JP6878702B2 - Electrodes for lithium-ion secondary batteries, their manufacturing methods, and lithium-ion secondary batteries - Google Patents

Description

The present invention relates to an electrode for a lithium ion secondary battery provided with an insulating layer, a method for manufacturing the electrode, and a lithium ion secondary battery.

Lithium-ion secondary batteries are used as large-scale stationary power sources for power storage, power sources for electric vehicles, etc., and in recent years, research on miniaturization and thinning of batteries has been progressing. A lithium ion secondary battery generally includes both electrodes having an electrode active material layer formed on the surface of a current collector such as a metal foil, and a separator arranged between the electrodes. The separator plays a role of preventing a short circuit between both electrodes and holding an electrolytic solution. Conventionally, it is known that the separator is oxidatively deteriorated on the contact surface with the electrode, and the deterioration tends to be remarkable especially on the positive electrode side.

Further, conventionally, in a lithium ion secondary battery, a porous insulating layer may be provided on the surface of the electrode active material layer (see, for example, Patent Document 1). The insulating layer is generally provided in order to secure the insulating property between the electrodes instead of the separator, or to have a good short-circuit suppressing function even when the separator shrinks in combination with the separator. Be done.
The insulating layer is formed by, for example, applying a slurry for an insulating layer containing insulating fine particles and a binder onto the electrode active material layer.

Patent No. 3253632

By the way, the current collector in which the electrode active material layer is formed on the surface has an end portion (also referred to as “uncoated end portion”) that is not covered by the electrode active material layer, and the uncoated end portion is grouped together to form an electrode tab. It is attached to. In such an uncoated end portion, an insulating layer formed on the electrode active material layer protrudes from the end portion of the electrode active material layer in order to prevent a short circuit to an adjacent electrode, and the uncoated end portion is formed. It is being studied to be formed so as to cover a part of the portion.

On the other hand, the insulating layer is often formed by intermittent coating, and at the end of the current collector described above, the coating start end, which is the start portion of the coating, and the coating end, which is the end portion of the coating. May become. However, the coating liquid for forming the insulating layer does not run out immediately at the end of the coating, which is the end of the coating, and the coating liquid is partially elongated in a slender shape. Liquidation may occur. When liquidation occurs, the end of the insulating layer will have a wavy contour in which a plurality of elongated protrusions are arranged side by side.

As described above, when the end of the insulating layer has a wavy shape, if the uncovered end of the current collector is shortened, the electrode tab will be overlapped on the convex portion made of the insulating material. , The strength of the electrode tab is reduced. On the other hand, if the uncoated end of the current collector is lengthened, the electrode tabs are prevented from overlapping with the insulating material, but the area of the electrode active material layer per current collector is reduced, and the energy density is reduced. The problem arises.

Therefore, an object of the present invention is to provide an electrode for a lithium ion secondary battery capable of improving the strength of an electrode tab without lowering the energy density.

As a result of diligent studies, the present inventors have adjusted the coating conditions of the insulating layer slurry appropriately so that the length of the liquid drainage (that is, the convex portion of the corrugated shape) is set to a predetermined value or less. We found that we could solve the problem, and completed the following invention. That is, the present invention provides the following [1] to [16].
[1] 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 are provided. ,
The current collector has an end that is not covered by the first electrode active material layer.
At the end of the current collector, the end of the first insulating layer protrudes from the first electrode active material layer and covers a part of the end of the current collector. Moreover, it has a wavy shape in which a plurality of elongated convex parts are arranged side by side.
An electrode for a lithium ion secondary battery in which the length D of the convex portion is 5 mm or less.
[2] The length A of the portion of the current collector that is not covered by any of the first electrode active material layer and the first insulating layer including the convex portion is 3 to 10 mm. The electrode for a lithium ion secondary battery according to the above [1].
[3] The lithium ion secondary battery according to the above [1] or [2], wherein the length B of the end portion of the first insulating layer protruding from the first electrode active material layer is 1 to 5 mm. Electrode for.
[4] A second electrode active material layer provided on the other surface of the current collector and a second insulating layer provided on the second electrode active material layer are further provided.
At the end of the current collector, the end of the second insulating layer protrudes from the second electrode active material layer and covers a part of the end of the current collector on the other surface. The electrode for a lithium ion secondary battery according to any one of the above [1] to [3], wherein the edge thereof is formed substantially linearly.
[5] The electrode for a lithium ion secondary battery according to any one of the above [1] to [4], wherein the end portion of the current collector is attached to an electrode tab.
[6] The electrode for a lithium ion secondary battery according to the above [5], wherein the distance C between the electrode tab and the first electrode active material layer is 3 to 8 mm.
[7] The length of the convex portion is D, the length of the end portion of the first insulating layer protruding from the first electrode active material layer is B, the electrode tab and the first electrode active material layer. The electrode for a lithium ion secondary battery according to the above [5] or [6], wherein D / (CB) is 1.5 or less, where C is defined as.
[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 the lithium ion secondary battery according to any one of the above [1] to [9].
[11] A lithium ion secondary battery in which a positive electrode and a negative electrode are alternately arranged so that a plurality of layers are provided.
At least one electrode of the positive electrode or the negative electrode is composed of the electrode for a lithium ion secondary battery, and the end portion of the current collector of the one electrode constituting each layer is put together. The lithium ion secondary battery according to the above [10], which is connected to the electrode tab.
[12] A coating liquid for a first insulating layer is applied onto the first electrode active material layer of the current collector sheet provided with the first electrode active material layer on one surface. , A method for manufacturing an electrode for a lithium ion secondary battery that forms a first insulating layer.
The current collector sheet has an uncoated portion that is not covered by the first electrode active material layer.
The coating of the coating liquid for the first insulating layer is performed so as to be the coating end at the uncoated portion of the current collector sheet.
The end portion of the first insulating layer made of the coating end protrudes from the first electrode active material layer on the one surface and covers a part of the uncoated portion of the current collector sheet. Formed like
A method for manufacturing an electrode for a lithium ion secondary battery, wherein the liquid drawing length at the end of coating is 5 mm or less.
[13] The method for manufacturing an electrode for a lithium ion secondary battery according to the above [12], wherein the viscosity of the coating liquid for the insulating layer at the time of coating is 2000 to 4000 mPa · s.
[14] Coating for a second insulating layer on the 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. Apply the liquid to form a second insulating layer,
The uncoated 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.
The coating of the coating liquid for the second insulating layer is performed so as to be the coating starting end at the position of the coating end of the uncoated portion of the current collector sheet.
The end portion of the second insulating layer made of the coating start end protrudes from the second electrode active material layer on the other surface and covers a part of the uncoated portion of the current collector sheet. The method for manufacturing an electrode for a lithium ion secondary battery according to the above [12] or [13], which is formed as described above.
[15] While feeding the current collector sheet, one of the first and second insulating layer coating liquids is applied onto the surface of the one or the other, and the first and second insulating layers are coated. Form one, wind it up in a roll,
While feeding out the current collector sheet wound up in a roll shape, the other of the first and second insulating layer coating liquids is applied onto the one or the other surface, and the first and second coating liquids are applied. The method for manufacturing an electrode for a lithium ion secondary battery according to the above [14], which forms the other side of the insulating layer of 2.
[16] The shear rate of the wetted portion with the current collector when the first coating liquid for the insulating layer is applied is 0.5 × 10 ⁴ to 40 × 10 ⁴ (1 / s). The method for manufacturing an electrode for a lithium ion secondary battery according to any one of the above [12] to [15].

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

It is the schematic sectional drawing which shows the electrode for the lithium ion secondary battery which concerns on 1st Embodiment. It is a top view which shows one surface of the electrode for a lithium ion secondary battery which concerns on 1st Embodiment. It is a top view which shows the other surface of the electrode for a lithium ion secondary battery which concerns on 1st Embodiment. It is the schematic sectional drawing which shows the electrode for the lithium ion secondary battery which concerns on 2nd Embodiment. It is a top view which shows the process of manufacturing the electrode for a lithium ion secondary battery which concerns on 1st Embodiment. It is a schematic cross-sectional view which shows the process of manufacturing the electrode for a lithium ion secondary battery which concerns on 1st Embodiment.

