JP4984422B2 - Method for manufacturing electrode for secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a secondary battery electrode, and more particularly, to a method for manufacturing a secondary battery electrode having excellent dispersibility of a conductive material.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done. The secondary battery for motor drive requires basic characteristics of a high energy density for storing the running energy of the automobile and a high output density for showing a large acceleration of the automobile. As a secondary battery for driving a motor, a lithium ion secondary battery having the highest theoretical energy among all practical batteries is rapidly being developed.

  A lithium ion secondary battery basically has a configuration in which a positive electrode and a negative electrode are disposed via a separator and filled with an electrolyte. The electrode used for the lithium ion secondary battery is such that an electrode active material layer including an electrode active material made of lithium cobalt composite oxide or the like and a conductive material made of carbon black or the like is formed on a current collector. Is used. When charging / discharging is performed in such a battery, Li ions are occluded / released from the electrode active material, and at the same time, electrons move through the conductive material, whereby the electrode reaction proceeds and charging / discharging is performed.

A general method for manufacturing an electrode for a lithium ion secondary battery is a method in which an electrode active material, a conductive material, and the like are kneaded in a solvent to form a slurry, and then the slurry is applied onto a current collector. Yes. In Patent Document 1, polyvinyl pyrrolidone is used as a dispersant, carbon black as a conductive material is dispersed in a solvent by a high-pressure jet mill, and the obtained dispersion is mixed with an electrode active material to prepare the slurry. A method is disclosed. According to Patent Document 1, it is possible to provide a lithium ion secondary battery having excellent cycle characteristics by highly dispersing a fine conductive material in an electrode.
JP 2004-289696 A

  In order to obtain a high-power lithium ion secondary battery even during charging and discharging at a high current rate, it is desirable to reduce the particle size of the electrode active material contained in the electrode active material layer. Thereby, the surface area of the electrode active material can be increased, the distance over which the Li ions diffuse on the surface of the electrode active material can be shortened, and the reaction resistance of the electrode reaction can be reduced.

  In addition, the electrode active material and the conductive material in the electrode active material layer are mixed in a state where the surface of the electrode active material 101 is uniformly coated with the conductive material 102 as shown in FIG. It is desirable that a conductive network is formed. Thereby, a large amount of the three-phase interface between the electrode active material, the conductive material, and the electrolyte exists, and the reaction resistance of the electrode reaction can be reduced, and quick charge / discharge can be performed.

  However, in the electrode active material layer manufactured by the conventional electrode manufacturing method using both the electrode active material and the conductive material that are miniaturized, the conductive material 102 aggregates as schematically shown in FIG. As a result, the surface of the electrode active material 101 cannot be sufficiently covered, and it is difficult to obtain a sufficient amount of conductive network formation. For this reason, in order to obtain sufficient electroconductivity in the electrode active material layer, a large amount of conductive material is required, resulting in an increase in manufacturing cost.

  Accordingly, an object of the present invention is to provide a method for producing an electrode for a secondary battery excellent in dispersibility of a conductive material.

  As a result of intensive studies by the present inventors in view of the above problems, the use of an ionic surfactant as a dispersing agent during the preparation of the slurry used for electrode production reduces the aggregation of the conductive material in the obtained electrode active material layer. It has been found that a sufficient amount of conductive network can be secured.

  That is, the present invention includes a step of preparing a slurry containing an electrode active material, a conductive material, and a dispersant composed of an ionic surfactant, and applying the slurry on a current collector to form an electrode active material layer. It aims at providing the manufacturing method of the electrode for secondary batteries which has a process to form.

  In the electrode manufactured by the method of the present invention, the amount of conductive network formation in the electrode active material layer can be sufficiently secured, so that not only the amount of conductive material used but also the electrode reaction resistance can be reduced. Therefore, according to the electrode, it is possible to provide a secondary battery that is low in manufacturing cost and excellent in output characteristics.

  As described above, the first of the present invention is a step of preparing a slurry containing an electrode active material, a conductive material, and a dispersant composed of an ionic surfactant, and applying the slurry onto a current collector. And a step of forming an electrode active material layer.

  The method of the present invention is characterized in that an ionic surfactant is used as a dispersant during the preparation of the slurry. By using the dispersant, the surface of the electrode active material can be uniformly coated with the conductive material in the slurry, and a sufficient conductive network can be formed in the electrode active material layer. The mechanism for obtaining such an effect is not clear, but the following may be considered.

