JPWO2020067379A1 - Electrodes for lithium-ion secondary batteries and lithium-ion secondary batteries - Google Patents

Abstract

The electrode (10) for a lithium ion secondary battery of the present invention includes a current collector (20), an electrode active material provided on the current collector, and an electrode active material layer (30) containing a binder. At least a part of the end portion (31) of the electrode active material layer (30) is composed of an inclined portion (31) whose thickness decreases as the distance from the central portion (32) of the electrode active material layer (30) increases. The edge factor represented by the ratio (W / T) of the width (W) of the inclined portion (31) to the thickness (T) of the active material layer (30) is 3 or more, and the inclined portion (31) has an edge factor of 3 or more. The width (W) is less than 1000 μm. The lithium ion secondary battery of the present invention includes the electrode for the lithium ion secondary battery of the present invention. 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 the occurrence of powder falling, and a lithium ion secondary battery provided with the electrode.

Description

The present invention relates to an electrode for a lithium ion secondary battery having an insulating resin layer arranged adjacent to an end portion of the electrode active material layer and arranged so as to cover the end portion, 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 is generally provided with both electrodes having an electrode active material layer formed on the surface of 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.
By the way, in a lithium ion secondary battery, the electrode active material expands and contracts during charging and discharging. In order to prevent the electrode from breaking due to the expansion and contraction of the electrode active material, a tapered portion is formed at the end of the electrode so that the thickness of the electrode active material layer becomes thinner as it approaches the end of the electrode active material layer. A lithium ion secondary battery is known as a prior art (for example, Patent Document 1). As a result, the step caused by the end of the electrode active material layer can be reduced, and the breakage of the current collector or the like due to the step at the end of the electrode active material layer can be suppressed.

International Publication No. 2012/081465

If the capacity of the negative electrode is smaller than that of the positive electrode, lithium may be 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, the negative electrode needs to have a larger coating amount of the electrode active material than the positive electrode. However, in this case, if 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 is generated, and the utilization rate of the electrode is lowered. There is a risk. As a result, the energy density of the lithium ion secondary battery may decrease. Further, when the electrode active material layer has a tapered portion at an end portion, a part of the electrode active material, the conductive auxiliary agent, or the like may be detached at the tapered portion, that is, so-called powder dropping may occur. If powder drops occur, 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 capable of increasing the utilization rate of the electrode and suppressing the occurrence of powder falling, and a lithium ion secondary battery provided with the electrode.

As a result of diligent studies, the present inventor sets 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 to a predetermined value or more and the inclination. We have found that the utilization rate of the electrode can be increased and the occurrence of powder falling can be suppressed by setting the width (W) of the portion to less than a predetermined value, and the following invention has been completed. The gist of the present invention is the following [1] to [7].
[1] A current collector, an electrode active material provided on the current collector, and an electrode active material layer containing a binder are provided, and at least a part of the end portion of the electrode active material layer is the electrode active material. It is composed of inclined portions whose thickness decreases as the distance from the central portion of the material layer increases, and is represented by the ratio (W / T) of the width (W) of the inclined portion to the thickness (T) of the electrode active material layer. An 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 auxiliary agent.
[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 [1], which comprises an insulating resin layer provided on the current collector, and the insulating resin layer is arranged so as to be adjacent to the inclined portion of the electrode active material layer and to cover the inclined portion. ] To the electrode for a lithium ion secondary battery according to any one of [3].
[5] A lithium ion secondary battery comprising the electrode for the 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], which includes a negative electrode and a positive electrode, and 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 collectively connected to the positive electrode terminal and constitute each layer. A lithium ion secondary battery in which the ends of the current collectors of each of the negative electrodes are grouped and connected to the negative electrode terminal, and the positive electrode or at least one of the negative electrodes is composed of the electrodes for the lithium ion secondary battery. The lithium ion secondary battery according to the above [5] or [6], wherein the inclined portion is provided on the end 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 the occurrence of powder falling, and a lithium ion secondary battery provided with the electrode.

