CN112753111A

CN112753111A - Electrode for lithium ion secondary battery, method for producing same, and lithium ion secondary battery

Info

Publication number: CN112753111A
Application number: CN201980063378.7A
Authority: CN
Inventors: 寺西利绘; 岩田瞬
Original assignee: Sekisui Chemical Co Ltd
Current assignee: Sekisui Chemical Co Ltd
Priority date: 2018-09-28
Filing date: 2019-09-27
Publication date: 2021-05-04
Also published as: JPWO2020067504A1; JP2021119568A; WO2020067504A1; JP7177210B2; JP6878702B2

Abstract

An electrode 10 for a lithium ion secondary battery, comprising: the collector includes a collector, a first electrode active material layer 12 provided on one surface of the collector, and a first insulating layer 13 provided on the first electrode active material layer 12, wherein the collector has an end portion 11A not covered with the first electrode active material layer 12, an end portion 13A of the first insulating layer 13 in the end portion 11A of the collector protrudes from the first electrode active material layer 12 and covers a part of the end portion 11A of the collector, the end portion 13A of the first insulating layer 13 has a waveform shape in which a plurality of elongated protrusions 13X are arranged in parallel, and a length D of the protrusion 13X is 5mm or less.

Description

Electrode for lithium ion secondary battery, method for producing same, and lithium ion secondary battery

Technical Field

The present invention relates to an electrode for a lithium ion secondary battery having an insulating layer, a method for producing the same, and a lithium ion secondary battery.

Background

Lithium ion secondary batteries are used as large stationary power sources for storing electric power and power sources for electric vehicles and the like, and in recent years, studies on reduction in size and thickness of batteries have been advanced. The lithium ion secondary battery generally includes: two electrodes in which an electrode active material layer is formed on a surface of a current collector made of a metal foil or the like; and a separator disposed between the two electrodes. The separator serves to prevent a short circuit between the two electrodes and to retain the electrolyte. Conventionally, it has been known that a separator undergoes oxidative degradation at a contact surface with an electrode, and particularly degradation on the positive electrode side tends to be remarkable.

In addition, conventionally, in a lithium ion secondary battery, a porous insulating layer is provided on a surface of an electrode active material layer (for example, refer to patent document 1). In general, the insulating layer is provided to provide a good short-circuit suppressing function even when the insulating layer is used in combination with a separator to secure insulation between electrodes or when the separator shrinks.

The insulating layer is formed by, for example, applying an insulating layer slurry containing insulating fine particles and a binder to the electrode active material layer.

Documents of the prior art

Patent document

Patent document 1 Japanese patent No. 3253632

Disclosure of Invention

Technical problem to be solved by the invention

However, the current collector having the electrode active material layer formed on the surface thereof has an end portion not covered with the electrode active material layer (also referred to as an "uncovered end portion"), and the uncovered end portions are joined together and attached to the electrode tab. The following are discussed: in the uncovered end portion, an insulating layer formed on the electrode active material layer is formed so as to protrude from the end portion of the electrode active material layer and cover a part of the uncovered end portion in order to prevent short-circuiting of adjacent electrodes.

On the other hand, the insulating layer is often formed by intermittent coating, and the insulating layer may become a coating start end as a coating start portion and a coating end as a coating end portion in the end portion of the current collector. However, in the coating end as the coating end portion, the coating liquid for forming the insulating layer is not immediately cut at the end of coating, but partially extended in an elongated shape, that is, so-called liquid drag occurs. When liquid drag occurs, the end of the insulating layer has a wavy profile with a plurality of elongated protrusions arranged in parallel.

As described above, when the end portion of the insulating layer has a corrugated shape, if the uncovered end portion of the current collector is shortened, the electrode tab is stacked on the convex portion made of the insulating material, which results in a decrease in strength of the electrode tab. On the other hand, if the uncovered end portions of the collectors are extended, the overlapping of the electrode tabs can be prevented, but there is a problem in that the area of the electrode active material layer corresponding to each collector is reduced, resulting in a reduction in energy density.

Therefore, the technical problem of the invention is as follows: provided is an electrode for a lithium ion secondary battery, wherein the strength of an electrode tab can be improved without reducing the energy density.

Means for solving the problems

The inventors of the present invention have intensively studied and as a result, found that the above-mentioned problems can be solved by appropriately adjusting the application conditions of the insulating layer paste and setting the liquid dragging (i.e., the convex portion of the wave shape) length to a specified value or less, and completed the present invention. Namely, the present invention provides the following [1] to [16 ].

[1] An electrode for a lithium ion secondary battery, comprising: a current collector, a first electrode active material layer provided on one surface of the current collector, and a first insulating layer provided on the first electrode active material layer,

the current collector has an end portion not covered with the first electrode active material layer,

an end portion of the first insulating layer that extends from the first electrode active material layer and covers a part of the end portion of the current collector, the end portion of the first insulating layer having a waveform shape in which a plurality of elongated protrusions are arranged in parallel,

the length D of the projection is 5mm or less.

[2] The electrode for a lithium-ion secondary battery according to the above [1], wherein a length A of a portion of the end portion of the current collector, which is not covered with both the first electrode active material layer and the first insulating layer including the convex portion, is 3 to 10 mm.

[3] The electrode for a lithium-ion secondary battery as recited in the above [1] or [2], wherein a length B of an end portion of the first insulating layer, which extends from the first electrode active material layer, is 1 to 5 mm.

[4] The electrode for a lithium-ion secondary battery according to any one of the above [1] to [3], further comprising: a second electrode active material layer provided on the other surface of the collector, and a second insulating layer provided on the second electrode active material layer,

in the end portion of the current collector, an end portion of the second insulating layer protrudes from the second electrode active material layer and covers a part of the end portion of the current collector on the other surface, and an edge portion thereof is formed in a substantially linear shape.

[5] The electrode for a lithium-ion secondary battery as recited in any one of the above [1] to [4], wherein the end portion of the current collector is attached to an electrode sheet.

[6] The electrode for a lithium ion secondary battery as described in the above [5], wherein a distance C between the electrode tab and the first electrode active material layer is 3 to 8 mm.

[7] The electrode for a lithium-ion secondary battery as recited in the above [5] or [6], wherein D/(C-B) is 1.5 or less, where D is a length of the protruding portion, B is a length of an end portion of the first insulating layer that protrudes from the first electrode active material layer, and C is a distance between the electrode sheet and the first electrode active material layer.

[8] The electrode for a lithium-ion secondary battery according to any one of the above [1] to [7], wherein the first electrode active material layer is a positive electrode active material layer.

[9] The electrode for a lithium-ion secondary battery according to any one of the above [1] to [8], wherein the first insulating layer contains insulating fine particles and a binder for an insulating layer.

[10] A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of the above [1] to [9 ].

[11] The lithium ion secondary battery according to the above [10], which is a lithium ion secondary battery in which a plurality of layers are provided by alternately arranging positive electrodes and negative electrodes,

at least one of the positive electrode and the negative electrode is formed of the electrode for a lithium ion secondary battery, and the ends of the current collector forming the one of the electrodes of each layer are joined together and connected to an electrode tab.

[12] A method for producing an electrode for a lithium ion secondary battery, comprising applying a first insulating layer coating solution to a first electrode active material layer of a collector sheet having the first electrode active material layer provided on one surface thereof to form a first insulating layer,

the collector sheet has an uncovered portion that is not covered with the first electrode active material layer,

coating of the coating liquid for the first insulating layer is performed with the uncovered portion of the collector sheet as a coating end,

an end portion of the first insulating layer constituted by the coating tip is formed as: protruding from the first electrode active material layer on the one surface and covering a part of the uncovered portion of the current collector sheet,

the liquid dragging length in the coating tip is 5mm or less.

[13] The method for producing an electrode for a lithium-ion secondary battery as recited in the above [12], wherein the coating liquid for the insulating layer has a viscosity of 2000 to 4000 mPas at the time of coating.

[14] The method for producing an electrode for a lithium-ion secondary battery according to the above [12] or [13], wherein,

applying a second insulating layer coating solution onto a second electrode active material layer of the current collector sheet provided with the second electrode active material layer on the other surface of the current collector sheet to form a second insulating layer,

the uncovered portion is a portion that is not covered by the first and second electrode active material layers on both sides of the current collector sheet,

coating the coating liquid for the second insulating layer with a position of the uncovered portion of the collector sheet as a coating end as a coating start end,

an end portion of the second insulating layer constituted by the application start end is formed as: protruding from the second electrode active material layer on the other surface and covering a part of the uncovered portion of the current collector sheet.

