JP7284920B2 - Method for manufacturing secondary battery - Google Patents

Description

The present disclosure relates to a method for manufacturing a secondary battery.

Secondary batteries are widely used as portable power sources for personal computers, mobile terminals, and the like, or as power sources for driving vehicles such as EVs (electric vehicles), HVs (hybrid vehicles), and PHVs (plug-in hybrid vehicles). As an example of a secondary battery, there is a secondary battery in which a wound electrode assembly and an electrolytic solution are housed in a battery case. When manufacturing a secondary battery using an electrolytic solution, it is necessary to impregnate the inside of the wound electrode body with the electrolytic solution. In the wound electrode body, the positive electrode, the negative electrode, and the separator are laminated, so that it takes time to impregnate the inside of the wound electrode body with the electrolytic solution in the conventional manufacturing method of the secondary battery.

For example, in the battery manufacturing method described in Patent Document 1, the injection of electrolyte into the battery case is started in a state in which the pressure inside the battery case is reduced below the atmospheric pressure. Next, the liquid level of the electrolytic solution is lowered by stopping the injection of the electrolytic solution and increasing the air pressure in the battery case. After that, injection of the electrolytic solution is resumed. The method described above attempts to shorten the impregnation time of the electrolytic solution.

JP 2018-106816 A

In the manufacturing method described in Patent Document 1, when the atmospheric pressure inside the battery case is increased from a reduced pressure state, there is a possibility that gas (for example, air) instead of the electrolytic solution may enter the wound electrode assembly due to the differential pressure. be. In this case, the impregnation effect of the electrolytic solution using the differential pressure is weakened, making it difficult to shorten the impregnation time.

A typical object of the present invention is to provide a method for manufacturing a secondary battery that can impregnate the inside of a wound electrode body with an electrolytic solution in a short period of time.

A method of manufacturing a secondary battery according to one aspect disclosed herein includes a battery case having a flat outer shape, a preparation step of preparing an assembly of a wound electrode assembly housed in the battery case, and the winding of the electrode assembly. a pressure reducing step of reducing the pressure inside the battery case in which the electrode assembly is accommodated; A space securing step of securing a sealed space inside the wound electrode body by compressing the battery case in the thickness direction at two positions sandwiching the central portion of the electrode body, and compressing the battery case. an injection step of injecting an electrolytic solution into the inside of the battery case, a step of increasing the internal pressure of the battery case into which the electrolytic solution is injected, and a step of releasing the compression in the thickness direction. and an impregnation promoting step of promoting impregnation of the electrolytic solution into the inside of the wound electrode assembly by executing the impregnation promoting step.

In the method for manufacturing a secondary battery according to the present disclosure, the battery case is compressed in the thickness direction, and the electrolytic solution is injected in a state in which a sealed space is secured inside the wound electrode body. After that, a step of increasing the pressure inside the battery case (hereinafter referred to as “pressure increasing step”) and a step of releasing the compression of the battery case (hereinafter referred to as “compression releasing step”) are performed. As a result, impregnation of the electrolytic solution into the inside of the wound electrode body is promoted by the differential pressure between the inside and outside of the wound electrode body inside the battery case. At the time when the pressure increasing process and the compression releasing process are executed, the electrolyte has already been injected into the inside of the battery case. is suppressed. Therefore, the time for impregnating the inside of the wound electrode body with the electrolytic solution is appropriately suppressed.

Either of the pressure increasing process and the compression releasing process which are executed after the injection process may be started first, or the two processes may be started simultaneously. Further, after the impregnation promoting step (including the pressure increasing step and the compression releasing step) is performed, a re-injecting step of re-injecting the electrolyte into the battery case may be performed. In this case, the inside of the wound electrode body is impregnated with a sufficient amount of electrolyte.

1 is a cross-sectional view schematically showing the internal structure of a secondary battery 1 of this embodiment; FIG. FIG. 2 is a schematic diagram showing the configuration of a wound electrode assembly 20 of the secondary battery 1 of the present embodiment; FIG. 4 is a schematic diagram of the secondary battery 1 placed in a chamber 80 in which the pressure has been lowered and in which a space securing step has been performed. FIG. 2 is a schematic diagram of secondary battery 1 in a state in which electrolytic solution 10 has been injected in an injection step and a pressure increasing step has been performed.

