JP5755870B2 - Positive electrode for secondary battery, secondary battery, and method for producing positive electrode for secondary battery - Google Patents

Description

  The present invention relates to a secondary battery electrode including an active material layer provided on a current collector, a secondary battery including a secondary battery electrode, and a method of manufacturing a secondary battery electrode.

  Conventionally, an electrode including a current collector and an active material layer provided on the current collector is known (see, for example, Patent Document 1 and Patent Document 2).

  Patent Document 1 discloses an electrode including an expanded metal (current collector) and a positive electrode mixture (active material layer) provided on the expanded metal. This electrode is wound in a spiral shape, and a crack extending in a direction orthogonal to the winding direction is formed in the positive electrode mixture.

  Patent Document 2 discloses a positive electrode including a positive electrode terminal plate (current collector) and a positive electrode mixture paste provided on the positive electrode terminal plate. The positive electrode mixture paste is dried at a surface temperature in the range of 100 ° C. to 200 ° C., whereby a notch due to a crack is formed at the center of the surface.

  Here, in recent years, there is a demand for higher capacity and lower cost of secondary batteries. Therefore, it is conceivable to increase the thickness of the active material layer in order to increase the capacity and cost of the secondary battery.

JP 59-180974 A Japanese Patent Laid-Open No. 3-84855

  However, when the active material layer is thickened, there is a problem that the active material layer peels off from the current collector during drying, thereby increasing the possibility of an internal short circuit and promoting the deterioration of the battery. . Note that the structures of Patent Document 1 and Patent Document 2 also have a problem that when the active material layer is thickened, the active material layer peels off from the current collector.

The present invention has been made in view of such a situation, and even when the active material layer is thick, the positive electrode for a secondary battery capable of suppressing the separation of the active material layer from the current collector, It aims at providing the manufacturing method of a secondary battery provided with the positive electrode for secondary batteries, and the positive electrode for secondary batteries.

The positive electrode for a secondary battery according to the present invention is a positive electrode for a secondary battery comprising a current collector and an active material layer provided on the current collector, wherein the active material layer is a secondary electrode. A slurry containing an active material having a particle median diameter of 0.5 μm to 10 μm and an aqueous styrene butadiene rubber binder using water or an alcohol that can be mixed with water as a solvent is formed by drying , and the active material The layer has a thickness of 100 μm to 400 μm and is divided into a plurality of regions, and each region has a predetermined area or less. The median diameter is a particle diameter indicating 50% of the volume-based cumulative particle size distribution measured by a laser diffraction / scattering method.

By being configured in this way, the active material layer is divided into a plurality of regions, so that even when the active material layer is thick, strain due to shrinkage during drying of the slurry can be dispersed. Can be prevented from peeling from the current collector. Moreover, since it is thought that the influence of the size of the secondary particle size on the behavior of the slurry during drying is large, the behavior of the slurry during drying can be within a certain range. Moreover, compared with the case where an organic solvent type binder is used, an environmental load can be reduced. Further, the capacity of the secondary battery provided with the positive electrode for the secondary battery can be increased.

In the positive electrode for a secondary battery according to the present invention, the predetermined area is 100 mm ² .

  By comprising in this way, the distortion | strain by shrinkage | contraction at the time of drying of a slurry can be disperse | distributed reliably.

In the positive electrode for a secondary battery according to the present invention, each region of the active material layer is separated.

  By comprising in this way, the distortion | strain by shrinkage | contraction at the time of drying of a slurry can be disperse | distributed completely.

In the positive electrode for a secondary battery according to the present invention, each region of the active material layer is connected.

  By comprising in this way, an active material layer can be divided easily.

In addition, the secondary battery according to the present invention includes a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolysis charged between the positive electrode and the negative electrode. a liquid, the positive electrode, the an anode, a secondary battery comprising an exterior member for sealing by covering the separator, and the electrolyte, wherein the positive electrode, second according to any one of the above It is a positive electrode for secondary batteries.

With such a configuration, it is possible to obtain a secondary battery including a secondary battery positive electrode that can suppress the active material layer from peeling from the current collector even when the active material layer is thick. it can.

