JP2006107753A - Coating composition for cathode active substance layer, cathode plate for nonaqueous electrolyte solution secondary battery, and nonaqueous electrolyte solution secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating composition for a cathode active substance layer capable of stably manufacturing a cathode plate for a nonaqueous electrolyte solution secondary battery hardly generating tailing at coating, excellent in battery safety, and with enough battery capacity, to provide a cathode plate for a nonaqueous electrolyte solution secondary battery hardly generating tailing, excellent in battery safety, and with enough battery capacity, as well as to provide a nonaqueous electrolyte solution secondary battery of high capacity and high quality assembled with the cathode plate. <P>SOLUTION: The coating composition for the cathode active substance layer contains 100 weight parts of cathode active substance, 0.5 to 2.5 weight parts of a conductive material, and 1.7 to 3.7 weight parts of a binding material, in which the binding material contains polyvinylidene fluoride with a weighted average molecular weight of 300 to 400 thousand by 50 wt.% or more in reference to a total binding material volume. Further, the cathode plate for the nonaqueous electrolyte solution secondary battery and the secondary battery using the cathode have the coating composition for the cathode active substance layer provided at one or both faces of a collector. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses a positive electrode active material layer coating composition for a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a positive electrode plate for a non-aqueous electrolyte secondary battery, and the positive electrode plate. The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, electronic devices and communication devices are rapidly becoming smaller and lighter, and secondary batteries used as power sources for driving these devices are also required to be smaller and lighter. For this reason, in place of the conventional alkaline storage battery, a non-aqueous electrolyte secondary battery having a high energy density and a high voltage, typically a lithium ion secondary battery has been proposed.

  A positive electrode plate (positive electrode plate) of a nonaqueous electrolyte secondary battery uses a composite oxide such as lithium manganate or lithium cobaltate as a positive electrode active material, and such a positive electrode active material and a binder ( A binder) is dispersed or dissolved in a suitable wetting agent (solvent) to prepare a slurry-like coating composition, and the coating composition is applied onto a current collector made of metal foil. It is produced by forming a material layer.

  On the other hand, the negative electrode plate (negative electrode plate) of the non-aqueous electrolyte secondary battery is made of a carbonaceous material such as carbon that can occlude cations such as lithium ions released from the positive electrode active material layer during charging. The negative electrode active material and the binder (binder) are dispersed or dissolved in an appropriate wetting agent (solvent) to prepare a slurry-like coating composition, and the coating composition is used as a metal foil. The negative electrode active material layer is formed by coating on a current collector made of

  Then, by attaching terminals for taking out current to each of the positive electrode plate and the negative electrode plate, sandwiching a separator for preventing a short circuit between the two electrode plates, winding it, and sealing it in a container filled with the nonaqueous electrolyte solution A secondary battery is assembled.

  In recent years, there has been a demand for higher capacity / high performance non-aqueous electrolyte secondary batteries, and various improvements have been made. For example, in order to increase the amount of the electrode active material in a certain volume, a method of densifying the electrode by pressing the electrode a plurality of times in a pressing step can be mentioned. In addition, in order to increase the amount of the active material directly attributable to the battery capacity in the active material layer, the active material ratio in the active material layer is increased, the active material layer coating amount is increased, the polymer binding is increased. The use of dressing materials has been made. However, by increasing the ratio of the active material, the adhesiveness becomes worse due to the relative decrease in the amount of the binder, and the workability at the time of pressing and cutting is deteriorated. Further, when the conductive material is relatively reduced, the formation of the conductive path becomes insufficient, the resistance of the coating film is increased, and the battery performance is deteriorated such as deterioration of cycle characteristics and increase of internal resistance.

  In addition, when the coating amount of the coating composition using the polymer binder is increased, the accuracy of forming the terminal part at the time of coating is reduced, and the coating terminal part is more tailed than the design. There is a problem that the tail becomes long, that is, tailing as shown in FIG. 1 occurs. FIG. 1A is a partially enlarged schematic view of the electrode plate viewed from the cross-sectional direction. In FIG. 1A, the positive electrode plate 1 has a positive electrode active material layer 4 formed on one surface of a current collector 3, but a tail 6 is generated at the end in the coating direction 5. On the other hand, in the negative electrode plate 2, the negative electrode active material layer 7 is formed on one surface of the current collector 3 without causing tailing. And the said positive electrode plate 1 and the negative electrode plate 2 are arrange | positioned facing the active material layer like the inside of a battery. FIG. 1B is a partially enlarged schematic view of the positive electrode plate as viewed from above.

