JP6609946B2 - Lithium ion secondary battery electrode, method for producing the same, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to an electrode for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery.

  Lithium-ion secondary batteries, which are already widely used as power sources for mobile devices such as notebook personal computers and mobile phones, have recently attracted attention in new fields such as being installed in hybrid vehicles and electric vehicles (EV). ing. In particular, in recent years, the number of hybrid vehicles has increased and the market has grown, and various performances are also required for lithium ion secondary batteries according to their characteristics. For example, in a micro hybrid (μHEV) battery, high-speed charge / discharge performance, that is, high output density is particularly emphasized in order to efficiently recover regenerative energy in addition to cost competitiveness.

A lithium ion secondary battery is generally composed of a positive electrode in which a positive electrode active material layer containing a lithium-containing metal oxide capable of reversibly occluding and releasing lithium ions is formed on a current collector, and a negative electrode active material layer containing carbon or a silicon material And a negative electrode formed on a current collector facing each other through a separator which is an insulator, and stored in a battery case such as a metal can or a laminate pack, and there are several types of carbonates A non-aqueous electrolyte solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed organic solvent is added and impregnated.

The method of housing the electrode and separator in the battery outer material varies depending on the shape of the outer material. For example, a method of alternately stacking electrodes and separators punched out to a certain standard, or winding electrodes and separators alternately There are ways to do this.
Conventionally, when manufacturing an electrode of a lithium ion secondary battery, an active material slurry containing an active material, a binder, a conductive auxiliary agent, and the like is prepared and applied to the surface of a current collector uniformly. A material layer is formed.

  In a battery including an electrode manufactured by such a conventional method, when charging / discharging is performed with an output not so high, the charging / discharging reaction can proceed uniformly even in an active material layer having a uniform composition. However, for charge / discharge reactions at a higher output as required for in-vehicle batteries, an active material layer having a uniform composition prepared by a conventional method is used to collect the current from the current collector. Therefore, there is a problem that the electron conductivity and the conduction of lithium ions from the electrolytic solution to the active material layer are not compatible, and sufficient charge / discharge reaction does not proceed.

  From the above viewpoints, a charge / discharge reaction can proceed sufficiently even when the active material layer having a thinner film thickness has a higher output. However, in the electrode for a lithium ion secondary battery housed in the battery pack, the electrolyte solution is mainly impregnated from the end of the electrode, so the electrode thickness is reduced in order to increase the battery capacity. As a result, the electronic conductivity from the current collector to the active material is not compatible with the conduction of lithium ions from the electrolytic solution to the active material layer.

  In order to improve the electron conductivity from the current collector to the active material, it is effective to increase the density of the active material layer and increase the number of contacts between the current collector and the active material or conductive auxiliary agent. If the pore volume of the electrolyte is reduced, it becomes difficult for the electrolytic solution to impregnate the active material layer. On the other hand, if the hole volume is sufficiently secured, not only the electron conductivity of the active material layer is deteriorated, but also the adhesiveness to the current collector is lowered and the cycle characteristics are lowered. Density decreases.

  Therefore, for example, in Patent Document 1, in a non-aqueous electrolyte secondary battery including a positive and negative electrode plate in which an active material mixture is applied to a current collector, at least one of the positive and negative electrode plates is an active material mixture. A density changing portion is provided in which the density changes at a substantially constant rate from one side in the plane direction to the other side. For this reason, an active material ratio becomes large in a high-density part, and an energy density can be improved, and the space | gap which a nonaqueous electrolyte solution impregnates in a low-density part is ensured, and output characteristics can be improved.

Further, in Patent Document 2, the surface of the active material layer after pressing is formed with a fine channel using a sword mountain having a base array of needles, so that the film thickness is thinner than other portions in the active material layer. The part improves lithium ion conductivity and improves output characteristics.
For example, in Patent Document 3, an electrode slurry to which a pore forming material larger than the active material average particle size is added together with an active material and a binder is applied to a current collector and compressed, and then the pore forming material is removed by heating. Thus, a void larger than the average particle size of the active material is formed in the active material layer, and high output characteristics are secured by storing the electrolytic solution.

JP2009-259502A JP2007-042386 JP 2011-204571 A

However, in Patent Document 1, the impregnation property of the electrolyte solution inside and outside the wound electrode of the wound electrode has been studied, but the electrolyte solution impregnation property in the short side direction of the electrode has not been studied, and the output The characteristics are not sufficiently secured. Further, in Patent Document 2, although the channels are uniformly formed on the entire electrode, the connection between the channels in the plane direction is insufficient. Therefore, it may take time to fill the electrolyte solution up to the center of the electrode. Similarly, in Patent Document 3, the connection of pores in the surface direction is weak, and there is a possibility that the electrolyte is insufficient at the center of the electrode when an extreme output of current is performed.
Accordingly, the present invention provides a lithium ion secondary battery that is required to have a high output and can improve the high output characteristics by sufficiently ensuring the lithium ion conductivity by improving the impregnation of the electrolyte. It aims at providing the electrode for secondary batteries, and a lithium ion secondary battery.

