WO2014133070A1

WO2014133070A1 - Negative electrode for nonaqueous electrolyte secondary batteries

Info

Publication number: WO2014133070A1
Application number: PCT/JP2014/054842
Authority: WO
Inventors: 真規末永; 嶋村　修; 文洋川村; 健児小原; 狩野　巌大郎; 康介萩山
Original assignee: 日産自動車株式会社
Priority date: 2013-02-28
Filing date: 2014-02-27
Publication date: 2014-09-04
Also published as: JP2016095897A

Abstract

[Problem] To provide a means which is capable of improving the long-term cycle durability of a large-sized nonaqueous electrolyte secondary battery that can be used in applications such as driving of an electric vehicle. [Solution] A negative electrode for nonaqueous electrolyte secondary batteries, which comprises a collector and a negative electrode active material layer that is arranged on the surface of the collector and contains a negative electrode active material. The negative electrode active material contains, as a main component, an artificial graphite, a coated natural graphite or a natural graphite; and if X (% by mass) is the content of the artificial graphite contained in the negative electrode active material, Y (% by mass) is the content of the coated natural graphite contained in the negative electrode active material, and Z (% by mass) is the content of the natural graphite contained in the negative electrode active material (provided that X + Y + Z = 100% by mass), Y ≥ Z and Y ≥ X are satisfied (excluding the case where (X, Y, Z) = (0, 1, 0)).

Description

Anode for non-aqueous electrolyte secondary battery

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery.

In recent years, the development of electric vehicles (EVs), hybrid electric vehicles (HEVs), and fuel cell vehicles (FCVs) has been promoted against the backdrop of the increasing environmental protection movement. A secondary battery that can be repeatedly charged and discharged is suitable as a power source for driving these motors, and a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery that can be expected to have a high capacity and a high output is attracting attention.

The nonaqueous electrolyte secondary battery has a positive electrode active material layer containing a positive electrode active material (for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, etc.) formed on the current collector surface. In addition, the non-aqueous electrolyte secondary battery includes a negative electrode active material formed on the current collector surface (for example, carbonaceous materials such as metallic lithium, coke and natural / artificial graphite, metals such as Sn and Si, and oxide materials thereof) Etc.).

Conventionally, a technique has been proposed in which two or more types of graphite crystals are used as a negative electrode active material in a lithium ion battery having a relatively small capacity for consumer use. For example, Japanese Patent Application Laid-Open No. 2004-127913 discloses a technique in which artificial graphite particles having predetermined physical properties are used as a negative electrode active material for a lithium ion secondary battery in a mixture with spherical graphite particles. The configuration disclosed in Japanese Patent Application Laid-Open No. 2004-127913 can greatly improve the charge / discharge cycle characteristics of the lithium ion secondary battery, and at the same time, discharge rate characteristics, low-temperature discharge characteristics and safety (heat resistance It is said that it becomes possible to provide a battery that is also excellent in the property.

As described above, conventionally, in consumer applications, various studies have been made on techniques for mixing and using two or more types of graphite crystals as negative electrode active materials. However, the conventional technology relating to the mixed negative electrode has not, of course, taken into consideration the required performance of a large battery for an electric vehicle. According to the study by the present inventors, it has been found that even if the technique proposed in the conventional consumer use is applied as it is to a large battery for an electric vehicle, sufficient battery performance is not exhibited. More specifically, with regard to long-term cycle durability, which is one of the most important performances in the practical application of large batteries for electric vehicles, a mixed negative electrode that is preferable from the viewpoint of cycle durability for conventional consumer use is a large size for electric vehicles. The present inventors have found that the long-term cycle durability of the battery does not necessarily show excellent performance.

Therefore, an object of the present invention is to provide means for improving long-term cycle durability in a large-sized non-aqueous electrolyte secondary battery that can be used for driving electric vehicles.

The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention has a current collector and a negative electrode active material layer including a negative electrode active material disposed on the surface of the current collector. The negative electrode active material contains artificial graphite, coated natural graphite or natural graphite as a main component. When the content of the artificial graphite contained in the negative electrode active material is X [mass%], the content of the coated natural graphite is Y [mass%], and the content of the natural graphite is Z [mass%]. (Where X + Y + Z = 100 mass%), Y ≧ Z and Y ≧ X are satisfied (except for the case of (X, Y, Z) = (0, 1, 0)). .

1 is a schematic cross-sectional view showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat (stacked) bipolar type. In the nonaqueous electrolyte secondary battery according to the embodiment of the present invention, the contents of artificial graphite, coated natural graphite and natural graphite that can constitute the main component of the negative electrode active material are X [mass%], Y [mass%] and It is a figure which shows the area | region (hatched area | region A) which satisfy | fills Y> = Z and Y> = X when it is set as Z [mass%]. As a more preferred embodiment of the present invention, a straight line of X = 0, a straight line of Z = 0, and coordinates (Example 1) of (X, Y, Z = 50, 50, 0) and (X, Y, Z) = 20, 60, 20) is a diagram showing a region (shaded region B) surrounded by a straight line connecting the coordinates (Example 7).

The present invention has a current collector and a negative electrode active material layer containing a negative electrode active material, which is disposed on the surface of the current collector, and the negative electrode active material is mainly composed of artificial graphite, coated natural graphite or natural graphite. The content of artificial graphite contained in the negative electrode active material is X [mass%], the content of coated natural graphite is Y [mass%], and the content of natural graphite is Z [mass%]. (Where X + Y + Z = 100% by mass), satisfying Y ≧ Z and Y ≧ X (except in the case of (X, Y, Z) = (0, 1, 0)) It is a negative electrode for water electrolyte secondary batteries. According to the present invention, since the coated natural graphite is contained more than the content of the artificial graphite, the artificial graphite having a high hardness can be replaced with other graphite particles (coated natural graphite or natural graphite) by pressing or the like during electrode production. The risk of deformation is reduced. And, since the coated natural graphite is contained more than the content of natural graphite, the amount of precipitates generated on the surface of the negative electrode active material after a long-term cycle is also reduced, and further the precipitation form of the precipitates is reduced in capacity. As a result, the long-term cycle characteristics can be improved because the shape is unlikely to cause a micro short circuit.

Hereinafter, as a preferred embodiment of the negative electrode for a non-aqueous electrolyte secondary battery, a case where it is used for a non-aqueous electrolyte lithium ion secondary battery will be described, but it is not limited to the following embodiment. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

FIG. 1 is a schematic cross-sectional view schematically showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat (stacked) bipolar type. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior body 29 that is an exterior body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. The separator 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with a separator 17 therebetween. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

In addition, although the negative electrode active material layer 13 is arrange | positioned only at one side in the outermost layer positive electrode collector located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost positive electrode current collector is disposed on one or both surfaces of the outermost layer positive electrode current collector. A positive electrode active material layer may be disposed.

