Electrode and battery

Abstract

An electrode 1 according to an embodiment of the present invention comprises a current collector 3, a conductive layer 5, an adhesive layer 7, and an electrode active material layer 9. The conductive layer 5 is a layer which includes a conductive agent and is formed on at least one surface of the current collector 3. The adhesive layer 7 is a layer which includes a binder and is formed, in a prescribed pattern, on the conductive layer so as to cover a part of the conductive layer 5. The electrode active material layer 9 is a layer which includes an electrode active material, and which is formed on the adhesive layer 7 and a portion of the conductive layer 5 not covered by the adhesive layer 7.

Description

Electrodes and batteries

[0001] The present invention relates to an electrode and a battery.

[0002] Electrodes used in lithium-ion secondary batteries and the like have an active material layer formed on a current collector. Methods for forming an active material layer on a current collector can be broadly divided into wet methods and dry methods. In wet methods, an electrode is fabricated by applying a slurry containing an active material, a binder, a solvent, and the like to the current collector and drying the mixture. In dry methods, for example, an electrode is formed by forming granules containing the active material in advance and pressing the granules onto the current collector. In dry methods, an active material layer can be formed on the current collector without going through a step of applying a slurry, so a step of drying the slurry is not required. This results in high electrode production efficiency.

[0003] Patent Literature 1 describes a method for fabricating an electrode using a dry process, in which a binder coating liquid is pattern-coated on the surface of a current collector to form regular binder-coated and binder-uncoated areas, and a powder of mix particles containing an active material and a binder is supplied onto the surface to form a mix layer on the current collector. According to this method, the binder coated on the surface of the current collector binds the current collector and the active material, and the active materials are also bound to each other by the binder contained in the mix particle powder, thereby ensuring the peel strength of the mix layer from the current collector. It is believed that providing such a binder on the current collector facilitates adhesion of the mix layer to the current collector during electrode fabrication, allowing for faster formation of the active material layer and improved yield.

[0004] JP 2014-78497 A

[0005] However, it has been found that batteries using electrodes in which an active material layer is formed on a current collector by pattern coating as described above may experience increased resistance with repeated charge and discharge, resulting in poor cycle characteristics.

[0006] Therefore, an object of the present invention is to provide an electrode that can be produced with a high yield and that can provide a battery with good cycle characteristics, and a battery including such an electrode.

[0007] One aspect of the present invention is an electrode comprising: a current collector, a conductive layer containing a conductive agent and formed on at least one surface of the current collector, an adhesive layer containing a binder and formed in a predetermined pattern on the conductive layer so as to cover a portion of the conductive layer, and an electrode active material layer containing an electrode active material and formed on the portion of the conductive layer not covered by the adhesive layer and on the adhesive layer.

[0008] Another aspect of the present invention is a battery including the electrode.

[0009] According to the above-described embodiment, a battery with good cycle characteristics can be obtained, and electrodes can be produced with a high yield.

[0010] 1 is a diagram showing a schematic view of a laminated structure of an electrode; FIG. 2 is a plan view showing an example of a pattern shape of an adhesive layer;

[0011] Hereinafter, an embodiment of the present invention will be described.

[0012] 1 is a diagram schematically illustrating the layered structure of an electrode 1 according to an embodiment of the present invention. The electrode 1 includes a current collector 3, a conductive layer 5, an adhesive layer 7, and an electrode active material layer 9.

[0013] The current collector 3 has two surfaces facing opposite each other. The shape of the current collector 3 is not particularly limited and may be a foil, a flat plate, a mesh, or the like. The thickness of the current collector 3 is, for example, 0.001 mm or more and 0.5 mm or less.

[0014] The material of the current collector 3 is not particularly limited, but when the current collector 3 is used for the negative electrode of a battery, it is preferably selected from copper, stainless steel, nickel, titanium, and alloys containing two or more of these, and copper is particularly preferred. When the current collector 3 is used for the positive electrode of a battery, the material of the current collector 3 is preferably aluminum.

[0015] The conductive layer 5 contains a conductive agent and is formed on at least one surface of the current collector 3. For ease of explanation, FIG. 1 shows the conductive layer 5, adhesive layer 7, and electrode active material layer 9 formed only on one surface of the current collector 3. However, the conductive layer 5, adhesive layer 7, and electrode active material layer 9 may be formed on both surfaces of the current collector 3. In a battery employing an electrode in which an active material layer is formed on a current collector by pattern coating as described above, the active material layer may not adhere sufficiently to the current collector in areas not coated with the binder. If the active material layer does not adhere sufficiently to the current collector, the internal resistance of the battery is likely to increase. According to the inventor's studies, when the conductive layer 5 is provided on the surface of the current collector 3, the electrode active material layer 9 adheres well to the current collector 3 via the portion of the conductive layer 5 not covered by the adhesive layer 7, and the electrode active material layer 9 is less likely to peel off from the current collector 3 than when the electrode active material layer is formed directly on the current collector. A battery employing such an electrode 1 has good conductivity at the interface between the electrode active material layer 9, the conductive layer 5, and the current collector 3, and tends to have low internal resistance. Furthermore, with such an electrode 1, the electrode active material layer 9 is less likely to peel off from the current collector 3, and therefore the internal resistance is less likely to increase even with repeated charge and discharge, resulting in good cycle characteristics.

