Lithium-ion secondary battery

Abstract

To provide a lithium ion secondary battery which can easily determine the presence / absence of a content of a metal impurity using an insulation inspection test in the lithium ion secondary battery having a groove in at least one of a positive electrode active material layer and a negative electrode active material layer.SOLUTION: A lithium ion secondary battery comprises an electrode body laminating a positive electrode that has a positive electrode active material layer and a positive electrode collector body, and a negative electrode having a negative electrode active material layer and a negative electrode collector body via a separator with a conductive layer. The positive electrode active material layer and the negative electrode active material layer are contacted to the separator, at least one of the positive electrode active material layer and the negative electrode active material layer includes a groove in a thickness direction. On a front surface of the separator faced to the front surface having the groove of at least one of the positive electrode active material layer and the negative electrode active material layer, the conductive layer is provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a lithium-ion secondary battery.

Background Art

[0002] Lithium-ion secondary batteries are widely used as portable power sources for personal computers, mobile terminals, etc., and as power sources for vehicle drive, such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs), because they are lightweight and can provide a high energy density. For example, Patent Document 1 proposes "a separator for a non-aqueous electrolyte secondary battery including a positive electrode and a negative electrode capable of occluding and releasing lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, the separator having a conductive layer containing a conductive material and a binder, the apparent volume resistivity of the conductive layer being 1×10 -4 Ω·cm to 1×10 6 Ω·cm, and the film thickness of the conductive layer being less than 5 μm, and a non-aqueous electrolyte secondary battery including the separator."

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a lithium-ion secondary battery, when at least one of the positive electrode active material layer and the negative electrode active material layer contains metal impurities, an internal short circuit may occur. Therefore, it is preferable that it is easy to determine the presence or absence of the inclusion of metal impurities. Here, for example, a method called an insulation inspection test or a spike leak test is used to determine the presence or absence of the inclusion of metal impurities. Here, in a lithium secondary battery, grooves may be formed in at least one of the positive electrode active material layer and the negative electrode active material layer so that the non-aqueous electrolyte quickly penetrates the electrode body. In this case, in a lithium ion secondary battery having grooves in at least one of the positive electrode active material layer and the negative electrode active material layer, if metal impurities are present in the grooves, it may be difficult to determine the presence or absence of metal impurities using an insulation inspection test. This is because the contact area between the metal impurities and the electrode becomes small.

[0005] Here, the problem to be solved by the present disclosure is to provide a lithium ion secondary battery in which it is easy to determine the presence or absence of the inclusion of metal impurities using an insulation inspection test in a lithium ion secondary battery having grooves in at least one of the positive electrode active material layer and the negative electrode active material layer.

Means for Solving the Problem

[0006] The means for solving the above problems include the following means. <1> An electrode body in which a positive electrode having a positive electrode active material layer and a positive electrode current collector and a negative electrode having a negative electrode active material layer and a negative electrode current collector are laminated via a separator having a conductive layer, The positive electrode active material layer and the negative electrode active material layer are in contact with the separator, At least one of the positive electrode active material layer and the negative electrode active material layer has grooves in the thickness direction, A lithium ion secondary battery having the conductive layer on the surface of the separator facing the surface having the grooves in at least one of the positive electrode active material layer and the negative electrode active material layer. <2> The lithium ion secondary battery according to <1>, wherein the positive electrode active material layer has the grooves. <3> The lithium ion secondary battery according to <1> or <2>, wherein the separator has the conductive layer only in a portion facing the grooves.

Advantages of the Invention

[0007] According to the present disclosure, there is provided a lithium-ion secondary battery having a groove in at least one of a positive electrode active material layer and a negative electrode active material layer, and it is easy to determine the presence or absence of metal impurities using an insulation inspection test.

Brief Description of Drawings

[0008]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments which are examples of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerically described range. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0010] Each component may contain a plurality of corresponding substances. When referring to the amount of each component in a composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition. The term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended action of the step is achieved.

