JP6647113B2 - Manufacturing method of all solid state secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing an all-solid secondary battery using, for example, a lithium ion conductive solid electrolyte.

  In recent years, an all-solid secondary battery using a lithium ion conductive solid electrolyte as a battery electrolyte has been known. This all-solid-state secondary battery includes a positive electrode mixture layer, a negative electrode mixture layer, a solid electrolyte layer, a positive electrode current collector, and a negative electrode current collector. Here, the positive electrode mixture layer includes a positive electrode active material and a lithium ion conductive solid electrolyte. The negative electrode mixture layer includes a negative electrode active material and a lithium ion conductive solid electrolyte. The solid electrolyte layer is disposed between the positive electrode mixture layer and the negative electrode mixture layer. The positive electrode current collector is made of metal and provided on the surface of the positive electrode mixture layer. The negative electrode current collector is made of metal and provided on the surface of the negative electrode mixture layer.

  This all-solid-state secondary battery is, for example, after filling a powdery positive electrode mixture layer in a cylindrical mold, filling a powdery solid electrolyte, and then filling a powdery negative electrode mixture layer. Thereafter, it was manufactured by press-molding with high pressure using a pressing tool such as a press pin.

  By the way, according to the above-described manufacturing method, since the pressing is performed at a high pressure, the inside of the positive electrode mixture layer and the negative electrode mixture layer (hereinafter, both may be collectively referred to as “electrode mixture layer”). Stress occurs. Further, when the molding pressure is released, the battery is bent in the thickness direction due to the difference in the elongation rate between the positive electrode mixture, the negative electrode mixture, the positive electrode current collector, and the negative electrode current collector.

  As a method for preventing such a curvature, an electrode assembly which is symmetrically deformed on both surfaces of a positive electrode current collector and a negative electrode current collector (hereinafter, sometimes collectively referred to as an “electrode current collector”). There is one in which a material layer is arranged so that the battery itself does not curve (for example, Patent Document 1). When this battery is manufactured by, for example, a dry method, an electrode mixture layer is formed on both surfaces of an electrode current collector by electrostatic coating or the like.

Japanese Patent No. 5131686

According to the manufacturing method of Patent Document 1 described above, electrostatic coating is used to form an electrode mixture layer on both surfaces of an electrode current collector. Therefore, in actual manufacturing, the electrode mixture is electrostatically applied to one surface, then inverted, and the electrode mixture is electrostatically applied to the other surface. When the electrode mixture is electrostatically applied to the other surface after being turned over, there is a possibility that the electrode mixture electrostatically applied to one surface falls. Further, in order to avoid such a situation, it is conceivable that the electrode current collector is vertical and the electrode mixture is electrostatically applied to both surfaces thereof, but there is a problem that the operation becomes extremely difficult.
Therefore, an object of the present invention is to provide a method of manufacturing an all-solid secondary battery that can easily prevent the bending of the all-solid secondary battery that occurs during manufacturing.

  In order to solve the above-mentioned problems, a method for manufacturing an all-solid secondary battery of the present invention is a method for manufacturing an all-solid secondary battery including a plurality of temporary battery bodies, and includes a positive electrode mixture, a solid electrolyte, and a negative electrode composite. Pressing the laminated material between the positive electrode current collector and the negative electrode current collector to form a plurality of temporary battery bodies, respectively; Pressure molding in a state in which a plurality of temporary battery bodies are overlapped so that the current collectors or the negative electrode current collectors face each other, and after the pressure molding step, a pressure equal to or less than the pressure of the pressure molding. And a step of continuously adding.

  The method for manufacturing an all-solid secondary battery of the present invention includes a step of using a plurality of temporary battery bodies and performing pressure molding with these positive electrode current collectors or negative electrode current collectors facing each other. Further, after the pressure molding step, the method includes a step of continuously applying a pressure equal to or lower than the molding pressure without immediately releasing the molding pressure. Therefore, the pair of temporary battery bodies is maintained without being deformed, the residual stress remaining in these temporary battery bodies is reduced, and the pair of temporary battery bodies can be joined to each other to prevent bending. This makes it possible to easily prevent the all-solid secondary battery from bending.

