JP2011165389A - Method of manufacturing electrode for lithium ion secondary battery, electrode for lithium ion secondary battery, and lithium ion secondary battery using the same electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which is excellent in input/output characteristics at low temperature. <P>SOLUTION: The electrode for a lithium ion secondary battery includes a collector sheet with many through-holes formed, and an electrode active material layer formed on a surface of the collector sheet and containing electrode active material. The electrode for a lithium ion secondary battery shows an outline formed of outer walls of many through-holes, and includes an air gap in which the electrode active material layer does not penetrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing an electrode for a lithium ion secondary battery, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the electrode.

  A lithium ion secondary battery is disposed between a positive electrode formed by forming a positive electrode active material layer on the surface of the positive electrode current collector, a negative electrode formed by forming a negative electrode active material layer on the surface of the negative electrode current collector, and the positive electrode and the negative electrode. An insulating separator and a non-aqueous electrolyte for moving lithium ions.

  For example, the following Patent Document 1 is a comb-shaped perforated current collector made of a metal foil provided with a large number of through holes, and the long diameter of the through holes is in the range of 5 to 1000 μm. A current collector having a minor axis in the range of 2 to 100 μm and a ratio of major axis to minor axis of each through hole is 2.5 ≦ major axis / minor axis ≦ 100 is disclosed. is doing. And according to the electrode provided with such a current collector, the gas generated by the decomposition of the solvent in the electrolytic solution by repeating the charge and discharge of the secondary battery through the holes formed in the current collector. It is described that gas can be discharged out of the electrode portion by permeation. Further, it is described that the active material does not enter the hole when the active material layer is formed on the surface of the current collector because the hole is a fine hole having a specific shape.

Patent Document 2 below discloses an electrode laminate including a positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator, and non-aqueous electrolysis. A negative electrode included in a negative electrode active material layer, wherein the negative electrode current collector is made of a copper foil having a through-hole, and the porosity of the copper foil by the through-hole is 10% or more and 70% or less. The active material is a non-graphitic carbonaceous material having a BET specific surface area of 1 m ² / g or more and 1500 m ² / g or less, and the thickness of the negative electrode active material layer is 20 μm or more and 100 μm or less. A power storage element is disclosed. And according to such an electrical storage element, in the case of sticking lithium foil on the surface of the negative electrode active material layer in order to make up for the loss of lithium that is irreversibly taken into the negative electrode active material during the initial charge It is described that the negative electrode can efficiently absorb lithium foil.

JP-A-11-97035 JP 2006-286218 A

  By the way, a lithium ion secondary battery used in an electric vehicle is required to have high output characteristics and high input / output characteristics. Especially regarding input / output characteristics, since automobiles are used even in extremely cold regions, excellent input / output characteristics at low temperatures that enable input / output in a short time in a low temperature environment are required. However, non-aqueous electrolytes used for lithium ion secondary batteries have low activity at low temperatures. Therefore, improving the input / output characteristics of the lithium ion secondary battery at a low temperature is an important issue when used as a power source for an electric vehicle.

  An object of this invention is to provide the lithium ion secondary battery excellent in the input-output characteristic at the time of low temperature.

  A method of manufacturing an electrode for a lithium ion secondary battery according to one aspect of the present invention includes a filling step of filling a large number of through holes of a current collector sheet in which a large number of through holes are formed, and a filling step. Later, an active material layer is formed by applying a mixture paste containing an electrode active material, a binder, and a dispersion medium of the electrode active material to the surface of the current collector sheet to form a coating film and heating the coating film A pore forming material is removed after the formation of the coating film. In the electrode for a lithium ion secondary battery obtained by such a manufacturing method, there is a void having the outline of the outer wall of the through hole in the surface of the current collector sheet. When a lithium ion secondary battery is assembled using such an electrode, the electrolyte solution can also penetrate from the back side of the current collector sheet into the active material layer formed on the current collector sheet surface. I can do it. Moreover, when the active material layer is formed on both surfaces of the current collector sheet, a void is located at the center of the active material layer laminated on both surfaces. Such voids store the non-aqueous electrolyte. As a result, the nonaqueous electrolytic solution can be infiltrated into the layer from both the front side and the back side of the active material layer. Thereby, the input / output characteristics of the lithium ion secondary battery, in particular, the input / output characteristics at a low temperature can be improved.

  An electrode for a lithium ion secondary battery according to another aspect of the present invention includes a current collector sheet in which a large number of through holes are formed, and an electrode active material formed on the surface of the current collector sheet. And an active material layer. The outer wall of a large number of through-holes is contoured and has a void in which the electrode active material layer does not enter. Such an electrode for a lithium ion secondary battery can constitute a lithium ion secondary battery having high input / output characteristics of a lithium ion secondary battery, in particular, high input / output characteristics at a low temperature.

  The lithium ion secondary battery according to another aspect of the present invention includes a positive electrode in which a positive electrode active material layer is formed on the surface of a positive electrode current collector, and a negative electrode in which a negative electrode active material layer is formed on the surface of a negative electrode current collector. And an insulating separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte for moving lithium ions, wherein at least one of the positive electrode and the negative electrode is any one of the above lithium ion secondary batteries The electrode is used. Such a lithium ion secondary battery has high input / output characteristics, particularly high input / output characteristics at low temperatures.

  The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

  According to the present invention, it is possible to provide a lithium ion secondary battery exhibiting excellent input / output characteristics, particularly excellent input / output characteristics at low temperatures.

The schematic cross section of the electrode 10 for lithium ion secondary batteries of this embodiment is shown. The enlarged schematic cross section of the space | gap v formed in the electrode 10 for secondary batteries is shown. It is a schematic cross section explaining each process of manufacture of the electrode for lithium ion secondary batteries of this embodiment. The schematic cross section of a wound type lithium ion secondary battery is shown.

