WO2016152833A1 - Method for producing electrode for lithium secondary batteries - Google Patents

Method for producing electrode for lithium secondary batteries Download PDF

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Publication number
WO2016152833A1
WO2016152833A1 PCT/JP2016/058921 JP2016058921W WO2016152833A1 WO 2016152833 A1 WO2016152833 A1 WO 2016152833A1 JP 2016058921 W JP2016058921 W JP 2016058921W WO 2016152833 A1 WO2016152833 A1 WO 2016152833A1
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Prior art keywords
positive electrode
electrode mixture
binder
mixture layer
lithium secondary
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PCT/JP2016/058921
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French (fr)
Japanese (ja)
Inventor
徹也 光本
真奈 上野
松嶋　英明
蔭井　慎也
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三井金属鉱業株式会社
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Priority to JP2016567437A priority Critical patent/JP6229078B2/en
Publication of WO2016152833A1 publication Critical patent/WO2016152833A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a method for producing an electrode using, as a positive electrode active material, an electrode used for a lithium secondary battery, particularly a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential.
  • Lithium secondary batteries have features such as high energy density and long life. For this reason, lithium secondary batteries are widely used as power sources for home appliances such as video cameras, portable electronic devices such as notebook computers and mobile phones, and power tools such as power tools. (EV) and hybrid electric vehicles (HEV) are also applied to large batteries.
  • EV electric and hybrid electric vehicles (HEV) are also applied to large batteries.
  • a lithium secondary battery is a secondary battery with a structure in which lithium is melted as ions from the positive electrode during charging, moves to the negative electrode and is stored, and reversely, lithium ions return from the negative electrode to the positive electrode during discharging. It is known to be caused by the potential of the positive electrode material.
  • Examples of the positive electrode active material for this type of lithium secondary battery include lithium transition metal oxides such as LiCoO 2 , LiNiO 2 and LiMnO 2 having a layer structure, and manganese such as LiMn 2 O 4 and LiNi 0.5 Mn 1.5 O 4.
  • a spinel type lithium manganese-containing composite oxide having a spinel structure (Fd-3m or P4 3 32) is known.
  • This type of spinel-type lithium manganese-containing composite oxide has low raw material price, is non-toxic and safe, and has a strong property against overcharging, so that it can be used in electric vehicles (EV) and hybrid electric vehicles (HEV). It is attracting attention as a next-generation positive electrode active material for large batteries.
  • spinel lithium transition metal oxide (LMO) capable of three-dimensional Li ion insertion / extraction is superior in output characteristics to lithium transition metal oxides such as LiCoO 2 having a layer structure. Therefore, it is expected to be used in applications that require excellent output characteristics such as EV batteries and HEV batteries.
  • Patent Document 1 as a positive electrode active material of a lithium secondary battery exhibiting a 5V class electromotive force, high capacity obtained by adding spinel-type lithium manganese composite oxide with chromium as an essential additive component and further adding nickel or cobalt.
  • a spinel type lithium manganese composite oxide positive electrode active material is disclosed.
  • Patent Document 2 discloses a spinel crystal LiMn 2-yz Ni y M z O 4 that charges and discharges at a potential of 4.5 V or more with respect to Li metal (where M: Fe, Co, Ti, V , Mg, Zn, Ga, Nb, Mo, Cu, at least one selected from the group consisting of 0.25 ⁇ y ⁇ 0.6, 0 ⁇ z ⁇ 0.1) is disclosed.
  • Patent Document 3 as a positive electrode active material capable of generating an electromotive force of 4.5 V or more and maintaining a discharge capacity, a general formula: Lia (M x Mn 2 ⁇ xy A y ) O 4 ( In the formula, 0.4 ⁇ x, 0 ⁇ y, x + y ⁇ 2, 0 ⁇ a ⁇ 1.2 M is selected from the group consisting of Ni, Co, Fe, Cr and Cu, and contains at least Ni A includes at least one metal element, A includes at least one metal element selected from Si and Ti, provided that when A includes only Ti, the value of the ratio y of A is 0.1 ⁇ y
  • the positive electrode active material for secondary batteries characterized by including the spinel type lithium manganese complex oxide represented by this is disclosed.
  • Patent Document 4 in a spinel-type lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential, a part of Mn sites in LiMn 2 O 4- ⁇ contains Li and Ni.
  • a metal element M1 (M1 is a metal element containing at least one of Ni, Co and Fe) and another metal element M2 (M2 is Ti or Ti and Mg, Al, Ba, Cr and
  • M1 is a metal element containing at least one of Ni, Co and Fe
  • M2 is Ti or Ti and Mg, Al, Ba, Cr
  • a spinel type lithium manganese-containing composite oxide is disclosed.
  • Patent Document 6 does not show an electromotive force of 5 V class, but as a method for producing a positive electrode, proton-containing lithium nickelate powder as a positive electrode active material, acetylene black as a conductive auxiliary agent, and a binder Polyvinylidene fluoride (PVDF) was mixed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture paste, and this positive electrode mixture paste was applied onto an aluminum foil as a current collector. Then, after drying under reduced pressure at 150 ° C., a method of producing a positive electrode having a positive electrode mixture layer on both sides of an aluminum foil current collector by pressurizing with a roller so as to have a porosity of 35% is disclosed. .
  • PVDF Polyvinylidene fluoride
  • lithium manganese-containing composite oxide having an operating potential of 4.5 V or more is used as a positive electrode active material of a lithium secondary battery, and when a 4 V class spinel type lithium manganese-containing composite oxide is used as the positive electrode active material. It is known that there is not a problem, that is, a problem that a large amount of gas is generated due to the reaction with the electrolytic solution. Such suppression of gas generation is one of the important problems to be solved in using a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more as a positive electrode active material of a lithium secondary battery. Further, improvement of energy density is one of important solutions for using a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more as a positive electrode active material of a lithium secondary battery.
  • the present invention focuses on an electrode manufacturing method, and from this point of view, it is possible to effectively suppress gas generation, and to improve energy density, and to manufacture a new electrode for a lithium secondary battery. It is intended to propose a method.
  • the present invention provides a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersant containing a lithium manganese-containing composite oxide having a working potential of 4.5 V or more at a metal Li reference potential, and collecting current
  • the positive electrode mixture slurry is applied to a base material as a body and dried to form a positive electrode mixture layer, and then pressed in the thickness direction with respect to the positive electrode mixture layer, the melting point of the binder is equal to or higher than
  • a method of manufacturing an electrode for a lithium secondary battery, characterized by heating to a temperature of less than 220 ° C., is proposed.
  • the method for producing an electrode for a lithium secondary battery proposed by the present invention can suppress the amount of gas generated by pressing the positive electrode mixture layer and then heating to a temperature equal to or higher than the melting point of the binder. Energy density can be increased.
  • the present manufacturing method A method for manufacturing an electrode for a lithium secondary battery (referred to as “the present manufacturing method”) as an example of an embodiment of the present invention will be described.
  • the present invention is not limited to the embodiment described below.
  • This manufacturing method is a step of preparing a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersant containing a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential ( (Referred to as “slurry preparation step”), a step of coating the positive electrode mixture slurry on a base material as a current collector and drying it to form a positive electrode mixture layer (referred to as “positive electrode mixture layer formation step”) And a manufacturing method comprising a step of pressing the positive electrode mixture layer in the thickness direction (referred to as “pressing step”) and a step of heating the positive electrode mixture layer (referred to as “heating drying step”). is there.
  • this manufacturing method is provided with said process, it is also possible to insert or add another process.
  • a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersant is prepared.
  • the positive electrode active material used in this production method contains a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at the metal Li reference potential.
  • This lithium manganese-containing composite oxide is a spinel-type lithium manganese-containing composite oxide having a crystal structure belonging to space group Fd-3m or P4 3 32, and has an operating potential of 4.5 V or more at a metal Li reference potential. Anything is acceptable. In this case, “having an operating potential of 4.5 V or higher at the metal Li reference potential” does not need to have only an operating potential of 4.5 V or higher as the plateau region, It is intended to include the case of having a part. From this point of view, the present invention is not limited to the lithium manganese-containing composite oxide composed only of “5V class lithium manganese-containing composite oxide” having an operating potential of 4.5 V or more as a plateau region.
  • a “4V class lithium manganese-containing composite oxide” having an operating potential of less than 4.5 V as the plateau region may be included.
  • the 5V-class lithium manganese-containing composite oxide only needs to occupy 30% by mass or more, preferably 50% by mass or more, and particularly preferably 80% by mass or more (including 100% by mass).
  • a lithium-manganese-containing composite oxide is allowed.
  • lithium manganese-containing composite oxide a crystal phase formed by substituting a part of Mn sites in LiMn 2 O 4- ⁇ with Li, a metal element M1, and another metal element M2 is used.
  • metal element M1 a metal element M1
  • another metal element M2 examples thereof include spinel type lithium manganese-containing composite oxides.
  • the metal element M1 is a substitution element that mainly contributes to developing an operating potential of 4.5 V or higher at the metal Li reference potential, and examples thereof include Ni, Co, and Fe. It may be included, and other metal elements may be included as M1.
  • the metal element M2 is a substitution element that mainly contributes to stabilizing the crystal structure and improving the characteristics. For example, as a substitution element that contributes to an improvement in capacity retention rate, for example, Mg, Ti, Al, Ba, Cr, W , Mo, Y, Zr, Nb and the like. It suffices to include at least one of these Mg, Ti, Al, Ba, Cr, W, Mo, Y, Zr, and Nb, or a combination of two or more of these. M2 may contain other metal elements.
  • M1 and M2 in the formula (1) are as described above.
  • “a” may be 0.00 to 0.20, particularly 0.01 or more and 0.10 or less, and more preferably 0.02 or more and 0.08 or less. Even more preferred.
  • “B” indicating the content of M1 may be 0.20 to 1.20, more preferably 0.30 or more and 1.10 or less, and more preferably 0.35 or more and 1.05 or less. Even more preferred.
  • “C” indicating the M2 content may be 0.001 to 0.400, more preferably 0.002 or more and 0.400 or less, and more preferably 0.005 or more and 0.300 or less. Even more preferred. Note that “4- ⁇ ” in each of the above formulas indicates that oxygen deficiency may be included, and a part of oxygen may be substituted with fluorine.
  • the 5V class lithium manganese-containing composite oxide may contain other components as long as the functions of Li, Mn, M1, M2 and O are not completely hindered.
  • other elements may be contained as long as each is 0.5 wt% or less. This is because it is considered that the amount of this amount hardly affects the performance of the 5V-class lithium manganese-containing composite oxide.
  • the 5V-class lithium manganese-containing composite oxide may contain B.
  • the existence state of B may contain a complex oxide phase containing Ni, Mn and B in addition to the spinel crystal phase.
  • Examples of the conductive material used in this production method include artificial graphite and carbon black (acetylene black). However, it is not limited to these. These may be used alone or in combination of two or more.
  • binder examples of the binder (binder) used in this production method, that is, a binder that binds an active material and swells in an electrolyte solution include, for example, polyvinylidene fluoride (PVDF), PVDF and hexafluoropropylene (HFP), and perfluoromethyl vinyl ether (PFMV) and PVDF copolymer resins such as copolymers with tetrafluoroethylene, fluorine resins such as polytetrafluoroethylene and fluororubber, and hydrocarbons such as styrene-butadiene copolymers and styrene-acrylonitrile copolymers Examples thereof include polymers, carboxymethyl cellulose, and polyimide resins.
  • PVDF polyvinylidene fluoride
  • HFP hexafluoropropylene
  • PFMV perfluoromethyl vinyl ether
  • PVDF copolymer resins such as copolymers with t
  • a binder containing fluorine and among them, a binder containing polyvinylidene fluoride (PVDF) from the viewpoint of enhancing oxidation resistance.
  • PVDF polyvinylidene fluoride
  • Dispersant examples include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like. Can be mentioned. However, it is not limited to these. These may be used alone or in combination of two or more. It is also possible to use an aqueous solution as a dispersant.
  • NMP N-methyl-2-pyrrolidone
  • dimethylformamide dimethylacetamide
  • methyl ethyl ketone cyclohexanone
  • methyl acetate methyl acrylate
  • diethyltriamine NN-dimethylaminopropylamine
  • ethylene oxide ethylene oxide
  • tetrahydrofuran tetrahydrofuran
  • the blending ratio of the positive electrode active material, the conductive material, the binder, and the dispersant may be adjusted as appropriate, and these may be mixed to adjust the viscosity and prepare the positive electrode mixture slurry.
  • the positive electrode active material, the conductive material, the binder and the dispersing agent may be mixed at the same time.
  • the binder is dispersed or dissolved in the dispersant in advance, and the positive electrode active material and the conductive material are added thereto and mixed.
  • a positive electrode mixture slurry may be prepared.