FIG. 4 is a cross-sectional view for explaining the method for manufacturing the all-solid-state secondary battery according to Embodiment 1 of the present invention. It is sectional drawing explaining the manufacturing method of the all-solid-state secondary battery. It is a figure explaining the mechanism which curvature of a temporary battery body generates. It is a figure explaining the mechanism which curvature of a temporary battery body generates. It is a figure explaining the mechanism which curvature of a temporary battery body generates. It is a figure explaining the mechanism which prevents bending of a temporary battery body. It is a figure explaining the mechanism which prevents bending of a temporary battery body. It is a figure which shows the temporary battery body of the curved state. It is sectional drawing which shows the manufacturing method of the all-solid-state secondary battery. FIG. 3 is a diagram illustrating a pit which is an example of an uneven portion. It is a figure explaining the hole which is an example of an uneven part. It is a figure explaining the mountain valley which is an example of an uneven part. FIG. 7 is a cross-sectional view illustrating a method for manufacturing an all-solid secondary battery according to Embodiment 2 of the present invention. It is sectional drawing explaining the manufacturing method of the all-solid-state secondary battery.

(Embodiment 1)
Hereinafter, an all-solid secondary battery and a method for manufacturing the same according to an embodiment of the present invention will be described with reference to the drawings.

(Step of forming temporary battery body)
First, as shown in FIG. 1, a thin plate-shaped metal positive electrode current collector 1, a positive electrode mixture layer 2 disposed on the upper surface of the positive electrode current collector 1, and an upper surface of the positive electrode mixture layer 2 , A negative electrode mixture layer 4 disposed on the upper surface of the solid electrolyte layer 3, and a thin plate-shaped metal disposed on the upper surface of the negative electrode mixture layer 4. And a negative electrode current collector 5 made of the same to form a laminate.

  Powder (powder) is used as the positive electrode mixture layer 2, the solid electrolyte 3, and the negative electrode mixture layer 4. In FIG. 1, hatching is omitted for the positive electrode current collector 1 and the negative electrode current collector 5. The same applies to other drawings. The specific method of forming each of the positive electrode mixture layer 2, the solid electrolyte 3, and the negative electrode mixture layer 4 is an electrostatic screen method, an electrostatic spray method, or any other method for depositing powder. It may be.

  Thereafter, the temporary battery body 7 is formed by pressing (temporarily pressing) the laminate with a required force (for example, a force of 0.1 to 100 MPa). Here, on both surfaces (both surfaces) of the positive electrode current collector 1 and both surfaces of the negative electrode current collector 5, a surface subjected to a roughening treatment (hereinafter, also referred to as an uneven portion) is formed. Due to this pressing, a state in which the powdered positive electrode mixture and the negative electrode mixture are bitten into the uneven portions on the inner surface (the surface in contact with the positive electrode mixture layer 2 or the negative electrode mixture layer 4) (also expressed as a biting state) Can be). Further, the pressing force at this time is so large that the temporary battery body 7 is not deformed, so that the temporary battery body 7 has a substantially flat shape.

(Press molding process)
Next, as shown in FIG. 2, the pair of temporary battery bodies 7, 7 are overlapped so that the respective positive electrode current collectors 1, 1 are in contact with each other, and a predetermined molding pressure (for example, a pressure of 100 MPa to 1000 MPa) is applied. ). This step is performed by, for example, pressing the pair of temporary battery bodies 7 and 7 between the pair of flat plate blocks 9 and 9 and pressing them. If the pressure is released immediately after this pressure molding step, the temporary battery bodies 7 will be greatly curved.