  A preferred embodiment of an electrode for a lithium ion secondary battery according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic cross-sectional view of a lithium ion secondary battery electrode 10 of the first embodiment. The electrode 10 for a lithium ion secondary battery is used as, for example, a positive electrode or a negative electrode of a wound lithium ion secondary battery 100 as shown in FIG.

  As shown in FIG. 1, the electrode 10 includes a current collector sheet 1 and active material layers 2 a and 2 b formed on both surfaces of the current collector sheet 1. Each of the active material layers 2a and 2b contains an active material 3, a binder 4, and a conductive material 5 used as necessary. The active material 3 includes a positive electrode active material when the electrode 10 is used as a positive electrode, and a negative electrode active material when the electrode 10 is used as a negative electrode.

  A large number of through holes h are formed in the current collector sheet 1, and the through holes h form voids v without being filled with the constituent components of the active material layers 2 a and 2 b.

  In this way, the active material layers 2a and 2b are formed so as to retain the voids v formed by the through holes h without filling the numerous through holes h of the current collector sheet 1 with the active material layers 2a and 2b. Thus, as shown by an arrow L in FIG. 1, a path through which the electrolytic solution permeates is formed between the front surface and the back surface of the current collector sheet 1a. In the electrode 10, since the active material layers 2 a and 2 b are formed on both surfaces of the current collector sheet 1, the gap v also serves as a liquid reservoir for storing the nonaqueous electrolytic solution. As a result, the periphery of the non-aqueous electrolyte with respect to the active material layers 2a and 2b can be improved. That is, the presence of the void v allows the nonaqueous electrolytic solution to enter the active material layer 2a or the active material layer 2b from either the front surface or the back surface. As a result, the non-aqueous electrolyte is evenly distributed in the active material layers 2a and 2b, thereby improving input / output characteristics. In particular, when a lithium ion secondary battery is used in a low temperature environment, the non-aqueous electrolyte spreads evenly in the active material layers 2a and 2b in a short time, so that the input / output characteristics are remarkably improved.

  The size of the large number of through holes h formed in the current collector sheet 1 is not particularly limited. Specifically, for example, the average diameter of the equivalent area circle is in the range of 3 to 50 μm, and more preferably in the range of 4 to 30 μm. It is preferable. The average diameter of the equivalent area circle means the diameter of the circle when converted to a circle having an area equivalent to the area of the hole. When the size of the through-hole h is in such a range, the non-aqueous electrolyte can easily pass between the front surface and the back surface of the current collector sheet 1 and the active material layer is formed on both surfaces Can store a sufficient amount of the non-aqueous electrolyte in the gap v. If the average diameter of the through-holes h is too small, the non-aqueous electrolyte is difficult to permeate, and if the average diameter is too large, the active material layer is difficult to be supported by the current collector sheet 1 and peeling or the like occurs. There is a fear. The size of the through hole h is larger than the average particle diameter of the active material contained in the active material layers 2a and 2b, from the point that the non-aqueous electrolyte L can be sufficiently brought into contact with the active material. preferable.

  Moreover, as a hole area rate of the electrical power collector sheet | seat 1, it is preferable that it is 10 to 60%, Furthermore, it is preferable that it is 20 to 50%. When the aperture ratio is too low, the non-aqueous electrolyte solution tends to be insufficient, and when the aperture ratio is too high, the active material layer becomes difficult to be supported by the current collector sheet 1 and is peeled off. Etc. may occur.

  The shape of many through-holes h formed in the current collector sheet 1 is not particularly limited, but the outer shape is preferably a shape close to a circle from the viewpoint of excellent fluidity of the electrolyte, specifically, The ratio of the major axis to the minor axis of the through hole h (major axis / minor axis) is preferably in the range of 1 to 50, more preferably 1 to 20, and particularly preferably 1 to 2.

  As the material for the current collector sheet 1, those conventionally used as current collectors for lithium ion batteries can be used without any particular limitation. Specific examples thereof include foils and sheets made of aluminum, stainless steel, nickel, copper, titanium, or an alloy containing them as a main component. In addition, when the electrode 10 is used as a negative electrode, copper or a copper alloy is preferably used, and when used as a positive electrode, aluminum or an aluminum alloy is preferably used.

  Although the thickness of the electrical power collector sheet | seat 1 is not specifically limited, As the specific example, the range of 5-50 micrometers, Furthermore, 10-20 micrometers is preferable, for example.

  As shown in FIG. 2 (a), the shape of the gap v formed in the lithium ion secondary battery electrode 10 is such that the outline of the through hole h is the outer wall of the side surface, and the top and bottom openings are active. In the columnar shape formed so as to be covered substantially horizontally by the material layers 2a and 2b, as shown in FIG. 2 (b), the outline of the through hole h is the outer wall of the side surface, and at the top and bottom openings, Examples thereof include columnar shapes that form convex top portions and bottom portions from which the active material layers 2a and 2b are removed. In particular, in the case where the gap V has a shape as shown in FIG. 2B, the surface area where the active material layer and the gap are in contact with each other is increased, so that the periphery of the liquid is further improved.

  Next, an example of a method for manufacturing the above-described electrode 10 for a lithium ion secondary battery will be described with reference to schematic cross-sectional views of FIGS. 3 (a) to 3 (e).

  First, the current collector sheet 1 having a large number of through holes h is prepared (preparation step) (FIG. 3A). Then, the pore-forming material f is filled in the numerous through holes h of the current collector sheet 1 (filling step) (FIG. 3B). Then, after the filling step, an active material is formed by applying a mixture paste containing an electrode active material and a solvent to both surfaces of the current collector sheet 1 to form a coating film, and drying the coating film by heating. Coating films 2a ′ and 2b ′ of layer 2 are formed (active material layer forming step) (FIG. 3C). And after performing the heat processing for drying a solvent, active material layer 2a, 2b is formed by rolling coating-film 2a ', 2b' (FIG.3 (d)). In this case, the outer wall of the through hole h is contoured by disposing or removing the pore forming material f filled in the through hole h by providing a heat treatment step after the heat treatment for rolling the solvent or rolling, and rolling. A void v is formed (FIG. 3E). As another method, when a solvent-soluble pore-forming material f is used, it may be dissolved and removed by dipping in a solvent. Hereinafter, each step will be described in more detail.