  • ⁇ Positive electrode mixture layer forming step> the positive electrode mixture slurry prepared in the above step is applied to the substrate surface as a current collector and dried to form a positive electrode mixture layer.
  • Base material As the base material as the current collector, a material having excellent oxidation stability is preferably used. Specific examples include iron, copper, stainless steel, nickel, aluminum, and carbon. Examples of the shape of the substrate include sheets, foams, meshes, porous bodies, and expanded lattices.
  • the coating method is arbitrary, but a gravure coating method, a die coating method, a knife coating method, or the like can be employed. In addition, it is also possible to apply using a doctor blade or a bar coater.
  • the coating amount (coating thickness) may be adjusted so that the positive electrode mixture layer is 20 ⁇ m to 200 ⁇ m after pressing.
  • the positive electrode mixture slurry is applied to the surface of the substrate, it is preferably dried so that the dispersant does not bump.
  • it may be dried at 70 to 120 ° C., and it is particularly preferable to dry by heating to 70 to 120 ° C. stepwise.
  • the dispersant can be effectively volatilized by drying in a negative pressure environment. By such drying, the dispersant in the positive electrode mixture slurry can be volatilized, and appropriate voids are generated in the positive electrode mixture layer.
  • the positive electrode mixture layer is pressed in the thickness direction.
  • the positive electrode active material, the conductive material, the binder, and the substrate can be firmly bound while adjusting the void amount.
  • the porosity after pressing is preferably 5 to 30%, and more preferably 25% or less.
  • Examples of the pressing method include a roll press that pressurizes with rollers set up and down, a method that presses with rollers while applying heat, and a surface press that presses with plates set up and down.
  • a pressing condition it is preferable to press at a linear pressure of 0.5 t / cm or more and less than 10 t / cm in the thickness direction of the positive electrode mixture layer.
  • the gap can be filled and firmly bonded, while if it is pressed at a linear pressure of 10 t / cm or more, it causes peeling. there is a possibility.
  • the linear pressure at the time of pressing is preferably 0.5 t / cm or more and less than 10 t / cm, particularly 1 t / cm or more or 7 t / cm or less, and more preferably 2 t / cm or more or 5 t / cm or less. Is more preferable.
  • ⁇ Heat drying process> it is preferable to heat to a temperature not lower than the melting point of the binder and lower than 220 ° C.
  • the amount of gas generation can be suppressed, and the energy density per volume can be increased. This is because when heated above the melting point of the binder, the binder melts and penetrates into the positive electrode layer after pressing, covering the positive electrode active material and reducing the active sites, thereby suppressing the amount of gas generated. It is possible to estimate that the energy density per volume can be increased because the void amount in the electrode active material layer is reduced.
  • the heating method is not particularly limited.
  • the heating may be performed using a high-temperature dryer or an electric furnace.
  • the atmosphere during heating is preferably a vacuum state.
  • a vacuum state here means the state in the space filled with the gas of the pressure lower than atmospheric pressure (refer JIS).
  • the atmosphere during heating is preferably a vacuum state, particularly a vacuum state of a vacuum degree of 2500 Pa or less, of which 1000 Pa or less, more preferably of 500 Pa or less, of which a vacuum degree of 100 Pa or less. Is particularly preferred.
  • the high-temperature dryer and the electric furnace include a vacuum pump.
  • the heating temperature is preferably higher than the melting point of the binder and lower than 220 ° C.
  • the binder can be melted by heating it above the melting point of the binder (for example, the melting point of PVDF is about 134 to 169 ° C. depending on the molecular weight).
  • the heating temperature is preferably less than 220 ° C. From this viewpoint, the heating temperature is preferably 135 ° C. or higher and lower than 220 ° C., particularly 150 ° C. or higher or 210 ° C. or lower, and more preferably 180 ° C. or higher or 200 ° C. or lower.
  • the positive electrode obtained by the present production method as described above can be used as a battery material by being laminated with other materials, for example, a separator, a negative electrode, an electrolyte, and the like.
  • the positive electrode mixture layer and the substrate may be laminated with the separator and then heat-dried as described above. Therefore, it is preferable to heat and dry as described above before laminating with the separator.
  • Example 1 Spinel-type lithium manganese-containing composite oxide as a positive electrode active material (chemical analysis values are Li: 4.0 wt%, Ni: 14.0 wt%, Mn: 42.0 wt%, Ti: 3.5 wt%, D50: 15 um, SSA: 0.2 m 2 / g) 89 parts by mass, 5 parts by mass of acetylene black, polyvinylidene fluoride (PVDF, melting point 175 ° C.) PVDF dissolved in 1-methyl-2-pyrrolidone (NMP) Each part by mass was weighed. The weighed positive electrode active material, acetylene black and the PVDF were added, mixed and kneaded.
  • PVDF polyvinylidene fluoride
  • NMP 1-Methyl-2-pyrrolidone
  • the aluminum foil with the positive electrode mixture layer is punched out into an electrode of 50 mm ⁇ 100 mm and then pressed and thickened at a press linear pressure of 3 t / cm using a roll press machine. Processed to size. That is, for use in the production of a 2032 type coin battery for battery evaluation, it is punched into 13 mm ⁇ , when used in the production of a laminate type battery, it is punched into 40 mm ⁇ 29 mm square, and when used in a peel strength test, it is punched into 25 mm ⁇ 100 mm square. It was. Next, in a vacuum state with a degree of vacuum of 1000 Pa or less, the sample was heated from room temperature to 180 ° C. and dried by heating so as to hold at 180 ° C. (drying temperature) for 6 hours (drying time) to obtain a positive electrode (sample). The “electrode thickness” of the obtained sample was measured and shown in Table 1.
  • Example 2-4 a positive electrode (sample) was obtained in the same manner as in Example 1 except that the press linear pressure, the drying temperature, and the electrode thickness were changed to the values shown in the table.
  • Example 5 Spinel-type lithium manganese-containing composite oxide as a positive electrode active material (chemical analysis values are Li: 4.0 wt%, Ni: 15.6 wt%, Mn: 39.4 wt%, Ti: 5.0 wt%, D50: 24 um, SSA: 0.1 m 2 / g) 91 parts by mass, 4.1 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) The amount was 4.9 parts by mass, respectively. The weighed positive electrode active material, acetylene black and the PVDF were added, mixed and kneaded.
  • PVDF polyvinylidene fluoride
  • NMP 1-Methyl-2-pyrrolidone
  • the aluminum foil with the positive electrode mixture layer is punched out into an electrode of 50 mm ⁇ 100 mm and then pressed and thickened at a press linear pressure of 3 t / cm using a roll press machine. Processed to size. That is, for use in the production of a 2032 type coin battery for battery evaluation, it is punched into 13 mm ⁇ , when used in the production of a laminate type battery, it is punched into 40 mm ⁇ 29 mm square, and when used in a peel strength test, it is punched into 25 mm ⁇ 100 mm square. It was. Next, in a vacuum state with a degree of vacuum of 1000 Pa or less, the sample was heated from room temperature to 200 ° C. and dried by heating so as to hold at 200 ° C. (drying temperature) for 6 hours (drying time) to obtain a positive electrode (sample). The “electrode thickness” of the obtained sample was measured and shown in Table 1.
  • Example 6 ⁇ Example 6> In Example 5, 93 parts by mass of the positive electrode active material, 3.2 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were mixed in PVDF. A positive electrode (sample) was obtained in the same manner as in Example 5 except that the amount was 3.8 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • PVDF polyvinylidene fluoride
  • Example 7 In Example 5, PVDF was blended with 95 parts by mass of the positive electrode active material, 2.3 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP). A positive electrode (sample) was obtained in the same manner as in Example 5 except that the amount was 2.7 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • PVDF polyvinylidene fluoride
  • Example 8 In Example 5, 90 parts by mass of the positive electrode active material, 4 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content.
  • a positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • Example 9 ⁇ Example 9>
  • 91 parts by mass of the positive electrode active material 3 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content.
  • a positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • Example 10 ⁇ Example 10>
  • 92 parts by mass of the positive electrode active material 2 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content.
  • a positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • Example 11 In Example 5, 93 parts by mass of the positive electrode active material, 1 part by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content.
  • a positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • Example 12 Polyvinylidene fluoride (PVDF, melting point 130 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) was changed, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
  • a positive electrode (sample) was obtained in the same manner as Example 1 except for the above.
  • Example 13-14> a positive electrode (sample) was obtained in the same manner as in Example 12 except that the press linear pressure, the drying temperature, and the electrode thickness were changed to the values shown in the table.
  • Example 15 In Example 1, it was changed to polyvinylidene fluoride (PVDF, melting point 165 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP), and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table. A positive electrode (sample) was obtained in the same manner as Example 1 except for the above.
  • PVDF polyvinylidene fluoride
  • NMP 1-methyl-2-pyrrolidone
  • Example 16 a positive electrode (sample) was obtained in the same manner as in Example 15 except that the press linear pressure, the drying temperature, and the electrode thickness were changed to the values shown in the table.
  • PVDF polyvinylidene fluoride
  • PVDF was dissolved in NMP in advance, and the positive electrode active material and acetylene black were added and kneaded to prepare a positive electrode mixture slurry (solid content concentration 50 mass%).
  • the coating machine After coating this positive electrode mixture slurry on an aluminum foil as a current collector at a conveying speed of 20 cm / min using a coating machine, the coating machine is used to hold 70 ° C. for 2 minutes. After heating as described above, drying was performed so as to hold 120 ° C. for 2 minutes to form a positive electrode mixture layer to obtain an aluminum foil with a positive electrode mixture layer.
  • the thickness of the positive electrode mixture layer at that time was 0.08 mm.
  • the aluminum foil with the positive electrode mixture layer is punched out into an electrode of 50 mm ⁇ 100 mm and then pressed and thickened at a press linear pressure of 3 t / cm using a roll press machine. Processed to size. That is, for use in the production of a 2032 type coin battery for battery evaluation, it is punched into 13 mm ⁇ , when used in the production of a laminate type battery, it is punched into 40 mm ⁇ 29 mm square, and when used in a peel strength test, it is punched into 25 mm ⁇ 100 mm square. It was. Next, in a vacuum state with a degree of vacuum of 1000 Pa or less, the sample was heated from room temperature to 200 ° C. and dried by heating so as to hold at 200 ° C. (drying temperature) for 6 hours (drying time) to obtain a positive electrode (sample). The “electrode thickness” of the obtained sample was measured and shown in Table 1.
  • the sample stage on which the positive electrode was set was installed, Ar gas was allowed to flow at 0.07 to 0.1 cm 3 / min, and the acceleration voltage was 6 kV and the discharge voltage was 1
  • the ion milling was performed while swinging the sample stage at a swing angle of ⁇ 30 ° and a swing speed of 3 reciprocations / min, with a processing time of 0.5 kV and a processing time of 1 hour.
  • the cross section of the positive electrode cross section after processing was photographed using a scanning electron microscope at a magnification of 2000 times.
  • the microscope images of the positive electrode cross sections obtained in Example 2 and Comparative Example 1 are shown in FIGS. 1 and 2 as representative examples.
  • the length of the positive electrode was longer than that of the double-sided tape, and the positive electrode was bonded to the double-sided tape so that the positive electrode mixture layer was on the lower side.
  • the positive electrode was pinched and fixed with a film chuck attached to the tip of a digital force gauge. By moving the digital force gauge directly above, the positive electrode mixture layer sticks to the double-sided tape and can be peeled off from the aluminum foil.
  • the force applied when the positive electrode mixture layer was peeled from the aluminum foil was measured as “peel strength” (unit: N).
  • the rate at which the positive electrode mixture layer was peeled from the aluminum foil was 17 mm / s. The peel strength was not the maximum value, but the average value of the stable intervals was used.
  • the negative electrode is a metal Li of ⁇ 14 mm ⁇ thickness 0.6 mm, and a separator (made of a porous polyethylene film) impregnated with an electrolytic solution in which LiPF 6 is dissolved to 1 mol / L in a carbonate-based mixed solvent is placed, A 2032 type coin battery was produced.
  • the energy density was calculated by the following method. That is, from the discharge capacity (shown in [Table 1]) when a constant current discharge is performed at a voltage range of 4.999-3.0V at 0.1 C, the capacity at which SOC is 50% is calculated, and the capacity is reached. The battery voltage at the time was defined as V m (middle point voltage). Next, the energy density (Wh / g) was calculated by discharge capacity (mAh / g) ⁇ Vm (V). Furthermore, the energy density per volume of the positive electrode mixture layer is calculated by multiplying the energy density by the amount of the active material contained in the positive electrode mixture layer and dividing it by the positive electrode mixture layer. It was described in the table as an index (%).
  • the negative electrode used was a negative electrode sheet coated with natural spherical graphite (Piotrek Corporation, electrode capacity 1.6 mAh / cm 2 ).