One typical embodiment of the present disclosure will be described in detail below with reference to the drawings. Matters other than those specifically referred to in this specification that are necessary for implementation can be grasped as design matters for those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. In the drawings below, members and portions having the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships.

As used herein, the term “battery” is a general term for power storage devices from which electrical energy can be extracted, and is a concept that includes primary batteries and secondary batteries. "Secondary battery" refers to a general electricity storage device that can be repeatedly charged and discharged, and in addition to so-called storage batteries (that is, chemical batteries) such as lithium ion secondary batteries, nickel hydrogen batteries, and nickel cadmium batteries, electric double layer capacitors, etc. It contains a capacitor (ie a physical battery). Hereinafter, the method for manufacturing a secondary battery according to the present disclosure will be described in detail by exemplifying a method for manufacturing a flat prismatic lithium-ion secondary battery, which is a type of secondary battery. However, the method for manufacturing a secondary battery according to the present disclosure is not intended to be limited to those described in the following embodiments.

<Configuration of secondary battery>
A secondary battery 1 shown in FIG. 1 is a sealed lithium-ion secondary battery that includes a wound electrode body 20 , an electrolytic solution (non-aqueous electrolytic solution in this embodiment) 10 , and a battery case 30 . The battery case 30 accommodates the wound electrode assembly 20 and the electrolytic solution 10 in a hermetically sealed state. The shape of the battery case 30 in this embodiment is a flat rectangular shape. The battery case 30 includes a box-shaped main body 31 having an opening at one end, and a plate-like 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 external terminal 42 and a negative external terminal 44 for external connection, and a safety valve 36. As shown in FIG. 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 37 for injecting the electrolytic solution 10 therein. The battery case 30 is desirably made of a material that is lightweight and has good thermal conductivity. Further, when the battery case 30 is compressed in the thickness direction, the compressed portion is appropriately deformed inward. As an example, the battery case 30 of the present embodiment is made of aluminum, which has high thermal conductivity and moderate rigidity. 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, a long shaped negative electrode (negative electrode sheet) 60 and a long second separator 72 are superimposed and wound. Specifically, in the positive electrode 50 , a positive electrode active material layer 54 is coated along the longitudinal direction on one side or both sides (both sides in this embodiment) of a long positive electrode current collector 52 . In the negative electrode 60, a negative electrode active material layer 64 is coated on one side or both sides (both sides in this embodiment) of a long negative electrode current collector 62 along the longitudinal direction. The uncoated portions 52A and 62A are located at both ends of the wound electrode body 20 in the direction of the winding axis W, respectively. The uncoated portion 52A is a portion where the positive electrode current collector 52 is exposed without being coated with the positive electrode active material layer 54 . The positive collector terminal 43 (see FIG. 1) is joined to the uncoated portion 52A. A positive external terminal 42 (see FIG. 1) is electrically connected to the positive collector terminal 43 . An uncoated portion 62A is a portion where the negative electrode current collector 62 is exposed without being coated with the negative electrode active material layer 64 . The negative collector terminal 45 (see FIG. 1) is joined to the uncoated portion 62A. A negative external terminal 44 (see FIG. 1) is electrically connected to the negative collector terminal 45 .

Materials and members that constitute the positive and negative electrodes of the electrode assembly 20 can be the same as those used in conventional general secondary batteries without limitation. For example, for the positive electrode current collector 52, a material used as a positive electrode current collector for this type of secondary battery can be used without particular limitation. Typically, a positive electrode current collector made of metal with good electrical conductivity is preferred. For example, metal materials such as aluminum, nickel, titanium, and stainless steel can be used as the positive electrode current collector 52 . Aluminum foil is used for the positive electrode current collector 52 of the present embodiment. Examples of the positive electrode active material of the positive electrode active material layer 54 include lithium composite metal oxides having a layered structure or a spinel structure (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , _LiMn2O4 , _{LiNi0.5Mn1.5O4} , _{LiCrMnO4 ,} LiFePO4 _, etc. _{) .} The positive electrode active material layer 54 is formed by dispersing a positive electrode active material and optionally used materials (conductive materials, binders, etc.) in an appropriate solvent (eg, 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 this embodiment, the positive electrode active material layer 54 includes a ternary positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder.