  According to one aspect of the present invention, a first active material that is a large particle size component, a second active material that is a small particle size component having a smaller particle size than the large particle size component, a binder, and a conductive auxiliary agent. A large particle size region in which an active material layer is stacked on a current collector, and the active material layer has a weight ratio of the first active material to the second active material of 30:70 to 100: 0 And a small particle size region in which the content of the first active material is smaller than that of the large particle size region, and the large particle size region is closer to an end portion in contact with the non-aqueous electrolyte as an electrode. Provided is an electrode for a lithium ion secondary battery, characterized by being formed in a region on a current collector.

According to another aspect of the present invention, a first active material that is a large particle size component, a second active material that is a small particle size component having a smaller particle size than the large particle size component, a binder, and a conductive assistant. A first electrode slurry in which a weight ratio of the first active material to the second active material is 30:70 or more and 100: 0 or less, and a content of the first active material is the first active material Applying a second electrode slurry less than one electrode slurry onto a current collector such that the first electrode slurry is closer to an end in contact with the non-aqueous electrolyte as an electrode; And a step of roll-pressing a current collector coated with the first electrode slurry and the second electrode slurry. A method for producing an electrode for a lithium ion secondary battery is provided. .
According to another aspect of the present invention, there is provided a lithium ion secondary battery comprising the lithium ion secondary battery electrode of the above aspect as at least one of a positive electrode and a negative electrode. The

  According to one embodiment of the present invention, the active material layer includes a first active material that is a large particle size component and a second active material that is a small particle size component having a smaller particle size than the large particle size component. , A large particle size region in which the weight ratio of the first active material to the second active material is 30:70 or more and 100: 0 or less, and the content of the first active material is smaller than the large particle size region Including the particle size region, the large particle size region is formed in the region on the current collector near the end in contact with the non-aqueous electrolyte as an electrode, thereby improving the permeability of the non-aqueous electrolyte. A lithium ion secondary battery electrode capable of sufficiently ensuring lithium ion conductivity, and improving the output characteristics of the lithium ion secondary battery having the lithium ion secondary battery electrode Can do.

It is a plane schematic diagram which shows an example of the active material layer in the electrode for lithium ion secondary batteries in one Embodiment of this invention. It is a schematic block diagram which shows an example of the electrode for lithium ion secondary batteries in one Embodiment of this invention. It is a schematic block diagram which shows the other example of the electrode for lithium ion secondary batteries in one Embodiment of this invention. It is a cross-sectional schematic diagram which shows an example of the cylindrical lithium ion secondary battery to which the electrode for lithium ion secondary batteries in one Embodiment of this invention is applied. It is an example of the discharge capacity maintenance factor of the secondary battery which applied the electrode for lithium ion secondary batteries in one embodiment of the present invention.

Below, the electrode for lithium ion secondary batteries which concerns on one Embodiment of this invention is demonstrated.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, that one or more embodiments may be practiced without such specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
Further, the electrode for a lithium ion secondary battery in one embodiment of the present invention is not limited to the embodiment described below, and modifications such as design changes can be added based on the knowledge of those skilled in the art. Thus, embodiments to which such modifications are added can also be included in the scope of the embodiments of the present invention.

  As a result of intensive studies, the present inventor includes a first active material that is a large particle size component, and a second active material that is a small particle size component having a smaller particle size than the large particle size component, A large particle size region in which the weight ratio of the first active material to the second active material is 30:70 or more and 100: 0 or less, and a small particle in which the content of the first active material is smaller than the large particle size region For the lithium ion secondary battery by forming an active material layer including a diameter region and forming a large particle size region in a region on the current collector that is close to the end in contact with the non-aqueous electrolyte as an electrode. It has been found that the permeability of the non-aqueous electrolyte to the electrode can be improved.

FIG. 1 is a schematic plan view of an active material layer 1 of a secondary battery electrode according to an embodiment of the present invention.
The active material layer 1 includes a first active material 2 which is a large particle size component, a second active material 3 which is a small particle size component whose particle size is smaller than the particle size of the first active material 2, and is not illustrated. And a mixture of a binder and a conductive aid. The active material layer 1 includes a large particle size region 4 in which a weight ratio of the first active material 2 that is a large particle size component and the second active material 3 that is a small particle size component is defined, and a large particle size region 4. A small particle size region 5 having a smaller content of the first active material 2 than the particle size region 4 is formed.