  Here, a mechanism of bending the temporary battery body 7 will be described with reference to FIGS. Here, for the sake of explanation, the description will be made using one temporary battery body 7 instead of the pair of temporary battery bodies 7 and 7. The broken line part in FIG. 3 shows the temporary battery body 7 before the pressure molding step, and the solid line part shows the temporary battery body 7 during the pressure molding. As shown in FIG. 3, when the molding pressure p is applied to the temporary battery body 7 and compressed, a vertical internal stress a and a horizontal internal stress b are generated. At this time, the temporary battery body 7 receives the frictional force c from the flat plate block. During the pressure molding, the internal stress a in the vertical direction offsets the molding pressure p, and the internal stress b in the horizontal direction offsets the frictional force c.

  4 shows the temporary battery body 7 during the pressure molding process, and the solid line part shows the temporary battery body 7 after the molding pressure p (see FIG. 3) is released. When the molding pressure p shown in FIG. 3 is released, the frictional force c is also released at the same time, so that the internal stress a in the vertical direction and the internal stress b in the horizontal direction are released as shown in FIG. Therefore, the temporary battery body 7 extends in the horizontal direction and the vertical direction.

  However, it takes time to complete the extension of the electrode mixture layer. That is, the internal stresses a and b are not released instantaneously, but are gradually released as the electrode mixture layer extends while being accumulated as residual stress. Regarding the extension in the vertical direction, since the thickness of the temporary battery body 7 is about 100 to 500 μm, it is negligibly small, but regarding the horizontal extension, the width of the temporary battery body 7 is about 30 to 300 mm. It becomes so large that it cannot be ignored.

  Here, the elongation rate in the horizontal direction depends on the material of each layer and the particle size and thickness of the electrode mixture layer. When the extension rate of the negative electrode mixture layer 4 exceeds the extension rate of the positive electrode mixture layer 2, the internal stress b in the horizontal direction is released together with the release of the molding pressure p, and as shown in FIG. 7 is deformed into an arc shape so that the negative electrode mixture layer 4 expands outward. In other words, the concave portion 8 is formed on the positive electrode current collector 1 side of the temporary battery body 7.

  On the other hand, if the shape of the temporary battery body 7 is maintained for a certain period of time without completely releasing the molding pressure p, the residual stress is reduced without being deformed. As a specific method for maintaining the shape of the temporary battery body 7, there is, for example, a method shown in FIGS. In FIG. 6, in a pressure molding step, a molding pressure p is applied using a pair of flat plate blocks (jigs) 9, with the temporary battery body 7 sandwiched between the flat plate blocks 9, 9. . Next, in FIG. 7, the flat plate blocks 9, 9 are fixed to each other with the screw S while the molding pressure p is applied. Thereafter, the molding pressure p is released. At this time, the shape of the temporary battery body 7 is maintained by the weight of the flat plate block 9 and the pressing force of the screw S. Here, the weight of the flat plate block 9 and the pressing force of the screw S (hereinafter, referred to as a shape maintaining pressure) are, for example, 1000 N or less (0.1 MPa or less in terms of pressure) for a 100 mm square battery.

  Table 1 shows the relationship between the time (relaxation time) in which the flat plate blocks 9 and 9 are fixed to each other with the screws S after the molding pressure p is released and the temporary battery body 7 is bent. Here, the amount of bending is a value obtained by subtracting the battery thickness t from the overall height T of the temporary battery body 7 (see FIG. 8). The molding pressure p was 1000 MPa, and the shape maintaining pressure was 50 N to 1000 N (0.005 MPa to 0.1 MPa in terms of pressure) for a 100 mm battery because it was difficult to apply the same pressure. Within the range. The above pressure values do not take atmospheric pressure into consideration. As can be seen from Table 1, when the relaxation time was 2 hours or longer, the amount of bending could be suppressed to half or less as compared to when the relaxation time was 0.5 hour or 1 hour.