[Electrodes for lithium-ion secondary batteries]
<First Embodiment>
Hereinafter, the electrode for a lithium ion secondary battery of the present invention will be described in detail.
FIGS. 1 to 3 show an electrode 10 for a lithium ion secondary battery according to the first embodiment of the present invention.
As shown in FIGS. 1 and 2, the electrode for a lithium ion secondary battery (hereinafter, may be simply referred to as “electrode”) 10 of the first embodiment is one of a current collector 11 and a current collector 11. A first electrode active material layer 12 provided on the surface 11X and a first insulating layer 13 provided on the first electrode active material layer 12 are provided. Further, as shown in FIGS. 1 and 3, the lithium ion secondary battery electrode 10 further includes a second electrode active material layer 22 provided on the other surface 11Y of the current collector 11 and a second electrode. A second insulating layer 23 provided on the active material layer 22 is further provided.
Hereinafter, the lithium ion secondary battery electrode 10 according to the first embodiment will be described in detail.

(First electrode active material layer and first insulating layer)
The first electrode active material layer 12 is formed on one surface 11X so as not to cover one end 11Z of the current collector 11. Therefore, one surface 11X of one end portion 11Z of the current collector 11 becomes an end portion (hereinafter, also referred to as “uncovered end portion 11A”) in which the first electrode active material layer 12 is not covered.
The first insulating layer 13 is provided on the first electrode active material layer 12, and at the uncoated end portion 11A, the end portion protrudes from the edge portion 12B of the first electrode active material layer 12. It is formed. The protruding end portion (hereinafter, also referred to as “protruding end portion 13A”) covers the surface of the uncovered end portion 11A of the current collector 11.

The protruding end portion 13A covers a part of the uncovered end portion 11A and does not cover the region on the tip end side (that is, the edge portion 11B side of the current collector 11) of the uncovered end portion 11A. In the following description, the region not covered by the protruding end portion 13A (first insulating layer 13) on the tip end side of the uncoated end portion 11A may be described as the uncoated tip portion 11C.

As shown in FIGS. 2 and 3, the one end portion 11Z of the current collector 11 is attached to the electrode tab 15. The electrode tab 15 is arranged so as to be overlapped with the uncoated tip portion 11C of the current collector 11. In the lithium ion secondary battery, the electrodes 10 are preferably configured by stacking a plurality of layers, and in that case, a plurality of one end portions 11Z of the current collector 11 are also stacked and attached to the electrode tab 15. When a plurality of one end portions 11Z are overlapped, it is preferable that the uncoated tip portion 11C is overlapped with the uncoated tip portion 11C of another electrode and joined by fusion or the like, and then the electrode tab 15 is attached.

In the uncoated end portion 11A, the protruding end portion 13A of the first insulating layer 13 has a corrugated shape in which a plurality of elongated convex portions 13X are arranged in parallel when viewed in a plan view as shown in FIG. There is. Specifically, the protruding end portion 13A has a baseline 13B constituting the edge portion of the first insulating layer 13, and each convex portion 13X is a current collector so as to project from the baseline 13B. It extends toward the edge 11B of 11. Here, each convex portion 13X has an elongated shape, and its length d is sufficiently large (for example, three times or more) with respect to the width of each convex portion 13X, and such an elongated convex portion 13X is the base. By arranging a plurality of them along the line 13B, a wavy shape is formed.
The baseline 13B is substantially parallel to the end face 11B of the linearly formed current collector 11. In addition, substantially parallel means that when a straight line along the baseline 13B is drawn as described later, the straight line hardly tilts with respect to the edge portion 11B (for example, the tilt angle is less than 8 °, preferably less than 4 °). ) Means that.

The insulating layer of the lithium ion secondary battery electrode is usually formed by coating a slurry, but the slurry has a constant viscosity. Therefore, at the end of coating, which is the end of coating of the coating liquid, the coating liquid may be partially extended without running out, that is, so-called dripping may occur. As will be described later, the protruding end portion 13A of the first insulating layer 13 is a coating end, and therefore, liquidation inevitably occurs, and a plurality of convex portions 13X are formed as described above to form a corrugated shape. It becomes.

(Length of convex part)
In the present invention, the length D of the convex portion 13X is 5 mm or less. Since the length D is 5 mm or less, even if the length of the uncoated end portion 11A on one surface 11X is shortened, the tip side of the convex portion 13X is not covered with the insulating layer 13 and has a certain size. Is secured. Therefore, even if the electrode tab 15 is attached to the uncoated tip portion 11C, the electrode tab 15 is hardly overlapped on the convex portion 13X, and the strength of the electrode tab 15 is improved. When the strength of the electrode tab 15 is improved, the durability of the electrode is increased, the current collection is improved, and the capacity is increased.
On the other hand, when the length D is larger than 5 mm, the electrode tabs 15 are overlapped on many convex portions 13X, and the strength of the electrode tabs 15 decreases. Further, if the area of the convex portion 13X on which the electrode tabs 15 are overlapped is reduced, the length of the uncoated end portion 11A on one surface 11X becomes large, 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 above-mentioned length D, the length A described later, and the length B, and may be referred to as a length (A + B + D).

The length D of the convex portion 13X is preferably 3 mm or less. When it is 3 mm or less, the length (A + B + D) of the uncoated end portion 11A on one surface 11X can be further shortened, and the energy density of the lithium ion secondary battery can be easily improved. Further, the electrode tab 15 is less likely to be overlapped on the convex portion 13X, and the strength of the tab of the electrode 15 is more likely to be improved. The length D should be as short as possible, but as described above, it is inevitably formed at the time of coating, and has a length of, for example, about 0.5 mm or more.
As the length D of the convex portion 13X, as will be described later, the average value of the lengths d of all the plurality of convex portions 13X provided on the one end portion 11Z of the current collector 11 is defined as the length D. The length d is the shortest distance between the tip of the convex portion 13X and the baseline 13B, and corresponds to the height of the convex portion 13X. Further, those having a length / width of 3 or more are defined as convex portions.

(Lengths A, B, distance C)
The length B of the protruding end portion 13A of the first insulating layer 13 is preferably 1 to 5 mm. When the length B is 1 mm or more, safety can be easily ensured. On the other hand, by setting it to 5 mm or less, it is possible to prevent the protruding end portion 13A from becoming longer than necessary, and it becomes easy to secure a certain amount or more of the length A of the uncoated tip portion 11C on one surface 11X. Further, when the thickness is 5 mm or less, the area of the first electrode active material layer 12 on the current collector 11 is prevented from becoming small, and the energy density is prevented from decreasing.
From the above viewpoint, the length B is more preferably 2 to 4 mm. The details of the measurement method are as described in Examples.

In the present invention, the length A of the uncoated end portion 11A that is not covered by any of the first electrode active material layer 12 and the first insulating layer 11 including the convex portion 13X is 3 to 10 mm. preferable. Here, the length A is the length obtained by subtracting the total length of the length B and the length D from the length of the uncovered end portion 11A of the current collector 11. By setting the length A to 3 mm or more, the electrode tab 15 is less likely to be overlapped on the convex portion 13X, and the strength of the electrode tab is improved.
On the other hand, by setting the length A to 10 mm or less, the length of the protruding end portion 13A of the first insulating layer 13 can be secured by a certain amount without significantly reducing the energy density, and the safety is improved. Further, by setting the thickness to 10 mm or less, it is possible to prevent the area of the first electrode active material layer 12 on the current collector 11 from becoming small, and to prevent a decrease in energy density. From the above viewpoint, the length A is more preferably 5 to 8 mm.

As described above, the length of the uncoated end portion 11A is the total length (A + B + D) of the lengths A, B, and D. The length (A + B + D) of the uncoated end portion 11A is preferably 4 to 14 mm, more preferably 8 to 13 mm, still more preferably 9 to 12 mm. By setting the length to these upper limit values or less, it is possible to prevent the area of the first electrode active material layer 12 on the current collector 11 from becoming small, and to prevent a decrease in energy density. Further, when these lower limit values or more are set, the electrode tab 15 is less likely to be overlapped on the convex portion 13X, and the strength of the electrode tab 15 is improved.

