the gasket and surrounding parts can be suppressed when the temperature changes from high to low during a thermal cycle without increasing the load more than necessary when assembling the gasket, thereby making it possible to manufacture a battery with a reduced incidence of leakage during thermal cycles.

[0009] In one embodiment of the method for producing a sealed battery disclosed herein, the cooling step includes cooling the gasket to a temperature of −60° C. or higher and 0° C. or lower. By cooling the gasket to a temperature of −60° C. or higher and 0° C. or lower, a decrease in the contact surface pressure between the gasket and surrounding components can be more suitably suppressed, and deterioration of battery performance can be prevented.

[0010] In the method for producing a sealed battery according to one embodiment disclosed herein, the crimping step is performed while maintaining the temperature of the cooled gasket, thereby more reliably suppressing a decrease in contact surface pressure during thermal cycles.

[0011] In the method for producing a sealed battery according to one embodiment disclosed herein, the crimping step is performed in a working environment below freezing, which makes it easy to adjust the temperature when assembling the gasket. [Brief description of the drawings]

[0012] [Figure 1] 1 is a perspective view of a sealed secondary battery according to one embodiment disclosed herein; [Diagram 2] 1 is a cross-sectional view of a sealed secondary battery according to an embodiment disclosed herein. [Diagram 3] 1 is an enlarged view of a main portion of a cross-sectional view of a sealed secondary battery according to an embodiment disclosed herein. [Figure 4] 1 is a graph showing the relationship between temperature and change in contact pressure during thermal cycle testing of one embodiment disclosed herein. [Diagram 5] 1 is a graph showing the minimum surface pressure in a thermal cycle test of one embodiment disclosed herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, typical embodiments of the present disclosure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in this specification and necessary for implementation can be understood as design matters of a person skilled in the art based on the prior art in the field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the field. In the following drawings, members and parts that perform the same function are described with the same reference numerals. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

[0014] In this specification, when a numerical range is described as "A to B (where A and B are any numerical values)," this means "A or more and B or less," and also includes the meanings of "greater than A and less than B," "greater than A and B or less," and "greater than A and less than B."

[0015] In this specification, the term "battery" refers to a general term for an electricity storage device capable of extracting electric energy, and is a concept including a primary battery and a secondary battery. In addition, the term "secondary battery" refers to a general electricity storage device capable of repeatedly charging and discharging, and includes so-called storage batteries (i.e., chemical batteries) such as lithium ion secondary batteries, nickel hydrogen batteries, and nickel cadmium batteries, as well as capacitors such as electric double layer capacitors (e.g., lithium ion capacitors). And the term "sealed battery" refers to a secondary battery in which an electrode body and an electrolyte are accommodated in a sealed case. Hereinafter, the method for manufacturing a sealed secondary battery according to the present disclosure will be described in detail, taking as an example a method for manufacturing a flat rectangular sealed lithium ion secondary battery, which is a type of secondary battery. However, it is not intended that the method for manufacturing a sealed secondary battery according to the present disclosure be limited to the one described in the following embodiment.

[0016] Fig. 1 is a perspective view showing a schematic external shape of a sealed lithium-ion secondary battery 1 according to an embodiment disclosed herein. Fig. 2 is a schematic longitudinal sectional view taken along line II-II in Fig. 1. In the following description, the symbols L, R, U, and D in the drawings represent left, right, top, and bottom, and the symbols X, Y, and Z in the drawings represent the long side direction, short side direction perpendicular to the long side direction, and up-down direction, respectively, of the sealed lithium-ion secondary battery 1. However, these directions are merely for the sake of convenience in the description, and do not limit the installation form of the sealed lithium-ion secondary battery 1 in any way.

[0017] As shown in FIG. 2, the lithium ion secondary battery 1 according to one embodiment is a sealed lithium ion secondary battery including an electrode assembly 30, an electrolyte (not shown), and a battery case 20.

[0018] In this embodiment, the electrode body 30 is a wound electrode body in which a positive electrode sheet 50, a negative electrode sheet 60, and a separator sheet 70 are wound. The electrode body 30 is not limited to this, and may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with separators interposed therebetween. In addition, the battery case 20 may house a plurality of electrode bodies.

[0019] The wound electrode body 30 has a configuration in which a long positive electrode sheet 50 and a long negative electrode sheet 60 are overlapped with two long separator sheets 70 interposed therebetween and wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (both sides here) of a long positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (both sides here) of a long negative electrode current collector 62. The positive electrode active material layer-free portion 52a (i.e., a portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer-free portion 62a (i.e., a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed) are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction perpendicular to the longitudinal direction) of the wound electrode body 30. The positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a are joined to the positive electrode internal terminal 42a and the negative electrode internal terminal 42b, respectively.