  This result is applicable not only to one temporary battery body 7 but also to a pair of temporary battery bodies 7 and 7. Therefore, the method of manufacturing the all-solid secondary battery according to the present embodiment does not completely release the pressure after the step of pressure-forming the pair of temporary battery bodies 7 A step of continuously applying pressure at a pressure (shape maintaining pressure) for 2 hours or more. Thereby, the residual stresses remaining in these temporary battery bodies 7, 7 are relaxed without the pair of temporary battery bodies 7, 7 being deformed. Therefore, it is possible to suppress the bending of the pair of temporary battery bodies 7 and 7.

  As a specific mode for maintaining the shape of the pair of temporary battery bodies 7, 7, as shown in FIG. 9, the pair of flat plate blocks 9, 9 are fixed with screws S, and between the flat plate blocks 9, 9. Is carried out by applying a shape maintaining pressure between the pair of temporary battery bodies 7 and 7 by the weight of the flat plate block 9 and the pressing force of the screw S. In this case, there is no need to continuously apply pressure to the pair of temporary batteries 7, 7, and the shape of the pair of temporary batteries 7, 7 can be maintained only by leaving the battery. However, the present invention is not limited to this mode, and includes a mode in which the shape maintaining pressure is continuously applied to the temporary battery body 7 with a press pin or the like.

  Further, in the present embodiment, as described above, the concave and convex portions are formed on both surfaces of the positive electrode current collector 1 and the negative electrode current collector 5. Then, by the pressure molding process, the concave and convex portions on the surfaces of the positive electrode current collectors 1 and 1 are brought into a state of being engaged with each other (also referred to as a biting state). Bond (adhere) to each other. For this reason, the force that tends to separate the temporary battery bodies 7 from each other is canceled out by the bending, whereby the all-solid-state secondary battery 10 that does not bend even when the molding pressure is released is obtained.

Here, the positive electrode mixture layer 2 is a mixture of a positive electrode active material and a lithium ion conductive inorganic solid electrolyte. As the positive electrode active material, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), or the like is used. As the inorganic solid electrolyte, for example, sulfide-based Li ₂ S (80 mol%)-P ₂ S ₅ (20 mol%) is used. The mixing ratio between the positive electrode active material and the solid electrolyte is in the range of 95: 5 to 30:70, for example, 70:30.

The negative electrode mixture layer 4 is obtained by mixing a lithium ion conductive inorganic solid electrolyte with a negative electrode active material. As the negative electrode active material, for example, natural graphite, artificial graphite, graphite carbon fiber, carbon materials such as resin calcined carbon, silicon, tin, lithium and the like are used, and as the solid electrolyte, the same as the case of the positive electrode mixture layer 2 The same Li ₂ S (80 mol%)-P ₂ S ₅ (20 mol%) is used. The mixing ratio between the negative electrode active material and the solid electrolyte is in the range of 95: 5 to 30:70, for example, 60:40.

As described above, the solid electrolyte layer 3 is made of Li ₂ S—P ₂ S ₅ (for example, having a composition ratio of 80 to 20), which is a sulfide-based inorganic solid electrolyte. Further, a material having a strain at the time of compression at 1000 MPa of 40% or more is used.

  As the positive electrode current collector 1, for example, etched aluminum (also referred to as a surface electrolytically treated aluminum foil) having a thickness of 20 μm is used. This etched aluminum has both surfaces (both surfaces) subjected to a roughening treatment. Specifically, as shown in FIG. 10, a surface enlargement treatment is performed by etching to form a large number of pits (narrow pits). (Hole) d is formed. In addition, as a roughening treatment of the etched aluminum, instead of the pit d, a hole e which is depressed so that the inside may expand as shown in FIG. 11 may be used. It may be formed. The thickness of the positive electrode current collector 1 is, for example, in the range of 5 to 40 μm, while the depth h of the pits d, the holes e, the valleys f, and the like can be 2 to 20 μm. It is preferably 10 μm. The surface subjected to the above-described roughening treatment is collectively referred to as an uneven portion.

