Whole solid secondary battery

Abstract

To provide a whole solid secondary battery capable of preventing damages of a current collector foil due to an isotropic pressure.SOLUTION: A whole solid secondary battery of the present invention, comprises: a power generation element including electric cells in each of which a negative electrode having a negative electrode active material on a front surface of a current collector foil, a solid electrolyte, and a positive electrode having a positive electrode material on the front surface of the current collector foil, are laminated in this order; laminate outer casing bodies that house and seal the power generation element; and tub leads that are each laminated on and bonded to the current collector foils outside power generation regions having the active materials. Then, each of the bonding region of the current collector foil and the tub lead is configured to include a portion with a thickness of the current collector foil or less at least one part of an edge of the tub lead. Thereby, the present invention can provide the whole solid secondary battery capable of preventing damages to the current collector foil due to an isotropic pressure, and having enhanced reliability and durability.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to all-solid-state secondary batteries, and more particularly to all-solid-state secondary batteries manufactured through isostatic pressing treatment.

Background Art

[0002] Since all-solid-state secondary batteries do not use an organic solvent (liquid) as an electrolyte, leakage of the electrolyte and gasification at high temperatures do not occur, and the operating temperature range can be widened.

[0003] In such all-solid-state secondary batteries, since the contact area between the solid electrolyte particles and the electrode active material particles is smaller than the contact area between the electrolyte and the electrode active material particles, it is necessary to improve the adhesion between the particles and reduce the ionic conduction resistance. The manufacturing process includes a step of pressing a power generation element containing a solid electrolyte.

[0004] If uneven compression occurs in the above pressing step, it will affect the performance and life of the all-solid-state secondary battery. Therefore, high-quality management is essential for the pressing treatment. Isostatic pressing (also referred to as "hydrostatic pressing") in which pressure is evenly applied from all directions by a liquid in a high-pressure container containing a liquid such as water is used.

[0005] Patent Document 1 discloses a method for manufacturing an all-solid-state secondary battery in which isostatic pressing is performed on the entire all-solid-state secondary battery together with a laminated exterior body containing a power generation element.

[0006] It is described that by surrounding the periphery of the tab lead laminated on the current collector foil with an electrode material and supporting the tab lead with the electrode material, the bonding area of the tab lead is increased, and breakage of the tab lead due to isostatic pressing can be suppressed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, generally, the tab lead is a member that is thicker and stronger than the current collector foil. Therefore, due to isostatic pressing, the tab lead sinks into the current collector foil, and shear stress is applied to the current collector foil with the edge of the tab lead as the boundary, which may cause the strength of the current collector foil to decrease and lead to cutting, resulting in a decrease in reliability and durability.

[0009] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide an all-solid-state secondary battery capable of preventing damage to the current collector foil by isostatic pressing.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by providing a portion where the thickness of the edge of the tab lead in the joining region between the current collector foil and the tab lead is made equal to or less than the thickness of the current collector foil to be joined there, and has completed the present invention.

[0011] That is, the all-solid-state secondary battery of the present invention includes a power generation element including a single battery in which a negative electrode having a negative electrode active material, a solid electrolyte, and a positive electrode having a positive electrode active material are laminated in this order on the surface of a current collector foil, a laminate exterior body that houses and seals the power generation element, and a tab lead that is laminated and joined to the current collector foil outside the power generation region having the active material. And the joining region between the current collector foil and the tab lead is characterized in that at least a part of the edge of the tab lead has a portion equal to or less than the thickness of the current collector foil.

Effects of the Invention

[0012] According to the present invention, a portion is provided where the thickness of the edge of the tab lead in the joining region between the current collector foil and the tab lead is made equal to or less than the thickness of the current collector foil joined thereto. Therefore, breakage of the current collector foil due to isostatic pressing can be prevented, and a all-solid-state secondary battery with improved reliability and durability can be provided.

Brief Description of Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0014] The all-solid-state secondary battery of the present invention will be described in detail. As shown in FIG. 1, the all-solid-state secondary battery 1 of the present invention is formed by housing a power generation element 3 in a laminate exterior body 2, and is manufactured by subjecting the power generation element 3 housed in the laminate exterior body 2 to isostatic pressing.

[0015] As shown in FIG. 2, the power generation element includes a single battery 31 in which a negative electrode having a negative electrode active material 35 on the surface of a current collector foil 32, a solid electrolyte 34, and a positive electrode having a positive electrode active material 33 on the surface of the current collector foil 32 are laminated in this order.

[0016] Tabs 5 are laminated and joined to the ends of the current collector foils 4 outside the power generation regions to which the active materials of the negative electrode current collector foil and the positive electrode current collector foil are applied, respectively, and the tabs 5 protrude from the laminate exterior body 2 to perform power input / output.