[0020] The electrolyte can be a non-aqueous electrolyte in which a supporting salt is dissolved in a suitable non-aqueous solvent. Conventionally known non-aqueous electrolytes can be used without any particular restrictions. Examples of non-aqueous solvents that can be used include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Examples of supporting salts that can be used include lithium salts (e.g., LiBOB, LiPF6, etc.).

[0021] As shown in FIG. 1, in this embodiment, the shape of the battery case 20 is a rectangular parallelepiped, which is a flattened square shape. However, the shape of the battery case 20 is not limited thereto, and may be, for example, a cylindrical shape. The battery case 20 is composed of a main body 22 that contains the electrode body 30 and the electrolyte, and a sealing plate (lid) 24 that seals the opening of the main body. The main body 22 and the sealing plate 24 are welded and sealed by laser welding or the like, and the wound electrode body 30 and the electrolyte are contained in a sealed state inside the battery case. The material of the battery case 20 may be the same as that used in conventional secondary batteries of this type, and is not particularly limited. As an example, a lightweight metal material with good thermal conductivity such as aluminum is used. However, it is also possible to change the configuration of the battery case. For example, a flexible laminate may be used as the battery case.

[0022] In this embodiment, the battery case body 22 is composed of a bottom wall and integral short side walls extending from the bottom wall and facing each other. In this embodiment, the sealing plate 24 of the battery case 20 is provided with a thin-walled safety valve 26 that is set to release the internal pressure of the battery case when the internal pressure of the battery case rises to a predetermined level or higher, and an injection port 27 for injecting an electrolyte. In addition, a positive electrode external terminal 44a and a negative electrode external terminal 44b for external connection are provided. These electrode terminals are electrically connected to the wound electrode body 30 housed in the battery case via internal terminals 42a and 42b.

[0023] The external terminals 44a, 44b are made of metal. For example, aluminum or an aluminum alloy may be used as the positive external terminal. For example, copper or a copper alloy may be used as the negative external terminal.

[0024] The internal terminals 42a, 42b are made of metal. For example, aluminum or an aluminum alloy may be used as the positive electrode internal terminal from the viewpoint of improving the bonding strength with the positive electrode active material layer non-forming portion 52a. For example, copper or a copper alloy may be used as the negative electrode internal terminal from the viewpoint of improving the bonding strength with the negative electrode active material layer non-forming portion 62a.

[0025] In this embodiment, the conductive member 43 is a metal member that connects the internal terminals 42a, 42b and the external terminals 44a, 44b. The material of the conductive member 43 is usually the same as that of the internal terminals 42a, 42b and the external terminals 44a, 44b, but is not limited thereto. In one example of the conductive member 43 disclosed herein, a part of the conductive member penetrates the external terminals 44a, 44b, and a bus bar can be connected to the penetrated portion.

[0026] 3 is a schematic enlarged cross-sectional view taken along line III-III in FIG. 2. In FIG. 3, an enlarged cross-sectional view of a portion where the negative electrode external terminal 44b and the conductive member 43 are attached to the sealing plate is shown. The portion where the positive electrode external terminal 44a and the conductive member 43 are attached to the sealing plate can have a similar configuration, and therefore a description thereof will be omitted. As shown in FIG. 3, the sealing plate 24 has an opening 28 to which the conductive member 43 is attached via a gasket 40. The opening 28 penetrates the sealing plate 24 at a predetermined position of the sealing plate 24.

[0027] The gasket 40 is a resin sealant attached to the opening 28 of the sealing plate 24. In this embodiment, the gasket 40 ensures insulation between the sealing plate 24 and the conductive member 43 and the external terminals 44a and 44b. It also ensures airtightness of the battery case 20. The gasket 40 is preferably made of a material having excellent chemical resistance and weather resistance. For example, tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polypropylene (PP), polyethylene (PE), polyphenylene sulfide resin (PPS), etc. may be used, and PFA is preferable because it is difficult to break below freezing. In addition to the resin material, an inorganic filler may be added.

[0028] In this embodiment, the insulating member 46 ensures insulation between the sealing plate 24 and the internal terminals 42a, 42b. The material of the insulating member 46 is not particularly limited as long as it has a predetermined insulating property, and the same material as that of the gasket 40 may be used.

[0029] <Method of manufacturing sealed secondary battery> In the manufacturing method of a sealed battery disclosed herein, the battery case 20, the wound electrode body 30, the positive electrode internal terminal 42a and the negative electrode internal terminal 42b, the gasket 40, and the positive electrode external terminal 44a and the negative electrode external terminal 44b as described above are prepared.

