Positive electrode for secondary battery, secondary battery, method for producing positive electrode for secondary battery, and method for producing secondary battery

Abstract

This positive electrode for a secondary battery has a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, wherein: the positive electrode mixture layer contains a positive electrode active material, a binder, and a nonionic surfactant; and when a positive electrode mixture slurry is prepared by dispersing the positive electrode mixture layer in an N-methyl-2-pyrrolidone solvent, a viscosity curve R of the positive electrode mixture slurry is divided into an overlapping region A, in which the viscosity curve R overlaps with an apparent viscosity curve L, of the positive electrode mixture slurry, obtained on the basis of Andrade's equation, and a deviation region B, in which the viscosity curve R deviates toward a higher viscosity side than the apparent viscosity curve L, and the reciprocal of the absolute temperature (1 / T [K-1]) of the positive electrode mixture slurry at a boundary point D between the overlapping region A and the deviation region B is at most 0.0033 [K-1].

Description

Positive electrode for secondary battery, secondary battery, method for manufacturing positive electrode for secondary battery, and method for manufacturing secondary battery

[0001] The present disclosure relates to technologies of a positive electrode for a secondary battery, a secondary battery, a method for manufacturing a positive electrode for a secondary battery, and a method for manufacturing a secondary battery.

[0002] In recent years, as a secondary battery with high output and high energy density, a secondary battery including a positive electrode, a negative electrode, and an electrolyte, which performs charge and discharge by moving lithium ions or the like between the positive electrode and the negative electrode, has been widely used.

[0003] The positive electrode is manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, and a solvent onto a positive electrode current collector, then heating and drying to form a positive electrode mixture layer, and rolling the positive electrode mixture layer.

[0004] By the way, when the viscosity of the positive electrode mixture slurry is high during the application of the positive electrode mixture slurry, the swelling at the application start end of the positive electrode mixture slurry applied on the positive electrode current collector becomes large. Therefore, in the positive electrode mixture layer after rolling, the coating weight at the application start end becomes higher than that of other parts. As a result, for example, Li precipitation is likely to occur in the negative electrode facing part facing the application start end of the positive electrode mixture layer, or when the positive electrode and the negative electrode are wound to produce a wound electrode, the stress applied to the positive electrode increases, and cracks may occur.

[0005] In order to suppress the swelling at the application start end, when the viscosity of the positive electrode mixture slurry is lowered, the amount of movement of the binder becomes large during the heating and drying of the positive electrode mixture slurry, and the binder moves to the surface of the positive electrode mixture layer, so the adhesion between the positive electrode mixture layer and the positive electrode current collector decreases.

[0006] For example, Patent Document 1 discloses an electrode plate for a battery in which the thickness of the swelling part at the start end is controlled to be 10% to 80% of the thickness of the flat part.

[0007] Japanese Patent Application Laid-Open No. 2002-124249

[0008] Therefore, an object of the present disclosure is to provide a positive electrode for a secondary battery and a method for manufacturing a positive electrode for a secondary battery that suppress an increase in the coating weight at the application start end of the positive electrode mixture layer and suppress a decrease in the adhesion between the positive electrode mixture layer and the positive electrode current collector.

[0009] The positive electrode for a secondary battery according to one aspect of the present disclosure has a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode mixture layer contains a positive electrode active material, a binder, and a nonionic surfactant. When a positive electrode mixture slurry in which the positive electrode mixture layer is dispersed in an N-methyl-2-pyrrolidone solvent is prepared, the reciprocal of the absolute temperature (1 / T: [K －１ ]) is plotted on the horizontal axis, and the natural logarithm (ln η: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry is plotted on the vertical axis. The viscosity curve of the positive electrode mixture slurry obtained by plotting is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviating region that deviates to a higher viscosity side than the apparent viscosity curve. The reciprocal of the absolute temperature (1 / T: [K －１ ]) of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviating region is 0.0033 [K －１ ].

[0010] Further, the secondary battery according to one aspect of the present disclosure includes the positive electrode for a secondary battery described above.

[0011] Further, the method for manufacturing a positive electrode for a secondary battery according to one aspect of the present disclosure includes a step of applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a nonionic surfactant, and a solvent onto a positive electrode current collector and then heating and drying to form a positive electrode mixture layer. In the positive electrode mixture slurry, the reciprocal of the absolute temperature (1 / T: [K －１ ]) is plotted on the horizontal axis, and the natural logarithm (ln η: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry is plotted on the vertical axis. The viscosity curve of the positive electrode mixture slurry obtained by plotting is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviating region that deviates to a higher viscosity side than the apparent viscosity curve. The reciprocal of the absolute temperature (1 / T: [K －１ ]) of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviating region is 0.0033 [K －１ ].

