JP2021089800A - Wound electrode body of secondary battery - Google Patents

Abstract

To provide a wound electrode body of a secondary battery, which includes a collector terminal that is joined to an uncoated part in a more stable state.SOLUTION: A wound electrode body 20 has a flat shape and is formed by stacking and winding sheet-shaped positive electrode and negative electrode via a separator. The wound electrode body 20 includes a collector terminal joined by ultrasonic joining to at least one of a pair of uncoated portions where an electrode mixture is not coated, the uncoated portions being located at both ends in a winding axis direction. The actual thickness Ta of the wound electrode body 20 satisfies the condition of Ta/Tt<0.97 where Tt represents the theoretical thickness of the wound electrode body 20 when the component of the wound electrode body 20 is not compressed in a thickness direction.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to a wound electrode body of a secondary battery.

The secondary battery is widely used as a portable power source for personal computers and mobile terminals, or as a vehicle drive power source for EVs (electric vehicles), HVs (hybrid vehicles), PHVs (plug-in hybrid vehicles), and the like. As an example of a secondary battery, there is a secondary battery provided with a wound electrode body. The wound electrode body is formed into a flat shape by winding a sheet-shaped positive electrode and a negative electrode via a separator. An uncoated portion in which the electrode mixture is not coated is formed on each of both ends of the wound electrode body in the winding axial direction. A current collecting terminal is used to electrically connect the wound electrode body and the external terminal. The current collecting terminal is joined to the uncoated portion of the wound electrode body and is electrically connected to the external terminal. The current collector terminal may be bonded to an uncoated portion by ultrasonic bonding.

For example, the wound electrode body described in Patent Document 1 is formed into a flat shape by being wound so that the separator is located on the innermost circumference and then compressed in the radial direction.

JP-A-2017-208255

In the wound electrode body formed in a flat shape, a force that tries to restore the cylindrical shape is generated (hereinafter, this phenomenon is referred to as "springback"). When springback occurs, the gap between the stacked current collectors may widen. If a current collector terminal is bonded to an uncoated portion by ultrasonic bonding in a state where a gap exists between a plurality of current collectors, the bonding strength may decrease.

A typical object of the present invention is to provide a wound electrode body of a secondary battery in which a current collecting terminal is joined to an uncoated portion in a more stable state.

In the winding electrode body of the secondary battery of one aspect disclosed herein, a sheet-shaped positive electrode and a negative electrode are wound in layers via a separator, and the secondary battery is wound in a flat shape. A collection of electrodes that are joined by ultrasonic bonding to at least one of a pair of uncoated portions that are not coated with electrode mixture and are located at both ends of the wound electrode body in the winding axis direction. The actual thickness Ta of the wound electrode body having an electric terminal and having a flat shape is defined as Tt, which is the theoretical thickness of the wound electrode body when the constituent members of the wound electrode body are not contracted in the thickness direction. If so, the condition of Ta / Tt <0.97 is satisfied.

That is, when the theoretical thickness of the wound electrode body when the constituent members (positive electrode, negative electrode, and separator) are not shrunk in the thickness direction is Tt, the actual thickness Ta is Ta / Tt <0.97. After the wound electrode body is compressed in the thickness direction so as to satisfy the above conditions, the current collecting terminal is bonded to the uncoated portion by ultrasonic bonding. When the wound electrode body is compressed in the thickness direction so as to satisfy the above conditions, it is possible to suppress the formation of a gap between the current collectors due to springback during ultrasonic bonding. Therefore, the decrease in the strength of ultrasonic bonding is suppressed, and the current collecting terminal is bonded to the uncoated portion in a more stable state.