The distance C between the electrode tab 15 attached to the end portion 11A of the current collector 11 and the first electrode active material layer 12 is preferably 3 to 8 mm. When the distance C is 3 mm or more, the electrode tab 15 is less likely to be overlapped on the convex portion 13X, and the strength of the electrode tab is improved. On the other hand, when the distance C is 8 mm or less, the area of the first electrode active material layer 12 formed on the current collector 11 becomes large, and the energy density tends to be high. From the above viewpoint, the distance C is more preferably 4 to 7 mm.
The details of the methods for measuring the lengths 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 (that is, the base line 13B) of the first insulating layer 13 and the electrode tab 15 represented by D / (CB) is , 1.5 or less is preferable. When D / (CB) is 1.5 or less, the electrode tab 15 is less likely to be overlapped on the convex portion 13X, and the strength of the electrode tab 15 is improved.
From the viewpoint of improving the strength of the electrode tab 15, the D / (CB) is more preferably 1.4 or less, still more preferably less than 1, and even more preferably 0.8 or less. If it is less than 1, the electrode tabs 15 are less likely to overlap due to the convex portion 13X.
The lower the D / (CB), the lower the better, but for example, it is 0.1 or more, and practically 0.3 or more.

Further, in the present invention, the length ratio represented by A / (A + B) is preferably 0.2 to 0.9. By setting this length ratio to 0.2 or more, it is possible to sufficiently secure a region where the convex portion 13X is not provided on the uncoated tip portion 11C, and it is possible to sufficiently secure the strength of the electrode tab 15. Further, by setting the value to 0.9 or less, the length of the protruding end portion 13A of the first insulating layer 13 can be sufficiently secured, and the safety is improved. From these viewpoints, A / (A + B) is more preferably 0.5 to 0.8.
Further, the length ratio represented by B / (A + B + D) is preferably 0.1 to 0.4, more preferably 0.2 to 0.4. Within these ranges, the area of the electrode active material layer 12 can be increased while sufficiently ensuring the 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 current collector 11, and the second electrode active material layer 22 is further placed on the second electrode active material layer 22. Insulation layer 23 is provided. The second electrode active material layer 22 is formed so as not to cover one end 11Z of the current collector 11, and the other surface 11Y of the one end 11Z of the current collector 11 is an electrode like the one surface 11X. The edges are not covered by the active material layer. That is, in the current collector 11, both surfaces 11X and 11Y of one end portion 11Z become uncovered end portions 11A. It should be noted that the regions of the uncoated end portions 11A do not have to completely coincide with each other on both surfaces 11X and 11Y, and therefore, the edge portion 12B of the first electrode active material layer 12 and the second electrode active material layer 22 The position of the edge portion 22B may be appropriately displaced.

In the uncoated end portion 11A, the end portion of the second insulating layer 23 is formed so as to protrude from the second electrode active material layer 22, and the end portion thereof (hereinafter, also referred to as “protruding end portion 23A”). Covers a part of the uncovered end 11A of the current collector 11. The region on the tip end side (that is, the edge portion 11B side of the current collector 11) with respect to the protruding end portion 23A is a region that is not covered by the second insulating layer 23. That is, the current collector 11 has, on both surfaces 11X and 11Y, the uncoated tip portion 11C in which the electrode active material layer and the insulating layer are not coated on the tip side of the protruding end portions 13A and 23A. It should be noted that the regions of the uncoated tip portion 11C do not have to completely coincide with each other on both surfaces 11X and 11Y, and therefore, the positions of the baseline 13B (that is, the edge portion of the first insulating layer 13) and the edge portion 23B. May be appropriately deviated.

In the uncoated end portion 21A, the edge portion 23B of the protruding end portion 23A of the second insulating layer 23 is formed substantially linearly when viewed in a plan view as shown in FIG. Here, the substantially straight line means that when a straight line is drawn along the edge portion 23B, there is no unevenness that deviates from the straight line, or even if there is unevenness, there are some fine irregularities, which are provided on one surface 11X. A plurality of elongated convex portions are not provided as in the protruding end portion 13A. Further, the edge portion 23B is substantially parallel to the edge portion 11B of the current collector 11. Approximately parallel means that when a straight line along the edge 23B is drawn, the straight line hardly tilts with respect to the edge 11B of the current collector 11 (for example, the tilt angle is less than 8 °, preferably 4 °). Less than) means.

The insulating layer of the lithium ion secondary battery electrode is usually formed by coating a slurry having a constant viscosity, but unlike the coating end, liquidation does not occur at the coating end. As will be described later, the protruding end portion 23A of the second insulating layer 23 becomes the coating start end, so that liquidation does not occur, and the edge portion 23B becomes substantially linear as described above.
That is, in the present embodiment, one end portion 11Z of the current collector 11 has one surface 11X side as the coating end of the first insulating layer 13 and the other surface side as the coating starting end of the second insulating layer 23. .. According to such an aspect, as described later, it is sufficient to apply the coating liquid for the insulating layer on both surfaces without rewinding, so that the insulating layers are formed on both sides of the current collector 11 by a simple method. become able to.

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

In the present embodiment, the lithium ion secondary battery electrode 10 described above preferably constitutes a positive electrode. Therefore, the current collector 11 becomes a positive electrode current collector, and the first and second electrode active material layers 12 and 22 become positive electrode active material layers.
Since the positive electrode generally has a smaller area than the negative electrode, the end portion of the positive electrode (that is, one end portion 11Z) overlaps with the negative electrode, and a short circuit is likely to occur. Therefore, at such an end, the first and second insulating layers 13 and 23 are formed so as to protrude from the first and second electrode active material layers 12 and 22, as shown in FIGS. Therefore, a short circuit can be effectively prevented.
However, the electrode 10 for the lithium ion secondary battery may form a negative electrode. In this case, the current collector 11 is a negative electrode current collector, and the first and second electrode active material layers 12 and 22 are negative electrode active material layers.

Next, the materials constituting each member will be described in detail.
(Current collector)
When the electrode is a positive electrode, the current collector 11 becomes a positive electrode current collector. Examples of the material constituting the positive electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and aluminum is more preferable.
On the other hand, if the electrode is a negative electrode, the current collector 11 becomes a negative electrode current collector. The material to be the negative electrode current collector is the same as the compound used for the positive electrode current collector, but aluminum or copper is preferably used, and copper is more preferable.

The first and second electrode active material layers 12 and 22 contain an electrode active material and an electrode binder, respectively. When the electrode 10 is a positive electrode, the electrode active material becomes a positive electrode active material, and the first and second electrode active material layers 12 and 22 both serve as a positive electrode active material layer. 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 the negative electrode active material, and the first and second electrode active material layers 12 and 22 are both negative electrode active material layers. The negative electrode active material layer may or may not contain a conductive auxiliary agent.

(Electrode active material)
Examples of the positive electrode active material used for the positive electrode active material layer include a lithium metallic acid compound. Examples of the lithium metal acid compound include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and the like. Further, it may be olivine type lithium iron phosphate (LiFePO ₄ ) or the like. Further, a plurality of metals other than lithium may be used, and an NCM (nickel cobalt manganese) oxide, an NCA (nickel cobalt aluminum) oxide, or the like, which is called a ternary system, may be used. Among these, NCA-based oxides are 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 for the negative electrode active material layer include carbon materials such as graphite and hard carbon, composites of tin compounds, silicon and carbon, and lithium. Among these, carbon materials are preferable, and graphite is preferable. More preferred. 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 and second electrode active material layers 12 and 22 is preferably 50 to 99% by mass, more preferably 70 to 98% by mass, based on the total amount of the electrode active material layer.