The positive electrode current collector 12 and the negative electrode current collector 11 are each provided with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has the structure led out to the exterior of the battery exterior body 29 so that it may be pinched | interposed into the edge part. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

Note that FIG. 1 shows a flat battery (stacked battery) that is not a bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and the opposite side of the current collector. And a bipolar battery including a bipolar electrode having a negative electrode active material layer electrically coupled to the surface. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

Hereinafter, each member will be described in more detail.

[Negative electrode active material layer]
The negative electrode active material layer includes a negative electrode active material. In the non-aqueous electrolyte lithium ion secondary battery according to this embodiment, the negative electrode active material contains artificial graphite, coated natural graphite, or natural graphite as a main component. There are various advantages when the negative electrode active material contains these graphite crystals as a main component. For example, when lithium ions are inserted into a graphite crystal, it shows the same potential as lithium metal (0.1 to 0.3 V vs. Li ⁺ / Li), and the capacity per unit volume is relatively high (> 800 mAh / L). There are advantages that the volume expansion is small, the potential flatness is excellent, the cost is low, and the battery can be manufactured in a discharged state. Here, “the negative electrode active material contains artificial graphite, coated natural graphite or natural graphite as a main component” means the content of the above three types of graphite crystals in the total amount of 100% by mass of the negative electrode active material (including two or more types). In this case, it means that the total content) is 50% by mass or more. The proportion of graphite crystals in the total amount of 100% by mass of the negative electrode active material is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and still more preferably 95% by mass. % Or more, particularly preferably 98% by mass or more, and most preferably 100% by mass.

Graphite crystal is a layered material in which graphene sheets (sheets with a thickness of 1 atom in which carbon atoms (C) are connected by sp ² hybrid orbitals) are stacked at intervals of 0.3354 nm according to AB or ABC stacking order. is there. Here, the crystallite size Lc of the graphite crystal is preferably 20 to 90 nm, more preferably 35 to 85 nm, and still more preferably 40 to 75 nm. If the crystallite size is 90 nm or less, the low-temperature output characteristics are excellent. The average interplanar spacing (d002) is preferably 0.3354 to 0.3365 nm, more preferably 0.3354 to 0.3368 nm, and still more preferably 0.3354 to 0.3370 nm. Since the lower limit of 0.3354 nm is a theoretical value of graphite crystals, the closer to this value, the better. Moreover, if it is below an upper limit, crystallinity will be maintained high enough and the possibility of the voltage fall at the time of a capacity | capacitance fall and charge / discharge will be reduced. These values are values calculated based on the Gakushin method from the results of XRD analysis using a Rigaku wide-angle X-ray diffractometer. These values can be controlled to some extent by adjusting the heat treatment temperature.

“Artificial graphite” is artificially and industrially synthesized graphite, also called synthetic graphite or synthetic graphite, and is a polycrystalline body made of graphite crystallites. Artificial graphite is obtained, for example, by graphitizing a carbon material such as coke at a high temperature of 2800 ° C. or higher in an inert atmosphere. Further, there are high orientation pyrolytic graphite (HOPG) obtained by compressing pyrolytic carbon at a high temperature of 3000 ° C. or higher to enhance the orientation of crystallites, and quiche graphite obtained by precipitation from molten iron. Furthermore, the thermal decomposition product of silicon carbide (SiC) is also artificial graphite having a very high degree of graphitization. The method for producing artificial graphite is not particularly limited, but, for example, at least a graphitizable aggregate or graphite and a graphitizable binder are heated and mixed, pulverized, and then the pulverized product and a graphitization catalyst are mixed. It can be manufactured by firing and processing. Here, examples of aggregates that can be graphitized include coke powder and resin carbide. Of these, coke powder that is easily graphitized such as needle coke is preferable. In addition to tar and pitch, the binder is preferably an organic material such as a thermosetting resin or a thermoplastic resin. The blending amount of the binder is preferably 10 to 80% by mass, more preferably 20 to 80% by mass, and further preferably 30 to 80% by mass with respect to the graphitizable aggregate or graphite. If the amount of the binder is within such a range, the aspect ratio and specific surface area of the produced graphite particles do not become too large, which is preferable. There is no particular limitation on the mixing method, and for example, a kneader can be used, but it is preferable to mix at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, 50 to 300 ° C. is preferable, and when the binder is a thermosetting resin, 20 to 180 ° C. is preferable. The mixture is pulverized, the pulverized product and the graphitization catalyst are mixed, graphitized at 2000 ° C. or higher, and then pulverized to obtain artificial graphite.

“Natural graphite” is a graphite crystal that is calculated in nature as a mineral, as its name suggests. Compared to artificial graphite, it has a large amount of impurities such as allotrope, strong crystal structure, low hardness, and high electrical resistance. . In general, many natural graphites that have not been processed or treated have a flake shape, a large aspect ratio, and a large specific surface area, so that they easily react with the electrolyte and generate a large amount of gas. There is a problem that an active material slurry (ink) cannot be prepared because the solvent is absorbed during the production of the layer. The nuclear material (natural graphite) has different crystallinity and structure depending on the production area and mine, and there are scale-like, scale-like, earthy graphite, etc., but there is no particular limitation as long as the surface can be modified into spherical graphite particles. . From the viewpoint of crystallinity (capacity), scaly and scaly ones are more preferable. As a spheroidization method, mechanical surface modification such as pulverization, compression, shearing, and granulation is preferable in that rounded and well-shaped particles can be obtained. Examples of the apparatus for performing the mechanical surface modification treatment include a ball mill, a vibration mill, a mechano mill, a medium stirring mill, and an apparatus having a structure in which particles pass between a rotating container and a taper attached to the inside of the rotating container. Here, “spherical” means a rounded shape when a particle image of graphite particles is observed with an SEM image. The circularity is preferably 0.8 or more, more preferably 0.85 or more, and still more preferably 0.9 or more. By setting it as such a structure, the negative electrode active material layer formed can be densified more. The “circularity” is a circumference measured as a circle calculated from a projected image of graphite particles, by calculating the circle equivalent diameter, which is the diameter of a circle having the same area as the projected area of the graphite particles. The value obtained by dividing the value is 1.00 for a perfect circle. In addition, whether or not it is natural graphite can be confirmed from the state in which the scaly particles are originally folded by observing the cross section of the graphite particles with an SEM image.