  • the amount of voids in the electrode active material layer is reduced by pressing the positive electrode mixture layer, and the volume that can relieve stress caused by expansion and contraction of the active material is reduced.
  • the peel strength is high, the electrical resistance between the positive electrode mixture layer and the aluminum foil as the current collector can be reduced.
  • the energy density per volume could be increased.
  • the resistance as an electrode is small, it can be inferred that a local overvoltage can be avoided, and as a result, the amount of gas generation can be reduced.
  • the electrode peel strength measured by the above method is greater than 1.2N, and the binder melts and penetrates into the positive electrode mixture layer after pressing to coat the active surface of the positive electrode active material. It can be inferred that an electrode that is observed to have high energy density and low gas generation amount.
  • FIG.1 and FIG.2 shows, the positive electrode (for example, FIG. 1) obtained by the Example was obtained by the comparative example.
  • the positive electrode for example, FIG. 2
  • the processing electrode was hard to be damaged by ion milling and was a strong electrode.

Abstract

The present invention improves the energy density, while effectively suppressing the generation of a gas by focusing attention on a method for producing an electrode. Proposed is a method wherein: a positive electrode mixture slurry, which contains a positive electrode active material containing a lithium manganese-containing composite oxide that has an operating potential of 4.5 V or more relative to the reference potential of Li metal, a conductive material, a binder and a dispersant, is prepared; a positive electrode mixture layer is formed by applying the positive electrode mixture slurry to a base serving as a collector and drying the slurry thereon, and then the positive electrode mixture layer is pressed in the thickness direction; and subsequently, the positive electrode mixture layer is heated to a temperature that is not less than the melting point of the binder but less than 220°C.

Description

リチウム二次電池用電極の製造方法Method for producing electrode for lithium secondary battery
　本発明は、リチウム二次電池に用いる電極、中でも、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を、正極活物質として用いた電極の製造方法に関する。 The present invention relates to a method for producing an electrode using, as a positive electrode active material, an electrode used for a lithium secondary battery, particularly a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential.
　リチウム二次電池は、エネルギー密度が大きく、寿命が長いなどの特徴を有している。そのため、リチウム二次電池は、ビデオカメラ等の家電製品や、ノート型パソコン、携帯電話機等の携帯型電子機器、パワーツールなどの電動工具などの電源として広く用いられており、最近では、電気自動車（ＥＶ）やハイブリッド電気自動車（ＨＥＶ）などに搭載される大型電池へも応用されている。 Lithium secondary batteries have features such as high energy density and long life. For this reason, lithium secondary batteries are widely used as power sources for home appliances such as video cameras, portable electronic devices such as notebook computers and mobile phones, and power tools such as power tools. (EV) and hybrid electric vehicles (HEV) are also applied to large batteries.
　リチウム二次電池は、充電時には正極からリチウムがイオンとして溶け出して負極へ移動して吸蔵され、放電時には逆に負極から正極へリチウムイオンが戻る構造の二次電池であり、その高いエネルギー密度は正極材料の電位に起因することが知られている。 A lithium secondary battery is a secondary battery with a structure in which lithium is melted as ions from the positive electrode during charging, moves to the negative electrode and is stored, and reversely, lithium ions return from the negative electrode to the positive electrode during discharging. It is known to be caused by the potential of the positive electrode material.
　この種のリチウム二次電池の正極活物質としては、層構造をもつＬｉＣｏＯ2、ＬｉＮｉＯ2、ＬｉＭｎＯ2などのリチウム遷移金属酸化物のほか、ＬｉＭｎ2Ｏ4、ＬｉＮｉ0.5Ｍｎ1.5Ｏ4などのマンガン系のスピネル構造（Ｆｄ-３ｍやＰ４３３２）を有するスピネル型リチウムマンガン含有複合酸化物が知られている。 Examples of the positive electrode active material for this type of lithium secondary battery include lithium transition metal oxides such as LiCoO 2 , LiNiO 2 and LiMnO 2 having a layer structure, and manganese such as LiMn 2 O 4 and LiNi 0.5 Mn 1.5 O 4. A spinel type lithium manganese-containing composite oxide having a spinel structure (Fd-3m or P4 3 32) is known.
　この種のスピネル型リチウムマンガン含有複合酸化物は、原料価格が安く、毒性がなく安全であり、しかも過充電に強い性質を有することから、電気自動車（ＥＶ）やハイブリッド電気自動車（ＨＥＶ）などの大型電池用の次世代正極活物質として着目されている。また、３次元的にＬｉイオンの挿入・脱離が可能なスピネル型リチウム遷移金属酸化物（ＬＭＯ）は、層構造をもつＬｉＣｏＯ2などのリチウム遷移金属酸化物に比べて出力特性に優れているため、ＥＶ用電池、ＨＥＶ用電池などのように優れた出力特性が要求される用途に利用が期待されている。 This type of spinel-type lithium manganese-containing composite oxide has low raw material price, is non-toxic and safe, and has a strong property against overcharging, so that it can be used in electric vehicles (EV) and hybrid electric vehicles (HEV). It is attracting attention as a next-generation positive electrode active material for large batteries. In addition, spinel lithium transition metal oxide (LMO) capable of three-dimensional Li ion insertion / extraction is superior in output characteristics to lithium transition metal oxides such as LiCoO 2 having a layer structure. Therefore, it is expected to be used in applications that require excellent output characteristics such as EV batteries and HEV batteries.
　中でも、ＬｉＭｎ2Ｏ4におけるＭｎサイトの一部を他の遷移金属（Ｃｒ、Ｃｏ、Ｎｉ、Ｆｅ、Ｃｕ）で置換することで、５Ｖ付近に作動電位を持つことが知られるようになり、現在、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有する５Ｖ級リチウムマンガン含有複合酸化物型リチウムマンガン含有複合酸化物の開発が行われている。 Among them, it has become known that a part of the Mn site in LiMn 2 O 4 is replaced with other transition metals (Cr, Co, Ni, Fe, Cu) and has an operating potential near 5 V. Development of a 5V class lithium manganese-containing composite oxide type lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential has been underway.
　例えば特許文献１には、５Ｖ級の起電力を示すリチウム二次電池の正極活物質として、スピネル型リチウムマンガン複合酸化物にクロムを必須添加成分とし、さらにニッケルまたはコバルトを添加してなる高容量スピネル型リチウムマンガン複合酸化物正極活物質が開示されている。 For example, in Patent Document 1, as a positive electrode active material of a lithium secondary battery exhibiting a 5V class electromotive force, high capacity obtained by adding spinel-type lithium manganese composite oxide with chromium as an essential additive component and further adding nickel or cobalt. A spinel type lithium manganese composite oxide positive electrode active material is disclosed.
　特許文献２には、Ｌｉ金属に対して４．５Ｖ以上の電位で充放電を行うスピネル構造の結晶ＬｉＭｎ２－ｙ－ｚＮｉｙＭｚＯ４（但し、Ｍ：Ｆｅ，Ｃｏ，Ｔｉ，Ｖ，Ｍｇ，Ｚｎ，Ｇａ，Ｎｂ，Ｍｏ，Ｃｕよりなる群から選ばれた少なくとも一種、０．２５≦ｙ≦０．６、０≦ｚ≦０．１）が開示されている。 Patent Document 2 discloses a spinel crystal LiMn 2-yz Ni y M z O 4 that charges and discharges at a potential of 4.5 V or more with respect to Li metal (where M: Fe, Co, Ti, V , Mg, Zn, Ga, Nb, Mo, Cu, at least one selected from the group consisting of 0.25 ≦ y ≦ 0.6, 0 ≦ z ≦ 0.1) is disclosed.
　特許文献３には、４．５Ｖ以上もの起電力を発生し、且つ放電容量を維持することができる正極活物質として、一般式：Ｌｉａ（ＭｘＭｎ２－ｘ－ｙＡｙ）Ｏ４（式中、０．４＜ｘ、０＜ｙ、ｘ＋ｙ＜２、０＜ａ＜１．２である。Ｍは、Ｎｉ、Ｃｏ、Ｆｅ、ＣｒおよびＣｕよりなる群から選ばれ、少なくともＮｉを含む一種以上の金属元素を含む。Ａは、Ｓｉ、Ｔｉから選ばれる少なくとも一種の金属元素を含む。但し、ＡがＴｉだけを含む場合には、Ａの比率ｙの値は、０．１＜ｙである。）で表されるスピネル型リチウムマンガン複合酸化物を含むことを特徴とする二次電池用正極活物質が開示されている。 In Patent Document 3, as a positive electrode active material capable of generating an electromotive force of 4.5 V or more and maintaining a discharge capacity, a general formula: Lia (M x Mn 2−xy A y ) O 4 ( In the formula, 0.4 <x, 0 <y, x + y <2, 0 <a <1.2 M is selected from the group consisting of Ni, Co, Fe, Cr and Cu, and contains at least Ni A includes at least one metal element, A includes at least one metal element selected from Si and Ti, provided that when A includes only Ti, the value of the ratio y of A is 0.1 <y The positive electrode active material for secondary batteries characterized by including the spinel type lithium manganese complex oxide represented by this is disclosed.
　特許文献４には、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するスピネル型リチウムマンガン含有複合酸化物において、ＬｉＭｎ2Ｏ4-δにおけるＭｎサイトの一部を、Ｌｉと、Ｎｉを含む金属元素Ｍ1（Ｍ1はＮｉ、Ｃｏ及びＦｅのうちの少なくとも一種を含む金属元素である）と、他の金属元素Ｍ2（Ｍ2はＴｉであるか、又は、ＴｉとＭｇ、Ａｌ、Ｂａ、Ｃｒ及びＮｂのうちの少なくとも一種とを含む金属元素である）とで置換してなる結晶相を含有するスピネル型リチウムマンガン含有複合酸化物であって、Ｎｉ、Ｍｎ及びＢを含む複合酸化物相を含有することを特徴とするスピネル型リチウムマンガン含有複合酸化物が開示されている。 In Patent Document 4, in a spinel-type lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential, a part of Mn sites in LiMn 2 O 4-δ contains Li and Ni. A metal element M1 (M1 is a metal element containing at least one of Ni, Co and Fe) and another metal element M2 (M2 is Ti or Ti and Mg, Al, Ba, Cr and A spinel-type lithium-manganese-containing composite oxide containing a crystalline phase formed by substitution with a metal element containing at least one of Nb and containing a composite oxide phase containing Ni, Mn, and B A spinel type lithium manganese-containing composite oxide is disclosed.
　特許文献５には、Ｌｉ[ＮｉyＭｎ2-(a+b)-y-zＬｉaＴｉｂＭz]Ｏ4（式中、０≦z≦0.3、0.3≦y＜0.6であって、Ｍ＝Ａｌ、Ｍｇ、Ｆｅ及びＣｏからなる群のうちから少なくとも１つ以上選ばれる金属元素）で示されるマンガン系スピネル型リチウム遷移金属酸化物であって、前記式において、ａ＞０であり、ｂ＞０であり、２-（ａ+ｂ）-ｙ-ｚ＜１．７であり、かつ３≦ｂ／ａ≦８であることを特徴とするマンガン系スピネル型リチウム遷移金属酸化物が開示されている。 Patent Document 5, Li in [Ni y Mn 2- (a + b) -yz Li a Ti b M z] O4 ( wherein A 0 ≦ z ≦ 0.3,0.3 ≦ y < 0.6, M = Al , Mg, Fe, and Co), a manganese-based spinel-type lithium transition metal oxide represented by the formula: a> 0, b> 0 There is disclosed a manganese-based spinel-type lithium transition metal oxide characterized by 2- (a + b) -yz <1.7 and 3 ≦ b / a ≦ 8 .
　また、特許文献６には、５Ｖ級の起電力を示すものではないが、正極の作製方法として、正極活物質としてのプロトン含有ニッケル酸リチウム粉末と、導電助剤としてのアセチレンブラックと、バインダーとしてのポリフッ化ビニリデン（ＰＶＤＦ）とを、Ｎ－メチル－２－ピロリドン（ＮＭＰ）中で混合して正極合剤ペーストを作製し、この正極合剤ペーストを集電体としてのアルミニウム箔上に塗布して、１５０℃で減圧乾燥した後、ローラーで加圧して多孔度が３５％となるようにし、アルミニウム箔集電体の両面に正極合剤層を備えた正極を製作する方法が開示されている。 Patent Document 6 does not show an electromotive force of 5 V class, but as a method for producing a positive electrode, proton-containing lithium nickelate powder as a positive electrode active material, acetylene black as a conductive auxiliary agent, and a binder Polyvinylidene fluoride (PVDF) was mixed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture paste, and this positive electrode mixture paste was applied onto an aluminum foil as a current collector. Then, after drying under reduced pressure at 150 ° C., a method of producing a positive electrode having a positive electrode mixture layer on both sides of an aluminum foil current collector by pressurizing with a roller so as to have a porosity of 35% is disclosed. .