[15] The method for producing an electrode for a lithium-ion secondary battery as recited in the above [14], wherein,

one of the first and second insulating layers is formed by applying one of the first and second insulating layer coating liquids to the one or the other surface while feeding the current collector sheet, and the current collector sheet is wound in a roll shape,

the other of the first and second insulating layer coating liquids is applied to the one or the other surface while the collector sheet wound in a roll shape is drawn out, thereby forming the other of the first and second insulating layers.

[16]As described above [12]～[15]The method for producing an electrode for a lithium-ion secondary battery, wherein the shear rate of the liquid contact portion with respect to the current collector when the first coating liquid for an insulating layer is applied is 0.5 × 10⁴～40×10⁴(1/s)。

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide an electrode for a lithium ion secondary battery, which can improve the strength of an electrode tab without lowering the energy density.

Drawings

Fig. 1 is a schematic cross-sectional view showing an electrode for a lithium-ion secondary battery according to a first embodiment. Fig. 2 is a plan view showing one surface of the electrode for a lithium-ion secondary battery according to the first embodiment.

Fig. 3 is a plan view showing the other surface of the electrode for a lithium-ion secondary battery according to the first embodiment.

Fig. 4 is a schematic cross-sectional view showing an electrode for a lithium-ion secondary battery according to a second embodiment.

Fig. 5 is a plan view showing a process of preparing the electrode for a lithium-ion secondary battery according to the first embodiment.

Fig. 6 is a schematic cross-sectional view showing a process of producing the electrode for a lithium-ion secondary battery according to the first embodiment.

Detailed Description

[ electrode for lithium ion Secondary Battery ]

< first embodiment >

The electrode for a lithium ion secondary battery of the present invention will be described in detail below.

Fig. 1 to 3 show an electrode 10 for a lithium ion secondary battery according to a first embodiment of the present invention.

As shown in fig. 1 and 2, a lithium-ion secondary battery electrode (hereinafter, may be simply referred to as "electrode") 10 according to a first embodiment includes: a current collector 11, a first electrode active material layer 12 provided on one surface 11X of the current collector 11, and a first insulating layer 13 provided on the first electrode active material layer 12. As shown in fig. 1 and 3, the electrode 10 for a lithium ion secondary battery further includes a second electrode active material layer 22 provided on the other surface 11Y of the current collector 11, and a second insulating layer 23 provided on the second electrode active material layer 22.

The lithium-ion secondary battery electrode 10 according to the first embodiment will be described in detail below.

(first electrode active material layer and first insulating layer)

First electrode active material layer 12 is formed so as not to cover one end 11Z of current collector 11 on one surface 11X. Therefore, one surface 11X of one end portion 11Z of current collector 11 becomes an end portion not covered with the first electrode active material layer (hereinafter, also referred to as "uncovered end portion 11A").

The first insulating layer 13 is provided on the first electrode active material layer 12, and an end portion of the insulating layer protrudes from the edge portion 12B of the first electrode active material layer 12 without covering the end portion 11A. The end portion formed so as to protrude (hereinafter also referred to as "protruding end portion 13A") covers the surface of current collector 11 that does not cover end portion 11A.

Protruding end portion 13A covers a part of uncovered end portion 11A, and does not cover a region on the leading end side of uncovered end portion 11A (i.e., the edge portion 11B side of current collector 11). In the following description, a region not covered with the protruding end portion 13A (first insulating layer 13) on the tip end side of the uncovered end portion 11A will be described as an uncovered tip end portion 11C.

As shown in fig. 2 and 3, electrode tab 15 is attached to one end 11Z of current collector 11. The electrode tab 15 is disposed so as to overlap the uncovered tip portion 11C. In the lithium ion secondary battery, it is preferable that the electrode 10 is formed by stacking a plurality of layers, and in this case, the one end portion 11Z of the current collector 11 is stacked in a plurality and attached to the electrode tab 15. In the case where the plurality of one end portions 11Z are stacked, the uncovered tip end portions 11C may be stacked on the uncovered tip end portions 11C of the other electrodes, and then joined by fusing or the like, and then the electrode tab 15 may be attached.

As shown in fig. 2, the uncovered end portion 11A has a waveform shape in which a plurality of elongated convex portions 13X are arranged in parallel when the protruding end portion 13A of the first insulating layer 13 is viewed in a plan view. Specifically, protruding end portion 13A has a base line 13B constituting an edge portion of first insulating layer 13, and each protruding portion 13X extends toward edge portion 11B of current collector 11 and protrudes from base line 13B. Here, each convex portion 13X is elongated and has a length d sufficiently large (for example, 3 times or more) with respect to the width of each convex portion 13X, and thus a plurality of convex portions are arranged in parallel along the base line 13B in the elongated shape to form a wave shape in the convex portions 13X.

Base line 13B is substantially parallel to end face 11B of current collector 11 formed in a linear shape. The term "substantially parallel" means that when a straight line is drawn along the base line 13B as described later, the straight line is hardly inclined with respect to the edge portion 11B (for example, the inclination angle is less than 8 °, preferably less than 4 °).

Generally, an insulating layer of an electrode for a lithium ion secondary battery is formed by applying a slurry, but the slurry has a certain viscosity. Therefore, at the coating end which is the coating end portion of the coating liquid, the liquid is not cut off, and the coating liquid is partially extended, that is, a so-called liquid dragging phenomenon occurs. As described later, since the protruding end portion 13A of the first insulating layer 13 is an application end, liquid drag inevitably occurs, and the plurality of convex portions 13X described above are formed to have a wave shape.

(Length of convex part)

In the present invention, the length D of the projection 13X is 5mm or less. By setting the length D to 5mm or less, even if the length of the uncovered end portion 11A is shortened on the one surface 11X, a region of a certain size not covered with the insulating layer 13 can be secured on the tip end side of the convex portion 13X. Therefore, even if the electrode tab 15 is attached to the uncovered distal end portion 11C, the electrode tab 15 hardly overlaps the convex portion 13X, thereby improving the strength of the electrode tab 15. When the strength of the electrode tab 15 is improved, the durability and the like of the electrode are improved, and the current collection is improved, thereby improving the capacity.

On the other hand, if the length D is greater than 5mm, the electrode tab 15 overlaps the plurality of projections 13X, resulting in a reduction in the strength of the electrode tab 15. Further, when the area of the protruding portion 13X on which the electrode tab 15 is superimposed is intended to be reduced, the length of the uncovered end portion 11A on the one surface 11X increases, and the energy density of the lithium-ion secondary battery decreases. The length of the uncovered end portion 11A is the total length of the length D and the length a and the length B described later, and may be referred to as a length (a + B + D).

The length D of the projection 13X is preferably 3mm or less. If the thickness is 3mm or less, the length (a + B + D) of the uncovered end portion 11A on the one surface 11X can be further shortened, and the energy density of the lithium-ion secondary battery can be easily increased. Further, the electrode tab 15 is less likely to overlap the convex portion 13X, and the strength of the tab of the electrode 15 is more likely to be increased. The shorter the length D, the better, the length inevitably formed at the time of the above coating, and may be, for example, a length of about 0.5mm or more.

As described later, length D of projection 13X is an average value of all projection lengths D of a plurality of projections 13X provided at one end 11Z of current collector 11. The length d is the shortest distance between the tip of the projection 13X and the base line 13B, and corresponds to the height of the projection 13X. Meanwhile, portions having a length/width of 3 or more are defined as convex portions, respectively.

(Length A, B, distance C)

The length B of the protruding end 13A of the first insulating layer 13 is preferably 1 to 5 mm. By setting the length B to 1mm or more, it is easier to ensure safety. On the other hand, by setting the length B to 5mm or less, the protruding end portion 13A can be prevented from being excessively lengthened, and it is easier to ensure the length a not covering the tip end portion 11C on the one surface 11X to be a certain amount or more. Further, if the thickness is 5mm or less, the area of the first electrode active material 12 on the current collector 11 can be prevented from becoming small, and a decrease in energy density can be prevented.

From the above viewpoint, the length B is more preferably 2 to 4 mm. Further, detailed measurement methods are as described in examples.

In the present invention, the length a of the uncovered end portion 11A, which is not covered by any one of the first electrode active material layer 12 and the first insulating layer 11 including the convex portion 13X, is preferably 3 to 10 mm. Here, length a is a length obtained by subtracting the total length of length B and length D from the length of uncovered end 11A of current collector 11. When the length a is 3mm or more, the electrode tab 15 is less likely to overlap the projection 13X, and the strength of the electrode tab is improved.