“Coated natural graphite” is a graphite crystal in which the surface of natural graphite particles is coated with amorphous or low crystalline carbon. By covering the surface of natural graphite, the above-described problems of natural graphite are solved. The coated natural graphite is obtained, for example, by attaching an amorphous layer to the surface of natural graphite particles. The method for attaching the amorphous layer to the surface of the graphite particles is not particularly limited. For example, first, the surface of the natural graphite particles is coated with pitches such as a molten pitch. Thereafter, the surface of the natural graphite particles coated with the surface is baked at a temperature of about 500 to 2000 ° C. to be carbonized, and if necessary, pulverized and classified so that at least a part of the surface becomes amorphous. Coated natural graphite particles are obtained. The amorphous layer is not limited to that formed in such a liquid phase, and may be formed in a gas phase by a CVD method or the like. Here, the method for forming the low crystalline carbon layer on the surface of the negative electrode material is not particularly limited, and examples thereof include a wet mixing method, a chemical vapor deposition method, and a mechanochemical method. The chemical vapor deposition method and the wet mixing method are preferable from the viewpoint that the reaction system can be controlled uniformly and the shape of the negative electrode material can be maintained. Further, the carbon source for forming the low crystalline carbon layer is not particularly limited, but in the chemical vapor deposition method, aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, and the like can be used. Methane, ethane, propane, benzene, toluene, xylene, styrene, naphthalene, or derivatives thereof. In the wet mixing method and mechanochemical method, a polymer compound such as a phenol resin or a styrene resin, or a carbonizable solid material such as pitch can be processed as a solid or dissolved material. Regarding the treatment temperature, it is preferable to perform heat treatment at 800 to 1200 ° C. in the chemical vapor deposition method. If it is 800 degreeC or more, the production | generation speed | rate of vapor deposition carbon will be sufficiently fast, and shortening of processing time is possible. On the other hand, if it is 1200 degrees C or less, a production | generation rate will not become quick too much and control of film formation will be easy. In the wet mixing method and mechanochemical method, heat treatment is preferably performed at 700 to 2000 ° C. In the wet mixing method and the mechanochemical method, the carbon source is uniformly deposited in advance on the surface of the negative electrode material and fired, so that heat treatment can be performed even at a relatively high temperature. If it is 700 degreeC or more, carbon crystallinity is high enough and it can suppress electrolyte solution degradability low. On the other hand, if it is 2000 degrees C or less, carbon crystallinity will not become high too much and the fall of an output characteristic can be prevented. The coating amount can be calculated from a weight loss amount of 550 ° C. or higher (depending on the coating material), CO ₂ adsorption amount, low crystal layer precursor charge amount, etc. by thermogravimetric analysis TG / DTA. In addition, regarding the amount of the low crystalline carbon layer formed on the surface of the negative electrode material, in the present invention, the carbon residue rate of the carbon source is measured in advance by thermogravimetric analysis, etc. The product of rate is the amount of carbon covered. The amount of carbon in the low crystalline carbon layer is not particularly limited, but is preferably 1.0 to 20% by mass, more preferably 1.5 to 15% by mass, and further preferably 2 to 10% by mass of the core negative electrode material. Within such a range, the input / output characteristics and the life characteristics can be more balanced. That is, if it is 1.0 mass% or more, the distribution of the low crystal layer can be made uniform, and the life characteristics can be maintained by making the formation of the electrolyte additive uniform (the SEI film thickness). . On the other hand, if the amount is 20% by mass or less, a decrease in low-temperature output characteristics due to a reduction in specific surface area can be prevented, and the possibility of a decrease in capacity due to agglomeration of particles or a large amount of low crystalline components can be reduced. As a method of distinguishing surface modified (coated) natural graphite, the presence or absence of low crystalline carbon is clearly different from the structure of low crystalline carbon layer and normal graphite graphite layer. (TEM).

In the non-aqueous electrolyte secondary battery according to this embodiment, the contents of artificial graphite, coated natural graphite, and natural graphite that can constitute the main component of the negative electrode active material are X [mass%], Y [mass%], and Z [ Mass%] is characterized in that Y ≧ Z and Y ≧ X (see the hatched area A in FIG. 2). In this specification, X + Y + Z = 100 mass%. Further, the case of (X, Y, Z) = (0, 1, 0) is excluded from the scope of the present invention. Here, the hatched area A in FIG. 2 is an area surrounded by four straight lines X = 0, Z = 0, Y = Z, and Y = X. With such a configuration, it is possible to improve the long-term (for example, 1000 cycles) cycle durability of the nonaqueous electrolyte secondary battery. In this way, since the coated natural graphite is contained in excess of the artificial graphite content, the artificial graphite having high hardness deforms other graphite particles (coated natural graphite and natural graphite) by pressing during electrode production. Is less likely to occur. And, since the coated natural graphite is contained more than the content of natural graphite, the amount of precipitates generated on the surface of the negative electrode active material after a long-term cycle is also reduced, and further the precipitation form of the precipitates is reduced in capacity. It is estimated that the long-term cycle characteristics are improved as a result because the shape does not easily cause a micro short-circuit.

In a more preferred embodiment, X, Y, and Z may be determined so as to be included in the hatched area B in FIG. Here, the hatched area B in FIG. 3 includes a straight line of X = 0, a straight line of Z = 0, and coordinates (Example 1) of (X, Y, Z = 50, 50, 0) and (X, Y , Z = 20, 60, 20) is a region surrounded by a straight line connecting the coordinates (Example 7).

The negative electrode active material may further include a material other than the above-mentioned artificial graphite, coated natural graphite, and natural graphite as the negative electrode active material. For example, the negative electrode active material may further include hard carbon (non-graphitizable carbon material) or soft carbon (graphitizable carbon material). Hard carbon is also called non-graphitizable carbon material, and is hard to graphitize at high temperatures. Soft carbon is also referred to as an easily graphitizable carbon material, and is easily graphitized at high temperatures. These are determined according to the type of the graphitization precursor. Here, since the hard carbon does not have an ordered arrangement of crystallites, graphitization is difficult to proceed even if heat treatment is performed at a high temperature. On the other hand, since soft carbon has crystallites arranged in the same direction, carbon is graphitized by diffusing carbon over a short distance during heat treatment. Soft carbon and graphite (graphite) have a layered structure in which a large number of carbon hexagonal mesh surfaces (graphene surfaces) are laminated, while hard carbon has several layers of carbon hexagonal mesh surfaces (graphene surfaces). The size of the crystal is small and the spread of the crystals is small, and they are characterized by having a nanoscale layer space by being randomly arranged. When the negative electrode active material further contains these amorphous carbon materials, there is an advantage that the long-term cycle durability can be further improved. The ratio of the content of the amorphous carbon material in the negative electrode active material is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass based on the above-mentioned X + Y + Z = 100% by mass. %, More preferably 1 to 10% by mass. If the value is equal to or greater than the lower limit, the effect of addition is manifested. On the other hand, if the value is equal to or less than the upper limit value, the risk of negative electrode capacity reduction and cell capacity reduction can be reduced.

