Secondary battery

Abstract

To provide a secondary battery that can suppress short circuits caused by burrs during cutting.SOLUTION: A secondary battery includes an electrode stack in which a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated in this order, and in the laminated surface of the positive electrode current collector layer and the positive electrode active material layer or the laminated surface of the negative electrode current collector layer and the negative electrode active material layer, the positive electrode active material layer or the negative electrode active material layer includes an exposed portion where the surface is exposed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present application relates to a secondary battery. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing a battery component for a secondary battery, which includes the steps of providing an electrolyte material layer between a pair of electrode material layers to form a laminate, and cutting the laminate all at once. Patent Document 1 also describes that by including the cutting step, a substantially continuous surface is formed on the side surface of the laminate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 221010 Summary of the Invention [Problem to be solved by the invention]

[0004] If the laminate is cut all at once as described in Patent Document 1, there is a risk that foil sagging will occur in the current collector layer and burrs will occur in the active material layer, and if the foil sagging or burrs come into contact with other electrode layers, there is a problem of a short circuit occurring.

[0005] In view of the above circumstances, a main object of the present disclosure is to provide a secondary battery that can suppress short circuits caused by burrs or the like when cutting. [Means for solving the problem]

[0006] In one aspect for solving the above-described problems, the present disclosure provides a secondary battery having an electrode laminate in which a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated in this order, wherein the positive electrode active material layer or the negative electrode active material layer has an exposed portion where the surface is exposed at the laminated surface between the positive electrode current collector layer and the positive electrode active material layer or the laminated surface between the negative electrode current collector layer and the negative electrode active material layer. [Effects of the Invention]

[0007] According to the secondary battery of the present disclosure, it is possible to prevent a short circuit even if burrs or the like are generated during cutting. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a secondary battery 100. FIG. [Figure 2] 2 is an enlarged schematic cross-sectional view showing the area indicated by II in FIG. 1 in an enlarged manner. [Figure 3] 10A and 10B are diagrams illustrating how an end portion of a laminate electrode is cut in a test example. [Figure 4] 10 is a 3D cross-sectional analysis image of a cut surface of a laminate electrode of a test example. DETAILED DESCRIPTION OF THE INVENTION

[0009] The secondary battery of the present disclosure will be described with reference to a secondary battery 100 as one embodiment.

[0010] [Secondary battery 100] Fig. 1 shows a schematic cross-sectional view of a secondary battery 100. Hereinafter, the vertical direction in Fig. 1 may be referred to as the stacking direction, and the horizontal direction as the width direction.

[0011] 1, the secondary battery 100 has an electrode stack 60 in which a positive electrode current collector layer 10, a positive electrode active material layer 20, an electrolyte layer 30, a negative electrode active material layer 40, and a negative electrode current collector layer 50 are stacked in this order. Fig. 1 shows a configuration in which four electrode stacks 60 are stacked.

[0012] <Positive electrode current collector layer 10> The material of the positive electrode current collector layer 10 is not particularly limited and can be appropriately selected from known materials depending on the purpose. Examples include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The thickness of the positive electrode current collector layer 10 is not particularly limited and can be appropriately set depending on the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

[0013] <Cathode active material layer 20> The positive electrode active material layer 20 contains a positive electrode active material. The positive electrode active material can be appropriately selected from known positive electrode active materials used in lithium-ion secondary batteries. Examples include lithium cobalt oxide, nickel cobalt lithium aluminum oxide (NCA), nickel cobalt lithium manganese oxide (NCM), and lithium manganese oxide. The particle size of the positive electrode active material is not particularly limited, but is, for example, in the range of 1 μm to 100 μm. The content of the positive electrode active material in the positive electrode active material layer 20 is not particularly limited, but is, for example, in the range of 50 wt % to 99 wt %. The surface of the positive electrode active material may be coated with an oxide layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer.

[0014] The positive electrode active material layer 20 may optionally include a solid electrolyte, which can be appropriately selected from known solid electrolytes used in lithium ion secondary batteries. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes. The solid electrolyte may be a sulfide solid electrolyte. The content of the solid electrolyte in the positive electrode active material layer 20 is not particularly limited, but is, for example, in the range of 1 wt % to 50 wt %.

[0015] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y(where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.)

[0016] Examples of oxide solid electrolytes include lithium lanthanum zirconium-containing composite oxide (LLZO), Al-doped LLZO, lithium lanthanum titanium-containing composite oxide (LLTO), Al-doped LLTO, and lithium phosphate oxynitride (LIPON). Examples of nitride solid electrolytes include LiN and LiN-LiI-LiOH. Examples of halide solid electrolytes include LiF, LiCl, LiBr, LiI, and LiI-AlO.