[0011] <Lithium-Ion Secondary Battery> The lithium-ion secondary battery according to the present disclosure (hereinafter, also simply referred to as "secondary battery") includes an electrode body in which a positive electrode having a positive electrode active material layer and a positive electrode current collector and a negative electrode having a negative electrode active material layer and a negative electrode current collector are laminated via a separator having a conductive layer. The positive electrode active material layer and the negative electrode active material layer are in contact with the separator, at least one of the positive electrode active material layer and the negative electrode active material layer has a groove in the thickness direction, and a conductive layer is provided on the surface of the separator facing the surface having the groove of at least one of the positive electrode active material layer and the negative electrode active material layer.

[0012] Due to the above configuration, the secondary battery according to the present disclosure facilitates the determination of the presence or absence of metal impurities using an insulation inspection test. The reason is presumed as follows.

[0013] The separator included in the secondary battery according to the present disclosure has a conductive layer on the surface of the separator facing the surface having the groove of at least one of the positive electrode active material layer and the negative electrode active material layer having the groove. Therefore, even when the groove contains metal impurities, the conductive layer and the metal impurities are likely to come into contact, and it becomes easy to determine the presence or absence of metal impurities when performing an insulation inspection test.

[0014] Hereinafter, the details of the secondary battery according to the present disclosure will be described.

[0015] (Electrode body) The electrode body is formed by laminating a positive electrode having a positive electrode active material layer and a positive electrode current collector and a negative electrode having a negative electrode active material layer and a negative electrode current collector via a separator having a conductive layer. The positive electrode active material layer and the negative electrode active material layer are in contact with the separator. That is, it has a layer structure of positive electrode current collector / positive electrode active material layer / separator / negative electrode active material layer / negative electrode current collector. Note that " / " represents the interface of each layer.

[0016] Here, both the positive electrode active material layer and the negative electrode active material layer of the electrode body may have grooves. In this case, it is preferable that the separator has a conductive layer on both the surface facing the surface of the positive electrode active material layer and the surface facing the surface of the negative electrode active material layer (that is, both surfaces of the separator).

[0017] - Positive electrode - The positive electrode has a positive electrode active material layer and a positive electrode current collector. Examples of the positive electrode current collector include aluminum foil and the like. The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material include lithium transition metal oxides (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.), lithium transition metal phosphate compounds (e.g., LiFePO4, etc.), and the like. In addition to the positive electrode active material, the positive electrode active material layer may contain, for example, a conductive assistant, a binder, etc. As the conductive assistant, carbon black such as acetylene black (AB) or other carbon materials (e.g., graphite, etc.) can be preferably used. As the binder, for example, polyvinylidene fluoride (PVdF) etc. can be used.

[0018] The thickness of the positive electrode active material layer is not particularly limited, and it is preferably 50 μm or more and 250 μm or less, more preferably 100 μm or more and 200 μm or less, and still more preferably 130 μm or more and 170 μm or less.

[0019] From the viewpoint of facilitating the determination of the presence or absence of the inclusion of metal impurities, the positive electrode active material layer preferably has grooves. The depth of the groove is not particularly limited, but it is preferably the same as the thickness of the positive electrode active material layer. The width of the groove is not particularly limited, but it is preferably 0.5 mm or more and 5 mm or less, more preferably 1 mm or more and 3 mm or less, and still more preferably 2 mm or more and 3 mm or less. The shape of the groove is not particularly limited, and it may be linear, curved, etc., but it is preferably linear.

[0020] The positive electrode active material layer preferably has a plurality of linear grooves at regular intervals, and the grooves do not intersect with each other. When the positive electrode active material layer has a plurality of linear grooves, the interval between the grooves is preferably 50 mm or more and 200 mm or less, more preferably 70 mm or more and 150 mm or less, and still more preferably 80 mm or more and 120 mm or less. Here, the interval between the grooves means the shortest distance between two adjacent grooves.