[0016] The conductive layer 5 is preferably formed (formed by solid coating) over the entire area of ​​the current collector 3 that overlaps with the area where the electrode active material layer 9 is formed, when viewed from the stacking direction of the conductive layer 5, the adhesive layer 7, and the electrode active material layer 9 (the vertical direction in FIG. 1 ).

[0017] The conductive agent is not particularly limited as long as it can provide good conductivity, and is a material for reducing the resistance of the electrode 1. Examples of the conductive agent include carbon black such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, and carbon fibers such as carbon nanotubes, carbon nanofibers, and carbon nanobrushes.

[0018] The conductive layer 5 preferably contains a binder in addition to the conductive agent. Examples of the binder for the conductive layer 5 include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF), conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles, synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR), polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin, and acrylic resins such as acrylate and methacrylate.

[0019] The adhesive layer 7 contains a binder and is formed on the conductive layer 5 in a predetermined pattern so as to cover a portion of the conductive layer 5. The adhesive layer 7 has a predetermined pattern shape when viewed in the stacking direction. FIG. 2 shows an example of the pattern shape of the adhesive layer 7. The adhesive layer 7 shown in FIG. 2 has a plurality of dot-shaped regions 7a spaced apart from one another in a direction perpendicular to the stacking direction. Therefore, uncovered regions 5a that are not covered by the adhesive layer 7 are formed on the surface of the conductive layer 5. When the adhesive layer 7 is provided, the electrode active material layer 9 is adhered to the conductive layer 5 by the adhesive layer 7 during fabrication of the electrode 1. Therefore, even if the electrode active material layer 9 is formed quickly, the electrode active material layer 9 is firmly bonded to the conductive layer 5. This allows the electrode 1 to be produced with a high yield. Furthermore, because the adhesive layer 7 is formed in a predetermined pattern, the conductive layer 5 can provide good adhesion of the electrode active material layer 9 to the current collector 3 in the uncovered regions 5a, as described above, ensuring conductivity at the interface between the electrode active material layer 9, the conductive layer 5, and the current collector 3. If the adhesive layer is formed so as to cover the entire surface of the conductive layer 5, the conductivity at the interface will decrease, increasing the resistance of the electrode 1. As a result, the internal resistance of a battery using the electrode 1 will increase.

[0020] The pattern shape of the adhesive layer 7 may be a dotted shape, striped shape, grid shape, or the like. The dot shape may be a regular shape such as a circle, ellipse, or polygon (triangle, square, pentagon, hexagon, etc.), or an irregular shape. The dot arrangement, the spacing between adjacent dots, the spacing between stripes, and the spacing between intersections of the grid lines may be regular or random. The size (maximum length) of the dots is, for example, 50 to 500 μm, and the spacing between adjacent dots is, for example, 5 to 100 μm. The spacing between stripes is, for example, 50 to 200 μm. The spacing between intersections of the grid lines is, for example, 50 to 200 μm. These dimensions are determined so that the electrode active material layer 9 and the conductive layer 5 are uniformly bonded along the interface.

[0021] The adhesive layer 7 can be produced, for example, by gravure printing. Specifically, the adhesive layer 7 is produced by retaining a binder liquid, in which a binder is dissolved or dispersed in a solvent, in recesses (cells) engraved on the circumferential surface of a gravure roll, transferring the binder liquid to the surface of the conductive layer 5, and drying the resulting liquid. The recesses of the gravure roll are formed to have a shape corresponding to the pattern shape of the adhesive layer 7. The concentration of the binder in the binder liquid is determined in consideration of the thickness of the adhesive layer 7 and the accuracy of transfer to the conductive layer 5, and is, for example, 1 to 40% by mass.

[0022] Examples of the binder for the adhesive layer 7 include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin; and acrylic resins such as acrylate and methacrylate.

[0023] The adhesive layer 7 preferably does not contain a conductive agent. The conductive agent is, for example, a conductive agent having the same composition as the conductive agent contained in the conductive layer 5.

[0024] The electrode active material layer 9 is a layer containing an electrode active material, and is a layer formed on the adhesive layer 7 and on the portion of the conductive layer 5 that is not covered by the adhesive layer 7 .

[0025] When the electrode 1 is an electrode used as the negative electrode of a battery, the electrode active material layer 9 is a negative electrode active material layer containing a negative electrode active material as an electrode active material, and when the electrode 1 is an electrode used as the positive electrode of a battery, the electrode active material layer 9 is a positive electrode active material layer containing a positive electrode active material as an electrode active material.

[0026] A carbon-based active material can be used as the negative electrode active material. Examples of the carbon-based active material include natural graphite, artificial graphite, hard carbon, soft carbon, carbon black, and any mixture thereof. Natural graphite includes natural graphite particles coated with amorphous carbon, while artificial graphite includes artificial graphite particles coated with amorphous carbon. These natural graphite and artificial graphite particles can be used in the form of primary particles, particles formed by agglomeration of primary particles to form secondary particles, or mixtures thereof. Alternatively, a mixture of a carbon-based active material and a silicon-based active material can be used as the negative electrode active material. The negative electrode active material can also include metal materials such as aluminum, silver, bismuth, calcium, cerium, indium, magnesium, tin, zinc, and nickel.