  In this manufacturing method, first, a current collector sheet 1 having a large number of through holes h is prepared (preparation step, FIG. 3A).

  As the current collector sheet 1 having a large number of through holes h, a metal foil or a metal sheet having a large number of holes formed by punching metal or the like, which is industrially produced, is used. Alternatively, a flat metal foil or metal sheet may be perforated using a punching metal or the like. In the case of producing a negative electrode, a sheet made of copper or a copper-based alloy is preferably used as the current collector sheet 1, and in the case of a positive electrode, a sheet made of aluminum or an aluminum-based alloy is preferably used.

  Next, the pore forming material f is filled in the through holes h of the current collector sheet 1 (filling step, FIG. 3B).

  In the filling step, the pore forming material f to be removed later is filled into the through holes h of the current collector sheet 1 to close the through holes h, so that the through holes h are activated in the active material layer forming step of the next step. This is a process for preventing the material layer from being filled with the material layer forming component.

  In the filling step, as shown in FIG. 3B, the through holes h of the current collector sheet 1 are filled with the pore forming material f.

  The method of filling the through hole h with the pore forming material f is not particularly limited. Specifically, for example, a method of filling the through hole h by pushing the paste-like pore forming material into the through hole h, It is possible to use a method in which a granular pore forming material is placed on the surface of the current collector sheet 1 and the through holes h are filled by rubbing with a metal blade.

  The pore forming material f is removed in a later step. As a specific example of the method for removing the pore forming material f, for example, an organic material having a lower thermal decomposition temperature or vaporization temperature than the thermal decomposition temperature of a binder described later contained in the active material layer as the pore forming material f. After forming the active material layer or the coating film using the material, the pore forming material f is heated and decomposed or vaporized, or the pore forming material f is a material that dissolves in a predetermined solvent. Examples thereof include a method of dissolving and removing the pore forming material f in a solvent after the formation of the coating film.

  Specific examples of the organic material having a thermal decomposition temperature lower than the thermal decomposition temperature of the binder used as the pore-forming material f include, for example, polyvinyl butyral (thermal) depending on the type of the binder used. Decomposition temperature about 250 ° C), polyvinylpyrrolidone (about 220 ° C), ethylmalonic acid (about 160 ° C), 5-amino-1 naphthol (about 170 ° C), indophenol (about 160 ° C), etc. It is done. These are all organic materials having a thermal decomposition temperature of 250 ° C. or less, and are preferable from the viewpoint of excellent dispersibility in the paste. The thermal decomposition temperature is the temperature at the time of 5% weight loss when measured with a suggestion scanning thermobalance under the condition of nitrogen flow and a temperature increase rate of 15 ° C./min.

  In addition, specific examples of the organic material having a vaporization temperature lower than the thermal decomposition temperature of the binder used as the pore-forming material f are, for example, 2-amino depending on the type of the binder used. -2 methyl 1,3-propanediol (boiling point 151 ° C), m-anisic acid (boiling point 172 ° C), orcinol (boiling point 147 ° C), 2,3-dihydroxybenzaldehyde (boiling point 135 ° C), benzylic acid (boiling point 180 ° C) ), Flavone (boiling point 185 ° C.), N phenylmaleide (boiling point 135 ° C.), piperazine (boiling point 145 ° C.), and the like.

  When an organic material having a thermal decomposition temperature or vaporization temperature lower than the thermal decomposition temperature of the binder is used as the pore forming material, pore formation is performed after the active material layer is formed or in the drying process at the time of active material formation. By heating to a temperature higher than the thermal decomposition temperature or vaporization temperature of the material and lower than the decomposition temperature of the binder, only the pore-forming material can be gasified and decomposed and removed. Thereby, the space | gap v is formed.

  Specific examples of the material used as the pore-forming material f and dissolved and removed in the solvent include a metal salt of sulfuric acid such as magnesium sulfate, an inorganic salt of phosphoric acid such as ammonium phosphate, a metal salt of acetic acid such as lithium acetate, Inorganic acid salts such as, organic metal complex hydrates such as bis (2,4-pentanedionato) zinc monohydrate, water-soluble polymers such as polyvinyl alcohol and starch, and the like. These should be dissolved in aqueous solvents or polar solvents, preferably water or aprotic polar solvents such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA), dimethylsulfoxide (DMSO), etc. Can do. Among these, bis (2,4-pentanedionato) zinc monohydrate is particularly preferable from the viewpoint of excellent solubility.

  The paste-like pore forming material can be prepared by stirring and mixing the pore forming material and a solvent or a dispersion medium, for example, with a double-arm kneader. As the dispersion medium, any liquid that does not impair the effects of the present invention can be used without any particular limitation. Specifically, for example, NMP is preferably used.

  Moreover, you may mix | blend a small amount (for example, about 0.5-4%) binder with the pore formation material paste as needed. Specific examples of the binder include PVDF. Since the amount of the binder component is small, even if it finally remains in the through-hole, there is no particular effect on the periphery of the electrolyte solution.

  In the filling step, it is preferable to adjust the particle diameter of the pore-forming material f, the viscosity of the organic material, and the like so as to be suitable for filling the through-holes h.

  Next, as shown in FIG. 3C, after the filling step, a mixture paste containing an electrode active material, a binder, a conductive material, a solvent, and the like is applied to both surfaces of the current collector sheet 1. Then, a coating film is formed, and coating films 2a ′ and 2b ′ for forming the active material layer 2 are formed by heating and drying the coating film (active material layer forming step).