The negative electrode active material may further contain other materials. For example, a lithium-transition metal composite oxide (for example, Li ₄ Ti ₅ O ₁₂ ), a metal material, a lithium alloy-based negative electrode material, or the like is used as the negative electrode active material. Further, it may be included.

The average particle diameter of the negative electrode active material contained in the negative electrode active material layer is not particularly limited, but from the viewpoint of improving the initial charge capacity (handling), it is preferable as the median diameter (D50) by the laser diffraction particle size distribution meter. Is 10-30 μm. If the value is equal to or greater than the lower limit, the possibility of a decrease in coatability due to a decrease in bulk density and a decrease in charge / discharge characteristics due to an increase in specific surface area are reduced. On the other hand, if the value is less than or equal to the upper limit value, the risk of poor appearance of the electrode due to deterioration of coating properties due to clogging or streaking of the coater head is reduced.

The BET specific surface area of the negative electrode active material contained in the negative electrode active material layer is preferably 0.5 to 10 m ² / g, more preferably 1.0 to 6.0 m ² / g, and still more preferably 2. 0 to 4.2 m ² / g. If the specific surface area of the negative electrode active material is a value equal to or greater than the lower limit, the risk of deterioration of low temperature characteristics accompanying an increase in internal resistance is reduced. On the other hand, if the value is not more than the upper limit value, it is possible to prevent the side reaction from proceeding with an increase in the contact area with the electrolytic solution. In particular, if the specific surface area is too large, an overcurrent locally flows in the electrode surface due to the gas generated during the first charge (the film with the electrolyte additive is not fixed), and the film is coated in the electrode surface. However, if the value is equal to or less than the above upper limit value, the risk can be reduced.

Further, the value of the ratio of the BET specific surface area value of all graphite particles selected from the group consisting of artificial graphite, coated natural graphite and natural graphite contained in the negative electrode active material to the BET specific surface area value of the coated natural graphite Is preferably 1.7 or less, more preferably 1.0 to 1.7, still more preferably 1.0 to 1.6, and more preferably 1.0 to 1.5. Is particularly preferred. By adopting such a configuration, it is possible to reduce the amount of gas generated during the initial charge / discharge, and it is possible to shorten the tact time of the degassing step during battery production.

Furthermore, the tap density of the negative electrode active material contained in the negative electrode active material layer is preferably 0.7 g / cm ³ or more, more preferably 0.9 g / cm ³ or more. By setting it as such a structure, when compressing an electrode, it can compress to desired thickness, Therefore The capacity | capacitance per volume can fully be maintained.

The negative electrode active material layer preferably contains a binder. The binder has a function of binding particles of the negative electrode active material contained in the negative electrode active material layer, or binding the negative electrode active material and the current collector. The negative electrode active material layer preferably contains an aqueous binder as a binder. In addition to the easy procurement of water as a raw material, water-based binders can be greatly reduced in capital investment on the production line and reduced environmental load because it is water vapor that occurs during drying. There is an advantage.

The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder using water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, ) Acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl meta Acrylate, etc.), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer Polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80 Mol% or more, more preferably 90 mol% or more) and a modified product thereof (a saponified product of 1 to 80 mol% of vinyl acetate units of a copolymer of ethylene / vinyl acetate = 2/98 to 30/70 mol ratio) The 1 to 50 mol% partially acetalized vinyl alcohol), starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, And their salts), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, (meth) alkyl acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Mannich Degeneration , Formalin condensation type resins (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, and mannangalactan derivatives Etc. These aqueous binders may be used alone or in combination of two or more.

The aqueous binder may contain at least one rubber binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains styrene-butadiene rubber because of good binding properties.

When styrene-butadiene rubber is used as the water-based binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (such as carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose as a binder. The mass ratio of the styrene-butadiene rubber and the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.3 to 0.7. .

Among the binders used in the negative electrode active material layer, the content of the aqueous binder is preferably 80 to 100% by mass, preferably 90 to 100% by mass, and preferably 100% by mass. Examples of the binder other than the water-based binder include binders used in the following positive electrode active material layer.

The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it can bind the active material, but preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1 to 10% by mass, and further preferably 2 to 4% by mass. Since the water-based binder has high binding power, the active material layer can be formed with a small amount of addition as compared with the organic solvent-based binder. Accordingly, the content of the aqueous binder in the active material layer is preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass, and still more preferably 1% with respect to the active material layer. .5-4% by mass.

The negative electrode active material layer further includes other additives such as a conductive additive, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and a lithium salt for improving ion conductivity, as necessary.

The conductive assistant means an additive blended to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive aid include carbon materials such as carbon black such as acetylene black and carbon fibers. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

Examples of the ion conductive polymer include polyethylene oxide (PEO) and polypropylene oxide (PPO) polymers.

The compounding ratio of the components contained in the negative electrode active material layer and the positive electrode active material layer described later is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. The thickness of each active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. As an example, the thickness of each active material layer is about 2 to 100 μm.

In the present invention, the density of the negative electrode active material layer is preferably 1.2 to 1.6. In general, when a water-based binder is used in the negative electrode active material layer, there is a problem that the amount of gas generated during charging of the battery is larger than that of a solvent-based binder such as PVdF which has been conventionally used. In this connection, if the density of the negative electrode active material layer is 1.6 g / cm ³ or less, it is not necessary to increase the press pressure, and the occurrence of cracks in the graphite particles is prevented. Moreover, the void | hole in an active material layer is also ensured and liquid injection property is also ensured. As a result, it is possible to prevent the deterioration of the life characteristics due to liquid erosion or the like. Moreover, if the density of the negative electrode active material layer is 1.2 g / cm ³ or more, a decrease in electron conductivity due to an insufficient contact area between the active materials / active materials is prevented, and life characteristics are improved. Can improve. The density of the negative electrode active material layer is preferably 1.25 to 1.58 g / cm ³ , more preferably 1.3 to 1.55 g / cm ³ , since the effects of the present invention are more exerted. is there. Note that the density of the negative electrode active material layer represents the mass of the active material layer per unit volume. Specifically, after removing the negative electrode active material layer from the battery, removing the solvent and the like present in the electrolyte solution, the electrode volume is obtained from the long side, the short side, and the height, and after measuring the weight of the active material layer, It can be determined by dividing weight by volume.