[0027] The negative electrode active material layer preferably contains a conductive additive and a binder in addition to the negative electrode active material.

[0028] The conductive additive contained in the negative electrode active material layer is a material for reducing the resistance of the electrode, and examples of the conductive additive include carbon black such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, and carbon fibers such as carbon nanotubes, carbon nanofibers, and carbon nanobrushes.

[0029] Examples of the binder contained in the negative electrode active material layer include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. In addition, polyacrylic acid, polymethacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, sodium polymethacrylate, potassium polymethacrylate; ethyl polyacrylate, butyl polyacrylate, methyl polymethacrylate, ethyl polymethacrylate, butyl polymethacrylate, polyacrylamide, polyacrylonitrile, and any mixture thereof can be used as the binder. Furthermore, metal salts of carboxymethyl cellulose (e.g., sodium carboxymethyl cellulose, potassium carboxymethyl cellulose) can also be used as the binder. In addition, electrode additives commonly used for electrode formation, such as thickeners, dispersants, and stabilizers, can be appropriately used in the negative electrode active material layer.

[0030] The positive electrode active material may be a composite oxide of lithium and a transition metal, such as lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt composite oxide, lithium-nickel-aluminum composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-manganese-cobalt composite oxide, lithium-nickel-manganese-aluminum composite oxide, or lithium-nickel-cobalt-manganese-aluminum composite oxide; TiS ２ , FeS, MoS ２ transition metal sulfides such as MnO, V ２ O ５ , V ６ O １３ , TiO ２and one or more transition metal oxides selected from the group consisting of olivine-type lithium phosphates. The olivine-type lithium phosphates contain, for example, one or more elements selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, Nb, and Fe, as well as lithium, phosphorus, and oxygen. These compounds may have some elements partially substituted with other elements to improve their properties. Among these, the positive electrode active material is preferably a Li-based phosphate having an average particle size of 3 to 15 μm. ａ Ni ｂ Mn ｃ Co ｄ M ｘ O ２ (wherein a, b, c, d, and x satisfy 0.9≦a≦1.2, 0<b<1, 0<c≦0.5, 0<d≦0.5, 0≦x≦0.3, and b+c+d=1, and M is at least one element selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr) is preferably used.

[0031] The positive electrode active material layer preferably contains a binder and a conductive additive in addition to the positive electrode active material.

[0032] Examples of binders contained in the positive electrode active material layer include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF), conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles, synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR), hydrocarbon resins such as polystyrene, polypropylene, and polyethylene, and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. Examples of conductive additives contained in the positive electrode active material layer include carbon blacks such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, and carbon fibers such as carbon nanofibers, carbon nanotubes, and carbon nanobrushes. In addition, the positive electrode active material layer may contain appropriate electrode additives that are generally used for forming electrodes, such as thickeners, dispersants, and stabilizers.

[0033] According to the electrode 1 described above, a battery having good cycle characteristics can be obtained and can be produced with a good yield. The electrode 1 can be used as a negative electrode or a positive electrode.

[0034] The coverage of the conductive layer 5, which is the ratio of the area of ​​the portion of the conductive layer 5 covered by the adhesive layer 7 to the entire area of ​​the conductive layer 5, is preferably 30 to 60% when the electrode 1 is a negative electrode, and preferably 30 to 70% when the electrode 1 is a positive electrode. If the coverage of the conductive layer 5 is 60% or less when the electrode 1 is a negative electrode, or if the coverage of the conductive layer 5 is 70% or less when the electrode 1 is a positive electrode, the cycle characteristics of a battery using the electrode 1 are likely to be improved. Furthermore, if the coverage of the conductive layer 5 is 60% or less when the electrode 1 is a negative electrode, or if the coverage of the conductive layer 5 is 70% or less when the electrode 1 is a positive electrode, the resistance of the electrode 1 is likely to be reduced, and the internal resistance of a battery using the electrode 1 is likely to be reduced. If the coverage of the conductive layer 5 exceeds 60% when the electrode 1 is a negative electrode, or if the coverage of the conductive layer 5 exceeds 70% when the electrode 1 is a positive electrode, the uncovered region 5a where the electrode active material layer 9 contacts the conductive layer 5 becomes narrow, locally restricting the movement of electrons between the conductive layer 5 and the electrode active material layer 9, resulting in an increase in the resistance of the electrode 1. The coverage of the conductive layer 5 is preferably 50% when the electrode 1 is a negative electrode, and preferably 60% or less when the electrode 1 is a positive electrode. The coverage of the conductive layer 5 is more preferably 45% or less. On the other hand, if the coverage of the conductive layer 5 is 30% or more, a larger portion of the electrode active material layer 9 is adhered to the conductive layer 5 during the production of the electrode 1, thereby improving the yield. The coverage of the conductive layer 5 is preferably 35% or more, more preferably 40% or more. The coverage of the conductive layer 5 can be adjusted by changing the pattern shape of the adhesive layer 7.