[0017] The current collector foils 32 and 4 are generally formed very thin for improving the energy density. Preferably, as shown in FIG. 3, the width of the region 4 outside the power generation region where no active material is applied is made as wide as the width of the power generation region 32, so that an increase in electrical resistance can be suppressed.

[0018] On the other hand, since the tab lead 5 is connected to an external terminal, a certain degree of strength is required, and it has a thickness about 10 to 50 times that of the current collector foils 32 and 4 having a thickness of about 20 μm.

[0019] When pressing in a state where such a thick and high-strength tab lead 5 is laminated and joined to a part of the current collector foil 4 outside the power generation region, which is wide in width and thin in thickness, the high-strength tab lead 5 sinks into the low-strength current collector foil 4, and a shear stress is applied with the edge of the tab lead 5 as a boundary.

[0020] Therefore, the strength of the current collector foil 4 at the portion where the edge of the tab lead 5 abuts decreases, and there may be a case where the current collector foil 4 breaks and power input / output cannot be performed.

[0021] That is, rather than the bonding surface between the current collector foil 4 and the tab lead 5 peeling off, a part of the current collector foil 4 is cut at the edge of the tab lead 5, and while the current collector foil 4 remains attached to the tab lead 5, a part of the current collector foil 4 is cut into the shape of the tab lead 5.

[0022] In the all-solid-state secondary battery of the present invention, the bonding region 6 between the current collector foil 4 and the tab lead 5 has a portion at least partially along the edge of the tab lead that is less than or equal to the thickness of the current collector foil joined thereto, and has a portion where the strength of the tab lead 5 is less than or equal to the strength of the current collector foil 4 there.

[0023] Therefore, when pressurized by isostatic pressing, the compression amount of the current collector foil 4 at this portion becomes less than or equal to the compression amount of the tab lead 5, so that it is possible to prevent being cut into the shape of the tab lead along the edge of the tab lead.

[0024] Furthermore, if the entire circumference of the edge of the tab lead in the bonding region is less than or equal to the thickness of the current collector foil, it is possible to prevent the current collector foil 4 from being cut by the tab lead.

[0025] In the present invention, "the thickness of the tab lead is equal to or less than the thickness of the current collector foil" refers to the thickness when comparing the thickness of one current collector foil with the thickness of the tab lead. Even when a plurality of current collector foils are laminated, it does not refer to the total thickness of the laminated plurality of current collector foils. Also, the "joint region between the current collector foil and the tab lead" refers to the entire overlapping portion of the current collector foil and the tab lead.

[0026] As a method of making the thickness of the current collector foil and the tab lead the same, the tab lead in the joint region may be made thinner than other portions, or the thickness of the current collector foil in the joint region may be made thicker than other portions. However, from the perspective of energy density, it is preferable to make the tab lead in the joint region thinner.

[0027] An example of the cross-sectional shape of the tab lead in the joint region is shown in FIG. 4. Among them, as shown at the bottom of FIG. 4, the thickness of the portion joined to the current collector foil is constant, so that the shear stress applied to the current collector foil is evenly distributed over the entire circumference of the edge of the tab lead, and partial breakage of the current collector foil can be suppressed.

[0028] It is preferable that the edge of the surface of the tab lead joined to the current collector foil is chamfered. The edge of the surface of the tab lead in contact with the current collector foil is chamfered, and the ridge line of the tab lead is shaved off. Even if the tab lead is pressed into the current collector foil by isotropic pressing, the shear stress at the edge of the tab lead is dispersed and relaxed in the chamfered width direction, so that the current collector foil can be prevented from being cut into the shape of the tab lead.

[0029] As the shape of the chamfer, either R-chamfer or C-chamfer may be used. However, in the case of R-chamfer, the corner of the ridge line disappears, so that a decrease in the strength of the current collector foil can be more effectively prevented.

[0030] As the material constituting the tab lead, conventionally known materials used in secondary batteries can be used, but it is preferable that the tab lead on the positive electrode side is formed of aluminum and the tab lead on the negative electrode side is formed of nickel-plated copper.

[0031] When the power generation element is formed by laminating a plurality of single cells, it is preferable to join the negative electrode current collector foils of the power generation element and the positive electrode current collector foils to each other on the power generation element side rather than at the joining region between the current collector foil and the tab lead.

[0032] Thereby, the joining strength between the current collector foils is improved, and since the conductive path becomes thicker, the electrical resistance can be reduced.

