Method for manufacturing sealed secondary batteries

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 high energy density, are preferred for use as high-output power sources for vehicles.

[0003] Among these types of secondary batteries, a widely known sealed battery is one in which a wound electrode assembly, 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 assembly is drawn out to the upper end (lid) of the battery case and 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] Gaskets are also used to prevent electrolyte leakage from a predetermined space 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 sufficient compression of the convex portions suppresses electrolyte penetration. The gasket of the prior art prevents leakage from gaps between the gasket and surrounding components by increasing the compressive force. This configuration is said to be effective against increases in internal pressure in sealed secondary batteries at high temperatures. [Prior art documents] [Patent documents]

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

[0006] Before shipping, sealed batteries such as those described above may undergo a thermal cycle test in which low and high temperature conditions are repeatedly cycled multiple times to confirm their durability. The inventors discovered that during the thermal cycle test (temperature cycle test), when the temperature changes from high to low, the amount of thermal contraction of the gasket is greater than the amount of thermal contraction of the surrounding components, which can temporarily reduce the contact 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 or surrounding components may break due to durability issues. Therefore, 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 cycling without increasing the load during gasket assembly above a certain level. [Means for solving the problem]

[0008] One embodiment of a method for manufacturing a sealed battery disclosed herein is a method for manufacturing a sealed battery comprising an electrode body, a battery case that houses the electrode body, a sealing plate that seals the 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, and includes a step of creating a temperature difference of 10°C or more between the gasket and 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, the load applied to the gasket during assembly is not increased more than necessary, and a temporary decrease in contact pressure between the gasket and surrounding components can be suppressed when the temperature changes from high to low during thermal cycling, thereby enabling the manufacture of a battery with a reduced incidence of leakage during thermal cycling.

[0009] In one embodiment of the method for manufacturing 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 pressure between the gasket and peripheral components can be more effectively suppressed, and deterioration of battery performance can be prevented.

[0010] In the method for manufacturing a sealed battery according to one aspect 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 cycling.

[0011] In the method for manufacturing 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 during assembly of the gasket. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view of a sealed secondary battery according to an embodiment disclosed herein; [Figure 2] 1 is a cross-sectional view of a sealed secondary battery according to one embodiment disclosed herein. [Figure 3] 1 is an enlarged cross-sectional view of a main portion 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 surface pressure in a thermal cycle test of one embodiment disclosed herein. [Figure 5] 1 is a graph showing the minimum surface pressure in a thermal cycle test of one embodiment disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0013] Exemplary embodiments of the present disclosure will be described in detail below with reference to the drawings. Matters necessary for implementation other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. In the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Furthermore, 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)," it means "A or more and B or less," and also encompasses 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 generally to an energy storage device capable of extracting electrical energy, and is a concept that includes primary batteries and secondary batteries. Furthermore, the term "secondary battery" refers generally to an energy storage device that can be repeatedly charged and discharged, and encompasses so-called storage batteries (i.e., chemical batteries) such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, as well as capacitors (e.g., lithium-ion capacitors) such as electric double-layer capacitors. Furthermore, the term "sealed battery" refers to a secondary battery in which an electrode assembly and an electrolyte are housed in a sealed case. Below, a 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, prismatic sealed lithium-ion secondary battery, which is one 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 that described in the following embodiments.

[0016] FIG. 1 is a perspective view schematically illustrating the external shape of a sealed lithium-ion secondary battery 1 according to one embodiment disclosed herein. FIG. 2 is a schematic longitudinal cross-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 of the sealed lithium-ion secondary battery 1, the short side direction perpendicular to the long side direction, and the up-down direction, respectively. However, these directions are merely used for the sake of convenience 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 assembly 30 is a wound electrode assembly in which a positive electrode sheet 50, a negative electrode sheet 60, and a separator sheet 70 are wound together. However, the electrode assembly 30 is not limited to this, and may be a stacked electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween. Furthermore, the battery case 20 may house multiple electrode assemblies.

[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 in this case) 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 in this case) 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. A positive electrode internal terminal 42a and a negative electrode internal terminal 42b are joined to the positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a, 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 limitations. 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 battery case 20 has a rectangular parallelepiped shape and a flat, rectangular 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 houses the electrode assembly 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 assembly 30 and the electrolyte are housed inside the battery case in a sealed state. The material of the battery case 20 is not particularly limited as long as it is the same as that used in conventional secondary batteries of this type. As an example, a lightweight metal material with good thermal conductivity, such as aluminum, is used. However, the configuration of the battery case can also be changed. 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 that extend from the bottom wall and face 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 designed to release the internal pressure of the battery case when the internal pressure rises above a predetermined level, and an injection port 27 for injecting electrolyte. Also provided are a positive electrode external terminal 44a and a negative electrode external terminal 44b for external connection. These electrode terminals are electrically connected to the wound electrode assembly 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 can be used as the positive external terminal. For example, copper or a copper alloy can 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 in order to improve 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 in order to improve 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 typically the same as that of the internal terminals 42a, 42b and the external terminals 44a, 44b, but is not limited to this. In one example of the conductive member 43 disclosed herein, a portion 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. FIG. 3 shows an enlarged cross-sectional view of the area where the negative electrode external terminal 44b and the conductive member 43 are attached to the sealing plate. The area 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 in which the conductive member 43 is attached via a gasket 40. The opening 28 penetrates the sealing plate 24 at a predetermined position on the sealing plate 24.