The joint between the current collecting terminal and the uncoated portion by ultrasonic bonding may be formed at a position within 12 mm from the end of the uncoated portion on the side of the external terminal connected to the current collecting terminal. In this case, since the distance from the end of the uncoated portion on the external terminal side to the welded portion is shortened, it becomes easy to shorten the length of the current collecting terminal. Therefore, it becomes easy to reduce the amount of material of the current collecting terminal. On the other hand, the position of the uncoated portion within 12 mm from the end portion on the external terminal side is close to the R portion where the wound electrode body is curved. The part close to the R part is more susceptible to springback than the other parts. Therefore, in the conventional wound electrode body, when the current collector terminal is ultrasonically bonded to the portion near the R portion, a gap is formed between the current collectors and the bonding strength tends to decrease. On the other hand, in the present disclosure, after the wound electrode body is compressed in the thickness direction so as to satisfy the condition of Ta / Tt <0.97, the current collecting terminal is bonded to the wound electrode body by ultrasonic bonding. .. Therefore, the current collecting terminal is joined to the uncoated portion in a more stable state while shortening the distance from the end portion of the uncoated portion on the external terminal side to the welded portion.

The manufacturing method for manufacturing the wound electrode body of the secondary battery according to the present disclosure can also be expressed as follows. The sheet-shaped positive electrode and the negative electrode are stacked and wound via a separator to form a wound electrode body, and the wound electrode body is compressed in a direction perpendicular to the winding axis. Therefore, the actual thickness Ta of the rolled electrode body having a flat shape is set to Ta with respect to the theoretical thickness Tt of the wound electrode body when the constituent members of the wound electrode body are not contracted in the thickness direction. At least one of a compression step of <0.97 Tt and a pair of uncoated portions where the electrode mixture is not coated, which are located at both ends in the winding axis direction of the wound electrode body compressed in the compression step. A method for manufacturing a wound electrode body, which comprises an ultrasonic joining step of joining the current collecting terminals by ultrasonic joining.

It is sectional drawing which shows typically the internal structure of the secondary battery 1 of this embodiment. It is a schematic diagram which shows the structure of the winding electrode body 20 of the secondary battery 1 of this embodiment. It is sectional drawing of the wound electrode body 20 in the state of being compressed from the side surface direction. It is a graph which shows the result of the evaluation test.

Hereinafter, one of the typical embodiments in the present disclosure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. In the following drawings, members and parts that perform the same action are described with the same reference numerals. Further, the dimensional relations (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relations.

As used herein, the term "battery" refers to a general storage device capable of extracting electrical energy, and is a concept including a primary battery and a secondary battery. "Secondary battery" refers to a general storage device that can be charged and discharged repeatedly, and includes so-called storage batteries (that is, chemical batteries) such as lithium ion secondary batteries, nickel hydrogen batteries, and nickel cadmium batteries, as well as electric double layer capacitors and the like. Includes capacitors (ie physical batteries). Hereinafter, the manufacturing method of the secondary battery according to the present disclosure will be described in detail by exemplifying a manufacturing method of a flat square lithium ion secondary battery which is a kind of secondary battery. However, it is not intended to limit the manufacturing method of the secondary battery according to the present disclosure to those described in the following embodiments.

<Rechargeable battery configuration>
The secondary battery 1 shown in FIG. 1 is a sealed lithium ion secondary battery including a wound electrode body 20, a non-aqueous electrolyte solution 10, and a battery case 30. The battery case 30 houses the wound electrode body 20 and the non-aqueous electrolytic solution 10 in a sealed state. The shape of the battery case 30 in this embodiment is a flat square shape. The battery case 30 includes a box-shaped main body 31 having an opening at one end, and a plate-shaped lid 32 that closes the opening of the main body. The battery case 30 (specifically, the lid 32 of the battery case 30) is provided with a positive electrode external terminal 42 and a negative electrode external terminal 44 for external connection, and a safety valve 36. The safety valve 36 releases the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. Further, the battery case 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolytic solution 10 into the inside. As the material of the battery case 30, for example, a lightweight metal material having 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.