FIG. 1 is a schematic cross-sectional view of an electrode for a lithium ion secondary battery according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the utilization rate of the electrodes. FIG. 3 is a diagram showing an example of a die head used for coating the composition for the electrode active material layer. FIG. 4 is a diagram for explaining the application of the composition for the electrode active material layer. FIG. 5 is a diagram for explaining the division of the current collector forming the electrode active material layer. FIG. 6 is a schematic cross-sectional view of a modified example of the electrode for a lithium ion secondary battery according to the embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a modified example of the electrode for a lithium ion secondary battery according to the embodiment of the present invention. FIG. 8 is a schematic cross-sectional view of the lithium ion secondary battery according to the embodiment of the present invention.

[Electrodes for lithium-ion secondary batteries]
Hereinafter, the electrode for a lithium ion secondary battery according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of an electrode for a lithium ion secondary battery according to an embodiment of the present invention.
As shown in FIG. 1, the electrode 10 for a lithium ion secondary battery according to the embodiment of the present invention is provided on both sides of the current collector 20 and the current collector, and contains an electrode active material and a binder. 30 and. Then, at least a part of the end portion 31 of the electrode active material layer 30 is composed of 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 of the inclined portion 31 (W). ) 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, and more preferably 20 to 90 μm per side 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 inclined portion of 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. When 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 and the electrode active material layer facing the inclined portion overlap with each other becomes large, and the portion not used as an electrode may become large. As a result, the utilization rate of the electrodes may decrease. For example, in the case of a set of the negative electrode 10A and the positive electrode 10B shown in FIG. 2, 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 are not formed in the region 33A of the negative electrode active material layer 30A. 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 often 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, so that the utilization rate of the electrode becomes low. Therefore, as the width (W) of the inclined portion 31 in the electrode active material layer 30 increases, the region 33A also increases, so that the utilization rate of the electrode decreases. From the viewpoint of the utilization rate of the electrodes, the width (W) of the inclined portion 31 is preferably 990 μm or less, more preferably 950 μm or less, and further 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 dropping of the electrode active material may occur at the inclined portion 31 of the electrode active material layer. From the viewpoint of powder removal 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 the material constituting the current collector 20 include conductive metals 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 the thickness thereof 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, the current collector can be easily handled and the decrease in energy density can be suppressed.

(Electrode active material layer)
The electrode active material layer 30 contains 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 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, as the positive electrode active material, olivine-type lithium iron phosphate (LiFePO ₄ ) or the like may be used. Further, as the positive electrode active material, a material using a plurality of metals other than lithium may be used, and NCM (nickel cobalt manganese) oxide, NCA (nickel cobalt aluminum) oxide, etc., which are called ternary oxides, may be used. You may use it. As the positive electrode active material, these substances may be used alone or in combination of two or more.

<Negative electrode active material>
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, lithium and the like. Among these, carbon materials are preferable, and graphite is preferable. More preferred. As the negative electrode active material, one of the above substances may be used alone, or two or more of them may be used in combination.

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

<Contents 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 90 to 90 to 99% by mass based on the total amount of the electrode active material layer. 98% by mass is particularly preferable.

<Binder>
Specific examples of the binder include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), fluorine-containing resin such as polytetrafluoroethylene (PTFE), polymethyl acrylate (PMA), and the like. Acrylic resin such as polymethylmethacrylate (PMMA), polyvinylidene acetate, polyimide (PI), polyamide (PA), polyvinylidene chloride (PVC), polyethernitrile (PEN), polyethylene (PE), polypropylene (PP), poly Examples thereof include acrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene butadiene rubber (SBR), poly (meth) acrylic acid, carboxymethyl cellulose (CMC), 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 binder in the electrode active material layer 30 is preferably 0.5% by mass or more, preferably 0.5 to 20% by mass, based on the total amount of the electrode active material layer, from the viewpoint of powder removal of the electrode active material. It is more preferable, and 1.0 to 10% by mass is further preferable. By setting the content of the binder to the above lower limit value or more, it becomes difficult for the electrode active material, the conductive auxiliary agent, and the like to fall off.