Moreover, the manufacturing method of the positive electrode for secondary batteries which concerns on this invention is a positive electrode for secondary batteries provided with a collector and the active material layer which is provided on the said collector and is 100 micrometers-400 micrometers in thickness. A process for preparing a slurry comprising a water-based styrene-butadiene rubber binder using water or an alcohol that can be mixed with water as a solvent, and an active material having a median diameter of secondary particles of 0.5 μm to 10 μm And applying a slurry to the slurry in the step of applying the slurry to the current collector, the step of drying the slurry applied to the current collector, and the step of drying the slurry. And a step of forming an active material layer divided into a plurality of regions having a predetermined area or less.

With such a configuration, it is possible to obtain a positive electrode for a secondary battery that can suppress the separation of the active material layer from the current collector even when the active material layer is thick.

According to the secondary battery positive electrode according to the present invention, the secondary battery including the secondary battery positive electrode , and the method for manufacturing the secondary battery positive electrode , even when the active material layer is thick, the active material layer Peeling from the current collector can be suppressed.

1 is a perspective view schematically showing a schematic configuration of a secondary battery according to an embodiment of the present invention. It is an expanded sectional view which expands and shows the internal structure of the secondary battery in arrow BB of FIG. 1A in the thickness direction. It is sectional drawing which expanded and showed the positive electrode and negative electrode of the secondary battery which were shown to FIG. 1B partially. It is the top view which showed the active material layer of the positive electrode shown in FIG. It is the top view which showed the active material layer of the negative electrode shown in FIG. It is a figure explaining the manufacturing method of the positive electrode of the secondary battery which concerns on embodiment, and is sectional drawing which showed the state by which the slurry was coated on the surface of an electrical power collector. It is a figure explaining the manufacturing method of the positive electrode of the secondary battery which concerns on embodiment, and is the top view which showed the type | mold which forms a groove | channel. It is a figure explaining the manufacturing method of the positive electrode of the secondary battery which concerns on embodiment, and is sectional drawing which showed the state before pressing a type | mold to the slurry apply | coated to the electrical power collector. It is a figure explaining the manufacturing method of the positive electrode of the secondary battery which concerns on embodiment, and is sectional drawing which showed the state by which the type | mold was pressed by the slurry coated on the electrical power collector. It is a figure explaining the manufacturing method of the positive electrode of the secondary battery which concerns on embodiment, and is sectional drawing which showed the state in which the active material layer was formed on the surface of an electrical power collector. It is the table | surface which showed the experimental result performed in order to confirm the effect of the positive electrode of the secondary battery which concerns on embodiment. It is the top view which showed the active material layer of the positive electrode which concerns on the modification 1 of this Embodiment. It is sectional drawing which showed the active material layer of the positive electrode which concerns on the modification 2 of this Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  With reference to FIG. 1A and FIG. 1B, the secondary battery 10 which concerns on embodiment is demonstrated.

  FIG. 1A is a perspective view schematically showing a schematic configuration of a secondary battery 10 according to an embodiment of the present invention.

  FIG. 1B is an enlarged cross-sectional view showing the internal structure of the secondary battery 10 taken along arrows BB in FIG. 1A in the thickness direction. In addition, the hatching in the cross section is omitted in consideration of the visibility of the drawing.

  The secondary battery 10 according to the embodiment is charged between the positive electrode 11, the negative electrode 12 facing the positive electrode 11, the separator 13 disposed between the positive electrode 11 and the negative electrode 12, and the positive electrode 11 and the negative electrode 12. And an outer packaging material 15 that covers and seals the positive electrode 11, the negative electrode 12, the separator 13, and the electrolytic solution 17. The positive electrode 11 is connected to the positive electrode terminal 11t, and the negative electrode 12 is connected to the negative electrode terminal 12t via appropriate connecting members (for example, the positive electrode is an Al plate or wire, the negative electrode is a Cu or Ni plate or wire, etc.). Yes.

  Hereinafter, the details of the specific internal configuration and constituent materials of the secondary battery 10 according to the embodiment are classified into items (<about the separator 13> <about the positive electrode terminal 11t and the negative electrode terminal 12t> <about the electrolyte solution 17> <exterior packaging> The material 15 is described with>). In addition, the secondary battery 10 which concerns on embodiment is formed as a lithium ion secondary battery, for example. Therefore, below, it demonstrates centering on the material applied to a lithium ion secondary battery. The positive electrode 11 and the negative electrode 12 will be described in detail later.