[0012] Furthermore, a method for manufacturing a secondary battery according to one aspect of this disclosure involves manufacturing a secondary battery using a positive electrode manufactured by the above-described method for manufacturing a positive electrode for a secondary battery.

[0013] According to one aspect of this disclosure, it is possible to suppress an increase in the amount of material at the starting end of the coating of the positive electrode mixture layer and to suppress a decrease in the adhesion between the positive electrode mixture layer and the positive electrode current collector.

[0014] This is a cross-sectional view of a secondary battery, which is an example of an embodiment. This is a diagram showing the viscosity curve of the positive electrode mixture slurry of this embodiment.

[0015] An example of an embodiment will be described in detail below. The drawings referenced in the description of the embodiment are schematic representations, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual objects.

[0016] Figure 1 is a cross-sectional view of a secondary battery, which is an example of an embodiment. The secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, an electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, respectively, a battery case 15, a positive electrode lead 20, and a negative electrode lead 21. The battery case 15 is composed of a case body 16 having an opening and housing the electrode body 14, etc., and a sealing body 17 that closes the opening of the case body 16. In addition, other forms of electrode bodies may be used instead of the wound electrode body 14, such as a laminated electrode body in which the positive electrode and negative electrode are alternately stacked with a separator. Furthermore, the battery case 15 can be exemplified by metal cases such as cylindrical, rectangular, coin-shaped, or button-shaped cases, or resin cases (so-called pouch type) formed by laminating resin sheets.

[0017] The electrolyte, for example, has lithium ion conductivity. The electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0018] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0019] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc. Although the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may also be an aqueous electrolyte.

[0020] The case body 16 is, for example, a metal container in the shape of a bottomed cylinder. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22 that supports the sealing body 17, which is a part of the side surface that protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and its upper surface supports the sealing body 17.

[0021] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 towards the cap 27, thus interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0022] In the secondary battery 10 shown in Figure 1, the positive electrode lead 20 attached to the positive electrode 11 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 attached to the negative electrode 12 extends outside the insulating plate 19 towards the bottom of the case body 16. The positive electrode lead 20 is connected by welding or the like to the lower surface of the filter 23, which is the bottom plate of the sealing body 17, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner surface of the bottom of the case body 16, and the case body 16 becomes the negative electrode terminal.

[0023] The positive electrode 11, negative electrode 12, and separator 13 are described in detail below.

[0024] The positive electrode 11 comprises a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector. The positive electrode mixture layer may be provided on one side of the positive electrode current collector or on both sides of the positive electrode current collector.

[0025] The positive electrode current collector can be made of a metal foil that is stable within the positive electrode potential range, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode current collector has a thickness of, for example, about 1 μm to 100 μm.

[0026] The positive electrode mixture layer contains a positive electrode active material, a binder, and a nonionic surfactant. The positive electrode mixture layer may also contain a conductive agent.

[0027] The positive electrode 11 of the present embodiment is produced, for example, by a production method having a step of forming a positive electrode mixture layer by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a nonionic surfactant, an optional conductive agent, and a solvent onto a positive electrode current collector and then drying by heating. The solvent in the positive electrode mixture slurry may be a conventionally known one, and examples thereof include N-methyl-2-pyrrolidone and the like.

[0028] The positive electrode active material includes, for example, a lithium-containing composite oxide containing lithium (Li) and transition metal elements such as cobalt (Co), manganese (Mn), and nickel (Ni). The lithium-containing composite oxide may contain other additive elements other than Co, Mn, and Ni, and examples thereof include aluminum (Al), zirconium (Zr), magnesium (Mg), scandium (Sc), yttrium (Y), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), lead (Pb), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), Sb (antimony), boron (B), and silicon (Si).

[0029] The lithium-containing composite oxide preferably contains Ni, for example, in terms of increasing the capacity of the battery. The content of Ni in the lithium-containing composite oxide is preferably in the range of 50 mol% or more and 100 mol% or less, more preferably 65 mol% or more and 97 mol% or less, based on the total number of moles of metal elements excluding Li. As the lithium-containing composite oxide, for example, the formula: Li ｙ Ni ｘ Co ｃ M （１－ｘ） O ２－δ (wherein x, y, and δ satisfy 0.5 ≦ x ≦ 1, 0 < y ≦ 1.2, -0.05 ≦ δ ≦ 0.05, and M contains at least one element selected from Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B) is preferred. Further, x more preferably satisfies 0.8 ≦ x ≦ 1. The content of the elements constituting the lithium-containing composite oxide can be measured, for example, by an inductively coupled plasma optical emission spectrometer (ICP-AES).