On the other hand, by setting the length a to 10mm or less, it is possible to secure a constant length of the protruding end portion 13A of the first insulating layer 13 without significantly decreasing the energy density, and to improve the safety. Further, by setting the length a to 10mm or less, the area of the first electrode active material layer 12 on the current collector 11 can be prevented from becoming small, and the energy density can be prevented from decreasing. From the above viewpoint, the length A is more preferably 5 to 8 mm.

As described above, the length of the uncovered end portion 11A is the total length (a + B + D) of the length A, B, D. The length (A + B + D) of the uncovered end portion 11A is preferably 4 to 14mm, more preferably 8 to 13mm, and still more preferably 9 to 12 mm. By setting the length to the above upper limit or less, the area of the first electrode active material layer 12 on the current collector 11 can be prevented from becoming small, and the energy density can be prevented from decreasing. When the length is set to be equal to or greater than the lower limit value, the electrode tab 15 is less likely to overlap the projection 13X, and the strength of the electrode tab is improved.

The distance C between the electrode tab 15 attached to the end 11A of the collector 11 and the first electrode active material layer 12 is preferably 3 to 8 mm. When the distance C is 3mm or more, the electrode tab 15 is less likely to overlap the projection 13X, and the strength of the electrode tab is improved. On the other hand, if C is 8mm or less, the area of the first electrode active material layer 12 formed on the current collector 11 increases, and the energy density tends to increase. From the above viewpoint, the distance C is more preferably 4 to 7 mm.

In addition, the specific measurement methods of the length A, B, D and the distance C described above are as described in the examples.

In the present invention, the ratio of the length D of the convex portion 13X to the distance between the edge portion of the first insulating layer 13 (i.e., the base line 13B) and the electrode tab 15, which is expressed by D/(C-B), is preferably 1.5 or less. When D/(C-B) is 1.5 or less, the electrode tab 15 is less likely to overlap the convex portion 13X, and the strength of the electrode tab 15 is improved.

From the viewpoint of enhancing the strength of the electrode tab 15, D/(C-B) is more preferably 1.4 or less, still more preferably less than 1, and still more preferably 0.8 or less. If D/(C-B) is less than 1, the electrode tab 15 is less likely to overlap the projection 13X.

The smaller D/(C-B) is, the better, and for example, it may be 0.1 or more, and from the viewpoint of practical use, it may be 0.3 or more.

In the present invention, the length ratio represented by A/(A + B) is preferably 0.2 to 0.9. By setting the length ratio to 0.2 or more, the area of the end portion 11C where the protruding portion 13X is not provided can be sufficiently secured, and the strength of the electrode tab 15 can also be sufficiently secured. Further, if the thickness is set to 0.9 or less, the length of the protruding end portion 13A of the first insulating layer 13 can be sufficiently secured, and safety can be improved. From this viewpoint, A/(A + B) is more preferably 0.5 to 0.8.

The length ratio B/(A + B + D) is preferably 0.1 to 0.4, more preferably 0.2 to 0.4. By setting this length ratio within the above range, the area of the electrode active material layer 12 can be increased while securing a sufficient length of the protruding end portion 13A of the first insulating layer 13.

(second electrode active material layer, second insulating layer)

As described above, in the first embodiment, the second electrode active material layer 22 is provided on the other surface 11Y of the collector 11, and the second insulating layer 23 is further provided on the second electrode active material layer 22. Second electrode active material layer 22 is formed so as not to cover one end portion 11Z of current collector 11, and the other surface 11Y of one end portion 11Z of current collector 11 is an end portion not covered with the electrode active material layer, like one surface 11X. That is, in current collector 11, both

surfaces

11X and 11Y of one end portion 11Z are uncovered with end portion 11A. In addition, in both

surfaces

11X and 11Y, the regions not covering the end portions 11A do not need to be completely coincident, and therefore, the positions of the edge portion 12B of the first electrode active material layer 12 and the edge portion 22B of the second electrode active material layer 22 can be appropriately shifted.

In the uncovered end portion 11A, an end portion of the second insulating layer 23 is formed so as to protrude from the second electrode active material layer 22, and this end portion (hereinafter, also referred to as "protruding end portion 23A") covers a part of the uncovered end portion 11A of the current collector 11. In addition, a region located on the leading end side (i.e., the edge portion 11B side of the current collector 11) from the protruding end portion 23A is a region not covered with the second insulating layer 23. That is, current collector 11 has uncovered leading end portion 11C, which is not covered with the electrode active material layer and the insulating layer, on both

surfaces

11X and 11Y on the leading end sides of protruding

end portions

13A and 23A. In addition, in both

surfaces

11X, 11Y, the regions not covering the leading end portion 11C do not need to completely coincide, and therefore, the positions of the base line 13B (i.e., the edge portion of the first insulating layer 13) and the edge portion 22B can be appropriately shifted.

As shown in fig. 3, in the uncovered end portion 21A, when an edge portion 23B of the protruding end portion 23A of the second insulating layer 23 is viewed in a plan view, the edge portion is formed substantially linearly. Here, the substantially straight line means that, when a straight line is drawn along the edge portion 23B, there is no unevenness deviating from the straight line at all, or even if there is unevenness, there is fine unevenness, and a plurality of elongated projections are not formed like the protruding end portion 13A provided on the one surface 11X. Edge portion 23B is substantially parallel to edge portion 11B of current collector 11. Substantially parallel means that when a straight line is drawn along edge portion 23B, the straight line is hardly inclined with respect to edge portion 11B of current collector 11 (for example, the inclination angle is less than 8 °, preferably less than 4 °).

The insulating layer of the lithium ion secondary battery electrode is generally formed by applying a slurry having a certain viscosity, but in the application start end, unlike the application end, no liquid drag occurs. As described later, since the projecting end portion 23A of the second insulating layer 23 becomes the application start end, liquid drag does not occur, and the edge portion 23B is formed substantially linearly as described above.

That is, in the present embodiment, one surface 11X side of one end portion 11Z of current collector 11 serves as the application end of first insulating layer 13, and the other surface side serves as the application start end of second insulating layer 23. According to this embodiment, as described later, since the coating liquid for insulating layers is applied to both surfaces without rewinding, it is possible to form insulating layers on both surfaces of current collector 11 by a simple method.

The current collector 11 is usually made of a metal foil, and the thickness thereof is not particularly limited, but is preferably 1 to 50 μm. The thicknesses of the first electrode active material layer 12 and the second electrode active material layer 22 are not particularly limited, but are preferably 10 to 100 μm, and more preferably 20 to 80 μm. The thicknesses of the first insulating layer 13 and the second insulating layer 23 are preferably 1 to 20 μm, and more preferably 2 to 10 μm, respectively.

In the present embodiment, the electrode 10 for a lithium-ion secondary battery described above preferably constitutes a positive electrode. Therefore, the current collector 11 is a positive electrode current collector, and the first electrode active material layer 12 and the second electrode active material layer 22 are positive electrode active material layers.

Since the positive electrode is generally smaller in area than the negative electrode, the end portion of the positive electrode (i.e., the end portion 11Z) overlaps with the negative electrode, and short-circuiting is likely to occur. Therefore, as shown in fig. 2 and 3, the first insulating layer 13 and the second insulating layer 23 are formed to protrude from the first electrode active material layer 12 and the second electrode active material layer 22, respectively, in the end portions, and thus, short circuits can be effectively prevented.

However, the electrode 10 for a lithium ion secondary battery may constitute a negative electrode. In this case, the current collector 11 is a negative electrode current collector, and the first electrode active material layer 12 and the second electrode active material layer 22 are negative electrode active material layers.

Next, the materials constituting the respective members will be described in detail.

(Current collector)

When the electrode is a positive electrode, the current collector 11 is a positive electrode current collector. Examples of the material constituting the positive electrode current collector include metals having conductivity such as copper, aluminum, titanium, nickel, and stainless steel, and among them, aluminum or copper is preferably used, and aluminum is more preferably used.

On the other hand, when the electrode is a negative electrode, the current collector 11 is a negative electrode current collector. The material constituting the negative electrode current collector is the same as the compound for the positive electrode current collector, but aluminum or copper is preferably used, and copper is more preferably used.

The first electrode active material layer 12 and the second electrode active material layer 22 each contain an electrode active material and a binder for an electrode. If the electrode 10 is a positive electrode, the electrode active material is a positive electrode active material, and the first electrode active material layer 12 and the second electrode active material layer 22 are both positive electrode active material layers. The positive electrode active material layer preferably further contains a conductive auxiliary agent.