<Conductive aid>
The electrode active material layer 30 preferably further contains a conductive auxiliary agent. As the conductive auxiliary agent, 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 nanotubes, and rod-shaped carbon. The conductive auxiliary agent may be used alone or in combination of two or more. When the conductive auxiliary material is contained in the electrode active material layer 30, the content of the conductive auxiliary agent is preferably 0.5 to 15% by mass based on the total amount of the electrode active material layer, and is preferably 1 to 10% by mass. Is more preferable. When the content of the conductive auxiliary agent is within the above range, it is possible to suppress a decrease in output performance due to an increase in battery resistance, and it is possible to prevent the conductive auxiliary agent from absorbing the binder and causing powder to fall off. In addition, since the electrode active material layer 30 further contains a conductive auxiliary agent, powder falling from the electrode active material layer 30 is likely to occur. However, in the electrode 10 for a lithium ion secondary battery according to the embodiment of the present invention, by adjusting the value of the edge factor (W / T) within the above range as described above, powder falling is less likely to occur.

The electrode active material layer 30 may contain an optional component 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, the total content of the electrode active material, the conductive auxiliary agent, and the binder in the total mass of the electrode active material layer is preferably 90% by mass or more, and more preferably 95% by mass or more.

[Manufacturing method of electrodes for lithium-ion secondary batteries]
The electrode for a lithium ion secondary battery in one embodiment of the present invention can be manufactured by, for example, the following manufacturing method. In an example of the method for manufacturing an electrode for a lithium ion secondary battery according to an embodiment of the present invention, first, a composition for an electrode active material layer is applied onto a current collector to form an electrode active material layer on the current collector. To do. Then, the current collector on which the electrode active material layer is formed is pressure-pressed and divided to manufacture an electrode for a lithium ion secondary battery.

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

(Electrode active material layer forming process)
In the electrode active material layer forming step, first, a composition for an electrode active material layer containing an electrode active material, a binder, and a solvent is prepared. Examples of the solvent used in the composition for the 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 the electrode active material layer may contain other components such as a conductive additive to be blended if necessary. Details of the electrode active material, the binder, etc. are as described above. The composition for the electrode active material layer is in the state of a slurry.

From the viewpoint that the width (W) of the inclined portion 31 of the electrode active material layer 30 is less than 1000 μm, when the electrode active material is a positive electrode active material, the viscosity of the composition for the electrode active material layer is preferably 2500 to 12000 mPa. It is s, more preferably 3000 to 10000 mPa · s. On the other hand, when the electrode active material is a negative electrode active material, the viscosity of the composition for the electrode active material layer is preferably 1600 to 12000 mPa · s, and more preferably 1800 to 10000 mPa · s. The viscosity is a viscosity measured 2 minutes after the start of rotation of the spindle under the conditions of 60 rpm and 25 ° C. with a B-type viscometer.

The electrode active material layer can be formed, for example, by applying the composition for an electrode active material layer on a current collector and drying it by a known coating method. Examples of the method of applying the composition for the electrode active material layer on the current collector sheet include 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. Examples include the method, the doctor blade method, the bar coating method, the gravure coating method, and the screen printing method. Among these coating methods, the die coating method is preferable from the viewpoint that an inclined portion can be easily formed at the end portion of the electrode active material layer. Hereinafter, the application of the composition for the electrode active material layer onto the current collector will be described with reference to FIGS. 3 and 4 by taking the die coating method as an example.

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

As shown in FIG. 4, the composition for the electrode active material layer is discharged from the die head 50 onto the current collector 120 moving in the direction of reference numeral 121. As a result, the electrode active material layer 130 can be formed on the current collector 120. In one embodiment of the present invention, the side surface 131 of the electrode active material layer 130 can be tilted by adjusting the viscosity of the composition for the 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 the 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 dryer (not shown). As a result, 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, but 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 also formed on the surface opposite to the current collector 120 in the same manner.

(Pressure press process)
The current collector 120 having the electrode active material layer 130 formed on the electrode active material layer 130 is preferably pressure-pressed. The electrode density can be increased by pressure pressing. 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 the current collector does not wrinkle or the like and the desired electrode density can be reached. In the case of a roll press, for example, the pressure of the pressure press is a linear pressure, preferably 100 to 2000 kN / m, and more preferably 200 to 1000 kN / m.

(Split)
The current collector 120 forming the electrode active material layer 130 is cut, for example, along the dotted line of reference numeral 150 in FIG. 5, and is divided into a plurality of electrodes for a lithium ion secondary battery. As a result, 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 deformed as follows.
(Modification example 1)
The electrode 10 for a lithium ion secondary battery in the above embodiment of the present invention has an electrode active material layer 30 formed on both surfaces of the current collector 20. However, as in the lithium ion secondary battery electrode 10C shown in FIG. 6, the electrode active material layer 30 may be formed only on one surface of the current collector 20.