[0035] The coverage of the conductive layer 5 can be calculated using image analysis software from an image taken with a microscope, scanning electron microscope, or the like after peeling the electrode active material layer 9 from the adhesive layer 7. Because the conductive layer 5 is formed below the adhesive layer 7, the image can be recognized without being affected by the gloss of the current collector 3, and the dot-shaped regions 7 a can be identified on the image.

[0036] The binder content of the conductive layer 5 is preferably 10% by mass or more of the total mass of the conductive layer 5. When the binder content of the conductive layer 5 is 10% by mass or more, the cycle characteristics of a battery using the electrode 1 are likely to be improved. When the binder content is less than 10% by mass, the electrode active material layer 9 may not adhere sufficiently to the current collector 3 via the conductive layer 5. Therefore, when a battery using the electrode 1 is repeatedly charged and discharged, the conductive layer 5 may peel off from the current collector 3, resulting in deterioration of the cycle characteristics. Furthermore, when the binder content of the conductive layer 5 is 10% by mass or more, the electrode active material layer 9 adheres sufficiently to the current collector 3 via the conductive layer 5, which tends to reduce the resistance of the electrode 1. Therefore, the internal resistance of a battery using the electrode 1 is likely to be reduced. The binder content of the conductive layer 5 is preferably 25% by mass or more, and more preferably 35% by mass or more.

[0037] On the other hand, the binder content of the conductive layer 5 is preferably 90% by mass or less of the total mass of the conductive layer 5. When the binder content of the conductive layer 5 is 90% by mass or less, the cycle characteristics of a battery using the electrode 1 are also likely to be improved. Furthermore, since the amount of conductive agent in the conductive layer 5 is ensured, the resistance of the electrode 1 is likely to be reduced, and the internal resistance of a battery using the electrode 1 is likely to be small. According to the electrode 1 of the embodiment, as described above, a battery with good cycle characteristics can be obtained and can be produced with a high yield. Therefore, when the binder content of the conductive layer 5 is 90% by mass or less, a battery with good cycle characteristics can be obtained, the electrode 1 can be produced with a high yield, and a battery with low internal resistance can be obtained. The binder content of the conductive layer 5 is preferably 80% by mass or less, and more preferably 70% by mass or less.

[0038] The aspect ratio of the conductive agent particles contained in the conductive layer 5 is preferably 10 or less. When the aspect ratio of the conductive agent particles is 10 or less, the cycle characteristics of a battery using the electrode 1 are less likely to deteriorate. Furthermore, when the aspect ratio of the conductive agent particles is 10 or less, the resistance of the electrode 1 is likely to be reduced, and the internal resistance of a battery using the electrode 1 is likely to be small. The aspect ratio is obtained by calculating the ratio of the major axis to the minor axis (major axis / minor axis) for multiple conductive agent particles, where the maximum distance between parallel lines sandwiching the conductive agent particle is the major axis and the minimum distance is the minor axis, and averaging the calculated values. The aspect ratio of the conductive agent particles is preferably 5 or less, more preferably 3 or less. The aspect ratio of the conductive agent particles is preferably 1.5 or more, more preferably 2 or more. The conductive agent particles may have a spherical, elliptical, cylindrical, polygonal columnar, scale-like, or amorphous shape.

[0039] The thickness of the adhesive layer 7 is preferably 0.5 μm or less. When the thickness of the adhesive layer 7 is 0.5 μm or less, the resistance of the electrode 1 is likely to be reduced, and the internal resistance of a battery using the electrode 1 is likely to be reduced. Furthermore, when the thickness of the adhesive layer 7 exceeds 0.5 μm, the cycle characteristics of a battery including the electrode 1 may be deteriorated. The thickness of the adhesive layer 7 is preferably 0.35 μm or less, more preferably 0.2 μm or less. On the other hand, the thickness of the adhesive layer 7 is preferably 0.01 μm or more. When the thickness of the adhesive layer 7 is less than 0.01 μm, when the electrode active material layer 9 is formed quickly, the electrode active material layer 9 may not be sufficiently bonded to the conductive layer 5 by the adhesive layer 7, which may result in a reduced yield. The thickness of the adhesive layer 7 is preferably 0.05 μm or more, more preferably 0.1 μm or more. The thickness of the adhesive layer 7 can be adjusted, for example, by adjusting the depth of the recesses provided on the circumferential surface of the gravure roll or the viscosity of the binder liquid.

[0040] The thickness of the conductive layer 5 is preferably 3 μm or less. When the conductive layer 5 is thin, the energy density of a battery incorporating the electrode 1 is increased, thereby enabling the volume of the battery to be reduced. Furthermore, when the conductive layer 5 is thin, the rate characteristics of a battery incorporating the electrode 1 are more likely to be ensured. The thickness of the conductive layer 5 is preferably 1 μm or less, and more preferably 0.5 μm or less. On the other hand, the thickness of the conductive layer 5 is preferably 0.04 μm or more. If the conductive layer 5 is too thin, the resistance of the electrode 1 is likely to increase, and the internal resistance of a battery incorporating the electrode 1 is likely to increase. Furthermore, if the conductive layer 5 is too thin, the cycle characteristics of a battery incorporating the electrode 1 are likely to deteriorate. The thickness of the conductive layer 5 is preferably 0.1 μm or more, and more preferably 0.2 μm or more. The thickness of the conductive layer 5 can be adjusted, for example, by adjusting the supply amount and solids concentration of the slurry containing the conductive agent to be attached to the current collector 3.