  When a positive electrode plate with such tailing and a negative electrode plate without tailing are wound up as designed, there may be no negative electrode as a counter electrode in the part that is longer than the design of the positive electrode plate. Comes out. As a result, a short circuit may occur in a portion where the positive electrode is opposed but the negative electrode is not present, heat may be generated, and a problem may occur in battery safety. On the other hand, with emphasis on the safety of the battery, if the length of the coating part is included by adding the tail part, the coating amount of the tail part is reduced with respect to the length of the coating part. As a result, there was a problem that the battery capacity was insufficient.

  The present invention has been accomplished in view of the above-mentioned circumstances, and the first object thereof is a non-aqueous electrolyte secondary that is less likely to cause tailing during coating, has excellent battery safety, and has sufficient battery capacity. It is providing the coating composition for positive electrode active material layers which can manufacture the positive electrode plate for batteries stably.

  A second object of the present invention is to provide a positive electrode plate for a non-aqueous electrolyte secondary battery that is less prone to tailing, is excellent in battery safety, and has a sufficient battery capacity.

  The third object of the present invention is to provide a high-capacity and high-quality non-aqueous electrolyte secondary battery that is assembled using the electrode plate and is excellent in safety.

  The positive electrode active material layer coating composition according to the present invention is a positive electrode active material layer coating composition containing at least a positive electrode active material, a conductive material and a binder, and 100 parts by weight of the positive electrode active material, Polyvinylidene fluoride containing 0.5 to 2.5 parts by weight of a conductive material and 1.7 to 3.7 parts by weight of a binder, and having a weight average molecular weight of 300,000 to 400,000 as the binder In an amount of 50% by weight or more based on the total amount of the binder.

  The positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention has 100 parts by weight of the positive electrode active material, 0.5 to 2.5 parts by weight of the conductive material, and 1.7 to 3 parts of the binder. An active material layer containing 7 parts by weight and containing, as the binder, 50% by weight or more of polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 based on the total amount of the binder; It is provided on one side or both sides.

  In the present invention, the positive electrode active material, the conductive material, and the binder are blended at the specific ratio, and the binder is mainly composed of polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000. Since it is selected and used, it does not easily cause tailing during coating, has excellent battery safety, and can stably produce a positive electrode plate for a non-aqueous electrolyte secondary battery with sufficient battery capacity. A construction composition can be realized. Further, by using the composition, it is possible to provide a positive electrode plate for a non-aqueous electrolyte secondary battery that hardly causes tailing, is excellent in battery safety, and has a sufficient battery capacity.

In the coating composition for a positive electrode active material layer and the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention, the conductive material has a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ^3. It is preferable to contain at least carbon black. In this case, the volume resistance value is kept low, and problems such as deterioration in cycle characteristics and increase in internal resistance are unlikely to occur.

Moreover, in the coating composition for positive electrode active material layers and the positive electrode plate for non-aqueous electrolyte secondary battery according to the present invention, the conductive material has a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / It is preferable to contain at least carbon black of m ³ and carbon black having a specific gravity of 2.2 g / cc or more. In this case, the volume resistance value is kept low, problems such as deterioration of cycle characteristics and increase in internal resistance are unlikely to occur, and the porosity of the active material layer is increased and the liquid injection property is improved. Furthermore, since the porosity becomes high, the amount of the binder can be made relatively high. As a result, the non-aqueous electrolyte secondary battery has good adhesion and excellent workability during pressing and cutting. A positive electrode plate can be manufactured.

  Furthermore, in the positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the active material layer is provided on both sides according to the test method of JIS-K6854-1, for the adhesion of the active material layer to the current collector. In this case, it is preferably 10 N / m or more, and when the active material layer is provided on one side, it is preferably 4 N / m or more from the viewpoint of excellent workability at the time of pressing or cutting.

  Further, in the positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the volume resistivity of the active material layer is 200 Ω · cm or less according to the test method of JIS-K7194. It is preferable from the point that the rise of is difficult to occur.

Furthermore, in the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention, the coating amount of the active material layer is 300 to 800 g / m ² in terms of the total amount on both sides of the current collector. It is preferable from the point.

  In the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention, the density of the active material layer after pressing is preferably 1.85 to 4.35 g / cc from the viewpoint of battery characteristics.

