WO2020067379A1

WO2020067379A1 - Electrode for lithium ion secondary batteries, and lithium ion secondary battery

Info

Publication number: WO2020067379A1
Application number: PCT/JP2019/038037
Authority: WO
Inventors: 和徳小関; 純之介秋池
Original assignee: 積水化学工業株式会社
Priority date: 2018-09-28
Filing date: 2019-09-26
Publication date: 2020-04-02
Also published as: TW202034560A; JPWO2020067379A1; JP6876880B2

Abstract

This electrode (10) for lithium ion secondary batteries is provided with a current collector (20) and an electrode active material layer (30) that is provided on the current collector and that includes an electrode active material and a binder. At least part of an end (31) of the electrode active material layer (30) is formed from an inclined section (31) in which the thickness decreases as the distance from a central section (32) of the electrode active material layer (30) increases. An edge factor represented by the ratio (W/T) of the width (W) of the inclined section (31) to the thickness (T) of the electrode active material layer (30) is 3 or more, and the width (W) of the inclined section (31) is less than 1,000 µm. A lithium ion secondary battery according to the present invention is provided with the electrode for lithium ion secondary batteries. The present invention makes it possible to provide an electrode for lithium ion secondary batteries enabling a high electrode utilization rate and the suppression of the occurrence of powder loss, and a lithium ion secondary battery provided with the electrode.

Description

Electrode for lithium ion secondary battery and lithium ion secondary battery

(4) The present invention relates to an electrode for a lithium ion secondary battery including an insulating resin layer disposed adjacent to and covering the end of the electrode active material layer, and a lithium ion secondary battery.

Lithium ion secondary batteries are used as power sources for large stationary power storage devices, power sources for electric vehicles, and the like. In recent years, research into miniaturization and thinning of batteries has been progressing. A lithium ion secondary battery generally includes two electrodes each having an electrode active material layer formed on a surface of a metal foil, and a separator disposed between the two electrodes. The separator plays a role in preventing a short circuit between the two electrodes and holding the electrolytic solution.
By the way, in a lithium ion secondary battery, during charge and discharge, the electrode active material expands and contracts. In order to prevent the electrode from being broken due to such expansion and contraction of the electrode active material, a tapered portion is formed at the end of the electrode, where the thickness of the electrode active material layer becomes thinner as approaching the end of the electrode active material layer. Lithium ion secondary batteries are known as a conventional technology (for example, Patent Document 1). Thus, a step caused by the end of the electrode active material layer can be reduced, and breakage of the current collector and the like due to the step at the end of the electrode active material layer can be suppressed.

International Publication No. WO2012 / 081465

When the capacity of the negative electrode is smaller than that of the positive electrode, lithium is deposited on the surface of the positive electrode, and the deposited lithium may break through the separator and cause a short circuit. Therefore, when the capacity of the negative electrode is smaller than that of the positive electrode, it is necessary to increase the coating amount of the electrode active material of the negative electrode as compared with the positive electrode. However, in this case, when the electrode active material layer has a tapered portion at the end, a portion where the negative electrode active material layer and the tapered portion of the positive electrode active material layer overlap occurs, and the utilization rate of the electrode decreases. There is a risk. Thereby, the energy density of the lithium ion secondary battery may be reduced. Further, when the electrode active material layer has a tapered portion at an end, a part of the electrode active material, the conductive auxiliary agent, and the like may be detached at the tapered portion, that is, so-called powder dropping may occur. When powder fall occurs, a short circuit may occur in the lithium ion secondary battery.
Therefore, an object of the present invention is to provide an electrode for a lithium ion secondary battery that can increase the utilization rate of the electrode and suppress the occurrence of powder drop, and a lithium ion secondary battery including the electrode.