[0017] The positive electrode active material layer 20 may optionally contain a conductive additive. The conductive additive can be appropriately selected from known conductive additives used in lithium ion secondary batteries. Examples include carbon materials such as acetylene black, ketjen black, and vapor-grown carbon fiber (VGCF), and metal materials such as nickel, aluminum, and stainless steel. The content of the conductive additive in the positive electrode active material layer 20 is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0018] The positive electrode active material layer 20 may optionally contain a binder. The binder can be appropriately selected from known binders used in lithium ion secondary batteries. Examples include butadiene rubber (BR), butylene rubber (IIR), acrylate butadiene rubber (ABR), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP). The content of the binder in the positive electrode active material layer 20 is not particularly limited, but is, for example, in the range of 0.1% by weight to 10% by weight.

[0019] The shape of the positive electrode active material layer 20 is not particularly limited, but a sheet shape is preferable. The thickness of the positive electrode active material layer 20 is not particularly limited and may be appropriately set depending on the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

[0020] <Electrolyte layer 30> When the secondary battery 100 is an all-solid-state battery, the electrolyte layer 30 is a sheet-shaped solid electrolyte layer. The solid electrolyte layer includes a solid electrolyte. The solid electrolyte can be appropriately selected from solid electrolytes that can be used in a positive electrode active material layer. The solid electrolyte layer may also include a binder. The binder can be appropriately selected from binders that can be used in a positive electrode active material layer. The content of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is, for example, in the range of 60 to 99% by weight. The content of the binder in the solid electrolyte layer is not particularly limited, but is, for example, in the range of 0.1 to 10% by weight. The thickness of the solid electrolyte layer may be, for example, 0.1 μm to 1 mm.

[0021] When the secondary battery 100 is a liquid battery, the electrolyte layer 30 includes an electrolytic solution and a separator. The electrolyte and separator are not particularly limited as long as they are suitable for use in lithium-ion secondary batteries. Examples of separators include porous sheets (films) made of polyolefins such as polyethylene (PE) and polypropylene (PP). The separator may have a thickness of, for example, 0.1 μm to 1 mm. The electrolyte typically contains a non-aqueous solvent and a supporting salt. Examples of non-aqueous solvents include carbonates, ethers, esters, nitriles, sulfones, and lactones. Examples of supporting salts include LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethane)sulfonimide (LiTFSI). The concentration of the supporting salt in the electrolyte is not particularly limited, but may be, for example, 0.5 mol / L to 5 mol / L. The electrolyte may also contain optional components such as a gas generating agent, a film-forming agent, a dispersant, and a thickener.

[0022] <Negative electrode active material layer 40> The negative electrode active material layer 40 contains a negative electrode active material. The negative electrode active material can be appropriately selected from known negative electrode active materials used in lithium-ion secondary batteries. Examples include silicon and Si alloys, tin and tin alloys, silicon oxide and other silicon-based active materials, graphite, hard carbon and other carbon-based active materials, lithium titanate and other oxide-based active materials, metallic lithium and lithium alloys.

[0023] The negative electrode active material layer 40 may optionally include a solid electrolyte. The solid electrolyte can be appropriately selected from solid electrolytes that can be used in positive electrode active material layers. The content of the solid electrolyte in the negative electrode active material layer 40 is not particularly limited, but is, for example, in the range of 1 wt % to 50 wt %.

[0024] The negative electrode active material layer 40 may optionally contain a conductive additive. The conductive additive can be appropriately selected from conductive additives that can be used in positive electrode active material layers. The content of the conductive additive in the negative electrode active material layer 40 is not particularly limited, but is, for example, in the range of 0.1 wt % to 10 wt %.

[0025] The negative electrode active material layer 40 may optionally contain a binder. The binder can be appropriately selected from binders that can be used in positive electrode active material layers. The content of the binder in the negative electrode active material layer 40 is not particularly limited, but is, for example, in the range of 0.1 wt % to 10 wt %.

[0026] The shape of the negative electrode active material layer 40 is not particularly limited, but a sheet shape is preferable. The thickness of the negative electrode active material layer 40 is not particularly limited and may be appropriately set depending on the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

[0027] <Negative electrode current collector layer 50> The material of the negative electrode current collector layer 50 can be appropriately selected from known materials depending on the purpose. Examples of the material include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. The thickness of the negative electrode current collector layer 50 is not particularly limited and may be appropriately set depending on the desired battery performance. For example, it is in the range of 0.1 μm to 1 mm.

[0028] <Electrode laminate 60> 1 shows a configuration in which a plurality of electrode stacks 60 are stacked, however, the secondary battery of the present disclosure only needs to include at least one electrode stack.