特開平１１―７３９６２号公報JP-A-11-73962 特開２０００－２３５８５７号公報JP 2000-235857 A 特開２００３－１９７１９４号公報JP 2003-197194 A 特開２０１４－１３０８５１号公報JP 2014-130851 A 特開２０１４－１６６９５１号公報JP 2014-166951 A 特開２００８－２２６７５２号公報JP 2008-226752 A
　４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を、リチウム２次電池の正極活物質として用いる場合、４Ｖ級スピネル型リチウムマンガン含有複合酸化物を該正極活物質として用いる場合には生じない課題、すなわち、電解液との反応により発生するガスの発生量が多いという課題が生じることが知られている。このようなガス発生の抑制は、４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物をリチウム２次電池の正極活物質として用いる上での重要な解決課題の一つである。
　また、エネルギー密度の向上も、４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物をリチウム２次電池の正極活物質として用いる上での重要な解決課題の一つである。 It occurs when a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more is used as a positive electrode active material of a lithium secondary battery, and when a 4 V class spinel type lithium manganese-containing composite oxide is used as the positive electrode active material. It is known that there is not a problem, that is, a problem that a large amount of gas is generated due to the reaction with the electrolytic solution. Such suppression of gas generation is one of the important problems to be solved in using a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more as a positive electrode active material of a lithium secondary battery.
Further, improvement of energy density is one of important solutions for using a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more as a positive electrode active material of a lithium secondary battery.
　そこで本発明は、電極の製造方法に着目し、かかる観点から、ガス発生を効果的に抑制することができ、しかも、エネルギー密度を向上させることもできる、新たなリチウム二次電池用電極の製造方法を提案せんとするものである。 Therefore, the present invention focuses on an electrode manufacturing method, and from this point of view, it is possible to effectively suppress gas generation, and to improve energy density, and to manufacture a new electrode for a lithium secondary battery. It is intended to propose a method.
　本発明は、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を含有する正極活物質、導電材、バインダー及び分散剤を含む正極合剤スラリーを調製し、集電体としての基材に前記正極合剤スラリーを塗工して乾燥させて正極合剤層を形成した後、該正極合剤層に対して厚さ方向にプレスし、前記バインダーの融点以上で且つ２２０℃未満の温度に加熱することを特徴とするリチウム二次電池用電極の製造方法を提案する。 The present invention provides a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersant containing a lithium manganese-containing composite oxide having a working potential of 4.5 V or more at a metal Li reference potential, and collecting current The positive electrode mixture slurry is applied to a base material as a body and dried to form a positive electrode mixture layer, and then pressed in the thickness direction with respect to the positive electrode mixture layer, the melting point of the binder is equal to or higher than A method of manufacturing an electrode for a lithium secondary battery, characterized by heating to a temperature of less than 220 ° C., is proposed.
　本発明が提案するリチウム二次電池用電極の製造方法は、正極合剤層をプレス処理した後、前記バインダーの融点以上の温度に加熱することによって、ガス発生量を抑制できると共に、体積当たりのエネルギー密度を高めることができる。 The method for producing an electrode for a lithium secondary battery proposed by the present invention can suppress the amount of gas generated by pressing the positive electrode mixture layer and then heating to a temperature equal to or higher than the melting point of the binder. Energy density can be increased.
実施例２で得た正極の断面を、走査型電子顕微鏡を用いて撮影した顕微鏡画像（倍率２０００倍）である。It is the microscope image (2000-times multiplication factor) which image | photographed the cross section of the positive electrode obtained in Example 2 using the scanning electron microscope. 比較例１で得た正極の断面を、走査型電子顕微鏡を用いて撮影した顕微鏡画像（倍率２０００倍）である。It is the microscope image (magnification 2000 times) which image | photographed the cross section of the positive electrode obtained by the comparative example 1 using the scanning electron microscope.
　本発明の実施形態の一例としてのリチウム二次電池用電極の製造方法（「本製造方法」と称する）について説明する。但し、本発明が次に説明する実施形態に限定されるものではない。 A method for manufacturing an electrode for a lithium secondary battery (referred to as “the present manufacturing method”) as an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.
＜本製造方法＞
　本製造方法は、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を含有する正極活物質、導電材、バインダー及び分散剤を含む正極合剤スラリーを調製する工程（「スラリー調製工程」と称する）、集電体としての基材に前記正極合剤スラリーを塗工して乾燥させて正極合剤層を形成する工程（「正極合剤層形成工程」と称する）、該正極合剤層に対して厚さ方向にプレスする工程（「プレス工程」と称する）、及び、正極合剤層を加熱する工程（「加熱乾燥工程」と称する）を備えた製造方法である。
　なお、本製造方法は、上記の工程を備えていれば、他の工程を挿入したり追加したりすることも可能である。 <This manufacturing method>
This manufacturing method is a step of preparing a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersant containing a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential ( (Referred to as “slurry preparation step”), a step of coating the positive electrode mixture slurry on a base material as a current collector and drying it to form a positive electrode mixture layer (referred to as “positive electrode mixture layer formation step”) And a manufacturing method comprising a step of pressing the positive electrode mixture layer in the thickness direction (referred to as “pressing step”) and a step of heating the positive electrode mixture layer (referred to as “heating drying step”). is there.
In addition, if this manufacturing method is provided with said process, it is also possible to insert or add another process.
＜スラリー調製工程＞
　本工程では、正極活物質、導電材、バインダー及び分散剤を含む正極合剤スラリーを調製する。 <Slurry preparation process>
In this step, a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and a dispersant is prepared.
（正極活物質）
　本製造方法で用いる正極活物質は、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を含有するものである。 (Positive electrode active material)
The positive electrode active material used in this production method contains a lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at the metal Li reference potential.
　このリチウムマンガン含有複合酸化物は、空間群Ｆｄ-３ｍやＰ４３３２に属する結晶構造を有するスピネル型リチウムマンガン含有複合酸化物であって、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するものであればよい。
　この際、「金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有する」とは、プラトー領域として４．５Ｖ以上の作動電位のみを有している必要はなく、４．５Ｖ以上の作動電位を一部有している場合も包含する意である。
　この観点から、プラトー領域として４．５Ｖ以上の作動電位を有する「５Ｖ級リチウムマンガン含有複合酸化物」のみからなるリチウムマンガン含有複合酸化物に限定するものではない。例えば、プラトー領域として４．５Ｖ未満の作動電位を有する「４Ｖ級リチウムマンガン含有複合酸化物」を含んでいてもよい。具体的には、当該５Ｖ級リチウムマンガン含有複合酸化物が３０質量％以上を占めていればよく、好ましくは５０質量％以上、その中でも特に好ましくは８０質量％以上（１００質量％含む）を占めるリチウムマンガン含有複合酸化物を許容するものである。 This lithium manganese-containing composite oxide is a spinel-type lithium manganese-containing composite oxide having a crystal structure belonging to space group Fd-3m or P4 3 32, and has an operating potential of 4.5 V or more at a metal Li reference potential. Anything is acceptable.
In this case, “having an operating potential of 4.5 V or higher at the metal Li reference potential” does not need to have only an operating potential of 4.5 V or higher as the plateau region, It is intended to include the case of having a part.
From this point of view, the present invention is not limited to the lithium manganese-containing composite oxide composed only of “5V class lithium manganese-containing composite oxide” having an operating potential of 4.5 V or more as a plateau region. For example, a “4V class lithium manganese-containing composite oxide” having an operating potential of less than 4.5 V as the plateau region may be included. Specifically, the 5V-class lithium manganese-containing composite oxide only needs to occupy 30% by mass or more, preferably 50% by mass or more, and particularly preferably 80% by mass or more (including 100% by mass). A lithium-manganese-containing composite oxide is allowed.
　前記「５Ｖ級リチウムマンガン含有複合酸化物」としては、ＬｉＭｎ2Ｏ4-δにおけるＭｎサイトの一部を、Ｌｉと、金属元素Ｍ1と、他の金属元素Ｍ2とで置換してなる結晶相を含むスピネル型リチウムマンガン含有複合酸化物を挙げることができる。 As the “5V-class lithium manganese-containing composite oxide”, a crystal phase formed by substituting a part of Mn sites in LiMn 2 O 4-δ with Li, a metal element M1, and another metal element M2 is used. Examples thereof include spinel type lithium manganese-containing composite oxides.
　上記金属元素Ｍ1は、主に金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を発現させるのに寄与する置換元素であり、Ｎｉ、Ｃｏ及びＦｅなどを挙げることができ、これらのうち少なくとも一種を含んでいればよく、Ｍ1として他の金属元素を含んでいてもよい。
　金属元素Ｍ2は、主に結晶構造を安定化させて特性を高めるのに寄与する置換元素であり、例えば容量維持率向上に寄与する置換元素として、例えばＭｇ、Ｔｉ、Ａｌ、Ｂａ、Ｃｒ、Ｗ、Ｍｏ、Ｙ、Ｚｒ、Ｎｂなどを挙げることができる。これらＭｇ、Ｔｉ、Ａｌ、Ｂａ、Ｃｒ、Ｗ、Ｍｏ、Ｙ、Ｚｒ及びＮｂのうちの少なくとも一種を含んでいればよく、これらの二種以上を組み合わせて含んでいてもよい。Ｍ2として他の金属元素を含んでいてもよい。 The metal element M1 is a substitution element that mainly contributes to developing an operating potential of 4.5 V or higher at the metal Li reference potential, and examples thereof include Ni, Co, and Fe. It may be included, and other metal elements may be included as M1.
The metal element M2 is a substitution element that mainly contributes to stabilizing the crystal structure and improving the characteristics. For example, as a substitution element that contributes to an improvement in capacity retention rate, for example, Mg, Ti, Al, Ba, Cr, W , Mo, Y, Zr, Nb and the like. It suffices to include at least one of these Mg, Ti, Al, Ba, Cr, W, Mo, Y, Zr, and Nb, or a combination of two or more of these. M2 may contain other metal elements.
　このような５Ｖ級リチウムマンガン含有複合酸化物の一例として、式（１）：Ｌｉ[ＬｉaＭｎ2-a-b-cＭ1bＭ2c]Ｏ4-δで示されるスピネル型リチウムマンガン含有複合酸化物を挙げることができる。式（１）におけるＭ1及びＭ2は上記のとおりである。 As an example of such a 5V-class lithium manganese-containing composite oxide, a spinel-type lithium manganese-containing composite oxide represented by the formula (1): Li [Li a Mn 2 -abc M1 b M2 c ] O 4-δ is given. be able to. M1 and M2 in the formula (1) are as described above.
　上記式（１）において、「ａ」は、０．００～０．２０であればよく、中でも０．０１以上或いは０．１０以下、その中でも０．０２以上或いは０．０８以下であるのがより一層好ましい。
　Ｍ1の含有量を示す「b」は、０．２０～１．２０であればよく、中でも０．３０以上或いは１．１０以下、その中でも０．３５以上或いは１．０５以下であるのがより一層好ましい。
　Ｍ2の含有量を示す「ｃ」は、０．００１～０．４００であればよく、中でも０．００２以上或いは０．４００以下、その中でも０．００５以上或いは０．３００以下であるのがより一層好ましい。
　なお、上記各式における「４－δ」は、酸素欠損を含んでいてもよいことを示しており、酸素の一部がフッ素で置換されていてもよい。 In the above formula (1), “a” may be 0.00 to 0.20, particularly 0.01 or more and 0.10 or less, and more preferably 0.02 or more and 0.08 or less. Even more preferred.
“B” indicating the content of M1 may be 0.20 to 1.20, more preferably 0.30 or more and 1.10 or less, and more preferably 0.35 or more and 1.05 or less. Even more preferred.
“C” indicating the M2 content may be 0.001 to 0.400, more preferably 0.002 or more and 0.400 or less, and more preferably 0.005 or more and 0.300 or less. Even more preferred.
Note that “4-δ” in each of the above formulas indicates that oxygen deficiency may be included, and a part of oxygen may be substituted with fluorine.
　但し、５Ｖ級リチウムマンガン含有複合酸化物は、Ｌｉ、Ｍｎ、Ｍ1、Ｍ2及びＯの機能を完全に妨げない限りにおいて、他の成分を含有してもよい。特にその他の元素をそれぞれ０．５重量％以下であれば含んでいてもよい。この程度の量であれば、５Ｖ級リチウムマンガン含有複合酸化物の性能にほとんど影響しないと考えられるからである。 However, the 5V class lithium manganese-containing composite oxide may contain other components as long as the functions of Li, Mn, M1, M2 and O are not completely hindered. In particular, other elements may be contained as long as each is 0.5 wt% or less. This is because it is considered that the amount of this amount hardly affects the performance of the 5V-class lithium manganese-containing composite oxide.
