JP2014165156A - Nonaqueous electrolyte secondary battery and manufacturing method of negative electrode plate of the nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with a superior high input performance.SOLUTION: The manufacturing method of the negative electrode plate of the nonaqueous electrolyte secondary battery includes the steps of: preparing a negative electrode mixture coating 7 which includes at least graphite powder and binder mixed together with a solvent in a range from 55 Wt% to 85 Wt% at a solid weight ratio; forming a wet state negative electrode mixture layer 2 by applying the negative electrode mixture coating 7 to at least one surface of a negative electrode collector 1; and allowing the solvent to evaporate from the wet state negative electrode mixture layer 2 to dry the same.

Description

  The present invention relates to a method for producing a non-aqueous electrolyte secondary battery, in particular, a high-power lithium ion secondary battery and a negative electrode plate for the non-aqueous electrolyte secondary battery.

In recent years, lithium-ion secondary batteries have been put into practical use as power sources for mobile electronic devices such as mobile phones, notebook computers and mobile phones as secondary batteries with high operating voltage and high energy density, and have achieved rapid growth. Production volume continues to increase as a battery system that leads small secondary batteries.

  Recently, not only these small-sized consumer applications, but also technology development for high-capacity secondary ponds for power storage and electric vehicles has been accelerated. In particular, in hybrid electric vehicles (HEV), vehicles equipped with lithium ion secondary batteries have already been marketed on a mass production basis. In addition, although fuel cell vehicles are expected to spread in the future, lithium ion secondary batteries are promising as secondary batteries capable of high input / output for assisting fuel cells.

Lithium ion secondary batteries used for such vehicle applications differ greatly from those for small consumer applications in terms of their application and required performance, and it is necessary to instantaneously perform power assist or regeneration of the engine with a limited capacity. A fairly high output is required. Accordingly, priority is given to higher input / output density rather than higher energy density for the battery, and it is necessary to minimize the internal resistance of the battery as much as possible. For this purpose, not only the development and selection of active materials and electrolytes, but also a significant increase in input / output due to the reduction of battery structural component resistance, such as a review of the current collection structure of the electrodes, and the increase of the electrode reaction area due to the thin and long electrodes It is planned.

  When designing a non-aqueous electrolyte secondary battery with high input / output specifications, as described above, reviewing the current collecting structure and reducing the resistance of structural components are important factors. In addition, improvement or selection of the active material is an important factor. In particular, in the low temperature environment, the latter factor greatly affects the high input / output characteristics of the battery. Among these, the ability of the carbon material used for the negative electrode to occlude and release lithium is important. Increasing this capability greatly contributes to the achievement of higher battery input / output.

  Conventionally, a carbon material capable of occluding and releasing lithium ions is generally used for the negative electrode of a lithium ion secondary battery. Among these, graphite materials are dominant from the viewpoint of realizing a flat discharge potential and a high capacity density. Various improvements have also been attempted in the graphite material. For example, in Patent Document 1, two types of graphite materials having different physical properties are mixed and used to increase the packing density of the graphite material in the negative electrode mixture layer. .

JP 2010-92649 A

  However, in the lithium ion secondary battery using the negative electrode plate in which the packing density of the graphite material of the negative electrode mixture layer is increased by mixing the two kinds of graphite materials having different physical properties, the capacity density required for small consumer applications is low. It is possible to improve, but the amount of electrolyte and lithium ions that can be held in the negative electrode mixture layer is reduced, and the speed at which lithium ions are transferred between the graphite powder and the electrolyte decreases. There is a problem that the required high output power characteristics cannot be improved.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a non-aqueous electrolyte secondary battery excellent in input / output characteristics and a method for manufacturing a negative electrode plate of the non-aqueous electrolyte secondary battery. .

The first aspect of the present invention is
A positive electrode plate provided with a positive electrode mixture layer on at least one surface of the positive electrode current collector; a negative electrode plate provided with a negative electrode mixture layer on at least one surface of the negative electrode current collector; and the positive electrode plate; A non-aqueous electrolyte secondary battery in which a separator provided between the negative electrode plates is housed in a case together with a non-aqueous electrolyte,
The negative electrode mixture layer includes at least graphite powder as a negative electrode active material, and a binder for fixing the graphite powder to the surface of the negative electrode current collector,
A non-aqueous electrolyte secondary battery, wherein the oil absorption of the graphite powder is less than 100 cm ^3/100 g from 50 cm ^3/100 g or more.