The weight ratio of the first active material 2 and the second active material 3 in the large particle size region 4 is 30:70 or more and 100: 0 or less in one embodiment of the present invention, and in other embodiments, 60:40 or more and 100: 0 or less. That is, the active material layer 1 does not necessarily include both the first active material 2 and the second active material 3, and does not include the second active material 3 that is a small particle size component. Also good.
If the first active material 2 is less than 30 wt% in the large particle size region 4, voids are not sufficiently formed in the large particle size region 4, and the effects of the invention cannot be sufficiently obtained. In the embodiment, the first active material 2 is 30 wt% or more in the large particle size region 4.

  In one embodiment of the present invention, the average particle size of the first active material 2 is 1.2 times or more and 10 times or less than the average particle size of the second active material 3. The average particle diameter of the active material 2 is not less than 2 times and not more than 5 times the average particle diameter of the second active material 3. When the average particle size of the first active material 2 is smaller than 1.2 times the average particle size of the second active material 3, the average particle size of the first active material 2 and the second active material 3 If the difference from the average particle diameter is too small, the voids are not sufficiently formed, and the effects of the invention cannot be sufficiently obtained. On the other hand, when the average particle size of the first active material 2 is larger than 10 times the average particle size of the second active material 3, the first active material 2 and the second active material 3 are active. In an embodiment of the present invention, the average particle diameter of the first active material 2 is the second because the difference in the diffusibility of electrons and lithium ions in the material is too great and the output characteristics may be degraded. The average particle size of the active material 3 is 10 times or less.

  The first active material 2 only needs to be capable of occluding and releasing lithium ions, and a known active material for a lithium ion secondary battery can be used, but it is crushed compared to the second active material 3. A hard active material is preferred. For example, a combination in which the first active material 2 is a single particle and the second active material 3 is an aggregate can be given. In the case where the first active material 2 is more easily crushed than the second active material 3, the first active material 2 is the second active material in the press step of roll-pressing a coating film coated and dried with an electrode slurry described later. The active material 3 is pulverized before the active material 3, and when it is molded to a predetermined electrode density, a sufficient gap cannot be secured and impregnation with the electrolytic solution is not promoted, so that output characteristics may be deteriorated. . Therefore, in one embodiment of the present invention, the first active material 2 is formed so as to be harder to crush than the second active material 3.

  The average particle diameter of the first active material 2 is 5 μm or more and 20 μm or less in an embodiment of the present invention. When the average particle diameter of the first active material 2 is smaller than 5 μm, there is a possibility that sufficient voids cannot be secured between the active material particles and the permeability of the electrolytic solution is lowered. When the average particle diameter of the first active material 2 is larger than 20 μm, the diffusibility of electrons and lithium ions in the active material may be lowered, and output characteristics may be lowered.

  When a positive electrode active material is used as the first active material 2 and the second active material 3, a known positive electrode active material for a lithium ion secondary battery can be used. For example, lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide, lithium iron oxide and lithium nickel manganese oxide, lithium nickel cobalt oxide, lithium nickel manganese cobalt oxide, lithium transition metal phosphate compound, etc. are used. be able to. Note that a plurality of the above active materials may be mixed and used as the positive electrode active material.

  When a negative electrode active material is used as the first active material 2 and the second active material 3, a known negative electrode active material for a lithium ion secondary battery can be used. For example, carbon materials such as graphite-based carbon materials, hard carbon, soft carbon, activated carbon, lithium metal oxides such as lithium titanium oxide, Li alloy metals such as silicon and tin, and the like can be used. Note that a plurality of the above active materials may be mixed and used as the negative electrode active material.

FIG. 2 is an example of a side view showing a schematic configuration of an electrode 10 for a lithium ion secondary battery having the active material layer 1 shown in FIG.
For example, when the lithium ion secondary battery electrode 10 is applied to a cylindrical lithium ion secondary battery 30 shown in FIG. 4 to be described later, the direction in which the current collector 6 extends in FIG. 2, that is, the vertical direction in FIG. Is the longitudinal direction of the cylindrical lithium ion secondary battery 30 shown in FIG. 4, and the electrode 10 for the lithium ion secondary battery is as shown in the positive electrode 10a and the negative electrode 10b which are electrodes for the lithium ion secondary battery in FIG. The cylindrical lithium ion secondary battery 30 has a long shape along the longitudinal direction. Hereinafter, the direction in which the current collector 6 extends (the vertical direction in FIG. 2) is referred to as the longitudinal direction of the electrode 10 for a lithium ion secondary battery.

  In FIG. 2, the active material layer 1 of the lithium ion secondary battery electrode 10 formed on the current collector 6 includes a large particle size region 4 and a small particle size region 5. The active material layer 1 has a large particle size region 4 formed in regions on both ends in the longitudinal direction of the lithium ion secondary battery electrode 10 and a small particle size region 5 formed in the longitudinal direction of the lithium ion secondary battery electrode 10. The large particle size region 4 and the small particle size region 5 may be arranged in any manner as long as it is formed between the two large particle size regions 4 arranged on both ends.