In the present invention, the surface centerline average roughness (Ra) of the surface on the separator side of the negative electrode active material layer is preferably 0.5 to 1.0 μm. If the center line average roughness (Ra) of the negative electrode active material layer is 0.5 μm or more, the long-term cycle characteristics can be further improved. This is considered to be because if the surface roughness is 0.5 μm or more, the gas generated in the power generation element is easily discharged out of the system. Moreover, if the centerline average roughness (Ra) of the negative electrode active material layer is 1.0 μm or less, the electron conductivity in the battery element is sufficiently secured, and the battery characteristics can be further improved.

Here, the centerline average roughness Ra means that only the reference length is extracted from the roughness curve in the direction of the average line, the x axis is in the direction of the average line of the extracted portion, and the y axis is in the direction of the vertical magnification. When the roughness curve is expressed by y = f (x), the value obtained by the following formula 1 is expressed in micrometers (μm) (JIS-B0601-1994).

The value of Ra is measured by using a stylus type or non-contact type surface roughness meter that is generally widely used, for example, by a method defined in JIS-B0601-1994. There are no restrictions on the manufacturer or model of the device. In the examination in the present invention, Ra was obtained according to the method defined in JIS-B0601 using a model number: DEKTAK3030 manufactured by SLOAN. Either the contact method (stylus type with a diamond needle or the like) or the non-contact method (non-contact detection with a laser beam or the like) can be measured.

Also, since it can be measured relatively easily, the surface roughness Ra specified in the present invention is measured at the stage where the active material layer is formed on the current collector in the manufacturing process. However, the measurement can be performed even after the battery is completed, and the results are almost the same as those in the manufacturing stage. Therefore, the surface roughness after the battery is completed may satisfy the above Ra range. The surface roughness of the negative electrode active material layer is that on the separator side of the negative electrode active material layer.

The surface roughness of the negative electrode takes into account the active material shape, particle diameter, active material blending amount, etc. contained in the negative electrode active material layer, for example, by adjusting the press pressure during active material layer formation, etc. It can adjust so that it may become the said range. The shape of the active material varies depending on the type and manufacturing method, and the shape can be controlled by pulverization, for example, spherical (powder), plate, needle, column, square Etc. Therefore, in order to adjust the surface roughness in consideration of the shape used for the active material layer, active materials having various shapes may be combined.

[Positive electrode active material layer]
The positive electrode active material layer contains an active material and, if necessary, other additives such as a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and a lithium salt for increasing ionic conductivity. An agent is further included.

The positive electrode active material layer includes a positive electrode active material. Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-- such as those in which some of these transition metals are substituted with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. More preferably, a composite oxide containing lithium and nickel is used, and more preferably Li (Ni—Mn—Co) O ₂ and a part of these transition metals substituted with other elements (hereinafter, referred to as “following”) Simply referred to as “NMC composite oxide”). The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Co, d represents the atomic ratio of Mn, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

Generally, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of the material and improving the electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable from the viewpoint of improving the balance between capacity and life characteristics. For example, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ is LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Mn _1/3 Co _1/3 O _2, etc. that have been proven in general consumer batteries. Compared to the above, the capacity per unit weight is large, and the energy density can be improved, so that a battery having a compact and high capacity can be produced, which is preferable from the viewpoint of cruising distance. In addition, LiNi _0.8 Co _0.1 Al _0.1 O ₂ is more advantageous in terms of a larger capacity, but there are difficulties in life characteristics. On the other hand, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ has life characteristics as excellent as LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

Of course, positive electrode active materials other than those described above may be used.

The average particle diameter of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluoropolymer), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Examples thereof include vinylidene fluoride type fluoro rubber such as rubber (VDF-CTFE type fluoro rubber), epoxy resin and the like. These binders may be used independently and may use 2 or more types together.

The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1 to 10% by mass.

As other additives other than the binder, the same additives as those in the negative electrode active material layer column can be used.

[Separator (electrolyte layer)]
The separator has a function of holding an electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

Here, in order to further improve the release of the gas generated during the initial charge of the battery from the power generation element, it is preferable to consider the release of the gas that has passed through the negative electrode active material layer and reached the separator. From such a viewpoint, it is more preferable that the air permeability and the porosity of the separator are within an appropriate range.

Specifically, the air permeability (Gurley value) of the separator is preferably 200 (seconds / 100 cc) or less. When the separator has an air permeability of 200 (seconds / 100 cc) or less, the escape of gas generated is improved, the battery has a good capacity retention rate after cycling, and the short circuit prevention and machine functions as a separator The physical properties are also sufficient. The lower limit of the air permeability is not particularly limited, but is usually 300 (second / 100 cc) or more. The air permeability of the separator is a value according to the measurement method of JIS P8117 (2009).

In addition, the porosity of the separator is preferably 40 to 65%. When the separator has a porosity of 40 to 65%, the release of the generated gas is improved, the battery has better long-term cycle characteristics, and the short circuit prevention and mechanical properties that are functions as a separator are also provided. It will be enough. For the porosity, a value obtained as a volume ratio from the density of the resin as the raw material of the separator and the density of the separator of the final product is adopted. For example, when the density of the raw material resin is ρ and the bulk density of the separator is ρ ′, the porosity is expressed by 100 × (1−ρ ′ / ρ).

Examples of the form of the separator include a separator made of a porous sheet made of a polymer or fiber that absorbs and holds the electrolyte and a nonwoven fabric separator.

As the separator of the porous sheet made of polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte.

The porosity of the nonwoven fabric separator is preferably 50 to 90%. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, and is preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

Here, the separator may be a separator in which a heat-resistant insulating layer is laminated on at least one surface of the resin porous substrate. The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the electrical device manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength. Further, the ceramic layer is preferable because it can also function as a gas releasing means for improving the gas releasing property from the power generation element.

Also, as described above, the separator includes an electrolyte. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. As the lithium _{_{_{_{salt, Li (CF 3 SO 2)}}}} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiClO 4, LiAsF 6, LiTaF such 6, LiCF ₃ SO ₃ A compound that can be added to the active material layer of the electrode can be similarly employed. The liquid electrolyte may further contain additives other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate. 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinyl vinylene carbonate, allyl ethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacrylate Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among these, vinylene carbonate, methyl vinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. These cyclic carbonates may be used alone or in combination of two or more.