<About Separator 13>
As the separator 13 according to the embodiment, a microporous film made of an olefin resin such as polyethylene, polypropylene, and polyester can be used singly or in combination, and an inexpensive separator such as a nonwoven fabric can be used as necessary. It is also possible to use it.

  The thickness of the separator 13 is suitably about 5 to 100 μm, and more preferably about 10 to 30 μm. If the thickness is less than 5 μm, the mechanical strength of the separator 13 is insufficient, which causes an internal short circuit of the battery, which is not preferable. If the thickness is greater than 100 μm, the distance between the positive electrode and the negative electrode is increased, and the internal resistance of the battery is increased. Absent.

  The porosity of the separator 13 is suitably about 30 to 90%, and more preferably about 40 to 80%. When the porosity is lower than 30%, the content of the electrolytic solution is reduced and the internal resistance of the battery is increased, which is not preferable. When the porosity is higher than 90%, the positive electrode and the negative electrode are brought into physical contact with each other. This is not preferable because it causes an internal short circuit.

  Here, the thickness and the porosity of the separator 13 are values obtained by calculating the thickness of the separator with a micrometer, measuring the weight with an electronic balance, calculating the density of the separator, and calculating the ratio with the true density of the resin. is there.

<About positive electrode terminal 11t and negative electrode terminal 12t>
The lead plates (positive electrode terminal 11t, negative electrode terminal 12t) function as electrode terminals for the positive electrode 11 and the negative electrode 12, and the material is not particularly limited as long as it has conductivity, and a current collector is formed. In particular, the same material as the current collector 111 (see FIG. 2) is used for the positive electrode terminal 11t, and the same material as the conductive film of the current collector 121 (see FIG. 2) is used for the negative electrode terminal 12t. It is preferable to use it. For example, an Al plate can be suitably used for the positive electrode terminal 11t, and a Cu plate or Ni plate can be suitably used for the negative electrode terminal 12t.

  The positive electrode terminal 11t and the negative electrode terminal 12t are formed in a size and a shape that can be attached in surface contact with all of the current collectors 111 and 121 having the same polarity, and a thickness of about 50 to 300 μm is appropriate. Yes, about 80-200 micrometers is more preferable.

<About the electrolytic solution 17>
As the electrolytic solution 17, a known material of a lithium ion secondary battery is applied. Hereinafter, the electrolytic solution 17 of the lithium ion secondary battery will be specifically described. As the electrolytic solution 17, a nonaqueous electrolytic solution containing a lithium salt is applied.

Examples of lithium salts used in lithium ion secondary batteries include lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium trifluoroacetate ( Examples include lithium salts such as LiCF ₃ COO) and lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO ₂ ) ₂ ), and these can be used alone or in admixture of two or more thereof. The salt concentration of the nonaqueous electrolyte is preferably 0.5 to 3 mol / L.

  Moreover, it is also possible to use a gel electrolyte or the like in which an electrolytic solution is held in a polymer matrix instead of the nonaqueous electrolytic solution. As the polymer matrix, a polymer matrix having a copolymer of polyethylene oxide and polypropylene oxide as a basic structure and having a polyfunctional acrylate at the terminal crosslinked is preferable. This is because the solid cross-linking gel has a stronger cross-linking structure, so that the non-aqueous electrolyte oozes out from the gel and the battery reliability is increased.

  Non-aqueous electrolyte solvents include propylene carbonate (PC), ethylene carbonate (EC), cyclic carbonates such as butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dicarbonate Chain carbonates such as propyl carbonate, γ-butyrolactone (hereinafter sometimes abbreviated as GBL), lactones such as γ-valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2 -Ethers such as dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate, etc. Or these 2 or more types can be mixed and used. In particular, when a graphite-based material is used as the negative electrode active material, it is preferable that ethylene carbonate (EC) is included.

  It is also possible to use an ionic liquid to improve safety. Furthermore, an additive such as vinylene carbonate (VC) or cyclohexylbenzene (CHB) may be added in order to form a good film on the surfaces of the positive electrode 11 and the negative electrode 12 or to improve charge / discharge stability. Is possible.