　また、５Ｖ級リチウムマンガン含有複合酸化物は、Ｂを含有していてもよい。この際、Ｂの存在状態としては、スピネルの結晶相のほかに、Ｎｉ、Ｍｎ及びＢを含む複合酸化物相を含有していてもよい。 Further, the 5V-class lithium manganese-containing composite oxide may contain B. At this time, the existence state of B may contain a complex oxide phase containing Ni, Mn and B in addition to the spinel crystal phase.
（導電材）
　本製造方法に用いる導電材としては、例えば人造黒鉛、カーボンブラック（アセチレンブラック）などを挙げることができる。但し、これらに限定されるものではない。また、これらは単独でも２種類以上を混合して用いても構わない。 (Conductive material)
Examples of the conductive material used in this production method include artificial graphite and carbon black (acetylene black). However, it is not limited to these. These may be used alone or in combination of two or more.
（バインダー）
　本製造方法に用いるバインダー（結着剤）、すなわち活物質を結着させ電解液に膨潤するバインダーとしては、例えばポリフッ化ビニリデン（ＰＶＤＦ）、ＰＶＤＦとヘキサフルオロプロピレン（ＨＦＰ）やパーフルオロメチルビニルエーテル（ＰＦＭＶ）及びテトラフルオロエチレンとの共重合体などのＰＶＤＦ共重合体樹脂、ポリテトラフルオロエチレン、フッ素ゴムなどのフッ素系樹脂や、スチレン－ブタジエン共重合体、スチレン－アクリロニトリル共重合体などの炭化水素ポリマーや、カルボキシメチルセルロース、ポリイミド樹脂などを挙げることができる。但し、これらに限定されるものではない。また、これらは単独でも２種類以上を混合して用いても構わない。
　中でも、主に高電圧下で使用されるため、耐酸化性を高める観点から、フッ素を含有するバインダー、その中でもポリフッ化ビニリデン（ＰＶＤＦ）を含有するバインダーを用いるのが好ましい。 (binder)
Examples of the binder (binder) used in this production method, that is, a binder that binds an active material and swells in an electrolyte solution include, for example, polyvinylidene fluoride (PVDF), PVDF and hexafluoropropylene (HFP), and perfluoromethyl vinyl ether ( PFMV) and PVDF copolymer resins such as copolymers with tetrafluoroethylene, fluorine resins such as polytetrafluoroethylene and fluororubber, and hydrocarbons such as styrene-butadiene copolymers and styrene-acrylonitrile copolymers Examples thereof include polymers, carboxymethyl cellulose, and polyimide resins. However, it is not limited to these. These may be used alone or in combination of two or more.
Especially, since it is mainly used under a high voltage, it is preferable to use a binder containing fluorine, and among them, a binder containing polyvinylidene fluoride (PVDF) from the viewpoint of enhancing oxidation resistance.
（分散剤）
　分散剤としては、例えばＮ－メチル－２－ピロリドン（ＮＭＰ）、ジメチルホルムアミド、ジメチルアセトアミド、メチルエチルケトン、シクロヘキサノン、酢酸メチル、アクリル酸メチル、ジエチルトリアミン、Ｎ－Ｎ－ジメチルアミノプロピルアミン、エチレンオキシド、テトラヒドロフランなどを挙げることができる。但し、これらに限定されるものではない。また、これらは単独でも２種類以上を混合して用いても構わない。
　また、水溶液を分散剤として用いることも可能である。 (Dispersant)
Examples of the dispersant include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like. Can be mentioned. However, it is not limited to these. These may be used alone or in combination of two or more.
It is also possible to use an aqueous solution as a dispersant.
（スラリーの調製）
　正極活物質、導電材、バインダー及び分散剤の配合割合は適宜調整すればよく、これらを混合して、粘度調整を行い、正極合剤スラリーを調製すればよい。 (Preparation of slurry)
The blending ratio of the positive electrode active material, the conductive material, the binder, and the dispersant may be adjusted as appropriate, and these may be mixed to adjust the viscosity and prepare the positive electrode mixture slurry.
　この際、正極活物質、導電材、バインダー及び分散剤を同時に混合してもよいし、また、予めバインダーを分散剤に分散または溶解させておき、これに正極活物質及び導電材を加えて混合して正極合剤スラリーを調製するようにしてもよい。
　また、正極活物質、導電材、バインダー及び分散剤を混合した後、バインダーが均一に分散するように混練するのが好ましい。 At this time, the positive electrode active material, the conductive material, the binder and the dispersing agent may be mixed at the same time. Alternatively, the binder is dispersed or dissolved in the dispersant in advance, and the positive electrode active material and the conductive material are added thereto and mixed. Thus, a positive electrode mixture slurry may be prepared.
Moreover, it is preferable to knead | mix so that a binder may disperse | distribute uniformly, after mixing a positive electrode active material, a electrically conductive material, a binder, and a dispersing agent.
＜正極合剤層形成工程＞
　本工程では、前記工程で調製した正極合剤スラリーを、集電体としての基材表面に塗工して乾燥させて正極合剤層を形成する。 <Positive electrode mixture layer forming step>
In this step, the positive electrode mixture slurry prepared in the above step is applied to the substrate surface as a current collector and dried to form a positive electrode mixture layer.
（基材）
　集電体としての基材としては、酸化安定性の優れた材料が好適に用いられる。具体的には、例えば鉄、銅、ステンレス、ニッケル、アルミニウム、炭素などを挙げることができる。
　基材の形状としては、シート、発泡体、メッシュ、多孔体およびエキスパンド格子などを挙げることができる。 (Base material)
As the base material as the current collector, a material having excellent oxidation stability is preferably used. Specific examples include iron, copper, stainless steel, nickel, aluminum, and carbon.
Examples of the shape of the substrate include sheets, foams, meshes, porous bodies, and expanded lattices.
（塗工）
　塗工機などを使用することによって、正極合剤スラリーを基材表面に塗工すればよい。塗工の方式については任意であるが、グラビアコート方式、ダイコート方式、ナイフコート方式などを採用することができる。
　その他、ドクターブレードやバーコーターなどを使用して塗工することも可能である。
　塗工量（塗工厚さ）は、プレス後に正極合剤層が２０μｍ～２００μｍになるように調整すればよい。 (Coating)
What is necessary is just to apply a positive mix slurry on the base-material surface by using a coating machine etc. The coating method is arbitrary, but a gravure coating method, a die coating method, a knife coating method, or the like can be employed.
In addition, it is also possible to apply using a doctor blade or a bar coater.
The coating amount (coating thickness) may be adjusted so that the positive electrode mixture layer is 20 μm to 200 μm after pressing.
（乾燥）
　上記のように、正極合剤スラリーを基材表面に塗工した後、分散剤が突沸しないようにして乾燥させることが好ましい。
　この際、乾燥方法としては、７０～１２０℃で乾燥すればよく、段階的に７０～１２０℃に加熱して乾燥させるのが特に好ましい。このとき、負圧環境下で乾燥させると、分散剤を効果的に揮発させることができる。このような乾燥によって、正極合剤スラリー内の分散剤を揮発させることができ、正極合剤層内に適度な空隙が生じることになる。 (Dry)
As described above, after the positive electrode mixture slurry is applied to the surface of the substrate, it is preferably dried so that the dispersant does not bump.
At this time, as a drying method, it may be dried at 70 to 120 ° C., and it is particularly preferable to dry by heating to 70 to 120 ° C. stepwise. At this time, the dispersant can be effectively volatilized by drying in a negative pressure environment. By such drying, the dispersant in the positive electrode mixture slurry can be volatilized, and appropriate voids are generated in the positive electrode mixture layer.
＜プレス工程＞
　本工程では、正極合剤層に対して厚さ方向にプレスする。
　上記のように空隙が生じた正極合剤層をプレスすることで、空隙量を調整しつつ、正極活物質と、導電材、バインダー及び基材とをしっかり結着させることができる。
　この際、プレス後の空隙率は５～３０％であるのが好ましく、中でも２５％以下であるのがより一層好ましい。 <Pressing process>
In this step, the positive electrode mixture layer is pressed in the thickness direction.
By pressing the positive electrode mixture layer in which voids are generated as described above, the positive electrode active material, the conductive material, the binder, and the substrate can be firmly bound while adjusting the void amount.
At this time, the porosity after pressing is preferably 5 to 30%, and more preferably 25% or less.
　プレス方法としては、上下にセットされたローラーで加圧するロールプレス、熱をかけながらローラーで加圧する方法、上下にセットされたプレートで加圧する面プレスなどを挙げることができる。
　プレス条件としては、正極合剤層の厚さ方向に０．５ｔ／ｃｍ以上１０ｔ／ｃｍ未満の線圧でプレスするのが好ましい。
　この際、厚さ方向に０．５ｔ／ｃｍ以上の線圧でプレスすれば、空隙を埋めてしっかり結着させることができる一方、１０ｔ／ｃｍ以上の線圧でプレスすると、剥がれの原因となる可能性がある。
　よって、プレス時の線圧は、０．５ｔ／ｃｍ以上１０ｔ／ｃｍ未満であるのが好ましく、中でも１ｔ／ｃｍ以上或いは７ｔ／ｃｍ以下、その中でも２ｔ／ｃｍ以上或いは５ｔ／ｃｍ以下であるのがより好ましい。 Examples of the pressing method include a roll press that pressurizes with rollers set up and down, a method that presses with rollers while applying heat, and a surface press that presses with plates set up and down.
As a pressing condition, it is preferable to press at a linear pressure of 0.5 t / cm or more and less than 10 t / cm in the thickness direction of the positive electrode mixture layer.
At this time, if it is pressed at a linear pressure of 0.5 t / cm or more in the thickness direction, the gap can be filled and firmly bonded, while if it is pressed at a linear pressure of 10 t / cm or more, it causes peeling. there is a possibility.
Therefore, the linear pressure at the time of pressing is preferably 0.5 t / cm or more and less than 10 t / cm, particularly 1 t / cm or more or 7 t / cm or less, and more preferably 2 t / cm or more or 5 t / cm or less. Is more preferable.
＜加熱乾燥工程＞
　本工程では、前記バインダーの融点以上で且つ２２０℃未満の温度に加熱するのが好ましい。 <Heat drying process>
In this step, it is preferable to heat to a temperature not lower than the melting point of the binder and lower than 220 ° C.
　従来、４Ｖ級のスピネル型リチウムマンガン含有複合酸化物を正極活物質として用いた場合には、正極合剤層を高温、例えば１３０℃以上の高温に加熱すると、バインダーが変質し、高温特性悪化などが生じる問題点があることが知られていた。そのため、通常の電極の製造方法においては、プレスした後、吸着した大気中の水分を飛ばすために１００～１３０℃で加熱乾燥する程度であった。
　これに対し、４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を正極活物質とする本製造方法では、プレス後に前記バインダーの融点以上で且つ２２０℃未満の温度に加熱することにより、ガス発生量を抑制できると共に、体積当たりのエネルギー密度を高めることができる。これは、バインダーの融点以上で加熱することにより、バインダーが溶融して、プレス後の正極電極層内に浸透して、正極活物質が被覆されて活性点が低減する結果、ガス発生量を抑制できると共に、電極活物質層内の空隙量が減少するため、体積当たりのエネルギー密度を高めることができるものと推定することができる。 Conventionally, when a 4V-class spinel-type lithium manganese-containing composite oxide is used as a positive electrode active material, heating the positive electrode mixture layer to a high temperature, for example, a high temperature of 130 ° C. or more, changes the binder and deteriorates the high temperature characteristics. It was known that there was a problem that occurred. Therefore, in an ordinary electrode manufacturing method, after pressing, heating and drying are performed at 100 to 130 ° C. in order to remove moisture in the adsorbed air.
On the other hand, in the present production method in which the lithium manganese-containing composite oxide having an operating potential of 4.5 V or higher is used as the positive electrode active material, by heating to a temperature not lower than the melting point of the binder and lower than 220 ° C. after pressing, The amount of gas generation can be suppressed, and the energy density per volume can be increased. This is because when heated above the melting point of the binder, the binder melts and penetrates into the positive electrode layer after pressing, covering the positive electrode active material and reducing the active sites, thereby suppressing the amount of gas generated. It is possible to estimate that the energy density per volume can be increased because the void amount in the electrode active material layer is reduced.
　加熱方法は、特に限定するものではない。例えば、高温乾燥機や電気炉等を使用して加熱すればよい。 The heating method is not particularly limited. For example, the heating may be performed using a high-temperature dryer or an electric furnace.