As shown in FIG. 2, in the wound electrode body (hereinafter, simply referred to as “electrode body”) 20 of the present embodiment, a long positive electrode (positive electrode sheet) 50, a long first separator 71, and a long length are used. A negative electrode (negative electrode sheet) 60 and a long second separator 72 are overlapped and wound. Specifically, in the positive electrode 50, an electrode mixture (positive electrode active material layer) 54 is coated on one side or both sides (both sides in the present embodiment) of the long positive electrode current collector 52 along the longitudinal direction. There is. In the negative electrode 60, an electrode mixture (negative electrode active material layer) 64 is coated on one side or both sides (both sides in the present embodiment) of the long negative electrode current collector 62 along the longitudinal direction. The uncoated portions 52A and 62A are located at both ends of the winding electrode body 20 in the direction of the winding axis W (the sheet width direction orthogonal to the longitudinal direction). The uncoated portion 52A is a portion where the positive electrode current collector 52 is exposed without coating the electrode mixture 54. A positive electrode current collecting terminal 43 (see FIG. 1) is joined to the uncoated portion 52A at the joint portion 43A. A positive electrode external terminal 42 (see FIG. 1) is electrically connected to the positive electrode current collecting terminal 43. Further, the uncoated portion 62A is a portion where the negative electrode current collector 62 is exposed without coating the electrode mixture 64. A negative electrode current collecting terminal 45 (see FIG. 1) is joined to the uncoated portion 62A at the joint portion 45A. A negative electrode external terminal 44 (see FIG. 1) is electrically connected to the negative electrode current collecting terminal 45.

As the materials and members constituting the positive and negative electrodes of the electrode body 20, the same materials and members as those used for conventional general secondary batteries can be used without limitation. For example, as the positive electrode current collector 52, those used as the positive electrode current collector of this type of secondary battery can be used without particular limitation. Typically, a metal positive electrode current collector having good conductivity is preferred. For example, a metal material such as aluminum, nickel, titanium, or stainless steel can be used as the positive electrode current collector 52. Aluminum foil is used for the positive electrode current collector 52 of this embodiment. Examples of the positive electrode active material of the positive electrode active material layer 54 include lithium composite metal oxides such as a layered structure and a spinel structure (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO). ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO _4, etc.). In the positive electrode active material layer 54, the positive electrode active material and a material (conductive material, binder, etc.) used as needed are dispersed in an appropriate solvent (for example, N-methyl-2-pyrrolidone: NMP) to form a paste (or It can be formed by preparing a (slurry) composition, applying an appropriate amount of the composition to the surface of the positive electrode current collector 52, and drying the composition. In the present embodiment, the positive electrode active material layer contains a ternary positive electrode active material, acetylene black (AB) which is a conductive material, and polyvinylidene fluoride (PVDF) which is a binder.

As the negative electrode current collector 62, those used as the negative electrode current collector of this type of secondary battery can be used without particular limitation. Typically, a metal negative electrode current collector having good conductivity is preferable, and for example, copper (for example, copper foil) or an alloy mainly composed of copper can be used. A copper foil is used for the negative electrode current collector 62 of the present embodiment. Examples of the negative electrode active material of the negative electrode active material layer 64 include a particle-like (or spherical or scaly) carbon material containing a graphite structure (layered structure) at least in part, and a lithium transition metal composite oxide (for example, Li _4). Lithium-titanium composite oxides such as Ti ₅ O ₁₂ ), lithium transition metal composite nitrides and the like. In the negative electrode active material layer 64, a negative electrode active material and a material (binder or the like) used as needed are dispersed in an appropriate solvent (for example, ion-exchanged water) to prepare a paste-like (or slurry-like) composition. , An appropriate amount of the composition can be applied to the surface of the negative electrode current collector 62 and dried to form the composition. In the present embodiment, the graphite-based negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are contained in the negative electrode active material layer 64.