[0021] -Negative electrode- The negative electrode has a negative electrode active material layer and a negative electrode current collector. Examples of the negative electrode current collector include a copper foil. The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include graphite-based carbon materials; lithium titanate (Li4Ti5O 12 :LTO); Sn; Si-based materials and the like. In addition to the negative electrode active material, the negative electrode active material layer may contain, for example, a binder, a thickener, and the like. As the binder, for example, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

[0022] The thickness of the negative electrode active material layer is not particularly limited, and is preferably 50 μm or more and 250 μm or less, more preferably 100 μm or more and 200 μm or less, and still more preferably 130 μm or more and 170 μm or less.

[0023] From the viewpoint of facilitating the determination of the presence or absence of the inclusion of metal impurities, when the positive electrode active material layer does not have grooves, it is preferable that the negative electrode active material layer has grooves. Here, the preferred form of the grooves of the negative electrode active material layer is the same as that of the grooves of the positive electrode active material layer described above.

[0024] -Separator- The separator has a conductive layer. And the conductive layer is provided on the surface of the separator facing at least one of the positive electrode active material layer and the negative electrode active material layer having grooves.

[0025] The conductive layer preferably contains a conductive material and a binder. Examples of the conductive material include metals and carbon materials. Examples of the metal include simple metals such as aluminum, tungsten, molybdenum, titanium, tantalum, copper, nickel, titanium, iron, molybdenum, and chromium; alloys such as stainless steel; and the like. Examples of the carbon material include graphite, carbon black, needle coke, carbon nanotubes, and the like. The binder is not particularly limited, and for example, polyvinylidene fluoride (PVdF) or the like can be used. In the conductive layer, the content of the conductive material with respect to the binder is preferably 10% by mass or more and 50% by mass or less, more preferably 20% by mass or more and 40% by mass or less, and still more preferably 25% by mass or more and 35% by mass or less.

[0026] The thickness of the conductive layer is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 7 μm or less, and still more preferably 3 μm or more and 5 μm or less.

[0027] From the viewpoint of facilitating the determination of the presence or absence of metal impurities, it is preferable that the separator has a conductive layer only in a portion facing the groove of the positive electrode active material layer or the negative electrode active material layer.

[0028] The separator preferably has a conductive layer on the surface of a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide.

[0029] Here, the aspect of the electrode body will be described with reference to FIGS. 1 and 2. Note that FIGS. 1 and 2 are merely examples of the electrode body and are not limited thereto. FIG. 1 is a schematic front view showing a cross section in the thickness direction of an electrode body according to an embodiment. As shown in FIG. 1, the electrode body 100A is laminated via a separator 30A having a conductive layer 5A, with a positive electrode 10A having a positive electrode active material layer 1A and a positive electrode current collector 2A, and a negative electrode 20A having a negative electrode active material layer 3A and a negative electrode current collector 4A. The separator 30A has a porous sheet 7A. In the electrode body 100A shown in FIG. 1, the positive electrode active material layer 1A has a groove 6A in the thickness direction of the positive electrode active material layer 1A. And the conductive layer 5A is disposed on the surface of the separator 30A on the side of the positive electrode active material layer 1A having the groove 6A. Here, the groove 6A extends linearly in the observation direction of the schematic front view.

[0030] FIG. 2 is a schematic front view showing a cross section in the thickness direction of an electrode body according to another embodiment. As shown in FIG. 2, the electrode body 100B is laminated via a separator 30B having a conductive layer 5B, with a positive electrode 10B having a positive electrode active material layer 1B and a positive electrode current collector 2B, and a negative electrode 20B having a negative electrode active material layer 3B and a negative electrode current collector 4B. The separator 30B has a porous sheet 7B. In the electrode body 100B shown in FIG. 2, the positive electrode active material layer 1B has a groove 6B in the thickness direction of the positive electrode active material layer 1B. And the conductive layer 5B is disposed only on the surface of the separator 30B on the side of the positive electrode active material layer 1B having the groove 6B and at the portion where the conductive layer 5B faces the groove. Here, the groove 6B extends linearly in the observation direction of the schematic front view.