When the electrode 10 is a negative electrode, the electrode active material is a negative electrode active material, and the first electrode active material layer 12 and the second electrode active material layer 22 are both negative electrode active material layers. The negative electrode active material layer may or may not contain a conductive auxiliary.

(electrode active Material)

As the positive electrode active material used in the positive electrode active material layer, a lithium metal oxide compound can be mentioned. As the lithium metal oxide compound, there can be exemplified: lithium cobaltate (LiCoO)₂) Lithium nickelate (LiNiO)₂) Lithium manganate (LiMn)₂O₄) And the like. Further, olivine-type lithium iron phosphate (LiFePO) may be used₄) And the like. Further, a plurality of metals other than lithium may be used, and NCM (nickel cobalt manganese) oxide, NCA (nickel cobalt aluminum) oxide, or the like, which is called a ternary system, may be used. Among them, the NCA-based oxide is preferable. The positive electrode active material may be used alone or in combination of two or more.

Examples of the negative electrode active material used in the negative electrode active material layer include carbon materials such as graphite and hard carbon, tin compound/silicon/carbon composite, and lithium. The negative electrode active material may be used alone or in combination of two or more.

The content of the electrode active material in each of the first electrode active material layer 12 and the second electrode active material layer 22 is preferably 50 to 99% by mass, and more preferably 70 to 98% by mass, based on the total amount of the electrode active material layers.

The electrode active material is preferably in the form of particles. The electrode active material is not particularly limited, but the average particle diameter is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. The average particle diameter of the electrode active material and the insulating fine particles described later in the particle size distribution of the insulating fine particles determined by the laser diffraction/scattering method means the particle diameter at which the volume cumulative distribution is 50% (D50).

(conductive auxiliary agent)

The conductive auxiliary used in each of the first electrode active material layer 12 and the second electrode active material layer 22 may be a material having higher conductivity than the electrode active material, and specifically, carbon black such as ketjen black and acetylene black, carbon nanotubes, carbon nanohorns, graphene, fullerene, or other carbonaceous materials may be used. The conductive additive may be used alone or in combination of two or more.

The content of the conductive additive in the electrode active material layer is preferably 1 to 15 mass%, more preferably 2 to 10 mass%, based on the total amount of the electrode active material layer. When the content of the conductive auxiliary agent is set within the above range, the conductivity of the electrode active material layer can be suitably improved.

(Binder for electrode)

The first electrode active material layer 12 and the second electrode active material layer 22 are each configured by bonding an electrode active material and a conductive auxiliary agent with an electrode binder. Specific examples of the binder for an electrode include: examples of the thermoplastic resin include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), Polytetrafluoroethylene (PTFE), acrylic resins such as polymethyl acrylate (PMA) and polymethyl methacrylate (PMMA), polyvinyl acetate, Polyimide (PI), Polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), Polyethylene (PE), polypropylene (PP), Polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber, poly (meth) acrylic acid, carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. These binders may be used alone or in combination of two or more. Carboxymethyl cellulose and the like may be used in the form of a salt such as a sodium salt.

The content of the binder for electrode in each of the first electrode active material layer 12 and the second electrode active material layer 22 is preferably 1 to 40% by mass, and more preferably 2 to 20% by mass, based on the total amount of the electrode active material layers. When the content of the binder for electrode is not less than the lower limit, the electrode active material and the conductive assistant can be appropriately held by the binder. When the content is not more than the upper limit, the electrode active material layer can contain an electrode active material in an amount of not less than a certain amount, or the electrode active material and the conductive assistant can be contained.

The first electrode active material layer 12 and the second electrode active material layer 22 may contain any other components than the electrode active material, the conductive auxiliary agent, and the electrode binder, respectively, within a range not to impair the effects of the present invention. However, the total content of the electrode active material, the conductive auxiliary agent, and the electrode binder in the total amount of the electrode active material layer is preferably 90 mass% or more, more preferably 95 mass% or more, and still more preferably 100 mass%.

Generally, the first insulating layer 13 and the second insulating layer 23 contain insulating fine particles and an insulating binder, respectively. The first insulating layer 13 and the second insulating layer 23 are each a layer in which insulating fine particles are bonded to each other with an adhesive through an insulating layer, and the insulating layers have a porous structure.

(insulating Fine particles)

The insulating fine particles contained in each of the first insulating layer 13 and the second insulating layer 23 are not particularly limited as long as they are insulating, and may be organic particles or inorganic particles. Specific examples of the organic particles include particles made of organic compounds such as crosslinked polymethyl methacrylate, crosslinked styrene-acrylic acid copolymer, crosslinked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamido-2-methylpropanesulfonate), polyacetal resin, epoxy resin, polyester resin, phenol resin, and melamine resin. Examples of the inorganic particles include silica, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, and niobium oxide (Nb)₂O₅) Tantalum oxide (Ta)₂O₅) And particles of inorganic compounds such as potassium fluoride, lithium fluoride, clay, zeolite, and calcium carbonate. The inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide.

The insulating fine particles may be particles using 1 of the above materials alone, or may be particles using two or more kinds at the same time. The insulating fine particles may contain both an inorganic compound and an organic compound. For example, inorganic-organic composite particles in which inorganic oxide is coated on the surface of particles made of an organic compound may be used.

Among the particles, inorganic particles are preferable, and among them, alumina particles and boehmite particles are preferable, and alumina particles are more preferable.

The average particle diameter of the insulating fine particles is not particularly limited as long as it is smaller than the thickness of the insulating layer, and is, for example, 0.001 to 1 μm, preferably 0.05 to 0.8 μm, and more preferably 0.1 to 0.6 μm. By controlling the average particle diameter of the insulating layer within the above range, it is easier to adjust the porosity within the above range and to prevent the oxidative deterioration of the separator.

In addition, the insulating fine particles may be used alone having an average particle diameter within the above range, or two kinds of insulating fine particles having different average particle diameters may be used in combination.

The content of the insulating fine particles contained in each of the first insulating layer 13 and the second insulating layer 23 is preferably 30 to 96 mass%, more preferably 45 to 94 mass%, and still more preferably 65 to 93 mass% based on the total amount of the insulating layers. If the content of the insulating fine particles is within the above range, the first insulating layer 13 and the second insulating layer 23 can each have a uniform porous structure and can easily prevent short circuits.

(adhesive for insulating layer)

As a specific example of the binder for an insulating layer, a compound exemplified as a compound that can be used in a binder for an electrode can be cited. One kind of the binder for the insulating layer may be used alone, or two or more kinds may be used simultaneously.

The content of the binder for the insulating layer contained in each of the first insulating layer 13 and the second insulating layer 23 is preferably 4 to 60 mass%, more preferably 5 to 50 mass%, and still more preferably 6 to 35 mass% based on the total amount of the insulating layer components. If the content of the binder is within the above range, a uniform porous structure can be formed on the insulating layer and short circuits are easily prevented.

The first insulating layer 13 and the second insulating layer 23 may contain any other components than the insulating fine particles and the binder for insulating layers within a range not to impair the effects of the present invention. However, the total content of the insulating fine particles and the insulating layer binder in the total mass of the first insulating layer 13 and the second insulating layer 23 is preferably 85 mass% or more, and more preferably 90 mass% or more.

< second embodiment >

The following describes differences from the first embodiment in a lithium-ion secondary battery electrode according to a second embodiment of the present invention.

In the first embodiment, the first electrode active material layer 12 and the first insulating layer 13, and the second electrode active material layer 22 and the second insulating layer 23 are provided on the two

surfaces

11X and 11Y of the current collector 11, respectively, but as shown in fig. 4, in the lithium-ion secondary battery electrode 30 according to the second embodiment, the second electrode active material layer 22 and the second insulating layer 23 provided on the other surface 11Y are omitted.

In the present embodiment, as in embodiment 1, the length D (see fig. 2 and 3) of the convex portion 13X of the first insulating layer 13 formed on the uncovered end portion 11A is set to a predetermined value or less, whereby the strength of the electrode tab can be increased without lowering the energy density.

The electrode for a lithium ion secondary battery according to the present invention is not limited to the

electrodes

10 and 30 for a lithium ion secondary battery according to the first and second embodiments, and various modifications may be made without departing from the scope of the present invention. For example, in the first embodiment, the edge portion 23B of the second insulating layer 23 is substantially linear, but is not limited to linear, and may have a waveform shape similar to the edge portion of the first insulating layer 13. At this time, the second insulating layer 23 formed on the other surface 10Y is constituted as described above in the description of the first insulating layer 13, and the details thereof are omitted here.