As the first separator 71 and the second separator 72, conventionally known separators made of a porous sheet can be used without particular limitation. For example, a porous sheet (film, non-woven fabric, etc.) made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP) can be mentioned. Such a porous sheet may have a single-layer structure, or may have a plurality of structures having two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). Further, the porous sheet may have a structure in which a porous heat-resistant layer is provided on one side or both sides of the porous sheet. This heat-resistant layer can be, for example, a layer containing an inorganic filler and a binder (also referred to as a filler layer). As the inorganic filler, for example, alumina, boehmite, silica and the like can be preferably adopted.

The non-aqueous electrolyte solution 10 housed in the battery case 30 together with the electrode body 20 contains a supporting salt in an appropriate non-aqueous solvent, and a conventionally known non-aqueous electrolyte solution can be used without particular limitation. For example, as the non-aqueous solvent, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like can be used. Further, as the supporting salt, for example, a lithium salt (for example, LiBOB, LiPF _6, etc.) can be preferably used. In this embodiment, LiBOB is adopted.

<Outline of manufacturing method>
Next, the outline of the manufacturing method of the wound electrode body 20 of the present embodiment will be described. The method for manufacturing the wound electrode body 20 of the present embodiment includes a winding step, a compression step, and an ultrasonic bonding step. In the winding step, the wound electrode body 20 is formed by winding the constituent material. In the compression step, the winding electrode body 20 formed in the winding step is compressed. In the ultrasonic bonding step, a current collecting terminal is bonded to at least one of a pair of uncoated portions 52A and 62A in the wound electrode body 20 by ultrasonic bonding.

In the present embodiment, the positive electrode current collecting terminal 43 is bonded to the uncoated portion 52A by ultrasonic bonding, which is less likely to be affected by changes in the structure of the metal. Further, in the present embodiment, in order to prevent a part of the copper foil constituting the negative electrode current collector 62 from scattering and remaining inside the secondary battery 1, the negative electrode current collector terminal 45 is not formed by resistance welding. It is joined to the coating portion 62A. That is, in the present embodiment, in addition to the winding step, the compression step, and the ultrasonic bonding step, the resistance welding step is also executed. Either the ultrasonic bonding step or the resistance welding step may be executed first.

<Turning process>
In the winding step of the present embodiment, as shown in FIG. 2, the long positive electrode 50, the long first separator 71, the long negative electrode 60, and the long second separator 72 are overlapped with each other. The wound electrode body 20 is formed by being wound and wound. In the winding electrode body 20, for example, the positive electrode 50, the first separator 71, the negative electrode 60, and the second separator 72 are wound around a winding core having a flat cross section orthogonal to the winding axis W. It may be formed in a flat shape. Further, the wound electrode body 20 is, for example, in the side surface direction (direction perpendicular to the winding axis W) after the positive electrode 50, the first separator 71, the negative electrode 60, and the second separator 72 are wound in a cylindrical shape. It may be formed into a flat shape by compressing (crushing) from. The step of compressing the cylindrical wound electrode body 20 from the side surface direction may be executed in the compression step described later.

<Compression process>
The compression step in this embodiment will be described with reference to FIG. In the compression step, the winding electrode body 20 is compressed in the direction perpendicular to the winding axis W (see FIG. 2) (from the side surface direction). The method of compressing the wound electrode body 20 can be appropriately selected. As an example, in the present embodiment, the winding electrode body 20 is arranged between two compression plates 80 facing each other, and a compressive force is applied in a direction to reduce the distance between the two compression plates 80. The rotating electrode body 20 is compressed.