[0031] (Non-aqueous electrolyte) The secondary battery according to the present disclosure preferably contains a non-aqueous electrolyte. The non-aqueous electrolyte is not particularly limited, and conventionally known non-aqueous electrolytes can be used. The non-aqueous electrolyte preferably contains a non-aqueous solvent and a supporting salt. Examples of the non-aqueous solvent include carbonates such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate, ethers, esters, and the like. Examples of the supporting salt include lithium salts such as LiPF6 and LiBF4.

[0032] (Method for manufacturing a secondary battery) The secondary battery according to the present disclosure is preferably manufactured by producing a separator having a positive electrode, a negative electrode, and a conductive layer, obtaining an electrode body by laminating these, and then housing the electrode body in a battery case (outer container).

[0033] The positive electrode and the negative electrode are preferably produced by applying a slurry containing an active material (i.e., a positive electrode active material or a negative electrode active material) and a solvent onto a current collector (i.e., a positive electrode current collector or a negative electrode current collector) and drying it. Here, as a method of forming a groove in the positive electrode active material layer or the negative electrode active material layer, there is a method of forming a groove by partially cutting the positive electrode active material layer or the negative electrode active material layer obtained by applying and drying the slurry onto the current collector.

[0034] The separator having a conductive layer is preferably produced by applying a slurry containing a conductive material, a binder, and a solvent onto the surface of the porous sheet and drying it.

Examples

[0035] Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0036] <Fabrication of Positive Electrode> Positive electrodes 1 and 2 were fabricated by the following procedure.

[0037] (Positive Electrode 1) Positive electrode active material (LiNi1 / 3Co1 / 3Mn 1 / 3 O2): Conductive aid (acetylene black): Binder (PVdF) = 91:4:4 (mass ratio) was mixed with N-methyl-2-pyrrolidone as a solvent to prepare a slurry for forming a positive electrode active material layer, which was applied to and dried on an aluminum foil. Then, by removing the applied positive electrode active material layer with a laser, a positive electrode 1 having a plurality of linear positive electrode active material layers with a width of 100 mm and a thickness of 150 μm at intervals of 2 mm was obtained. The linear positive electrode active material layers did not intersect each other and were parallel to each other.

[0038] (Positive electrode 2) The positive electrode 2 was obtained by applying and drying the slurry for forming the positive electrode active material layer prepared in (Positive electrode 1) on an aluminum foil.

[0039] <Fabrication of negative electrode> The negative electrode 1 and the negative electrode 2 were fabricated according to the following procedure.

[0040] (Negative electrode 1) The negative electrode active material (natural graphite): binder (styrene-butadiene rubber (SBR)): thickener (carboxymethyl cellulose (CMC)) were mixed in a ratio (mass ratio) of 91:4:4 in water as a solvent to prepare a slurry for forming a negative electrode active material layer, and the negative electrode 1 was obtained by applying and drying it on a copper foil.

[0041] (Negative electrode 2) The slurry for forming the negative electrode active material layer prepared in (Negative electrode 1) was applied and dried on a copper foil. Then, by removing the negative electrode active material layer after application with a laser, a negative electrode 2 having a plurality of linear negative electrode active material layers with a width of 100 mm × a thickness of 150 μm at intervals of 2 mm was obtained. The linear negative electrode active material layers did not intersect with each other and were parallel to each other.

[0042] <Fabrication of separator> The separator 1, the separator 2, and the separator 3 were fabricated according to the following procedure.