(Modification 2)
Further, as in 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. As a result, a short circuit between the electrodes can be prevented more reliably. In addition, powder falling from the inclined portion 31 of the electrode active material layer 30 can be further suppressed.

The insulating resin layer 40 may include a resin component as long as it can secure insulation at the end of the electrode. Examples of the resin component include fluorine-containing resins such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and polytetrafluoroethylene (PTFE), and polymethyl acrylate (PMA). Acrylic resin such as polymethylmethacrylate (PMMA), polyvinylidene acetate, polyimide (PI), polyamide (PA), polyvinylidene chloride (PVC), polyethernitrile (PEN), polyethylene (PE), polypropylene (PP), poly Examples thereof include acrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene butadiene rubber (SBR), poly (meth) acrylic acid, carboxymethyl cellulose (CMC), 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. These polymers may be used alone or may be used as a multilayer body by superimposing these polymers. Further, 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, the rigidity of the insulating layer can usually be increased and the drying shrinkage can be reduced. Examples of the material of such inorganic particles include aluminum oxide (alumina), hydrate of aluminum oxide (bemite (AlOOH)), gibsite (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, covalent crystals such as silicon and diamond. Examples thereof include particles, sparingly soluble ion 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 electrolytic solution and potential stability, and among them, titanium oxide and aluminum oxide are preferable from the viewpoint of low water absorption and excellent heat resistance (for example, resistance to high temperatures of 180 ° C. or higher). , Aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferable, aluminum oxide, aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferable, and aluminum oxide is particularly preferable.
As the organic particles, polymer particles are usually used. By adjusting the type and amount of functional groups on the surface of the organic particles, the affinity for water can be controlled, and the amount of water contained in the insulating layer can be controlled. In addition, organic particles are usually excellent in that metal ions are less eluted. 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 kinds of polymer compounds.
One of these inorganic particles and organic particles may be used alone, or two or more of them may be mixed and used.

The electrode for a lithium ion secondary battery and a modification thereof in one embodiment of the present invention 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 and a modification thereof in one embodiment of the present invention do not limit the electrode for a lithium ion secondary battery of the present invention.

[Lithium secondary ion battery]
A lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIG. FIG. 8 is a schematic cross-sectional view of the lithium ion secondary battery according to the embodiment of the present invention. As shown in FIG. 8, the lithium ion secondary battery 1 according to the embodiment of the present invention includes the electrode 10 for the lithium ion secondary battery according to the embodiment of the present invention. From the viewpoint that the utilization rate of the electrodes can be increased and the occurrence of powder falling can be suppressed, the lithium ion secondary battery 1 according to the embodiment of the present invention includes a negative electrode 10 and a positive electrode 10, and includes a positive electrode 10 and a negative electrode. It is preferable that both are the electrodes 10 for a lithium ion secondary battery in one embodiment of the present invention.

Further, in the lithium ion secondary battery 1 according to the embodiment of the present invention, it is preferable that the positive electrode 10 and the negative electrode 10 are alternately arranged so that a plurality of layers are provided. Further, the ends of the current collectors 20 of each of the positive electrodes 10 constituting each layer are grouped together and connected to the positive electrode terminal 2, and the ends of the current collectors 20 of each of the negative electrodes 10 constituting each layer are grouped together to form the negative electrode terminal 3. It is preferable to be connected to. Then, at least one of the positive electrode 10 and the negative electrode 10 is composed of the electrode 10 for the lithium ion secondary battery according to the embodiment of the present invention, and the inclined portion 31 is provided on the bundled end side of the current collector 20. Is preferable. As a result, it is possible to obtain a lithium ion secondary battery provided with an electrode for a lithium ion secondary battery, which can increase the utilization rate of the electrode and suppress the occurrence of powder falling.

In the lithium ion secondary battery 1 according to the embodiment of the present invention, the laminated electrodes 10 are preferably housed in the housings 6 and 7. The housings 6 and 7 may be of a square type, a cylindrical type, a laminated type, or the like.

