JP4830180B2 - Method for producing electrode plate for non-aqueous electrolyte secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the improvement of the binding force of a binder used for a nonaqueous electrolyte secondary battery, particularly for its electrode plate.
[0002]
[Prior art]
Currently, a carbon material is used as a negative electrode active material of a non-aqueous electrolyte secondary battery. As a characteristic of the carbon material, carbon absorbs lithium ions during charge / discharge and the active material particles expand, and during discharge, the active material particles contract by releasing lithium ions. Due to the expansion and contraction associated with this charge / discharge, the network of electron conduction existing in the electrode plate is cut, and the battery capacity and charge / discharge rate characteristics deteriorate. In particular, the deterioration of the electrode plate accumulates as the charge / discharge cycle is repeated, causing the cycle life characteristics of the battery to deteriorate.
[0003]
As a cause of the electron conduction network in the electrode plate being cut along with the expansion and contraction of the active material particles, the binder in the mixture layer is cut in the step of rolling the electrode plate to a predetermined mixture density, It is thought that the cause is that the binding power is not sufficiently exhibited. Therefore, the above problem can be solved if the rolling process is not performed, but the capacity per electrode plate volume is lowered, and the high energy density of the battery cannot be achieved. In addition, there is a method of adding an excessive amount of binder so that a strong binding force can be maintained even after rolling, but the surface of the active material particles is excessively covered, and the high rate characteristics in charge / discharge of the battery are reduced. I will let you.
[0004]
As a means for solving these problems, JP-A-8-203500 discloses that the electrode plate is rolled at a predetermined temperature to cause plastic deformation of the binder, thereby minimizing the damage to the binder during rolling. Thus, a method for preventing the deterioration of the binder accompanying the charge / discharge cycle has been proposed. However, even in this method, with slippery particles such as graphite particles, the movement of the particles is large at the time of usual roll rolling, and it cannot be handled only by plastic deformation of the binder. As a result, the binding force is insufficient and the electron conduction network is destroyed during charging and discharging.
[0005]
[Problems to be solved by the invention]
This invention solves the said subject, suppresses that the binder in the mixture accompanying the cycle of charging / discharging deteriorates and destroys an electronic network, and improves the cycle life characteristic of a battery. It is the purpose.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the method for producing the electrode plate for a non-aqueous electrolyte secondary battery of the present invention is as follows.
(1) A step of preparing an electrode plate by pasting a mixture containing a carbon material as an active material and a binder, applying the mixture onto a conductive support, providing a mixture layer, and drying the electrode plate; The step of pressure-molding, the step of including a solvent capable of dissolving or dispersing the binder in the mixture layer of the electrode plate after pressure molding, and the step of removing the solvent ,
(2) Pasting a carbon material as an active material and a binder containing a binder, applying the mixture onto a conductive support, providing a mixture layer, and drying to prepare an electrode plate; A step of including a solvent capable of dissolving or dispersing and holding the binder, and a step of pressure-molding the electrode plate containing the solvent at a temperature equal to or higher than the glass transition point of the binder,
(3) Pasting a carbon material as an active material and a binder containing a binder into a conductive support and providing a mixture layer, followed by drying to produce an electrode plate; And the step of re-adding the binder into the mixture layer after the pressure molding, and the step of re-adding the binder into the mixture layer comprises the step of: A solvent dissolved or dispersed and held is included in the mixture layer, and then the electrode plate is dried .
[0007]
In the production method of ( 1 ), by adding a solvent capable of dissolving or dispersing and holding the binder in the mixture layer after pressure molding, the solvent dissolves the binder and cuts in the pressure rolling step. The formed particles and the binder can be joined again to maximize the effect of the input binder.
[0008]
In the production method ( 2 ), the following two steps are performed in order to give the binder flexibility before performing pressure molding. One is to include a solvent that can dissolve or disperse the binder in the mixture layer so that the binder is included in a flexible state. The other is pressure molding at a temperature equal to or higher than the glass transition point of the binder used. Thereby, it is possible to maintain a sufficient binding force even after the pressure rolling without cutting the joint by improving the flexibility of the binder.
[0009]
In the production method ( 3 ), the binder is introduced again after the pressure molding. That is, the initial binder mixed in the mixture paste is kept in an amount sufficient to connect the active material at a minimum. The bonding between the particles and the initial binder is cut by pressure molding. Therefore, the bonding between the particles and the binder can be regenerated by introducing the binder again. At this time, it is necessary to include an amount of the binder capable of withstanding the charge / discharge cycle in the bonding between the particles and the binder. Since a necessary binder is added after pressure molding, since the binder is not deformed, the production method can obtain a stronger electrode plate than the production methods (1) to ( 2 ) above. Oh Ru.