[0030] Examples of binders include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0031] The binder preferably contains polyvinylidene fluoride (PVDF) in terms of adhesion between the positive electrode mixture layer and the positive electrode current collector. The polyvinylidene fluoride content in the positive electrode mixture slurry may be, for example, 0.1% by mass or more and 3% by mass or 0.1% by mass or more and 1% by mass or less, based on the total mass of solids in the positive electrode mixture slurry. That is, the polyvinylidene fluoride content in the prepared positive electrode mixture layer may be, for example, 0.1% by mass or more and 3% by mass or 0.1% by mass or more and 1% by mass or less, based on the total mass of the positive electrode mixture layer.

[0032] Examples of conductive agents include carbon black such as acetylene black and Ketjenblack, carbon nanotubes (CNTs), graphene, and carbon-based particles such as graphite. These may be used individually or in combination of two or more types. The content of the conductive agent may be 0.01% by mass or more, or 0.1% by mass or more, or 0.5% by mass or more, based on the total mass of solids in the positive electrode mixture slurry (i.e., the total mass of the prepared positive electrode mixture layer), for example, in terms of improving battery capacity.

[0033] The BET specific surface area of ​​the conductive agent is 80 m², for example, in terms of imparting conductivity to the positive electrode mixture layer and ensuring adhesion. ２ It is preferable that it be 100m or more per gram. ２ / g or more, 500m ２ It is more preferable that the amount is less than or equal to / g. The BET specific surface area can be measured by a known method, for example, by measuring it based on the BET method using a specific surface area measuring device (e.g., manufactured by Mountec Co., Ltd.).

[0034] Examples of nonionic surfactants include fatty acid glycerol esters, fatty acid sorbitan esters, fatty acid sucrose esters, alkyl polyglucosides, polyoxyethylene propylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene polyoxypropylene glycol, among other polyoxyalkylene alkyl ethers.

[0035] The viscosity of the positive electrode mixture slurry is described below. Figure 2 shows the viscosity curve of the positive electrode mixture slurry in this embodiment. The viscosity curve R of the positive electrode mixture slurry shown in Figure 2 is the reciprocal of the absolute temperature of the positive electrode mixture slurry (1 / T: [K]). －１ This can be obtained by plotting the coefficient of viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm (lnη: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry on the vertical axis.

[0036] The shear viscosity of the positive electrode mixture slurry was measured using a rheometer "MCR302" (manufactured by Anton Paar) at a shear rate of 50 s⁻¹. －１ The values ​​were measured under the conditions of a starting temperature of 20°C and a heating rate of 0.05°C / s.

[0037] In the positive electrode mixture slurry of this embodiment, the viscosity curve R of the positive electrode mixture slurry is divided into an overlapping region A, which overlaps with the apparent viscosity curve L of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviation region B, which deviates from the apparent viscosity curve L to the higher viscosity side. The reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point D between overlapping region A and deviation region B is (1 / T: [K]). －１ ]) is 0.0033 [K －１ The following applies. Note that the reciprocal of the absolute temperature of the positive electrode mixture slurry at boundary point D shown in Figure 2 (1 / T: [K]) is the same as above. －１ ]) is 0.0031 [K －１ ]

[0038] Here, the apparent viscosity curve L of the positive electrode mixture slurry obtained based on Andrade's equation is obtained as follows. First, Andrade's equation is expressed by equation (1): η = B・exp(-E / (R・T)) ... (1) η: viscosity of the positive electrode mixture slurry at absolute temperature T [K] [Pa・s] R: gas constant [J・K] －１ ・mol －１ ] E: Fluid activation energy [J・mol －１ ] B: Constant [Pa・s]

[0039] Then, taking the logarithm of both sides of Andrade's equation above, we obtain equation (2): lnη = lnA + (E / (RT)) ... (2)

[0040] In the viscosity curve R of the positive electrode mixture slurry based on actual measurements, the linear portion is 1 / T:[K －１ The slope and intercept of the viscosity curve R are calculated for the range of 0.0033 to 0.0034. The calculated slope corresponds to E / R in equation (2), and the calculated intercept corresponds to lnA.

[0041] Using equation (2) to which the obtained E / R and lnA are applied, the reciprocal of the absolute temperature (1 / T: [K]) is calculated. －１ By plotting ) on the horizontal axis and lnη on the vertical axis, the apparent viscosity curve L of the positive electrode mixture slurry obtained based on Andrade's equation can be obtained.