  For example, as shown in FIG. 2, the large particle size region 4 may be formed only in the regions on both ends in the longitudinal direction of the lithium ion secondary battery electrode 10, and as shown in FIG. The large particle size region 4 may be formed in a region on both ends in the longitudinal direction of the secondary battery electrode 10 and a region in the vicinity of the central portion in the longitudinal direction, and the large particle size region 4 has a plurality of intervals in the longitudinal direction. It may be arranged in a space.

  When the large particle size region 4 is not formed in the region on both ends in the longitudinal direction of the electrode 10 for the lithium ion secondary battery and the small particle region 5 is formed in the region on both ends in the longitudinal direction, Insufficient impregnation of the electrolyte into the active material layer 1 from both ends in the direction, the electrolyte is insufficient in the vicinity of the center in the longitudinal direction of the electrode 10 for the lithium ion secondary battery, and sufficient lithium ion conductivity is not ensured, Output characteristics may deteriorate.

  In one embodiment of the present invention, the large particle size region 4 has a weight ratio of the first active material 2 and the second active material 3 of 30:70 or more and 100: 0 or less, and the small particle size region 5 is As long as the content of the first active material 2 is smaller than that of the large particle size region 4, the composition is not particularly limited. If the ratio of the first active material 2 is too small in the large particle size region 4, there is a possibility that voids are not sufficiently formed and impregnation with the electrolytic solution is not promoted.

  The surface area of the large particle size region 4 constituting the active material layer 1 is not particularly limited as long as it is smaller than the surface area of the small particle size region 5. When the surface area of the large particle size region 4 is equal to or larger than the surface area of the small particle size region 5, there is less harmful effect if the basis weight of the active material layer 1 is a certain level or more. When the basis weight is small, the active material, the conductive auxiliary agent and the binder are likely to be unevenly distributed, so that sufficient electronic conductivity may not be ensured.

  The film thickness of the active material layer 1 is 10 μm or more and 100 μm or less in one embodiment of the present invention, and 10 μm or more and 50 μm or less in another embodiment. When the thickness of the active material layer 1 is smaller than 10 μm, the basis weight of the active material layer 1 becomes too small, which is disadvantageous in terms of energy density, and the first active material which is a large particle size component in the pressing process Since 2 becomes easy to be crushed, it becomes impossible to ensure a sufficient space for the electrolyte to penetrate. Moreover, when larger than 100 micrometers, the impregnation property of electrolyte solution becomes bad in the thickness direction of the active material layer 1, and lithium ion conductivity falls.

  As the current collector 6, a material conventionally used as a current collector material for a secondary battery may be appropriately employed. For example, aluminum, nickel, copper, iron, stainless steel (SUS), titanium, or the like can be used. What material should be adopted as the current collector 6 may be selected in consideration of the battery operating potential and the electronic conductivity applied to the current collector 6. The general thickness of the current collector 6 is 8 μm or more and 30 μm or less. If the thickness of the current collector 6 is less than 8 μm, the strength of the current collector is low and handling becomes difficult, which may increase the manufacturing cost. If it is thicker than 30 μm, the electrode volume increases and the capacity per battery volume decreases.

The electrode 10 for lithium ion secondary batteries of this invention may contain the conductive support agent. As the conductive aid, carbon black, natural graphite, artificial graphite, metal oxides such as titanium oxide and ruthenium oxide, metal fibers, and the like can be used. In one embodiment of the present invention, carbon black having a structure structure is used, and in other embodiments, furnace black, ketjen black, and acetylene black (AB), which are a kind of carbon black, are used. In addition, it is also possible to use a mixed system of carbon black and other conductive assistants such as vapor grown carbon fiber (VGCF) as the conductive assistant.
In one embodiment of the present invention, the content of the conductive assistant is 1% by weight or more and less than 90% by weight with respect to the weight of the active material. If the content of the conductive assistant is less than 1% by weight with respect to the weight of the active material, the conductivity may be insufficient and the electrode resistance may increase, and if it is 90% by weight or more, the amount of the active material is insufficient. As a result, the lithium storage capacity may decrease.

The electrode 10 for lithium ion secondary batteries in one embodiment of the present invention may contain a binder. The binder is not particularly limited as long as the mixture of the active material and the conductive additive can be adhered to the current collector. For example, a fluorine-containing binder such as polyvinylidene fluoride or polytetrafluoroethylene, a synthetic rubber binder, or the like may be used. it can.
The binder contained in the electrode 10 for lithium ion secondary batteries is 3 to 40 weight% with respect to the weight of all active materials in one Embodiment of this invention. When the binder is less than 3% by weight with respect to the total weight of the active material, sufficient binding cannot be achieved, and when the binder is more than 40% by weight, the capacity per electrode volume is greatly reduced. In another embodiment of the present invention, the binder is 3% by weight or more and 25% by weight or less based on the total weight of the active material.