As a result of intensive studies, the present inventor has set the edge factor expressed by the ratio (W / T) of the width (W) of the inclined portion to the thickness (T) of the electrode active material layer to a predetermined value or more, and By finding that the width (W) of the portion is less than the predetermined value, it has been found that the utilization rate of the electrode can be increased and the occurrence of powder drop can be suppressed, and the present invention described below has been completed. The gist of the present invention is the following [1] to [7].
[1] A current collector, provided on the current collector, an electrode active material, and an electrode active material layer containing a binder, wherein at least a part of the end of the electrode active material layer is It is constituted by an inclined portion whose thickness decreases as the distance from the center of the material layer increases, and is expressed by a ratio (W / T) of the width (W) of the inclined portion to the thickness (T) of the electrode active material layer. The electrode for a lithium ion secondary battery having an edge factor of 3 or more and a width (W) of the inclined portion of less than 1000 μm.
[2] The electrode for a lithium ion secondary battery according to the above [1], wherein the electrode active material layer further contains a conductive additive.
[3] The electrode for a lithium ion secondary battery according to the above [1] or [2], wherein the content of the binder in the electrode active material layer is 1.5% by mass or more.
[4] The above-mentioned [1], further comprising an insulating resin layer provided on the current collector, wherein the insulating resin layer is disposed adjacent to the inclined portion of the electrode active material layer and covers the inclined portion. ] The electrode for a lithium ion secondary battery according to any one of [3] to [3].
[5] A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of the above [1] to [4].
[6] The lithium ion secondary battery according to the above [5], comprising a negative electrode and a positive electrode, wherein both the positive electrode and the negative electrode are electrodes for the lithium ion secondary battery.
[7] The positive electrode and the negative electrode are alternately arranged so that a plurality of layers are provided, and the ends of the current collectors of the positive electrodes constituting each layer are combined and connected to the positive electrode terminal to form each layer. A lithium ion secondary battery in which the ends of the current collectors of the negative electrodes are combined and connected to a negative electrode terminal, wherein the positive electrode, or at least one of the negative electrodes, is configured by the lithium ion secondary battery electrode, The lithium ion secondary battery according to the above [5] or [6], wherein the inclined portion is provided on an end portion side of the current collector.

According to the present invention, it is possible to provide an electrode for a lithium ion secondary battery capable of increasing the utilization rate of the electrode and suppressing generation of powder, and a lithium ion secondary battery including the electrode.

FIG. 1 is a schematic sectional view of an electrode for a lithium ion secondary battery in one embodiment of the present invention. FIG. 2 is a diagram for explaining an electrode utilization rate. FIG. 3 is a diagram illustrating an example of a die head used for applying the composition for an electrode active material layer. FIG. 4 is a diagram for explaining the application of the composition for an electrode active material layer. FIG. 5 is a diagram for explaining the division of the current collector on which the electrode active material layer is formed. FIG. 6 is a schematic cross-sectional view of a modification of the electrode for a lithium ion secondary battery in one embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a modification of the electrode for a lithium ion secondary battery in one embodiment of the present invention. FIG. 8 is a schematic sectional view of a lithium ion secondary battery according to one embodiment of the present invention.

[Electrode for lithium ion secondary battery]
Hereinafter, an electrode for a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic sectional view of an electrode for a lithium ion secondary battery in one embodiment of the present invention.
As shown in FIG. 1, an electrode 10 for a lithium ion secondary battery according to one embodiment of the present invention includes a current collector 20 and an electrode active material layer provided on both surfaces of the current collector and including an electrode active material and a binder. 30. Then, at least a part of the end portion 31 of the electrode active material layer 30 is constituted by an inclined portion 31 whose thickness decreases as the distance from the central portion 32 of the electrode active material layer 30 increases. Further, the edge factor represented by the ratio (W / T) of the width (W) of the inclined portion 31 to the thickness (T) of the electrode active material layer 30 is 3 or more, and the width (W) of the inclined portion 31 ) Is less than 1000 μm.

(Thickness of electrode active material layer (T))
The thickness (T) of the electrode active material layer 30 is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 90 μm per one surface. When the thickness of the electrode active material layer changes depending on the position of the electrode active material layer, the average value of the thickness of the electrode active material layer excluding the inclined portion is defined as the thickness (T) of the electrode active material layer.

(Width of the inclined portion of the electrode active material layer (W))
The width (W) of the inclined portion 31 in the electrode active material layer 30 is less than 1000 μm. If the width (W) of the inclined portion 31 is 1000 μm or more, the portion where the inclined portion of the electrode active material layer overlaps with the electrode active material layer facing the inclined portion increases, and the portion not used as an electrode may increase. And there is a possibility that the utilization rate of the electrode is reduced. For example, in the case of a pair of the negative electrode 10A and the positive electrode 10B shown in FIG. 2, the region 33A of the negative electrode active material layer 30A does not have the inclined portion 31B and the positive electrode active material layer 10B in the positive electrode active material layer 10B of the positive electrode 10B. It overlaps with the current collector 20B. This region 33A is a region that is not often used as an electrode. When the region 33A that is not much used as an electrode becomes large, the region that is not used as an electrode in the negative electrode active material layer 30A becomes large, and the utilization rate of the electrode becomes low. Therefore, when the width (W) of the inclined portion 31 in the electrode active material layer 30 increases, the region 33A also increases, and the utilization factor of the electrode decreases. From the viewpoint of electrode utilization, the width (W) of the inclined portion 31 is preferably 990 μm or less, more preferably 950 μm or less, and even more preferably 900 μm or less.