　加熱時の雰囲気は、真空状態であるのが好ましい。ここでの真空状態とは、大気圧よりも低い圧力の気体で満たされた空間内の状態をいう（ＪＩＳ参照）。
　中でも、真空度２５００Ｐａ以下の真空状態において加熱するのが好ましい。２５００Ｐａ以下の真空度の真空雰囲気下で加熱させることで、正極合剤層内に残留する揮発成分をより確実に揮発させることができるからである。かかる観点から、加熱時の雰囲気は、真空状態、中でも２５００Ｐａ以下の真空度の真空状態であるのが好ましく、その中でも１０００Ｐａ以下、さらにその中でも５００Ｐａ以下、その中でもさらに１００Ｐａ以下の真空度であるのが特に好ましい。
　加熱時の雰囲気を真空状態とするため、上記の高温乾燥機や電気炉が真空ポンプを備えているのが好ましい。 The atmosphere during heating is preferably a vacuum state. A vacuum state here means the state in the space filled with the gas of the pressure lower than atmospheric pressure (refer JIS).
Especially, it is preferable to heat in a vacuum state with a vacuum degree of 2500 Pa or less. This is because the volatile components remaining in the positive electrode mixture layer can be more reliably volatilized by heating in a vacuum atmosphere with a vacuum degree of 2500 Pa or less. From this point of view, the atmosphere during heating is preferably a vacuum state, particularly a vacuum state of a vacuum degree of 2500 Pa or less, of which 1000 Pa or less, more preferably of 500 Pa or less, of which a vacuum degree of 100 Pa or less. Is particularly preferred.
In order to make the atmosphere at the time of heating into a vacuum state, it is preferable that the high-temperature dryer and the electric furnace include a vacuum pump.
　加熱温度は、前記バインダーの融点以上で且つ２２０℃未満の温度に加熱するのが好ましい。バインダーの融点（例えばＰＶＤＦの融点は、分子量に応じて１３４～１６９℃程度）以上に加熱すれば、バインダーを溶融させることができる。一方、例えばフッ素を含むバインダーを使用する場合、２２０℃以上の高温に加熱すると、正極材料であるリチウム含有複合酸化物と反応してフッ化リチウムなどが生成してしまう。そのため、加熱温度は２２０℃未満とするのが好ましい。
　かかる観点から、加熱温度としては、例えば、１３５℃以上２２０℃未満であるのが好ましく、中でも１５０℃以上或いは２１０℃以下、さらにその中でも１８０℃以上或いは２００℃以下であるのが特に好ましい。 The heating temperature is preferably higher than the melting point of the binder and lower than 220 ° C. The binder can be melted by heating it above the melting point of the binder (for example, the melting point of PVDF is about 134 to 169 ° C. depending on the molecular weight). On the other hand, when using a binder containing fluorine, for example, when heated to a high temperature of 220 ° C. or higher, it reacts with the lithium-containing composite oxide that is the positive electrode material to produce lithium fluoride and the like. Therefore, the heating temperature is preferably less than 220 ° C.
From this viewpoint, the heating temperature is preferably 135 ° C. or higher and lower than 220 ° C., particularly 150 ° C. or higher or 210 ° C. or lower, and more preferably 180 ° C. or higher or 200 ° C. or lower.
＜その他＞
　上記の如き本製造方法で得られた正極は、他の材料、例えばセパレータ、負極、電解質などと積層して電池材料として用いることができる。
　なお、本製造方法におけるプレス工程後、正極合剤層及び基材を、セパレータと積層した後、上述のように加熱乾燥することも考えられるが、セパレータと積層した後に加熱乾燥すると、セパレータの孔が閉塞してしまうおそれがあるため、セパレータと積層する前に上述のように加熱乾燥するのが好ましい。 <Others>
The positive electrode obtained by the present production method as described above can be used as a battery material by being laminated with other materials, for example, a separator, a negative electrode, an electrolyte, and the like.
In addition, after the pressing step in this production method, the positive electrode mixture layer and the substrate may be laminated with the separator and then heat-dried as described above. Therefore, it is preferable to heat and dry as described above before laminating with the separator.
＜語句の説明＞
　本明細書において「Ｘ～Ｙ」（Ｘ，Ｙは任意の数字）と表現する場合、特にことわらない限り「Ｘ以上Ｙ以下」の意と共に、「好ましくはＸより大きい」或いは「好ましくはＹより小さい」の意も包含する。
　また、「Ｘ以上」（Ｘは任意の数字）或いは「Ｙ以下」（Ｙは任意の数字）と表現した場合、「Ｘより大きいことが好ましい」或いは「Ｙ未満であることが好ましい」旨の意図も包含する。 <Explanation of words>
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It also includes the meaning of “smaller”.
In addition, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), it is “preferably greater than X” or “preferably less than Y”. Includes intentions.
　次に、実施例及び比較例に基づいて、本発明について更に説明する。但し、本発明が以下に示す実施例に限定されるものではない。 Next, the present invention will be further described based on examples and comparative examples. However, the present invention is not limited to the following examples.
＜実施例１＞
　正極活物質としてのスピネル型リチウムマンガン含有複合酸化物（化学分析値はＬｉ：４．０ｗｔ％、Ｎｉ：１４．０ｗｔ％、Ｍｎ：４２．０ｗｔ％、Ｔｉ：３．５ｗｔ％、Ｄ５０：１５ｕｍ、ＳＳＡ：０．２ｍ２／ｇ）８９質量部と、アセチレンブラック５質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）ＰＶＤＦの配合量として６質量部とを、それぞれ秤量した。秤量した正極活物質、アセチレンブラックおよび前記ＰＶＤＦを加えて混合し固練りした。これに１－メチル－２－ピロリドン（ＮＭＰ）を加えて正極合剤スラリー（固形分濃度５０質量％）を調製した。
　この正極合剤スラリーを、集電体であるアルミ箔上に、塗工機を用いて搬送速度２０ｃｍ／ｍｉｎにて塗工した後、該塗工機を使用して７０℃を２分間保持するように加熱した後、１２０℃を２分間保持するように乾燥させて、正極合剤層を形成して正極合剤層付きアルミ箔を得た。この際、正極合剤層の厚みは０．０８ｍｍであった。 <Example 1>
Spinel-type lithium manganese-containing composite oxide as a positive electrode active material (chemical analysis values are Li: 4.0 wt%, Ni: 14.0 wt%, Mn: 42.0 wt%, Ti: 3.5 wt%, D50: 15 um, SSA: 0.2 m 2 / g) 89 parts by mass, 5 parts by mass of acetylene black, polyvinylidene fluoride (PVDF, melting point 175 ° C.) PVDF dissolved in 1-methyl-2-pyrrolidone (NMP) Each part by mass was weighed. The weighed positive electrode active material, acetylene black and the PVDF were added, mixed and kneaded. 1-Methyl-2-pyrrolidone (NMP) was added thereto to prepare a positive electrode mixture slurry (solid content concentration 50 mass%).
After coating this positive electrode mixture slurry on an aluminum foil as a current collector at a conveying speed of 20 cm / min using a coating machine, the coating machine is used to hold 70 ° C. for 2 minutes. After heating as described above, drying was performed so as to hold 120 ° C. for 2 minutes to form a positive electrode mixture layer to obtain an aluminum foil with a positive electrode mixture layer. At this time, the thickness of the positive electrode mixture layer was 0.08 mm.
　次に、この正極合剤層付きアルミ箔を、５０ｍｍ×１００ｍｍのサイズに電極を打ち抜いてからロールプレス機を使用してプレス線圧３t／ｃｍでプレス厚密した後、用途に応じて所定のサイズに加工した。すなわち、電池評価のために２０３２型コイン電池の作製に用いる場合は１３ｍｍφに打ち抜き、ラミネート型電池の作製に用いる場合は４０ｍｍ×２９ｍｍ角に打ち抜き、ピール強度試験に用いる場合は２５ｍｍ×１００ｍｍ角に打ち抜いた。
　次に、真空度１０００Ｐａ以下の真空状態において、室温から１８０℃まで加熱し、１８０℃（乾燥温度）で６時間（乾燥時間）保持するように加熱乾燥させて正極（サンプル）を得た。得られたサンプルの「電極厚み」を測定し、表１に示した。 Next, the aluminum foil with the positive electrode mixture layer is punched out into an electrode of 50 mm × 100 mm and then pressed and thickened at a press linear pressure of 3 t / cm using a roll press machine. Processed to size. That is, for use in the production of a 2032 type coin battery for battery evaluation, it is punched into 13 mmφ, when used in the production of a laminate type battery, it is punched into 40 mm × 29 mm square, and when used in a peel strength test, it is punched into 25 mm × 100 mm square. It was.
Next, in a vacuum state with a degree of vacuum of 1000 Pa or less, the sample was heated from room temperature to 180 ° C. and dried by heating so as to hold at 180 ° C. (drying temperature) for 6 hours (drying time) to obtain a positive electrode (sample). The “electrode thickness” of the obtained sample was measured and shown in Table 1.
＜実施例２－４及び比較例１－２＞
　実施例１において、プレス線圧、乾燥温度、電極厚みを、表に示した値に変更した以外、実施例１と同様にして正極（サンプル）を得た。 <Example 2-4 and Comparative Example 1-2>
In Example 1, a positive electrode (sample) was obtained in the same manner as in Example 1 except that the press linear pressure, the drying temperature, and the electrode thickness were changed to the values shown in the table.
＜実施例５＞
　正極活物質としてのスピネル型リチウムマンガン含有複合酸化物（化学分析値はＬｉ：４．０ｗｔ％、Ｎｉ：１５．６ｗｔ％、Ｍｎ：３９．４ｗｔ％、Ｔｉ：５．０ｗｔ％、Ｄ５０：２４ｕｍ、ＳＳＡ：０．１ｍ２／ｇ）９１質量部と、アセチレンブラック４．１質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として４．９質量部とを、それぞれ秤量した。秤量した正極活物質、アセチレンブラックおよび前記ＰＶＤＦを加えて混合し固練りした。これに１－メチル－２－ピロリドン（ＮＭＰ）を加えて正極合剤スラリー（固形分濃度５０質量％）を調製した。
　この正極合剤スラリーを、集電体であるアルミ箔上に、塗工機を用いて搬送速度２０ｃｍ／ｍｉｎにて塗工した後、該塗工機を使用して７０℃を２分間保持するように加熱した後、１２０℃を２分間保持するように乾燥させて、正極合剤層を形成して正極合剤層付きアルミ箔を得た。 <Example 5>
Spinel-type lithium manganese-containing composite oxide as a positive electrode active material (chemical analysis values are Li: 4.0 wt%, Ni: 15.6 wt%, Mn: 39.4 wt%, Ti: 5.0 wt%, D50: 24 um, SSA: 0.1 m 2 / g) 91 parts by mass, 4.1 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) The amount was 4.9 parts by mass, respectively. The weighed positive electrode active material, acetylene black and the PVDF were added, mixed and kneaded. 1-Methyl-2-pyrrolidone (NMP) was added thereto to prepare a positive electrode mixture slurry (solid content concentration 50 mass%).
After coating this positive electrode mixture slurry on an aluminum foil as a current collector at a conveying speed of 20 cm / min using a coating machine, the coating machine is used to hold 70 ° C. for 2 minutes. After heating as described above, drying was performed so as to hold 120 ° C. for 2 minutes to form a positive electrode mixture layer to obtain an aluminum foil with a positive electrode mixture layer.
　次に、この正極合剤層付きアルミ箔を、５０ｍｍ×１００ｍｍのサイズに電極を打ち抜いてからロールプレス機を使用してプレス線圧３t／ｃｍでプレス厚密した後、用途に応じて所定のサイズに加工した。すなわち、電池評価のために２０３２型コイン電池の作製に用いる場合は１３ｍｍφに打ち抜き、ラミネート型電池の作製に用いる場合は４０ｍｍ×２９ｍｍ角に打ち抜き、ピール強度試験に用いる場合は２５ｍｍ×１００ｍｍ角に打ち抜いた。
　次に、真空度１０００Ｐａ以下の真空状態において、室温から２００℃まで加熱し、２００℃（乾燥温度）で６時間（乾燥時間）保持するように加熱乾燥させて正極（サンプル）を得た。得られたサンプルの「電極厚み」を測定し、表１示した。 Next, the aluminum foil with the positive electrode mixture layer is punched out into an electrode of 50 mm × 100 mm and then pressed and thickened at a press linear pressure of 3 t / cm using a roll press machine. Processed to size. That is, for use in the production of a 2032 type coin battery for battery evaluation, it is punched into 13 mmφ, when used in the production of a laminate type battery, it is punched into 40 mm × 29 mm square, and when used in a peel strength test, it is punched into 25 mm × 100 mm square. It was.
Next, in a vacuum state with a degree of vacuum of 1000 Pa or less, the sample was heated from room temperature to 200 ° C. and dried by heating so as to hold at 200 ° C. (drying temperature) for 6 hours (drying time) to obtain a positive electrode (sample). The “electrode thickness” of the obtained sample was measured and shown in Table 1.