The second aspect of the present invention
In the negative electrode mixture layer, the density A of the first region having a thickness of ½ of the thickness of the negative electrode mixture layer on the surface side of the negative electrode current collector, and the negative electrode of the thickness of the negative electrode mixture layer The ratio A / B with the density B of the second region having a thickness of 1/2 on the surface side of the mixture layer is 0.5 or more and 2.0 or less. It is a non-aqueous electrolyte secondary battery.

The third aspect of the present invention
In the negative electrode mixture layer, the amount C of the binder contained in the first region having a thickness of ½ of the thickness of the negative electrode mixture layer on the surface side of the negative electrode current collector, and the negative electrode mixture layer Of these, the ratio C / D to the amount D of the binder contained in the second region having a thickness of ½ on the surface side of the negative electrode mixture layer is 0.67 or more and 1.5 or less. The nonaqueous electrolyte secondary battery according to the first aspect of the present invention.

The fourth aspect of the present invention is
The graphite powder according to any one of the first to third aspects of the present invention, wherein the graphite powder contains 90% or more of those having a circularity of 0.5 or more.

The fifth aspect of the present invention provides
The non-aqueous electrolyte secondary battery according to any one of the first to fourth aspects, wherein the graphite powder contains 90% or more of particles having an average particle diameter of 3 μm to 30 μm.

The sixth aspect of the present invention provides
The nonaqueous electrolyte secondary battery according to any one of the first to fifth aspects, wherein the density of the negative electrode mixture layer is 0.8 g / cm ³ or more and 1.6 g / cm ³ or less. It is.

The seventh aspect of the present invention
A method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to any one of the first to sixth aspects,
Producing a negative electrode mixture paint in which at least the graphite powder and the binder are mixed together with a solvent in a solid weight ratio of 55 Wt% to 85 Wt%;
Applying the negative electrode mixture paint to at least one surface of the negative electrode current collector to provide the wet negative electrode mixture layer;
And a step of evaporating and drying the solvent from the wet negative electrode mixture layer. A method for producing a negative electrode plate of a non-aqueous electrolyte secondary battery.

In addition, the eighth aspect of the present invention
As a means for applying the negative electrode mixture paint, at least one of a first roll supporting the negative electrode current collector and a second roll disposed to face the first roll through the negative electrode current collector It is a manufacturing method of the negative electrode plate of the nonaqueous electrolyte secondary battery according to the seventh aspect of the present invention, wherein two rolls are used.

The ninth aspect of the present invention provides
The first roll and the second roll are both rotated in the same direction as the traveling direction of the negative electrode current collector, The nonaqueous electrolyte secondary battery according to the eighth aspect of the present invention, It is a manufacturing method of a negative electrode plate.

The tenth aspect of the present invention is
The circumferential speed of the first roll is the same as the traveling speed of the negative electrode current collector, and the circumferential speed of the second roll is the circumferential speed of the first roll and the traveling speed of the negative electrode current collector. It is a manufacturing method of the negative electrode plate of the nonaqueous electrolyte secondary battery according to the ninth aspect of the present invention, which is different.

The eleventh aspect of the present invention is
The non-aqueous electrolyte secondary battery according to the tenth aspect of the present invention is characterized in that a peripheral speed of the second roll is smaller than a peripheral speed of the first roll and a traveling speed of the negative electrode current collector. It is a manufacturing method of a negative electrode plate.

The twelfth aspect of the present invention is
The nonaqueous electrolysis according to any one of the eighth to eleventh aspects, wherein the negative electrode mixture layer is not pressed after the step of volatilizing and drying the solvent from the wet negative electrode mixture layer. It is a manufacturing method of the negative electrode plate of a liquid secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the negative electrode plate of the nonaqueous electrolyte secondary battery excellent in the input / output characteristic and a nonaqueous electrolyte secondary battery can be provided.

Schematic cross-sectional view showing the structure of a negative electrode plate according to an embodiment of the present invention. (A)-(d): The figure which shows the example of calculation of the circularity of particle | grains Schematic cross-sectional view showing a coating apparatus according to an embodiment of the present invention. Cross-sectional schematic diagram showing a coating apparatus in another embodiment of the present invention

  The nonaqueous electrolyte secondary battery according to one embodiment of the present invention will be described in detail below.

  The non-aqueous electrolyte secondary battery of the present invention includes an electrode body composed of a positive electrode plate, a negative electrode plate, and a separator, a non-aqueous electrolyte solution, and a case for housing them.