With this configuration, as will be described later, the

protruding end portions

13A and 23A of the first insulating layer 13 and the second insulating layer 23 are both coating terminals. In addition, on the

respective surfaces

11X, 11Y, the length D of the convex portion 13X of the first insulating layer 13 and the second insulating layer 23 formed on the uncovered end portion 11A is set to a predetermined value or less, whereby the strength of the electrode tab can be improved without lowering the energy density.

[ method for producing electrode for lithium ion Secondary Battery ]

Next, a method for manufacturing an electrode for a lithium-ion secondary battery according to a first embodiment of the present invention will be described with reference to fig. 5 and 6. A method for manufacturing an electrode for a lithium-ion secondary battery according to a first embodiment of the present invention includes: as shown in fig. 5, a first electrode active material layer 52 is formed on one surface 51X of the collector sheet 51, and a first insulating layer 53 is formed by applying a first insulating layer coating liquid on the first electrode active material layer 52.

(formation of first electrode active Material layer)

In the process of forming the first electrode active material layer 52, first, a first electrode active material layer coating solution containing an electrode active material, a binder for an electrode, and a solvent is prepared. The coating liquid for an electrode active material layer may contain other components such as a conductive assistant, if necessary. The electrode active material, the binder for electrodes, the conductive assistant, and the like are as described above. The coating liquid for the first electrode active material layer is a slurry.

The solvent in the coating liquid for the first electrode active material layer is water or an organic solvent. Specific examples of the organic solvent include one or two or more selected from N-methylpyrrolidone, N-ethylpyrrolidone, dimethylacetamide, and dimethylformamide. Among them, N-methylpyrrolidone is particularly preferably used.

The solid content concentration of the first electrode active material layer coating liquid is preferably 5 to 75% by mass, and more preferably 20 to 65% by mass.

The first electrode active material layer 52 can be formed by a known method using a first electrode active material layer coating solution, and for example, can be formed by applying the first electrode active material layer coating solution on the one surface 51X of the collector sheet 51 and drying it.

The first electrode active material layer 52 may be formed by applying a first electrode active material layer coating liquid to a substrate other than the collector sheet 51 and drying the coating liquid. As the substrate other than the collector sheet 51, a known release sheet can be given. The first active material layer formed on the substrate may be peeled off from the substrate and transferred onto one surface 51X of the collector sheet.

The first electrode active material layer 52 formed on the current collector sheet 51 is preferably pressed under pressure. By performing the pressure pressing, the electrode density can be increased. The press pressing may be performed by a roll press or the like.

The first electrode active material layer 52 is preferably applied to the current collector sheet 51 by intermittent application. Since the coating is performed by the intermittent coating method, as shown in fig. 5, the current collector sheet 51 alternately has: a covered portion 51A covered with the first electrode active material layer 52, and an uncovered portion 51B uncovered with the first electrode active material layer 52. In fig. 5, the region where the first electrode active material layer 52 is formed is indicated by a hatched line.

(formation of first insulating layer)

As described above, after the first electrode active material layer 52 is formed, the coating liquid for a first insulating layer is applied onto the first electrode active material layer 52 to form the first insulating layer 53.

The first insulating layer coating liquid for forming the first insulating layer 53 contains insulating fine particles, a binder for an insulating layer, and a solvent. As the solvent, water or an organic solvent can be used, and the specific contents of the organic solvent are the same as those described in the description of the coating liquid for an electrode active material layer. The first insulating layer coating liquid is a slurry (insulating layer slurry).

The solid content concentration of the first insulating layer coating liquid is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. By adjusting the solid content concentration to be within the above range, the viscosity can be easily adjusted to be within a desired range described later.

The first insulating layer 53 can be formed by applying a coating liquid for a first insulating layer on the surface of the first electrode active material layer 52 and drying it. The method of applying the first insulating layer coating liquid to the surface of the first electrode active material layer 52 is not particularly limited, and a known coating apparatus may be used, and examples thereof include a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a bar coating method, a gravure coating method, a screen printing method, and the like. Among them, the gravure coating method is preferably used from the viewpoint of uniform coating of the insulating layer.

The drying temperature is not particularly limited as long as the solvent can be removed, and is, for example, 50 to 130 ℃ and preferably 60 to 100 ℃. The drying time is not particularly limited, and is, for example, 30 seconds to 30 minutes, preferably 2 to 20 minutes.

Here, the coating of the first insulating layer coating liquid may be performed while the collector sheet 51 is transferred. For example, the collector sheet 51 is conveyed from left to right in fig. 5, and the application of the first insulating layer coating liquid is performed from right to left. The coating liquid for the first insulating layer is applied so that the first insulating layer 13 protrudes from both sides of the first electrode active material layer 52 (covered portion 51A), and an end portion (protruding end portion 53A) of the protruding first insulating layer 53 is formed so as to cover a part of the uncovered portion 51B. That is, the application start end 55 as an application start portion for forming each first insulating layer 53, and the application end 54 as an application end portion are arranged on the uncovered portion 51B. In fig. 5, the region where the first insulating layer 53 is formed is indicated by a hatched solid line.

In the coating tip 54, the coating liquid is not immediately cut but partially extended into an elongated shape, and so-called liquid drag inevitably occurs. When the liquid dragging occurs, the application tip 54 (the end portion of the first insulating layer 52) has a waveform-shaped profile in which a plurality of elongated protrusions 13X are arranged in parallel as shown in fig. 2.

In the present manufacturing method, by shortening the inevitable liquid dragging length (i.e., the length of the convex portion 13X), the strength of the electrode tab 15 can be increased without decreasing the energy density as described above. The specific liquid-drawing length is 5mm or less, preferably 3mm or less, as described above. Further, the liquid drag length is, for example, about 0.5mm or more.

In the present manufacturing method, as a method for shortening the liquid drag length, a method of adjusting the viscosity of the first insulating layer coating liquid and the shear rate at the time of coating the first insulating layer coating liquid can be used.

The viscosity of the coating liquid for the first insulating layer is preferably 2000 to 4000 mPas, more preferably 2500 to 3500 mPas. By setting the viscosity to be equal to or lower than the above upper limit, the liquid drag can be suppressed from becoming long, and the strength and density of the electrode tab can be suppressed from decreasing. Further, by setting the viscosity to be equal to or higher than the lower limit value, the thickness variation of the insulating layer is suppressed from increasing, and the safety is suppressed from lowering. The viscosity is measured at 60rpm with a B-type viscometer under the temperature condition during coating.

Further, when the composition for the first insulating layer is applied, the shear rate of the liquid contact portion with respect to the current collector sheet is preferably 0.5 × 10⁴～40×10⁴(1/s), more preferably 0.7X 10⁴～20×10⁴(1/s), more preferably 1.0X 10⁴～10×10⁴(1/s). The shearing speed can be adjusted according to the transfer speed of the collector sheet 51 and the liquid surface distance between the liquid contact portion and the collector sheet 51. The shear rate at the time of coating can be calculated, for example, according to the following equation. By setting the shear rate to the upper limit or less, the liquid drag is suppressed from becoming long, and the strength and density of the tab are suppressed from decreasing. Further, when the shear rate is not more than the lower limit, productivity is improved.

The liquid contact portion refers to a portion of the coating device that comes into contact with the coating liquid applied to the collector sheet, and in the gravure coating method, it refers to a tip portion 60A of the gravure roll shaft 60 shown in fig. 6 that is closest to the collector sheet 51, and the liquid surface distance refers to the liquid thickness of the coating liquid to be applied in the liquid contact portion (tip portion 60A), and when a groove is provided on the surface of the roll shaft 60, the liquid surface distance refers to the depth of the groove.

(shear rate (1/s))/(transfer rate m/sec)/(liquid surface distance m)

(formation of second electrode active Material layer and second insulating layer)

In the present manufacturing method, after the first insulating layer 53 is formed on the one surface 51X of the collector sheet 51 as described above, the second insulating layer 63 is formed on the other surface 51Y as shown in fig. 6.

In the present manufacturing method, the second electrode active material layer 62 may be formed on the other surface 51Y of the current collector sheet 51 before the second insulating layer 63 is formed. Here, the second electrode active material layer 62 may be formed before the first insulating layer 53 is formed, or may be formed after the first insulating layer 53 is formed.

In the present manufacturing method, the collector sheet 51 having the first insulating layer 53 and the second insulating layer 63 formed on the both

surfaces

51X and 51Y is cut along the alternate dotted line shown in fig. 5, and divided into the electrodes 10.