  When a positive electrode is manufactured as the electrode 10, a positive electrode active material layer is formed as the active material layer 2, and when a negative electrode is manufactured, a negative electrode active material layer is formed as the active material layer 2.

  The positive electrode active material layer is, for example, a positive electrode obtained by mixing an additive such as a positive electrode active material, a conductive material, a binder, and a thickener used as necessary at a predetermined mixing ratio in the presence of a solvent. A coating film is formed by applying the mixture paste on both surfaces of the current collector sheet, and the coating film is formed by heating and drying and rolling.

As a positive electrode active material, the material conventionally used as a positive electrode active material of a lithium ion secondary battery is used without limitation. Specific examples thereof include, for example, lithium-containing transition metal composite oxides such as lithium cobaltate, lithium nickelate, and lithium manganate, olivine type lithium salts such as LiFePO ₄ , titanium disulfide, and molybdenum disulfide. Examples include chalcogen compounds and manganese dioxide. The lithium-containing transition metal composite oxide is a metal composite oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal composite oxide is substituted with a different element. Here, examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Mn, Al, Co, Ni, Mg and the like are preferable. One kind or two or more kinds of different elements may be used.

The volume average particle diameter of the positive electrode active material is not particularly limited, but is preferably 0.1 to 50 μm, and more preferably 0.5 to 30 μm. The mixing ratio of the positive electrode active material is based on the whole positive electrode active material layer. Thus, it is preferably 50 to 99.5% by mass, more preferably 80 to 99% by mass, and particularly preferably 90 to 99% by mass.

  As the conductive material, a material conventionally used as a conductive material for a lithium ion secondary battery can be used without any particular limitation. Specific examples thereof include, for example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, and carbon fiber. Conductive fibers such as metal fibers; metal powders such as aluminum; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; And carbonized carbon. These may be used alone or in combination of two or more.

  The blending ratio of the conductive material is 1 to 50% by mass, further 1 to 30% by mass, particularly 2 to 15% by mass with respect to the amount of the positive electrode active material contained in the entire positive electrode active material layer. A range is preferable.

  As the binder for the positive electrode, a material conventionally used as a binder for the positive electrode of a lithium ion secondary battery can be used without any particular limitation. Specific examples thereof include, for example, polyethylene (thermal decomposition temperature: about 471 ° C.), polypropylene (about 445 ° C.), polyvinyl acetate (about 320 ° C.), polymethyl methacrylate (about 330 ° C.), polytetrafluoroethylene. Fluorine resin such as (PTFE) (approximately 549 ° C.). Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. These may be used alone or in combination of two or more.

  The blending ratio of the binder is preferably 1 to 10% by mass, more preferably 1 to 7% by mass, and particularly preferably 1 to 5% by mass with respect to the whole positive electrode active material layer.

  Moreover, as a thickener used as needed, carboxymethylcellulose (CMC), polyethylene oxide, soluble modified acrylonitrile rubbers (“BM-720H (trade name)” manufactured by Nippon Zeon Co., Ltd.) and the like can be mentioned. .

  Specific examples of the solvent include N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, dimethylformamide, ethanol, methanol, butanol, isopropyl alcohol, isobutyl alcohol, deionized water, and the like. These may be used alone or in combination of two or more.

  The positive electrode mixture paste is prepared by mixing the above components and then kneading them by a known kneading method.

  On the other hand, the negative electrode active material layer is obtained, for example, by mixing an additive such as a negative electrode active material, a binder, a conductive material used as necessary, a thickener, and the like at a predetermined mixing ratio in the presence of a solvent. The negative electrode mixture paste is applied to both surfaces of the current collector sheet to form a coating film, and the coating film is formed by heating and drying and rolling.

  As the negative electrode active material, a material conventionally used as a negative electrode active material of a lithium ion secondary battery is used without particular limitation. Specific examples thereof include, for example, graphite materials such as natural graphite (such as flake graphite) and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon. Carbon materials such as fibers; metal lithium, lithium alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, organic polymer compounds, and the like. These may be used alone or in combination of two or more. Among these materials, graphite-based materials, particularly graphite-based materials having an amorphous layer formed on the surface are preferable. In such a graphite-based material having an amorphous layer formed on its surface, lithium is inserted into the crystal not only from the basal plane but also from various directions. Therefore, since the solid-liquid interface reaction is fast, the reaction is governed by diffusion. Therefore, by forming the void v to improve the periphery of the liquid and increase the diffusion rate, the effect is more remarkably exhibited.

  The volume average particle diameter of the negative electrode active material is not particularly limited, but is preferably 0.1 to 50 μm, more preferably 0.5 to 30 μm.

  The mixing ratio of the negative electrode active material is preferably 50 to 99.5% by mass, more preferably 80 to 99% by mass, and particularly preferably 90 to 99% by mass with respect to the entire negative electrode active material layer. .

  As a specific example of the negative electrode binder, a material conventionally used as a negative electrode binder of a lithium ion secondary battery can be used without any particular limitation. Specific examples thereof include polyethylene (thermal decomposition temperature: about 471 ° C.), polypropylene (about 445 ° C.), polytetrafluoroethylene (about 549 ° C.), polyvinylidene fluoride (about 375 ° C.), modified styrene- Examples thereof include butadiene rubber (about 360 ° C.).

  The blending ratio of the negative electrode binder is preferably 1 to 10% by mass, more preferably 1 to 7% by mass, and particularly preferably 1 to 5% by mass with respect to the entire negative electrode active material layer. .

  As the conductive material used as necessary, the same conductive agent used in the positive electrode can be used without any particular limitation. The blending ratio of the conductive material is 0 to 25% by mass, more preferably 0 to 10% by mass, and particularly 0 to 5% by mass with respect to the amount of the negative electrode active material contained in the entire negative electrode active material layer. A range is preferable.