  In the present invention, the positive electrode plate, the separator, the nonaqueous electrolytic solution, and the case are not particularly limited, but for example, those described below can be used.

  The positive electrode plate includes a positive electrode current collector made of a conductive film and a positive electrode mixture layer provided on at least one surface of the positive electrode current collector.

  The positive electrode current collector is, for example, a metal foil or expanded metal such as aluminum, aluminum alloy, titanium, copper, or nickel, a laminate obtained by depositing metal on the surface of a polymer film such as PET, or a conductive polymer film. Although the thing similar to can be used, it is not specifically limited.

  The positive electrode mixture layer includes at least a positive electrode active material, a conductive additive, and a binder.

  The positive electrode active material is, for example, lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide (these are usually represented by LiNiO2, LiCoO2, LiMn2O4, the ratio of Li to Ni, the ratio of Li to Co, Lithium-containing composite metal oxides such as the ratio of Li to Mn often deviates from the stoichiometric composition can be used. These can be used alone, as a mixture of two or more kinds, or as a solid solution thereof, but is not particularly limited.

  For example, carbon black such as ketjen black and acetylene black, fiber-like carbon, and flake graphite can be used as the conductive aid, but it is not particularly limited.

  As the binder, for example, a thermoplastic resin, a polymer having rubber elasticity, and a polysaccharide alone or a mixture thereof can be used. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, copolymer with hexafluoropropene, polyethylene, polypropylene, ethylene-propylene-diene copolymer, styrene-butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, polyvinyl Cellulose resins such as pyrrolidone, polyester resin, acrylic resin, phenol resin, epoxy, polyvinyl alcohol, hydroxypropyl cellulose, and carboxymethyl cellulose can be used, but are not particularly limited.

  Further, the separator insulates the positive electrode plate from the negative electrode plate, and allows lithium ions to move inside (in the material constituting the separator or in the pores formed in the separator), and a lithium ion battery The material is not particularly limited as long as it is a stable material when used, for example, an insulating polymer porous film made of polyethylene or polypropylene, or an insulating nonwoven fabric made of cellulose. The separator is made of inorganic particles such as alumina, silica, magnesium oxide, titanium oxide, zirconia, silicon carbide, silicon nitride, polyethylene, polypropylene, polystyrene, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, It can also be formed by coating, drying, and rolling organic particles such as polyimide, a mixture of the inorganic particles and organic particles, a binder, a solvent, various additives, and the like. Although the thickness of a separator is not specifically limited, For example, it is 10-50 micrometers.

  The nonaqueous electrolytic solution is composed of a nonaqueous solvent and an electrolyte.

  The non-aqueous solvent is not particularly limited. For example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3- Dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone and the like. These nonaqueous solvents may be used alone or in combination of two or more. It is also preferable to use vinylene carbonate (VC), cyclohexylbenzene (CHB), or a modified product thereof in order to form a good film on the positive electrode and the negative electrode, or to ensure stability during overcharge.

  The electrolyte is not particularly limited. For example, lithium perchlorate (LiClO 4), lithium hexafluorophosphate (LiPF 6), lithium borofluoride (LiBF 4), lithium hexafluoroarsenide (LiAsF 6), lithium trifluorometasulfonate Lithium salts such as (LiCF3SO3) and bistrifluoromethylsulfonylimide lithium [LiN (CF3SO2) 2].

  For example, a case in which a metal such as aluminum, iron, or stainless steel is formed, or a film in which a metal layer such as aluminum and a polymer layer are laminated can be used, but the case is not particularly limited.

  Next, a characteristic negative electrode plate and a manufacturing method thereof in the present invention will be described in detail below with reference to the drawings.

  The negative electrode plate is composed of a negative electrode current collector 1 made of a conductive film as shown in FIG. 1 and a negative electrode mixture layer 2 provided on at least one surface of the negative electrode current collector 1.

  The negative electrode current collector 1 is, for example, a metal foil or expanded metal such as copper, aluminum, an aluminum alloy, titanium, or nickel, a laminate in which metal is deposited on the surface of a polymer film such as PET, a conductive polymer film, or the like. Although the same thing as the past can be used, it is not specifically limited.

  The negative electrode mixture layer 2 includes at least a negative electrode active material 3 and a binder 4 for immobilizing the negative electrode active material 3 on the surface of the negative electrode current collector 1.