<About the exterior material 15>
An exterior material used for a general battery can be applied to the exterior material 15. The exterior material 15 may be, for example, an aluminum laminate that can be heat-sealed or a transparent resin film, or a metal can (for example, iron, stainless steel, aluminum, or the like).

  With reference to FIG. 2, FIG. 3A, and FIG. 3B, the positive electrode 11 and the negative electrode 12 of the secondary battery 10 which concern on embodiment are demonstrated.

  FIG. 2 is a cross-sectional view showing a partially enlarged view of the positive electrode 11 and the negative electrode 12 of the secondary battery 10 shown in FIG. 1B. In addition, the hatching in the cross section is omitted in consideration of the visibility of the drawing.

  3A is a plan view showing the active material layer 112 of the positive electrode 11 shown in FIG. 2, and FIG. 3B is a plan view showing the active material layer 122 of the negative electrode 12 shown in FIG.

The positive electrode 11 is a positive electrode for a secondary battery including a current collector 111 and an active material layer 112 provided on the current collector 111. Note that the active material layer 112 is provided on both surfaces (upper surface and lower surface) of the current collector 111.

  A known material of a lithium ion secondary battery is applied to the current collector 111. For the current collector 111, for example, a conductive metal foil or thin plate such as SUS (Steel-Use-Stainless: JIS standard) or aluminum can be applied. Note that the surface of the current collector 111 may be flat or uneven.

The thickness of the active material layer 112 is 20 μm to 500 μm, and preferably 100 μm to 400 μm. By increasing the thickness of the active material layer 112 in this manner, the capacity of the secondary battery 10 can be increased and the cost can be reduced. The active material layer 112 is divided into a plurality of regions 112a. The region 112a is square in plan view and is arranged in a matrix. Note that the region 112a may be rectangular in plan view. The region 112a has a predetermined area (100 mm ² ) or less. A groove (crack) 112b (see FIG. 3A) is formed between the regions 112a. The groove 112b (see FIG. 2) is formed so as to reach the surface of the current collector 111, and each region 112a is separated. By separating each region 112a in this way, strain due to shrinkage during drying of the slurry can be completely dispersed. Each region 112a of the active material layer 112 has a protruding (island-like) portion protruding from the surface of the current collector 111, and the area of the surface (upper surface) of the protruding portion is a predetermined area (100 mm ² ) or less. . The width of the groove 112b is preferably 50 μm (for example, 5 μm to 40 μm) or less. Thereby, the influence (deterioration of cycle characteristics, etc.) on the electrode characteristics due to the groove 112b can be suppressed.

  In addition to the active material, the active material layer 112 may include a conductive material, an aqueous binder (binder), a thickening material, a filler, a dispersion material, an ionic conductive material, a pressure enhancing material, and the like. When the active material layer 112 includes a water-based binder, it is possible to reduce the environmental burden as compared with a case where an organic solvent-based binder is used.

In the case of a lithium ion secondary battery, an oxide containing lithium can be used as the active material of the active material layer 112 of the positive electrode 11. That is, as the active material, for example, titanium, molybdenum, copper, niobium, vanadium, manganese, chromium, nickel, iron, cobalt, phosphorus, etc. and lithium complex oxide, sulfide, selenide, etc. are preferable, specifically, _{, LiMnO 2, LiMn 2 O 4} , LiNiO 2, LiCoO 2, LiCrO 2, LiFeO 2, LiVO 2 and LiMPO ₄ (M is Co, Ni, Mn, at least one element selected from Fe) 1 of Two or more can be used alone or in combination. Here, the secondary particles of the active material preferably have a median diameter of 0.5 μm to 10 μm. The median diameter is a particle diameter indicating 50% of the volume-based cumulative particle size distribution measured by a laser diffraction / scattering method. With this configuration, it is considered that the size of the secondary particle size has a great influence on the behavior of the slurry when it is dried, so that the behavior of the slurry when it is dried can be kept within a certain range.