  Next, the non-aqueous electrolyte secondary battery according to the present invention includes the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention. In this secondary battery, the electrode plate loaded therein is less likely to be tailed, has excellent battery safety, and has a sufficient battery capacity. Therefore, the secondary battery has excellent safety and high capacity and high quality.

  The coating composition for a positive electrode active material layer of the present invention comprises a positive electrode active material, a conductive material, and a binder in the above-mentioned specific proportions, and has a weight average molecular weight of 300,000 to 40 as the binder. Since the selected polyvinylidene fluoride is used as the main component, it is difficult to cause tailing during coating, and the positive electrode plate for non-aqueous electrolyte secondary batteries with excellent battery safety and sufficient battery capacity is stable. Can be manufactured.

  The positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention contains, in the active material layer, the positive electrode active material, the conductive material, and the binder in the specific ratio, and the main material of the binder. Since the component is polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000, tailing hardly occurs, battery safety is excellent, and battery capacity is sufficient.

In particular, in the coating composition for a positive electrode active material layer and the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention, the conductive material has a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / When at least carbon black of m ³ and carbon black with a specific gravity of 2.2 g / cc or more are contained, the volume resistance value is kept low, causing problems such as deterioration of cycle characteristics and increase of internal resistance. In addition, it has the effect that the porosity of the active material layer is increased and the liquid injection property is increased. Furthermore, since the porosity becomes high, the amount of the binder can be made relatively high. As a result, the non-aqueous electrolyte secondary battery has good adhesion and excellent workability during pressing and cutting. The positive electrode plate can be manufactured.

  In addition, the nonaqueous electrolyte secondary battery according to the present invention has an electrode plate loaded therein, without tailing, excellent battery safety, sufficient battery capacity, and good adhesion, Excellent workability at the time of pressing and cutting, so it has excellent safety and high capacity and high quality.

<Coating composition for positive electrode active material layer>
The positive electrode active material layer coating composition according to the present invention is a positive electrode active material layer coating composition containing at least a positive electrode active material, a conductive material and a binder, and 100 parts by weight of the positive electrode active material, Polyvinylidene fluoride containing 0.5 to 2.5 parts by weight of a conductive material and 1.7 to 3.7 parts by weight of a binder, and having a weight average molecular weight of 300,000 to 400,000 as the binder In an amount of 50% by weight or more based on the total amount of the binder.

  The main component of the binder used in the present invention, that is, the binder used by 50% by weight or more based on the total amount of the binder is polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000. Here, the weight average molecular weight is one measure indicating the average molecular weight of a polymer having a non-uniform molecular weight, and in this specification, refers to a weight average molecular weight in terms of polystyrene by gel permeation chromatography. For example, a 0.13 M LiCl solution in N-methyl-2-pyrrolidone was flowed at a flow rate of 1 ml / min through a Plgel Mixed B column manufactured by Polymer Laboratories held at 80 ° C., and 0.4 weight of polyvinylidene fluoride was added thereto. Inject 0.1 ml of% N-methyl-2-pyrrolidone solution and measure the outflow time and outflow amount. Moreover, the same measurement is performed using several types of polystyrene having a known molecular weight, and a calibration curve is created from this, and the weight average molecular weight of polyvinylidene fluoride is determined. The apparatus is not particularly limited.

  The polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 is more preferably polyvinylidene fluoride having a weight average molecular weight of 300,000 to 350,000. Examples of commercially available products that can be used as polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 in the present invention include SOLEF # 1013 (manufactured by SOLVAY), KF # 1300 (manufactured by Kureha Chemical Industry), and the like. . Among these, SOLEF # 1013 (manufactured by SOLVAY) is preferable because tailing does not occur.

  In the present invention, polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 is less likely to cause a tail during coating of the active material layer coating composition, and therefore is based on the total binder amount of 50. Containing at least% by weight. Among them, it is preferable that a polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 is contained in a large amount from the viewpoint of making tailing difficult to occur, and 50% by weight or more based on the total amount of binder, It is preferable to contain 70% by weight or more based on the amount of binder, and particularly 100% by weight based on the total amount of binder.

  On the other hand, from the viewpoint of balance with other physical properties, the other binder is used in combination with polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000, with the upper limit being 50% by weight based on the total amount of the binder. May be. Other binders used in combination include, for example, thermoplastic resins, more specifically polyester resins, polyamide resins, polyacrylate resins, polycarbonate resins, polyurethane resins, cellulose resins, polyolefin resins, polyvinyl resins, Fluorine resins such as polyvinylidene fluoride and vinylidene fluoride copolymers having a weight average molecular weight other than 300,000 to 400,000, or rubber resins such as polyimide resin or styrene butadiene rubber can be used. In addition, thermosetting resins such as urethane resins, ionizing radiation curable resins composed of acrylate monomers, acrylate oligomers, or mixtures thereof, and mixtures of the various resins described above can also be used.