That is, the ionic surfactant used as a dispersant in the present invention has both cation (+) and anion (-) charges when ionized in a solvent such as water. For example, a dialkyl sulfosuccinate sodium (NaSO ₃ CHCOOR ₁ CH ₂ COOR ₂ ; where R ₁ is an alkylene group such as a methylene group or a butylene group), and R ₂ is hydrogen. . atom, in the case of using it) alkyl group such as a methyl group, an ethyl group, etc. in a solvent of water ^{_{(Na + sO 3 CHCOOR 1 CH}} 2 COOR 1 - ionizes as indicated by). On the other hand, in a slurry using a solvent such as water, the surface of lithium cobalt composite oxide or the like preferably used as an electrode active material has a negative charge, and the surface of carbon black or the like used as a conductive material has a positive charge. Yes. When the surfactant according to the present invention is mixed in such a slurry, as schematically shown in FIG. 2, positive and negative charges are attracted to each other, so that the dissociated surfactant (Na ⁺ SO ₃ CHCOOR ₁ CH ₂ COOR ₁ ^-) is surrounding each surface of the electrode active material 101 or the conductive material 102. As a result, the electrode active material and the conductive material are highly dispersed in the slurry, and the surfactant covering the surface of each particle can further attract the electrode active material 101 and the conductive material 102. Thus, an electrode active material layer in which the surface of the active material 101 is uniformly coated and the conductive material 102 is connected to form a conductive network as shown in FIG. 1 can be obtained.

  In a slurry in which only a conductive material and an electrode active material are mixed without using the dispersant, the conductive material is likely to aggregate due to van der Waals force and Brownian motion. However, in the present invention, the above effect can be obtained by using a dispersant composed of an ionic surfactant. However, the mechanism is speculative, and the effect of the dispersant of the present invention is not limited to the mechanism.

  Hereinafter, the method of the present invention will be described step by step.

  In the method of the present invention, first, a slurry containing an electrode active material, a conductive material, and a dispersant composed of an ionic surfactant is prepared. Specifically, the slurry is prepared by mixing an electrode active material, a conductive material, and a dispersant composed of an ionic surfactant in a solvent.

  The electrode active material may be any material that can occlude and release lithium ions, and is not particularly limited as long as it is generally used in conventional secondary batteries.

The electrode active material is preferably a lithium-transition metal composite oxide which is a composite oxide of a transition metal and lithium. Specifically, Li · Co-based composite oxide such as LiCoO _2, Li · Ni-based composite oxide such as LiNiO _2, Li · Mn-based composite oxide such as spinel LiMn ₂ O _4, Li · such LiFeO ₂ Fe-based composite oxides and those obtained by replacing some of these transition metals with other elements can be used. These lithium-transition metal composite oxides are excellent in reactivity and cycle characteristics, and are low-cost materials. Therefore, it is possible to form a battery having excellent output characteristics by using these materials for electrodes. In addition, examples of the electrode active material include transition metal oxides such as LiFePO ₄ and lithium phosphate compounds and sulfate compounds; transition metal oxides such as V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , and MoO ₃ , and sulfides. _objects; PbO 2, AgO, or the like can be used NiOOH.

  In order to reduce electrode reaction resistance, it is preferable to use an electrode active material having a primary particle size of 0.1 to 5 μm.

  The content of the electrode active material in the slurry is preferably 10 to 80% by mass, more preferably 20 to 40% by mass with respect to the slurry mass. Thereby, the electrode active material can be highly dispersed in the slurry.

  The conductive material used for the slurry is not particularly limited, but preferred examples include graphite (granular, scaly, fibrous, acicular, etc.), carbon black, acetylene black, carbon fiber, and carbon nanotube.

  A conductive material is preferably used in order to uniformly coat the surface of the electrode active material and reduce the electrode reaction resistance. More preferably, a conductive material having a primary particle diameter of 0.01 to 1 μm, particularly 0.01 to 0.1 μm is used.

  The content of the conductive material in the slurry is preferably 1 to 20% by mass, more preferably 1 to 6% by mass with respect to the electrode active material. Thereby, the conductive material can be highly dispersed in the slurry.

  As the dispersant used in the slurry, an ionic surfactant is used. Specific examples of the ionic surfactant include at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. Of these, sodium dialkylsulfosuccinate, sodium alkylbenzenesulfonate, alkenyl succinate, alkyltrimethylammonium chloride and polyoxyethylene alkyl ether are particularly preferred. Moreover, these dispersing agents may be used individually by 1 type, and may mix and use 2 or more types.