Next, an example of the manufacturing method of the electrode 10 for lithium ion secondary batteries which concerns on one Embodiment of this invention is demonstrated.
The electrode 10 for a lithium ion secondary battery in one embodiment of the present invention includes a first active material 2 that is a large particle size component, a second active material 3 that is a small particle size component, a binder, and a conductive additive. The first electrode slurry in which the weight ratio of the first active material 2 and the second active material 3 is 30:70 or more and 100: 0 or less, similarly, the first active material 2 and the second active material 2 A second electrode slurry containing an active material 3, a binder, and a conductive auxiliary agent, and containing less content of the first active material 2 than the first electrode slurry, is applied onto a current collector, dried, and roll-pressed. Produced.

The composition of the electrode slurry other than the above is not particularly limited, and each of the first active material 2 and the second active material 3 may be composed of one type of active material or a mixture of a plurality of types of active materials. .
That is, the first electrode slurry that becomes the large particle size region 4 only needs to contain the first active material 2, the second active material 3, the binder, and the conductive additive, and the first electrode slurry that becomes the small particle size region 5. 2 electrode slurry should just contain the 1st active material 2, the 2nd active material 3, or the 1st active material 2, the binder, and the conductive support agent. The first active material 2 and the second active material 3 included in the second electrode slurry have the same particle size as the first active material 2 and the second active material 3 included in the first electrode slurry. Any substance may be used. The binder and conductive additive contained in the second electrode slurry may be the same as or different from the binder and conductive aid contained in the first electrode slurry.

In addition, when the first active material 2 and the second active material 3 are composed of a plurality of types of active materials, all of the active materials included in the first active material 2 and the second active material 3 All the active materials included may satisfy the above-described various conditions.
The first electrode slurry and the second electrode slurry are preferably adjusted with the same solvent. The solvent is not particularly limited as long as it can dissolve the binder resin, and organic solvents such as N-methylpyrrolidone and N, N-dimethylformamide and water can be used.

The means for applying the electrode slurry onto the current collector 6 is not particularly limited as long as the first electrode slurry and the second electrode slurry can be simultaneously applied onto the current collector. For example, simultaneous multi-layer coating is possible. A slit die coater or the like can be used.
When the electrode density is adjusted in accordance with the small particle size region 5 by pressing the coating film on which the electrode slurry is applied and dried, voids remain between the active material particles in the large particle size region 4, so that the electrolyte solution is impregnated. Can be encouraged. The means for pressing the active material layer 1 is not particularly limited, and generally used means such as a flat plate press and a roll press can be used.

Next, with reference to FIG. 4, the lithium ion secondary battery which concerns on one Embodiment of this invention is demonstrated.
FIG. 4 is a schematic cross-sectional view showing an example of a cylindrical lithium ion secondary battery 30 to which the electrode 10 for lithium ion secondary batteries according to the present invention is applied.
The cylindrical lithium ion secondary battery 30 to which the present invention is applied has a bottomed cylindrical battery can 11 made of iron and plated with nickel as a battery container. In the battery can 11, a large particle size region 4 is formed on both ends of the current collector 6 in the width direction on the strip-shaped current collector 6, and a small particle size region is provided between the two large particle size regions 4 on both ends. The positive electrode 10a and the negative electrode 10b in which 5 is formed, and the separator 12 are wound and accommodated in a spiral cross section.

  The separator 12 is disposed between the positive electrode 10a and the negative electrode 10b disposed to face each other, and the positive electrode 10a and the negative electrode 10b are electrically insulated by the separator 12. As the separator 12, for example, a microporous film made of polyolefin such as polyethylene or polypropylene, a microporous film made of aromatic polyamide resin, a nonwoven fabric, a porous resin coat containing inorganic ceramic powder, or the like can be used.

  On one end side (upper end side in FIG. 4) of the winding group of the positive electrode 10a, the negative electrode 10b, and the separator 12, a ribbon-shaped aluminum positive electrode tab terminal 13 having one end fixed to the positive electrode current collector 6a is led out. . The other end of the positive electrode tab terminal 13 is ultrasonically welded to the lower surface of a disk-shaped upper lid 14 that is disposed on the upper portion of the battery can 11 and serves as a positive electrode external terminal. On the other hand, a ribbon-like nickel negative electrode tab terminal 15 having one end fixed to the negative electrode current collector 6b is led out to the other end side (the lower end side in FIG. 4) of the wound group. The other end of the negative electrode tab terminal 15 is joined to the inner bottom surface of the battery can 11 by resistance welding. That is, the positive electrode tab terminal 13 and the negative electrode tab terminal 15 are led out from the opposite ends of the wound group, respectively. Although not shown, resin insulating plates are arranged on both the upper and lower sides of the wound group, respectively, and an insulating coating is also applied to the entire outer peripheral surface of the wound group.