(Edge factor of electrode active material layer)
The edge factor of the electrode active material layer 30 is represented by the ratio (W / T) of the width (W) of the inclined portion 31 to the thickness (T) of the electrode active material layer 30. The edge factor of the electrode active material layer 30 is 3 or more. If the edge factor of the electrode active material layer 30 is less than 3, powder falling of the electrode active material may occur in the inclined portion 31 of the electrode active material layer. From the viewpoint of powder dropping of the electrode active material, the edge factor of the electrode active material layer 30 is preferably 4 or more, more preferably 5 or more, and further preferably 6 or more.

(Current collector)
Examples of a material forming the current collector 20 include metals having conductivity, such as copper, aluminum, titanium, nickel, and stainless steel. Among these, when the current collector 20 is a positive electrode current collector, aluminum, titanium, nickel, and stainless steel are preferable, and aluminum is more preferable. When the current collector 20 is a negative electrode current collector, copper, titanium, nickel, and stainless steel are preferable, and copper is more preferable. The current collector 20 is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 20 μm. When the thickness of the current collector is within the above range, handling of the current collector becomes easy and a decrease in energy density can be suppressed.

(Electrode active material layer)
The electrode active material layer 30 includes an electrode active material and a binder. When the electrode is a positive electrode, the electrode active material layer becomes a positive electrode active material layer, and the electrode active material becomes a positive electrode active material. On the other hand, when the electrode is a negative electrode, the electrode active material layer becomes a negative electrode active material layer, and the electrode active material becomes a negative electrode active material. Usually, the electrode area of the positive electrode is smaller than the electrode area of the negative electrode.

<Positive electrode active material>
Examples of the positive electrode active material used for the positive electrode active material layer include a lithium metal oxide compound. Examples of the lithium metal oxide compound include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and the like. Alternatively, olivine-type lithium iron phosphate (LiFePO ₄ ) may be used as the positive electrode active material. Further, as the positive electrode active material, a material using a plurality of metals other than lithium may be used. For example, an NCM (nickel-cobalt-manganese) -based oxide, an NCA (nickel-cobalt-aluminum-based) -based oxide, etc. May be used. As the positive electrode active material, one of these materials may be used alone, or two or more thereof may be used in combination.

<Negative electrode active material>
Examples of the negative electrode active material used in the negative electrode active material layer include graphite, a carbon material such as hard carbon, a composite of a tin compound and silicon and carbon, and lithium. Among these, a carbon material is preferable, and graphite is preferable. More preferred. As the negative electrode active material, one of the above materials may be used alone, or two or more thereof may be used in combination.

<Average particle diameter of electrode active material>
The average particle diameter of the electrode active material is not particularly limited, but is preferably 0.5 to 50 μm, more preferably 1 to 30 μm, and further preferably 5 to 25 μm. The average particle diameter means the particle diameter (D50) at a volume integration of 50% in the particle size distribution of the electrode active material obtained by the laser diffraction / scattering method.

<Content of electrode active material>
The content of the electrode active material in the electrode active material layer 30 is preferably 50 to 99% by mass, more preferably 60 to 99% by mass, further preferably 80 to 99% by mass, and more preferably 90 to 99% by mass, based on the total amount of the electrode active material layer. 98% by weight is particularly preferred.

<Binder>
Specific examples of the binder include fluorine-containing resins such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polytetrafluoroethylene (PTFE); polymethyl acrylate (PMA); Acrylic resin such as polymethyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), poly Acrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), poly (meth) acrylic acid, carboxymethylcellulose (CMC), hydroxyethylcellulose, polyvinyl alcohol, and the like. It is. 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 binder in the electrode active material layer 30 is preferably 0.5% by mass or more, and more preferably 0.5 to 20% by mass, based on the total amount of the electrode active material layer, from the viewpoint of powder fall of the electrode active material. More preferably, the content is more preferably 1.0 to 10% by mass. By setting the content of the binder to be equal to or more than the above lower limit value, powder fall of the electrode active material, the conductive auxiliary agent, and the like becomes difficult to occur.