[0041] The electrode active material layer 9 preferably contains granulated particles formed by solidifying the electrode active material. The granulated particles formed by solidifying the electrode active material are particles in which the electrode active material, a conductive additive, and a binder are aggregated. Each of the overlapping ellipses in the electrode active material layer 9 shown in FIG. 1 schematically represents a granulated particle. Granulated particles can be used as a material for the electrode active material layer 9 formed by a dry process. Therefore, when the electrode active material layer 9 is formed using the granulated particles, the slurry drying step required when forming the electrode active material layer 9 by a wet process is not required. When forming the electrode active material layer 9 using a wet process, if the current collector coated with the slurry is transported at high speed to improve production efficiency, the transport path required for drying the slurry becomes long, resulting in an increase in the size of the equipment used to form the electrode active material layer 9. To avoid such an increase in the size of the equipment, it is necessary to limit the transport speed of the current collector and the speed at which the electrode active material layer 9 is formed. However, if the drying step is not required, a transport path for drying the slurry is also not required, eliminating the need to limit the transport speed of the current collector and the rate at which the electrode active material layer 9 is formed. Therefore, forming the electrode active material layer 9 using granulated particles can improve the production efficiency of the electrode 1. In this case, if the current collector is transported at high speed to quickly form the electrode active material layer using granulated particles, the granulated particles may not adhere well to the current collector, resulting in insufficient bonding strength. In particular, since the electrode active material layer generally contains only the amount of binder necessary to form the particles, the bonding strength between the granulated particles and the current collector is likely to be insufficient. The electrode 1 of this embodiment includes the adhesive layer 7, which adheres the granulated particles to the conductive layer 5 during the formation of the electrode active material layer 9. Therefore, when the electrode active material layer 9 is formed quickly, the electrode active material layer 9 is firmly bonded to the conductive layer 5. This allows the electrode 1 to be produced with a high yield using granulated particles.

[0042] The method for forming granulated particles is not particularly limited, and examples thereof include spray granulation, stirring granulation, fluidized bed granulation, rolling granulation, extrusion granulation, and compression granulation. These granulation methods may be selected or combined as desired. Examples of spray granulation methods include spray-drying granulation. In the spray-drying granulation method, for example, granulation is performed by spraying a dispersion of an electrode active material and a conductive additive into high-temperature gas in a spray dryer. In the stirring granulation method, for example, granulation is performed by adding a dispersion of a conductive additive dispersed therein to the electrode active material particles while spraying the dispersion while mixing and stirring the electrode active material. The average particle size of the granulated particles is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more, and preferably 90 μm or less, more preferably 80 μm or less, and even more preferably 70 μm or less. The average particle size of the granulated particles means the particle size at 50% of the integrated value (median size: D50) in the particle size distribution (volume basis) measured by a laser diffraction scattering method.

[0043] The electrode active material layer 9 may not contain granulated particles. The electrode active material layer 9 may be produced by a wet method.

[0044] (Battery) A battery according to an embodiment includes the electrode 1 according to the above embodiment as an electrode. According to one example, the battery according to the embodiment includes a positive electrode, a negative electrode, a separator, an electrolyte, an outer container, a positive electrode terminal, and a negative electrode terminal. In the battery according to the above example, a stack in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween is housed in an outer container together with the electrolyte. A positive electrode terminal electrically connected to the current collector of the positive electrode and a negative electrode terminal electrically connected to the current collector of the negative electrode are each partially or entirely drawn out to the outside of the outer container. One or more positive electrodes, negative electrodes, and separators may be provided.

[0045] Of the electrodes 1 in the above embodiment, the electrode located between both ends in the stacking direction has a conductive layer 5, an adhesive layer 7, and an electrode active material layer 9 formed on both sides of the current collector 3. The electrodes (e.g., negative electrodes) located at both ends in the stacking direction of the laminate have a conductive layer 5, an adhesive layer 7, and an electrode active material layer 9 formed only on the surface of the current collector 3 on the side where the separator is located.

[0046] The separator may be, for example, a porous separator. The separator may be in the form of, for example, a membrane, a film, or a nonwoven fabric. The porous separator may be, for example, a polyolefin-based porous separator such as a polypropylene-based or polyethylene-based porous separator; a porous separator formed from polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or a polyvinylidene fluoride-hexafluoropropylene copolymer; or the like.

[0047] The laminate may be in the form of a flat plate or a spiral.

[0048] The electrolyte is preferably a non-aqueous electrolyte, and is a mixture containing a chain carbonate such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), di-n-propyl carbonate, di-isopropyl carbonate, di-n-butyl carbonate, di-isobutyl carbonate, or di-t-butyl carbonate, and a cyclic carbonate such as propylene carbonate (PC) or ethylene carbonate (EC). The electrolyte is preferably a mixture of such a carbonate mixture and lithium hexafluorophosphate (LiPF ６ ), lithium fluoroborate (LiBF ４ ), lithium perchlorate (LiClO ４ ) or other lithium salts dissolved therein.