[0010]
By producing an electrode plate by any of the above manufacturing methods, the effectiveness of the binder is maintained even after the mixture is pressure-molded, and the deterioration of the binder accompanying the charge / discharge cycle is minimized. The cycle life characteristics can be improved.
[0011]
Further, it is preferable to use highly crystalline graphite having a (002) plane spacing of 0.337 nm or less as measured by XRD.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to a longitudinal sectional view of the cylindrical battery in FIG.
[0013]
The negative electrode plate is produced by any of the production methods of the present invention described above. Examples of the binder include polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene. -Perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetra Fluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoroethylene-tetrafluoroethylene copolymer, vinylidene fluoride -Perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or Na ion crosslinked body of the material, ethylene-methacrylic acid copolymer or Na ion crosslinked body of the material, ethylene-acrylic acid Mention may be made of methyl copolymers or Na ion crosslinked bodies of the above materials, ethylene-methyl methacrylate copolymers or Na ion crosslinked bodies of the above materials. A particularly preferred material is polyvinylidene fluoride. Examples of the current collector include copper and aluminum. Particularly preferable as the active material is a carbon material in which the effects of the present invention are remarkably exhibited. In particular, highly crystalline graphite having a (002) plane spacing of 0.337 nm or less by XRD measurement is desirable. Moreover, this graphite may be included in a ratio of 0.1 to 1 with respect to the total mass of the active material, and may be used by mixing with other active material particles.
[0014]
The positive electrode plate can be obtained by an ordinary electrode plate manufacturing method. A positive electrode active material is mixed with a conductive agent and a binder, a slurry is further prepared using a solvent, applied onto a current collector, dried and rolled.
[0015]
The produced positive electrode plate and negative electrode plate are spirally wound a plurality of times through a separator to form the electrode plate group 4 and accommodated in the battery case 1. A positive electrode lead 5 is drawn from the positive electrode plate to the sealing plate 2, and a negative electrode lead 6 is drawn from the negative electrode plate to be connected to the bottom of the battery case 1. Insulating rings 7 are provided above and below the electrode plate group 4, respectively. After injecting the electrolyte, the battery is sealed using the sealing plate 2 to produce a cylindrical battery.
[0016]
【Example】
Examples of the present invention will be specifically described below.
[0017]
( Reference Example 1)
The negative electrode plate was produced as follows. A mixture of 97% by weight of graphite and 3% by weight of a polyvinylidene fluoride resin as a binder was dispersed in a 1% aqueous solution of carboxymethylcellulose to prepare a slurry, which was applied onto a negative electrode current collector made of copper foil. An agent layer was provided and dried. The negative electrode plate thus produced was sandwiched between flat plates, and pressure forming of the electrode plate was performed by pressing at a temperature of 120 ° C., which is the glass transition point of polyvinylidene fluoride. The graphite used is Timcal graphite SFG44 (the (002) plane spacing by XRD measurement is 0.337 nm or less), and this is pulverized by a turbo mill and the particle size is adjusted to have a specific surface area of 2.4 m ^2. / G, a graphite powder sample having a particle size measured by a wet laser particle size meter in the range of 15 to 22 μm was used. In addition, it pressure-molded so that it might become 1.3 g / cm < ³ > or more about an active material density.
[0018]
On the other hand, for the positive electrode plate, 85% by weight of lithium cobaltate powder is mixed with 10% by weight of carbon powder as a conductive agent and 5% by weight of polyvinylidene fluoride resin as a binder, and these are dispersed in a 1% aqueous solution of carboxymethyl cellulose. A slurry was prepared, applied on a positive electrode current collector made of aluminum foil, dried and rolled. In addition, lithium cobaltate used the material whose specific surface area is 0.4 m < ² > / g.
[0019]
As the organic electrolyte, a solution obtained by dissolving 1.5 mol / liter of LiPF _{6 in} a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1 was used.
[0020]
A cylindrical nonaqueous electrolyte secondary battery as shown in FIG. 1 having a diameter of 18 mm and a height of 65 mm was constructed using the electrode plate produced as described above.