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

(Conductive aid)
As the conductive auxiliary agent used in each of the first and second electrode active material layers 12 and 22, for example, a material having a higher conductivity than the above-mentioned electrode active material is used, and specifically, Ketjen black and acetylene black. Examples thereof include carbon black, carbon nanotubes, carbon nanohorns, graphene, and carbonaceous materials such as fullerenes. The conductive auxiliary agent may be used alone or in combination of two or more.
The content of the conductive auxiliary agent in the electrode active material layer is preferably 1 to 15% by mass, more preferably 2 to 10% by mass, based on the total amount of the electrode active material layer. By setting the content of the conductive auxiliary agent within these ranges, the conductivity of the electrode active material layer can be appropriately improved.

(Binder for electrodes)
Each of the first and second electrode active material layers 12 and 22 is configured by binding the electrode active material and the conductive auxiliary agent with an electrode binder. Specific examples of the binder for the electrode include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), fluorine-containing resin such as polytetrafluoroethylene (PTFE), and polymethyl acrylate (PMA). ), Acrylic resin such as polyvinylidene methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinylidene 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, polyvinyl alcohol and the like. These binders may be used alone or in combination of two or more. Further, carboxymethyl cellulose and the like may be used in the form of a salt such as a sodium salt.

The content of the electrode binder in each of the first and second electrode active material layers 12 and 22 is preferably 1 to 40% by mass, more preferably 2 to 20% by mass, based on the total amount of the electrode active material layers. .. By setting the content of the electrode binder to these lower limit values or more, the electrode active material and the conductive auxiliary agent are appropriately retained by the binder. Further, by setting the value to the upper limit or less, the electrode active material, or the electrode active material and the conductive auxiliary agent can be contained in the electrode active material layer in a certain amount or more.

Each of the first and second electrode active material layers 12 and 22 may contain an optional component other than the electrode active material, the conductive auxiliary agent, and the binder for the electrode, as long as the effects of the present invention are not impaired. However, the total content of the electrode active material, the conductive auxiliary agent, and the electrode binder in the total mass of the electrode active material layer is preferably 90% by mass or more, more preferably 95% by mass or more. , 100% by mass is more preferable.

Each of the first and second insulating layers 13 and 23 typically contains insulating fine particles and a binder for the insulating layer. Each of the first and second insulating layers 13 and 23 is a layer formed by binding insulating fine particles with a binder for an insulating layer, and has a porous structure.

(Insulating fine particles)
The insulating fine particles contained in each of the first and second insulating layers 13 and 23 are not particularly limited as long as they are insulating, and may be either organic particles or inorganic particles. Specific organic particles include, for example, crosslinked polymethyl methacrylate, crosslinked styrene-acrylic acid copolymer, crosslinked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamide-2-methylpropanesulfonate), and the like. Examples thereof include particles composed of organic compounds such as polyacetal resin, epoxy resin, polyester resin, phenol resin, and melamine resin. Inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), potassium fluoride, and foot. Examples thereof include particles composed of inorganic compounds such as lithium pentoxide, clay, zeolite, and calcium carbonate. Further, the inorganic particles may be particles composed of known composite oxides such as niobium-tantalum composite oxide and magnesium-tantalum composite oxide.
The insulating fine particles may be particles in which each of the above materials is used alone, or particles in which two or more of the above materials are used in combination. Further, the insulating fine particles may be fine particles containing both an inorganic compound and an organic compound. For example, it may be an inorganic-organic composite particle in which the surface of a particle made of an organic compound is coated with an inorganic oxide.
Among these, inorganic particles are preferable, alumina particles and boehmite particles are preferable, and alumina particles are more preferable.

The average particle size 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. is there. By setting the average particle size of the filler within these ranges, the porosity can be set within an appropriate range to easily prevent oxidative deterioration of the separator.
Further, as the insulating fine particles, one type having an average particle size within the above range may be used alone, or two types of insulating fine particles having different average particle sizes may be used in combination.

The content of the insulating fine particles contained in each of the first and second insulating layers 13 and 23 is preferably 30 to 96% by mass, more preferably 45 to 94% by mass, still more preferably, based on the total amount of the insulating layer components. Is 65 to 93% by mass. When the content of the insulating fine particles is within the above range, the first and second insulating layers 13 and 23 can each form a uniform porous structure, and it becomes easy to prevent a short circuit.

(Binder for insulating layer)
Specific examples of the binder for the insulating layer include compounds exemplified as compounds that can be used in the binder for electrodes. The binder used for the insulating layer may be used alone or in combination of two or more.

The content of the binder for the insulating layer contained in each of the first and second insulating layers 13 and 23 is preferably 4 to 60% by mass, more preferably 5 to 50% by mass, based on the total amount of the insulating layer components. It is preferably 6 to 35% by mass. Within the above range, a uniform porous structure can be formed in the insulating layer, and a short circuit can be easily prevented.
Each of the first and second insulating layers 13 and 23 may contain optional components other than the insulating fine particles and the binder for the insulating layer as long as the effects of the present invention are not impaired. However, of the total mass of each of the first and second insulating layers 13 and 23, the total content of the insulating fine particles and the binder for the insulating layer is preferably 85% by mass or more, preferably 90% by mass or more. Is more preferable.

<Second embodiment>
Next, the difference between the lithium ion secondary battery electrode according to the second embodiment of the present invention and the first embodiment will be described.
In the first embodiment, on both surfaces 11X and 11Y of the current collector 11, the first electrode active material layer 12 and the first insulating layer 13, and the second electrode active material layer 22 and the second Although the insulating layer 23 was provided, as shown in FIG. 4, in the electrode 30 for the lithium ion secondary battery according to the second embodiment, the second electrode active material provided on the other surface 11Y. The layer 22 and the second insulating layer 23 are omitted.
Also in the present embodiment, as in the first embodiment, the length D (see FIGS. 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. Therefore, the strength of the electrode tab can be improved without lowering the energy density.

The electrodes for lithium ion secondary batteries of the present invention are not limited to the electrodes 10 and 30 for lithium ion secondary batteries according to the first and second embodiments, and are various as long as the effects of the present invention are not impaired. Can be changed. For example, in the first embodiment, the edge portion 23B of the second insulating layer 23 is substantially linear, but is not limited to a linear shape, and is corrugated like the edge portion of the first insulating layer 13. It may be in shape. In this case, the configuration of the second insulating layer 23 formed on the other surface 10Y is as described in the first insulating layer 13 described above, and the details thereof will be omitted.
With such a configuration, as will be described later, the protruding ends 13A and 23A of the first and second insulating layers 13 and 23 are all coating ends. Further, on the surfaces 11X and 11Y, the energy density is lowered by setting the length D of the convex portions 13X of the first and second insulating layers 13 and 23 formed on the uncoated end portions 11A to a predetermined value or less. The strength of the electrode tab can also be improved without causing the problem.

[Manufacturing method of electrodes for lithium-ion secondary batteries]
Next, a method for manufacturing an electrode for a lithium ion secondary battery according to the first embodiment of the present invention will be described with reference to FIGS. 5 and 6. In the method for manufacturing an electrode for a lithium ion secondary battery according to the first embodiment of the present invention, as shown in FIG. 5, the first electrode active material layer 52 is placed on one surface 51X of the current collector sheet 51. Is formed, and the coating liquid for the first insulating layer is applied onto the first electrode active material layer 52 to form the first insulating layer 53.

(Formation of the first electrode active material layer)
In the formation of the first electrode active material layer 52, first, a coating liquid for the first electrode active material layer containing the electrode active material, the binder for the electrode, and the solvent is prepared. The coating liquid for the electrode active material layer may contain other components such as a conductive additive to be blended as needed. The electrode active material, the binder for the electrode, the conductive auxiliary agent, and the like are as described above. The coating liquid for the first electrode active material layer is a slurry.
Water or an organic solvent is used as the solvent in the coating liquid for the first electrode active material layer. Specific examples of the organic solvent include one or more selected from N-methylpyrrolidone, N-ethylpyrrolidone, dimethylacetamide, and dimethylformamide. Of these, N-methylpyrrolidone is particularly preferred.
The solid content concentration of the coating liquid for the first electrode active material layer is preferably 5 to 75% by mass, more preferably 20 to 65% by mass.