  The binder 4 can be the same as that of the positive electrode plate. For example, a thermoplastic resin, a polymer having rubber elasticity, and a polysaccharide can be used singly or as a mixture. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, copolymer with hexafluoropropene, polyethylene, polypropylene, ethylene-propylene-diene copolymer, styrene-butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, polyvinyl Cellulose resins such as pyrrolidone, polyester resin, acrylic resin, phenol resin, epoxy, polyvinyl alcohol, hydroxypropyl cellulose, and carboxymethyl cellulose can be used, but are not particularly limited.

Negative electrode active as the material 3, using a graphite powder, and used as the oil absorption is 100 cm ^3/100 g or less from 50 cm ^3/100 g or more.

  Oil absorption is one of the characteristic factors that express the performance of powder. Add oil little by little to 100g of powder, check the state of powder while kneading, and the point where it becomes a solid state from scattered state. The volume of the oil at that time is called the oil absorption. The amount of oil absorption greatly affects the size and shape of the powder. The smaller the particle size, the more irregular the shape, the larger the amount of oil absorption. For carbon black for rubber, the measurement method using DBP as the oil is JIS K6217. -4. The oil absorption amount measurement in the present invention was performed using linseed oil by an absorption amount measuring device (S-410, manufactured by Asahi Research Institute, Ltd.) based on JIS K6217-4.

By oil absorption used graphite powder is 50 cm ^3/100 g or more as an anode active material, and more amounts of electrolyte can be held in the vicinity of the surface of the graphite powder, insertion and extraction of lithium ions from the graphite powder This makes it easy to realize a non-aqueous electrolyte secondary battery with excellent input / output characteristics. However, the use of graphite powder oil absorption of greater than 100 cm ^3/100 g as a negative active material, too much amount of solvent required for the negative electrode mixture-coating material obtained by mixing a negative electrode active material, a binder and a solvent, the solvent The volatile drying process takes a long time or requires a long drying furnace, which reduces productivity and reduces the density of the mixture layer after volatile drying of the solvent. descend.

  Also, in order to keep a sufficient amount of electrolyte near the surface of the graphite powder, avoid a state where the voids between the graphite powders are locally small, that is, the density of the negative electrode mixture layer is within the layer. It is desirable to be equal. In particular, when two or more types of graphite powder having different physical properties are mixed, the filling property is improved, and the graphite powder tends to be in a state of being densely packed locally. In order to avoid such local filling improvement due to the mixing of different particles, the graphite powder of the present invention includes 90% or more of a powder having a circularity of 0.5 or more close to a sphere in addition to the oil absorption value described above. It is desirable to include it. If more than 10% of graphite powder having a low degree of circularity of less than 0.5 is contained in the negative electrode mixture layer with respect to the graphite powder having a degree of circularity of 0.5 or more, which is close to a spherical shape and has a high degree of filling, Since the filling property is locally reduced, the density of the negative electrode mixture layer is increased. In addition, when graphite powder having a low circularity of less than 0.5 is mainly used, if the average particle diameter of the graphite powder is as small as less than 3 μm, the graphite powder is locally and densely packed. . Here, in the battery having excellent input / output characteristics as an object of the present invention, it is necessary to shorten the distance from the negative electrode current collector to the surface of the negative electrode mixture layer, that is, to reduce the thickness of the negative electrode mixture layer. Therefore, it is desirable that the average particle diameter of the graphite powder be at most 30 μm in order to design the thin film to a minimum of 30 μm. Therefore, when the graphite powder having a circularity of less than 0.5 is mainly used, it is desirable to use a graphite powder having an average particle diameter of 3 μm to 30 μm.

  Here, the circularity is a value obtained by dividing the circumference of a circle having an area equal to the projected area S in the projection direction, which is the smallest area of the particle, by the circumference L of the particle cross section.

It is obtained by the above (formula 1) and becomes 1 in the case of a perfect circle, and becomes smaller as the shape becomes irregular. Recently, it can be easily calculated with commercially available image analysis software or the like, and for reference, an example in which the circularity of several types of particles is obtained is shown in FIGS.

  2A is an example with a circularity of 0.81, FIG. 2B is an example with a circularity of 0.73, FIG. 2C is an example with a circularity of 0.47, and FIG. This is an example of a circularity of 0.30.