  The conductive material may be an electron conductive material that is generally used as a battery material and that does not cause a chemical change in a configured battery. That is, as the conductive material, for example, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), graphite such as artificial graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, etc. Carbon blacks, vapor grown graphite fibers (VGCF), carbon fibers, conductive fibers such as metal fibers, metal powders such as copper, nickel, aluminum and silver, conductive whiskers such as zinc oxide and potassium titanate In addition, a conductive metal oxide such as titanium oxide, an organic conductive material such as a polyphenylene derivative, or a mixture thereof can be used alone. Of these conductive materials, acetylene black, VGCF, graphite and acetylene black are particularly preferred.

  The aqueous binder may be any material that is generally used as a battery material. That is, as the aqueous binder, one of polysaccharides, thermoplastic resins, and polymers having rubber elasticity, or a mixture thereof can be used. Specifically, as the aqueous binder, starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene- Mention may be made of propylene-diene terpolymers (EPDM), sulfonated EPDM, styrene butadiene rubber, polybutadiene, fluororubber and polyethylene oxide. The aqueous binder is a binder using water or alcohol that can be mixed with water as a solvent.

  Examples of the thickener include starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride and the like.

  The filler may be any fibrous material that is generally used as a battery material and that does not cause a chemical change in a configured battery. That is, as the filler, for example, an olefin polymer such as polypropylene or polyethylene, a fiber such as glass or carbon can be used.

  As an ionic conductive material, a polyethylene oxide derivative or a polymer containing the derivative, a polypropylene oxide derivative, a polymer containing the derivative, a phosphate ester polymer, or the like, which is generally known as an inorganic or organic solid electrolyte, is used. Can do.

  The pressure enhancing material is a compound that increases the internal pressure of the battery, and carbonate is a typical example.

  The negative electrode 12 is a secondary battery electrode including a current collector 121 and an active material layer 122 provided on the current collector 121. Note that the active material layer 122 is provided on both surfaces of the current collector 121. In addition, for the outermost negative electrode 12 of the positive electrode 11 and the negative electrode 12 (see FIG. 1B) arranged so as to overlap, the active material layer is provided only on one surface of the current collector 121 (the surface on which the positive electrode 11 is opposed) 122 may be provided.

  A known material of a lithium ion secondary battery is applied to the current collector 121. For the current collector 121, for example, a metal foil such as copper can be used. Note that the surface of the current collector 121 may be flat or uneven.

The thickness of the active material layer 122 is 20 μm to 500 μm, and preferably 100 μm to 400 μm. By increasing the thickness of the active material layer 122 in this manner, the capacity of the secondary battery 10 can be increased and the cost can be reduced. The active material layer 122 is divided into a plurality of regions 122a. The region 122a is square in plan view and is arranged in a matrix. Note that the region 122a may be rectangular when viewed in plan. The region 122a has a predetermined area (100 mm ² ) or less. A groove (crack) 122b (see FIG. 3B) is formed between the regions 122a. The groove 122b (see FIG. 2) is formed so as to reach the surface of the current collector 121, and each region 122a is separated. As the regions 122a are separated in this way, strain due to shrinkage during drying of the slurry can be completely dispersed. Each region 122a of the active material layer 122 has a protruding (island-like) portion protruding from the surface of the current collector 121, and the area of the surface (upper surface) of the protruding portion is a predetermined area (100 mm ² ) or less. . The width of the groove 122b is preferably 50 μm (for example, 5 μm to 40 μm) or less. Thereby, the influence (deterioration of cycle characteristics, etc.) on the electrode characteristics due to the groove 122b can be suppressed.

  In addition to the active material, the active material layer 122 may include a conductive material, an aqueous binder (binder), a thickening material, a filler, a dispersion material, an ionic conductive material, a pressure enhancing material, and the like. By including an aqueous binder in the active material layer 122, it is possible to reduce the environmental load as compared with the case where an organic solvent binder is used. Note that the conductive material, the aqueous binder, the thickener, the filler, the dispersion material, the ionic conductive material, and the pressure enhancing material are the same as those of the active material layer 112 of the positive electrode 11, and thus the description thereof is omitted.