[0042] Incidentally, in the case of a typical positive electrode mixture slurry that does not contain nonionic surfactants, the viscosity decreases with increasing temperature, so the viscosity curve of the measured positive electrode mixture slurry follows the apparent viscosity curve based on Andrade's equation. Therefore, when the positive electrode mixture slurry applied to the positive electrode current collector is heated and dried, the viscosity of the positive electrode mixture slurry decreases, causing the binder in the slurry to move to the surface. As a result, the adhesion between the positive electrode mixture layer and the positive electrode current collector decreases. On the other hand, in the positive electrode mixture slurry of this embodiment having the viscosity curve described above, when the positive electrode mixture slurry applied to the positive electrode current collector is heated and dried, the dispersibility of the nonionic surfactant changes, suppressing the decrease in viscosity of the positive electrode mixture slurry, or even increasing its viscosity compared to before heating and drying. This makes it difficult for the binder in the positive electrode mixture slurry applied to the positive electrode current collector to move to the surface, thus suppressing the decrease in adhesion between the positive electrode mixture layer and the positive electrode current collector. Furthermore, since the viscosity decrease of the positive electrode mixture slurry during heating and drying can be suppressed or increased, a low-viscosity positive electrode mixture slurry can be used when applying the positive electrode mixture slurry to the positive electrode current collector, thus suppressing the bulging at the beginning of the application of the positive electrode mixture slurry. Consequently, the increase in the basis weight at the beginning of the positive electrode mixture layer after rolling can be suppressed. As a result, for example, Li deposition can be suppressed at the negative electrode facing portion opposite the application beginning of the positive electrode mixture layer, and crack generation when the positive electrode is wound can be suppressed.

[0043] In the viscosity curve of the positive electrode mixture slurry of this embodiment, the reciprocal of the absolute temperature of the positive electrode mixture slurry at boundary point D (1 / T: [K]) is used. －１ ]) is effective in further suppressing the increase in basis weight at the starting point of coating the positive electrode mixture layer, or in further suppressing the decrease in adhesion between the positive electrode mixture layer and the positive electrode current collector, and is 0.028 [K －１ ] or more, 0.0033[K －１ Preferably less than or equal to 0.0028 [K －１ ] or more, 0.0031[K －１ It is more preferable that the following conditions be met.

[0044] In the viscosity curve of the positive electrode mixture slurry of this embodiment, the deviation region B is preferably a curve that is convex downwards. That is, in the deviation region B, it is preferable that there is a region in which the value of the natural logarithm of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry (lnη: [Pa·s]) rises from its lowest value. This makes it possible to increase the viscosity of the positive electrode mixture slurry when it is heated and dried, and the binder in the positive electrode mixture slurry applied to the positive electrode current collector is less likely to move to the surface, so the decrease in adhesion between the positive electrode mixture layer and the positive electrode current collector can be further suppressed.

[0045] The nonionic surfactant is preferably one that has a cloud point in the temperature range when the positive electrode mixture slurry is heated and dried, more preferably one that has a cloud point in the range of 30°C to 100°C, and more preferably one that has a cloud point in the range of 50°C to 100°C. By using such a nonionic surfactant, for example, it is possible to further suppress the increase in basis weight at the starting point of coating the positive electrode mixture layer, or to further suppress the decrease in adhesion between the positive electrode mixture layer and the positive electrode current collector.

[0046] The content of nonionic surfactant in the positive electrode mixture slurry is preferably, for example, 0.001% by mass or more and 0.05% by mass or less, and more preferably 0.003% by mass or more and 0.01% by mass or less, relative to the mass of the total solids in the positive electrode mixture slurry. That is, the content of nonionic surfactant in the prepared positive electrode mixture layer is preferably, for example, 0.001% by mass or more and 0.05% by mass or less, and more preferably 0.003% by mass or more and 0.01% by mass or less, relative to the total mass of the positive electrode mixture layer. By setting the content of nonionic surfactant within the above range, for example, in the viscosity curve of the positive electrode mixture slurry, the reciprocal of the absolute temperature of the positive electrode mixture slurry at boundary point D (1 / T: [K]) can be obtained. －１ ]) is 0.0033 [K －１ It is likely to be as follows:

[0047] The amount of solvent in the positive electrode mixture slurry is preferably 15% by mass or more and 45% by mass or less, relative to the total mass of the positive electrode mixture slurry, in order to further suppress the increase in the amount of material at the starting point of coating the positive electrode mixture layer, or to further suppress the decrease in adhesion between the positive electrode mixture layer and the positive electrode current collector.