<Conduction aid>
It is preferable that the electrode active material layer 30 further includes a conductive auxiliary. As the conductive additive, a material having higher conductivity than the above-mentioned electrode active material is used, and specific examples thereof include carbon materials such as Ketjen black, acetylene black, carbon nanotube, and rod-like carbon. The conductive auxiliary may be used alone or in combination of two or more. When the conductive additive is contained in the electrode active material layer 30, the content of the conductive additive is preferably 0.5 to 15% by mass, preferably 1 to 10% by mass, based on the total amount of the electrode active material layer. Is more preferable. When the content of the conductive auxiliary agent is in the above range, a decrease in output performance due to an increase in battery resistance can be suppressed, and at the same time, the conductive auxiliary agent absorbs a binder and can prevent powder dropping from occurring. In addition, when the electrode active material layer 30 further contains a conductive auxiliary, powder dropout from the electrode active material layer 30 is likely to occur. However, in the electrode 10 for a lithium ion secondary battery according to one embodiment of the present invention, powder falling hardly occurs by adjusting the value of the edge factor (W / T) to the above-described range as described above.

(4) The electrode active material layer 30 may contain any other components other than the electrode active material, the conductive auxiliary agent, and the binder as long as the effects of the present invention are not impaired. However, of the total mass of the electrode active material layer, the total content of the electrode active material, the conductive additive, and the binder is preferably 90% by mass or more, and more preferably 95% by mass or more.

[Method for producing electrode for lithium ion secondary battery]
The electrode for a lithium ion secondary battery in one embodiment of the present invention can be manufactured, for example, by the following manufacturing method. In one example of the method for manufacturing an electrode for a lithium ion secondary battery according to one embodiment of the present invention, first, a composition for an electrode active material layer is applied on a current collector to form an electrode active material layer on the current collector. I do. Thereafter, the current collector on which the electrode active material layer is formed is pressed under pressure and divided to produce an electrode for a lithium ion secondary battery.

Note that the thickness (T) of the electrode active material layer 30 and the width (W) of the inclined portion of the electrode active material layer can be controlled by adjusting the viscosity of the composition for an electrode active material layer. The viscosity of the composition for an electrode active material layer can be controlled, for example, by adjusting the solid concentration in the composition for an electrode active material layer.

(Electrode active material layer forming step)
In the electrode active material layer forming step, first, an electrode active material layer composition including an electrode active material, a binder, and a solvent is prepared. Examples of the solvent used in the composition for an electrode active material layer include cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, toluene, isopropyl alcohol, N-methylpyrrolidone (NMP), ethanol, water, and the like. The composition for an electrode active material layer may include other components such as a conductive auxiliary compounded as necessary. Details of the electrode active material, the binder, and the like are as described above. The composition for an electrode active material layer is in a slurry state.

From the viewpoint of setting the width (W) of the inclined portion 31 of the electrode active material layer 30 to less than 1000 μm, when the electrode active material is a positive electrode active material, the viscosity of the composition for an electrode active material layer is preferably 2500 to 12000 mPa · s. s, more preferably 3,000 to 10,000 mPa · s. On the other hand, when the electrode active material is a negative electrode active material, the viscosity of the composition for an electrode active material layer is preferably 1600 to 12000 mPa · s, more preferably 1800 to 10000 mPa · s. The viscosity is a viscosity measured by a B-type viscometer at 60 rpm and 25 ° C., two minutes after the start of rotation of the spindle.

The electrode active material layer can be formed, for example, by applying the above-mentioned composition for an electrode active material layer on a current collector by a known coating method, and drying. The method for applying the composition for an electrode active material layer on a current collector sheet includes, for example, a die coating method, a slit coating method, a comma coating method, a lip coating method, a dip coating method, a spray coating method, and a roll coating method. Method, doctor blade method, bar coating method, gravure coating method, screen printing method and the like. Among these coating methods, the die coating method is preferred from the viewpoint that an inclined portion can be easily formed at the end of the electrode active material layer. Hereinafter, the application of the composition for an electrode active material layer on a current collector will be described with reference to FIGS. 3 and 4 using a die coating method as an example.

FIG. 3 is a view showing an example of a die head used for applying the composition for an electrode active material layer. A discharge port 51 is provided in the die head 50. The composition for an electrode active material layer supplied to the die head 50 is discharged from a discharge port 51.