[0029] The stacking format of the multiple electrode stacks 60 is not particularly limited, and they may be connected in series or in parallel. Fig. 1 shows a stacking format in which they are connected in parallel. Furthermore, when multiple electrode stacks 60 are stacked, adjacent electrode stacks 60 may share a current collector layer as shown in Fig. 1. Alternatively, the current collector layers may overlap each other.

[0030] Here, the secondary battery 100 has one feature in the end structure of the electrode stack 60. Fig. 2 shows an enlarged view of the area indicated by II in Fig. 1.

[0031] 2 , at the stacking surface of the positive electrode current collector layer 10 and the positive electrode active material layer 20, the positive electrode active material layer 20 has an exposed portion 21 where the surface is exposed. In other words, the surface of the positive electrode active material layer 20 facing the positive electrode current collector layer 10 is not in contact with the positive electrode current collector layer 10, and has the exposed portion 21 that is exposed to the outside. This means that the end of the positive electrode current collector layer 10 is located more inward than the end of the positive electrode active material layer 20.

[0032] Similarly, at the stacking surface between the negative electrode current collector layer 50 and the negative electrode active material layer 40, the negative electrode active material layer 40 has an exposed portion 41 where the surface is exposed. In other words, the surface of the negative electrode active material layer 40 facing the negative electrode current collector layer 50 is not in contact with the negative electrode current collector layer 50, and has the exposed portion 41 that is exposed to the outside. This means that the end of the negative electrode current collector layer 50 is located more inward than the end of the negative electrode active material layer 40.

[0033] Here, the term "laminated surface of the positive electrode current collector layer 10 and the positive electrode active material layer 20" refers to a combination of the surface of the positive electrode current collector layer 10 facing the positive electrode active material layer 20 and the surface of the positive electrode active material layer 20 facing the positive electrode current collector layer 10. Similarly, the term "laminated surface of the negative electrode current collector layer 50 and the negative electrode active material layer 40" refers to a combination of the surface of the negative electrode current collector layer 50 facing the negative electrode active material layer 40 and the surface of the negative electrode active material layer 40 facing the negative electrode current collector layer 50.

[0034] By providing such an end structure to the electrode laminate 60, even when the end of the electrode laminate 60 is cut to align the end, the end of the active material layer and the end of the current collector layer are spaced a predetermined distance apart in the width direction across the exposed portion. This prevents burrs from coming into contact with the current collector layer of the other electrode (e.g., the negative electrode current collector layer 50) even if burrs are generated on the cut surface of the active material layer (e.g., the cut surface of the positive electrode active material layer 10) due to cutting. In this way, the current collector layer is recessed relative to the active material layer in the cross section in the stacking direction, allowing for a wide edge distance between the current collector layers of the positive and negative electrodes, thereby preventing short circuits due to burrs or the like that occur during cutting. Therefore, the secondary battery 100 prevents short circuits even if burrs or the like occur during cutting.

[0035] The widthwise length W of exposed portions 21, 41 (the length from the end of the active material layer to the end of the current collector layer) is not particularly limited, but may be 5 μm or more, 10 μm or more, 50 μm or less, or 40 μm or less. If the length W of exposed portions 21, 41 is less than 5 μm, the short-circuit suppression effect is reduced. If the length W of exposed portions 21, 41 exceeds 50 μm, the contact area between the current collector layer and the active material layer is reduced, which may result in reduced battery performance.

[0036] 2, the ends of the positive electrode active material layer 20, the electrolyte layer 30, and the negative electrode active material layer 40 may be aligned. Such an end shape can be obtained by cutting the ends of the positive electrode active material layer 20, the electrolyte layer 30, and the negative electrode active material layer 40 all at once.

[0037] Here, in FIG. 2 , exposed portions exist in both the positive electrode active material layer 20 and the negative electrode active material layer 40, but the secondary battery of the present disclosure is not limited to this form, and it is sufficient that either the positive electrode active material layer or the negative electrode active material layer has an exposed portion on the stacked surface between the positive electrode current collector layer and the positive electrode active material layer or on the stacked surface between the negative electrode current collector layer and the negative electrode active material layer.

[0038] <Supplementary information> The secondary battery 100 may include an exterior body that houses the electrode stack 60. The secondary battery 100 may also include various terminals.

[0039] <Method of manufacturing the secondary battery 100> The method for manufacturing the secondary battery 100 is not particularly limited, but the following manufacturing method can be mentioned, for example. The method for manufacturing a secondary battery includes an electrode stack fabrication step S1 for fabricating an electrode stack 60 by stacking a positive electrode current collector layer 10, a positive electrode active material layer 20, an electrolyte layer 30, a negative electrode active material layer 40, and a negative electrode current collector layer 50 in this order, and a cutting step S2 for cutting the ends of the obtained electrode stack.