  As the negative electrode current collector 5, a thin plate-shaped copper having a thickness of about 18 μm in which both surfaces are roughened, that is, in which uneven portions are formed, is used. Specifically, a roughening treatment for depositing copper particles on the surface of the negative electrode current collector 5 is performed. This plate-shaped copper is also called a surface electrolytically treated copper foil. In this case, the depth of the concavo-convex portion can be 2 to 20 μm (or less than 20 μm when the thickness of the negative electrode current collector 5 is 20 μm or less), and preferably 4 to 10 μm.

  Although the present embodiment is an embodiment in which the time (relaxation time) for continuously applying the shape maintaining pressure is 2 hours or more, the present invention is not limited to this embodiment. The relaxation time depends on the size of the temporary battery bodies 7, the elongation of each component, and the like, and the relaxation time is appropriately determined based on these factors. From the results in Table 1, in particular, when the width of the temporary battery bodies 7 and 7 is about 30 mm to 300 mm and the above-described material is used as the material forming the temporary battery body 7, the shape maintaining pressure is maintained for 2 hours or more. It is preferable to add them.

  By the way, in the above-described embodiment, the mode in which the temporary battery bodies 7 are pressure-formed so that the positive electrode current collectors 1 face each other has been described, but the present invention is not limited to this. That is, when the extension ratio of the positive electrode mixture layer 1 exceeds the extension ratio of the negative electrode mixture layer 4, a concave portion is formed in the negative electrode current collector 5. In this case, in order to face the concave portions, not the positive electrode current collectors 1 but the negative electrode current collectors 5 face each other.

  Further, the electrode current collectors 1 and 5 are not limited to those having both surfaces roughened. Of the surfaces of the electrode current collectors 1 and 5, only the surface that is in contact with the electrode mixture layers 2 and 4 and the surface of another temporary battery body 7 that is bonded to the electrode current collectors 1 and 5 are roughened. It may be an aspect. That is, with respect to these surfaces, the powder of the electrode mixture layers 2 and 4 and the uneven portions of the electrode current collectors 1 and 5 of the other temporary battery body 7 bite into the uneven portions of the electrode current collectors 1 and 5. In order to obtain a bonding force, it is necessary to perform a roughening treatment. On the other hand, the surface that does not contact the electrode mixture layers 2 and 4 and the surface of the temporary battery body 7 that does not join with the electrode current collectors 1 and 5 do not need to be roughened.

  Further, in the above-described embodiment, the case where the concave portions 8 face each other when the temporary battery bodies are overlapped with each other has been described, but the present invention is not limited to this. That is, you may overlap so that the convex parts of the opposite side of the concave part 8 may face each other.

  Further, in the above-described embodiment, the all-solid-state secondary battery 10 including the two temporary batteries 7 has been described, but the present invention is not limited to this embodiment. In the case where three or more temporary battery bodies 7 are held in an overlapping manner without being limited to two, an all-solid-state secondary battery may be configured with three or more temporary battery bodies 7. In the case of three or more, the negative electrode current collectors 5 facing each other are in a state of being joined to each other by the uneven portions on the respective surfaces.

(Embodiment 2)
Next, a method for manufacturing the all-solid-state secondary battery according to Embodiment 2 will be described with reference to FIGS. Hereinafter, description of the same parts as in the first embodiment will be omitted, and different parts will be mainly described.

  The method for manufacturing the all-solid-state secondary battery 10 according to Embodiment 1 is a mode in which the positive electrode current collectors 1 and 1 of the temporary battery bodies 7 and 7 are joined to each other by respective concave and convex portions. As shown in FIGS. 13 and 14, the method of manufacturing the all-solid-state secondary battery 10a according to No. 2 is a mode in which the positive and negative electrode current collectors 1 and 1 are joined by interposing a joining material 11 therebetween.