  Similarly to the positive electrode mixture paste, the negative electrode mixture paste is prepared by mixing the above-mentioned components and then kneading by a known kneading method.

  The positive electrode mixture layer paste or the negative electrode mixture layer paste applied to the surface of the current collector sheet 1 is applied and then dried. Examples of the drying conditions include 20 to 250 ° C., preferably 80 to 150 ° C., for 1 minute to 8 hours, preferably 3 minutes to 1 hour. At this time, if the thermal decomposition temperature or vaporization temperature of the pore-forming material f is lower than the drying temperature, the pore-forming material f is decomposed or vaporized by this drying step, and the outer wall of the through-hole h is contoured. A void v is formed.

  And the coating film formed by applying and drying in this way is usually further rolled. The active material layers 2a and 2b obtained can be flattened by rolling. The apparatus and conditions used for rolling are not particularly limited, and a conventionally known roll press or the like can be appropriately used. The rolling may be performed before or after removing the pore-forming material f, but from the viewpoint of suppressing the active material layer from being embedded in the through-holes h during rolling, It is preferable to block h with a pore-forming material f and remove the pore-forming material f after rolling. By processing in this order, the gap v can be formed reliably.

  After rolling, heat treatment is performed at a temperature equal to or higher than the thermal decomposition temperature or vaporization temperature of the pore forming material f and lower than the thermal decomposition temperature of the binder, and only the pore forming material is thermally decomposed or gasified. The pore forming material f can be removed. The heating conditions depend on the type of pore-forming material and binder, but for example, when a pore-forming material having a decomposition temperature or boiling point of less than 250 ° C. and a binder having a decomposition temperature of 250 ° C. or higher are used. The conditions of heating in the range of 100 to 250 ° C., further in the range of 150 to 200 ° C. for 10 minutes to 1 hour are preferably used. More specifically, for example, when a modified styrene-butadiene rubber is used as a binder and 2-amino-2methyl 1,3-propanediol is used as a pore-forming material, at a temperature of 170 to 200 ° C., Conditions for heating for 10 minutes to 1 hour are preferably used. By drying under such heating conditions, only the pore-forming material f can be selectively thermally decomposed and removed while leaving the binder.

  Further, when a water-soluble material is used as the pore-forming material f, the pore-forming material is obtained by immersing in a solvent after applying the mixture layer and drying, and before or after the rolling treatment. f can be dissolved and removed.

  The thickness of the active material layer after rolling thus formed is preferably 10 to 100 μm, and more preferably about 20 to 70 μm.

  The electrode 10 for lithium ion secondary batteries is obtained by the manufacturing method as described above.

  Next, a configuration of the lithium ion secondary battery 100 using the above-described lithium ion secondary battery electrode 10 as a positive electrode or a negative electrode will be described. In the lithium ion secondary battery 100 of the present embodiment, the positive electrode plate 10a and the negative electrode plate 10b having the gap v obtained by the above-described manufacturing method of the positive electrode 65 and the negative electrode 66 are used. However, the electrode plate described above may be used only for at least one of the positive electrode 65 and the negative electrode 66, and a conventionally known electrode plate may be used for the other one.

  FIG. 4 shows a partial cross-sectional view of the cylindrical lithium ion secondary battery 100 of the present embodiment. A lithium ion secondary battery 100 shown in FIG. 4 includes an electrode group and a non-aqueous electrolyte (not shown) enclosed in a battery case 61. The electrode group is formed by winding a positive electrode 65 and a negative electrode 66 through a separator 67. A positive electrode lead 65 a is drawn from the positive electrode 65 and connected to the sealing plate 62, and a negative electrode lead 66 a is drawn from the negative electrode 66 and connected to the bottom of the battery case 61. Insulating rings 68a and 68b are provided above and below the electrode group, respectively. Then, a non-aqueous electrolyte is injected, and the battery case 61 is sealed by the sealing plate 62 through the gasket 63.

  As the battery case, for example, an aluminum case, an iron case whose inner surface is nickel-plated, a case made of an aluminum laminate film, or the like can be used. The shape of the battery case may be any shape such as a cylindrical shape or a square shape. For the cross section of the electrode plate group, a shape such as a circle or an ellipse is selected according to the shape of the battery case.

  As a material constituting the positive electrode lead, the negative electrode lead, and the like, aluminum that has been conventionally used as a material for the positive electrode lead, nickel, aluminum, and the like that have been used as a material for the negative electrode lead are not particularly limited.

  As the non-aqueous electrolyte, a non-aqueous solvent in which a lithium salt is dissolved is preferably used. Specific examples of the non-aqueous solvent include, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC); dimethyl carbonate (DMC), diethyl carbonate ( DEC), ethyl carbonate (EMC), chain carbonates such as dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ Lactones such as valerolactone; chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME); tetrahydrofuran, 2-methyltetrahydrofuran, etc. Cyclic ethers; dimethylsulfoxy 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl -2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, N-methyl-2-pyrrolidone and the like. These may be used alone or in combination of two or more.

Specific examples of the lithium salt dissolved in the non-aqueous solvent include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lithium lower aliphatic carboxylate, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, lithium imide salt and the like. These may be used alone or in combination of two or more. The amount of lithium salt dissolved in the non-aqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / L, and more preferably 0.5 to 1.5 mol / L.

  In addition, various additives may be further added to the non-aqueous electrolyte for the purpose of improving the charge / discharge characteristics of the battery. Specific examples of such additives include, for example, vinylene carbonate, vinyl ethylene carbonate, phosphazene and fluorobenzene, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphate triamide, nitrobenzene derivatives, Examples include crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ethers, and the like. These additives are preferably blended in an amount of about 0.5 to 10% by mass of the non-aqueous electrolyte.