As shown in FIG. 4, the composition for an electrode active material layer is discharged from the die head 50 onto the current collector 120 moving in the direction of reference numeral 121. Thus, the electrode active material layer 130 can be formed over the current collector 120. In one embodiment of the present invention, the side 131 of the electrode active material layer 130 can be inclined by adjusting the viscosity of the composition for an electrode active material layer. The side surface 131 of the electrode active material layer 130 corresponds to the inclined portion 31 of the electrode active material layer 30. Further, by adjusting the viscosity of the composition for an electrode active material layer, the thickness (T) and the edge factor (W / T) of the electrode active material layer 30 can also be adjusted (see FIG. 1). The current collector 120 on which the electrode active material layer 130 is formed passes through a drier (not shown). Thus, the electrode active material layer 130 formed on the current collector 120 is dried. The drying temperature is not particularly limited as long as the solvent can be removed, and is, for example, 40 to 120 ° C, preferably 50 to 90 ° C. The drying time is not particularly limited, but is, for example, 30 seconds to 10 minutes.
After the electrode active material layer 130 is dried, the electrode active material layer 130 is formed on the surface on the opposite side of the current collector 120 in the same manner.

(Pressing press process)
The current collector 120 having the electrode active material layer 130 formed thereon is preferably pressed under pressure. By pressing under pressure, the electrode density can be increased. The pressure press may be performed by a roll press or the like. The pressure of the pressure press is not particularly limited as long as wrinkles or the like are not generated on the current collector and a desired electrode density can be reached. The pressure of the pressure press is, for example, a linear pressure in the case of a roll press, preferably 100 to 2000 kN / m, more preferably 200 to 1000 kN / m.

(Split)
The current collector 120 on which the electrode active material layer 130 is formed is cut, for example, along a dotted line 150 in FIG. 5 and divided into a plurality of electrodes for a lithium ion secondary battery. Thereby, the electrode 10 for a lithium ion secondary battery according to the embodiment of the present invention shown in FIG. 1 can be manufactured.

The electrode 10 for a lithium ion secondary battery in one embodiment of the present invention can be modified as follows.
(Modification 1)
In the electrode 10 for a lithium ion secondary battery according to the embodiment of the present invention described above, the electrode active material layers 30 are formed on both surfaces of the current collector 20. However, the electrode active material layer 30 may be formed only on one surface of the current collector 20 like the electrode 10C for a lithium ion secondary battery shown in FIG.

(Modification 2)
Further, like the lithium ion secondary battery electrode 10D shown in FIG. 7, the lithium ion secondary battery electrode 10D may further include an insulating resin layer 40 provided on the current collector. In this case, the insulating resin layer 40 is arranged so as to be adjacent to the inclined portion 31 of the electrode active material layer 30 and to cover the inclined portion 31. Thereby, a short circuit between the electrodes can be more reliably prevented. Further, powder falling from the inclined portion 31 of the electrode active material layer 30 can be further suppressed.

The insulating resin layer 40 only needs to be able to secure insulation at the end of the electrode, and contains a resin component. Examples of the resin component include fluorine-containing resins such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polytetrafluoroethylene (PTFE); polymethyl acrylate (PMA); Acrylic resin such as polymethyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), poly Acrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), poly (meth) acrylic acid, carboxymethylcellulose (CMC), hydroxyethylcellulose, polyvinyl alcohol, and the like. That. 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. These polymers may be used alone or may be used as a multilayer body by superposing these polymers. Furthermore, various additives may be used for these polymers, and the type and content thereof are not particularly limited. In addition, insulating fine particles may be added to the resin component, if necessary. Examples of the insulating fine particles include inorganic particles and organic particles.
When inorganic particles are used as an additive, usually, the rigidity of the insulating layer can be increased and drying shrinkage can be reduced. Examples of the material of such inorganic particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH)), gibbsite (Al (OH) ₃ ), silicon oxide, magnesium oxide (magnesia), and water. Oxide particles such as magnesium oxide, calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO ₂ , alumina-silica composite oxide, nitride particles such as aluminum nitride and boron nitride, and covalent crystals such as silicon and diamond Particles, hardly soluble ionic crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; and clay fine particles such as talc and montmorillonite. Among these, oxide particles are preferable from the viewpoint of stability in an electrolyte and potential stability, and titanium oxide and aluminum oxide are preferable from the viewpoint of low water absorption and excellent heat resistance (eg, resistance to high temperatures of 180 ° C. or higher). Hydrate of aluminum oxide, magnesium oxide and magnesium hydroxide are more preferable, aluminum oxide, hydrate of aluminum oxide, magnesium oxide and magnesium hydroxide are more preferable, and aluminum oxide is particularly preferable.
Generally, polymer particles are used as the organic particles. By adjusting the type and amount of the functional group on the surface of the organic particles, the affinity of the organic particles for water can be controlled, and the amount of water contained in the insulating layer can be controlled. Further, the organic particles are generally excellent in that elution of metal ions is small. Examples of the material of such organic particles include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer compound forming the particles may be, for example, a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked product, or the like. Further, the organic particles may be formed of a mixture of two or more polymer compounds.
These inorganic particles and organic particles may be used alone or in a combination of two or more.