[0049] The positive electrode terminal may be made of aluminum or an aluminum alloy, and the negative electrode terminal may be made of copper, a copper alloy, or a nickel-plated copper or copper alloy.

[0050] The outer container may be, for example, a flexible film having a resin layer on the front and back surfaces of a metal layer such as aluminum as a base material, or a metal can such as aluminum, iron, or stainless steel.

[0051] Examples of the shape of the battery include a pouch-type battery housed in an outer container mainly made of aluminum film, and also square, cylindrical, coin, and button-type batteries housed in an outer container using a metal can.

[0052] The battery of this embodiment is suitable as a non-aqueous electrolyte secondary battery, particularly as a lithium ion secondary battery.

[0053] (1) First Experimental Example In order to examine the effects of the present invention, test batteries were fabricated using negative electrodes and positive electrodes fabricated with various specifications.

[0054] (Production of Negative Electrode) A slurry containing carbon black (manufactured by Imerys) as a conductive agent and polyvinylidene fluoride (PVDF) as a binder was applied to a copper foil serving as a negative electrode current collector, and then dried to form a conductive layer on the negative electrode current collector with various specifications shown in Table 1, thereby obtaining a negative electrode current collector with a conductive layer. Note that in Comparative Example 2, the formation of the conductive layer was omitted.

[0055] Next, polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) were dissolved or dispersed in a solvent to prepare a binder solution with the desired viscosity. The binder solution was applied to the peripheral surface of a gravure roll, and excess binder solution was scraped off with a doctor blade to retain it in the recesses of the gravure roll. The binder solution was then transferred to a negative electrode current collector with a conductive layer, which was then dried. An adhesive layer with various specifications shown in Table 1 was formed on the negative electrode current collector with a conductive layer (negative electrode current collector in Comparative Example 2), thereby obtaining a negative electrode current collector with an adhesive layer. The binder / solvent mass ratio of the binder solution was 30:70. Recesses were formed on the peripheral surface of the gravure roll to obtain dot-shaped regions 7a as shown in FIG. 2. In Comparative Example 1, the formation of an adhesive layer was omitted.

[0056] Separately from the formation of the conductive layer and adhesive layer, granulated particles for the negative electrode active material layer were prepared. As the negative electrode active material particles, a negative electrode dispersion was prepared in which artificial graphite with an average particle size of 12 μm, silicon monoxide with an average particle size of 5 μm, single-walled carbon nanotubes (SWCNT) as a conductive additive, and polyacrylic acid (PAA) and styrene butadiene rubber (SBR) as binders were highly dispersed together with a solvent. The negative electrode dispersion prepared by the above procedure was then sprayed into a spray dryer by rotating an atomizer at a predetermined rotation speed to obtain granulated particles. The mass ratio of artificial graphite / silicon monoxide / SWCNT / PAA / SBR was 92.4:5.0:0.1:2.0:0.5. The artificial graphite was manufactured by Nippon Graphite Industries Co., Ltd., the PAA was manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and the SWCNT was manufactured by OCSiAl.

[0057] Next, the obtained granulated particles were supplied at a constant supply rate to a negative electrode current collector with an adhesive layer (a negative electrode current collector with a conductive layer in Comparative Example 1) traveling at 5 m / min from the delivery side toward the take-up side of an electrode coater, and the amount of granulated particles supplied to the press roll was adjusted by the squeegee roll until the granulated particles were compressed by the press roll. Thereafter, the negative electrode current collector with an adhesive layer was passed between the press rolls to form an active material layer, thereby obtaining a negative electrode.

[0058] For each of the examples and comparative examples, multiple negative electrodes were prepared, and the thickness of the conductive layer, the thickness of the adhesive layer, the coverage of the conductive layer, and the aspect ratio of the conductive agent particles of one arbitrarily selected negative electrode were determined. The thickness of the conductive layer and the thickness of the adhesive layer were both the average of the thicknesses at three locations selected within an image of the cross section of the negative electrode observed by SEM. The coverage of the conductive layer was calculated as described above after peeling the active material layer from the negative electrode. Multiple observation regions were selected within the image of the adhesive layer photographed with a microscope or SEM, and the proportion of the area of ​​the dot-shaped regions 7a included in each observation region was calculated for each observation region, and the average value was used as the coverage of the conductive layer. When observing an image of the pattern shape of the adhesive layer 7 in Example 1, the size (maximum length) of the dot-shaped regions 7a was 200 to 250 μm, and the spacing between adjacent dot-shaped regions 7a was 30 to 70 μm. The aspect ratio of the conductive agent particles was determined as the average value of the ratio of the major axis to the minor axis (major axis / minor axis) calculated for each of 100 conductive agent particles randomly selected from the SEM image.

[0059] (Battery manufacturing) As the positive electrode active material, LiNi with an average particle size of 4.5 μm ０．９２ Mn ０．０３ Co ０．０５ O ２ A slurry containing carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder was applied to an aluminum foil serving as a positive electrode current collector, and then the aluminum foil was dried and pressed to form an active material layer on the positive electrode current collector, thereby obtaining a positive electrode.