In the case of a lithium ion secondary battery, the active material of the active material layer 122 of the negative electrode 12 includes graphite-based materials such as natural graphite, artificial graphite, and highly crystalline graphite, amorphous carbon-based materials, Nb ₂ O _5, and LiTiO _4. Among these metal oxides, at least one or more can be used alone or in combination. Here, the secondary particles of the active material preferably have a median diameter of 0.5 μm to 10 μm. With this configuration, it is considered that the size of the secondary particle size has a great influence on the behavior of the slurry when it is dried, so that the behavior of the slurry when it is dried can be kept within a certain range.

  A method for manufacturing positive electrode 11 of secondary battery 10 according to the embodiment will be described with reference to FIGS. 4A to 4E. In addition, about the manufacturing method of the negative electrode 12, since it is substantially the same as the case of the positive electrode 11, description is abbreviate | omitted. In order to simplify the description, the case where the active material layer 112 is formed only on one surface of the current collector 111 will be described.

  FIG. 4A is a cross-sectional view showing a state in which the slurry 50 is applied on the surface of the current collector 111. FIG. 4B is a plan view showing a mold 60 for forming a groove. FIG. 4C is a cross-sectional view showing a state before the mold 60 is pressed against the slurry 50 applied to the current collector 111. FIG. 4D is a cross-sectional view showing a state in which the mold 60 is pressed against the slurry 50 applied to the current collector 111. FIG. 4E is a cross-sectional view showing a state where the active material layer 112 is formed on the surface of the current collector 111.

  First, a slurry 50 containing an active material is prepared. The slurry 50 may be added with a conductive material, an aqueous binder, a thickening material, a filler, a dispersion material, an ionic conductive material, a pressure enhancing material, and the like. Then, the slurry 50 containing the active material is applied to the current collector 111 (see FIG. 4A). Thereafter, the slurry 50 applied to the current collector 111 is dried.

  Then, during the drying of the slurry 50, grooves are formed in the slurry 50 using a mold 60 (see FIG. 4B). In the mold 60, square openings 60a in a plan view are formed in a matrix.

  Then, the mold 60 is pressed against the slurry 50 by moving the mold 60 in the downward direction Z (see FIG. 4C) from above the slurry 50 coated on the current collector 111. As a result, the slurry 50 is pushed by the mold 60 and moves until the mold 60 contacts the current collector 111 as shown in FIG. 4D. Thereafter, the mold 60 is extracted from the slurry 50.

Thereafter, by drying and pressing, an active material layer 112 divided into a plurality of regions 112a is formed on the surface of the current collector 111 as shown in FIG. 4E. The region 112a is formed with a predetermined area (100 mm ² ) or less.

  Next, with reference to FIG. 5, the experiment conducted in order to confirm the effect of the positive electrode 11 of the secondary battery 10 by embodiment mentioned above is demonstrated.

  FIG. 5 is a list showing the results of experiments conducted to confirm the effect of the positive electrode 11 of the secondary battery 10 according to the embodiment.

In this experiment, first, lithium iron phosphate (LiFePO ₄ ) as an active material, acetylene black as a conductive material, styrene butadiene rubber as an aqueous binder, and carboxymethyl cellulose as a thickener in a weight ratio, A slurry was prepared by mixing at a ratio of 100: 9: 6.2: 3.5. In addition, lithium iron phosphate had a median diameter of secondary particles of 0.5 μm.

And the slurry produced on the aluminum foil whose thickness is 20 micrometers and whose area is 20000 mm < ² > (100 mm x 200 mm) was applied. Here, five types of samples having thicknesses of 50 μm, 100 μm, 200 μm, 300 μm, and 400 μm of the slurry (active material layer) applied on the aluminum foil were prepared.

And about these 5 types of samples, the sample which does not form a groove | channel in a slurry in the middle of drying of a slurry, ie, the sample which does not classify | segment an active material layer, was produced. In addition, for the five types of samples, during the drying of the slurry, grooves were formed in the slurry with a mold having an opening with a side length of 2 mm, so that the active material layer had an area of 4 mm ² (2 mm × 2 mm). A sample divided into a certain region was prepared. In addition, for the five types of samples, during the drying of the slurry, grooves were formed in the slurry with a mold having an opening with a side length of 5 mm, so that the active material layer had an area of 25 mm ² (5 mm × 5 mm). A sample divided into a certain region was prepared. In addition, for the five types of samples, during the drying of the slurry, grooves are formed in the slurry with a mold having an opening with a side length of 10 mm, so that the active material layer has an area of 100 mm ² (10 mm × 10 mm). A sample divided into a certain region was prepared. Further, for the five types of samples, during the drying of the slurry, grooves were formed in the slurry with a mold having an opening with a side length of 15 mm, so that the active material layer had an area of 225 mm ² (15 mm × 15 mm). A sample divided into a certain region was prepared.