Grooving is applied to the upper part of the battery can 11. The upper lid 14 is caulked and fixed to the upper portion of the battery can 11 via a gasket 16 designed to fit into the grooving portion. For this reason, the inside of the cylindrical lithium ion secondary battery 30 is sealed.
The gasket 16 is a member for preventing a short circuit and preventing leakage of the electrolytic solution, and an insulating material such as polypropylene can be used.

  In addition, the battery can 11 is filled with a non-aqueous electrolyte composed of a solvent and an electrolyte. Examples of the solvent of the electrolytic solution used for the cylindrical lithium ion secondary battery 30 in the embodiment of the present invention include low-viscosity chain carbonate ester, high dielectric constant cyclic carbonate ester, γ-butyrolactone, 1,2-dimethoxyethane. , Tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, methyl propionate, vinylene carbonate, dimethylformamide, sulfolane, or a mixed solvent thereof can be used. Examples of the low viscosity chain carbonate ester include dimethyl carbonate and diethyl carbonate. Examples of the high dielectric constant cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, and the like.

The electrolyte contained in the electrolytic solution is not particularly limited, and any one of LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiI, and LiAlCl _4, etc. Alternatively, a mixture thereof or the like can be used. A lithium salt obtained by mixing one or more of LiBF ₄ and LiPF ₆ is preferable.
In addition, in the said embodiment, although the case where it had a winding structure as an electrode for lithium ion secondary batteries was demonstrated, even if it has a laminated structure, it is applicable.

  Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to these descriptions. From the description of the invention, other embodiments of the invention will be apparent to persons skilled in the art, along with various variations of the disclosed embodiments. Therefore, it is to be understood that the claims encompass these modifications and embodiments that fall within the scope and spirit of the present invention.

Below, the specific example and comparative example are given and demonstrated about the electrode 10 for lithium ion secondary batteries which concerns on this invention, and its manufacturing method. In addition, this invention is not restrict | limited by the following Example.
<Preparation of positive electrode>
Example 1
A lithium manganese composite oxide having an average particle diameter (D50) of 5 μm as an active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder are mixed at a ratio of 86: 8: 6, respectively. A first positive electrode slurry was obtained by kneading with a planetary mixer and adding an appropriate amount of N-methyl-2-pyrrolidone as a solvent to adjust the viscosity.
A second positive electrode slurry was obtained in the same manner as the first electrode slurry except that a lithium manganese composite oxide having an average particle diameter (D50: median diameter) of 13 μm was used as the active material.
That is, only the active material having an average particle diameter of 5 μm was used for the first positive electrode slurry, and only the active material having an average particle diameter of 13 μm was used for the second positive electrode slurry.

The obtained first positive electrode slurry and second positive electrode slurry were applied to a positive electrode current collector with a die coater capable of simultaneous multi-layer application, and dried to obtain a coating film. The first positive electrode slurry is applied with a width of about 100 mm, and the second positive electrode slurry is applied to both ends in the flow direction of the first positive electrode slurry (that is, about 10 mm at both ends in the longitudinal direction of the positive electrode current collector). Thus, the flow path in the die coater was designed and applied.
The film thickness after drying of the coating film was 50 μm, and an aluminum foil (15 μm thickness) was used as the positive electrode current collector. The obtained positive electrode coating film was roll-pressed so that the electrode density of the coating film formed from the first positive electrode slurry was 2.8 g / cm ³ to complete the positive electrode.

(Example 2)
As an active material of the first positive electrode slurry, a lithium manganese composite oxide having an average particle diameter (D50) of 13 μm and a lithium manganese composite oxide having an average particle diameter (D50) of 5 μm are mixed at a weight ratio of 70:30. The same procedure as in Example 1 was carried out except that was used.
That is, the small particle size region was formed by mixing active materials having an average particle size of 5 μm and 13 μm at a weight ratio of 70:30, and the large particle size region was formed only by an active material having an average particle size of 13 μm.

Example 3
When the first positive electrode slurry and the second positive electrode slurry are applied to the positive electrode current collector with a die coater capable of simultaneous multi-layer application, the first positive electrode slurry is separated into two strips having a width of about 45 mm with a margin of about 10 mm. The flow path in the die coater is designed and applied so that the second positive electrode slurry is applied to both ends of the first positive electrode slurry in the flow direction by about 10 mm and the first positive electrode slurry. Except for this, the procedure was the same as in Example 1.
(Example 4)
A mixture of lithium manganese composite oxide having an average particle diameter (D50) of 13 μm and lithium manganese composite oxide having an average particle diameter (D50) of 5 μm in a weight ratio of 40:60 as the active material of the second positive electrode slurry. The same procedure as in Example 1 was carried out except that was used.