  Further, as the vinylidene fluoride copolymer, a copolymer of 80 mol% or more of vinylidene fluoride and 20 mol% or less of one or more monomers copolymerizable with vinylidene fluoride is preferably used. be able to. In this case, other functions for improving physical properties can be imparted to the copolymerized monomer. Examples of monomers copolymerizable with vinylidene fluoride include hydrocarbon monomers such as ethylene and propylene; vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether Or a fluorine-containing monomer such as allyl glycidyl ether or crotonic acid glycidyl ester may be contained as a copolymer component. In order to further improve the adhesion to current collectors such as metals, monoesters of unsaturated dibasic acid, vinylene carbonate, etc. were copolymerized to introduce polar groups such as carbonyl groups, carboxyl groups, etc. A copolymer may be used. Furthermore, in a solvent that dissolves or swells the vinylidene fluoride polymer, a silane coupling agent or titanate cup having both a reactive group and a hydrolyzable group with a vinylidene fluoride polymer such as an amino group or a mercapto group. You may use the modified vinylidene fluoride polymer processed in a ring agent.

  In the present invention, as the other binder used in combination with polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000, polyvinylidene fluoride is preferable from the viewpoint of battery characteristics, and the weight average molecular weight is more than 400,000. Large polyvinylidene fluoride is preferred.

  In the present invention, the mixing ratio of the binder in the coating composition for the positive electrode active material layer is a non-aqueous electrolyte secondary battery that does not easily generate a tail during coating, has excellent battery safety, and has a sufficient battery capacity. From the point that the positive electrode plate can be stably manufactured, the binder is 1.7 to 3.7 parts by weight with respect to 100 parts by weight of the positive electrode active material. Among these, from the viewpoint of balance between battery safety and battery capacity, the positive electrode active material is preferably 100 to parts by weight, and the binder is preferably 1.7 to 3.0 parts by weight, and more preferably 1.7 to 2. 8 parts by weight is preferred.

On the other hand, as the positive electrode active material, a material conventionally used as a positive electrode active material of a non-aqueous electrolyte secondary battery can be used. For example, LiMn ₂ O ₄ (lithium manganate), LiCoO ₂ ( Examples thereof include lithium oxides such as lithium cobaltate) or LiNiO ₂ (lithium nickelate), or chalcogen compounds such as TiS ₂ , MnO ₂ , MoO _3, or V ₂ O ₅ . In particular, by using LiCoO ₂ as the positive electrode active material and the carbonaceous material as the negative electrode active material, a lithium secondary battery having a high discharge voltage of about 4 volts can be obtained.

  The positive electrode active material is preferably a powder having a particle diameter in the range of 1 to 100 μm and an average particle diameter of 3 to 30 μm in order to uniformly disperse it in the coating layer. These positive electrode active materials may be used alone or in combination of two or more.

  The blending ratio of the positive electrode active material in the coating composition for the positive electrode active material layer may be 90 to 98.5% by weight on the basis of solid content from the viewpoint of realizing a high battery capacity and cycle characteristics. More preferably, it is preferable to set it as 96 to 98.5 weight%.

  Examples of the conductive material used in the present invention include carbonaceous materials such as graphite, carbon black, and acetylene black.

The conductive material contains at least carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ , the volume resistance value is kept low, and the cycle characteristics are deteriorated. This is preferable because problems such as an increase in internal resistance are unlikely to occur.

When carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ is used, the conductivity is ensured even if only a small amount is used, and the volume resistivity is low. Aggregation of the material hardly occurs and the material is uniformly dispersed, so that current stagnation due to aggregation can be prevented and storage stability is improved. Here, the BET specific surface area refers to a BET specific surface area by a nitrogen adsorption method, and can be determined by ASTM D3037-89. The density can be determined by ERACHEM26. Examples of the carbon black exhibiting the above properties include SuperP manufactured by MMMCarbon (BET specific surface area of 62 ± 5 m ² / g, density of 160 ± 20 kg / m ³ ).