The gel polymer electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. Moreover, it is excellent also in the point that the long-term cycle durability of a battery can be improved through the improvement of the adhesiveness of a separator and an active material layer. Accordingly, in a preferred embodiment of the present invention, the separator holds the gel polymer electrolyte. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Current collector]
There is no particular limitation on the material constituting the current collector, but a metal is preferably used.

Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material or different materials.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Battery exterior]
The battery outer body 29 is a member that encloses the power generation element therein, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the electric power generation element applied from the outside can be adjusted easily, the exterior body is more preferably a laminate film containing aluminum.

The internal volume of the battery exterior body 29 is configured to be larger than the volume of the power generation element 21 so that the power generation element 21 can be enclosed. Here, the internal volume of the exterior body refers to the volume in the exterior body before evacuation after sealing with the exterior body. The volume of the power generation element is the volume of the space occupied by the power generation element, and includes a hole in the power generation element. Since the inner volume of the exterior body is larger than the volume of the power generation element, there is a space in which gas can be stored when gas is generated. Thereby, the gas release property from the power generation element is improved, the generated gas is less likely to affect the battery behavior, and the battery characteristics are improved.

In automobile applications and the like, recently, larger batteries are required. The effect of the present invention of improving long-term cycle characteristics by reducing the influence of precipitates on the surface of the negative electrode active material while preventing the deformation of the graphite particles is that the amount of coating (SEI) formed on the surface of the negative electrode active material In the case of a large-area battery with a large amount, the effect is more effectively exhibited. Therefore, in this invention, it is preferable in the meaning that the effect of this invention is exhibited more that the battery structure which covered the electric power generation element with the exterior body is large sized. Specifically, the negative electrode active material layer is preferably rectangular, and the length of the short side of the rectangle is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the negative electrode active material layer refers to the side having the shortest length among the electrodes. The upper limit of the length of the short side of the battery structure is not particularly limited, but is usually 250 mm or less.

Further, as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to regulate the size of the battery from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated battery, the ratio of the battery area (projected area of the battery including the battery outer package) to the rated capacity is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. In some batteries, since the battery area per unit capacity is large, the problem of deterioration of battery characteristics (cycle characteristics) due to distortion of active material particles due to expansion / contraction due to charge / discharge cycles is more likely to be manifested. Therefore, it is preferable that the nonaqueous electrolyte secondary battery according to the present embodiment is a battery having a large size as described above, because the merit due to the expression of the effects of the present invention is greater.

Furthermore, the size of the battery can be specified by the volume energy density, the single cell rated capacity, and the like. For example, in a general electric vehicle, a travel distance (cruising range) by one charge is 100 km, which is a market requirement. Considering such cruising distance, the single cell rated capacity is preferably 20 Wh or more, and the volume energy density of the battery is preferably 153 Wh / L or more. The volume energy density and the rated discharge capacity are measured by the methods described in the following examples. Further, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular positive electrode active material layer. Setting the aspect ratio in such a range is preferable because the gas generated during charging can be discharged uniformly in the surface direction.

[Battery]
The assembled battery is configured by connecting a plurality of batteries. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series.

It is also possible to form a small assembled battery that can be attached and detached by connecting a plurality of batteries in series or in parallel. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The electric device has excellent output characteristics, maintains discharge capacity even after long-term use, and has good cycle characteristics. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the electric device can be suitably used as a vehicle power source, for example, a vehicle driving power source or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on the vehicle. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

Hereinafter, although it demonstrates in detail using an Example and a comparative example, this invention is not necessarily limited only to the following Examples.

(Example 1)
1. Preparation of Electrolyte Solution A mixed solvent (30:30:40 (volume ratio)) of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) was used as a solvent. Further, 1.0M LiPF ₆ was used as a lithium salt. Furthermore, 2% by mass of vinylene carbonate was added to the total of 100% by mass of the solvent and the lithium salt to prepare an electrolytic solution. Note that “1.0 M LiPF ₆ ” means that the lithium salt (LiPF ₆ ) concentration in the mixture of the mixed solvent and the lithium salt is 1.0 M.

2. Preparation of positive electrode Sodium hydroxide and ammonia were continuously supplied to an aqueous solution (1.0 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved at 60 ° C. to adjust the pH to 11.0. A metal composite hydroxide in which nickel, manganese, and cobalt were dissolved at a molar ratio of 50:30:20 was prepared by a coprecipitation method.

The metal composite hydroxide and lithium carbonate were weighed so that the ratio of the total number of moles of metals other than Li (Ni, Co, Mn) and the number of moles of Li was 1: 1, and then mixed well. The temperature was raised at a rate of temperature increase of 5 ° C / min, pre-baked at 450 ° C for 4 hours in an air atmosphere, then heated at a rate of temperature increase of 3 ° C / min, finally baked at 730 ° C for 10 hours, and cooled to room temperature. NMC composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ ) was obtained.

90% by weight of the positive electrode active material obtained above, 5% by weight of ketjen black (average particle size: 300 nm) as a conductive assistant, 5% by weight of polyvinylidene fluoride (PVDF) as a binder, and a slurry viscosity adjusting solvent An appropriate amount of N-methyl-2-pyrrolidone (NMP) was mixed to prepare a positive electrode active material slurry, and the obtained positive electrode active material slurry was applied to an aluminum foil (thickness: 20 μm) as a current collector. After drying at 0 ° C. for 3 minutes, a positive electrode was produced by compression molding with a roll press. Similarly, a positive electrode active material layer was formed on the back surface to produce a positive electrode in which a positive electrode active material layer was formed on both surfaces of a positive electrode current collector (aluminum foil).

3. Production of negative electrode Artificial graphite (average particle diameter (D50): 20.2 μm, BET specific surface area: 3.5 m ^{2 /} g) 48.5% by mass as a negative electrode active material, coated natural graphite (average particle diameter (D50): 21 0.1 μm, BET specific surface area: 2.0 m ^{2 /} g) A solid content of 48.5% by mass, ² % by mass of SBR as a binder, and 1% by mass of CMC was prepared. An appropriate amount of ion-exchanged water, which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to both sides of a copper foil (10 μm) as a current collector, dried and pressed, and a negative electrode having a thickness of 130 μm (including foil) was produced.

In addition, the BET specific surface area of the negative electrode active material, the initial charge capacity and the initial efficiency of the obtained negative electrode were measured by the following methods. The results are shown in Table 1 below.

[BET specific surface area]
The BET specific surface area of the negative electrode active material can be measured using the AMS8000 type automatic powder specific surface area measuring device (manufactured by Okura Riken), nitrogen as the adsorbing gas, helium as the carrier gas, and BET one-point method measurement by continuous flow went. Specifically, the powder sample is heated and deaerated with a mixed gas at a temperature of 150 ° C., then cooled to liquid nitrogen temperature to adsorb the nitrogen / helium mixed gas, and then heated to room temperature with water. The adsorbed nitrogen gas was desorbed, the amount was detected by a heat conduction detector, and the specific surface area of the sample was calculated from this.