[0030] <Step of Providing a Temperature Difference Between the Gasket and the Sealing Plate and the Conductive Member> Next, a preferred example of the method for manufacturing a sealed lithium-ion secondary battery disclosed herein will be described in detail. In this embodiment, the method is performed by cooling the gasket 40 to provide a temperature difference of 10°C or more between the gasket and the peripheral members of the gasket (i.e., the sealing plate 24 and the conductive member 43). By cooling a gasket with a large amount of thermal contraction, leakage can be more effectively prevented when the temperature is changed from high to low, and when the temperature is changed from low to high, the contact surface pressure between the gasket and the sealing plate is improved due to thermal expansion, so that leakage due to an increase in the internal pressure of the battery can be prevented. Here, if the temperature of the gasket is t1 and the temperature of the peripheral members is t2, the temperature difference is Δt. Note that t2 means the lower temperature of the sealing plate or the conductive member, and there may be a temperature difference between the two.

[0031] In addition, as another aspect of this embodiment, instead of cooling the gasket 40, it is also possible to heat or cool the peripheral members. When the sealed lithium ion secondary battery is used in a tropical or desert region, the gasket or the peripheral members will thermally expand excessively, and stress will concentrate near the contact surface between the gasket and the sealing plate. Therefore, when it is expected to be used in a severe thermal environment, it is preferable to heat both or one of the gasket and the peripheral members. When it is expected to be used in a cold region, it is expected that the contact pressure will be further reduced due to thermal contraction, so it is preferable to further cool both or one of the gasket and the peripheral members. This makes it possible to more reliably suppress the reduction in contact pressure when transitioning from a high temperature to a low temperature.

[0032] In the process of providing a temperature difference between gasket 40 and the surrounding members disclosed herein, the temperature t1 of the gasket and the temperature t2 of the surrounding members are adjusted so that the temperature difference Δt is 10° C. or more. Here, in order to further improve the contact surface pressure between the gasket and sealing plate 24, Δt is more preferably adjusted to 25° C. or more, and particularly preferably 45° C. or more. The lower limit of the temperature t1 of the gasket is preferably -60°C, more preferably -40°C, and particularly preferably -20°C so as not to break due to cooling. The upper limit of t1 is preferably 60°C, more preferably 35°C, and particularly preferably 0°C from the viewpoint of suppressing thermal expansion during assembly. The lower limit of the temperature t2 of the peripheral member is not particularly limited, but is preferably -40°C, more preferably -10°C, and particularly preferably 0°C. The upper limit of t2 is not particularly limited, but is preferably 60°C, more preferably 45°C, and particularly preferably 25°C. The heating and cooling of these members is performed using a blower-type incubator, but is not limited thereto, and may be performed using a water bath or running water, and it is also possible to set the room in which the assembly process is actually performed to a target temperature and keep it warm in advance.

[0033] <Step of crimping the conductive member to the sealing plate with the gasket interposed therebetween> In the manufacturing method of the sealed lithium ion secondary battery according to this embodiment, as described above, a temperature difference is created between the gasket 40, the sealing plate 24, and the conductive member 43, and then the gasket is interposed between the sealing plate and the conductive member, and the conductive member is crimped to the periphery of the opening of the sealing plate to fix the above-mentioned components. The crimping process may be performed by a press or by using a rotary crimping machine having a rotating head, and the rotary crimping machine is preferable because it is superior in that it can reduce the load. This further reduces breakage of the gasket and its surrounding members.

[0034] The step of crimping the conductive member 43 to the sealing plate 24 is preferably performed while maintaining the temperature of both or either of the gasket and the surrounding members adjusted as above. This allows the gasket and the surrounding members to be crimped without applying more load than necessary, and more reliably suppresses a decrease in contact surface pressure during thermal cycles. However, when the gasket, the conductive member, and the sealing body are assembled and load application actually begins, it is sufficient if there is a difference of about 10°C or more between the gasket, the conductive member, and the sealing body.

[0035] In addition, it is preferable to set the working environment at 0° C. or lower, since the gasket is more susceptible to the effects of thermal shrinkage. This increases the difference in thermal shrinkage rate between the gasket and the surrounding members, and allows the gasket to be crimped while being cooled, improving working efficiency.

[0036] <Cold-heat cycle test> FIG. 4 is a diagram showing the temperature change inside the chamber and the change in the contact surface pressure between the gasket 40 and the sealing plate 24 in the cold-hot cycle test in this embodiment. The cold-hot cycle test is a test in which low temperature and high temperature conditions are repeated multiple times to confirm durability. In the cold-hot cycle test, the sealed lithium ion secondary battery was held at -40°C for 4 hours and then held at 60°C for 4 hours, and this cycle was repeated three times. FIG. 4 is an example. However, the set temperature and the number of cycles are not limited to these. The set temperature, time, and number of cycles can be changed in consideration of the actual temperature range in the market and harsh conditions considering the season and environment, and it is possible to start from either high temperature or low temperature.