Further, the conductive material contains at least carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ and a specific gravity of 2.2 g / cc or more. Is preferred. In particular, the carbon black preferably has a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ and a carbon black having a specific gravity of 2.2 g / cc or more.

  When carbon black having a specific gravity of 2.2 g / cc or more is used, the volume resistance value can be lowered and the porosity of the active material layer can be maintained or increased by the large specific gravity. The carbon black having a specific gravity of 2.2 g / cc or more is preferably carbon black having a specific gravity of 2.5 g / cc or more. Examples of carbon black having a specific gravity of 2.2 g / cc or more include, for example, Timcal Co. Ltd .. Manufactured by KS4.

Therefore, the conductive material contains carbon black having a BET specific surface area of 57 to 67 m ² / g and density of 140 to 180 kg / m ³ and carbon black having a specific gravity of 2.2 g / cc or more in combination. In such a case, the volume resistance value is suppressed to a low level, and problems such as deterioration of cycle characteristics and an increase in internal resistance are unlikely to occur. In addition, the porosity of the active material layer increases and the liquid injection property increases. Furthermore, since the porosity becomes high, the amount of the binder can be made relatively high. As a result, the non-aqueous electrolyte secondary battery has good adhesion and excellent workability during pressing and cutting. The positive electrode plate can be manufactured.

The carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ may contain 50 to 100% by weight, further 70 to 90% by weight, based on the total amount of conductive material. preferable. Carbon black having a specific gravity of 2.2 g / cc or more is preferably contained in an amount of 0 to 50% by weight, more preferably 10 to 30% by weight, based on the total amount of conductive material.

Further, when both the carbon black (1) having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ and a carbon black (2) having a specific gravity of 2.2 g / cc or more are contained. The content ratio of (1) :( 2) = 1: 1 to 6: 1, more preferably 3: 1 to 5: 1.

  The blending ratio of the conductive material in the coating composition is 0.5 to 4.0 parts by weight of the conductive material from the viewpoint of conductivity and battery performance with respect to 100 parts by weight of the positive electrode active material. Furthermore, it is preferable that it is 1.0-2.5 weight part.

  As a solvent for preparing the coating composition for the positive electrode active material layer, an organic solvent such as toluene, methyl ethyl ketone, N-methyl-2-pyrrolidone, or a mixture thereof can be used. The solvent in the coating composition is usually blended so that the solid content is 40 to 85% by weight, preferably 50 to 80, more preferably 60 to 80% by weight, based on the entire composition, Is prepared in a slurry state.

  The coating composition for the positive electrode active material layer is prepared by placing an appropriately selected positive electrode active material, a binder, a conductive material, and other blending components in an appropriate solvent, and a homogenizer, ball mill, sand mill, roll mill, or planetary mixer. It can be mixed and dispersed by a dispersing machine such as a slurry to prepare a slurry.

  The coating composition for the positive electrode active material layer according to the present invention has a volume resistivity of 200 Ω · cm or less after standing at 25 ° C. for 5 days after preparation, storage stability, and low volume resistivity. This is preferable from the viewpoint of realizing an active material layer and improving the cycle characteristics of the battery. In addition, volume resistivity is a resistivity meter about the obtained coating film which applied and dried so that the coating film after drying the active material layer coating composition may be 100 μm on one side of a 100 μm PET film. (For example, manufactured by Mitsubishi Chemical, Loresta-EP) and measured by a four-terminal four-probe method.

<Positive electrode plate for non-aqueous electrolyte secondary battery>
The positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention is 100 parts by weight of the positive electrode active material, 0.5 to 2.5 parts by weight of the conductive material, and 1.7 to 3.7 of the binder. An active material layer containing 50 parts by weight or more of polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 as the binder, based on the total amount of binder, Alternatively, it is provided on both sides.

  The positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention contains, in the active material layer, the positive electrode active material, the conductive material, and the binder in the specific ratio, and the main material of the binder. Since the component is polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000, tailing hardly occurs, battery safety is excellent, and battery capacity is sufficient.

  The positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode active material layer coating composition containing at least a positive electrode active material, a binder, and a conductive material on one side or both sides of a current collector. It is produced by coating to form a positive electrode active material layer.