[0060] The positive and negative electrodes were stacked with a polyolefin-based porous separator interposed therebetween, and a negative electrode terminal electrically connected to each negative electrode and a positive electrode terminal electrically connected to each positive electrode were provided to obtain a laminate. Next, a mixed solvent of ethylene carbonate and diethyl carbonate (ethylene carbonate:diethyl carbonate=3:7 (volume ratio)) was added with LiPF as an electrolyte. ６ The resulting laminate was housed in an outer container made of a flexible film, and the container was sealed with the positive electrode terminal and the negative electrode terminal extended to the outside, thereby obtaining a secondary battery.

[0061] (Yield) For each of the Examples and Comparative Examples, 2 The yield was evaluated as "high" when the total number of defects per test, such as granulated particle shedding, dents, or striations that appeared in the negative electrode active material layer, was one or zero, and was evaluated as "low" when the total number of defects was two or more. "Dent" refers to a portion of the negative electrode active material layer where the granulated particles slid against the conductive layer or current collector when the squeegee roll came into contact with the granulated particles, resulting in localized accumulation. "Striations" refers to a portion of the negative electrode active material layer where the granulated particles were removed due to contact with the squeegee roll.

[0062] (Resistance Ratio) A test battery with a remaining capacity (SOC) of 50% was prepared, and a constant current discharge of 1.0 C was performed for 10 seconds at 25°C. The voltage at the end of the discharge was measured to determine the direct current resistance (DCR) of the battery. The volume of the battery was measured in accordance with JIS Z 8807, "Method for measuring density and specific gravity of solids - Method for measuring density and specific gravity by the submerged weighing method." The measured resistance value was normalized by the resistance value of Example 1 and is shown in Table 1 as a resistance ratio. The smaller the resistance ratio, the smaller the internal resistance of the battery. The resistance value of Example 1 was 0.7 Ω.

[0063] (Resistance Increase Rate) At a temperature of 45°C, the battery was charged at a constant current of 1.0 C up to a voltage of 4.2 V, and then charged at a constant voltage of 4.2 V down to a charge cut-off current of 0.015 C. CC discharge was then performed at a discharge rate of 1.0 C and a discharge cut-off voltage of 2.5 V. This charge / discharge cycle was repeated 300 times. The resistance increase rate (%) was calculated by dividing the direct current resistance (DCR) of the battery after 300 cycles by the direct current resistance (DCR) of the battery at the first cycle. The smaller the resistance increase rate, the smaller the increase rate of the internal resistance of the battery. A resistance increase rate of less than 15% was evaluated as having good cycle characteristics, and a resistance increase rate of 15% or more was evaluated as having poor cycle characteristics.

[0064]

[0065] As can be seen from a comparison between Example 1 and Comparative Example 1, electrodes having an adhesive layer can be produced with a high yield. As can be seen from a comparison between Example 1 and Comparative Example 2, batteries produced using electrodes having a conductive layer have a low rate of increase in the internal resistance of the battery and good cycle characteristics.

[0066] As can be seen from the comparison between Example 9 and Example 15, when the thickness of the adhesive layer is 0.5 μm or less, the resistance of the battery is reduced.

[0067] As can be seen from the comparison between Example 1 and Example 17, when a conductive layer is provided and the binder content is 90 mass % or less, the resistance of the battery is reduced.

[0068] (2) Second Experimental Example In order to examine the effect of the present invention, test batteries were fabricated using positive electrodes and negative electrodes fabricated with various specifications.

[0069] (Production of Positive Electrode) A slurry containing carbon black (manufactured by Imerys) as a conductive agent and polyvinylidene fluoride (PVDF) as a binder was applied to an aluminum foil serving as a positive electrode current collector, and then dried to form a conductive layer on the positive electrode current collector with various specifications shown in Table 2, thereby obtaining a positive electrode current collector with a conductive layer. Note that in Comparative Example 22, the formation of the conductive layer was omitted.

[0070] Next, polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) were dissolved or dispersed in a solvent to prepare a binder solution with the desired viscosity. The binder solution was applied to the peripheral surface of a gravure roll, and excess binder solution was scraped off with a doctor blade to retain it in the recesses of the gravure roll. The binder solution was then transferred to a positive electrode current collector with a conductive layer, which was then dried. An adhesive layer with various specifications shown in Table 2 was formed on the positive electrode current collector with a conductive layer (positive electrode current collector in Comparative Example 22), thereby obtaining a positive electrode current collector with an adhesive layer. The binder / solvent mass ratio of the binder solution was 30:70. Recesses were formed on the peripheral surface of the gravure roll to obtain dot-shaped regions 7a as shown in Figure 2. In Comparative Example 21, the formation of the adhesive layer was omitted.

[0071] Separately from the formation of the conductive layer and adhesive layer, granulated particles for the positive electrode active material layer were prepared. A dispersion of the conductive additive was prepared by highly dispersing acetylene black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder together with a solvent. Next, LiNi particles with an average particle size of 4 μm, which are the positive electrode active material particles, were dispersed. ０．９２ Mn ０．０３ Co ０．０５ O ２ Nickel manganese cobalt lithium oxide (NMC) represented by the formula (I) was placed in an agitator granulator, and while stirring by rotating the agitator blades and chopper at a predetermined rotation speed, the dispersion of the conductive additive prepared by the above procedure was sprayed into the agitator granulator to obtain granulated particles. The mass ratio of NMC / acetylene black / PVDF was 96:2:2. NMC from Nichia Corporation, acetylene black from Fujifilm Wako Pure Chemical Industries, Ltd., and PVDF from Kureha Corporation can be used.