Here, the constituent members of the wound electrode body 20 (that is, the laminated positive electrode 50, the first separator 71, the negative electrode 60, and the second separator 72) are not compressed in the thickness direction, and the gaps between the constituent members are not compressed. Let Tt be the theoretical thickness of the wound electrode body when the wound electrode body 20 is formed in a flat shape without the above. In the compression step of the present embodiment, the wound electrode body 20 is compressed from the side surface so that the actual thickness Ta of the flat wound electrode body 20 satisfies the condition of Ta / Tt <0.97. .. That is, in the compression step of the present embodiment, the actual thickness Ta of the wound electrode body 20 is set to Ta <0.97 Tt by compressing the wound electrode body 20 from the side surface direction. As a result, it is possible to prevent a gap from being generated by springback between the positive electrode current collectors 50 laminated in the uncoated portion 52 at the time of ultrasonic bonding described later. In the present embodiment, the condition of Ta / Tt <0.97 was satisfied by increasing the pressure to more than 50 kN in the compression step.

<Ultrasonic bonding process>
In the ultrasonic bonding step, the positive electrode current collecting terminal 43 is bonded to the uncoated portion 52A of the wound electrode body 20 compressed in the compression step by ultrasonic bonding. In the present embodiment, the bonding tip (not shown) is pressed against the surface of the uncoated portion 52A in a state where the plate surface of the substantially plate-shaped positive electrode current collecting terminal 43 is in surface contact with the surface of the uncoated portion 52A to give ultrasonic vibration. As a result, the positive electrode current collecting terminal 43 is bonded to the uncoated portion 52A by ultrasonic bonding.

When the ultrasonic bonding step is executed, the wound electrode body 20 is compressed in the thickness direction so as to satisfy the condition of Ta / Tt <0.97. Therefore, the positive electrode current collector terminal 43 is joined to the uncoated portion 52A in a state where a gap is suppressed due to springback between the laminated positive electrode current collectors 50. Therefore, the decrease in the bonding strength of the positive electrode current collecting terminal 43 is suppressed.

As shown in FIG. 1, in the present embodiment, the distance from the uncoated portion 52A of the wound electrode body 20 to the end portion E on the positive electrode external terminal 42 side connected to the positive electrode current collecting terminal 43 is within 12 mm. A joint portion 43A between the positive electrode current collecting terminal 43 and the uncoated portion 52A is formed in the range of. In this case, the length of the positive electrode current collecting terminal 43 (the length in the vertical direction in FIG. 1) can be easily shortened, so that the material of the positive electrode current collecting terminal 43 can be easily reduced. In the present embodiment, the distance from the end E of the uncoated portion 52A to the center of the joint 43A is set to about 4 mm. Further, in the present embodiment, the joint portion 45A between the negative electrode current collecting terminal 45 and the uncoated portion 62A is also on the negative electrode external terminal 44 side of the uncoated portion 62A, similarly to the joint portion 43A of the positive electrode current collecting terminal 43. It is formed within 12 mm from the end. Therefore, it becomes easy to reduce the material of the negative electrode current collecting terminal 45.

Here, the position within 12 mm from the end E of the uncoated portion 52A on the positive electrode external terminal 42 side is close to the R portion 21 (see FIG. 3) in which the wound electrode body is curved, and the portion close to the R portion 21. , More susceptible to springback than other parts. On the other hand, in the present embodiment, the positive electrode current collecting terminal 43 is ultrasonically bonded to the uncoated portion 52A of the wound electrode body 20 compressed in the thickness direction so as to satisfy the condition of Ta / Tt <0.97. Bonded by. Therefore, the positive electrode current collecting terminal 43 is joined to the uncoated portion 52A in a more stable state while shortening the distance from the end E of the uncoated portion 52A to the joining portion 43A.

In this embodiment, the ultrasonic bonding step is executed after the compression in the thickness direction of the wound electrode body 20 in the compression step is released. However, the ultrasonic bonding step may be executed while the wound electrode body 20 is compressed in the thickness direction.