[0027] The gasket 40 is a resin sealing material 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 external terminals 44a and 44b. It also ensures airtightness of the battery case 20. The gasket 40 is preferably made of a material with excellent chemical resistance and weather resistance. Examples of materials that may be used include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polypropylene (PP), polyethylene (PE), and polyphenylene sulfide resin (PPS). PFA is preferred because it is less likely to break at sub-zero temperatures. 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 the predetermined insulating properties, and the same material as that of the gasket 40 may be used.

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

[0030] <Step of creating a temperature difference between the gasket and the sealing plate and 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 create a temperature difference of 10°C or more between the gasket and its surrounding components (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 during a transition from a high temperature to a low temperature. Furthermore, during a transition from a low temperature to a high temperature, the contact pressure between the gasket and the sealing plate increases due to thermal expansion, which is advantageous in preventing leakage due to an increase in the battery's internal pressure. Here, if the temperature of the gasket is t1 and the temperature of the surrounding components is t2, the temperature difference is Δt. Note that t2 refers to the lower temperature of the sealing plate or the conductive member, and there may be a temperature difference between the two.

[0031] In another aspect of this embodiment, instead of cooling the gasket 40, the peripheral components can be heated or cooled. When the sealed lithium-ion secondary battery is used in tropical or desert regions, the gasket or peripheral components may undergo excessive thermal expansion, resulting in stress concentration near the contact surface between the gasket and the sealing plate. Therefore, when the battery is expected to be used in a severe thermal environment, it is preferable to heat both or either of the gasket and peripheral components. Furthermore, when the battery 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 either of the gasket and peripheral components. This more reliably suppresses the decrease in contact pressure when transitioning from high to low temperatures.

[0032] In the process of creating a temperature difference between the gasket 40 and the surrounding components disclosed herein, the temperature t1 of the gasket and the temperature t2 of the surrounding components 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 the 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 to prevent rupture 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 members 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. Alternatively, heating and cooling may be performed using a water bath or running water. It is also possible to heat the room in which the assembly process is actually performed to the target temperature and maintain the temperature 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. Then, the gasket is interposed between the sealing plate and the conductive member, and the conductive member is crimped around the periphery of the opening of the sealing plate to secure the components. The crimping process may be performed using a press or a rotary crimping machine with a rotating head. Rotary crimping machines are preferred because they can reduce the load. This further reduces the risk of breakage of the gasket and its surrounding components.

[0034] The process of crimping the conductive member 43 to the sealing plate 24 is preferably performed while maintaining the temperature of both or one of the gasket and surrounding components adjusted as described above. This allows the gasket and surrounding components to be crimped without applying an excessive load to them, more reliably suppressing a decrease in contact surface pressure during thermal cycles. However, when the gasket, conductive member, and sealing body are assembled and the load is actually applied, a difference of approximately 10°C or more between the gasket, the conductive member, and the sealing body is sufficient.

[0035] Furthermore, it is preferable to keep the working environment at 0°C or below, since this makes the gasket more susceptible to the effects of thermal shrinkage. This increases the difference in thermal shrinkage rate between the gasket and the surrounding components, allowing the gasket to be crimped while being cooled, improving working efficiency.

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

[0037] During a thermal cycle, when the temperature changes from high to low, the contact pressure between the gasket and the sealing plate temporarily decreases, creating a gap and resulting in leakage. This is due to the difference in the amount of thermal contraction between the resin gasket and the metal connecting member and sealing plate adjacent to the gasket. Resin gaskets are more susceptible to temperature changes than metal sealing plates, etc., and expand more at high temperatures and contract 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] A battery case 20 shown in FIG. 2, a wound electrode assembly 30 connected to internal terminals 42a and 42b, external terminals 44a and 44b, and a 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 temperatures of -20°C, 0°C, 15°C, 22°C, and 50°C. The kept warm gasket was then removed, and the external terminal was crimped around the opening of the sealing plate while the gasket was interposed between the sealing plate and the conductive member. To maintain the temperature of the kept warm gasket during the crimping process, the temperature in the working chamber was kept approximately the same as the temperature at which the gasket was kept warm.

[0040] The battery case body and the sealing plate were welded together to seal the battery case, and then a non-aqueous electrolyte solution was poured into the sealing plate through the filling hole, which was then sealed airtight.

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

[0042] Although the present invention has been described above with reference to 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 comprising an electrode assembly, a battery case that houses the electrode assembly, a sealing plate that seals the opening of the battery case, an external terminal provided on the outside of the sealing plate, an internal terminal connected to the electrode assembly, 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: creating 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 internal terminal 42b Negative internal terminal 43 Conductive materials 44a Positive external terminal 44b Negative external terminal 46 Insulating material 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 the 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, a step of cooling the gasket to a temperature of −60° C. or higher and 0° C. or lower to provide a temperature difference of 10° C. or higher between the gasket and the sealing plate, the external terminals, the internal terminals, and the conductive member; 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.

2. The manufacturing method according to claim 1 , wherein the crimping step is performed while maintaining the temperature of the cooled gasket.

3. The manufacturing method according to claim 1 or 2, wherein the caulking step is performed in a working environment below freezing point.

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