  The content of the dispersant in the slurry may be appropriately determined according to the type, amount, and the like of the dispersant, the electrode active material, and the conductive material, but is preferably 100 ppm to 10% by mass with respect to the slurry mass. Is preferably 500 ppm to 5 mass%. Thereby, the conductive material can be highly dispersed in the slurry.

  The slurry solvent and mixing means may be any known technique and are not particularly limited. For example, dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone (NMP) or the like can be used as a solvent for the slurry. As the mixing means, a homogenizer, an ultrasonic dispersion device, or the like is used.

  In the method of the present invention, the slurry is prepared by separately preparing a dispersion containing an electrode active material and a dispersion containing a conductive material using a dispersant made of an ionic surfactant, and then preparing each dispersion. It is preferable to carry out by mixing. That is, the slurry is prepared by mixing the dispersion liquid (I) containing the electrode active material and the dispersant and the dispersion liquid (II) containing the conductive material and the dispersant. Is preferred. Accordingly, higher dispersibility of the electrode active material and the conductive material can be obtained, and the surface of the electrode active material can be more uniformly covered with the conductive material.

  Dispersion (I) is prepared by mixing the electrode active material and the dispersant in a solvent. The electrode active material, the dispersant, the solvent, and the mixing means are the same as described above. The content of the electrode active material in the dispersion (I) is preferably about 1 to 50% by mass with respect to the slurry mass. The content of the dispersant in the dispersion (I) is preferably about 100 ppm to 10% by mass with respect to the slurry mass. Thereby, the high dispersibility of an electrode active material is acquired.

  Dispersion (II) is prepared by mixing the conductive material and the dispersant in a solvent. The conductive material, the dispersant, the solvent, and the mixing means are the same as described above. The content of the conductive material in the dispersion (II) is preferably about 10 to 80% by mass with respect to the slurry mass. The content of the dispersant in the dispersion (II) is preferably about 100 ppm to 10% by mass with respect to the slurry mass. Thereby, the high dispersibility of a electrically conductive material is acquired.

  The viscosity of the slurry prepared as described above is preferably 10000 cPs or less, particularly 10 to 3000 cPs at 25 ° C. Accordingly, the electrode active material and the conductive material can be uniformly dispersed in the slurry, and the thickness of the obtained electrode active material layer can be made uniform.

  Furthermore, other components such as a binder, an ion conductive polymer, a lithium salt as a supporting electrolyte, and a polymerization initiator may be added to the slurry as necessary.

  As the binder, polyvinylidene fluoride (PVDF), SBR, polyimide, or the like can be used. However, it is not necessarily limited to these.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers. The ion conductive polymer contained in the electrode active material layer may be the same as or different from the ion conductive polymer used in the electrolyte impregnated in the separator of the battery in which the electrode of the present invention is employed. Good, but preferably the same.

Examples of the lithium salt include LiBETI (lithium bis (perfluoroethylenesulfonylimide); also referred to as Li (C ₂ F ₅ SO ₂ ) ₂ N), LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiBOB (lithium bisoxide borate) or a mixture thereof can be used. However, it is not necessarily limited to these.

  The polymerization initiator is added to act on the crosslinkable group of the ion conductive polymer to advance the crosslinking reaction. Depending on the external factor for acting as an initiator, it is classified into a photopolymerization initiator, a thermal polymerization initiator and the like. Examples of the polymerization initiator include azobisisobutyronitrile (AIBN) (for thermal polymerization) and benzyldimethyl ketal (BDK) (for photopolymerization).

  The addition amount of these other materials is not particularly limited and can be adjusted as appropriate. However, it may be about 3 to 10% by mass with respect to the slurry mass.

  Next, the process of forming the electrode active material layer by applying the slurry prepared as described above onto the current collector will be described.

  The current collector is not particularly limited as long as it is used in a conventional secondary battery, and may be composed of a conductive material such as an aluminum foil, a copper foil, or a stainless steel (SUS) foil. That's fine. The thickness of the current collector may be about 10 to 50 μm.

  In order to apply the slurry onto the current collector, a known method such as a slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, or a dip coater may be used.

  As described above, the electrode active material layer can be obtained on the current collector by drying the slurry applied on the current collector. The drying means is not particularly limited. What is necessary is just to dry a slurry using a well-known means. The drying time and drying temperature are determined according to the amount of slurry supplied and the volatilization rate of the solvent of the slurry, but may be performed at 80 to 150 ° C. for about 5 to 100 minutes.