[0048] For applying the positive electrode mixture slurry onto the positive electrode current collector, general application methods such as roll coating or gravure coating may be used.

[0049] The temperature at which the positive electrode mixture slurry coated on the positive electrode current collector is heated and dried is preferably above the temperature (°C) corresponding to the boundary point D mentioned above, specifically preferably above 30°C, and more preferably above 50°C and below 100°C.

[0050] It is preferable that the process includes a step of rolling the positive electrode mixture layer after the step of forming the positive electrode mixture layer on the positive electrode current collector. The rolling of the positive electrode mixture layer can be done by any known method, for example, by passing it between a pair of press rollers.

[0051] According to the positive electrode obtained by the manufacturing method of this embodiment, when a positive electrode slurry is prepared by dispersing the positive electrode slurry layer in N-methyl-2-pyrrolidone solvent, the viscosity curve of the positive electrode slurry has the same characteristics as the viscosity curve of the positive electrode slurry described above. That is, in a positive electrode slurry prepared by dispersing the positive electrode slurry layer in N-methyl-2-pyrrolidone solvent, the reciprocal of the absolute temperature of the positive electrode slurry (1 / T: [K]) －１ The viscosity curve of the positive electrode mixture slurry obtained by plotting the coefficient of viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm of the shear viscosity of the positive electrode mixture slurry (η: [Pa·s]) on the vertical axis is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviation region that deviates to the higher viscosity side of the apparent viscosity curve. The reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K)) －１ ]) is 0.0033 [K －１ The following is true. Also, the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point (1 / T: [K]) is true. －１ ]) is 0.028 [K －１] or more, 0.0033[K －１ Preferably less than or equal to 0.0028 [K －１ ] or more, 0.0031[K －１ It is more preferable that the value is below the specified limit. Furthermore, it is preferable that the deviation region is a curve that is convex downwards. The measurement conditions for the shear viscosity of the positive electrode mixture slurry are the same as those described above.

[0052] When dispersing the positive electrode mixture layer in N-methyl-2-pyrrolidone solvent, it is preferable to pulverize the positive electrode mixture layer that has been peeled off from the positive electrode current collector to powderize it, and then disperse it in N-methyl-2-pyrrolidone solvent. The content of N-methyl-2-pyrrolidone solvent in the positive electrode mixture slurry may be 30% by mass relative to the total mass of the positive electrode mixture slurry.

[0053] The secondary battery of this embodiment is manufactured, for example, using a positive electrode obtained by the positive electrode manufacturing method of this embodiment.

[0054] The negative electrode 12 comprises, for example, a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector. The negative electrode mixture layer includes, for example, a negative electrode active material, a binder, etc. The negative electrode mixture layer may be provided on one side of the negative electrode current collector or on both sides of the negative electrode current collector. The negative electrode is manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., onto the negative electrode current collector, drying it to form a negative electrode mixture layer, and then rolling the negative electrode mixture layer.

[0055] The negative electrode current collector can be made of a metal foil that is stable in the negative electrode potential range, such as copper, or a film with the metal arranged on its surface. The negative electrode current collector has a thickness of, for example, 1 μm to 100 μm.

[0056] The negative electrode active material is, for example, a material capable of intercalating and releasing lithium ions. For example, the negative electrode active material can be metallic lithium, lithium-aluminum alloy, lithium-lead alloy, lithium-silicon alloy, lithium-tin alloy, and other lithium alloys, as well as carbon materials such as graphite, coke, and calcined organic materials, and SnO ２ SnO, TiO ２ Examples include metal oxides such as those listed above. These may be used individually or in combination of two or more.

[0057] For example, the binder used is the material exemplified in the positive electrode 11. The negative electrode composite layer may also contain the conductive agent mentioned above.

[0058] For the separator 13, for example, a porous sheet having ion permeability and insulating properties can be used. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator include olefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it may be a multilayer separator containing a polyethylene layer and a polypropylene layer, or a separator with a material such as aramid resin or ceramic coated on its surface may be used.

[0059] The present disclosure will be further illustrated below with reference to examples, but the present disclosure is not limited to these examples.

[0060] <Example 1> [Preparation of positive electrode mixture slurry] A positive electrode active material, a nonionic surfactant, PVdF as a binder, and acetylene black as a conductive agent were mixed in a solid content mass ratio of 100:0.01:1:0.9, an appropriate amount of N-methyl-2-pyrrolidone solvent (NMP solvent) was added, and the mixture was kneaded to prepare a positive electrode mixture slurry. The positive electrode active material contained Li １．０ Ni ０．８９ Co ０．０５ Mn ０．０６ O ２ A lithium-containing composite oxide represented by [formula] was used. Furthermore, a nonionic surfactant with a cloud point of 45°C was used.