  The graphite powder is not particularly limited as long as it satisfies the above oil absorption, for example, by a method of pulverizing, washing, granulating natural graphite ore, and making it spherical, A carbon base material such as coke is granulated with tar pitch, etc., calcined, graphitized, then pulverized, particle size adjusted, mesophase spherules extracted from tar pitch are calcined, graphitized, crushed, particle size adjusted It is possible to use a method according to the manufacturing method.

Furthermore, in the present invention, in order to retain a sufficient amount of electrolyte on the surface of the graphite powder, in addition to the physical properties of the graphite powder itself, the state of the negative electrode mixture layer as an aggregate of the graphite powder is also important. The density of the negative electrode mixture layer is desirably in the range of 0.8 g / cm ³ to 1.6 g / cm ³ . When the density of the negative electrode mixture layer exceeds 1.6 g / cm ³ , it becomes difficult to have a space sufficient to hold a sufficient amount of electrolyte around the graphite powder, and conversely, 0.8 g / cm ^3. If it is less than this, the amount of the electrolyte solution retained around the graphite powder will be ample, but the contact between the graphite powders will be insufficient, and the electronic conductivity of the negative electrode mixture layer will be reduced.

  Further, in the cross section of the negative electrode mixture layer, the density A of the first region having a thickness of ½ of the thickness of the negative electrode mixture layer on the side close to the negative electrode current collector, and the negative electrode of the thickness of the negative electrode mixture layer It is desirable that the ratio A / B with the density B in the second region having a thickness of 1/2 on the surface side of the mixture layer is 0.5 or more and 2.0 or less.

  In the negative electrode mixture layer, when the density ratio between the side close to the negative electrode current collector and the surface side exceeds 2.0, that is, when the surface side of the negative electrode mixture layer is in a rough state, it is separated from the negative electrode current collector. Therefore, the electron conductivity on the surface side of the negative electrode mixture layer, which is originally difficult to collect current, is remarkably insufficient, and the high input / output characteristics of the battery are greatly deteriorated.

  Conversely, the density ratio between the side close to the negative electrode current collector and the surface side in the negative electrode mixture layer is less than 0.5, that is, the positive electrode plate passes through the separator even if the surface side of the negative electrode mixture layer becomes dense. The movement of lithium ions in the electrolyte solution going back and forth between the battery and the negative electrode plate is blocked by the surface of the negative electrode mixture layer, making it difficult to move to the inside of the negative electrode mixture layer. Resulting in.

  In addition, regarding the existence state of the binder contained in the negative electrode mixture layer, the cross section of the negative electrode mixture layer is not to prevent the binder from being unevenly distributed around the graphite powder and hindering the occlusion and release of lithium ions. In the negative electrode mixture layer, the amount C of the binder contained in the first region having a thickness of ½ of the thickness close to the negative electrode current collector, and the surface side of the negative electrode mixture layer of the negative electrode mixture layer It is desirable that the ratio C / D with the amount D of the binder contained in the second region having a thickness of ½ is 0.67 or more and 1.5 or less.

  In particular, the ratio of the binder amount between the current collector side and the surface side of the negative electrode mixture layer is less than 0.67, and the binder is unevenly distributed on the surface side of the negative electrode mixture layer. As in the state where the density on the surface side is large, the lithium ion migration into the negative electrode mixture layer becomes an obstacle, and the high input / output characteristics of the battery are greatly deteriorated.

  Further, when the ratio of the binder amount between the current collector side and the surface side of the negative electrode mixture layer exceeds 2.0, that is, when the binder amount is greatly unevenly distributed on the current collector side of the negative electrode mixture layer, The delivery of lithium ions from the graphite powder is deteriorated, and the high input / output characteristics of the battery are deteriorated.

  Next, a method for producing a negative electrode plate of a non-aqueous electrolyte secondary battery, which is an embodiment of the present invention, that is, a negative electrode mixture layer comprising at least the above-described graphite powder and binder is provided on the surface of the negative electrode current collector. The method for this will be described in detail below.

  First, the graphite powder as a negative electrode active material and a binder are mixed together with a solvent in a solid weight ratio of 55 Wt% or more to 85 Wt% or less to prepare a negative electrode mixture paint. Here, the solid content weight ratio (Wt%) is the weight ratio occupied by the graphite powder and the binder when the graphite powder, the binder and the solvent are set to 100.