  The active material layer of the positive electrode plate contains at least a positive electrode active material, a binder and a conductive material, and further contains other components as necessary, and is contained in the dried active material layer. The mixing ratio of each component is the same as the mixing ratio based on the solid content of the coating composition for the positive electrode active material layer. Therefore, the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention is a positive electrode active material layer coating composition containing at least a positive electrode active material, a conductive material, and a binder. Parts by weight, 0.5 to 2.5 parts by weight of a conductive material and 1.7 to 3.7 parts by weight of a binder, and the binder has a weight average molecular weight of 300,000 to 400,000 Using the coating composition for a positive electrode active material layer according to the present invention, which contains 50% by weight or more of polyvinylidene fluoride based on the total amount of the binder, applied to one side or both sides of the current collector, It can be manufactured by forming an active material layer.

  In general, an aluminum foil is preferably used as the current collector of the positive electrode plate. The thickness of the current collector is usually about 5 to 50 μm.

  A method for applying the coating composition for the positive electrode active material layer is not particularly limited, but a method capable of forming a thick coating layer such as a slide die coat, a comma direct coat, a comma reverse coat, and the like is suitable. However, when the thickness required for the active material layer is relatively thin, it may be applied by gravure coating or gravure reverse coating. The active material layer may be formed by repeating application and drying a plurality of times.

  Whether or not tailing occurs at the time of coating can be evaluated by the presence and length of a portion that is longer than the set length at the terminal end in the coating direction.

  As a heat source in the drying process, hot air, infrared rays, far infrared rays, microwaves, high frequencies, or a combination thereof can be used. You may dry with the heat which discharge | released the metal roller and metal sheet which support or press a collector in a drying process. In addition, after drying, the active material layer can also be obtained by irradiating an electron beam or radiation to cause a crosslinking reaction of the binder. Application and drying may be repeated a plurality of times.

  Furthermore, the density of the active material layer, the adhesion to the current collector, and the homogeneity can be improved by pressing the obtained positive electrode active material layer.

  The press working is performed using, for example, a metal roll, an elastic roll, a heating roll, a sheet press machine, or the like. In the present invention, the pressing temperature may be performed at room temperature or may be performed as long as the temperature is lower than the temperature for drying the coating film of the active material layer. As a guide, it is 15 to 35 ° C.).

  The roll press is preferable because a long sheet-like positive electrode plate can be continuously pressed. When performing the roll press, either a stereotaxic press or a constant pressure press may be performed. The line speed of the press is usually 5 to 50 m / min. And When the pressure of the roll press is managed by linear pressure, the pressure is adjusted according to the diameter of the pressure roll, but the linear pressure is usually 500 kgf / cm to 2000 kgf / cm.

The coating amount of the positive electrode active material layer, 300 to 800 g / m ² in a total amount of both surfaces of the collector and further, it is 400~700g / m ² is preferable from the viewpoint of sufficiently the battery capacity. The thickness is preferably 10 to 200 μm, preferably 50 to 190 μm after drying and pressing. The density of the positive electrode active material layer is about 2.0 g / cc after coating, but increases to 3.0 g / cc or more after pressing. Therefore, the capacity of the battery can be increased by improving the volume energy density by performing the pressing without hindrance. In the positive electrode plate for a non-aqueous electrolyte secondary battery of the present invention, the density of the active material layer after pressing is 1.85 to 4.35 g / cc, and further 2.5 to 4.0 g / cc. Is preferable from the viewpoint of sufficient battery capacity.

  In the electrode plate of the present invention, the volume resistivity of the active material layer is 200 Ω · cm or less by the test method of JIS-K7194 because conductivity is ensured and problems such as deterioration in cycle characteristics and increase in internal resistance are unlikely to occur. It is preferable that Since the volume resistivity of the active material layer needs to be measured while being insulated from the current collector, the active material layer is formed on a non-conductive base material and measured. Specifically, the volume resistivity of the active material layer according to the test method of JIS-K7194 is the same as the volume resistivity of the active material layer coating composition, and the active material layer is coated on one side of the 100 μm PET film. The coating composition was applied and dried so that the coating film after drying was 100 μm, and the obtained coating film was subjected to a four-terminal four-probe method using a resistivity meter (for example, Loresta EP, manufactured by Mitsubishi Chemical Corporation). The one measured by.

  In order for the volume resistivity of the active material layer to be 200 Ω · cm or less, the active material layer is a positive electrode having a volume resistivity of 200 Ω · cm or less after standing at 25 ° C. for 5 days. It is preferable to form using the coating composition for active material layers.