  As the separator 67, an insulating microporous sheet conventionally used in lithium ion secondary batteries is used without particular limitation. The microporous thin film preferably has a function of closing the pores at a certain temperature or higher and increasing the resistance. As the material of the microporous thin film, polyolefin such as polypropylene and polyethylene having excellent organic solvent resistance and hydrophobicity is preferably used. In addition, a sheet made of glass fiber or the like, a nonwoven fabric, a woven fabric, or the like is also used.

  As the shape of the battery, any shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a flat shape, and a square shape can be applied. When the shape of the battery is a coin type or a button type, the positive electrode mixture or the negative electrode mixture is mainly compressed into a pellet shape and used. The thickness and diameter of the pellet may be determined depending on the size of the battery. In addition, the wound body of the electrode in the present invention does not necessarily have a true cylindrical shape, and may have a prismatic shape such as a long cylindrical shape or a rectangular shape whose cross section is an ellipse.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, the scope of the present invention is not limited at all by the following examples.

(Example 1: Production of negative electrode plate A)
As a pore-forming material, 900 g of 2-amino-2-methyl 1,3-propanediol (average particle size 20 μm, boiling point 152 ° C.), 360 g of Kureha Co., Ltd. # 1320 (NMP solution containing 12% by mass of PVDF), and A pore forming material paste was prepared by stirring with an appropriate amount of N-methyl-2-pyrrolidone (NMP) in a double-arm kneader. The obtained pore-forming material paste was applied to one side of a 12 μm-thick open copper foil (opening ratio 45%, through-hole diameter about 5 μm, long diameter / short diameter = 1) to fill the opening and dried. .

  On the other hand, artificial graphite (average particle size 15 μm), 3 kg, 200 g of BM-400B (modified styrene-butadiene rubber dispersion having a solid content of 40 wt%) manufactured by Nippon Zeon Co., Ltd., 50 g of carboxymethylcellulose (CMC), and A negative electrode mixture paste was prepared by stirring with an appropriate amount of water in a double-arm kneader.

  And after apply | coating the negative mix paste on both surfaces of the apertured copper foil with which the pore formation material was filled, it dried at 110 degreeC and rolled so that the total thickness might be set to 160 micrometers. Finally, this was heated to 170 ° C. to volatilize and remove the pore forming material filled in the opening of the open copper foil. Thereby, the electrode plate in which the space | gap which made the outer wall of a through-hole contour is formed was obtained. And the negative electrode plate A was obtained by cut | disconnecting the obtained electrode plate to the width | variety which can be inserted in the battery case of cylindrical type 18650.

(Example 2: Production of negative electrode plate B)
Stirring in a double-arm kneader with 1600 g of bis (2,4-pentanedionato) zinc monohydrate (average particle size 20 μm), 50 g of carboxymethylcellulose (CMC) and an appropriate amount of water as a pore-forming material A pore forming material paste was prepared. The pore forming material paste was applied to one side of a 12 μm-thick open copper foil (opening ratio: 45%, through hole diameter: about 5 μm, long diameter / short diameter = 1) to fill the opening and dried.

  And after apply | coating the negative mix paste similar to what was obtained in Example 1 to both surfaces of the apertured copper foil with which the pore formation material was filled, it dried at 110 degreeC and also the total thickness was set to 160 micrometers. Rolled as follows. Finally, this was immersed in 1 L of NMP solvent at 25 ° C. for 1 minute to dissolve and remove the pore forming material. Thereby, the electrode plate in which the space | gap which made the outer wall of a through-hole contour is formed was obtained. And the negative electrode plate B was obtained by cut | disconnecting the obtained electrode plate to the width | variety which can be inserted in the battery case of cylindrical type 18650.

(Example 3: Production of negative electrode plate C)
Example 1 except that piperazine (boiling point: 145 ° C.) was used instead of 2-amino-2-methyl 1,3-propanediol as the pore-forming material, and heating was performed at 190 ° C. instead of heating at 170 ° C. after rolling. A negative electrode plate C was obtained in the same manner as in the preparation of the negative electrode plate A.

(Example 4: Production of negative electrode plate D)
As a pore forming material, m-anisic acid (boiling point: 172 ° C.) was used instead of 2-amino-2-methyl 1,3-propanediol, and heated at 190 ° C. instead of heating at 170 ° C. after rolling. A negative electrode plate D was obtained in the same manner as in the preparation of the negative electrode plate A of Example 1.

(Example 5: Production of negative electrode plate E)
Example except that orcinol (boiling point: 147 ° C.) was used instead of 2-amino-2-methyl 1,3-propanediol as a pore-forming material, and heated at 190 ° C. instead of heating at 170 ° C. after rolling. The negative electrode plate E was obtained in the same manner as in the preparation of the negative electrode plate A in FIG.

(Example 6: Production of negative electrode plate F)
As the pore forming material, ethylmalonic acid (pyrolysis temperature of about 160 ° C) was used instead of 2-amino-2-methyl-1,3-propanediol, and it was heated at 190 ° C instead of heating at 170 ° C after rolling. Produced the negative electrode plate F in the same manner as in the preparation of the negative electrode plate A of Example 1.

(Example 7: Production of negative electrode plate G)
Instead of 2-amino-2-methyl 1,3-propanediol as a pore-forming material, 5-amino-1 naphthol (pyrolysis temperature of about 170 ° C.) was used, and at 190 ° C. instead of heating at 170 ° C. after rolling. A negative electrode plate G was obtained in the same manner as in the preparation of the negative electrode plate A of Example 1, except that heating was performed.

(Example 8: Production of negative electrode plate H)
As a pore-forming material, 2,3-dihydroxybenzaldehyde (boiling point 135 ° C.) was used instead of 2-amino-2-methyl 1,3-propanediol, and heated at 190 ° C. instead of heating at 170 ° C. after rolling Produced a negative electrode plate H in the same manner as in the preparation of the negative electrode plate A of Example 1.