[0061] The shear viscosity of the positive electrode mixture slurry was measured in the range of 20°C to 70°C. The reciprocal of the absolute temperature of the positive electrode mixture slurry (1 / T: [K]) was then calculated. －１A viscosity curve of the positive electrode mixture slurry was obtained by plotting the viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry (lnη: [Pa·s]) on the vertical axis. This viscosity curve of the positive electrode mixture slurry was compared with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation. The result showed that the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region where it overlaps with the apparent viscosity curve and the deviation region where it deviates to a higher viscosity side than the apparent viscosity curve was 1 / T: [K]. －１ ]) is 0.0031 [K －１ ]

[0062] [Preparation of the positive electrode] The above positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and then the positive electrode slurry was heated and dried at 90°C to form a positive electrode slurry layer. At this stage, the thickness of the raised portion at the beginning of the application of the positive electrode slurry layer was measured (the same was done for each comparative example described later).

[0063] Next, the positive electrode mixture layer on the positive electrode current collector was rolled using rolling rollers. In this way, a positive electrode was produced in which positive electrode mixture layers were formed on both sides of the positive electrode current collector. Furthermore, the positive electrode mixture layer was removed from the produced positive electrode, powdered, and then mixed with NMP solvent in a mass ratio of 7:3 to prepare a positive electrode mixture slurry. A viscosity curve was created for this positive electrode mixture slurry in the same manner as described above, and compared with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) was obtained. －１ ]) is 0.0031 [K －１ It was confirmed that this was the case.

[0064] <Example 2> A cathode mixture slurry was prepared in the same manner as in Example 1, except that a nonionic surfactant with a cloud point of 100°C was used as the nonionic surfactant, and the shear viscosity was measured. The viscosity curve of the cathode mixture slurry of Example 2 was compared with the apparent viscosity curve of the cathode mixture slurry based on Andrade's equation, and the reciprocal of the absolute temperature of the cathode mixture slurry at the boundary point between the overlapping region where it overlaps with the apparent viscosity curve and the deviation region where it deviates to the higher viscosity side than the apparent viscosity curve was found to be [K]. －１ ]) is 0.0027 [K－１ ]

[0065] A positive electrode was prepared in the same manner as in Example 1 using the positive electrode mixture slurry of Example 2. A positive electrode mixture slurry was prepared from the positive electrode mixture layer removed from the positive electrode in the same manner as in Example 1. A viscosity curve was created for this positive electrode mixture slurry in the same manner as described above, and compared with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) was obtained. －１ ]) is 0.0027 [K －１ It was confirmed that this was the case.

[0066] <Comparative Example 1> A cathode mixture slurry was prepared in the same manner as in Example 1, except that a nonionic surfactant was not used, and the shear viscosity was measured. The viscosity curve of the cathode mixture slurry of Comparative Example 1 only had an overlapping region with the apparent viscosity curve of the cathode mixture slurry based on Andrade's equation.

[0067] A positive electrode was prepared in the same manner as in Example 1 using the positive electrode mixture slurry of Comparative Example 1. A positive electrode mixture slurry was prepared from the positive electrode mixture layer removed from the positive electrode in the same manner as in Example 1. A viscosity curve was created for this positive electrode mixture slurry in the same manner as described above, and it was confirmed that there was only an overlapping region that coincided with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation.

[0068] <Comparative Example 2> A cathode mixture slurry was prepared in the same manner as in Example 1, except that a nonionic surfactant was not used and the amount of PVdF added was 1.2 times that of Example 1, and the shear viscosity was measured. The viscosity curve of the cathode mixture slurry of Comparative Example 2 only had an overlapping region with the apparent viscosity curve of the cathode mixture slurry based on Andrade's equation.

[0069] A positive electrode was prepared in the same manner as in Example 1 using the positive electrode mixture slurry of Comparative Example 2. A positive electrode mixture slurry was prepared from the positive electrode mixture layer removed from the positive electrode in the same manner as in Example 1. A viscosity curve was created for this positive electrode mixture slurry in the same manner as described above, and it was confirmed that there was only an overlapping region that coincided with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation.