[0040] (Electrode stack manufacturing process S1) The electrode stack fabrication step S1 is a step of fabricating an electrode stack 60 by stacking a positive electrode current collector layer 10, a positive electrode active material layer 20, an electrolyte layer 30, a negative electrode active material layer 40, and a negative electrode current collector layer 50 in this order.

[0041] The method for producing the electrode laminate 60 is not particularly limited, and any known method can be appropriately adopted. For example, the positive electrode current collector 10, the positive electrode active material layer 20, the solid electrolyte layer 30, the negative electrode active material layer 40, and the negative electrode current collector 50 may be prepared separately and then laminated to produce the electrode laminate 60. After lamination, the electrode laminate 60 may be appropriately pressed.

[0042] The electrode layers (positive electrode active material layer 20, solid electrolyte layer, and negative electrode active material layer 40) can be produced, for example, as follows. The electrode layers can be produced by mixing and pressing the materials that make up the electrode layers. Alternatively, the electrode layers can be produced by dispersing the materials that make up the electrode layers in an organic solvent to obtain a slurry, and then applying and drying the obtained slurry to a current collector or a substrate. Such methods are well known.

[0043] Here, when fabricating the electrode laminate 60, (1) the positive electrode current collector layer 10 and the positive electrode active material layer 20 are laminated so that the positive electrode current collector layer 10 is disposed inside the positive electrode active material layer 20. In other words, the positive electrode current collector layer 10 and the positive electrode active material layer 20 are laminated so that the outer edge of the positive electrode current collector layer 10 is disposed inside the outer edge of the positive electrode active material layer 20. Furthermore, (2) the negative electrode current collector layer 50 and the negative electrode active material layer 40 are laminated so that the negative electrode current collector layer 50 is disposed inside the negative electrode active material layer 40. In other words, the negative electrode current collector layer 50 and the negative electrode active material layer 40 are laminated so that the outer edge of the negative electrode current collector layer 50 is disposed inside the outer edge of the negative electrode active material layer 40. Either one of (1) or (2) or both may be implemented to obtain a desired secondary battery 100.

[0044] (Cutting process S2) Next, the edges of the electrode stack 60 are cut. Specifically, the edges of at least the positive electrode active material layer 20, the electrolyte layer 30, and the negative electrode active material layer 40 are cut. At this time, the cutting process is carried out so that the width direction length W of the exposed portion becomes a desired length. A known cutting device can be used to cut the edges. For example, a cutting device equipped with a saw blade can be used. The saw blade may be a circular saw blade.

[0045] When the secondary battery 100 includes a plurality of electrode stacks 60, the ends of the plurality of electrode stacks 60 may be cut after stacking the plurality of electrode stacks 60, or the ends may be cut before stacking the plurality of electrode stacks 60.

[0046] Here, one test example is shown. In the test example, multiple electrode laminates including a solid electrolyte layer were used, and these electrode laminates were stacked to produce a laminate electrode, and then the edge of the laminate electrode was cut. Figure 3 shows the cutting process. The cutting conditions were as follows: a circular saw blade with a diameter of 100 mm was used. The rotation speed of the circular saw blade was set to 1000 rpm, and the feed speed of the laminate electrode was set to 5 mm / s. The cutting depth of the edge by the circular saw blade was set to the thickness of the laminate electrode + 0.1 mm.

[0047] Figure 4 shows a 3D cross-sectional analysis of the cut surface of the laminate electrode after cutting. A laser microscope (model: VK-X3000, marker: Keyence Corporation) was used. As shown in Figure 4, it can be seen that the positive electrode current collector layer and the negative electrode current collector layer are located more inward than the other electrode layers. It can also be confirmed that burrs caused by cutting do not come into contact with these current collector layers. Therefore, it is believed that providing such an edge structure can suppress short circuits. However, to more accurately determine whether a short circuit has occurred, common methods such as a spike reel test or a self-discharge test may also be applied.

[0048] The secondary battery according to the present disclosure has been described above using one embodiment. The secondary battery according to the present disclosure has a predetermined end structure, which can prevent short circuits even if burrs are generated when the end is cut. [Explanation of symbols]

[0049] 10 Positive electrode current collector layer 20 Cathode active material layer 30 Electrolyte layer 40 Negative electrode active material layer 50 Negative electrode current collector layer 60 Electrode laminate 100 Secondary battery

Claims

[Claim 1] A secondary battery having an electrode stack in which a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are stacked in this order, the positive electrode active material layer or the negative electrode active material layer has an exposed portion at a stacking surface between the positive electrode current collector layer and the positive electrode active material layer or at a stacking surface between the negative electrode current collector layer and the negative electrode active material layer, The length of the exposed portion in the width direction along the stacking surface is greater than 0 μm and less than or equal to 50 μm. Secondary battery.

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