  Note that the width of the groove is desirably as small as possible in consideration of electrode characteristics. However, in consideration of mold workability and strength, the plate thickness (width) of the mold was set to about 45 μm to 55 μm to form grooves. The mold was made of SUS304. As a result, the width of the groove was about 5 to 40 μm.

  That is, the above 25 types of samples were produced. And about each sample, the presence or absence of peeling of an active material layer from a collector was investigated, and the result was shown in FIG.

  As shown in FIG. 5, when the active material layer was not divided and the thickness of the active material layer was 50 μm, the active material layer did not peel from the current collector. On the other hand, in the case where the active material layer is not divided, when the thickness of the active material layer is 100 μm, 200 μm, 300 μm, and 400 μm, the active material layer is peeled from the current collector. This is considered to be because when the thickness of the active material layer is larger than 50 μm, strain due to shrinkage during drying increases.

When the active material layer is divided into regions having an area of 4 mm ² and the thickness of the active material layer is 50 μm, 100 μm, 200 μm, 300 μm, and 400 μm, the active material layer is peeled from the current collector. There wasn't. In addition, when the active material layer is divided into regions having an area of 25 mm ² and the active material layer has a thickness of 50 μm, 100 μm, 200 μm, 300 μm, and 400 μm, the active material layer peels off from the current collector. There wasn't. Further, when the active material layer is divided into regions having an area of 100 mm ² and the thickness of the active material layer is 50 μm, 100 μm, 200 μm, 300 μm, and 400 μm, the active material layer is peeled from the current collector. There wasn't. This is because the active material layer is divided into regions having an area of 4 mm ² , 25 mm ^2, or 100 mm ² , thereby dispersing strain due to shrinkage during drying even when the thickness of the active material layer is larger than 50 μm. It is thought that it is because it is possible.

Further, when the active material layer was divided into regions having an area of 225 mm ² , the active material layer did not peel from the current collector when the thickness of the active material layer was 50 μm. On the other hand, when the active material layer was divided into regions having an area of 225 mm ² , when the thickness of the active material layer was 100 μm, 200 μm, 300 μm, and 400 μm, the active material layer was peeled from the current collector. This is because if the area of each region is larger than 100 mm ² , the strain due to shrinkage during drying cannot be dispersed, and the strain due to shrinkage during drying increases as in the case where the active material layer is not separated. It is thought that.

  In addition, it is thought that the effect similar to the effect of the above-mentioned positive electrode 11 is acquired also about the negative electrode 12. FIG.

As described above, the positive electrode 11 as the positive electrode for the secondary battery includes the current collector 111 and the active material layer 112 provided on the current collector 111, and the active material layer 112 includes a plurality of regions 112a. The region 112a has a predetermined area or less.

  With this configuration, the active material layer 112 is divided into a plurality of regions 112a, so that even when the active material layer 112 is thick, strain due to shrinkage during drying of the slurry 50 can be dispersed. Further, the active material layer 112 can be prevented from peeling from the current collector 111.

  The negative electrode 12 as a secondary battery electrode includes a current collector 121 and an active material layer 122 provided on the current collector 121. The active material layer 122 is divided into a plurality of regions 122a. The region 122a has a predetermined area or less.

  By being configured in this way, the active material layer 122 is divided into a plurality of regions 122a, so that even when the active material layer 122 is thick, strain due to shrinkage during drying of the slurry can be dispersed. The active material layer 122 can be prevented from peeling from the current collector 121.

  With reference to FIG. 6, the active material layer 70 of the positive electrode 11 which concerns on the modification 1 of this Embodiment is demonstrated.

  FIG. 6 is a plan view showing active material layer 70 of positive electrode 11 (see FIG. 2) according to Modification 1 of the present embodiment.