[0043] (Separator 1) A slurry for forming a conductive layer containing polyvinylidene fluoride as a binder, carbon black (acetylene black) as a conductive material, and N-methyl-2-pyrrolidone as a solvent was prepared. The content of the conductive material with respect to the binder in the slurry for forming the conductive layer was 30% by mass. The slurry for forming the conductive layer was applied to one surface of a porous sheet (a porous sheet made of a polyethylene resin) and dried to obtain a separator having a conductive layer with a thickness of 4 μm.

[0044] (Separator 2) The slurry for forming the conductive layer prepared in (Separator 1) was applied to the same porous sheet as that used in (Separator 1) with a masking tape (made of polyimide) pre - attached, coated on one - side surface and dried. Then, by peeling off the masking tape, a separator having a plurality of linear conductive layers with a width of 2 mm × a thickness of 4 μm at intervals of 100 mm was obtained. The linear conductive layers did not intersect with each other and were parallel to each other.

[0045] (Separator 3) The same porous sheet as that used in (Separator 1) was prepared as Separator 3.

[0046] <Example 1> The electrode body was obtained by laminating the positive electrode 1 and the negative electrode 1 via Separator 1. At this time, the positive electrode active material layer and the negative electrode active material layer were in contact with Separator 1, and the conductive layer of Separator 1 faced the positive electrode 1 side (that is, the state of FIG. 1). Also, a stainless - steel ball with a diameter of 200 μm as a metal impurity was placed in one of the grooves of the positive electrode active material layer of the positive electrode 1. The electrode body prepared by the above procedure was housed in a battery case to fabricate a secondary battery. Five secondary batteries for each example were fabricated by the same procedure.

[0047] <Example 2> The electrode body was obtained by laminating the positive electrode 1 and the negative electrode 1 via Separator 2. At this time, the positive electrode active material layer and the negative electrode active material layer were in contact with Separator 2, the conductive layer of Separator 2 faced the positive electrode 1 side, and the conductive layer was provided only at the portion facing the groove of the positive electrode active material layer (that is, the state of FIG. 2). Also, a stainless - steel ball with a diameter of 200 μm as a metal impurity was placed in one of the grooves of the positive electrode active material layer of the positive electrode 1. The electrode body prepared by the above procedure was housed in a battery case to fabricate a secondary battery.

[0048] <Example 3> An electrode body was obtained by laminating a positive electrode 2 and a negative electrode 2 with a separator 1 interposed therebetween. At this time, the positive electrode active material layer and the negative electrode active material layer were in contact with the separator 1, and the conductive layer of the separator 1 was oriented toward the negative electrode 2 side (that is, in FIG. 1, 1A was the negative electrode active material layer, 2A was the negative electrode current collector, 3A was the positive electrode active material layer, and 4A was the positive electrode current collector). Also, one stainless steel ball with a diameter of 200 μm was placed in the groove of the negative electrode active material layer of the negative electrode 2 as a metal impurity. The electrode body prepared by the above procedure was housed in a battery case to fabricate a secondary battery.

[0049] <Example 4> An electrode body was obtained by laminating a positive electrode 2 and a negative electrode 2 with a separator 2 interposed therebetween. At this time, the positive electrode active material layer and the negative electrode active material layer were in contact with the separator 2, and the conductive layer of the separator 2 was oriented toward the negative electrode 2 side, and the conductive layer was provided only at the portion facing the groove of the negative electrode active material layer (that is, in FIG. 2, 1B was the negative electrode active material layer, 2B was the negative electrode current collector, 3B was the positive electrode active material layer, and 4B was the positive electrode current collector). Also, one stainless steel ball with a diameter of 200 μm was placed in the groove of the negative electrode active material layer of the positive electrode 2 as a metal impurity. The electrode body prepared by the above procedure was housed in a battery case to fabricate a secondary battery.

[0050] <Comparative Example 1> An electrode body was obtained by laminating a positive electrode 1 and a negative electrode 1 with a separator 3 interposed therebetween. At this time, the positive electrode active material layer and the negative electrode active material layer were in contact with the separator 3. Also, one stainless steel ball with a diameter of 200 μm was placed in the groove of the negative electrode active material layer of the positive electrode 1 as a metal impurity. The electrode body prepared by the above procedure was housed in a battery case to fabricate a secondary battery.