リチウム The electrode for a lithium ion secondary battery in one embodiment of the present invention and the modification thereof are only one embodiment of the electrode for a lithium ion secondary battery of the present invention. Therefore, the electrode for a lithium ion secondary battery in one embodiment of the present invention and its modification do not limit the electrode for a lithium ion secondary battery of the present invention.

[Lithium secondary ion battery]
With reference to FIG. 8, a lithium ion secondary battery according to one embodiment of the present invention will be described. FIG. 8 is a schematic sectional view of a lithium ion secondary battery according to one embodiment of the present invention. As shown in FIG. 8, the lithium ion secondary battery 1 in one embodiment of the present invention includes the electrode 10 for a lithium ion secondary battery in one embodiment of the present invention. The lithium ion secondary battery 1 according to one embodiment of the present invention includes the negative electrode 10 and the positive electrode 10 from the viewpoint that the utilization rate of the electrode can be increased and generation of powder drop can be suppressed. Both are preferably the electrodes 10 for a lithium ion secondary battery in one embodiment of the present invention.

In addition, in the lithium ion secondary battery 1 according to one embodiment of the present invention, it is preferable that the positive electrode 10 and the negative electrode 10 are alternately arranged such that each of the positive electrode 10 and the negative electrode 10 is provided in a plurality of layers. Further, the ends of the current collectors 20 of the respective positive electrodes 10 constituting each layer are collected and connected to the positive electrode terminal 2, and the ends of the respective current collectors 20 of the respective negative electrodes 10 constituting each layer are collected and the negative electrode terminals 3 are formed. Is preferably connected to Then, at least one of the positive electrode 10 and the negative electrode 10 is configured by the electrode 10 for a lithium ion secondary battery according to one embodiment of the present invention, and the inclined portion 31 is provided on the integrated end side of the current collector 20. Preferably. Thereby, it is possible to obtain a lithium ion secondary battery provided with a lithium ion secondary battery electrode that can increase the utilization rate of the electrode and suppress the generation of powder drop.

において In the lithium ion secondary battery 1 according to one embodiment of the present invention, the stacked electrodes 10 are preferably housed in the housings 6 and 7. The casings 6 and 7 may be any of a square type, a cylindrical type, a laminate type, and the like.

The lithium ion secondary battery 1 according to one embodiment of the present invention preferably further includes a separator 8 disposed between the positive electrode 10 and the negative electrode 10. By providing the separator 8, a short circuit between the positive electrode 10 and the negative electrode 10 is more effectively prevented. Further, the separator 8 may hold an electrolyte 9 described later.

(4) Examples of the separator 8 include a porous polymer film, a nonwoven fabric, and a glass fiber. Among these, a porous polymer film is preferable. As the porous polymer film, an olefin-based porous film is exemplified.

リチウム The lithium ion secondary battery of the present invention includes the electrolyte 9. The electrolyte is not particularly limited, and a known electrolyte 9 used in the lithium ion secondary battery 1 may be used. As the electrolyte 9, for example, an electrolytic solution is used. The electrolyte 9 is filled in the housings 6 and 7 after the stacked electrodes 10 are housed in the housings 6 and 7, for example.

Examples of the electrolyte include an electrolyte containing an organic solvent and an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, and 1,2. Polar solvents such as -diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, and methyl acetate; or a mixture of two or more of these solvents. As the electrolyte salt, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ CO ₂ , LiPF ₆ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) _2, and a salt containing lithium such as LiN (COCF ₂ CF ₃ ) ₂ and lithium bisoxalate borate (LiB (C ₂ O ₄ ) ₂ ) can be given. Further, a complex such as a lithium hydride of an organic acid-boron trifluoride complex or a complex hydride such as LiBH ₄ may be used. These salts or complexes may be used alone or as a mixture of two or more. Further, the electrolyte 9 may be a gel electrolyte further containing a polymer compound in the electrolyte. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacryl-based polymer such as poly (methyl meth) acrylate. Note that the gel electrolyte may be used as a separator.