The first electrode active material layer 52 may be formed by a known method using the coating liquid for the first electrode active material layer. For example, the coating liquid for the first electrode active material layer may be collected. It can be formed by applying it on one surface 51X of the body sheet 51 and drying it.
Further, the first electrode active material layer 52 may be formed by applying a coating liquid for the first electrode active material layer on a base material other than the current collector sheet 51 and drying the first electrode active material layer 52. Examples of the base material other than the current collector sheet include known release sheets. The first electrode active material layer formed on the base material may be peeled off from the base material and transferred onto one surface 51X of the current collector sheet.
The first electrode active material layer 52 formed on the current collector sheet 51 is preferably pressure-pressed. By pressure pressing, it becomes possible to increase the electrode density. The pressure press may be performed by a roll press or the like.

The first electrode active material layer 52 is preferably applied onto the current collector sheet 51 by intermittent coating. By being applied by intermittent coating, as shown in FIG. 5, the current collector and other sheet 51 has a coating portion 51A coated on the first electrode active material layer 52 and a first coating portion 51A along the MD direction. The electrode active material layer 52 is alternately provided with uncoated portions 51B that are not coated. In FIG. 5, the region where the first electrode active material layer 52 is formed is indicated by a broken line.

(Formation of first insulating layer)
As described above, after the first electrode active material layer 52 is formed, the coating liquid for the first insulating layer is applied on the surface of the first electrode active material layer 52 to apply the first insulating layer 53. To form.
The coating liquid for the first insulating layer used for forming the first insulating layer 53 contains insulating fine particles, a binder for the insulating layer, and a solvent. Water or an organic solvent may be used as the solvent, and the details of the organic solvent are as described in the coating liquid for the electrode active material layer. The first coating liquid for the insulating layer is a slurry (slurry for the insulating layer).
The solid content concentration of the coating liquid for the first insulating layer is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. By adjusting the solid content concentration within these ranges, it becomes easy to adjust the viscosity to a desired range described later.

The first insulating layer 53 can be formed by applying the coating liquid for the first insulating layer to the surface of the first electrode active material layer 52 and then drying it. The method of applying the coating liquid for the first insulating layer to the surface of the first electrode active material layer 52 is not particularly limited, and may be performed by a known coating device, for example, a dip coating method or a spray coating method. , Roll coating method, doctor blade method, bar coating method, gravure coating method, screen printing method and the like. Among these, the gravure coating method is preferable from the viewpoint of uniformly applying the insulating layer.
The drying temperature is not particularly limited as long as the solvent can be removed, but is, for example, 50 to 130 ° C, preferably 60 to 100 ° C. The drying time is not particularly limited, but 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 feeding the current collector sheet 51. By feeding the current collector sheet 51 from left to right in FIG. 5, for example, the coating of the first insulating layer coating liquid is performed from right to left. The coating of the coating liquid for the first insulating layer is performed so that the first insulating layer 13 protrudes from both sides of the first electrode active material layer 52 (covered portion 51A), and the protruding first insulation The end portion (protruding portion 53A) of the layer 53 is formed so as to cover a part of the uncoated portion 51B. That is, the coating start end 55, which is the start portion of coating for forming each first insulating layer 53, and the coating end 54, which is the end portion of coating, are arranged on the uncoated portion 51B. It will be. The region where the first insulating layer 53 is formed is shown by a solid diagonal line in FIG.

At the end of the coating 54, the coating liquid is inevitably stretched in an elongated manner without immediately running out of liquid, so-called drainage. When liquidation occurs, the coating end 54 (the end of the first insulating layer 52) has a wavy contour in which a plurality of elongated convex portions 13X are arranged side by side, as shown in FIG. ..
In the present manufacturing method, by shortening the unavoidably generated liquid draining length (that is, the length of the convex portion 13X), the strength of the electrode tab 15 is lowered without lowering the energy density as described above. To prevent that. As described above, the specific liquiding length is 5 mm or less, preferably 3 mm or less. Further, the draining length is, for example, about 0.5 mm or more.

In the present manufacturing method, as a method of shortening the liquid drawing length, there is a method of adjusting the viscosity of the coating liquid for the first insulating layer and the shear rate at the time of applying the coating liquid for the first insulating layer.
The viscosity of the coating liquid for the first insulating layer is preferably 2000 to 4000 mPa · s, more preferably 2500 to 3500 mPa · s. By setting the viscosity to these upper limit values or less, it is possible to suppress the long liquidation, and to suppress the decrease in the strength of the electrode tab and the decrease in the energy density. Further, by setting the viscosity to be equal to or higher than these lower limit values, it is possible to suppress an increase in thickness unevenness of the insulating layer and suppress a decrease in safety. The viscosity is a viscosity measured with a B-type viscometer at 60 rpm under the temperature conditions at the time of coating.

Further, the shear rate of the wetted portion with the current collector sheet at the time of coating the first insulating layer composition is preferably 0.5 × 10 ⁴ to 40 × 10 ⁴ (1 / s). It is more preferably 0.7 × 10 ^{4 to} 20 × 10 ⁴ (1 / s), and even more preferably 1.0 × 10 ⁴ to 10 × 10 ⁴ (1 / s). The shear rate can be adjusted by the transport speed of the current collector sheet 51 and the liquid level distance from the current collector sheet 51 of the wetted part. Further, the shear rate at the time of coating can be calculated by, for example, the following formula. By setting the shear rate to the above upper limit value or less, it is possible to suppress the long liquidation, and to suppress the decrease in the strength of the tab and the decrease in the energy density. Further, when the shear rate is set to be equal to or higher than these lower limit values, the productivity is increased.
The wetted portion is a portion that comes into contact with the coating liquid applied to the current collector sheet of the coating device, and in the gravure coat, the current collector sheet 51 of the gravure roll 60 shown in FIG. 6 is the most. It means the tip portion 60A that is close to each other, and the liquid level distance is the liquid thickness of the coating liquid to be applied at the wetted portion (tip portion 60A), and when a groove is provided on the surface of the roll 60. , The groove depth.
(Shear velocity (1 / s)) = (Transport rate m / sec) ÷ (Liquid level distance m)

(Formation of a second electrode active material layer and a second insulating layer)
In the present manufacturing method, after forming the first insulating layer 53 on one surface 51X of the current collector sheet 51 as described above, the second insulating layer 63 is formed on the other surface 51Y as shown in FIG. Form.
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 formation of the second electrode active material layer 62 may be performed before the formation of the first insulating layer 53, or may be performed after the formation of the first insulating layer 53.
In the present manufacturing method, the current collecting sheet 51 in which the first and second insulating layers 53 and 63 are formed on both surfaces 51X and 51Y is divided by being cut along the alternate long and short dash line shown in FIG. It becomes the electrode 10.

The second electrode active material layer 62 and the second insulating layer 63 may be formed by the coating liquid for the second electrode active material layer and the coating liquid for the second insulating layer, respectively. The 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 points mentioned below.
The details of the coating liquid for the second electrode active material layer and the coating liquid for the second insulating layer are as described above for the coating liquid for the first electrode active material layer and the coating liquid for the first insulating layer, respectively. The description is as described for the liquid, and the description thereof will be omitted. Therefore, the viscosity of the coating liquid for the second insulating layer and the shear rate at the time of coating are also as described above.
However, the coating liquid for the second electrode active material layer and the coating liquid for the second insulating layer used when manufacturing each electrode are the coating liquid for the first electrode active material layer and the first coating liquid, respectively. It may be the same as or different from the composition of the coating liquid for the insulating layer of 1.

The second electrode active material layer 62 is preferably subjected to intermittent coating, and similarly to the first electrode active material layer 52, as shown in FIG. 6, the other surface 51Y of the current collector sheet 51 is in the MD direction. Along the above, 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.
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 above-mentioned covering portion 51A is a portion where the electrode active material layer is coated on both surfaces 51X and 51Y. Further, the uncoated portion 51B is a portion where the electrode active material layer is not coated on both surfaces 51X and 51Y. However, the portions where the electrode active material layers are coated on both surfaces 51X and 51Y do not have to be completely coincident, and may be appropriately displaced within a range that does not impair the effects of the present invention.