A groove 72 is formed on the surface of the active material layer 70. The active material layer 70 is divided into a plurality of regions 71 having different sizes and shapes in plan view. The region 71 has a predetermined area (100 mm ² ) or less. That is, the planar shape of the region into which the active material layer is divided may be other than a square, and the areas of the plurality of regions may be different. The same applies to the negative electrode 12.

  With reference to FIG. 7, the active material layer 80 of the positive electrode 11 which concerns on the modification 2 of this Embodiment is demonstrated.

  FIG. 7 is a cross-sectional view showing an active material layer 80 of positive electrode 11 (see FIG. 2) according to Modification 2 of the present embodiment.

The active material layer 80 is divided into a plurality of regions 81. The region 81 has a predetermined area (100 mm ² ) or less. A groove (crack) 82 is formed between the regions 80. The groove 82 is formed so as not to reach the surface of the current collector 111, and each region 81 is connected on the surface of the current collector 111. The depth of the groove 82 is 5 μm or more. By connecting the regions 81, the active material layer 80 can be easily separated.

  The present invention is not limited to the embodiment described above. For example, in the present embodiment, the active material layer 112 of the positive electrode 11 is divided and the active material layer 122 of the negative electrode 12 is divided. However, the present invention is not limited thereto, and the active material layer of the positive electrode and the active material layer of the negative electrode are illustrated. Only one of the material layers may be divided.

  Further, in the present embodiment, an example in which the groove is formed by pressing the mold against the slurry during the drying of the slurry is shown, but not limited to this, the drying conditions of the slurry, the solid content concentration, the aqueous binder Grooves may be formed when the slurry is dried by adjusting the type and amount.

  In this embodiment, an example in which a water-based binder is used as a binder has been described. However, the present invention is not limited thereto, and an organic solvent-based binder may be used as a binder.

10 Secondary battery 11 Positive electrode ( Positive electrode for secondary battery)
12 negative electrode <br/> 13 separator 15 outer package 17 electrolyte 50 slurry 60-inch 70 active material layer 71 region 72 grooves 80 active material layer 81 region 82 grooves 111 current collector 112 active material layer 112a region 112b groove 121 collector Body 122 Active material layer 122a Region 122b Groove

Claims (6)

A current collector,
A positive electrode for a secondary battery comprising an active material layer provided on the current collector,
The active material layer is formed by drying a slurry containing an active material in which the median diameter of secondary particles is 0.5 μm to 10 μm and an aqueous styrene butadiene rubber binder using water or an alcohol that can be mixed with water as a solvent. Has been
The active material layer has a thickness of 100 μm to 400 μm and is divided into a plurality of regions.
Each region has a predetermined area or less. A positive electrode for a secondary battery. The positive electrode for a secondary battery according to claim 1,
The positive electrode for a secondary battery, wherein the predetermined area is 100 mm ² . The positive electrode for a secondary battery according to claim 1 or 2 ,
Each area | region of the said active material layer is isolate | separated. The positive electrode for secondary batteries characterized by the above-mentioned. The positive electrode for a secondary battery according to claim 1 or 2 ,
Each area | region of the said active material layer is connected. The positive electrode for secondary batteries characterized by the above-mentioned. A positive electrode;
A negative electrode facing the positive electrode;
A separator disposed between the positive electrode and the negative electrode;
An electrolyte filled between the positive electrode and the negative electrode;
A secondary battery comprising the positive electrode, the negative electrode, the separator, and an exterior material that covers and seals the electrolyte solution,
The positive electrode, a secondary battery, which is a positive electrode for a secondary battery according to any one of claims 1 to 4. A method for producing a positive electrode for a secondary battery, comprising: a current collector ; and an active material layer provided on the current collector and having a thickness of 100 μm to 400 μm ,
Preparing a slurry containing water or a water-based styrene butadiene rubber binder using water-miscible alcohol as a solvent and an active material having a median diameter of secondary particles of 0.5 μm to 10 μm;
Applying the slurry to the current collector;
Drying the slurry applied to the current collector;
Forming the active material layer divided into a plurality of regions having a predetermined area or less by pressing a mold against the slurry in the step of drying the slurry. Manufacturing method of positive electrode.

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