  As the solvent, for example, water, various alcohols such as ethanol and N-methyl-2-pyrrolidone, and organic solvents can be used alone or in combination, and are not particularly limited. Further, in the present invention, the method for producing the negative electrode mixture paint is not particularly limited as long as it is within the range of the solid content weight ratio. For example, a planetary mixer, a three-roll mill, a high-speed mixer Various devices capable of kneading and dispersing a high-viscosity material such as an extrusion kneader can be used, and the obtained negative electrode mixture paint is subjected to processing such as filtering, magnetic separation, pulverization, granulation, and granulation. There is no problem with the application.

  Subsequently, the negative electrode mixture paint is applied to form a wet mixture layer on the surface of the negative electrode current collector.

  The negative electrode mixture paint used in the present invention has a solid weight ratio of 55 Wt% or more and is in a remarkably highly viscous clay-like state. With such a coating method, it is difficult to satisfy the required film thickness accuracy.

  For this reason, in the present invention, the coating apparatus 100 shown in FIG. 3 wraps the negative electrode current collector 1 that is the object to be traveled around the first roll 5 that rotates and supports the negative electrode current collector 1. Thus, it is desirable to form the negative electrode mixture layer 2 on the surface of the negative electrode current collector 1 by passing the negative electrode mixture paint 7 between at least two rolls of the second roll 6 arranged to face the first roll 5. As a coating apparatus preferable in the present invention, a configuration including three or more rolls in which the third roll 8 is added to the coating apparatus 100 of FIG. 3 may be used as in the coating apparatus 200 illustrated in FIG. 4.

  Further, as shown in FIGS. 3 and 4, both the first roll 5 and the second roll 6 are rotated in the same direction as the traveling direction of the negative electrode current collector 1, thereby significantly increasing the viscosity of the present invention. This negative electrode mixture paint can be applied with high film thickness accuracy.

  In the nonaqueous electrolyte secondary battery of the present invention, the thickness of the mixture layer provided on the negative electrode plate is smaller than that for small consumer applications in order to achieve high input / output performance. As a method for forming such a thin negative electrode mixture layer with high film thickness accuracy, the first negative electrode current collector 1 is wound around and supported at the same peripheral speed as the negative electrode current collector 1 while being rotated and supported. By making the peripheral speed of the second roll 6 smaller than that of the roll 5, a thin negative electrode mixture layer 5 can be formed without significantly narrowing the gap h between the first roll 5 and the second roll 6. Therefore, high film thickness accuracy can be realized without using a special apparatus that can ensure the gap accuracy between rotating rolls at a remarkably severe level of 1 μm or less.

  At the time of forming the negative electrode mixture layer on the surface of the negative electrode current collector, the mixture layer is in a wet state containing a solvent, and the solvent in the mixture layer is heated, steam, infrared, electromagnetic induction, It volatilizes and drys by arbitrary methods, such as a microwave. The method for volatile drying of the solvent and its conditions are not particularly limited, and the above methods may be used alone or in combination. The negative electrode mixture paint of the present invention has a solid content weight ratio of 55 Wt% or more, and the amount of solvent present around the graphite powder is very small. For this reason, the negative electrode that has been in a state in which the binder is substantially fixed in the negative electrode mixture layer from the initial stage of the volatile drying step of the solvent from the wet negative electrode mixture layer, and has completed the volatile drying of the solvent. In the mixture layer, a uniform binder distribution can be realized, and a high input / output characteristic can be obtained in a lithium ion secondary battery using this negative electrode plate.

  On the other hand, in order to obtain a viscous negative electrode mixture paint to which a general coating method such as a die method can be applied using the high oil absorption graphite powder of the present invention, the above-described negative electrode mixture of the present invention is used. Compared to the amount of solvent used in the paint, a solvent of about 1.5 to 4 times is required, and in the process of volatile drying of the solvent, the binder moves toward the surface of the negative electrode mixture layer, resulting in volatile drying of the solvent. In the negative electrode mixture layer in which is finished, the binder is unevenly distributed in the vicinity of the surface, and the input / output characteristics of the battery are deteriorated. Furthermore, since the amount of the solvent to be contained is large, it takes a long time to complete the volatile drying, and a long drying furnace is required, or the productivity is remarkably reduced.

Further, as described above, in order to realize the excellent high input / output characteristics of the battery, the density of the negative electrode mixture layer of the present invention is 0.8 g / cm ³ or more to 1.6 g / cm ³ or less. It is desirable to do. The density of the negative electrode mixture layer obtained by the above-described method of the present invention after volatile drying of the solvent is higher than the density of the negative electrode mixture layer obtained by a general die method. The density of the mixture layer within the above-described range can be realized without subjecting the subsequent negative electrode mixture layer to press treatment.