Further, after the first insulating layer 53 is formed by applying the coating liquid for the first insulating layer to one surface 51X of the current collector sheet 51, the current collector sheet may be wound into a roll. .. Then, the current collector sheet 51 wound up in a roll shape is unwound as it is and sent to the coating device, and as shown in FIG. 6, the other surface 51Y is coated with the coating liquid for the second insulating layer. It is advisable to form the second insulating layer 63 by working and then appropriately drying. Note that FIG. 6 shows a mode in which the coating device is a gravure coater and the coating liquid is supplied by the gravure roll 60, but coating may be performed by another coating device.

The end portion of the second insulating layer 63 constituting the coating start end 55 protrudes from the second electrode active material layer 62 on the other surface 51Y and partially covers the uncovered portion 51B of the current collector sheet. Is formed as follows. Similarly, the end portion of the second insulating layer 63 constituting the coating end 54 protrudes from the second electrode active material layer 62 on the other surface 51Y and partially covers the uncovered portion 51B of the current collector sheet 51. It is formed so as to cover the surface.

Further, in the present embodiment, as described above, the current collector sheet 51 wound in a roll shape is unwound as it is, and the coating liquid for the second insulating layer is applied to the other surface 51Y. The position where the coating end 54 was on the uncoated portion 51 of the surface 51X of the surface 51X becomes the coating start end 55 on the other surface 51Y. Further, the position where the coating start end 55 is on the uncoated portion 51 of one surface 51X becomes the coating end 54 on the other surface 51Y.
As a result, in the present manufacturing method, when the current collector sheet 51 is cut to form each electrode 10, one end portion 11Z of the current collector 11 has one surface 11X side as the coating end of the first insulating layer 53. The other surface side serves as the coating start end of the second insulating layer 23 (see FIG. 1).

Further, since the current collector sheet 51 wound in a roll shape need only be unwound as it is without being rewound, the process can be simplified. Further, even if the coating end and the coating start end are provided on both sides of one end 11Z of the current collector 11 without rewinding, the liquid drawing length at the coating end is short as described above. Therefore, even if the electrode tab 15 is attached in consideration of the liquid drainage, the electrode tab 15 and the second electrode active material layer are unnecessarily on the other surface 11Y side of the current collector 11 where the liquid drainage is not formed. There is no need to separate the 23.

In the above description, the electrode active material layer and the insulating layer formed on one surface 51X of the current collector sheet 51 are designated as the first electrode active material layer 52 and the first insulating layer 53, and the current collector is used. The electrode active material layer and the insulating layer formed on the other surface 51Y of the sheet 51 have been described as the second electrode active material layer 62 and the second insulating layer 63 for convenience. However, when the electrode 10 is produced by cutting as described above, the first electrode active material layer 52 and the first insulating layer 53 become the second electrode active material layer 22 and the second insulating layer in the electrode 10. It may be a layer 23, or the second electrode active material layer 62 and the second insulating layer 63 may be the first electrode active material layer 12 and the first insulating layer 13 in the electrode 10. is there.
In other words, after the insulating layer to be the second insulating layer 23 on the electrode 10 is coated as the first insulating layer 53, the insulating layer to be the first insulating layer 13 on the electrode 10 is the second insulating layer. It may be coated as layer 63.

Further, the above description shows a 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. By omitting the formation of the second electrode active material layer and the formation of the second insulating layer, the electrode 30 of the second embodiment shown in FIG. 4 can be manufactured.

Further, in the above manufacturing method, the second insulating layer 62 is formed on the other surface 51Y without rewinding, but the second insulating layer may be formed by rewinding. That is, the first insulating layer 53 is formed on one surface 51X, and the current collector sheet 51 wound in a roll shape is unwound, then wound in a roll shape again, and then unwound from the roll for coating. It is preferable to send it to an apparatus and apply a coating liquid for a second insulating layer on the other surface 51Y.
When rewinding is performed, the position where the coating end is on the uncoated portion 51 of one surface 51X becomes the coating end on the other surface 51Y. Further, the position where the coating start end is on the uncoated portion 51 of one surface 51X becomes the coating start end on the other surface 51Y. Therefore, at one end 11Z of the electrode 11, the first and second insulating layers 13 and 23 on both surfaces 11X and 11Y are both coated ends (corrugated edges shown in FIG. 2) or coated. It constitutes the start end (the linear edge shown in FIG. 3). Therefore, as described above, in addition to the first insulating layer 13, an electrode in which the second insulating layer 23 has a wavy shape can be obtained.

<Lithium-ion secondary battery>
The lithium ion secondary battery of the present invention has the above-described electrode for the lithium ion secondary battery of the present invention. Specifically, the lithium ion secondary battery of the present invention includes a positive electrode and a negative electrode arranged so as to face each other, and at least one electrode of the negative electrode and the positive electrode is the above-mentioned lithium ion secondary battery of the present invention. It becomes an electrode for use. Further, the positive electrode is preferably the electrode for the lithium ion secondary battery of the present invention described above, but both the positive electrode and the negative electrode may be the electrode for the lithium ion secondary battery of the present invention.

The lithium ion secondary battery of the present invention preferably further includes a separator arranged between the positive electrode and the negative electrode. By providing the separator, a short circuit between the positive electrode and the negative electrode is more effectively prevented. In addition, the separator may retain an electrolyte, which will be described later. The first insulating layer or the first and second insulating layers provided on the positive electrode or the negative electrode may or may not be in contact with the separator, but are preferably in contact with each other.
Examples of the separator include a porous polymer film, a non-woven fabric, and a glass fiber, and among these, a porous polymer film is preferable. Examples of the porous polymer film include an olefin-based porous film. The separator may be heated by heat generated when the lithium ion secondary battery is driven and may undergo heat shrinkage. Even during such heat shrinkage, the above-mentioned insulating layer makes it easier to suppress a short circuit.
Further, in the lithium ion secondary battery of the present invention, the separator may be omitted. Even if the separator is omitted, it is preferable that the insulating layer provided on at least one of the negative electrode and the positive electrode ensures the insulating property between the negative electrode and the positive electrode.

The lithium ion secondary battery preferably has a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are laminated. In this case, the negative electrode and the positive electrode may be provided alternately along the stacking direction. When a separator is used, the separator may be arranged between each negative electrode and each positive electrode.
Even in the case of a multi-layer structure, it is preferable that each positive electrode is the electrode for the lithium ion secondary battery of the present invention described above, and in this case, the electrode for the lithium ion secondary battery is as shown in the first embodiment. In addition, it is preferable that the electrode 10 is provided with an insulating layer (that is, first and second insulating layers) on both surfaces (see FIG. 1). Then, as described above, it is preferable that the electrode tab 15 is attached after the uncoated tip portion 11C of the one end portion 11Z of each electrode 10 is put together.

Further, in the case of a multilayer structure, each negative electrode may be the above-mentioned electrode for the lithium ion secondary battery of the present invention. At that time, as shown in the first embodiment, the electrode for the lithium ion secondary battery is preferably an electrode 10 in which an insulating layer (that is, a first and second insulating layer) is provided on both surfaces. Further, the uncoated tip portion 11C of one end portion 11Z of each electrode 10 may be collectively attached to the electrode tab 15 for the negative electrode (see FIG. 1). Of course, both the positive electrode and the negative electrode may be composed of the above-described electrodes for the lithium ion secondary battery of the present invention.

In the lithium ion secondary battery, the above-mentioned negative electrode and positive electrode, or the negative electrode, positive electrode, and separator may be housed in the casing with electrode tabs attached as described above. The battery cell may be a square type, a cylindrical type, a laminated type, or the like. Therefore, the casing is not particularly limited, but may be an outer can or the like, or may be an outer film. As the exterior film, it is preferable that the negative electrode and the positive electrode, or the negative electrode, the positive electrode and the separator are arranged between the two exterior films or one exterior film is folded in half and the negative electrode and the positive electrode are arranged between the exterior films.