The second electrode active material layer 62 and the second insulating layer 63 may be formed by a coating liquid for a second electrode active material layer and a coating liquid for a second insulating layer, respectively, but the formation method is the same as the method for forming the first electrode active material layer 52 and the first insulating layer 53 except for the following.

The specific contents of the coating liquid for the second electrode active material layer and the coating liquid for the second insulating layer are the same as those described above for the coating liquid for the first electrode active material layer and the coating liquid for the first insulating layer, respectively, and therefore, the description thereof is omitted. Therefore, the viscosity of the coating liquid for the second insulating layer and the shear rate at the time of coating are also the same as those described above.

However, the coating liquid for the second electrode active material layer and the coating liquid for the second insulating layer used in the preparation of each electrode may have the same composition as the coating liquid for the first electrode active material layer and the coating liquid for the first insulating layer, or may be different.

The second electrode active material layer 62 is preferably provided by intermittent coating in the same manner as the first electrode active material layer 52, and as shown in fig. 6, a portion where the second electrode active material layer 62 is formed and a portion where the second electrode active material layer 62 is not formed are provided on the other surface 51Y of the current collector sheet 51 along the MD direction.

Here, the position where the second electrode active material layer 62 is formed on the other surface 51Y coincides with the position where the first electrode active material layer 52 is formed on the one surface 51X. Therefore, the covering portion 51A is a portion covered with the electrode active material layer on both

surfaces

51X and 51Y. The uncovered portion 51B is a portion uncovered by the electrode active material layer on both

surfaces

51X and 51Y. However, the portions covered with the electrode active material layer on both

surfaces

51X and 51Y do not need to be completely uniform, and may be appropriately shifted within a range not impairing the effects of the present invention.

Further, the first insulating layer 53 is formed by applying the first insulating layer coating liquid on the one surface 51X of the collector sheet 51, and then, the collector sheet may be wound in a roll shape. Subsequently, the collector sheet 51 wound in a roll shape is directly drawn out to a coating apparatus, and as shown in fig. 6, a coating liquid for a second insulating layer may be coated on the other surface 51Y, followed by forming a second insulating layer 63 by appropriate drying or the like. In fig. 6, the coating device is a gravure coater, and a method of supplying the coating liquid by the gravure roll 60 is shown, but coating may be performed by using another coating device.

On the other surface 51Y, an end portion of the second insulating layer 63 constituting the application start end 55 is formed so that the insulating layer protrudes from the second electrode active material layer 62 and partially covers the uncovered portion 51B of the collector sheet. Likewise, on the other surface 51Y, the end portion of the application tip 54 of the second insulating layer 63 is constituted so that the insulating layer protrudes from the second electrode active material layer 62 and partially covers the uncovered portion 51B of the collector sheet 51.

In addition, in the present embodiment, as described above, since the current collector sheet 51 wound in a roll shape is directly drawn out and the second insulating layer coating liquid is applied on the other surface 51Y, the position that becomes the coating end 54 in the uncovered portion 51 of the one surface 51X becomes the coating start end 55 on the other surface 51Y. In addition, a position that becomes the coating start end 55 in the uncovered portion 51 of the one surface 51X becomes the coating end 54 on the other surface 51Y.

Thus, in the present manufacturing method, when the current collector sheet 51 is cut and used as each electrode 10, the one surface 11X side of the one end portion 11Z of the current collector 11 is the application end of the first insulating layer 53, and the other surface side is the application start end of the second insulating layer 23 (see fig. 1).

Further, the current collector sheet 51 wound in a roll shape may be directly drawn out without rewinding, and thus this process can be simplified. Further, even if the coating end and the coating start end are provided on both surfaces of one end portion 11Z of current collector 11 without performing rewinding, the liquid trailing length on the coating end is short as described above. Therefore, in view of this liquid dragging, even if the electrode tab 15 is attached, it is not necessary to separate the electrode tab 15 from the second electrode active material layer 23 to a desired extent or more on the other face 11Y side of the collector 11 where the liquid dragging is not formed.

In the above description, for convenience of description, the electrode active material layer and the insulating layer formed on the one surface 51X of the current collector sheet 51 are referred to as a first electrode active material layer 52 and a first insulating layer 53, and the electrode active material layer and the insulating layer formed on the other surface 51Y of the current collector sheet 51 are referred to as a second electrode active material layer 62 and a second insulating layer 63. However, when the electrode 10 is prepared by cutting as described above, the first electrode active material layer 52 and the first insulating layer 53 may be used as the second electrode active material layer 22 and the second insulating layer 23 in the electrode 10, and the second electrode active material layer 62 and the second insulating layer 63 may be used as the first electrode active material layer 12 and the first insulating layer 13 in the electrode 10.

That is, the insulating layer to be the second insulating layer 23 in the electrode 10 is applied as the first insulating layer 53, and after the application, the insulating layer of the first insulating layer 13 in the electrode 10 is applied as the second insulating layer 63.

In addition, the above description shows the method for manufacturing the electrode 10 of the first embodiment in which the first and second electrode active material layers and the first and second insulating layers are provided on both surfaces of the electrode, and the electrode 30 of the second embodiment as shown in fig. 4 can be manufactured by omitting the formation of the second electrode active material layer and the formation of the second insulating layer.

In the above manufacturing method, the second insulating layer 62 is formed on the other surface 51Y without being wound around, but the second insulating layer may be formed by being wound around. That is, the first insulating layer 53 may be formed on one surface 51X, and after the collector sheet 51 wound in a roll shape is drawn out, the collector sheet may be wound in a roll shape again, and then drawn out from the roll to a coating apparatus and coated on the other surface 51Y with the coating liquid for a second insulating layer.

When the winding is performed, a position as a coating end in the uncovered portion 51 of the one surface 51X is a coating end on the other surface 51Y. Further, a position as a coating start end in the uncovered portion 51 of the one surface 51X is a coating start end on the other surface 51Y. Therefore, in the one end portion 11Z of the electrode 11, the first insulating layer 13 and the second insulating layer 23 of both

surfaces

11X, 11Y constitute an application end (an edge portion of a waveform shape shown in fig. 2) or an application start end (a linear edge portion shown in fig. 3). Therefore, as described above, an electrode in which the second insulating layer 23 has a waveform shape can be obtained in addition to the first insulating layer 13.

< lithium ion Secondary Battery >

The lithium ion secondary battery of the present invention is a battery having the electrode for a lithium ion secondary battery of the present invention described above. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode and a negative electrode disposed to face each other, and at least one of the negative electrode and the positive electrode is the electrode for the lithium ion secondary battery of the present invention. The positive electrode is preferably the electrode for a lithium ion secondary battery of the present invention, and both the positive electrode and the negative electrode may be the electrode for a lithium ion secondary battery of the present invention.

The lithium ion secondary battery of the present invention preferably further includes a separator disposed between the positive electrode and the negative electrode. By providing the separator, short circuit between the positive electrode and the negative electrode can be further effectively prevented. The separator may hold an electrolyte described later. The first insulating layer or the first and second insulating layers provided on the positive electrode and the negative electrode may be in contact with the separator, may be in non-contact with the separator, and preferably are in contact with the separator.

Examples of the separator include a porous polymer film, a nonwoven fabric, and glass fibers, and among them, a porous polymer film is preferable. An olefin porous film is exemplified as the porous polymer film. The separator is heated by heat generated during driving of the lithium ion secondary battery, and thus, thermal shrinkage or the like occurs, but even when the thermal shrinkage occurs, short circuit is easily suppressed by providing the insulating layer.

In addition, in the lithium ion secondary battery of the present invention, the separator may be omitted. Even if the separator is omitted, the insulating property between the negative electrode and the positive electrode can be ensured by the insulating layer provided on at least one of the negative electrode and the positive electrode.

The lithium ion secondary battery preferably has a multilayer structure in which a negative electrode and a positive electrode are laminated in multiple layers. In this case, the negative electrodes and the positive electrodes may be alternately arranged in the stacking direction. When a separator is used, the separator may be disposed between each positive electrode and each negative electrode.

In the case of a multilayer structure, each positive electrode is preferably the lithium-ion secondary battery electrode of the present invention, and in this case, the lithium-ion secondary battery electrode may be an electrode 10 (see fig. 1) having insulating layers (i.e., first and second insulating layers) on both surfaces, as shown in the first embodiment. Then, as described above, the uncovered distal end portions 11C of the one end portions 11Z of the electrodes 10 may be collected and then the electrode tab 15 may be attached.