The lithium ion secondary battery 1 in one embodiment of the present invention preferably further includes a separator 8 arranged 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 the electrolyte 9 described later.

Examples of the separator 8 include a porous polymer film, a non-woven fabric, and glass fiber, and among these, a porous polymer film is preferable. Examples of the porous polymer film include an olefin-based porous film.

The lithium ion secondary battery of the present invention includes an 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, for example, after the laminated electrodes 10 are housed in the housings 6 and 7.

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, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2. Includes polar solvents such as −diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 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 , LiPF ₆ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , Examples thereof include salts containing lithium such as LiN (COCF ₃ ) _2, LiN (COCF ₂ CF ₃ ) ₂ , and lithium bisoxalate boronate (LiB (C ₂ O ₄ ) ₂ ). In addition, a complex such as an organic acid lithium salt-boron trifluoride complex and a complex hydride such as LiBH ₄ can be mentioned. These salts or complexes may be used alone or as a mixture of two or more. Further, the electrolyte 9 may be a gel-like electrolyte in which the above-mentioned electrolyte solution further contains a polymer compound. Examples of the polymer compound include a fluoropolymer such as polyvinylidene fluoride and a polyacrylic polymer such as methyl poly (meth) acrylate. The gel electrolyte may be used as a separator.

The lithium ion secondary battery according to the above embodiment of the present invention can be modified as follows.
(Modification example 1)
The lithium ion secondary battery according to the embodiment of the present invention includes the electrode 10 for the lithium ion secondary battery of the embodiment of the present invention as the positive electrode and the negative electrode, but the positive electrode and the negative electrode of the embodiment of the present invention. Modifications 10C and 10D of the electrodes for the lithium ion secondary battery may be provided.

The lithium ion secondary battery and its modifications according to the 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 and its modifications in one embodiment of the present invention do not limit the lithium ion secondary battery of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

The obtained electrode for a lithium ion secondary battery was evaluated by the following evaluation method.

(Powder drop)
In the production of electrodes for lithium-ion secondary batteries, the sliding of the electrode active material from the electrode end when the current collector coated with the slurry for the electrode active material layer on both sides was pressure-pressed by a roller was investigated, and the following criteria were used. Evaluated in.
◯: Electrode active material did not slip ×: Electrode active material slipped (utilization rate)
The length of the surplus portion is the sum (W1 + W2) of the width (W1) of the inclined portion of the positive electrode active material layer facing each other and the width (W2) of the inclined portion of the negative electrode active material layer in which the positive electrode and the negative electrode are laminated. The evaluation was based on the following criteria.
◯: The length of the surplus portion is less than 1500 μm ×: The length of the surplus portion is 15,000 μm or more

[Example 1]
(Preparation of positive electrode)
NCA-based oxide (average particle size 10 μm) as a positive electrode active material, acetylene black as a conductive auxiliary agent, polyvinylidene fluoride (PVdF) as a binder for electrodes, and N-methylpyrrolidone (NMP) as a solvent are mixed. A slurry for the 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. The PVdF content was 1.6% by mass, and the NMP content was 35% by mass. The solid content concentration of this slurry for the positive electrode active material layer was 67.2% by mass. The viscosity of the slurry for the positive electrode active material layer was 9060 mPa · s. The viscosity was measured with a B-type viscometer under the conditions of 60 rpm and 25 ° C., 2 minutes after the start of rotation of the spindle. This slurry for the positive electrode active material layer is applied to both sides of an aluminum foil having a thickness of 15 μm as a positive electrode current collector using a die coater, and after pre-drying, vacuum-dried at 120 ° C. to obtain the positive electrode active material layer. Formed on aluminum foil.

Then, the aluminum foil on which the electrode active material layer was formed was pressure-pressed by a roller at a linear pressure of 400 kN / m and further punched into an electrode size of 100 mm × 200 mm square to obtain a positive electrode having electrode active materials on both sides. Of the dimensions, the area coated with the positive electrode polar active material was 100 mm × 180 mm. The thickness of the positive electrode active material layer formed on both sides was 50 μm per side.

[Examples 2 to 4 and Comparative Example 1]
In Examples 2 to 4 and Comparative Example 1, the viscosity of the slurry for the positive electrode active material layer was changed as shown in Table 1. As a result, 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 produced. did.