4). Step of completing cell The positive electrode produced above was cut into a 220 × 200 mm rectangular shape, and the negative electrode was cut into a 225 × 205 mm rectangular shape (20 positive electrodes and 21 negative electrodes). The positive electrode and the negative electrode were alternately laminated via 230 × 210 mm separators (polyolefin microporous membrane, thickness 25 μm).

A tab is welded to each of the positive electrode and the negative electrode, and the battery is completed by sealing together with the electrolyte in an exterior body made of an aluminum laminate film, a urethane rubber sheet (thickness 3 mm) larger than the electrode area, and an Al plate (thickness) A cell was completed by sandwiching and pressing the battery at 5 mm).

(Examples 2 to 8 and Comparative Examples 1 to 6)
Instead of adopting the negative electrode active material composition described in Table 1 below in place of the composition of the negative electrode active material in Example 1 described above (artificial graphite: coated natural graphite = 50: 50 (mass%)) A battery was produced in the same manner as in Example 1. Natural graphite having an average particle diameter (D50) of 20.1 μm and a BET specific surface area of 5.5 m ² / g was used.

And about the obtained battery, the single cell rated capacity, volume energy density, initial charge / discharge efficiency, capacity maintenance rate after 1000 cycles, and initial cruising distance were obtained by the following methods. The results are shown in Table 1 below.

[Single cell rated capacity and volumetric energy density]
The batteries produced in each Example and Comparative Example were allowed to stand for 24 hours, and after the open circuit voltage (OCV) was stabilized, the current density with respect to the positive electrode was 0.2 mA / cm ² and the cut-off voltage was 4.15 V. The battery was charged to obtain an initial charge capacity, and the capacity when discharged to a cut-off voltage of 3.0 V after 1 hour of rest was defined as a single cell rated capacity (Wh). Moreover, the energy density per volume (volume energy density; Wh / L) was computed based on this.

[Capacity maintenance rate after 1000 cycles]
The current density with respect to the positive electrode was set to ² mA / cm ² , and the batteries produced in each Example and Comparative Example were charged to a cutoff voltage of 4.15 V to obtain an initial charge capacity, and discharged to a cutoff voltage of 3.0 V after 1 hour of rest. The capacity at this time was defined as the initial discharge capacity. This charge / discharge cycle was repeated 1000 times. The ratio of the discharge capacity at the 1000th cycle to the initial discharge capacity was calculated.

From the results shown in Table 1, it can be seen that according to the mixed negative electrode according to the present invention, the capacity retention rate after 1000 cycles can be improved.

(Relationship between specific surface area ratio and gas generation)
Further, for the batteries of Examples 1 to 8 produced above, the values of the BET specific surface areas of all graphite particles selected from the group consisting of artificial graphite, coated natural graphite and natural graphite contained in the negative electrode active material, The value of the ratio of the coated natural graphite to the value of the BET specific surface area was calculated ("specific surface area ratio" in Table 2 below). Moreover, the gas amount [cc] generated at the time of the first charge / discharge was measured by Archimedes method as the difference between the cell volume in the discharge state after the first charge / discharge and the cell volume one day after the injection (before the first charge / discharge) ( Table 2 below). Furthermore, the tact time [sec] in the degassing process was measured (Table 2 below). Here, in the degassing step, a part of the laminate cell was cut in order to degas, and the pressure in the cell was reduced by using a large vacuum sealer made by Tosei. In addition, this vacuum sealer can seal a laminate cut part after pressure reduction. If the tact time in the degassing process exceeds 30 seconds, the time until the gas is completely discharged from the power generation element (laminate structure) increases.

From the results shown in Table 2, it can be seen that if the specific surface area ratio is 1.7 or less, the amount of gas generated during the initial charge / discharge can be sufficiently reduced, and the tact time in the degassing process can be shortened.

(Examples 9 to 12)
In place of the artificial graphite and coated natural graphite used in Example 1 above, artificial graphite and coated natural graphite having different average particle diameters were used, and the median diameter (D50) was measured by a laser diffraction particle size distribution meter. A battery was produced in the same manner as in Example 1 except that the average particle size of the negative electrode active material was controlled to the value shown in Table 3 below, and the physical properties and characteristics were evaluated in the same manner. The results are shown in Table 3 below.

From the results shown in Table 3, it can be seen that when the D50 of the negative electrode active material is a value within the range of 10 to 30 μm, the long-term cycle characteristics are excellent.

(Examples 13 to 29)
A battery was prepared in the same manner as in Example 1 described above except that the cell size (and volume energy density and single cell rated capacity) of Example 1 was changed as shown in Table 4 below. And the characteristics were evaluated. The results are shown in Table 4 below. As for the cruising distance, the cruising distance in the JC08 mode by the first charging was defined as the cruising distance.

From the results shown in Table 4, the volume energy density and battery capacity at which a cruising range of 100 km can be achieved are known.

(Examples 30 to 31)
In place of LiNi _0.50 Mn _0.30 Co _0.20 O ₂ , LiNi _0.50 Mn _0.30 Co _0.20 Zr _0.01 O ₂ (Example 30) or LiNi _{0. A} battery was produced in the same manner as in Example 1 except that ₅₀ Mn _0.30 Co _0.20 Al _0.01 O ₂ (Example 31) was used, and the physical properties and characteristics were evaluated in the same manner. . In addition, for Example 1 and Examples 30 to 31, the batteries were disassembled in a 4.25 V charged state, the differential thermal analysis (DSC) of the positive electrode was performed, and the heat generation start temperature was determined. These results are shown in Table 5 below.

From the results shown in Table 5, when Zr or Al is further added as an additive element to the NMC composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ ) used in Example 1, the heat generation start temperature is increased. You can see that it rises.

(Example 32)
Sodium hydroxide and ammonia are supplied to an aqueous solution (1.0 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved so that the pH is 11.0, and the molar ratio of nickel, cobalt, and manganese is determined by a coprecipitation method. A metal composite hydroxide obtained by solid solution at 1/3: 1/3: 1/3 was prepared. The metal composite oxide and lithium carbonate were weighed so that the ratio of the total number of moles of metals other than Li (Ni, Co, Mn) to the number of moles of Li was 1: 1, and then mixed sufficiently. The temperature was raised at a temperature rate of 5 ° C./min, fired at 920 ° C. for 10 hours in an air atmosphere, cooled to room temperature, and LiNi _1/3 Mn _1/3 Co _1/3 O _{2 serving} as a shell material was obtained.