＜実施例６＞
　実施例５において、正極活物質を９３質量部と、アセチレンブラック３．２質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として３．８質量部とし、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例５と同様にして正極（サンプル）を得た。 <Example 6>
In Example 5, 93 parts by mass of the positive electrode active material, 3.2 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were mixed in PVDF. A positive electrode (sample) was obtained in the same manner as in Example 5 except that the amount was 3.8 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
＜実施例７＞
　実施例５において、正極活物質を９５質量部と、アセチレンブラック２．３質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として２．７質量部とし、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例５と同様にして正極（サンプル）を得た。 <Example 7>
In Example 5, PVDF was blended with 95 parts by mass of the positive electrode active material, 2.3 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP). A positive electrode (sample) was obtained in the same manner as in Example 5 except that the amount was 2.7 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
＜実施例８＞
　実施例５において、正極活物質を９０質量部と、アセチレンブラック４質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として６質量部とし、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例５と同様にして正極（サンプル）を得た。 <Example 8>
In Example 5, 90 parts by mass of the positive electrode active material, 4 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content. A positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
＜実施例９＞
　実施例５において、正極活物質を９１質量部と、アセチレンブラック３質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として６質量部とし、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例５と同様にして正極（サンプル）を得た。 <Example 9>
In Example 5, 91 parts by mass of the positive electrode active material, 3 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content. A positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
＜実施例１０＞
　実施例５において、正極活物質を９２質量部と、アセチレンブラック２質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として６質量部とし、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例５と同様にして正極（サンプル）を得た。 <Example 10>
In Example 5, 92 parts by mass of the positive electrode active material, 2 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content. A positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
＜実施例１１＞
　実施例５において、正極活物質を９３質量部と、アセチレンブラック１質量部と、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１７５℃）をＰＶＤＦの配合量として６質量部とし、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例５と同様にして正極（サンプル）を得た。 <Example 11>
In Example 5, 93 parts by mass of the positive electrode active material, 1 part by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 175 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) were used as the PVDF content. A positive electrode (sample) was obtained in the same manner as in Example 5 except that the mass was 6 parts by mass, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table.
＜実施例１２＞
　実施例１において、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１３０℃）に変更し、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例１と同様にして正極（サンプル）を得た。 <Example 12>
In Example 1, polyvinylidene fluoride (PVDF, melting point 130 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP) was changed, and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table. A positive electrode (sample) was obtained in the same manner as Example 1 except for the above.
＜実施例１３－１４＞
　実施例１２において、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例１２と同様にして正極（サンプル）を得た。 <Example 13-14>
In Example 12, a positive electrode (sample) was obtained in the same manner as in Example 12 except that the press linear pressure, the drying temperature, and the electrode thickness were changed to the values shown in the table.
＜実施例１５＞
　実施例１において、１－メチル－２－ピロリドン（ＮＭＰ）に溶解したポリフッ化ビニリデン（ＰＶＤＦ、融点１６５℃）に変更し、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例１と同様にして正極（サンプル）を得た。 <Example 15>
In Example 1, it was changed to polyvinylidene fluoride (PVDF, melting point 165 ° C.) dissolved in 1-methyl-2-pyrrolidone (NMP), and the press linear pressure, drying temperature, and electrode thickness were changed to the values shown in the table. A positive electrode (sample) was obtained in the same manner as Example 1 except for the above.
＜実施例１６＞
　実施例１５において、プレス線圧、乾燥温度、電極厚みを表に示した値に変更した以外、実施例１５と同様にして正極（サンプル）を得た。 <Example 16>
In Example 15, a positive electrode (sample) was obtained in the same manner as in Example 15 except that the press linear pressure, the drying temperature, and the electrode thickness were changed to the values shown in the table.
＜比較例３＞
　正極活物質としてのリチウムマンガン含有複合酸化物ＬｉＭｎ２Ｏ４（Ｄ５０：１１ｕｍ、ＳＳＡ：１．２ｍ２／ｇ）８９質量部と、アセチレンブラック５質量部と、ポリフッ化ビニリデン（ＰＶＤＦ、融点１３５℃）６質量部とを秤量して混合し、これに１－メチル－２－ピロリドン（ＮＭＰ）１００質量部を加えて正極合剤スラリー（固形分濃度５０質量％）を調製した。このとき、予めＰＶＤＦをＮＭＰに溶解させておき、正極活物質及びアセチレンブラックを加えて固練りして、正極合剤スラリー（固形分濃度５０質量％）を調製した。
　この正極合剤スラリーを、集電体であるアルミ箔上に、塗工機を用いて搬送速度２０ｃｍ／ｍｉｎにて塗工した後、該塗工機を使用して７０℃を２分間保持するように加熱した後、１２０℃を２分間保持するように乾燥させて、正極合剤層を形成して正極合剤層付きアルミ箔を得た。そのときの正極合剤層の厚みは０．０８ｍｍであった。 <Comparative Example 3>
89 parts by mass of lithium manganese-containing composite oxide LiMn 2 O 4 (D50: 11 μm, SSA: 1.2 m 2 / g) as a positive electrode active material, 5 parts by mass of acetylene black, and polyvinylidene fluoride (PVDF, melting point 135 ° C.) ) 6 parts by mass were weighed and mixed, and 100 parts by mass of 1-methyl-2-pyrrolidone (NMP) was added thereto to prepare a positive electrode mixture slurry (solid content concentration: 50% by mass). At this time, PVDF was dissolved in NMP in advance, and the positive electrode active material and acetylene black were added and kneaded to prepare a positive electrode mixture slurry (solid content concentration 50 mass%).
After coating this positive electrode mixture slurry on an aluminum foil as a current collector at a conveying speed of 20 cm / min using a coating machine, the coating machine is used to hold 70 ° C. for 2 minutes. After heating as described above, drying was performed so as to hold 120 ° C. for 2 minutes to form a positive electrode mixture layer to obtain an aluminum foil with a positive electrode mixture layer. The thickness of the positive electrode mixture layer at that time was 0.08 mm.
　次に、この正極合剤層付きアルミ箔を、５０ｍｍ×１００ｍｍのサイズに電極を打ち抜いてからロールプレス機を使用してプレス線圧３t／ｃｍでプレス厚密した後、用途に応じて所定のサイズに加工した。すなわち、電池評価のために２０３２型コイン電池の作製に用いる場合は１３ｍｍφに打ち抜き、ラミネート型電池の作製に用いる場合は４０ｍｍ×２９ｍｍ角に打ち抜き、ピール強度試験に用いる場合は２５ｍｍ×１００ｍｍ角に打ち抜いた。
　次に、真空度１０００Ｐａ以下の真空状態において、室温から２００℃まで加熱し、２００℃（乾燥温度）で６時間（乾燥時間）保持するように加熱乾燥させて正極（サンプル）を得た。得られたサンプルの「電極厚み」を測定し、表１に示した。 Next, the aluminum foil with the positive electrode mixture layer is punched out into an electrode of 50 mm × 100 mm and then pressed and thickened at a press linear pressure of 3 t / cm using a roll press machine. Processed to size. That is, for use in the production of a 2032 type coin battery for battery evaluation, it is punched into 13 mmφ, when used in the production of a laminate type battery, it is punched into 40 mm × 29 mm square, and when used in a peel strength test, it is punched into 25 mm × 100 mm square. It was.
Next, in a vacuum state with a degree of vacuum of 1000 Pa or less, the sample was heated from room temperature to 200 ° C. and dried by heating so as to hold at 200 ° C. (drying temperature) for 6 hours (drying time) to obtain a positive electrode (sample). The “electrode thickness” of the obtained sample was measured and shown in Table 1.
＜電極断面の観察＞
　実施例及び比較例で得た正極の断面写真を撮影するために、２０３２型コイン電池用に１３ｍｍφに打ち抜いて加熱処理した正極（サンプル）を用いて、下記の方法で断面加工を行った。
　実施例及び比較例で得た正極（サンプル）を専用の試料台にセットした。イオンミリング装置(日立ハイテクノロジーズ製ＩＭ４０００)内に、正極をセットした前記試料台を設置した後、Ａｒガスを０．０７～０．１ｃｍ３／ｍｉｎでフローさせて、加速電圧６ｋＶ、放電電圧１．５ｋＶ、加工時間を1時間とし、スイング角：±３０°、スイング速度３往復／ｍｉｎで試料台をスイングさせながらイオンミリング加工を行った。
　加工後の正極断面を、走査型電子顕微鏡を用いて、倍率を２０００倍にして断面の撮影を行った。実施例２及び比較例１で得た正極断面の顕微鏡画像を代表例として図１及び図２に示した。 <Observation of electrode cross section>
In order to take cross-sectional photographs of the positive electrodes obtained in Examples and Comparative Examples, cross-section processing was performed by the following method using a positive electrode (sample) punched to 13 mmφ for a 2032 type coin battery and heat-treated.
The positive electrode (sample) obtained in Examples and Comparative Examples was set on a dedicated sample stage. In the ion milling device (IM4000 manufactured by Hitachi High-Technologies Corporation), the sample stage on which the positive electrode was set was installed, Ar gas was allowed to flow at 0.07 to 0.1 cm 3 / min, and the acceleration voltage was 6 kV and the discharge voltage was 1 The ion milling was performed while swinging the sample stage at a swing angle of ± 30 ° and a swing speed of 3 reciprocations / min, with a processing time of 0.5 kV and a processing time of 1 hour.
The cross section of the positive electrode cross section after processing was photographed using a scanning electron microscope at a magnification of 2000 times. The microscope images of the positive electrode cross sections obtained in Example 2 and Comparative Example 1 are shown in FIGS. 1 and 2 as representative examples.
＜９０°剥離試験におけるピール強度＞
　株式会社イマダ製の縦型電動計測スタンド「ＭＸ－１０００Ｎ」にデジタルフォースゲージ「ＺＴＡ－５Ｎ」と９０度剥離試験用の治具「Ｐ９０－２００Ｎ」をセットし、ピール強度の測定準備をした。ステンレス土台に両面テープを貼りつけた後、両面テープの上部接着面に対して、実施例及び比較例で得た正極（サンプル）を上から貼りつけ、剥離試験用圧着ローラー「ＡＰＲ－９７」を使って接着した。このとき、正極の長さは両面テープより長くしておき、正極は正極合剤層が下側になるようにして両面テープに接着した。
　次に、デジタルフォースゲージの先に取り付けたフィルムチャックにて、正極をつまみ、固定した。デジタルフォースゲージを真上に動かすことで、両面テープに正極合剤層がくっつき、アルミ箔から剥がすことができる。このとき、アルミ箔から正極合剤層が剥がれるときにかかる力を「ピール強度」（単位：Ｎ）として測定した。なお、アルミ箔から正極合剤層が剥がれていく速度は１７ｍｍ／ｓであった。
　ピール強度は最大値ではなく、安定している区間の数値の平均値を採用した。 <Peel strength in 90 ° peel test>
A digital force gauge “ZTA-5N” and a jig for 90-degree peeling test “P90-200N” were set on a vertical electric measurement stand “MX-1000N” manufactured by Imada Co., Ltd., and preparation for measurement of peel strength was made. After affixing the double-sided tape on the stainless steel base, the positive electrode (sample) obtained in the examples and comparative examples was affixed from the top to the upper adhesive surface of the double-sided tape, and the pressure test roller “APR-97” for the peel test was attached. Used and glued. At this time, the length of the positive electrode was longer than that of the double-sided tape, and the positive electrode was bonded to the double-sided tape so that the positive electrode mixture layer was on the lower side.
Next, the positive electrode was pinched and fixed with a film chuck attached to the tip of a digital force gauge. By moving the digital force gauge directly above, the positive electrode mixture layer sticks to the double-sided tape and can be peeled off from the aluminum foil. At this time, the force applied when the positive electrode mixture layer was peeled from the aluminum foil was measured as “peel strength” (unit: N). The rate at which the positive electrode mixture layer was peeled from the aluminum foil was 17 mm / s.
The peel strength was not the maximum value, but the average value of the stable intervals was used.
＜電池評価＞
　実施例・比較例で作製した正極を用いて２０３２型コイン電池およびラミネート型電池を作製し、これを用いて以下に示す電池性能評価試験を行った。 <Battery evaluation>
2032 type coin batteries and laminate type batteries were produced using the positive electrodes produced in the examples and comparative examples, and the following battery performance evaluation tests were performed using the 2032 type coin batteries and laminate type batteries.
（コイン電池の作製）
　負極はφ１４ｍｍ×厚み０．６ｍｍの金属Ｌｉとし、カーボネート系の混合溶媒に、ＬｉＰＦ６を１ｍｏｌ／Ｌになるように溶解させた電解液を含浸させたセパレータ（多孔性ポリエチレンフィルム製）を置き、２０３２型コイン電池を作製した。 (Production of coin battery)
The negative electrode is a metal Li of φ14 mm × thickness 0.6 mm, and a separator (made of a porous polyethylene film) impregnated with an electrolytic solution in which LiPF 6 is dissolved to 1 mol / L in a carbonate-based mixed solvent is placed, A 2032 type coin battery was produced.