[0051] <Comparative Example 2> An electrode body was obtained by laminating a positive electrode 2 and a negative electrode 2 with a separator 3 interposed therebetween. At this time, the positive electrode active material layer and the negative electrode active material layer were in contact with the separator 3. Also, one stainless steel ball with a diameter of 200 μm was placed in the groove of the negative electrode active material layer of the negative electrode 2 as a metal impurity. The electrode body produced by the above procedure was housed in a battery case to fabricate a secondary battery.

[0052] <Insulation inspection test (spike leak) test> A spike leak test was performed on the secondary batteries obtained in each example. Specifically, in a room temperature (25 °C) environment, a load of 6 kN was applied to the secondary battery in the thickness direction of the battery case, and a spike voltage of 1000 V was applied between the positive and negative external terminals for 10 seconds to confirm the value of the leakage current (dielectric breakdown current). When the leakage current was 10 mA or more, it was determined that the secondary battery contained metal impurities. Among the five cells fabricated in each example, if it could be determined that three or more secondary batteries contained metal impurities, it was regarded as "qualified", and if two or fewer batteries could be determined to be secondary batteries containing metal impurities, it was regarded as "unqualified".

[0053]

Table 1

[0054] In Table 1, the reason why the item "Orientation of conductive layer" is described as "-" in Comparative Example 1 and Comparative Example 2 is that the separator does not have a conductive layer. In Table 1, "entire surface" in "Aspect of conductive layer" means having a conductive layer on the entire surface of the positive electrode side or negative electrode side of the separator, and "only groove facing part" means having a conductive layer only on the part of the positive electrode side or negative electrode side surface of the separator that faces the groove of the positive electrode active material layer or negative electrode active material layer. In Table 1, the "detection number" described in the lower column of "Insulation inspection test result" indicates the number of batteries that could be determined to be secondary batteries containing metal impurities.

[0055] From the above results, it can be seen that in the lithium-ion secondary battery having grooves in at least one of the positive electrode active material layer and the negative electrode active material layer of the secondary battery of this example, it is easy to judge the presence or absence of metal impurity content using the insulation inspection test.

Explanation of symbols

[0056] 1A, 1B Positive electrode active material layer 2A, 2B Positive electrode current collector 3A, 3B Negative electrode active material layer 4A, 4B Negative electrode current collector 5A, 5B Conductive layer 6A, 6B Groove 7A, 7B Porous sheet 10A, 10B Positive electrode 20A, 20B Negative electrode 30A, 30B Separator 100A, 100B Electrode body

Claims

1. An electrode body comprising a positive electrode having a positive electrode active material layer and a positive electrode current collector, and a negative electrode having a negative electrode active material layer and a negative electrode current collector, which are laminated via a separator having a conductive layer, wherein the positive electrode active material layer and the negative electrode active material layer are in contact with the separator, at least one of the positive electrode active material layer and the negative electrode active material layer has a groove in the thickness direction, the separator has the conductive layer on a surface of the separator facing a surface of at least one of the positive electrode active material layer and the negative electrode active material layer having the groove, A lithium ion secondary battery in which the positive electrode active material layer has the groove.

2. An electrode body comprising a positive electrode having a positive electrode active material layer and a positive electrode current collector, and a negative electrode having a negative electrode active material layer and a negative electrode current collector, which are laminated via a separator having a conductive layer, wherein the positive electrode active material layer and the negative electrode active material layer are in contact with the separator, at least one of the positive electrode active material layer and the negative electrode active material layer has a groove in the thickness direction, the separator has the conductive layer on a surface of the separator facing a surface of at least one of the positive electrode active material layer and the negative electrode active material layer having the groove, A lithium ion secondary battery in which the separator has the conductive layer only in a portion facing the groove.

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