In addition, if the structure is a multilayer structure, each negative electrode may be the electrode for a lithium ion secondary battery of the present invention described above. In this case, as shown in the first embodiment, the electrode for a lithium ion secondary battery may be the electrode 10 provided with the insulating layer (i.e., the first and second insulating layers) on both surfaces, and the uncovered front end portions 11C of the one end portions 11Z of the respective electrodes 10 may be collected and mounted on the electrode tab 15 (see fig. 1). Of course, both the positive electrode and the negative electrode may be constituted by the electrode for a lithium ion secondary battery of the present invention described above.

In the lithium ion secondary battery, the negative electrode and the positive electrode, or the negative electrode, the positive electrode, and the separator may be housed in a case by attaching an electrode tab as described above. The battery pack may be any one of a rectangular shape, a cylindrical shape, a stacked type, and the like. Therefore, the case is not particularly limited, but may be an outer can or an outer film. The outer film may be disposed between two outer films, or one outer film may be folded in two, for example, and the negative electrode and the positive electrode, or the negative electrode, the positive electrode, and the separator may be disposed between the outer films.

The lithium ion secondary battery includes an electrolyte. The electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used. As the electrolyte, for example, an electrolytic solution can be used.

Examples of the electrolytic solution include an organic solvent and an electrolytic solution containing an electrolyte salt. Examples of the organic solvent include polar solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ -butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1, 2-ethylene glycol dimethyl ether, 1, 2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, and methyl acetate, and mixtures of two or more of the above solvents. As the electrolyte salt, LiClO may be mentioned₄、LiPF₆、LiBF₄、LiAsF₆、LiSbF₆、LiCF₃CO₂、LiN(SO₂CF₃)₂、LiN(SO₂CF₂CF₃)₂、LiN(COCF₃)₂And LiN (COCF)₂CF₃)₂Lithium bis (oxalato) borate (LiB (C)₂O₄)₂) And the like lithium-containing salts. Further, lithium salt of organic acid-boron trifluoride complex and LiBH may be mentioned₄And complexes such as complex hydrides. These salts or complexes may be used singly or in admixture of two or more kinds.

The electrolyte may be a gel electrolyte in which the electrolytic solution further contains a polymer compound. Examples of the polymer compound include fluorine-based monomers such as polyvinylidene fluoride and polyacrylic-based monomers such as polymethyl (meth) acrylate. In addition, the gel electrolyte may also be used as a separator.

The electrolyte may be disposed between the positive electrode and the negative electrode, and for example, the electrolyte may be filled in a case that accommodates the positive electrode and the negative electrode. In addition, for example, the electrolyte may be coated on the positive electrode and the negative electrode and disposed between the positive electrode and the negative electrode.

The lithium ion secondary battery of the present invention can be produced using the electrode for a lithium ion secondary battery obtained by the above production method. The lithium ion secondary battery can be manufactured, for example, by preparing an electrode for a lithium ion secondary battery, attaching an electrode tab to an end of a current collector of the electrode for a lithium ion secondary battery, and housing the electrode tab in a case.

In this case, the negative electrode and the positive electrode, or the negative electrode, the positive electrode, and the separator may be housed in the case, as long as at least one of the negative electrode and the positive electrode is the electrode for a lithium ion secondary battery obtained by the above-described production method.

In the case where the positive electrode and the negative electrode are provided in a plurality of layers, if necessary, a separator may be disposed between the positive electrode and the negative electrode, and the positive electrode and the negative electrode stacked in a plurality of layers may be disposed in the case. At this time, the end portions (for example, the uncovered end portions 11C) of the collectors of the plurality of positive electrodes may be joined by fusion or the like, and the electrode tab may be attached. Similarly, the collectors of the plurality of negative electrodes may be joined at the end portions (for example, the end portions 11C are not covered) by fusion or the like, and an electrode tab may be attached.

Examples

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

The measurement method of each length and distance is as follows.

[ Length B ]

One piece of the electrode obtained in each of examples and comparative examples was prepared, and as shown in fig. 2, the surface of the side provided with the protruding end portion 13A of the insulating layer having a wavy shape composed of a plurality of convex portions 13X was arranged toward the surface side. Subsequently, a straight line is drawn on a portion to be the edge portion 12B of the electrode active material layer 12. A straight line is drawn as close as possible at the edge portion 12B, which is the same when a straight line is drawn below. Further, straight lines are drawn along the base line 13B of the first insulating layer 13, and the length between these straight lines is measured at 3, and the average value thereof is set as the length B of the protruding end portion 13A.

[ Length D ]

Subsequently, the length D from a straight line drawn along the base line 13B to the tip end portion of each convex portion 13X is measured, and the average of the lengths D of all convex portions 13X formed on the uncovered tip end portion 11C is set as the length D of the convex portion (liquid trailing length).

[ Length A ]

The length from a straight line drawn along the edge portion 12B of the electrode active material layer 12 to the edge portion 11B of the current collector 11 was obtained. The length at 3 was measured, and the average thereof was set as the length from the edge portion 12B to the edge portion 11B. The length a is obtained by subtracting the length D and the length B from the length.

[ distance C ]

In the electrode with the electrode tab 15 attached thereto, the distance from a straight line drawn along the edge portion 12B of the electrode active material layer 12 to the end of the electrode tab at position 3 in a plan view was measured, and the average value thereof was taken as the distance C.

The evaluation method in this example is as follows.

[ lug Strength ]

The positive electrodes 25 obtained in the respective examples and comparative examples were stacked, and aluminum sheets (type "a 1050-H24", 30mm × 50mm × 0.5mm in size) manufactured by Nets co were welded under the following conditions.

(welding conditions)

"brasson" (2000Xea 2500W) manufactured by Emerson corporation of japan was used, and 180 welding points were provided in an area of 20mm × 4mm by ultrasonic welding and welded. The conditions were as follows.

Welding time: 0.4 seconds, pressure: 0.1MPa, amplitude: 70 percent.

After welding, the strength was measured by the following experiment.

A peeling test was carried out under conditions of a peeling speed of 10mm/min and a temperature of 180 ℃ using Autogragh "EZ-LX series" manufactured by Shimadzu corporation, and the maximum strength was taken as the tab strength.

In addition, a positive electrode was prepared under the same conditions as in each example and comparative example except that the first and second insulating layers were not formed, and the maximum strength thereof was measured in the same manner and was regarded as blank strength.

The strength maintenance ratio was determined by dividing the lug strength by the blank strength, and evaluated according to the following criteria.

(evaluation criteria)

A is more than 95 percent

More than 90 percent and less than 95 percent of B

More than 80 percent and less than 90 percent of C

D less than 80 percent

[ evaluation of safety ]

The lithium ion secondary batteries prepared in the respective examples and comparative examples were subjected to constant current charging of 40A, and then the current was reduced after reaching 4.2V until the end of charging when it was 2A. Subsequently, the cell was heated to 130 ℃. After the temperature reached 130 ℃ and held for 1 hour, the maximum temperature of the battery in the 1 hour period was measured and evaluated according to the following criteria.

(evaluation criteria)

A, the highest temperature is less than 135 DEG C

B, the highest temperature is more than 135 ℃ and less than 145 DEG C

C, the highest temperature is more than 145 ℃ and less than 200 DEG C

And D, the highest temperature is more than 200 ℃.

[ energy Density ]

On the surface of the electrode provided with the insulating layer having a waveform shape, the area ratio (%) of the electrode active material layer with respect to the area of the current collector was calculated. In the electrode, the energy density is higher as the area ratio of the electrode active material layer is increased, and therefore the energy density is evaluated based on the area ratio as follows.

(evaluation criteria)

The area ratio of A to A is more than 96 percent

C, the area ratio is less than 96 percent.

Example 1

(preparation of Positive electrode)

100 parts by mass of Li (Ni-Co-Al) O having an average particle diameter of 10 μm as a positive electrode active material₂(NCA-based oxide), 4 parts by mass of acetylene black as a conductive auxiliary, and 4 parts by mass of polyvinylidene fluoride (PVdF) as an electrode binder were mixed with N-methylpyrrolidone (NMP) as a solvent to obtain a coating liquid for a positive electrode active material layer, the solid content concentration of which was adjusted to 60 mass%. The coating liquid for a positive electrode active material layer was intermittently applied to both surfaces of an aluminum foil having a thickness of 15 μm as a current collector sheet, predried, and then vacuum-dried at 120 ℃. Subsequently, the current collector sheet coated with the coating liquid for a positive electrode active material layer on both surfaces was subjected to pressure pressing at 400kN/m to prepare a current collector sheet having the first and second positive electrode active material layers on both surfaces, respectively. The thickness of each of the first and second positive electrode active material layers on each surface of the current collector sheet was 50 μm.