As the negative electrode current collector 62, any material used as a negative electrode current collector for 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. Copper foil is used for the negative electrode current collector 62 of the present embodiment. As the negative electrode active material of the negative electrode active material layer 64, for example, a particulate (or spherical or scale-like) carbon material containing at least a part of a graphite structure (layered structure), 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. The negative electrode active material layer 64 is prepared by dispersing a negative electrode active material and optionally used materials (binder etc.) in an appropriate solvent (eg ion-exchanged water) to prepare a paste (or slurry) composition. can be formed by applying an appropriate amount of the composition to the surface of the negative electrode current collector 62 and drying it. In this embodiment, the negative electrode active material layer 64 includes a graphite-based negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener.

As the first separator 71 and the second separator 72, separators made of conventionally known porous sheets can be used without particular limitation. Examples thereof include porous sheets (films, non-woven fabrics, etc.) made of polyolefin resins such as polyethylene (PE) and polypropylene (PP). Such a porous sheet may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). Moreover, one side or both sides of the porous sheet may be provided with a porous heat-resistant layer. This heat-resistant layer may be, for example, a layer containing an inorganic filler and a binder (also referred to as a filler layer). As inorganic fillers, for example, alumina, boehmite, silica, etc. can be preferably employed.

The electrolytic solution 10 contained in the battery case 30 together with the electrode body 20 contains a supporting salt in an appropriate non-aqueous solvent, and conventionally known electrolytic solutions can be employed without particular limitations. For example, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like can be used as non-aqueous solvents. Also, as the supporting salt, for example, a lithium salt (eg, LiBOB, _LiPF6, etc.) can be preferably used. LiBOB is adopted in this embodiment.

<Manufacturing method>
Next, a method for manufacturing the secondary battery 1 of this embodiment will be described. The manufacturing method of the secondary battery 1 of the present embodiment includes a preparation step, a pressure reduction step, a space securing step, an injection step, an impregnation promotion step, and a re-injection step.

In the preparation step, an assembly of the battery case 30 and the wound electrode body 20 housed in the battery case 30 is prepared. The preparation process includes an electrode body forming process and an electrode body accommodation process.

In the electrode body forming step, the wound electrode body 20 is formed. Specifically, as shown in FIG. 2, a long positive electrode 50, a first long separator 71, a long negative electrode 60, and a second long separator 72 are superimposed and wound. As a result, the flat wound electrode body 20 is formed. For example, the wound electrode body 20 is obtained by winding a positive electrode 50, a first separator 71, a negative electrode 60, and a second separator 72 around a winding core having a flat cross section perpendicular to the winding axis W, It may be formed in a flat shape. Further, the wound electrode body 20 may be formed into a flat shape by, for example, rolling the positive electrode 50, the first separator 71, the negative electrode 60, and the second separator 72 into a cylindrical shape and then crushing it from the side. good.

In the electrode body accommodating step, the wound electrode body 20 formed in the electrode body forming step is accommodated inside the battery case 30 . Specifically, as shown in FIG. 1, the positive collector terminal 43 is joined to the uncoated portion 52A of the wound electrode body 20, and the negative collector terminal 45 is joined to the uncoated portion 62A. The positive collector terminal 43 and the negative collector terminal 45 are joined together so as to protrude in the same direction from the wound electrode assembly 20 . Next, the positive collector terminal 43 and the negative collector terminal 45 are attached to the lid 32 of the battery case 30, and the positive collector terminal 43 and the positive external terminal 42, and the negative collector terminal 45 and the negative external terminal 44 are connected. are electrically connected. Next, the wound electrode body 20 is accommodated through the opening inside the main body 31 of the battery case 30 from the end opposite to the lid body 32 side. By joining the lid 32 and the main body 31 by welding or the like, the electrode assembly step is completed. A winding axis W (see FIG. 2 ) of the wound electrode body 20 is substantially parallel to the bottom surface of the main body 31 of the battery case 30 .