  Here, the negative electrode mixture layer obtained when the solid content weight ratio of the negative electrode mixture layer is less than 55 Wt% requires press treatment after volatile drying. When the negative electrode mixture layer is subjected to press treatment, the negative electrode mixture layer adjacent to the negative electrode current collector is difficult to compress, but the surface side is easily compressed. The density in the vicinity is high. That is, there are few voids between the graphite powders, and the input / output characteristics of the battery deteriorate.

  Moreover, when the solid content weight ratio of the negative electrode mixture paint exceeds 85 Wt%, it is difficult to wet the surface of all graphite powder with a solvent. There is no solvent in between, and the density of this portion of the solvent after volatile drying increases, resulting in coarseness and density in the negative electrode mixture layer, which degrades the high input / output characteristics of the battery.

  On the other hand, in the production method of the present invention, as described above, since high density can be realized without performing press treatment, the density in the negative electrode mixture layer can be made uniform regardless of the location, so that the battery is excellent. High input / output characteristics can be realized.

  Hereinafter, although the Example and comparative example in one embodiment of this invention are shown, this invention is not limited to these.

  In Examples 1 to 6 and Comparative Examples 1 and 2 below, the same positive electrode plate, separator, non-aqueous electrolyte, and case were used in all cases.

  The positive electrode plate uses a 15 μm-thick aluminum foil as the positive electrode current collector, and the positive electrode mixture layer provided on both surfaces thereof is 100 parts by weight of lithium cobaltate as an active material, and 5 weights of acetylene black as a conductive additive. Part, and 5 parts by weight of polyvinylidene fluoride as a binder, with a single-sided thickness of 30 μm.

  The separator uses a microporous membrane made of polypropylene having a thickness of 27 μm, and the non-aqueous electrolyte is 1 mol as a solute in a solvent in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are mixed at a weight ratio of 1: 1: 1. A solution in which / L lithium hexafluorophosphate was dissolved was used. As the case, a cylindrical case having a diameter of 26 mm and a height of 65 mm was used.

  For the negative electrode plate, an electrolytic copper foil having a thickness of 10 μm was used as a negative electrode current collector, and the negative electrode mixture layer provided on both surfaces thereof was 100 parts by weight of graphite powder as an active material and 1 part by weight of carboxymethyl cellulose as a binder. It is composed of 2 parts by weight of styrene-butadiene rubber, and the single-sided thickness of 50 μm is the same in each case of the examples and comparative examples, and is the characteristic condition of the present invention, the oil absorption amount of the graphite powder, the circularity, About average particle diameter, solid content weight ratio as negative electrode mixture paint, average density of negative electrode mixture layer after solvent volatilization drying, ratio of binder amount and density on current collector side and surface side, examples and comparative examples The conditions used in each case are summarized in Table 1. Here, as a method for forming the negative electrode mixture layer on the surface of the negative electrode current collector, Examples 1 to 6 in which the solid content ratio of the negative electrode mixture paint is in the range of 55 Wt% to 85 Wt% For the comparative examples 1 and 2 in which the solid content weight ratio of the negative electrode mixture paint is less than 55 Wt%, using the coating method using two rolls with different speeds described in the embodiment, coating by a general die method The method was used.

  The electrode body in which the above-described positive electrode plate and negative electrode plate are overlapped and wound through a separator is housed in a case together with a non-aqueous electrolyte, and the lithium ion batteries of Examples 1 to 6 and Comparative Examples 1 and 2 are manufactured. Produced.

  The above charging / discharging of each battery was repeated for 3 cycles under the conditions of a constant current of 400 mA, a charging upper limit voltage of 4.2 V, and a discharging lower limit voltage of 2.5 V in a 25 ° C. environment. Under the environment, a pulse charge / discharge test was performed, and the direct current internal resistance (DC-IR) of the battery was measured. The measurement results of direct current internal resistance (DC-IR) are also shown in Table 1.

As is clear from the above results, in any of the batteries of Examples 1 to 6 of the present invention, low DC resistance is realized at both normal temperature and low temperature, and excellent high input / output characteristics required for vehicle applications are realized. Is possible. On the other hand, in any of Comparative Examples 1 and 2 that are out of the scope of the present invention, the direct current resistance is high in any environment at normal temperature or low temperature, and the high input / output characteristics required for vehicle use can be satisfied. It is not a thing.