  Further, in the electrode plate of the present invention, the adhesion force of the active material layer to the current collector is 10 N / m or more when the active material layer is provided on both sides according to the test method of JIS-K6854-1. In the case where the active material layer is provided on one side, it is preferably 4 N / m or more from the viewpoint that the electrode plate is easily cut or rolled. In the present invention, the adhesion of the active material layer to the current collector is performed in accordance with a test method of JIS-K6854-1, which is a 90-degree peel strength test. When the active material layer is provided on one side, the adhesion of the coating to the substrate of the single-sided coating part is fixed on the surface of the electrode plate on the coating layer with double-sided tape. The end is pulled in a direction perpendicular to the coating layer surface, and continuously peeled off at about 50 mm at a speed of about 50 mm per minute. The minimum value of the load during this period is taken as the peeling strength, and the coating is applied to the substrate. Used for evaluation of film adhesion. In addition, when the active material layer is provided on both sides, the adhesive strength of the coating film to the base material of the double-sided coating part is determined by using a double-sided tape on the surface of the coating layer side of one side. It fixes and performs similarly to the adhesive force of the coating film to the base material of the said single side coating part.

  As described above, the positive electrode plate for a non-aqueous electrolyte secondary battery according to the present invention is obtained, and a non-aqueous electrolyte secondary battery can be produced using this electrode plate.

  When producing a secondary battery using the electrode plate according to the present invention, in order to remove moisture and / or solvent in the active material layer before moving to the battery assembly process, heat treatment or It is preferable to perform aging such as decompression in advance.

  The positive electrode plate and the negative electrode plate produced by the method as described above are spirally wound through a separator such as a polyethylene porous film and inserted into an outer container. After insertion, the terminal connection part of the positive electrode plate (exposed surface of the current collector) and the positive electrode terminal provided on the upper surface of the outer container are connected by leads, while the terminal connection part of the negative electrode plate (exposed surface of the current collector) The negative electrode terminal provided on the bottom surface of the outer container is connected with a lead, and the outer container is filled with a nonaqueous electrolyte and sealed, thereby completing a nonaqueous electrolyte secondary battery including the electrode plate according to the present invention. .

When producing a lithium secondary battery, a nonaqueous electrolytic solution in which a lithium salt as a solute is dissolved in an organic solvent is used. Examples of the lithium salt include inorganic lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, and LiBr, or LiB (C ₆ H ₅ ) ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiC ( _{SO 2 CF 3) 3, LiOSO} 2 CF 3, LiOSO 2 C 2 F 5, LiOSO 2 C 3 F 7, LiOSO 2 C 4 F 9, LiOSO 2 C 5 F 11, LiOSO 2 C 6 F 13, LiOSO 2 C An organic lithium salt such as ₇ F ₁₅ is used.

  Examples of the organic solvent for dissolving the lithium salt include cyclic esters, chain esters, cyclic ethers, chain ethers and the like. More specifically, examples of cyclic esters include propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, γ-valerolactone, and the like.

  Chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, butyl propyl carbonate, propionic acid alkyl ester, malon Examples thereof include acid dialkyl esters and acetic acid alkyl esters.

  Examples of cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane and the like.

  Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether. Can do.

Example 1 Production of Positive Electrode Plate for Nonaqueous Electrolyte Secondary Battery
100 parts by weight of LiCoO ₂ powder as the active material for the positive electrode, 2.5 parts by weight of carbon black (SuperP manufactured by MMMCarbon) as the conductive material, and polyvinylidene fluoride (SOLVY, SOLEF # 1013 as the binder); weight average molecular weight A coating composition for the positive electrode active material layer was prepared by mixing and dispersing 1.7 parts by weight of 300,000 to 400,000) and 35 parts by weight of N-methyl-pyrrolidone as a solvent using a planetary dispa. . The coating amount per side was about 300 g / m ^2, and the positive electrode active material layer coating composition was applied to both sides of a 15 μm thick aluminum foil using a die coat. After drying, pressing with a roll press machine at a linear pressure of 1.0 to 2.0 tf / cm can form a uniform positive electrode active material layer with an active material density of 3.3 to 3.8 g / cc. I got a plate. The evaluation results are shown in Table 1.

(Examples 2-7, Comparative Examples 1-4)
With the formulation shown in Table 1, a positive electrode active material layer coating composition was prepared in the same manner as in Example 1, and coated in the same manner as in Example 1, dried and rolled to obtain an electrode plate. The evaluation results are shown in Table 1.