[0070] <Comparative Example 3> A nonionic surfactant with a cloud point of 15°C was used as the nonionic surfactant, and the temperature was 25°C for 50 seconds. －１ A positive electrode mixture slurry was prepared in the same manner as in Example 1, except that the amount of NMP solvent added was doubled to the amount added in Example 1 so that the shear viscosity matched that of Example 1, and the shear viscosity was measured. The viscosity curve of the positive electrode mixture slurry of Comparative Example 3 was compared with the apparent viscosity curve of the positive electrode mixture slurry based on Andrade's equation, and the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region where it overlaps with the apparent viscosity curve and the deviation region where it deviates to the higher viscosity side than the apparent viscosity curve is 1 / T: [K]. －１ ]) is 0.0035 [K －１ ]

[0071] A positive electrode was prepared in the same manner as in Example 1 using the positive electrode mixture slurry of Comparative Example 3. A positive electrode mixture slurry was prepared from the positive electrode mixture layer removed from the positive electrode in the same manner as in Example 1. A viscosity curve was created for this positive electrode mixture slurry in the same manner as described above, and compared with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) was obtained. －１ ]) is 0.0035 [K －１ It was confirmed that this was the case.

[0072] [Adhesion between the positive electrode current collector and the positive electrode mixture layer] The positive electrode mixture layer surface of each example or comparative example (100 mm x 25 mm) was attached to a 120 mm x 30 mm acrylic plate using double-sided tape (Nichiban Co., Ltd. Nicetack NW-20). Next, using a small benchtop test machine (FGS-TV and FGP-5) manufactured by Nidec-Shimpo Corporation, a 90° peel was performed at a measurement temperature of 25°C and a tensile speed of 50 mm / min, and the strength of the peel strength of the positive electrode mixture layer when it peeled off from the positive electrode current collector was measured.

[0073] Table 1 summarizes the thickness of the raised portion at the coating start of the positive electrode mixture layer for each example and comparative example. However, the thickness of the raised portion at the coating start of Comparative Example 1 is set to 100, and the thicknesses of the raised portion at the coating start of the other examples and comparative examples are shown relatively. If the value of the thickness of the raised portion at the coating start exceeds 100, it indicates that the basis weight at the coating start of the positive electrode mixture layer after rolling has increased. Also, Table 1 summarizes the peel strength of the positive electrode mixture layer for each example and comparative example. However, the peel strength of the positive electrode mixture layer of Comparative Example 1 is set to 100, and the peel strengths of the positive electrode mixture layer of the other examples and comparative examples are shown relatively. The higher the peel strength, the more suppressed the decrease in adhesion between the positive electrode current collector and the positive electrode mixture layer. Furthermore, the shear viscosity of the positive electrode mixture slurry at 25°C and the amount of solvent in the positive electrode mixture slurry described in Table 1 are also shown relatively, with the value of Comparative Example 1 set to 100.

[0074]

[0075] As shown in Table 1, by using the positive electrode mixture slurries of Examples 1 and 2 to produce the positive electrode, it was possible to suppress the increase in the amount of material at the starting point of the coating of the positive electrode mixture layer and to suppress the decrease in adhesion between the positive electrode mixture layer and the positive electrode current collector.

[0076] [Note] Configuration 1: The device comprises a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the positive electrode mixture layer containing a positive electrode active material, a binder, and a nonionic surfactant, and when a positive electrode mixture slurry is prepared by dispersing the positive electrode mixture layer in an N-methyl-2-pyrrolidone solvent, the reciprocal of the absolute temperature of the positive electrode mixture slurry (1 / T: [K]) －１The viscosity curve of the positive electrode mixture slurry obtained by plotting the viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm (lnη: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry on the vertical axis is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviation region that deviates to the higher viscosity side from the apparent viscosity curve, and the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) －１ ]) is 0.0033 [K －１ A positive electrode for a secondary battery, which is as follows: Configuration 2: The reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point (1 / T): [K －１ ]) is 0.0028 [K －１ ] or more, 0.0033[K －１ The positive electrode for a secondary battery as described in Configuration 1, wherein the deviation region is a downwardly convex curve as described in Configuration 1 or 2. Configuration 4 The positive electrode mixture layer has a BET specific surface area of ​​80 m². ２ A positive electrode for a secondary battery according to any one of configurations 1 to 3, comprising a conductive agent in a quantity of 1 / g or more. Configuration 5: The positive electrode active material is of formula: Li ｙ Ni ｘ M （１－ｘ） O ２－δA positive electrode for a secondary battery according to any one of configurations 1 to 4, comprising a lithium-containing composite oxide represented by the formula (wherein x, y, and σ satisfy 0.5 ≤ x ≤ 1, 0 < y ≤ 1.2, and -0.05 ≤ δ ≤ 0.05, and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B). Configuration 6: A positive electrode for a secondary battery according to configuration 5, wherein in the formula, x satisfies 0.8 ≤ x ≤ 1. Configuration 7: A positive electrode for a secondary battery according to any one of configurations 1 to 6, wherein the content of the nonionic surfactant in the positive electrode mixture layer is 0.001% by mass or more and 0.05% by mass or less with respect to the total mass of the positive electrode mixture layer. Configuration 8: A secondary battery comprising the positive electrode for a secondary battery according to any one of configurations 1 to 7. Configuration 9: The process involves applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a nonionic surfactant, and a solvent onto a positive electrode current collector, then heating and drying it to form a positive electrode mixture layer, wherein the reciprocal of the absolute temperature of the positive electrode mixture slurry (1 / T: [K]) is used. －１ The viscosity curve of the positive electrode mixture slurry obtained by plotting the viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm (lnη: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry on the vertical axis is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviation region that deviates to the higher viscosity side from the apparent viscosity curve, and the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) －１ ]) is 0.0033 [K －１ The following is a method for manufacturing a positive electrode for a secondary battery. Configuration 10: A method for manufacturing a secondary battery, which involves manufacturing a secondary battery using a positive electrode manufactured by the method for manufacturing a positive electrode for a secondary battery described in Configuration 9.