The lithium ion secondary battery in one embodiment of the present invention described above can be modified as follows.
(Modification 1)
The lithium ion secondary battery according to one embodiment of the present invention includes the lithium ion secondary battery electrode 10 according to one embodiment of the present invention as a positive electrode and a negative electrode.

Modifications

10C and 10D of the electrode for the lithium ion secondary battery may be provided.

リチウム The lithium ion secondary battery and its modification in one embodiment of the present invention are only one embodiment of the lithium ion secondary battery of the present invention. Therefore, the lithium ion secondary battery in one embodiment of the present invention and its modifications do not limit the lithium ion secondary battery of the present invention.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

電極 The obtained lithium ion secondary battery electrode was evaluated by the following evaluation methods.

(Powdering)
In the production of electrodes for lithium ion secondary batteries, when the current collector coated with the slurry for the electrode active material layer on both sides was pressed under pressure with a roller, the slip of the electrode active material from the electrode end was examined. Was evaluated.
○: No sliding of electrode active material ×: Sliding of electrode active material (utilization rate)
The positive electrode and the negative electrode are stacked, and the sum (W1 + W2) of the width (W1) of the inclined portion of the positive electrode active material layer and the width (W2) of the inclined portion of the negative electrode active material layer facing each other is the length of the surplus portion. It was evaluated according to the following criteria.
：: length of surplus portion is less than 1500 μm ×: length of surplus portion is 15000 μm or more

[Example 1]
(Preparation of positive electrode)
An NCA-based oxide (average particle diameter: 10 μm) as a positive electrode active material, acetylene black as a conductive additive, polyvinylidene fluoride (PVdF) as an electrode binder, and N-methylpyrrolidone (NMP) as a solvent are mixed. A slurry for a positive electrode active material layer was obtained. The content of the NCA-based oxide in the slurry for the positive electrode active material layer was 62% by mass, and the content of acetylene black was 1.4% by mass. Further, the content of PVdF was 1.6% by mass, and the content of NMP was 35% by mass. The solid concentration of the slurry for the positive electrode active material layer was 67.2% by mass. The slurry for the positive electrode active material layer slurry had a viscosity of 9060 mPa · s. The viscosity was measured by a B-type viscometer at 60 rpm and 25 ° C., 2 minutes after the start of rotation of the spindle. The slurry for a positive electrode active material layer was applied to both sides of a 15 μm-thick aluminum foil as a positive electrode current collector using a die coater, preliminarily dried, and then vacuum dried at 120 ° C. to form a positive electrode active material layer. Formed on aluminum foil.

Thereafter, the aluminum foil on which the electrode active material layer was formed was pressed under pressure with a roller at a linear pressure of 400 kN / m, and was further punched into a 100 mm × 200 mm square of electrode dimensions to obtain a positive electrode having electrode active materials on both surfaces. Of the dimensions, the area where the positive electrode active material was applied was 100 mm × 180 mm. In addition, the thickness of the positive electrode active material layers formed on both surfaces was 50 μm per one surface.

[Examples 2 to 4 and Comparative Example 1]
In Examples 2 to 4 and Comparative Example 1, as shown in Table 1, the viscosity of the slurry for the positive electrode active material layer was changed. Thereby, the positive electrodes of Examples 2 to 4 and Comparative Example 1 having the thickness (T1) of the electrode active material layer, the width (W) of the inclined portion, and the edge factor (W / T) shown in Table 4 below were prepared. did.

[Example 5]
(Preparation of negative electrode)
Graphite (average particle diameter: 10 μm) as a negative electrode active material, sodium salt of carboxymethyl cellulose (CMC) as a negative electrode binder, acetylene black as a conductive additive, and styrene butadiene rubber (SBR) as a negative electrode binder; Water was mixed as a solvent to obtain a slurry for a negative electrode active material layer. The content of the negative electrode active material in the slurry for the negative electrode active material layer was 50% by mass, the content of the conductive additive was 0.5% by mass, and the content of the binder was 1.5% by mass. The content of the solvent was 48% by mass. The solid concentration of the slurry for the negative electrode active material layer was 52.0% by mass. The viscosity of the slurry for the negative electrode active material layer was 5,460 mPa · s. The viscosity was measured by a B-type viscometer at 60 rpm and 25 ° C., 2 minutes after the start of rotation of the spindle. This negative electrode active material layer slurry was applied to both surfaces of a 12 μm thick copper foil as a negative electrode current collector using a die coater, preliminarily dried, and then vacuum dried at 100 ° C. to form a negative electrode active material layer. Formed on copper foil.