  When the polymerization initiator for polymerizing the ion conductive polymer is contained in the slurry, the ion conductive polymer in the slurry is polymerized (crosslinked) by various methods after the coating step. The polymerization (crosslinking) method in this case is not particularly limited, and can be appropriately selected according to the type of polymerization initiator used. Examples thereof include thermal polymerization, photo (ultraviolet) polymerization, radiation polymerization, and electron beam polymerization. The apparatus and conditions for polymerizing (crosslinking) are not particularly limited, and conventionally known apparatuses and conditions can be used.

  Furthermore, you may perform press operation to the electrode active material layer manufactured by said method. By performing the pressing operation, the surface of the obtained electrode active material layer can be further flattened. The apparatus and conditions used for the press operation are not particularly limited, and conventionally known apparatuses and methods may be used as appropriate.

  In the method of the present invention, it is preferable to heat-treat the electrode active material layer produced on the current collector as described above. Thereby, impurities such as a surfactant used as a dispersant remaining in the electrode active material layer are burned out, and the output characteristics of the obtained electrode can be further improved. In some cases, the heat treatment may be performed by omitting the drying step.

  The temperature for the heat treatment is preferably not less than the decomposition temperature of the dispersant and less than the decomposition temperature of the electrode active material or binder, more preferably 200 to 300 ° C, particularly preferably 250 to 280 ° C. The heat treatment is preferably performed in a nitrogen atmosphere, an inert gas atmosphere such as argon, or an inert gas atmosphere such as hydrogen. As the heat treatment method, a known method is used, and a discharge plasma method, a hot press method, or the like may be used.

  The method of the secondary battery electrode of the present invention described above has been described based on a lithium ion secondary battery for convenience of explanation. However, the method of the present invention is not limited to lithium ion secondary batteries, nickel hydrogen secondary batteries, nickel cadmium secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries. It is also suitably used as a method for producing an electrode used for a secondary battery such as a battery.

  In particular, the above-described method of the present invention is more preferably used as a method for producing an electrode for a lithium ion secondary battery from the viewpoint of practicality, and is extremely useful as a method for producing an electrode containing an electrode active material having poor conductivity. It is particularly preferable to use as a method for producing a positive electrode for a lithium ion secondary battery.

  The second of the present invention is an electrode for a secondary battery produced by the method described above. In the electrode manufactured by the first method of the present invention, the conductive material and the electrode active material are highly dispersed in the electrode active material layer, and the conductive material can uniformly cover the surface of the electrode active material. Thereby, a sufficient conductive network is formed in the electrode active material layer, and a secondary battery electrode having excellent rate characteristics and output characteristics is obtained.

  The electrode for secondary batteries of the present invention has an electrode active material layer containing at least an electrode active material and a conductive material, and a current collector. Since the conductive material is uniformly dispersed in the electrode active material layer as described above, the abundance of conductive material aggregates can be reduced. Specifically, when the number of primary particles of the conductive material is A and the number of aggregates of the conductive material is B, the ratio of the primary particles and aggregates of the conductive material is 0.1 ≧ B. / (A + B), preferably 0.01 ≧ B / (A + B).

  The conductive material contained in the electrode active material layer is as described in the first aspect of the present invention, but preferably has a primary particle size of 0.01 to 1 μm, more preferably 0.01 to 0.1 μm. Use. When a conductive material having such a fine particle diameter is used, the conventional electrode active material layer easily aggregates the conductive material to form an aggregate having a large particle diameter. However, in the electrode active material layer of the present invention, the conductive material can be highly dispersed to reduce the aggregate diameter.

  In the present invention, the primary particle of the conductive material means one particle, and the secondary particle of the conductive material means a group of particles in which a plurality of primary particles are aggregated. The primary particle size is measured by measuring each primary particle size in an electron micrograph (magnification: 3000 times) of the surface of the electrode active material layer taken using a scanning electron microscope under conditions of an acceleration voltage of 3 kV. Done. The aggregate diameter is measured by measuring the maximum particle diameter of each aggregate in each photograph taken in the same manner as described above. Further, the abundance ratio of primary particles and aggregates (B / (A + B)) is an electron micrograph (magnification: 3000 times) taken in the same manner. Of the 100 particles shown in the photograph, the primary particles alone This is a value obtained from B / (A + B) by counting the number B of aggregates as agglomerates obtained by collecting a plurality of existing particles A and a plurality of primary particles.

  A more detailed description of the conductive material, electrode active material, current collector, etc. in the electrode of the present invention is as described in the first aspect of the present invention.