[0077] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket.

Claims

1. The positive electrode comprises a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer contains a positive electrode active material, a binder, and a nonionic surfactant, and when a positive electrode mixture slurry is prepared by dispersing the positive electrode mixture layer in an N-methyl-2-pyrrolidone solvent, the reciprocal of the absolute temperature of the positive electrode mixture slurry (1 / T: [K]) －１ The viscosity curve of the positive electrode mixture slurry obtained by plotting the viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm (lnη: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry on the vertical axis is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviation region that deviates to the higher viscosity side from the apparent viscosity curve, and the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) －１ ]) is 0.0033 [K －１ The following is the positive electrode for a secondary battery.

2. The reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point (1 / T: [K]) －１ ]) is 0.0028 [K －１ ] or more, 0.0033[K －１ The positive electrode for a secondary battery according to claim 1, which is as follows:

3. The positive electrode for a secondary battery according to claim 1 or 2, wherein the deviation region is a downwardly convex curve.

4. The positive electrode mixture layer has a BET specific surface area of ​​80 m². ２ A positive electrode for a secondary battery according to claim 1 or 2, comprising a conductive agent in a quantity of 1 g or more.

5. The positive electrode active material is of the formula: Li ｙ Ni ｘ M （１－ｘ） O ２－δ (wherein x, y, and δ satisfy 0.5 ≤ x ≤ 1, 0 < y ≤ 1.2, and -0.05 ≤ δ ≤ 0.05, and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B), and the positive electrode for a secondary battery according to claim 1 or 2, which contains a lithium-containing composite oxide represented by this formula.

6. The positive electrode for a secondary battery according to claim 5, wherein x satisfies 0.8 ≤ x ≤ 1 in the above formula.

7. The positive electrode for a secondary battery according to claim 1 or 2, wherein the content of the nonionic surfactant in the positive electrode mixture layer is 0.001% by mass or more and 0.05% by mass or less, based on the total mass of the positive electrode mixture layer.

8. A secondary battery comprising the positive electrode for a secondary battery as described in claim 1 or 2.

9. The process includes a step of applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a nonionic surfactant, and a solvent onto a positive electrode current collector, and then heating and drying it to form a positive electrode mixture layer, wherein the reciprocal of the absolute temperature of the positive electrode mixture slurry (1 / T: [K]) is used. －１ The viscosity curve of the positive electrode mixture slurry obtained by plotting the viscosity (η: [Pa·s]) on the horizontal axis and the natural logarithm (lnη: [Pa·s]) of the shear viscosity (η: [Pa·s]) of the positive electrode mixture slurry on the vertical axis is divided into an overlapping region that overlaps with the apparent viscosity curve of the positive electrode mixture slurry obtained based on Andrade's equation, and a deviation region that deviates to the higher viscosity side from the apparent viscosity curve, and the reciprocal of the absolute temperature of the positive electrode mixture slurry at the boundary point between the overlapping region and the deviation region (1 / T: [K]) －１ ]) is 0.0033 [K －１ The following is a method for manufacturing a positive electrode for a secondary battery.

10. A method for manufacturing a secondary battery, comprising manufacturing a secondary battery using a positive electrode manufactured by the method for manufacturing a positive electrode for a secondary battery described in claim 9.

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