Electrodes for secondary batteries

Abstract

The present invention provides an electrode for a secondary battery that can suppress the occurrence of short circuits even if metal impurities enter the grooves of the active material layer. [Solution] An electrode for a secondary battery having a current collector, a separator, and an active material layer disposed between the current collector and the separator, wherein the active material layer has grooves in the thickness direction, and an insulating layer, which is an insulating layer disposed on the surface of the separator, is provided inside the grooves.

Description

Technical Field

[0001] The present disclosure relates to an electrode for a secondary battery.

Background Art

[0002] Patent Document 1 discloses that at least one of the positive electrode active material layer and the negative electrode active material layer has grooves in the thickness direction, and a conductive layer is disposed in the grooves and on a separator. Patent Document 2 discloses that an active material layer provided on a current collector is divided into a plurality of regions by grooves. Patent Document 3 discloses that a core material exposed portion is formed between the active material layers on the current collector.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] When metal impurities enter the grooves of the active material layer and the metal impurities also come into contact with the conductive layer, the positive electrode, and the negative electrode current collector, a short circuit occurs.

[0005] An object of the present disclosure is to provide an electrode for a secondary battery that can suppress the occurrence of a short circuit even when metal impurities enter the grooves of the active material layer.

Means for Solving the Problems

[0006] This application discloses an electrode for a secondary battery having a current collector, a separator, and an active material layer disposed between the current collector and the separator, wherein the active material layer has grooves in the thickness direction, and an insulating layer, which is an insulating layer disposed on the surface of the separator, is provided inside the grooves.

[0007] The insulating layer may be thicker than the separator at its thickest point.

[0008] The insulating layer may be arranged along the entire length of the groove in the longitudinal direction.

[0009] The insulating layer may be made harder than the separator. [Effects of the Invention]

[0010] According to this disclosure, even if metal impurities enter the groove, the insulating layer suppresses electrical conduction between the separator and the current collector through the metal impurities, thereby suppressing the occurrence of short circuits. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the configuration of the electrode 10 for the secondary battery. [Modes for carrying out the invention]

[0012] Figure 1 is a diagram illustrating the configuration of an electrode 10 (hereinafter sometimes referred to as "electrode 10") for a secondary battery according to one embodiment. Note that the electrode 10 in this embodiment is an electrode for a lithium-ion secondary battery. As shown in Figure 1, the electrode 10 is a laminate in which a positive electrode having a positive electrode active material layer 11 and a positive electrode current collector 12, and a negative electrode having a negative electrode active material layer 13 and a negative electrode current collector 14 are laminated with a separator 15 in between. In this embodiment, the positive electrode active material layer 11 is laminated on one side of the positive electrode current collector 12 (the bottom side in Figure 1), and the separator 15 is laminated on the side of the positive electrode active material layer 11 opposite to the side on which the positive electrode current collector 12 is located. Furthermore, the negative electrode active material layer 13 is laminated on the side of the separator 15 opposite to the side on which the positive electrode active material layer 11 is located, and the negative electrode current collector 14 is laminated on the side of the negative electrode active material layer 13 opposite to the side on which the separator 15 is laminated. Furthermore, in this embodiment, grooves 11a are formed in the positive electrode active material layer 11, and an insulating layer 16 is arranged inside the grooves 11a. When multiple such laminates are stacked in succession, they form an electrode laminate, and electrode terminals are provided at its ends. When this laminate is then housed in an outer casing (not shown), it forms a secondary battery.

[0013] Furthermore, the electrodes of this disclosure can be applied to any type of electrode, such as bipolar multilayer electrodes or wound electrodes, as long as they are equipped with grooves in the active material layer and an insulating layer disposed therein, as described later. The components of electrode 10 are described in detail below.

[0014] [Positive electrode current collector] The positive electrode current collector 12 is a foil-shaped conductive material, such as metal foil. It does not need to be a single layer of metal foil; it may be a clad foil or laminated foil made by laminating different types of metal foil. The type of metal is not particularly limited, but for example, a foil made by laminating aluminum foil and copper foil can be used. Other metals include titanium, nickel, stainless steel (for example, SUS304, SUS316, SUS301 etc. as specified in JIS G 4305:2015), and steel (for example, cold-rolled steel sheet (SPCC etc.) as specified in JIS G 3141:2005).

[0015] [Positive electrode active material layer] The positive electrode active material layer 11 can contain a positive electrode active material, a conductive assistant, and a binder. The positive electrode active material is, for example, a lithium transition metal oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.), a lithium transition metal phosphate compound (LiFePO4, etc.), and the like. The binder serves to tie the active material or the conductive assistant to the surface of the current collector foil 12 and maintain the conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, acrylic resins containing monomer units such as acrylic acid and methacrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester cross-linked bodies, starch-acrylic acid graft polymers, and the like. These binders can be used alone or in combination. [[ID=二十]] Examples of the conductive assistant include acetylene black, carbon black, graphite, and the like.

[0016] The thickness of the positive electrode active material layer 11 is not particularly limited, but is preferably 50 μm or more and 250 μm or less, more preferably 100 μm or more and 200 μm or less, and even more preferably 130 μm or more and 170 μm or less.