In the pressure reduction step, the internal pressure of the battery case 30 in which the wound electrode body 20 is housed is reduced below the atmospheric pressure. As an example, in the present embodiment, the battery case 30 is placed inside a chamber 80 (see FIG. 3), and the pressure inside the chamber 80 is lowered below atmospheric pressure (vacuum pressure), whereby the battery case 30 reduce both the internal and ambient pressure of the In this embodiment, the degree of vacuum inside the chamber 80 is set to approximately 20 kPa. However, it is also possible to change the method of reducing the pressure inside the battery case 30 . For example, the pressure inside the battery case 30 may be lowered below the atmospheric pressure by discharging the gas inside the battery case 30 to the outside.

In the space securing step, as shown in FIG. 3, in a state where the pressure inside the battery case 30 is reduced, the wound electrode body 20 is moved in the direction of the winding axis W of the wound electrode body 20 (horizontal direction in FIG. 3). The battery case 30 is compressed in the thickness direction at at least two positions sandwiching the central portion of the battery case 20 . As a result, a sealed space S is secured inside the wound electrode body 20 . A method for compressing the battery case 30 can be selected as appropriate. As an example, in the present embodiment, a columnar (cylindrical) compression member 90 extending in a direction intersecting the winding axis W of the wound electrode body 20 (perpendicularly intersecting in the present embodiment) compresses the battery case 30 in the thickness direction. A sealed space S is ensured by being compressed from both sides. The longitudinal length of the compression member 90 is longer than the width of the wound electrode body 20 in the direction perpendicular to the winding axis W (vertical width in FIG. 3). Therefore, since the wound electrode body 20 is compressed over the entire vertical direction by the compressing member 90, the closed space S is appropriately secured. The shape of the compression member 90 can also be appropriately selected. The shape of the compression member 90 may be, for example, prismatic, plate-like, or the like.

Further, in the present embodiment, in the battery case 30, two locations inside the uncoated portions 52A and 62A of the wound electrode assembly 20 to which the positive collector terminal 43 and the negative collector terminal 45 are joined are It is compressed by compression member 90 . Therefore, the positive collector terminal 43 and the negative collector terminal 45 do not interfere with compression.

In the injection step, the electrolytic solution 10 is injected into the battery case 30 while the battery case 30 is compressed by the compressing member (that is, the sealed space S is secured). In this embodiment, a nozzle is inserted into the inlet 37 of the lid 32, and the electrolytic solution 10 is injected into the battery case 30 from the tip of the nozzle. In this embodiment, the electrolytic solution 10 is injected with a gap between the nozzle and the edge of the injection port 37 (that is, with the same pressure inside and outside the battery case 30). However, the electrolyte solution 10 may be injected in a state in which the nozzle is in contact with the edge of the injection port 37 without gaps (that is, in a state in which the inside of the battery case 30 is sealed).

The electrolytic solution 10 is impregnated inside the wound electrode body 20 from both ends in the direction of the winding axis W. As shown in FIG. Therefore, in the injection step, as shown in FIG. 4 , the electrolytic solution 10 may be injected so that both ends of the wound electrode assembly 20 in the direction of the winding axis W are entirely immersed in the electrolytic solution 10 . desirable. In this case, the possibility that the gas instead of the electrolytic solution 10 penetrates into the wound electrode body 20 in the impregnation promoting step described later is further reduced.

In the impregnation promoting step, impregnation of the electrolytic solution 10 into the inside of the wound electrode body 20 is promoted by performing the pressure increasing step and the compression releasing step.

In the pressure increasing step, the pressure inside the battery case 30 is increased. In the present embodiment, the pressure inside the chamber 80 is returned to the atmospheric pressure, so that the pressure inside the battery case 30 arranged in the chamber 80 rises. As a result, as shown in FIG. 4, in the battery case 30, the pressure in the closed space S inside the wound electrode body 20 is the pressure outside the wound electrode body 20 (the space K in the example shown in FIG. 4). becomes lower than That is, a differential pressure is generated between the sealed space S inside the wound electrode body 20 and the external space K of the wound electrode body 20 .