The above-mentioned 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 is used.
Examples of the electrolytic solution include an organic solvent and an electrolytic solution containing an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, and tetrohydra. Examples include polar solvents such as furan, 2-methyltetraethane, dioxolane, and methylacetamide, or mixtures of two or more of these solvents. Electrolyte salts include LiClO ₄ , LiPF ₆ , LiBF ₄ , _{LiAsF 6} , LiSbF ₆ , LiCF ₃ CO ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ). _{Examples include lithium-containing salts such as 2} and LiN (COCF ₂ CF ₃ ) ₂ , lithium bisoxalate boronate (LiB (C ₂ O ₄ ) ₂ ), and lithium organic acid salt-boron trifluoride complex, LiBH. _{Complexes such as 4 and the} like Complexes such as hydrides can be mentioned. These salts or complexes may be used alone or in admixture of two or more.
Further, the electrolyte may be a gel-like electrolyte in which the above-mentioned electrolytic solution further contains a polymer compound. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacrylic polymer such as methyl poly (meth) acrylate. The gel electrolyte may be used as a separator.
The electrolyte may be arranged between the negative electrode and the positive electrode. For example, the electrolyte is filled in the above-mentioned negative electrode and positive electrode, or in a casing in which the negative electrode, the positive electrode, and the separator are housed. Further, the electrolyte may be applied on the negative electrode or the positive electrode and arranged between the negative electrode and the positive electrode, for example.

The lithium ion secondary battery of the present invention may be manufactured using the electrodes for the lithium ion secondary battery obtained by the above manufacturing method. The lithium ion secondary battery may be manufactured, for example, by manufacturing an electrode for a lithium ion secondary battery, attaching an electrode tab to the end of a current collector of the electrode for the lithium ion secondary battery, and storing the electrode in a casing. ..
At this time, the negative electrode and the positive electrode, or the negative electrode, the positive electrode, and the separator may be housed in the casing, and at least one of the negative electrode and the positive electrode may be an electrode for a lithium ion secondary battery obtained by the above-mentioned manufacturing method. ..
When a plurality of layers of the positive electrode and the negative electrode are provided, it is preferable to arrange a separator between the positive electrode and the negative electrode as necessary, and then arrange the positive electrode and the negative electrode in which the plurality of layers are stacked in the casing. .. In this case, it is preferable that the electrode tabs are attached to the current collectors of the plurality of positive electrodes after the end portions (for example, the uncoated tip portion 11C) are joined by fusion or the like. Similarly, it is preferable that the electrode tabs are attached to the current collectors of the plurality of negative electrodes after the ends are joined by fusion or the like.

Hereinafter, the present invention will be described 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 electrode obtained in each Example and Comparative Example was prepared, and as shown in FIG. 2, a protruding end portion 13A of an insulating layer having a corrugated shape composed of a plurality of convex portions 13X was provided. The side surface was arranged so as to face the front side. Next, a straight line was drawn on the portion of the electrode active material layer 12 to be the edge portion 12B. The straight line is a straight line that is as close as possible to the edge portion 12B, and the same applies hereinafter when a straight line is drawn. Further, a straight line was drawn along the baseline 13B of the first insulating layer 13, the lengths between the straight lines were measured at three points, and the average value was taken as the length B of the protruding end portion 13A.
[Length D]
Next, the length d from the straight line drawn along the baseline 13B to the tip of each convex portion 13X is measured, and the length d of all the convex portions 13X formed on the uncoated tip portion 11C is measured. The average value was defined as the length D (pulling length) of the convex portion.
[Length A]
The straight line drawn along the edge 12B of the electrode active material layer 12 and the length to the edge 11B of the current collector 11 were determined. The length was measured at three points, and the average value was taken as the length from the edge portion 12B to the edge portion 11B. The length A was obtained by subtracting the length D and the length B from the length.
[Distance C]
In the electrode to which the electrode tab 15 is attached, when viewed in a plan view, the distances from the straight line drawn along the edge 12B of the electrode active material layer 12 to the end of the electrode tab are measured at three points and averaged. The value was defined as the distance C.

The evaluation method in this example is as follows.
[Tab strength]
Twenty-five positive electrodes obtained in each Example and Comparative Example were laminated, and an aluminum tab (model number "A1050-H24", size 30 mm x 50 mm x 0.5 mm) manufactured by Nets was welded under the following conditions.
(Welding conditions)
Welding was performed using "BRANSON" (2000Xea 2500W) manufactured by Emerson Japan, Ltd. so as to provide 180 welding points in an area of 20 mm × 4 mm by an ultrasonic welding method. The conditions were as follows.
Welding time: 0.4 seconds, pressure: 0.1 MPa, amplitude: 70%
After welding, the strength was measured by the following test.
A 180 ° peeling test was performed at a peeling speed of 10 mm / min using an autograph "EZ-LX series" manufactured by Shimadzu Corporation, and the maximum strength was defined as the tab strength.
Further, 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 was measured in the same manner to obtain a blank strength.
The tab strength was divided by the blank strength to obtain the tab strength retention rate, which was evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: 95% or more B: 90% or more and less than 95% C: 80% or more and less than 90% D: less than 80%

[Safety evaluation]
The lithium-ion secondary batteries produced in each of the Examples and Comparative Examples are charged with a constant current of 40 A, and then the current is reduced as soon as 4.2 V is reached, and the constant voltage charge is completed when the current reaches 2 A. It was. Then, the battery was heated to 130 ° C. After reaching 130 ° C., the battery was held for 1 hour, and the maximum temperature of the battery in that 1 hour was measured and evaluated according to the following evaluation criteria.
(Evaluation criteria)
A: Maximum temperature less than 135 ° C B: Maximum temperature 135 ° C or more and less than 145 ° C C: Maximum temperature 145 ° C or more and less than 200 ° C D: Maximum temperature 200 ° C or more

[Energy density]
The area ratio (%) of the electrode active material layer to the area of the current collector was calculated on the surface of the electrode provided with the insulating layer having a wavy shape. Since the energy density of the electrode increases as the area ratio of the electrode active material layer increases, the energy density was evaluated by the following evaluation criteria based on the above area ratio.
(Evaluation criteria)
A: Area ratio is 96% or more C: Area ratio is less than 96%

Example 1
(Preparation of positive electrode)
_{100 parts by mass of Li (Ni-Co-Al) O 2} (NCA-based oxide) having an average particle diameter of 10 μm as a positive electrode active material, 4 parts by mass of acetylene black as a conductive auxiliary agent, and vinylidene polyvinylfluoride as an electrode binder. 4 parts by mass of (PVdF) and N-methylpyrrolidone (NMP) as a solvent were mixed to obtain a coating liquid for a positive electrode active material layer adjusted to a solid content concentration of 60% by mass. This coating liquid for the positive electrode active material layer was intermittently applied to both sides of an aluminum foil having a thickness of 15 μm as a current collector sheet, pre-dried, and then vacuum dried at 120 ° C. Then, a current collector sheet coated with a coating liquid for a positive electrode active material layer on both surfaces is pressure-pressed at 400 kN / m, and a current collector having first and second positive electrode active material layers on both surfaces. A sheet was prepared. 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 liquid containing 100 parts by mass of alumina and 7 parts by mass of the resin binder and diluted with N-methyl-2-pyrrolidone as a solvent to have a concentration of 42% by mass was prepared. The viscosity of the coating liquid for the insulating layer at 25 ° C. (that is, at the time of coating) was 3000 mPa · s. Using a gravure coat type coating device, the coating liquid for the insulating layer was applied intermittently on the first positive electrode active material layer on one surface of the current collector sheet. At this time, as shown in FIGS. 5 and 6, the coating liquid for the insulating layer is applied so as to protrude 3 mm from each of both sides, dried at 90 ° C. for 1 minute, and then on one surface. The insulating layer of No. 1 was formed and wound into a roll. In the coating apparatus, the outer diameter of the transfer roll was 60 cm, the length in the axial direction was 70 cm, and the volume of the groove was 25 cc / m ² . The coating part temperature was 25 ° C., the coating speed was 20 m / sec, and the shear rate at the time of coating was as shown in Table 1.
The current collector sheet wound in a roll shape is unwound and sent to the gravure coat type coating device as it is, and a second insulating layer is formed under the same conditions as the condition for forming the first insulating layer, and then the second insulating layer is formed. , A positive electrode was obtained by cutting the current collector sheet. In the positive electrode, the size of the current collector was 110 mm × 290 mm, and the size of the portion where the positive electrode active material layer was formed was 110 mm × 279 mm. The length (A + B + D) of the uncoated portion (uncoated portion) of the positive electrode active material was 11 mm. Further, the thickness of the first and second insulating layers was 4 μm. Other lengths and distances are as shown in Table 1.