[0017] In this embodiment, the positive electrode active material layer 11 is provided with grooves 11a from the viewpoint of enhancing the impregnation property of the electrolytic solution. The depth of the grooves is preferably the same as the thickness of the positive electrode active material layer 11. In the thickness direction of the grooves (the lamination direction of each layer), in the grooves 11a, the positive electrode current collector 12 is exposed at one end and the separator 15 is exposed at the other end. The width of the groove (the size in the left - right direction of the drawing sheet of FIG. 1, the size in the direction in which a plurality of grooves 11a are arranged) 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 even more preferably 2 mm or more and 3 mm or less. The shape of the direction in which the groove 11a extends (the back / front direction of the drawing sheet of FIG. 1, the longitudinal direction of the groove) is not particularly limited, and it may be linear, curved, etc., but it is preferably linear.

[0018] A plurality of linearly extending grooves 11a are arranged at a predetermined interval in the width direction, and it is preferable that the plurality of grooves 11a do not intersect each other. When a plurality of linear grooves 11a are arranged, the interval between the grooves 11a is preferably 50 mm or more and 200 mm or less, more preferably 70 mm or more and 150 mm or less, and even more preferably 80 mm or more and 120 mm or less. Here, the groove interval means the shortest distance between two adjacent grooves.

[0019] [Negative electrode active material layer] The negative electrode active material layer 13 can contain a negative electrode active material, a conductive assistant, and a binder. The conductive assistant and the binder can be considered in the same way as the positive electrode active material layer 11. Examples of the negative electrode active material include carbon such as graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon, metal compounds, elements that can be alloyed with lithium or compounds of such elements, boron - added carbon, etc. Examples of the elements that can be alloyed with lithium include silicon, titanium, and tin.

[0020] The thickness of the negative electrode active material layer 13 is not particularly limited, but it is preferably 50 μm or more and 250 μm or less, more preferably 100 μm or more and 200 μm or less, and even more preferably 13 μm or more and 170 μm or less.

[0021] If grooves are not formed in the positive electrode active material layer 11, or if grooves are formed in the positive electrode active material layer 11, grooves may be formed in the negative electrode active material layer 13 as well. The groove shape when grooves are formed in the negative electrode active material layer 13 can be considered in the same way as the grooves 11a described for the positive electrode active material layer 11.

[0022] [Negative electrode current collector] The negative electrode current collector 14 can be considered in the same way as the positive electrode current collector 12, and can be made of materials such as copper foil.

[0023] [Separator / Electrolyte] The separator 15 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains liquid electrolytes. Examples of materials constituting the separator 15 include polypropylene, polyethylene, polyolefin, and polyester. The separator 15 may have a single-layer structure or a multi-layer structure. The electrolyte absorbed and retained by the separator 15 is, for example, a liquid electrolyte (electrolyte solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. When the separator 15 is impregnated with an electrolyte, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. In addition, known solvents such as cyclic carbonates, cyclic esters, linear carbonates, linear esters, and ethers can be used as the non-aqueous solvent.

[0024] [Insulating layer] The insulating layer 16 is a layer formed of an electrically insulating material. The insulating layer 16 is located inside the groove 16 and is laminated on the separator 15 exposed within the groove 16. The insulating layer 16 only needs to be made of an electrically insulating material. This prevents electrical conductivity (short circuit) between the positive electrode current collector 12 and the separator 15 even if metal impurities are mixed inside the groove 11a. Furthermore, it is preferable that the insulating layer 16 has high heat resistance. This allows it to withstand temperature increases during battery charging and discharging. Furthermore, it is preferable that the insulating layer 16 is harder than the separator 15. This increases the strength of the insulating layer 16 and suppresses penetration by metal impurities. Hardness can be determined, for example, by measuring and comparing Vickers hardness. From the above perspective, the specific materials are not particularly limited, but metal oxides such as alumina can be used, for example.

[0025] It is preferable that the insulating layer 16 is arranged over the entire groove 11a. That is, it is preferable that the separator 15 is laminated so as to cover the entire widthwise surface shown in Figure 1, and the entire longitudinal surface of the groove 11a (the back / front direction in Figure 1). This makes it possible to more reliably improve the insulating properties.

[0026] Furthermore, in a cross-section perpendicular to the longitudinal direction of the groove 11a (cross-section in Figure 1), it is preferable that the height h of the thickest part of the insulating layer 16 is equal to or greater than the thickness d of the separator 15. This suppresses the penetration of metal impurities into the separator 15. However, it is preferable that the volume of the insulating layer 16 relative to the internal volume of the groove 11a is 30% or less. This allows the groove 11a to fully achieve its original purpose of improving the impregnation of the electrolyte. The shape of the insulating layer 16 in the cross-section shown in Figure 1 is not particularly limited. It may be triangular as shown in Figure 1, but it may also be trapezoidal, semicircular, quadrilateral, semi-elliptical, or irregular in shape. [Explanation of Symbols]

[0027] 10...Electrode for secondary battery, 11...Positive electrode active material layer, 12...Positive electrode current collector, 13...Negative electrode active material layer, 14...Negative electrode current collector, 15...Separator, 16...Insulating layer

Claims

1. An electrode for a secondary battery having a current collector, a separator, and an active material layer disposed between the current collector and the separator, The active material layer has grooves in the thickness direction, The inside of the groove is provided with an insulating layer, which is an insulating layer placed on the surface of the separator. Electrodes for secondary batteries.

2. The electrode for a secondary battery according to claim 1, wherein the insulating layer is thicker than the separator at its thickest point.

3. The electrode for a secondary battery according to claim 1 or 2, wherein the insulating layer is arranged along the entire length in the longitudinal direction of the groove.

4. The electrode for a secondary battery according to claim 1 or 2, wherein the hardness of the insulating layer is harder than that of the separator.

Images