(Comparative Example 1)
Example 1 of Example 1 except that a lithium manganese composite oxide having an average particle diameter (D50) of 13 μm and a lithium manganese composite oxide having an average particle diameter (D50) of 5 μm were mixed as the active material at a weight ratio of 70:30. The first positive electrode slurry was prepared in the same manner as the first positive electrode slurry. The first positive electrode slurry was uniformly applied to the positive electrode current collector with a die coater and dried, and the obtained coating film was roll-pressed so that the electrode density was 2.8 g / cm 3. Was completed. That is, only the small particle size region was formed on the positive electrode current collector without forming the large particle size region and the small particle size region.

(Comparative Example 2)
When the first positive electrode slurry and the second positive electrode slurry are applied to the positive electrode current collector with a die coater capable of simultaneous multi-layer application, the first positive electrode slurry is about 65 mm wide with two strips with a margin of about 20 mm. The positive electrode was completed in the same manner as in Example 1 except that the coating was applied and the flow path in the die coater was designed so that the second positive electrode slurry was applied between the first positive electrode slurries. . That is, the large particle size region was not provided at the end of the positive electrode current collector.

(Comparative Example 3)
The first positive electrode slurry and the second positive electrode slurry were applied to the positive electrode current collector with a die coater capable of simultaneous multi-layer application, and dried to obtain a coating film. The length of the positive electrode current collector in the longitudinal direction of the electrode 10 for the lithium ion secondary battery is 150 mm, the first positive electrode slurry is applied with a width of about 50 mm, and the second positive electrode slurry is the first positive electrode slurry. A positive electrode was completed in the same manner as in Example 1 except that the flow path in the die coater was designed and applied so as to be applied to both ends in the flow direction of about 50 mm each.

(Comparative Example 4)
A lithium manganese composite oxide having an average particle size (D50) of 10 μm is used as the active material of the first positive electrode slurry, and a lithium manganese composite oxide having an average particle size (D50) of 11 μm as the active material of the second positive electrode slurry. The procedure was the same as Example 1 except that the product was used.
(Comparative Example 5)
The same procedure as in Example 1 was performed except that aggregated particles obtained by increasing the lithium manganese composite oxide having an average particle size (D50) of 1 μm were used as the active material for the second positive electrode slurry. The average particle diameter (D50) of the aggregated particles was 10 μm.

<Production of negative electrode>
Natural graphite as the negative electrode active material, acetylene black as the conductive additive, styrene butadiene rubber as the binder, and carboxymethyl cellulose as the thickener are mixed in a ratio of 90: 8: 1: 1, kneaded with a disper, and pure water as the solvent. Was added to adjust the viscosity to obtain a negative electrode slurry for a lithium ion secondary battery.
The obtained negative electrode slurry was applied to the negative electrode current collector with a die coater and dried to obtain a coating film. A copper foil (10 μm thick) was used as the negative electrode current collector. The negative electrode active material layer was applied with the basis weight adjusted to 1.1 times the capacity of the positive electrode active material layer.

<Production of cell>
The positive electrode and the negative electrode obtained by the above-described procedure were wound with a separator (model number 2200, manufactured by Celgard) facing each other, tabbed, and sealed in a battery can. The electrolyte was added to a 3: 7 (volume ratio) mixed solution of ethylene carbonate (EC) and diethyl carbonate (DMC) so that LiPF ₆ would be 1 M, and further 2% by weight of vinylene carbonate (VC) was added. We used what we did.

<Evaluation>
The discharge rate test was done with respect to the lithium ion secondary battery produced by each Example and the comparative example. The voltage at the time of charging / discharging was 3.0V-4.2V. First, constant current charge / discharge at 0.2 C was performed once as an initial discharge capacity evaluation, and subsequently, discharge rate tests were performed at 1 C, 5 C, 10 C, and 20 C. All charging during the discharge rate test was performed at 0.2C.
FIG. 5 shows the discharge capacity maintenance ratio when the discharge capacity in the initial discharge capacity evaluation is set to 100% for the batteries produced in the respective examples and comparative examples. In FIG. 5, the horizontal axis is the discharge rate [C], and the vertical axis is the discharge capacity retention rate [% VS. 0.2C].