  That is, in the method of manufacturing the all-solid-state secondary battery 10a according to the present embodiment, during the pressing and molding step shown in FIG. With the bonding material 11 interposed therebetween, the temporary battery bodies 7, 7 are overlaid and pressure molded. Here, the joining material 11 is plastically deformable, and is, for example, a resin sheet.

  According to the method of manufacturing all-solid-state secondary battery 10a according to the present embodiment, bonding material 11 is plastically deformed by the pressure molding step, so that outer surface of positive electrode current collector 1 is formed. The positive electrode current collectors 1 are firmly joined to each other by the anchor effect by being engaged with the concave and convex portions (the surface opposite to the surface). As a result, the positive electrode current collectors 1 are joined and integrated via the bonding material 11, thereby canceling the force of the temporary battery bodies 7a and 7b to be bent, and obtaining an all-solid secondary battery 10a having no bent. be able to.

  Further, in the method of manufacturing the all-solid-state secondary battery 10a according to the present embodiment, similarly to the manufacturing method according to the first embodiment, after the pressure molding step, the pressing is maintained at a shape maintaining pressure equal to or lower than the molding pressure. Process. Therefore, the residual stress remaining in the pair of temporary battery bodies 7 is alleviated, and the bending of the temporary battery body 7 can be suppressed.

  By the way, the joining material 11 is not limited to a plastically deformable material, and may be any material that can join the electrode current collectors. For example, in addition to the resin sheet, an adhesive, a double-sided pressure-sensitive adhesive tape, solder, and the like may be used. In the case where the electrode current collector has an uneven portion and a fluid adhesive or solder is used as the bonding material 11, the bonding material 11 is cured while flowing into the uneven portion, thereby forming a bonding force by an anchor effect. Occurs.

  In the second embodiment, an unevenness portion is provided on the surface of the electrode current collector, but the present invention is not limited to this. That is, the present invention is not limited to the one in which the electrode current collector is roughened. Even if the electrode current collectors are not roughened, the electrode current collectors can be joined to each other by a joining method other than the joining by the anchor effect, for example, an electrostatic force, a reduced pressure adsorption, a chemical joining method, or the like. The electrostatic force is obtained by frictionally charging the bonding material 11. The vacuum suction is obtained by using the principle of a suction cup by, for example, pressing the bonding material 11 having fine holes formed on the surface thereof, and releasing air from the fine holes to the outside of the bonding material 11. Can be Examples of the chemical bonding method include a van der Waals force and a covalent bond. Moreover, you may join by combining these joining methods.

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode mixture layer 3 Solid electrolyte layer 4 Negative electrode mixture layer 5 Negative electrode collector 6 Laminate 7 Temporary battery body 8 Concave part 9 Flat plate block 10 All solid secondary battery 11 Joining material

Claims (3)

A method for manufacturing an all-solid secondary battery including a plurality of temporary battery bodies,
A step of forming a plurality of temporary battery bodies, respectively, by pressing the positive electrode mixture, the solid electrolyte and the negative electrode mixture, which are laminated, between the positive electrode current collector and the negative electrode current collector.
Pressure molding in a state where a plurality of temporary battery bodies are overlapped so that the positive electrode current collectors or the negative electrode current collectors of the plurality of formed temporary battery bodies face each other,
A step of continuously applying a pressure equal to or lower than the pressure of the pressure molding after the pressure molding step. The method for manufacturing an all-solid secondary battery according to claim 1, wherein a surface roughened material is used as the positive electrode current collector and the negative electrode current collector. At the time of the step of press-molding, the plurality of temporary battery bodies are superimposed and press-molded in a state where a bonding material is interposed between the positive electrode current collectors or the negative electrode current collectors. The method for producing an all-solid secondary battery according to claim 1, wherein:

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