  In the above embodiment, the lithium ion battery has been described as an example of the nonaqueous electrolyte secondary battery of the present invention. However, the configuration of the negative electrode plate of the lithium ion battery described in each embodiment is different from that of other nonaqueous batteries. Needless to say, it can be applied as a negative electrode plate of an electrolyte secondary battery. For example, the present invention can also be applied to a nonaqueous electrolyte secondary battery using Mg ions, Na ions, or the like.

  The present invention can be applied to a non-aqueous electrolyte secondary battery, in particular, a lithium ion secondary battery having excellent input / output characteristics. The present invention can be applied to energy storage elements having various electrode plates, such as various batteries and capacitors.

DESCRIPTION OF SYMBOLS 1 Negative electrode collector 2 Negative electrode mixture layer 3 Negative electrode active material 4 Binder 5 1st roll 6 2nd roll 7 Negative electrode mixture paint 8 3rd roll

Claims (12)

A positive electrode plate provided with a positive electrode mixture layer on at least one surface of the positive electrode current collector; a negative electrode plate provided with a negative electrode mixture layer on at least one surface of the negative electrode current collector; and the positive electrode plate; A non-aqueous electrolyte secondary battery in which a separator provided between the negative electrode plates is housed in a case together with a non-aqueous electrolyte,
The negative electrode mixture layer includes at least graphite powder as a negative electrode active material, and a binder for fixing the graphite powder to the surface of the negative electrode current collector,
Non-aqueous electrolyte secondary battery, wherein the oil absorption of the graphite powder is 100 cm ^3/100 g or less from 50 cm ^3/100 g or more.   In the negative electrode mixture layer, the density A of the first region having a thickness of ½ of the thickness of the negative electrode mixture layer on the surface side of the negative electrode current collector, and the negative electrode of the thickness of the negative electrode mixture layer 2. The non-aqueous solution according to claim 1, wherein the ratio A / B with the density B of the second region having a thickness of ½ on the surface side of the mixture layer is 0.5 or more and 2.0 or less. Electrolyte secondary battery.   In the negative electrode mixture layer, the amount C of the binder contained in the first region having a thickness of ½ of the thickness of the negative electrode mixture layer on the surface side of the negative electrode current collector, and the negative electrode mixture layer Of these, the ratio C / D to the amount D of the binder contained in the second region having a thickness of ½ on the surface side of the negative electrode mixture layer is 0.67 or more and 1.5 or less. The nonaqueous electrolyte secondary battery according to claim 1.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the graphite powder includes 90% or more of those having a circularity of 0.5 or more.   5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the graphite powder contains 90% or more of particles having an average particle diameter of 3 μm to 30 μm. The density of the said negative mix layer is 0.8 g / cm < ³ > or more and 1.6 g / cm < ³ > or less, The nonaqueous electrolyte secondary battery as described in any one of Claims 1-5 characterized by the above-mentioned. . A method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6,
Producing a negative electrode mixture paint in which at least the graphite powder and the binder are mixed together with a solvent in a solid weight ratio of 55 Wt% to 85 Wt%;
Applying the negative electrode mixture paint to at least one surface of the negative electrode current collector to provide the wet negative electrode mixture layer;
And a step of evaporating and drying the solvent from the wet negative electrode mixture layer. A method for producing a negative electrode plate of a non-aqueous electrolyte secondary battery.   As a means for applying the negative electrode mixture paint, at least one of a first roll supporting the negative electrode current collector and a second roll disposed to face the first roll through the negative electrode current collector The method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 7, wherein two rolls are used.   The negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 8, wherein both the first roll and the second roll are rotated in the same direction as the traveling direction of the negative electrode current collector. Manufacturing method.   The circumferential speed of the first roll is the same as the traveling speed of the negative electrode current collector, and the circumferential speed of the second roll is the circumferential speed of the first roll and the traveling speed of the negative electrode current collector. The method for producing a negative electrode plate for a non-aqueous electrolyte secondary battery according to claim 9, wherein the method is different.   The negative electrode plate of a non-aqueous electrolyte secondary battery according to claim 10, wherein a peripheral speed of the second roll is smaller than a peripheral speed of the first roll and a traveling speed of the negative electrode current collector. Manufacturing method.   The nonaqueous electrolysis according to any one of claims 8 to 11, wherein the negative electrode mixture layer is not pressed after the step of volatilizing and drying the solvent from the wet negative electrode mixture layer. Manufacturing method of negative electrode plate of liquid secondary battery.