[0072] Next, the obtained granulated particles were supplied at a constant supply rate to a positive electrode current collector with an adhesive layer (a positive electrode current collector with a conductive layer in Comparative Example 21) traveling at 1 m / min from the delivery side toward the take-up side of an electrode coater, and the amount of granulated particles supplied to the press roll was adjusted by the squeegee roll until the granulated particles were compressed by the press roll.The granulated particles were then passed between the press rolls to form an active material layer on the positive electrode current collector with an adhesive layer, thereby obtaining a positive electrode.

[0073] For each of the examples and comparative examples, multiple positive electrodes were prepared, and the thickness of the conductive layer and the thickness of the adhesive layer of one arbitrarily selected positive electrode were determined in the same manner as described in the first experimental example. The aspect ratio of the conductive agent particles and the coverage of the conductive layer of one arbitrarily selected positive electrode were determined in the same manner as described in the first experimental example, except that a positive electrode was used instead of a negative electrode. When an image of the pattern shape of the adhesive layer 7 in Example 21 was observed, the size (maximum length) of the dot-shaped regions 7a was 200 to 250 μm, and the spacing between adjacent dot-shaped regions 7a was 30 to 70 μm.

[0074] (Manufacture of Battery) A slurry containing artificial graphite with an average particle size of 11 μm as the negative electrode active material, single-walled carbon nanotubes (SWCNT) as a conductive additive, and polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) as binders was applied to copper foil as a negative electrode current collector, followed by drying and pressing to form an active material layer on the negative electrode current collector, thereby obtaining a negative electrode.

[0075] The positive and negative electrodes were stacked with a polyolefin-based porous separator interposed therebetween, and a positive electrode terminal electrically connected to each positive electrode and a negative electrode terminal electrically connected to each negative electrode were provided to obtain a laminate. Next, a mixed solvent of ethylene carbonate and diethyl carbonate (ethylene carbonate:diethyl carbonate=3:7 (volume ratio)) was added with LiPF as an electrolyte. ６ The resulting laminate was housed in an outer container made of a flexible film, and the container was sealed with the positive electrode terminal and the negative electrode terminal extended to the outside, thereby obtaining a secondary battery.

[0076] For each of the examples and comparative examples, the yield was evaluated in the same manner as described in the first experimental example, except that a positive electrode was used instead of a negative electrode. Furthermore, for each of the examples and comparative examples, the resistance ratio and the resistance increase rate were calculated and evaluated in the same manner as described in the first experimental example. The resistance value of Example 21 was 0.8 Ω.

[0077]

[0078] As can be seen from a comparison between Example 21 and Comparative Example 21, a positive electrode having an adhesive layer can be produced with a high yield. As can be seen from a comparison between Example 21 and Comparative Example 22, a battery produced using a positive electrode having a conductive layer has a low rate of increase in the internal resistance of the battery and good cycle characteristics.

[0079] As can be seen from the comparison between Example 29 and Example 35, when the thickness of the adhesive layer is 0.5 μm or less, the resistance of the battery is reduced.

[0080] The electrodes and batteries of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments and experimental examples, and various improvements and modifications may be made without departing from the spirit and scope of the present invention.

[0081] 1 Electrode 3 Current collector 5 Conductive layer 5a Uncovered area 7 Adhesive layer 7a Dot-like area 9 Electrode active material layer

Claims

1. An electrode comprising: a current collector; a conductive layer containing a conductive agent and formed on at least one surface of the current collector; an adhesive layer containing a binder and formed in a predetermined pattern on the conductive layer so as to cover a portion of the conductive layer; and an electrode active material layer containing an electrode active material and formed on a portion of the conductive layer not covered by the adhesive layer and on the adhesive layer.

2. The electrode according to claim 1, wherein the coverage of the conductive layer, which is the ratio of the area of ​​the conductive layer covered by the adhesive layer to the area of ​​the conductive layer, is 30 to 60%.

3. The electrode according to claim 1 or 2, wherein the conductive layer further comprises a binder of 10% by mass or more of the conductive layer.

4. The electrode according to claim 1 or 2, wherein the aspect ratio of the particles of the conductive agent is 10 or less.

5. The electrode according to claim 1 or 2, wherein the thickness of the adhesive layer is 0.5 μm or less.

6. The electrode according to claim 1 or 2, wherein the conductive layer has a thickness of 3 μm or less.

7. The electrode according to claim 1 or 2, wherein the electrode active material layer contains granulated particles of the electrode active material.

8. The electrode of claim 1, wherein the conductive layer further comprises a binder, the binder being 90% or less by weight of the conductive layer.

9. The electrode according to claim 1 or 8, wherein the conductive layer has a thickness of 0.04 μm or more.

10. A battery comprising the electrode according to claim 1 or 2.

Images