When the discharge rates are 1C and 2C, there is no significant difference between Examples 1 to 4 and Comparative Examples 1 to 5, but Examples 1 to 4 discharge more than Comparative Examples 1 to 5 under high output conditions of 4C or higher. It was found that the capacity retention rate was good.
Examples 1-4 which have a large particle diameter area | region in an electrode edge part are electrode ends rather than the comparative example 1 which does not have a large particle diameter area | region in an electrode surface, and the comparative example 2 which does not have a large particle diameter area | region in an edge part. It is considered that the electrolytic solution is easily impregnated from the part and lithium ion conductivity is ensured. In addition, Comparative Example 3 has a large particle size region at the end of the electrode. However, since the large particle size region is larger than the area outside the large particle size region, the active material is unevenly distributed and sufficient electron conductivity cannot be ensured. It is thought. Furthermore, in Comparative Example 4, since the difference in average particle size between the large particle size active material and other small particle size active materials is small, the difference in density and porosity in the large particle size region after pressing and the small particle size region is small, It is considered that a sufficient gap could not be secured to allow the electrolytic solution to permeate at the electrode end. Similarly, in Comparative Example 5, since the aggregate active material having a large particle size was crushed in the pressing step, it is considered that sufficient voids could not be secured to allow the electrolytic solution to permeate at the electrode end. From the above, the effect of the present invention was confirmed.

  According to one embodiment of the present invention, the weight ratio of the first active material and the second active material includes the first active material that is the large particle size component and the second active material that is the small particle size component. Is provided with an active material layer including a large particle size region having a particle size of 30:70 or more and 100: 0 or less and a small particle size region in which the content of the first active material is smaller than that of the large particle size region. By forming the region in the region on the end side in contact with the non-aqueous electrolyte as an electrode, it is possible to form a region with a large porosity and improve the electrolyte permeability, that is, to improve the lithium ion conductivity in the electrode surface direction. Since the output characteristic is improved because it can be sufficiently secured, the industrial utility value is high. Therefore, the negative electrode for a lithium ion secondary battery of the present invention can be suitably used as a storage battery for a drive battery of an electric vehicle, a power storage facility for various energy, a home power storage facility, etc. that require high durability.

DESCRIPTION OF SYMBOLS 1 Active material layer 2 1st active material 3 2nd active material 4 Large particle diameter area | region 5 Small particle diameter area | region 6 Current collector 6a Positive electrode collector 6b Negative electrode collector 10 Electrode 10a for lithium ion secondary batteries Positive electrode 10b Negative electrode 12 Separator 30 Cylindrical lithium ion secondary battery

Claims (9)

An active material layer containing a first active material that is a large particle size component, a second active material that is a small particle size component having a smaller particle size than the large particle size component, a binder, and a conductive assistant is present on the current collector. Laminated to
The active material layer includes a said first active material and the second active material, the weight ratio of the first active material and the second active material is on 30:70 than large A diameter region, and a small particle size region having a smaller content of the first active material than the large particle size region,
When the direction in which the current collector extends is the longitudinal direction, the large particle size region is located in the longitudinal direction, and the current collector is in an area that is an end in contact with the non-aqueous electrolyte as an electrode. An electrode for a lithium ion secondary battery, wherein the electrode is formed in contact . Both ends are electrodes for a lithium ion secondary battery in contact with the non-aqueous electrolyte,
The large particle size region is formed in contact with the current collector in each of the two regions of the current collector that are located in the longitudinal direction and are end portions in contact with the non-aqueous electrolyte,
The small particle size region is formed between one large particle size region formed in contact with the current collector and the other large particle size region. The electrode for lithium ion secondary batteries as described.   3. The lithium ion according to claim 1, wherein an average particle diameter of the first active material is 1.2 times or more and 10 times or less of an average particle diameter of the second active material. Secondary battery electrode.   4. The electrode for a lithium ion secondary battery according to claim 1, wherein the first active material is an active material that is less likely to be crushed than the second active material. 5.   5. The electrode for a lithium ion secondary battery according to claim 1, wherein a surface area of the large particle size region in the active material layer is smaller than a surface area of the small particle size region. .   6. The electrode for a lithium ion secondary battery according to claim 1, wherein an average particle diameter of the first active material is 5 μm or more and 20 μm or less. A first active material that is a large particle size component; a second active material that is a small particle size component having a smaller particle size than the large particle size component; a binder and a conductive assistant; first electrode slurry weight ratio of the second active material is on 30:70 than, a second electrode slurry content is less than the first electrode slurry of the first active material the said first electrode slurry, and a longitudinal direction is the direction of extension of the collector, so that the end portion side in contact with the non-aqueous electrolyte solution as an electrode, is brought into contact with the current collector coating And a process of
And roll pressing the current collector coated with the first electrode slurry and the second electrode slurry. A method for producing an electrode for a lithium ion secondary battery, comprising:   A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to any one of claims 1 to 6 as at least one of a positive electrode and a negative electrode. The positive electrode and the negative electrode are formed by stacking and winding the current collector on which the active material layer is laminated,
9. The lithium ion secondary battery according to claim 8, wherein both ends of the formed positive electrode and negative electrode are in contact with a non-aqueous electrolyte.

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