The secondary battery 1 is manufactured by accommodating the wound electrode body 20 manufactured by each of the above steps inside the battery case 30. Specifically, as shown in FIG. 1, both the positive electrode current collecting terminal 43 and the negative electrode current collecting terminal 45 are joined so as to project from the wound electrode body 20 in the same direction. The positive electrode current collecting terminal 43 and the negative electrode current collecting terminal 45 are mounted on the lid 32 of the battery case 30, and the positive electrode current collecting terminal 43 and the positive electrode external terminal 42, and the negative electrode current collecting terminal 45 and the negative electrode external terminal 44 are electrically connected. Is connected. Next, the wound electrode body 20 is housed in the main body 31 of the battery case 30 through an opening from the end portion on the side opposite to the lid body 32 side. The lid 32 and the main body 31 are joined by welding or the like. After that, the secondary battery 1 is manufactured by injecting the non-aqueous electrolytic solution 10 into the battery case 30.

<Example>
The result of the evaluation test for evaluating the effect of the manufacturing method of this embodiment will be described with reference to FIG. In this evaluation test, four types of wound electrode bodies were manufactured by changing only the magnitude of the compression pressure in the compression step. The manufacturing process, material, size, and the like of the four types of wound electrode bodies other than the pressure in the compression step are all the same as those of the wound electrode body 20 described in the above embodiment. Next, for each of the four types of wound electrode bodies, the variation (σ) / N of the bonding strength of the positive electrode current collecting terminal 43 with respect to the uncoated portion 52A was determined.

As shown in FIG. 4, when the pressure in the compression step was 10 kN, the variation in strength was an unacceptable value (a value larger than 15). When the pressure was 10 kN, Ta / Tt was larger than 1.00. Similarly, even when the pressure in the compression step was set to 30 kN, the variation in strength became an unacceptable value. When the pressure was 30 kN, Ta / Tt was about 0.983. On the other hand, in the wound electrode body in which the pressure in the compression step was 60 kN and Ta / Tt was about 0.96, the variation in strength was an acceptable value. Further, in the wound electrode body in which the pressure in the compression step was 90 kN and the Ta / Tt was about 0.947, the variation in strength was further reduced as compared with the case where the pressure was 60 kN. From the above, by compressing the wound electrode body so that the actual thickness Ta of the wound electrode body satisfies the condition of Ta / Tt <0.97, the positive electrode current collecting terminal 43 is not coated in a more stable state. It can be seen that it is joined to the work part 52A.

The techniques disclosed in the above embodiments are merely examples. Therefore, it is possible to modify the techniques exemplified in the above embodiments. For example, in the above embodiment, ultrasonic bonding is used when bonding the positive electrode current collecting terminal 43 to the uncoated portion 52A. The negative electrode current collecting terminal 45 is joined to the uncoated portion 62A by resistance welding. However, ultrasonic bonding may be adopted when bonding the negative electrode current collecting terminal 45 to the uncoated portion 62A. Even in this case, if the actual thickness of the wound electrode body 20 satisfies the condition of Ta / Tt <0.97, the negative electrode current collecting terminal 45 is joined to the uncoated portion 62A in a stable state.

Although the detailed description has been given with reference to specific embodiments, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the above-described embodiments.

1 Rechargeable battery 20 Winding electrode body 42 Positive electrode external terminal 43 Positive electrode current collecting terminal 43A Joint part 50 Positive electrode 52A Uncoated part 54 Electrode mixture 71 First separator 72 Second separator

Claims (1)

A sheet-shaped positive electrode and a negative electrode are wound by being stacked with each other via a separator, and is a wound electrode body of a secondary battery formed in a flat shape.
A current collecting terminal joined by ultrasonic bonding is provided at least one of a pair of uncoated portions where the electrode mixture is not coated, which are located at both ends in the winding axis direction of the wound electrode body.
When the actual thickness Ta of the flat-shaped wound electrode body is Tt when the theoretical thickness of the wound electrode body when the constituent members of the wound electrode body are not contracted in the thickness direction is Tt. A wound electrode body of a secondary battery that satisfies the condition of / Tt <0.97.

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