(Preparation of negative electrode)
A mixture of 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 a sodium salt of carboxymethyl cellulose (CMC), and water as a solvent. Then, a composition for a negative electrode active material layer adjusted to a solid content of 50% by mass was obtained. This composition for the negative electrode active material layer was applied to both sides of a copper foil having a thickness of 12 μm as a negative electrode current collector and vacuum dried at 100 ° C.
Then, the negative electrode current collector coated with the composition for the negative electrode active material layer on both sides was pressure-pressed at a linear pressure of 500 kN / m, and then cut to obtain a negative electrode. The density of the negative electrode active material layer was 1.55 g / cc. The size of the negative electrode was 120 mm × 300 mm, and the area on which the negative electrode active material layer was applied was 120 mm × 290 mm.

(Preparation of electrolyte)
_{LiPF 6} as an electrolyte salt was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 (EC: DEC) so as to be 1 mol / liter, and the electrolytic solution was prepared. Prepared.

(Manufacturing of lithium-ion secondary batteries)
The 25 positive electrodes obtained above, 50 polyethylene porous membrane separators, and 24 positive electrodes were alternately laminated to obtain a temporary laminate. Here, the negative electrode and the positive electrode were arranged alternately. A laminate was obtained by pressing for 1 minute using a flat plate type hot press machine.
The uncoated tips of the current collectors of each positive electrode were joined together by ultrasonic fusion, and the positive electrode tabs protruding to the outside were joined. Similarly, the exposed ends of the negative electrode current collectors of each negative electrode were joined together by ultrasonic fusion, and the negative electrode tabs protruding to the outside were joined.
Next, the laminate was sandwiched between aluminum laminate films, the positive electrode tabs were projected to the outside, and the three sides were sealed by laminating. A laminated cell was manufactured by injecting the electrolytic solution obtained above from one side left unsealed and vacuum-sealing.

Example 2
The solid content concentration of the coating liquid for the insulating layer was changed to 35% by mass, and the viscosity at 25 ° C. was set to 2200 mPa · s.

Example 3
The solid content concentration of the coating liquid for the insulating layer was changed to 35% by mass, the viscosity at 25 ° C. was changed to 2200 mPa · 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 the insulating layer was changed to 25% by mass, and the viscosity at 25 ° C. was 1000 mPa · s.

Comparative Example 2
The solid content concentration of the coating liquid for the insulating layer was changed to 25% by mass, the viscosity at 25 ° C. was changed to 1000 mPa · s, and the length of the uncoated part (uncoated part) of the positive electrode active material was changed to 15 mm. ..

In Examples 1 to 3, the end portion of the first insulating layer has a wavy shape in which a plurality of elongated convex portions are arranged in parallel, and the length D of the convex portions is reduced to reduce the energy density. It was possible to increase the tab strength while maintaining good performance. On the other hand, in Comparative Examples 1 and 2, it was difficult to improve both the tab strength and the energy density because the length D of the convex portion was large.

10, 30 Electrodes for lithium-ion secondary batteries 11 Current collector 11A Uncoated end 11B Edge 11C Uncoated tip 11X, 51X One surface 11Y, 51Y The other surface 11Z One end 12, 52 First electrode activity Material layer 12B Edges 13, 53 First insulating layer 13A Overhanging end 13B Baseline (edge)
13X Convex part 15 Electrode tabs 22, 62 Second electrode active material layer 23, 63 Second insulating layer 23A Overhanging end 23B Edge part 51 Current collector sheet 51A Covered part 51B Uncoated part 54 Coating end 55 Coating Start 60 Gravure roll

Claims (14)

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 are provided.
The current collector has an end that is not covered by the first electrode active material layer.
At the end of the current collector, the end of the first insulating layer protrudes from the first electrode active material layer and covers a part of the end of the current collector. Moreover, it has a wavy shape in which a plurality of elongated convex parts are arranged side by side.
Ri length D is der less 5mm of the convex portion, and the first electrode active material layer of said end portion of the current collector, and also coated on both of the first insulating layer including the protrusion An electrode for a lithium ion secondary battery in which the length A of the portion not to be formed is 3 to 10 mm. The electrode for a lithium ion secondary battery according to claim 1, wherein the thickness of the first electrode active material layer is 20 to 80 μm, and the thickness of the first insulating layer is 2 to 10 μm. The electrode for a lithium ion secondary battery according to claim 1 or 2 , wherein the length B of the end portion of the first insulating layer protruding from the first electrode active material layer is 1 to 5 mm. A second electrode active material layer provided on the other surface of the current collector and a second insulating layer provided on the second electrode active material layer are further provided.
At the end of the current collector, the end of the second insulating layer protrudes from the second electrode active material layer and covers a part of the end of the current collector on the other surface. The electrode for a lithium ion secondary battery according to any one of claims 1 to 3 , wherein the edge thereof is formed substantially linearly. 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 tab. The electrode for a lithium ion secondary battery according to claim 5 , wherein the distance C between the electrode tab and the first electrode active material layer is 3 to 8 mm. The length of the convex portion is D, the length of the end portion of the first insulating layer protruding from the first electrode active material layer is B, and the distance between the electrode tab and the first electrode active material layer is The electrode for a lithium ion secondary battery according to claim 5 or 6 , wherein C is D / (CB) of 1.5 or less. 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. 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. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of claims 1 to 9. A lithium-ion secondary battery in which positive electrodes and negative electrodes are alternately arranged so that a plurality of layers are provided.
At least one electrode of the positive electrode or the negative electrode is composed of the electrode for a lithium ion secondary battery, and the end portion of the current collector of the one electrode constituting each layer is put together. The lithium ion secondary battery according to claim 10 , which is connected to an electrode tab. A coating liquid for a first insulating layer is applied onto the first electrode active material layer of the current collector sheet provided with the first electrode active material layer on one surface, and the first It is a method of manufacturing an electrode for a lithium ion secondary battery that forms an insulating layer of the above.
The current collector sheet has an uncoated portion that is not covered by the first electrode active material layer.
The coating of the coating liquid for the first insulating layer is performed so as to be the coating end at the uncoated portion of the current collector sheet.
The end portion of the first insulating layer made of the coating end protrudes from the first electrode active material layer on the one surface and covers a part of the uncoated portion of the current collector sheet. Formed like
Said liquid draw length in the coating terminations Ri der less 5 mm,
The viscosity of the first insulating layer coating liquid at the time of coating is 2000 to 4000 mPa · s, and the liquid contacting the current collector sheet when the first insulating layer coating liquid is applied. A method for manufacturing an electrode for a lithium ion secondary battery, in which the shear rate of the portion is 0.5 × 10 ⁴ to 40 × 10 ⁴ (1 / s). A coating liquid for a second insulating layer is applied onto the 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. Work to form a second insulating layer,
The uncoated 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.
The coating of the coating liquid for the second insulating layer is performed so as to be the coating starting end at the position of the coating end of the uncoated portion of the current collector sheet.
The end portion of the second insulating layer made of the coating start end protrudes from the second electrode active material layer on the other surface and covers a part of the uncoated portion of the current collector sheet. The method for manufacturing an electrode for a lithium ion secondary battery according to claim 12 , which is formed as described above. While feeding the current collector sheet, one of the first and second insulating layer coating liquids is applied onto the surface of the one or the other, and one of the first and second insulating layers is applied. Form, roll up,
While feeding out the current collector sheet wound up in a roll shape, the other of the first and second insulating layer coating liquids is applied onto the one or the other surface, and the first and second coating liquids are applied. The method for manufacturing an electrode for a lithium ion secondary battery according to claim 13 , wherein the other side of the insulating layer of 2 is formed.

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