Next, with respect to the NMC composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ 100% by mass produced in Example 1, LiNi _1/3 Mn so that the mass percentage becomes 5% by mass. _1/3 Co _1/3 (NMC111) was mixed and subjected to mechanical treatment for 30 minutes using a pulverizer, and then fired again at 930 ° C. for 10 hours in an air atmosphere to obtain LiNi _{0 as a} core. A positive electrode material in which 5% by mass of LiNi _1/3 Mn _1/3 Co _1/3 was coated on the surface of secondary particles of _.5 Mn _0.3 Co _0.2 O ₂ was obtained.

A battery was produced in the same manner as in Example 1 except that the positive electrode material obtained above was used instead of the positive electrode active material in Example 1, and the physical properties and characteristics were evaluated in the same manner. In addition, also in Example 32, the battery was disassembled in a 4.25 V charged state, and differential thermal analysis (DSC) of the positive electrode was performed to determine the heat generation start temperature. These results are shown in Table 6 below.

(Example 33)
As described above, except that LiNi _0.8 Co _0.1 Al _0.1 O ₂ (NCA) was used in place of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC111) as the shell material. A battery was produced in the same manner as in Example 32, and the physical properties and characteristics were evaluated in the same manner. The results are shown in Table 6 below.

(Example 34)
A battery was fabricated in the same manner as in Example 32 described above except that LiCoO ₂ (LCO) was used instead of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (NMC111) as the shell material. In the same manner, physical properties and characteristics were evaluated. The results are shown in Table 6 below.

From the results shown in Table 6, the NMC composite oxide (LiNi _0.50 Mn _0.30 Co _0.20 O ₂ ) used in Example 1 was used as a core, and further coated with a shell material. It can be seen that the heat generation start temperature can be increased when the positive electrode material of the mold is used.

(Example 35)
In the production of the battery of Example 1, a battery was produced in the same manner as in Example 1 except that the gel electrolyte was used as described below. That is, an electrode element is formed by laminating a positive electrode plate and a negative electrode plate having current collecting elements through a heat-resistant separator previously coated with a matrix polymer (polyvinylidene fluoride-hexafluoropropylene copolymer) that forms a gel. Produced. After storing this in a laminate film, a predetermined amount of electrolyte solution was injected and further heat-treated to produce a laminate battery having a length of 280 mm, a width of 210 mm, and a thickness of 7 mm, and the physical properties and characteristics were evaluated in the same manner as described above. The results are shown in Table 7 below.

From the results shown in Table 7, it can be seen that long-term cycle durability is improved when a gel polymer electrolyte is used instead of the liquid electrolyte.

(Examples 36 to 41)
The following negative electrode active material was further added to a total of 100% by mass of the graphite crystal mixture (artificial graphite 50% by mass + coated natural graphite 50% by mass) as the negative electrode active material used in Example 1 described above. A battery was produced in the same manner as in Example 1 except that the physical properties and characteristics were evaluated in the same manner. The results are shown in Table 8 below. In forming the negative electrode active material layer, 97% by mass was used as a negative electrode active material to which the following carbon materials were added, and 2% by mass of SBR and 1% by mass of CMC were added thereto.
Example 36: 1% by mass of hard carbon (non-graphitizable carbon material)
Example 37: 5% by mass of hard carbon (non-graphitizable carbon material)
Example 38: Hard carbon (non-graphitizable carbon material) 10% by mass
Example 39: 1% by mass of soft carbon (easily graphitized carbon material)
Example 40: 5% by mass of soft carbon (easily graphitized carbon material)
Example 41: 10% by mass of soft carbon (easily graphitized carbon material)

From the results shown in Table 8, it can be seen that the long-term cycle durability can be further improved when the negative electrode active material further contains hard carbon or soft carbon.

This application is based on Japanese Patent Application No. 2013-040113 filed on February 28, 2013, the disclosure of which is incorporated by reference in its entirety.

10 Lithium ion secondary battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layer,
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 Battery outer package.

Claims

A current collector,
A negative electrode active material layer including a negative electrode active material, disposed on a surface of the current collector;
Have
The negative electrode active material contains artificial graphite, coated natural graphite or natural graphite as a main component, the content of artificial graphite contained in the negative electrode active material is X [mass%], and the content of coated natural graphite is Y [mass %] And the content of natural graphite is Z [mass%] (where X + Y + Z = 100 mass%), Y ≧ Z and Y ≧ X are satisfied (where (X, Y, Z ) = (Except in the case of (0, 1, 0)), a negative electrode for a non-aqueous electrolyte secondary battery.
The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material further contains hard carbon or soft carbon.
The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the median diameter (D50) of the negative electrode active material measured by a laser diffraction particle size distribution analyzer is 10 to 30 µm.
The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the negative electrode active material has a BET specific surface area of 0.5 to 10 m 2 / g.
The value of the ratio of the BET specific surface area value of all graphite particles selected from the group consisting of artificial graphite, coated natural graphite and natural graphite contained in the negative electrode active material to the BET specific surface area value of the coated natural graphite is The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, which is 1.7 or less.
The negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein a tap density of the negative electrode active material is 0.7 g / cm 3 or more.
The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the negative electrode active material layer contains an aqueous binder.
The non-aqueous electrolyte according to claim 7, wherein the aqueous binder includes at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber. Negative electrode for secondary battery.
The negative electrode for a nonaqueous electrolyte secondary battery according to claim 8, wherein the aqueous binder contains styrene-butadiene rubber.
A positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on the surface of the positive electrode current collector;
A negative electrode according to any one of claims 1 to 9,
A separator interposed between the positive electrode and the negative electrode to hold a liquid electrolyte or a gel electrolyte;
A non-aqueous electrolyte secondary battery in which a power generation element having a structure is enclosed in an exterior body.
The non-aqueous electrolyte secondary battery according to claim 10, wherein the positive electrode active material includes a composite oxide containing lithium and nickel.
The nonaqueous electrolyte secondary battery according to claim 10 or 11, wherein the outer package is a laminate film containing aluminum.
The ratio of the battery area to the rated capacity (projected area of the battery including the battery outer casing) is 5 cm 2 / Ah or more, and the rated capacity is 3 Ah or more. The non-aqueous electrolyte secondary battery described in 1.
The non-aqueous electrolyte secondary battery according to any one of claims 10 to 13, wherein an aspect ratio of the electrode defined as an aspect ratio of the rectangular positive electrode active material layer is 1 to 3.