  3rd of this invention is the secondary battery using the electrode for secondary batteries manufactured by the 1st method of this invention mentioned above, or the 2nd electrode for secondary batteries of this invention. For the configuration of the secondary battery, conventionally known techniques can be appropriately referred to except that the secondary battery electrode produced by the first method or the second secondary battery electrode of the present invention is used. For example, in a secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte, a secondary battery using the above-described secondary battery electrode may be used as at least one of the positive electrode and the negative electrode.

  In the secondary battery of the present invention, the second electrode of the present invention may be used as at least one of the positive electrode and the negative electrode, but is used as the positive electrode because excellent dispersibility between the electrode active material and the conductive material is obtained. Is preferred. It does not restrict | limit especially as a negative electrode used at this time, What is necessary is just a negative electrode generally used conventionally. Specifically, the negative electrode has a conventional configuration in which a negative electrode active material layer containing at least a negative electrode active material such as carbon is applied on a current collector made of copper, nickel, titanium, SUS, or the like.

  The secondary battery of the present invention is obtained by superposing a positive electrode and a negative electrode through a separator and impregnating this with an electrolyte.

  As the separator used in the secondary battery of the present invention, any separator that is conventionally used can be used without particular limitation. Examples thereof include porous membranes or nonwoven fabrics of polyolefin resins such as microporous polyethylene film, microporous polypropylene film, microporous ethylene-propylene copolymer film, and laminates thereof. These have the outstanding effect that the reactivity with electrolyte (electrolyte solution) can be restrained low. In addition, a composite resin film in which a polyolefin resin non-woven fabric or a polyolefin resin porous film is used as a reinforcing material layer, and the reinforcing material layer is filled with a vinylidene fluoride resin compound may be used. Further, instead of the separator, an electrolyte layer made of a solid electrolyte or a polymer gel electrolyte may be employed.

  The thickness of the separator may be appropriately determined according to the usage, but may be about 15 to 50 μm in the usage of a secondary battery for driving a motor such as an automobile. Further, the porosity, size, etc. of the separator may be appropriately determined in consideration of the characteristics of the obtained secondary battery.

  As the electrolyte impregnated in the separator, a nonaqueous electrolyte is preferably mentioned. An electrolyte containing an aqueous solution may cause electrolysis at a high voltage. Therefore, a nonaqueous electrolytic solution using an organic solvent is preferably used as an electrolytic solution that can withstand a high voltage. Thereby, the ion conduction in the electrode active material layer becomes smooth, and the output of the entire battery can be improved.

  The nonaqueous electrolyte may be any of a liquid electrolyte (electrolytic solution), a solid electrolyte, and a polymer gel electrolyte. The nonaqueous electrolyte is not particularly limited as long as it is used in a normal secondary battery.

As an electrolytic solution, LiBOB (lithium bis oxide _{borate), LiPF 6, LiBF 4,} LiClO 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 inorganic acid anion salts ₁₀ such as _Cl, LiCF 3 _{SO 3,} It contains at least one electrolyte salt selected from organic acid anion salts such as Li (CF ₃ SO ₂ ) ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N, and includes propylene carbonate (PC), ethylene Cyclic carbonates such as carbonate (EC); chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2- Ethers such as dibutoxyethane; γ- Lactones such as butyrolactone; nitriles such as acetonitrile; esters such as methyl propionate; amides such as dimethylformamide; and at least one selected from methyl acetate and methyl formate, or a mixture of two or more The thing using organic solvents (plasticizer), such as a protic solvent, can be used.

  The solid electrolyte is not particularly limited as long as it is composed of a polymer having ion conductivity. Examples thereof include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. Such a polyalkylene oxide polymer can dissolve the above-described electrolyte salt well. Moreover, excellent mechanical strength is exhibited by forming a crosslinked structure.

  The polymer gel electrolyte is not particularly limited, but a polymer electrolyte for electrolyte having ion conductivity containing an electrolyte solution, or a similar electrolyte solution in an electrolyte polymer skeleton having no ion conductivity. Examples include those held.

  The electrolyte solution contained in the polymer gel electrolyte is the same as described above. In addition, as the electrolyte polymer having ion conductivity, the above-described solid electrolyte or the like is used. Examples of the polymer for electrolyte that does not have ion conductivity include monomers that form gelled polymers such as polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). Can be used. However, it is not necessarily limited to these. Note that PAN, PMMA, etc. are in a class that has almost no ionic conductivity, and therefore can be used as the polymer for electrolytes having the ionic conductivity. It is illustrated as a polymer for electrolyte that does not have ion conductivity used.