(Evaluation)
(1) Length of tailing The length of tailing is the longest length of the length of the part that is longer than the set position where the die coating is stopped at the end in the coating direction. It was evaluated with.
(2) Measurement of volume resistivity of active material layer The coated film obtained by applying and drying the active material layer coating composition on one side of a 100 μm PET film so that the coated film after drying becomes 100 μm. Was measured by a four-terminal four-probe method using a resistivity meter (for example, Loresta-EP, manufactured by Mitsubishi Chemical Corporation).

(3) Measurement of peel strength of active material layer (Evaluation of adhesion strength: 90 degree peel strength test)
This was performed according to JIS-K6854-1. Using a Tensilon universal testing machine (manufactured by Orientec Co., Ltd.), the adhesion of the coating film to the base material of the double-sided coating part is double-sided with the coating layer side of one side on the table Fix with tape, pull the edge of the electrode plate in a direction perpendicular to the coating layer surface, peel about 50 mm continuously at a speed of about 50 mm per minute, and peel off the minimum load during this period As an example, it was used to evaluate the adhesion of the coating film to the substrate.

(4) Evaluation of battery characteristics Using the positive electrode plate obtained in each Example and Comparative Example and the negative electrode plate formed by applying a coating composition mainly composed of carbon on a copper foil having a thickness of 5 to 50 μm. Each of them was wound up as designed, and the batteries were assembled and evaluated for charge and discharge.

  In Examples 1 to 7 which are electrode plates according to the present invention produced using the coating composition for positive electrode active material layer according to the present invention, the tailing did not occur or was short even if it occurred. When assembled, there was no heat or ignition, and the battery was excellent in safety. On the other hand, Comparative Examples 1 to 3 which do not contain polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 as a binder produced a long tail and generated heat when the battery was assembled. Moreover, the comparative example 4 which deviates from the specific compounding ratio which concerns on this invention has become a battery with poor electrical conductivity and low performance.

It is the schematic explaining the tailing which generate | occur | produces at the time of coating in the positive electrode plate for nonaqueous electrolyte secondary batteries.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Positive electrode plate 2 ... Negative electrode plate 3 ... Current collector 4 ... Active material layer for positive electrodes 5 ... Application direction 6 ... Trailing 7 ... Active material layer for negative electrodes

Claims (11)

  In the coating composition for the positive electrode active material layer containing at least the positive electrode active material, the conductive material, and the binder, the positive electrode active material is 100 parts by weight, the conductive material is 0.5 to 2.5 parts by weight, and the binder. The binder contains 1.7 to 3.7 parts by weight, and the binder contains polyvinylidene fluoride having a weight average molecular weight of 300,000 to 400,000 based on the total amount of binder. A coating composition for a positive electrode active material layer, comprising: The positive electrode active material layer coating according to claim 1, wherein the conductive material contains at least carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ^3. Work composition. The conductive material contains at least carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ and a carbon black having a specific gravity of 2.2 g / cc or more. The positive electrode active material layer coating composition according to claim 1 or 2.   100 parts by weight of the positive electrode active material, 0.5 to 2.5 parts by weight of the conductive material, and 1.7 to 3.7 parts by weight of the binder, and the binder has a weight average molecular weight. Positive electrode for non-aqueous electrolyte secondary battery, comprising an active material layer containing 300 to 400,000 polyvinylidene fluoride in an amount of 50% by weight or more based on the total amount of binder, on one or both sides of a current collector Board. 5. The non-aqueous electrolyte secondary according to claim 4, comprising at least carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ as the conductive material. Battery positive plate. The conductive material contains at least carbon black having a BET specific surface area of 57 to 67 m ² / g and a density of 140 to 180 kg / m ³ and a carbon black having a specific gravity of 2.2 g / cc or more. The positive electrode plate for nonaqueous electrolyte secondary batteries according to claim 4 or 5.   The adhesion of the active material layer to the current collector is 10 N / m or more when the active material layer is provided on both sides according to the test method of JIS-K6854-1, and the active material layer is provided on one side. 7. The positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 4, wherein the positive electrode plate is 4 N / m or more.   The positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 4, wherein the volume resistivity of the active material layer is 200 Ω · cm or less according to a test method of JIS-K7194. The positive electrode plate for a nonaqueous electrolyte secondary battery according to any one of claims 4 to 8, wherein the coating amount of the active material layer is 300 to 800 g / m ² in terms of the total amount on both sides of the current collector.   The positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 4, wherein the density of the active material layer after press working is 1.85 to 4.35 g / cc. A non-aqueous electrolyte secondary battery comprising the positive electrode plate for a non-aqueous electrolyte secondary battery according to claim 4.

Images