[0037] In a thermal cycle, when the temperature changes from high to low, the contact surface pressure between the gasket and the sealing plate temporarily decreases, causing a gap and resulting in leakage. This is caused by the difference in the amount of thermal contraction between the resin gasket and the metal connection member and sealing plate adjacent to the gasket. The resin gasket is more susceptible to temperature changes than the metal sealing plate, etc., and expands more at high temperatures and contracts more at low temperatures.

[0038] Test examples relating to the present invention will be described below, but it is not intended that the present invention be limited to those shown in the following test examples.

[0039] The battery case 20 shown in FIG. 2, the wound electrode body 30 connected to the internal terminals 42a and 42b, the external terminals 44a and 44b, and the conductive member 43 were prepared and kept warm at room temperature (25°C). A gasket 40 (made of PFA) was also prepared and kept warm in an incubator set at -20°C, 0°C, 15°C, 22°C, and 50°C. The gasket that had been kept warm was then taken out, and the external terminal was crimped to the periphery of the opening of the sealing plate while the gasket was interposed between the sealing plate and the conductive member. At this time, in order to maintain the temperature of the gasket that had been kept warm during the crimping process, the temperature in the working room was set to be approximately the same as the temperature at which the gasket was kept warm, and each member was crimped.

[0040] The battery case body and the sealing plate were welded together to seal the battery case. Then, a nonaqueous electrolyte was injected through the injection hole in the sealing plate, and the injection hole was airtightly sealed.

[0041] A thermal cycle test (-40°C to 60°C, 3 cycles) was conducted using the sealed lithium ion secondary battery manufactured as above. FIG. 5 is a graph showing the results of this test example. When the surface pressure (minimum surface pressure) at -40°C in the thermal cycle test was measured, it was confirmed that the lower the temperature of the gasket when keeping the gasket warm, i.e., at the start of the crimping process, the higher the minimum surface pressure. It was also confirmed that the minimum surface pressure increases favorably when the temperature of the gasket is 15°C or lower relative to the temperature of the surrounding members of the gasket (25°C), and the minimum surface pressure increases further when the temperature is 0°C or lower, which is a more favorable tendency.

[0042] Although the present invention has been described above with reference to the preferred embodiments, such description is not limiting and various modifications are possible.

[0043] In the technology disclosed herein, each component and each process mentioned herein may be omitted or combined as appropriate, unless a particular problem arises. This specification also includes the disclosures described in the following sections.

[0044] Item 1: A method for manufacturing a sealed battery including an electrode body, a battery case that houses the electrode body, a sealing plate that seals an opening of the battery case, an external terminal provided on the outside of the sealing plate, an internal terminal connected to the electrode body, a conductive member that connects the external terminal and the internal terminal, and a gasket interposed between the sealing plate and the conductive member, the method comprising the steps of: providing a temperature difference of 10°C or more between the gasket, the sealing plate, and the external terminal; and crimping the external terminal to the periphery of the opening of the sealing plate while interposing the gasket between the sealing plate and the conductive member.

[0045] Item 2: The manufacturing method according to item 1, wherein the step of creating the temperature difference includes cooling the gasket to a temperature between -60°C and 0°C.

[0046] Item 3: The manufacturing method according to item 1 or 2, wherein the crimping step is carried out while maintaining the temperature of the cooled gasket.

[0047] Item 4: The manufacturing method according to any one of Items 1 to 3, wherein the crimping step is carried out in a working environment below freezing point. [Explanation of symbols]

[0048] 1. Sealed lithium-ion battery 20 Battery case 22 Battery case body 24 Sealing plate 26 Safety valve 27 Inlet 28 Opening 30 Electrode body 40 Gasket 42a Positive inner terminal 42b Negative internal terminal 43 Conductive materials 44a Positive external terminal 44b Negative external terminal 46 Insulating materials 50 Positive electrode sheet 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 Negative electrode sheet 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 Separator sheet

Claims

1. An electrode body; A battery case that houses the electrode assembly; a sealing plate that seals an opening of the battery case; an external terminal provided on the outside of the sealing plate; An internal terminal connected to the electrode body; a conductive member connecting the external terminal and the internal terminal; a gasket interposed between the sealing plate and the conductive member, providing a temperature difference of 10° C. or more between the gasket and the sealing plate and between the gasket and the external terminal; a step of crimping the external terminal to a periphery of an opening of the sealing plate while interposing the gasket between the sealing plate and the conductive member.

2. The manufacturing method according to claim 1 , wherein the step of providing a temperature difference includes cooling the gasket to a temperature between −60° C. and 0° C.

3. The method according to claim 2 , wherein the crimping step is performed while maintaining the temperature of the cooled gasket.

4. The manufacturing method according to any one of claims 1 to 3, wherein the crimping step is performed in a working environment below freezing point.

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