[0033] The all-solid-state secondary battery of the present invention can be manufactured by accommodating a power generation element in which a current collector foil and a tab lead are welded and joined by ultrasonic welding or laser welding, etc. in a laminate exterior body, protruding a part of the tab lead outside the laminate exterior body, heat-sealing the laminate exterior body and a heat-sealing film under vacuum degassing, and performing isostatic pressing.

[0034] Next, the power generation element constituting the all-solid-state secondary battery will be described.

[0035] (Solid electrolyte) As the solid electrolyte, either a sulfide solid electrolyte or an oxide solid electrolyte can be used. However, in an all-solid-state secondary battery using a sulfide solid electrolyte, since sintering treatment is not performed like an oxide solid electrolyte and electrolyte particles are adhered by isostatic pressing, the effects of the present invention are great.

[0036] Examples of the sulfide solid electrolyte include LGPS-type sulfide solid electrolytes such as Li 10 GeP2S 12 and alditol-type sulfide solid electrolytes such as Li6PS5Cl.

[0037] (Negative electrode) The negative electrode has a negative electrode active material layer containing a negative electrode active material capable of occluding lithium on the surface of a current collector foil. Examples of the negative electrode active material include carbon materials, such as carbon black, carbon nanotubes (CNT), graphite, hard carbon, and the like.

[0038] The negative electrode active material layer can be formed by applying and drying a negative electrode active material slurry containing the negative electrode active material, a binder, and, if necessary, a sulfide solid electrolyte or a conductive auxiliary agent added thereto onto a current collector foil.

[0039] Examples of the binder include polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), and the like.

[0040] Examples of the material constituting the current collector foil include aluminum, nickel, iron, stainless steel, titanium, or copper.

[0041] (Positive Electrode) The positive electrode has a positive electrode active material layer containing a positive electrode active material capable of reversibly occluding and releasing lithium ions on the surface of a current collector foil.

[0042] As the positive electrode active material, a lithium metal composite oxide can be used. For example, as the lithium metal composite oxide, layered rock salt type compounds such as LiCoO2, LiMnO2, LiNiO2, LiVO2, or Li(Ni-Mn-Co)O2, spinel type compounds such as LiMn2O4 or LiNi 0.5 Mn 1.5 O4, olivine type compounds such as LiFePO4 or LiMnPO4, or Si-containing compounds such as Li2FeSiO4 or Li2MnSiO4 can be mentioned.

[0043] For the positive electrode, the same current collector foil, binder, sulfide solid electrolyte, and conductive assistant as those of the negative electrode can be used, and it can be produced by applying and drying a positive electrode active material slurry containing the positive electrode active material, the binder, the sulfide solid electrolyte, etc.

Explanation of Reference Signs

[0044] 1 All-solid-state secondary battery 2 Laminate exterior body 3 Power generation element 31 Single cell 32 Current collector foil 33 Positive electrode active material 34 Solid electrolyte 35 Negative electrode active material 4 Current collector foil outside the power generation region 5 Tab lead 6 Junction region

Claims

1. A power generation element including a single cell in which a negative electrode having a negative electrode active material on the surface of a current collector foil, a solid electrolyte, and a positive electrode having a positive electrode active material on the surface of the current collector foil are laminated in this order, A laminated exterior body that houses and seals the power generation element, A tab lead laminated and joined to the current collector foil outside the power generation region having the active material, and a all-solid-state secondary battery comprising: In the all-solid-state secondary battery, a joining region between the current collector foil and the tab lead has a portion equal to or less than the thickness of the current collector foil at at least a part of an edge of the tab lead.

2. The all-solid-state secondary battery according to claim 1, wherein the tab lead has a constant thickness at a portion joined to the current collector foil.

3. The all-solid-state secondary battery according to claim 1, wherein at least an edge of a joining surface of the tab lead with the current collector foil is chamfered.

4. The all-solid-state secondary battery according to claim 1, wherein the solid electrolyte is a sulfide solid electrolyte.

5. The power generation element has a plurality of single cells, The all-solid-state secondary battery according to claim 1, wherein the negative electrode current collector foils and / or the positive electrode current collector foils are joined on the power generation region side rather than the joining region between the current collector foil and the tab lead.

6. The all-solid-state secondary battery according to claim 1, wherein the tab lead on the positive electrode side is formed of aluminum, and the tab lead on the negative electrode side is formed of nickel-plated copper.

7. The all-solid-state secondary battery according to claim 1, wherein the tab lead has a greater thickness outside the joining region than the thickness of the joining region.

8. The all-solid-state secondary battery according to claim 1, wherein the joining region between the current collector foil and the tab lead has an entire circumference of an edge of the tab lead equal to or less than the thickness of the current collector foil.

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