  The ratio (mass ratio) between the electrolyte polymer (host polymer) and the electrolyte solution in the polymer gel electrolyte may be determined according to the purpose of use, but is in the range of 2:98 to 90:10. Thereby, it can seal effectively also about the oozing-out of the electrolyte from the outer peripheral part of an electrode active material layer by providing an insulating layer and an insulation process part. Therefore, it is possible to give priority to battery characteristics relatively with respect to the ratio (mass ratio) between the host polymer and the electrolytic solution in the polymer gel electrolyte.

  The positive electrode, the negative electrode, and the separator are housed in a battery case or the like. As the battery case, it is preferable to use a battery case that can prevent external impact and environmental degradation when the battery is used. For example, a battery case made of a laminate material in which a polymer film and a metal foil are laminated together is sealed by bonding the peripheral part thereof by heat sealing, or by heat-sealing the bag-shaped opening. Thus, the positive electrode lead terminal and the negative electrode lead terminal are taken out from the heat fusion part. At this time, the location where the lead terminals of the positive and negative electrodes are taken out is not particularly limited to one location. Moreover, the material which comprises a battery case is not limited to the above-mentioned thing, The material by plastics, a metal, rubber | gum, etc., or these combination is possible, and things, such as a film, a board, and a box shape, can be used for a shape. In addition, a method of providing a terminal that conducts between the inside and outside of the case, connecting a current collector inside the terminal, and connecting a lead terminal outside the terminal to take out current can be applied.

  The structure of the secondary battery of the present invention is not particularly limited, and can be applied to any conventionally known form / structure such as a stacked battery or a wound battery when distinguished by form / structure. It is. Further, when viewed in terms of electrical connection in the secondary battery, it can be applied to both an internal parallel connection type battery and a bipolar internal series connection type battery that are not bipolar. The secondary battery of the present invention is preferably a bipolar battery. Compared with a normal battery, the voltage of a single cell is high, and a battery excellent in capacity and output characteristics can be configured.

  The secondary battery of the present invention has various characteristics as described above. Therefore, it is suitable as a power source for driving vehicles that are particularly demanding regarding energy density and power density, such as electric vehicles, fuel cell vehicles, and hybrid electric vehicles, and can provide vehicles with excellent fuel efficiency and running performance. . In addition, it is convenient to install an assembled battery in which a plurality of the secondary batteries of the present invention are connected under the seat in the center of the body of an electric vehicle or hybrid electric vehicle as a driving power supply because a large in-house space and trunk room can be obtained. . However, the present invention is not limited to these, and the secondary battery of the present invention can be installed under the floor of a vehicle, in a trunk room, an engine room, a roof, a hood, and the like.

  The electrode of the present invention described above and the secondary battery using the electrode are preferably used as a lithium ion secondary battery from the viewpoint of practicality. In addition, a nickel hydride secondary battery, a nickel cadmium secondary battery, a sodium ion The present invention can also be applied to secondary batteries such as secondary batteries, potassium ion secondary batteries, magnesium ion secondary batteries, and calcium ion secondary batteries.

  Hereinafter, the present invention will be specifically described based on examples. The present invention is not limited to the following examples.

Example 1
1. Production of positive electrode 80 g of spinel manganese having a particle diameter of 1 μm as a positive electrode active material, 10 g of Denka black having a primary particle diameter of 50 nm as a conductive material, 5 g of PVdF as a binder, 1 g of sodium dialkylsulfosuccinate as a dispersant, and NMP (appropriate amount) as a solvent. A positive electrode slurry having a viscosity of 4000 cPs was prepared by stirring and mixing with a homogenizer. The positive electrode slurry was applied onto an aluminum foil (thickness 20 μm) by a bar coater and dried at 130 ° C. for 1 hour. Thereby, the aluminum foil on which the positive electrode active material layer (thickness 30 μm) was produced was punched out at 16 mmΦ to obtain a positive electrode. In the positive electrode active material layer, the conductive material had an aggregate diameter of 1 μm and an aggregate diameter ratio (B / (A + B)) of 0.1.

2. Production of negative electrode A negative electrode slurry having a viscosity of 4000 cPs was prepared by stirring and mixing 90 g of hard carbon having a primary particle size of 9 μm as a negative electrode active material, 10 g of PVdF as a binder, and NMP (appropriate amount) as a solvent by a homogenizer. The negative electrode slurry was applied onto a copper foil (thickness 20 μm) by a bar coater and dried at 130 ° C. for 1 hour. As a result, the copper foil on which the negative electrode active material layer (thickness 30 μm) was produced was punched out at 16 mmΦ to obtain a negative electrode.