(Example 9: Production of positive electrode plate α)
As a pore-forming material, N-phenylmaleide (average particle size 20 μm, boiling point 135 ° C.) 900 g, carboxymethyl cellulose (CMC) 50 g, and an appropriate amount of water were stirred in a double-arm kneader to prepare a pore-forming material paste. did. The pore-forming material paste was applied to one side of a 12 μm-thick open aluminum foil (opening ratio: 45%, through-hole diameter: about 5 μm, long diameter / short diameter = 1) to fill the opening and dried.

  On the other hand, positive electrode mixture paste was prepared by stirring 3 kg of lithium cobaltate (average particle size 10 μm) and Kureha Co., Ltd. # 1320 1200 g together with an appropriate amount of NMP in a double-arm kneader. .

  And after apply | coating the positive mix paste on both surfaces of the apertured aluminum foil with which the pore formation material was filled, it dried at 110 degreeC and rolled so that the total thickness might be set to 160 micrometers. Finally, this was heated to 150 ° C. to volatilize and remove the pore-forming material filled in the openings of the apertured aluminum foil. Thereby, the electrode plate in which the space | gap which made the outer wall of a through-hole contour is formed was obtained. The obtained electrode plate was slit to a width that can be inserted into a cylindrical 18650 battery case to obtain a positive electrode plate α.

(Example 10: Production of positive electrode plate β)
As a pore-forming material, 1200 g of magnesium sulfate (average particle diameter 20 μm), # 1320 360 g manufactured by Kureha Co., Ltd., and an appropriate amount of NMP were stirred in a double-arm kneader to prepare a pore-forming material paste. The pore-forming material paste was applied to one side of a 12 μm-thick open aluminum foil (opening ratio: 45%, through-hole diameter: about 5 μm, long diameter / short diameter = 1) to fill the opening and dried.

  And after apply | coating the positive mix paste similar to what was obtained in Example 9 to both surfaces of the apertured copper foil with which the pore formation material was filled, it dried at 110 degreeC and also the total thickness was set to 160 micrometers. Rolled as follows. Finally, this was immersed in 1 L of NMP solvent at 25 ° C. for 1 minute to dissolve and remove the pore forming material. Thereby, the electrode plate in which the space | gap which made the outer wall of a through-hole contour is formed was obtained. And the positive electrode plate (beta) was obtained by cut | disconnecting the obtained electrode plate to the width | variety which can be inserted in the battery case of cylindrical type 18650.

(Example 11: Production of positive electrode plate γ)
Preparation of positive electrode plate α of Example 9 except that benzylic acid (boiling point: 180 ° C.) was used as the pore forming material instead of N phenylmale, and heating was performed at 190 ° C. instead of heating at 150 ° C. after rolling. In the same manner as above, a positive electrode plate γ was obtained.

(Example 12: Production of positive electrode plate ε)
A positive electrode plate ε was obtained in the same manner as in the preparation of the positive electrode plate β of Example 10, except that lithium acetate was used instead of magnesium sulfate as the pore forming material.

(Example 13: Production of positive electrode plate δ)
A positive electrode plate δ was obtained in the same manner as in the preparation of the positive electrode plate β of Example 10, except that ammonium phosphate was used instead of magnesium sulfate as the pore forming material.

(Comparative Example 1: Production of negative electrode plate I)
A negative electrode mixture paste similar to that in Example 1 was prepared.

  And after apply | coating the negative mix paste on both surfaces of the 12-micrometer-thick copper foil without opening, it dried at 110 degreeC, and also rolled so that the total thickness might be 160 micrometers. And the negative electrode plate I was obtained by cut | disconnecting the obtained electrode plate to the width | variety which can be inserted in the battery case of cylindrical type 18650.

(Comparative Example 2: Production of positive electrode plate ν)
A positive electrode mixture paste similar to that in Example 9 was prepared.

  And after apply | coating the positive mix paste on both surfaces of the 12-micrometer-thick aluminum foil without opening, it dried at 110 degreeC, and also rolled so that the total thickness might be 160 micrometers. Then, the obtained electrode plate was slit to a width that can be inserted into a cylindrical 18650 battery case to obtain a positive electrode plate ν.

(Examples 14 to 30 and Comparative Example 3: Production of Lithium Ion Secondary Battery)
(I) Preparation of electrolyte solution Lithium hexafluorophosphate (LiPF6) was dissolved at a concentration of 1 mol / L in a mixed solvent containing ethylene carbonate and methylethyl carbonate in a volume ratio of 1: 3, and non-aqueous electrolysis was performed. A liquid was prepared.
(II) Battery assembly In the combinations shown in Tables 1 to 3, the negative plates A to I obtained in Examples 1 to 8 and Comparative Example 1 as negative plates and Examples 9 to 13 as positive plates, respectively. And the battery was assembled by the following method using the positive electrode plates α to ν obtained in Comparative Example 2.

  The positive electrode plate and the negative electrode plate were wound through a separator to form a spiral electrode plate group. As the separator, a composite film of polyethylene and polypropylene (2300 manufactured by Celgard Co., Ltd., thickness: 25 μm) was used.

  A positive electrode lead and a negative electrode lead made of nickel were respectively attached to the positive electrode plate and the negative electrode plate. An upper insulating plate was disposed on the upper surface of the electrode plate group, and a lower insulating plate was disposed on the lower surface. The electrode plate group was inserted into the battery case, and 5 g of non-aqueous electrolyte was injected into the battery case. Then, the sealing board which arranged the gasket around and the positive electrode lead were made to conduct, and the opening of the battery case was sealed with the sealing board. Thus, a cylindrical 18650 lithium ion secondary battery (nominal capacity 2 Ah) as shown in FIG. 4 was completed.