（電池性能評価試験）
　上記のようにして準備した２０３２型コイン電池を用いて次に記述する方法で初期活性を行った。２５℃にて０．１Ｃで４．９９９Ｖまで定電流定電位充電した後、０．１Ｃで３．０Ｖまで定電流放電した。これを３サイクル繰り返した。なお、実際に設定した電流値は正極中の正極活物質の含有量から算出した。 (Battery performance evaluation test)
Using the 2032 type coin battery prepared as described above, initial activation was performed by the method described below. After charging at a constant current and a constant potential at 25 ° C. and 0.1 C to 4.999 V, the battery was discharged at a constant current up to 3.0 V at 0.1 C. This was repeated for 3 cycles. The actually set current value was calculated from the content of the positive electrode active material in the positive electrode.
（正極合剤層体積当たりのエネルギー密度）
　エネルギー密度は下記の方法で算出した。すなわち、４．９９９－３．０Ｖの電圧レンジを０．１Ｃで定電流放電したときの放電容量（[表１]に示した）から、ＳＯＣ５０％となる容量を算出し、その容量に到達した時の電池電圧をＶｍ（ｍｉｄｄｌｅ　ｐｏｉｎｔ　ｖｏｌｔａｇｅ）とした。
　次にエネルギー密度（Ｗｈ／ｇ）は放電容量（ｍＡｈ／ｇ）×Ｖｍ（Ｖ）で計算した。
　さらに、エネルギー密度に対して、正極合剤層に含まれる活物質量をかけて、正極合剤層で除することで、正極合剤層体積当たりのエネルギー密度を算出し、比較例３を１００とした場合の指数（％）として表に記載した。 (Energy density per positive electrode mixture layer volume)
The energy density was calculated by the following method. That is, from the discharge capacity (shown in [Table 1]) when a constant current discharge is performed at a voltage range of 4.999-3.0V at 0.1 C, the capacity at which SOC is 50% is calculated, and the capacity is reached. The battery voltage at the time was defined as V m (middle point voltage).
Next, the energy density (Wh / g) was calculated by discharge capacity (mAh / g) × Vm (V).
Furthermore, the energy density per volume of the positive electrode mixture layer is calculated by multiplying the energy density by the amount of the active material contained in the positive electrode mixture layer and dividing it by the positive electrode mixture layer. It was described in the table as an index (%).
（ラミネート型電池の作製）
　負極は天然球状グラファイトを塗布した負極電極シート（パイオトレック株式会社　電極容量１．６ｍＡｈ/ｃｍ2）を使用した。
　上記で得た正極シートと負極シートを準備し、その間に、カーボネート系の混合溶媒に、ＬｉＰＦ６を１ｍｏｌ／Ｌになるように溶解させた電解液を含浸させたセパレータ（多孔性ポリエチレンフィルム製）を置き、ラミネート型電池を作製した。 (Production of laminated battery)
The negative electrode used was a negative electrode sheet coated with natural spherical graphite (Piotrek Corporation, electrode capacity 1.6 mAh / cm 2 ).
A separator obtained by preparing the positive electrode sheet and the negative electrode sheet obtained above, and impregnating an electrolytic solution obtained by dissolving LiPF 6 in a carbonate-based mixed solvent so as to be 1 mol / L (made of a porous polyethylene film) And a laminate type battery was produced.
（ガス発生量評価試験）
　上記した方法で作製したラミネート型電池を１２時間放置した後、２５℃にて０．０５Ｃで４．９Ｖまで定電流定電位充電した後、２．９Ｖまで定電流放電した。その後、測定環境温度を４５℃にして４時間放置し、０．０５Ｃにて４．９Ｖになるまで充電を行い、その電圧を７日間維持した後、２．９Ｖまで放電を行った。
　ここまでに発生するガス発生量（ｍＬ）は、浸漬容積法（アルキメデスの原理に基づく溶媒置換法）により計測した。なお、表には比較例２の数値を１００とした場合の指数（％）で示した。 (Gas generation evaluation test)
The laminate type battery produced by the above-described method was left for 12 hours, then charged at a constant current and a constant potential at 0.05 C to 4.9 V at 25 ° C., and then discharged at a constant current to 2.9 V. Thereafter, the measurement was carried out at 45 ° C. for 4 hours, and the battery was charged to 4.9 V at 0.05 C, maintained at that voltage for 7 days, and then discharged to 2.9 V.
The gas generation amount (mL) generated so far was measured by the immersion volume method (solvent replacement method based on Archimedes' principle). The table shows the index (%) when the value of Comparative Example 2 is 100.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
（考察）
　本発明が提案するリチウム二次電池用電極の製造方法によれば、正極合剤層をプレス処理した後、バインダーの融点以上の温度に加熱することによって、ガス発生量を抑制できると共に、正極合剤層体積当たりのエネルギー密度を高めることができることが分かった。
　ガス発生量について、バインダーの融点以上の温度に加熱することによって、バインダーが溶融して、プレス後の正極合剤層内に浸透して正極活物質活性表面の活性点を被覆するため、ガス発生量を抑制できたものと推察することができる。 (Discussion)
According to the method for producing an electrode for a lithium secondary battery proposed by the present invention, after the positive electrode mixture layer is pressed, it is heated to a temperature equal to or higher than the melting point of the binder. It was found that the energy density per agent layer volume can be increased.
As for the amount of gas generated, heating to a temperature equal to or higher than the melting point of the binder causes the binder to melt and penetrate into the positive electrode mixture layer after pressing to cover the active sites on the active surface of the positive electrode active material. It can be inferred that the amount could be suppressed.
　また、正極合剤層体積当たりのエネルギー密度については、正極合剤層をプレス処理することで電極活物質層内の空隙量を減少させ、活物質の膨張収縮により生じる応力を緩和できる体積を低減させても、本発明が提案するリチウム二次電池用電極の製造方法によれば、ピール強度が高いため、正極合剤層と集電体であるアルミ箔の間の電気抵抗を小さくすることができる結果、体積当たりのエネルギー密度を高めることができたものと推察することができる。
　さらに電極としての抵抗が小さいため、局所的な過電圧を避けることができ、ひいてはガス発生量の低減につなげることができると推察することができる。 Regarding the energy density per volume of the positive electrode mixture layer, the amount of voids in the electrode active material layer is reduced by pressing the positive electrode mixture layer, and the volume that can relieve stress caused by expansion and contraction of the active material is reduced. However, according to the method for manufacturing an electrode for a lithium secondary battery proposed by the present invention, since the peel strength is high, the electrical resistance between the positive electrode mixture layer and the aluminum foil as the current collector can be reduced. As a result, it can be inferred that the energy density per volume could be increased.
Furthermore, since the resistance as an electrode is small, it can be inferred that a local overvoltage can be avoided, and as a result, the amount of gas generation can be reduced.
　上記の方法で測定した電極のピール強度が１．２Ｎより大きい電極であって、且つ、バインダーが溶融して、プレス後の正極合剤層内に浸透して正極活物質活性表面を被覆していることが観察される電極であれば、エネルギー密度も高く、ガス発生量も低い可能性が高いものと推察できる。 The electrode peel strength measured by the above method is greater than 1.2N, and the binder melts and penetrates into the positive electrode mixture layer after pressing to coat the active surface of the positive electrode active material. It can be inferred that an electrode that is observed to have high energy density and low gas generation amount.
　また、実施例及び比較例で得た正極の断面写真を確認したところ、図１及び図２に示されるように、実施例で得られた正極（例えば図１）は、比較例で得られた正極(例えば図２)に比べて、イオンミリングでの加工傷がつきにくく、強固な電極であることが分かった。 Moreover, when the cross-sectional photograph of the positive electrode obtained by the Example and the comparative example was confirmed, as FIG.1 and FIG.2 shows, the positive electrode (for example, FIG. 1) obtained by the Example was obtained by the comparative example. Compared to the positive electrode (for example, FIG. 2), it was found that the processing electrode was hard to be damaged by ion milling and was a strong electrode.
　これまで本発明者が行ってきた試験結果と技術常識とを考慮すれば、このような効果は、かかる特有の課題と特性などから、金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物、特にスピネル型リチウムマンガン含有複合酸化物であれば同様の効果を得ることができるものと考えることができる。 Considering the test results and technical common sense that the present inventor has conducted so far, such effects can be obtained from lithium having a working potential of 4.5 V or more at the metal Li reference potential because of such unique problems and characteristics. It can be considered that the same effect can be obtained with a manganese-containing composite oxide, particularly a spinel type lithium manganese-containing composite oxide.

Claims (7)

  1. 　金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物を含有する正極活物質、導電材、バインダー及び分散剤を含む正極合剤スラリーを調製し、集電体としての基材に前記正極合剤スラリーを塗工して乾燥させて正極合剤層を形成した後、該正極合剤層に対して厚さ方向にプレスし、次に前記バインダーの融点以上で且つ２２０℃未満の温度に加熱することを特徴とするリチウム二次電池用電極の製造方法。 A positive electrode mixture slurry containing a lithium-manganese-containing composite oxide having a working potential of 4.5 V or more at a metal Li reference potential is prepared, and a positive electrode mixture slurry containing a conductive material, a binder, and a dispersant is prepared. The positive electrode mixture slurry is applied to the material and dried to form a positive electrode mixture layer, and then pressed in the thickness direction against the positive electrode mixture layer, and then the melting point of the binder is not less than 220 ° C. The manufacturing method of the electrode for lithium secondary batteries characterized by heating to the temperature below.
  2. 　真空状態において、前記バインダーの融点以上で且つ２２０℃未満の温度に加熱することを特徴とする請求項１に記載のリチウム二次電池用電極の製造方法。 2. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the electrode is heated to a temperature higher than the melting point of the binder and lower than 220 ° C. in a vacuum state.
  3. 　前記の真空状態が、２５００Ｐａ以下の真空度であることを特徴とする請求項２に記載のリチウム二次電池用電極の製造方法。 The said vacuum state is a vacuum degree of 2500 Pa or less, The manufacturing method of the electrode for lithium secondary batteries of Claim 2 characterized by the above-mentioned.
  4. 　前記正極合剤層に対して、厚さ方向に０．５ｔ／ｃｍ以上１０ｔ／ｃｍ未満の線圧でプレスすることを特徴とする請求項１～３の何れかに記載のリチウム二次電池用電極の製造方法。 The lithium secondary battery according to any one of claims 1 to 3, wherein the positive electrode mixture layer is pressed in the thickness direction at a linear pressure of 0.5 t / cm or more and less than 10 t / cm. Electrode manufacturing method.
  5. 　前記バインダーとして、ポリフッ化ビニリデン（ＰＶＤＦ）を含有するバインダーを用いることを特徴とする請求項１～４の何れかに記載のリチウム二次電池用電極の製造方法。 The method for producing an electrode for a lithium secondary battery according to any one of claims 1 to 4, wherein a binder containing polyvinylidene fluoride (PVDF) is used as the binder.
  6. 　予めバインダーを分散剤に分散または溶解させておき、これに正極活物質及び導電材を加えて正極合剤スラリーを調製することを特徴とする請求項１～５の何れかに記載のリチウム二次電池用電極の製造方法。 6. The lithium secondary slurry according to claim 1, wherein a binder mixture is previously dispersed or dissolved in a dispersant, and a positive electrode active material and a conductive material are added thereto to prepare a positive electrode mixture slurry. Manufacturing method of battery electrode.
  7. 　金属Ｌｉ基準電位で４．５Ｖ以上の作動電位を有するリチウムマンガン含有複合酸化物が、式（１）：Ｌｉ[ＬｉaＭｎ2-a-b-cＭ1bＭ2c]Ｏ4-δ（Ｍ1は、Ｎｉ、Ｃｏ及びＦｅからなる群から選択される一種又は二種以上の元素であり、Ｍ2は、Ｍｇ、Ｔｉ、Ａｌ、Ｂａ、Ｃｒ、Ｗ、Ｍｏ、Ｙ、Ｚｒ及びＮｂからなる群から選択される一種又は二種以上の元素であり、ａは０．００～０．２０、bは０．２０～１．２０、ｃは０．００１～０．４００である。）で表わされるものであることを特徴とする請求項１～６の何れかに記載のリチウム二次電池用電極の製造方法。
     
          A lithium manganese-containing composite oxide having an operating potential of 4.5 V or more at a metal Li reference potential is expressed by the formula (1): Li [Li a Mn 2 -abc M1 b M2 c ] O 4-δ (M1 is Ni, One or two or more elements selected from the group consisting of Co and Fe, and M2 is a type selected from the group consisting of Mg, Ti, Al, Ba, Cr, W, Mo, Y, Zr and Nb Or two or more elements, a is 0.00 to 0.20, b is 0.20 to 1.20, and c is 0.001 to 0.400. The method for producing an electrode for a lithium secondary battery according to any one of claims 1 to 6.

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