Thereafter, the negative electrode current collector coated with the slurry for the negative electrode active material layer on both sides is pressed with a roller at a linear pressure of 300 kN / m by a roller, and further punched into 110 mm × 210 mm square of the electrode dimensions, thereby forming the negative electrode active material on both sides. A negative electrode having a layer was obtained. Of the dimensions, the area where the negative electrode active material was applied was 110 mm × 190 mm. The thickness of the negative electrode active material layers formed on both sides was 50 μm per one side.

[Examples 6 to 8 and Comparative Example 1]
In Examples 6 to 8 and Comparative Example 2, as shown in Table 2, the viscosity of the negative electrode active material layer slurry was changed. Thereby, the negative electrodes of Examples 2 to 4 and Comparative Example 1 having the thickness (T1) of the electrode active material layer, the width (W) of the inclined portion, and the edge factor (W / T) shown in Table 5 below were prepared. did.

[Examples 9 to 15 and Reference Examples 1 and 2]
As shown in Table 3, the slurries of the positive electrode active material layer slurries were changed to produce positive electrodes of Examples 9 to 15 and Reference Examples 1 and 2. Further, as shown in Table 3, the viscosities of the slurries for the negative electrode active material layers were changed to produce the negative electrodes of Examples 9 to 15 and Reference Examples 1 and 2. And the positive electrode and the negative electrode of each Example and the reference example were combined, and it was set as the positive electrode and the negative electrode for utilization evaluation.

The measurement and evaluation results are shown in the following Tables 4 to 6.

As shown in Examples 1 to 8 above, by setting the edge factor (W / T) of the electrode active material layer to 3 or more and setting the width (W) of the inclined portion to less than 1000 μm, powder powder of the electrode is reduced. It was found to be suppressed. On the other hand, in Comparative Examples 1 and 2, since the edge factor was smaller than 3, powder dropping occurred.
As shown in Examples 9 to 14 above, by setting the edge factor (W / T) of the electrode active material layer to 3 or more and setting the width (W) of the inclined portion to less than 1000 μm, the utilization rate of the electrode is reduced. It turned out to be higher. On the other hand, in Reference Example 1, the width of the inclined portion of the electrode active material layer in the negative electrode was 1000 μm or more, and in Reference Example 2, the width of the inclined portion of the electrode active material layer in the positive electrode was 1000 μm or more. The rate dropped.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode terminal 3 Negative electrode terminal 6, 7 Case 8 Separator 9

Electrolyte

10, 10A-10D Lithium ion secondary battery electrode (positive electrode, negative electrode)
20, 20A, 20B, 120

Current collector

30, 30A, 30B, 130 Electrode active material layer 31 End (inclined portion)
32 Central part 50 Die head 51 Discharge port 131 Side surface of electrode active material layer

Claims

A current collector, provided on the current collector, including an electrode active material, and an electrode active material layer including a binder;
At least a part of the end of the electrode active material layer is constituted by an inclined portion whose thickness decreases as the distance from the center of the electrode active material layer increases,
The edge factor represented by the ratio (W / T) of the width (W) of the inclined portion to the thickness (T) of the electrode active material layer is 3 or more, and the width (W) of the inclined portion is An electrode for a lithium ion secondary battery having a size of less than 1000 μm.
The electrode for a lithium ion secondary battery according to claim 1, wherein the electrode active material layer further contains a conductive additive.
(3) The electrode for a lithium ion secondary battery according to (1) or (2), wherein the content of the binder in the electrode active material layer is 1.5% by mass or more.
Comprising an insulating resin layer provided on the current collector,
4. The electrode for a lithium ion secondary battery according to claim 1, wherein the insulating resin layer is disposed so as to be adjacent to the inclined portion of the electrode active material layer and to cover the inclined portion. .
(4) A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of (1) to (4).
Comprising a negative electrode and a positive electrode,
The lithium ion secondary battery according to claim 5, wherein both the positive electrode and the negative electrode are the electrodes for the lithium ion secondary battery.
The positive electrode and the negative electrode are alternately arranged so that each layer is provided in a plurality of layers, the ends of the current collectors of the respective positive electrodes forming each layer are combined and connected to the positive electrode terminal, and each of the negative electrodes forming each layer is formed. A lithium ion secondary battery in which ends of a current collector are combined and connected to a negative electrode terminal,
At least one of the positive electrode or the negative electrode is configured by the lithium ion secondary battery electrode,
7. The lithium ion secondary battery according to claim 5, wherein the inclined portion is provided on an integrated end side of the current collector. 8.