(III) Battery evaluation About each obtained lithium ion secondary battery, the battery characteristic was evaluated by the following method.
[Battery evaluation]
The obtained lithium ion secondary battery was conditioned and discharged twice, and then stored in a 40 ° C. environment for 2 days. Thereafter, the input / output characteristics were evaluated under the following conditions. The design capacity of the battery is 1 CmAh. The ratio of the discharge capacity at −10 ° C. to the discharge capacity at 25 ° C. was defined as the low temperature output characteristic, and the ratio of the charge capacity at −10 ° C. relative to the charge capacity at 25 ° C. was defined as the low temperature input characteristic.
<output>
(1) Constant current charging (25 ° C.): 1 CmA (end voltage 4.2 V)
(2) Constant voltage charging (25 ° C.): 4.2 V (end current 0.05 CmA)
(3) Charging rest (25 ° C): 30 minutes (4) Output (25 ° C, -10 ° C): 30 CmA (end voltage 3V)
<input>
(1) Constant current discharge (25 ° C.): 1 CmA (end voltage 3.0 V)
(2) Discharge rest (25 ° C.): 30 minutes (3) Input (25 ° C., −10 ° C.): 30 CmA (end voltage 4.2 V)
The results are shown in Tables 1 to 3 below.

  From the results of Tables 1 to 3, the batteries of Examples 14 to 30 using the positive electrode and the negative electrode obtained by Examples 1 to 13 and having voids formed by the openings of the current collectors are all output characteristics at low temperatures. It can be seen that the input characteristics are high. This is because the unfilled voids greatly increased the absolute amount of lithium ions in the vicinity of the current collector, so that a high lithium ion diffusion rate could be maintained even at low temperatures. It is believed that there is.

  On the other hand, the battery of Comparative Example 3 using the negative electrode plate I obtained in Comparative Example 1 and the positive electrode plate ν obtained in Comparative Example 2 had poor input / output characteristics at low temperatures. This is presumably because the liquid solution around the active material layer becomes difficult at low temperatures.

DESCRIPTION OF SYMBOLS 1 ... Current collector sheet, 1a ... Current collector sheet, 2a, 2b ... Active material layer, 2a ', 2b' ... Coating film, 3 ... Active material, 4 ... Binder, 5 ... Conductive material, 10 ... Lithium Electrode for ion secondary battery, 10a ... positive electrode plate, 10b ... negative electrode plate, 61 ... battery case, 62 ... sealing plate, 63 ... gasket, 65 ... positive electrode, 65a ... positive electrode lead, 66 ... negative electrode, 66a ... negative electrode lead, 67 ... Separator, 68a ... Upper insulating plate, 68a ... Insulating ring, 68b ... Lower insulating plate, 100 ... Lithium ion secondary battery, 101 ... Electrode plate group

Claims (12)

A method for producing an electrode for a lithium ion secondary battery, comprising:
A filling step of filling the large number of through holes of the current collector sheet in which the large number of through holes are formed;
After the filling step, on the surface of the current collector sheet, a coating paste is formed by applying a mixture paste containing an electrode active material, a binder, and a dispersion medium of the electrode active material, and the coating film An active material layer forming step of heating
The method for producing an electrode for a lithium ion secondary battery, wherein the pore forming material is removed after the coating film is formed.   The method for producing an electrode for a lithium ion secondary battery according to claim 1, wherein the pore forming material is made of a material that is decomposed or removed by heat treatment after the coating film is formed.   The manufacturing method of the electrode for lithium ion secondary batteries of Claim 2 whose decomposition temperature or boiling point of the said pore formation material is lower than the decomposition temperature of the said binder. The pore-forming material is an organic material having a decomposition temperature or boiling point of less than 250 ° C .;
The binder is an organic material having a decomposition temperature of 250 ° C. or higher;
The method for producing an electrode for a lithium ion secondary battery according to claim 3, wherein a heating temperature in the heat treatment is in a range of 100 to 250 ° C.   The method for producing an electrode for a lithium ion secondary battery according to claim 4, wherein the organic material having a boiling point of less than 250 ° C is 2-amino-2-methyl 1,3-propanediol. The pore-forming material is a material that dissolves in a predetermined solvent,
The method for producing an electrode for a lithium ion secondary battery according to claim 1, further comprising a dissolution removal step for dissolving and removing the pore forming material in the solvent after the formation of the coating film.   The method for producing an electrode for a lithium ion secondary battery according to claim 6, wherein the pore forming material is an inorganic acid salt or an organometallic complex hydrate.   The method for producing an electrode for a lithium ion secondary battery according to claim 6, wherein the pore forming material is bis (2,4-pentanedionato) zinc monohydrate. An electrode for a lithium ion secondary battery,
A current collector sheet in which a large number of through holes are formed, and an electrode active material layer containing an electrode active material formed on the surface of the current collector sheet,
An electrode for a lithium ion secondary battery, characterized by having an outer wall of the plurality of through holes as an outline and a void into which the electrode active material layer does not enter. A negative electrode plate for a lithium ion secondary battery,
The electrode for a lithium ion secondary battery according to claim 9, wherein the electrode active material is a negative electrode active material made of a graphite-based carbon material.   11. The lithium ion secondary battery according to claim 9, wherein the void is a void having an outer wall of the through hole as an outline and further having an upper bottom and a lower bottom formed so as to surround each active material layer. electrode. A positive electrode formed by forming a positive electrode active material layer on the surface of the positive electrode current collector, a negative electrode formed by forming a negative electrode active material layer on the surface of the negative electrode current collector, an insulating separator disposed between the positive electrode and the negative electrode, and It has a non-aqueous electrolyte for moving lithium ions,
A lithium ion secondary battery using the electrode for a lithium ion secondary battery according to any one of claims 9 to 11 as at least one of the positive electrode and the negative electrode.

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