3. Production of Coin Battery The negative electrode 311 produced above was fitted into a stainless steel battery lid 312 and pressed. Next, the positive electrode 310 produced above was placed in a stainless steel outer can 313, and a separator 314 of a polypropylene microporous film (thickness 30 μm) was placed thereon. An electrolyte of 1M LiPF ₆ / EC + PC (1: 1 (volume ratio)) was poured into this, the battery lid 312 was placed, and a sealant 315 made of a mixture of styrene butadiene rubber and pitch was filled without any gaps. The can was crimped and sealed to produce a coin battery as shown in FIG. The battery has a diameter of 20 mm and a height of 2 mm.

4). Evaluation A charge / discharge test was performed on the coin battery prepared above according to the following procedure, and the initial discharge capacity and rate characteristics were evaluated.

  Charging / discharging is performed at 25 ° C., charging is performed in a constant current-constant voltage mode of 0.2 C for up to 4.2 V for a total of 8 hours, and a constant current discharge is performed up to a cutoff voltage of 2.5 V at a discharge rate of 0.2 C. Thus, the discharge capacity was measured, and the initial charge / discharge efficiency was determined. Next, at 25 ° C., charging was performed in a constant current-constant voltage mode of 10 C to 4.2 V for a total of 2 hours, and a constant current discharge was performed up to a cutoff voltage of 2.5 V at a discharge rate of 10 C, thereby discharging capacity The rate characteristics (10C rate discharge capacity / 0.2C rate discharge capacity × 100) were determined. The results (initial charge / discharge efficiency, 0.2C rate discharge capacity, and rate characteristics) are shown in Table 1.

(Example 2)
1. Production of positive electrode 85 g of spinel manganese having a primary particle diameter of 1 μm as a positive electrode active material, 5 g of Denka black having a primary particle diameter of 50 nm as a conductive material, 5 g of PVdF as a binder, 1 g of sodium dialkylsulfosuccinate as a dispersant, and NMP (appropriate amount) as a solvent Was stirred and mixed with a homogenizer to prepare a positive electrode slurry having a viscosity of 4000 cPs. A positive electrode was produced in the same manner as in Example 1 except that the positive electrode ink was used. In the positive electrode active material layer in the positive electrode, the aggregate diameter of the conductive material was 1 μm, and the ratio of aggregate diameter (B / (A + B)) was 0.03.

  Next, using the positive electrode, a coin battery was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

Example 3
Using a homogenizer, 88 g of spinel manganese having a primary particle diameter of 1 μm as a positive electrode active material, 2 g of Denka black having a primary particle diameter of 50 nm as a conductive material, 5 g of PVdF as a binder, 1 g of sodium dialkylsulfosuccinate as a dispersant, and NMP (appropriate amount) as a solvent. A positive electrode slurry having a viscosity of 4000 cPs was prepared by stirring and mixing. A positive electrode was produced in the same manner as in Example 1 except that the positive electrode ink was used. In the positive electrode active material layer in the positive electrode, the aggregate diameter of the conductive material was 1 μm, and the aggregate diameter ratio (B / (A + B)) was 0.01.

  Next, using the positive electrode, a coin battery was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

Example 4
After producing a positive electrode active material layer on an aluminum foil in the same manner as in Example 1, this was further heat treated at 300 ° C. for 1 hour in a vacuum oven to obtain a positive electrode. In the positive electrode active material layer after the heat treatment, the aggregate diameter of the conductive material was 1 μm, and the ratio of aggregate diameter (B / (A + B)) was 0.1.

  Next, using the positive electrode, a coin battery was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

(Comparative Example 1)
1. Production of Positive Electrode 75 g of spinel manganese having a primary particle diameter of 1 μm as a positive electrode active material, 20 g of Denka Black having a primary particle diameter of 50 nm as a conductive material, 5 g of PVdF as a binder, and NMP (appropriate amount) as a solvent are mixed by stirring with a homogenizer. Prepared a positive electrode slurry of 4000 cPs. A positive electrode was produced in the same manner as in Example 1 except that the positive electrode ink was used. In the positive electrode active material layer of the positive electrode, the aggregate diameter of the conductive material was 2 μm, and the aggregate diameter ratio (B / (A + B)) was 0.9.