Further, as the coating liquid for the insulating layer, a slurry containing 100 parts by mass of alumina and 7 parts by mass of a resin binder and diluted with N-methyl-2-pyrrolidone as a solvent was prepared at a concentration of 42% by mass. The coating liquid for an insulating layer had a viscosity of 3000 mPas at 25 ℃ (i.e., at the time of coating). Using a gravure coating apparatus, a coating liquid for an insulating layer was coated on the first positive electrode active material layer on one surface of the current collector sheet by intermittent coating. At this time, the coating liquid for the insulating layer was applied so as to protrude 3mm from both sides, as shown in fig. 5 and 6, and dried at 90 ℃ for one minute to form a first insulating layer on one surface and wound into a roll. In the coating device, the transfer roller had an outer diameter of 60cm, an axial length of 70cm, and a groove volume of 25cc/m². The temperature of the coating section was 25 ℃ and the coating speed was 20 m/sec, and the shear rate at the time of coating was as shown in Table 1.

The collector sheet wound in a roll shape is drawn out, and is fed again into the gravure coating type coating apparatus to form the second insulating layer under the same conditions as those for forming the first insulating layer, and subsequently, the positive electrode is obtained by cutting the collector sheet. In the positive electrode, the size of the current collector was 110mm × 290mm, and the size of the portion where the positive electrode active material layer was formed was 110mm × 279 mm. Further, the length (a + B + D) of the uncoated portion (uncoated portion) of the positive electrode active material was 11 mm. Meanwhile, the thickness of the first and second insulating layers was 4 μm. Other lengths and distances are shown in table 1.

(preparation of negative electrode)

100 parts by mass of graphite (average particle diameter 10 μm) as a negative electrode active material, 1.5 parts by mass of styrene-butadiene rubber as a binder, 1.5 parts by mass of sodium salt of carboxymethyl cellulose (CMC), and water as a solvent were mixed, thereby obtaining a composition for a negative electrode active material layer in which the solid content concentration was adjusted to 50 mass%. The composition for a negative electrode active material layer was applied to both surfaces of a copper foil having a thickness of 12 μm as a negative electrode current collector, and vacuum-dried at 100 ℃.

Subsequently, the anode current collector coated with the composition for an anode active material layer on both surfaces was pressure-pressed at a line pressure of 500kN/m, followed by cutting, to obtain an anode. The density of the anode active material layer was 1.55 g/cc. The size of the negative electrode was 120mm × 300mm, and the area coated with the negative electrode active material layer in this size was 120mm × 290 mm.

(preparation of electrolyte)

LiPF as an electrolyte salt was added to a solvent in which Ethylene Carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3:7 (EC: DEC)₆The electrolyte was prepared by dissolving so that it was 1 mol/l.

(preparation of lithium ion Secondary Battery)

The 25 positive electrodes, 50 polyethylene porous membrane separators, and 24 positive electrodes obtained above were alternately stacked to obtain a temporary stack. Here, the positive electrodes and the negative electrodes are alternately arranged. The laminate was obtained by pressing for 1 minute using a flat plate type hot press.

The uncovered tip portions of the current collectors of the positive electrodes were collected and joined by ultrasonic welding, and were joined to a positive electrode tab protruding outward. Similarly, the ends of the exposed portions of the negative electrode current collectors of the respective negative electrodes are joined together by ultrasonic welding, and joined to a negative electrode tab protruding outward.

Subsequently, the laminate was sandwiched by an aluminum oxide laminated film, the positive electrode tab was protruded to the outside, and three sides were sealed by a lamination process. The electrolyte obtained by the above procedure was injected from one unsealed side and sealed by vacuum, to prepare a laminated type battery.

Example 2

The solid content concentration of the coating liquid for an insulating layer was changed to 35% by mass, and the viscosity at 25 ℃ was set to 2200 pas.

Example 3

The solid content concentration of the coating liquid for the insulating layer was changed to 35% by mass, the viscosity at 25 ℃ was set to 2200Pa · s, and the length of the uncoated portion (uncoated portion) of the positive electrode active material was changed to 12 mm.

Comparative example 1

The solid content concentration of the coating liquid for an insulating layer was changed to 25% by mass, and the viscosity at 25 ℃ was set to 1000 pas.

Comparative example 2

The solid content concentration of the coating liquid for the insulating layer was changed to 25 mass%, the viscosity at 25 ℃ was set to 1000Pa · s, and the length of the uncoated portion (uncoated portion) of the positive electrode active material was changed to 15 mm.

[ Table 1]

In examples 1 to 3, the end portion of the first insulating layer had a waveform shape in which a plurality of elongated protrusions were arranged in parallel, and by shortening the length D of the protrusions, it was possible to maintain a good energy density, and the strength of the tab was improved. In contrast, in comparative examples 1 and 2, since the length D of the convex portion was large, it was difficult to obtain both good tab strength and good energy density.

Description of the figures

10. 30 lithium ion secondary battery electrode

11 Current collector

11A uncovered end

11B edge part

11C uncovered tip

11X, 51X one surface

11Y, 51Y another surface

11Z end part

12. 52 first electrode active material layer

12B edge part

13. 53 first insulating layer

13A extended end part

13B Baseline (marginal portion)

13X convex part

15 electrode lug

22. 62 second electrode active material layer

23. 63 second insulating layer

23A extended end portion

23B edge part

51 collector sheet

51A covering part

51B uncovered part

54 coating start end

55 coating end

60 gravure roll shaft

Claims

1. An electrode for a lithium ion secondary battery, comprising: a current collector, a first electrode active material layer provided on one surface of the current collector, and a first insulating layer provided on the first electrode active material layer,

the length D of the projection is 5mm or less.

2. The electrode for a lithium-ion secondary battery according to claim 1, wherein a length a of a portion of the end portion of the current collector that is not covered with both the first electrode active material layer and the first insulating layer including the convex portion is 3 to 10 mm.

3. The electrode for a lithium ion secondary battery according to claim 1 or 2, wherein a length B of an end portion of the first insulating layer protruding from the first electrode active material layer is 1 to 5 mm.

4. The electrode for a lithium ion secondary battery according to any one of claims 1 to 3, further comprising: a second electrode active material layer provided on the other surface of the collector, and a second insulating layer provided on the second electrode active material layer,

5. The electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the end portion of the current collector is attached to an electrode sheet.

6. The electrode for a lithium ion secondary battery according to claim 5, wherein a distance C between the electrode tab and the first electrode active material layer is 3 to 8 mm.

7. The electrode for a lithium-ion secondary battery according to claim 5 or 6, wherein D/(C-B) is 1.5 or less, where D is the length of the protruding portion, B is the length of the end portion of the first insulating layer that protrudes from the first electrode active material layer, and C is the distance between the electrode tab and the first electrode active material layer.

8. The electrode for a lithium-ion secondary battery according to any one of claims 1 to 7, wherein the first electrode active material layer is a positive electrode active material layer.

9. The electrode for a lithium-ion secondary battery according to any one of claims 1 to 8, wherein the first insulating layer contains insulating fine particles and a binder for an insulating layer.

10. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of claims 1 to 9.

11. The lithium ion secondary battery according to claim 10, wherein the positive electrode and the negative electrode are alternately arranged and the lithium ion secondary battery is formed by arranging a plurality of layers, respectively,

12. A method for producing an electrode for a lithium ion secondary battery, comprising applying a first insulating layer coating solution to a first electrode active material layer of a collector sheet having the first electrode active material layer provided on one surface thereof to form a first insulating layer,

the liquid dragging length in the coating tip is 5mm or less.

13. The method for producing an electrode for a lithium-ion secondary battery according to claim 12, wherein the coating liquid for the insulating layer has a viscosity of 2000 to 4000 mPa-s at the time of coating.

14. The method for producing an electrode for a lithium-ion secondary battery according to claim 12 or 13, wherein,

15. The method for manufacturing an electrode for a lithium-ion secondary battery according to claim 14, wherein,

16. The method for producing an electrode for a lithium-ion secondary battery according to any one of claims 12 to 15, wherein a shear rate of the liquid contact portion with respect to the current collector when the first coating liquid for an insulating layer is applied is 0.5 x 10⁴～40×10⁴(1/s)。