In the compression releasing step, the compression in the thickness direction of battery case 30 by compressing member 90 is released. As a result, the electrolytic solution 10 injected into the inside of the battery case 30 is impregnated from both ends of the wound electrode body 20 into the inside in a short time due to the differential pressure between the inside and outside of the wound electrode body 20 . In other words, the impregnation of the electrolytic solution 10 into the inside of the wound electrode body 20 is promoted by the differential pressure by performing the pressure increasing process and the compression releasing process. Since both ends of the wound electrode body 20 are entirely immersed in the electrolytic solution 10 at the time when the pressure increasing process and the compression releasing process are performed, the gas instead of the electrolytic solution 10 is applied to the wound electrode body 20 due to the differential pressure. Hard to get inside. Therefore, the time for impregnating the inside of the wound electrode body 20 with the electrolytic solution 10 is appropriately suppressed.

In addition, in the impregnation promoting process, the pressure increasing process may be performed after the compression releasing process is performed. Even in this case, the impregnation of the electrolyte solution 10 is sufficiently promoted if the electrolyte solution 10 is appropriately injected into the battery case 30 at the time the pressure increasing step is performed. Alternatively, the pressure increase step and the compression release step may be initiated at the same time.

In the re-injection step, the electrolytic solution 10 is injected again into the battery case 30 . If the entire amount of the electrolyte solution 10 required to be injected into the battery case 30 is injected only by the above-described injection step, the electrolyte solution 10 may overflow from the battery case 30 . In the present embodiment, the wound electrode body 20 is impregnated with the electrolytic solution 10 by the impregnation promotion step, so that the space inside the battery case 30 is freed up. Therefore, a sufficient amount of the electrolytic solution 10 is appropriately injected into the battery case 30 by performing the re-injection process after the impregnation promotion process is executed.

<Evaluation test>
The results of evaluation tests using examples and comparative examples will be described. The materials, dimensions, and the like of the secondary batteries of the first comparative example, the second comparative example, and the working example are all the same as those of the secondary battery 1 described in the above embodiment. In the manufacturing process of the secondary battery of the first comparative example, the electrolyte solution 10 was poured into the battery case 30 at an injection flow rate of 40 g/min in the injection step without executing the space securing step and the impregnation promoting step of the above embodiment. injected into. In the first comparative example, the electrolytic solution 10 did not overflow from the battery case 30 in the injection step, but impregnation with the electrolytic solution 10 took a long time. In the manufacturing process of the secondary battery of the second comparative example, the electrolyte solution 10 was poured into the battery case 30 at an injection flow rate of 100 g/min in the injection step without executing the space securing step and the impregnation promotion step of the above embodiment. injected into. In the second comparative example, the impregnation speed of the electrolytic solution 10 was slow, so the electrolytic solution 10 overflowed the battery case 30 in the injection step. In the manufacturing process of the secondary battery of the example, the secondary battery was manufactured according to the manufacturing method of the above embodiment, and the injection flow rate in the injection step was set to 100 g/min. In the example, the electrolytic solution 10 did not overflow from the battery case 30 in the injection process even though the injection flow rate was 100 g/min. From the above results, it can be seen that the time for impregnating the inside of the wound electrode body with the electrolytic solution can be appropriately shortened by manufacturing the secondary battery according to the manufacturing method of the above embodiment.

Although detailed descriptions have been given above with reference to specific embodiments, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the embodiments described above.

1 secondary battery 10 electrolytic solution 20 wound electrode body 30 battery case 31 main body 32 lid body 80 chamber 90 compression member

Claims (1)

a preparation step of preparing a battery case having a flat outer shape and a wound electrode body assembly housed in the battery case;
a pressure reduction step of reducing the pressure inside the battery case in which the wound electrode body is accommodated;
In a state where the pressure inside the battery case is reduced, the battery case is compressed in the thickness direction at two positions sandwiching the central portion of the wound electrode body in the winding axial direction of the wound electrode body. a space securing step of securing a sealed space inside the wound electrode body;
an injection step of injecting the electrolytic solution into the battery case in a state in which the battery case is compressed so that both ends of the wound electrode body in the winding axial direction are entirely immersed in the electrolytic solution;
By executing a step of increasing the internal pressure and a step of releasing the compression in the thickness direction of the battery case into which the electrolytic solution has been injected, the electrolytic solution is injected into the wound electrode body. An impregnation promotion step for promoting impregnation;
A method of manufacturing a secondary battery, comprising:

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