  Next, using the positive electrode, a coin battery was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

(Comparative Example 2)
1. Preparation of positive electrode 85 g of spinel manganese having a primary particle diameter of 1 μm as a positive electrode active material, 10 g of Denka black having a primary particle diameter of 50 nm as a conductive material, 5 g of PVdF as a binder, and NMP (appropriate amount) as a solvent are mixed by stirring with a homogenizer. Prepared a positive electrode slurry of 4000 cPs. A positive electrode was produced in the same manner as in Example 1 except that the positive electrode ink was used. In the positive electrode active material layer in the positive electrode, the aggregate diameter of the conductive material was 2 μm, and the ratio of aggregate diameter (B / (A + B)) was 0.8.

  Next, using the positive electrode, a coin battery was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

(Comparative Example 3)
1. Preparation of positive electrode 90 g of spinel manganese having a primary particle diameter of 1 μm as a positive electrode active material, 5 g of Denka black having a primary particle diameter of 50 nm as a conductive material, 5 g of PVdF as a binder, and NMP (appropriate amount) as a solvent are mixed by stirring with a homogenizer. Prepared a positive electrode slurry of 4000 cPs. A positive electrode was produced in the same manner as in Example 1 except that the positive electrode ink was used. In the positive electrode active material layer in the positive electrode, the aggregate diameter of the conductive material was 2 μm, and the aggregate diameter ratio (B / (A + B)) was 0.6.

  Next, using the positive electrode, a coin battery was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

  In Table 1, the rate characteristics of Comparative Examples 1 to 3 are lower than those of Examples 1 to 4. This is considered because the dispersibility of the conductive material and the electrode active material is low because the dispersant is not contained, and the conductive network in the electrode is not sufficiently formed. In Examples 1 to 4, since the conductive material is uniformly dispersed around the electrode active material due to the effect of the dispersant to form a conductive network, the rate characteristics are 20% or more better than those of Comparative Examples 1 to 3. It has become. In particular, in Example 4, since the dispersing agent was removed, it turns out that the more excellent characteristic is shown.

  According to the method of the present invention, an electrode for a secondary battery excellent in dispersibility of an electrode active material and a conductive material can be obtained. According to the electrode for a secondary battery, it is possible to provide a secondary battery that is excellent in rate characteristics, discharge characteristics, and the like, even with a small amount of dispersant.

The dispersion state of the electrode active material and the conductive material in the electrode active material layer of the electrode for a secondary battery produced by the method of the present invention is shown. It is a schematic diagram which shows the state of the electrode active material in a slurry used for the method of this invention, an electrically conductive material, and the dissociated dispersing agent. The schematic cross section of the coin-type secondary battery produced in the Example is shown. The electrode active material in the electrode active material layer of the electrode for secondary batteries produced by the conventional method and the dispersion state of a electrically conductive material are shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Electrode active material, 102 ... Conductive material, 310 ... Positive electrode, 311 ... Negative electrode, 312 ... Battery cover, 313 ... Outer can, 314 ... Separator, 315 ... Sealant.

Claims (10)

Preparing a slurry containing an electrode active material having a negative charge on the surface, a conductive material having a positive charge on the surface, and a dispersant comprising an ionic surfactant;
Have a, and forming an electrode active material layer by coating the slurry on the current collector,
The step of preparing the slurry is performed by mixing the dispersion liquid (I) containing the electrode active material and the dispersant, and the dispersion liquid (II) containing the conductive material and the dispersant. A method for producing an electrode for a secondary battery. The electrode active material is a positive electrode active material comprising a lithium-transition metal composite oxide, a transition metal and lithium phosphate compound or sulfate compound; a transition metal oxide or sulfide; PbO ₂ The manufacturing method of the electrode for secondary batteries of Claim 1 which is AgO or NiOOH. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein the conductive material is graphite, carbon black, acetylene black, carbon fiber, or carbon nanotube. 4. The secondary battery according to claim 1, wherein the dispersant is at least one selected from the group consisting of a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. 5. Electrode manufacturing method. The method for manufacturing an electrode for a secondary battery according to claim 4, wherein the dispersant is sodium dialkylsulfosuccinate. Method for producing the electrode active material layer further comprising a step of heat-treating, claim 1 according to any one of the 5 secondary battery electrode. A method for producing a lithium ion secondary battery positive electrode, method of manufacturing a secondary battery electrode according to any one of claims 1-6. A secondary battery electrode manufactured by the manufacturing method according to claim 1,
The ratio of the primary particles of the conductive material and the aggregates of the conductive material in the electrode active material layer is 0.1 ≧ B /, where A is the number of primary particles and B is the number of aggregates. (a + B) is a secondary battery electrode. Any one secondary battery electrode manufactured by the method according to claim 1-7 or a secondary battery using the electrode for a secondary battery according to claim 8. The secondary battery according to claim 9, which is a bipolar battery.

Images