[Example 5]
(Preparation of negative electrode)
Graphite (average particle size 10 μm) as the negative electrode active material, sodium salt of carboxymethyl cellulose (CMC) as the negative electrode binder, acetylene black as the conductive auxiliary agent, styrene butadiene rubber (SBR) as the negative electrode binder, and Water was mixed as a solvent to obtain a slurry for the negative electrode active material layer. The content of the negative electrode active material in the slurry for the negative electrode active material layer is 50% by mass, the content of the conductive auxiliary agent is 0.5% by mass, and the content of the binder is 1.5% by mass. , The content of the solvent was 48% by mass. The solid content concentration of this 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 5460 mPa · s. The viscosity was measured with a B-type viscometer under the conditions of 60 rpm and 25 ° C., 2 minutes after the start of rotation of the spindle. This slurry for the negative electrode active material layer is applied to both sides of a copper foil having a thickness of 12 μm as a negative electrode current collector using a die coater, and after pre-drying, vacuum-dried at 100 ° C. to obtain the negative electrode active material layer. Formed on copper foil.

After that, the negative electrode current collector coated with the slurry for the negative electrode active material layer on both sides is pressure-pressed by a roller at a linear pressure of 300 kN / m, and further punched into an electrode size of 110 mm × 210 mm square, and the negative electrode active material is punched on both sides. It was a negative electrode having a layer. Of the dimensions, the area to which the negative electrode active material was applied was 110 mm × 190 mm. The thickness of the negative electrode active material layer formed on both sides was 50 μm per side.

[Examples 6 to 8 and Comparative Example 1]
In Examples 6 to 8 and Comparative Example 2, the viscosity of the slurry for the negative electrode active material layer was changed as shown in Table 2. As a result, 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 produced. did.

[Examples 9 to 15 and Reference Examples 1 and 2]
As shown in Table 3, the viscosities of the slurry for the positive electrode active material layer were changed to prepare the positive electrodes of Examples 9 to 15 and Reference Examples 1 and 2. Further, as shown in Table 3, the negative electrodes of Examples 9 to 15 and Reference Examples 1 and 2 were prepared by changing the viscosity of the slurry for the negative electrode active material layer. Then, the positive electrode and the negative electrode of each Example and the reference example were combined to form a set of the positive electrode and the negative electrode for utilization rate evaluation.

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

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 the width (W) of the inclined portion to be less than 1000 μm, the electrode powder can be removed. It turned out to be suppressed. On the other hand, in Comparative Examples 1 and 2, since the edge factor was smaller than 3, powder falling occurred.
As shown in Examples 9 to 14 above, the utilization rate of the electrode is increased 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. 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 has dropped.

1 Lithium-ion secondary battery 2 Positive electrode terminal 3 Negative electrode terminal 6, 7 Housing 8 Separator 9 Electrolyte 10, 10A-10D Electrode for lithium-ion secondary battery (positive electrode, negative electrode)
20, 20A, 20B, 120 Current collectors 30, 30A, 30B, 130 Electrode active material layer 31 End (inclined part)
32 Central part 50 Die head 51 Discharge port 131 Side surface of electrode active material layer

Claims (7)

A current collector, an electrode active material provided on the current collector, and an electrode active material layer containing a binder are provided.
At least a part of the end portion of the electrode active material layer is composed of an inclined portion whose thickness decreases as the distance from the central portion 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 Electrodes for lithium ion secondary batteries that are 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 auxiliary agent. The electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the content of the binder in the electrode active material layer is 1.5% by mass or more. An insulating resin layer provided on the current collector is provided.
The electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the insulating resin layer is arranged so as to be adjacent to the inclined portion of the electrode active material layer and to cover the inclined portion. .. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of claims 1 to 4. It has 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 electrodes for the lithium ion secondary battery. 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 collectively connected to the positive electrode terminal, and each of the negative electrodes constituting each layer is connected. A lithium-ion secondary battery in which the ends of the current collector are grouped together and connected to the negative electrode terminal.
At least one of the positive electrode and the negative electrode is composed of the electrode for a lithium ion secondary battery.
The lithium ion secondary battery according to claim 5 or 6, wherein the inclined portion is provided on the end side of the current collector.

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