[0021]
(Example 1 )
A negative electrode plate was produced as follows. A mixture of 97% by weight of graphite and 3% by weight of a polyvinylidene fluoride resin as a binder was dispersed in a 1% aqueous solution of carboxymethylcellulose to prepare a slurry, which was applied onto a negative electrode current collector made of copper foil. The agent layer was provided and dried. The negative electrode plate thus produced was subjected to pressure molding so that the mixture layer had a constant density. Next, the electrode plate was dried after an aqueous solution containing 0.1% by weight of a surfactant capable of dispersing and retaining the polyvinylidene fluoride resin in the aqueous solution was contained in the mixture layer of the electrode plate. In addition, the polyvinylidene fluoride resin is not contained in the aqueous solution.
[0022]
A cylindrical nonaqueous electrolyte secondary battery was constructed in the same manner as in Reference Example 1 except that the production process of the negative electrode plate was changed.
[0023]
(Example 2 )
A negative electrode plate was produced as follows. A mixture of 97% by weight of graphite and 3% by weight of a polyvinylidene fluoride resin as a binder was dispersed in a 1% aqueous solution of carboxymethylcellulose to prepare a slurry, which was applied onto a negative electrode current collector made of copper foil. The agent layer was provided and dried. Next, an aqueous solution containing 0.1% by weight of a surfactant capable of dispersing and holding the polyvinylidene fluoride resin in the aqueous solution was included in the mixture layer of the electrode plate. The aqueous solution does not contain polyvinylidene fluoride. Thereafter, this electrode plate was subjected to pressure molding at a temperature of 120 ° C. so that the mixture layer had a constant density.
[0024]
A cylindrical nonaqueous electrolyte secondary battery was constructed in the same manner as in Reference Example 1 except that the production process of the negative electrode plate was changed.
[0025]
(Example 3 )
A negative electrode plate was produced as follows. A mixture of 97% by weight of graphite and 1% by weight of a polyvinylidene fluoride resin as a binder was dispersed in a 1% aqueous solution of carboxymethyl cellulose to prepare a slurry, which was applied onto a negative electrode current collector made of copper foil. The agent layer was provided and dried. The negative electrode plate thus produced was subjected to pressure molding so that the mixture layer had a constant density. Next, an aqueous solution containing 20% by weight of a polyvinylidene fluoride resin and 0.1% by weight of a surfactant capable of dispersing and retaining the resin in the aqueous solution was included in the mixture layer of the electrode plate. At this time, the aqueous solution was included in the mixture layer so that the amount of the polyvinylidene fluoride resin as a binder was 3% by weight with respect to 97% by weight of graphite, together with the mixture of the resin previously mixed in the slurry. Thereafter, the electrode plate was dried.
[0026]
A cylindrical nonaqueous electrolyte secondary battery was constructed in the same manner as in Reference Example 1 except that the production process of the negative electrode plate was changed.
[0027]
(Comparative Example 1)
A negative electrode plate was produced as follows. A mixture of 97% by weight of graphite and 3% by weight of a polyvinylidene fluoride resin as a binder was dispersed in a 1% aqueous solution of carboxymethylcellulose to prepare a slurry, which was applied onto a negative electrode current collector made of copper foil. The agent layer was provided and dried. The negative electrode plate thus produced was subjected to pressure molding so that the mixture had a constant density.
[0028]
A cylindrical nonaqueous electrolyte secondary battery was constructed in the same manner as in Reference Example 1 except that the production process of the negative electrode plate was changed.
[0029]
(Evaluation)
A charge / discharge cycle test was performed on the batteries of the reference example and Examples 1 to 3 and Comparative Example 1. CVCC charging with an upper limit of the battery voltage of 4.2 V was performed, the maximum limiting current was set to 1 A, and charging was terminated when the current reached 100 mA. The discharge was performed at a constant current of 1400 mA until 3.0 V, and the resting time when switching between charge and discharge was 20 minutes. In addition, charging / discharging was performed in a 20 degreeC thermostat.
[0030]
The number of cycles when the discharge capacity of the battery was reduced to 50% when the discharge capacity at the first cycle was 100% was used as an index for evaluating the cycle characteristics as the cycle life of the battery. In the first cycle and the 100th cycle, the discharged battery was disassembled, the thickness of the negative electrode plate was measured, and the density of the mixture was calculated. (Density change rate of mixture with cycle) = ((mixture density at 100th cycle) − (mixture density at first cycle)) / (mixture density at first cycle) It was used as an index of density change. Table 1 shows the results.
[0031]
[Table 1]
[0032]
In the batteries of Reference Examples and Examples 1 to 3 of the present invention, it can be confirmed that the negative electrode plate is small and the cycle characteristics are good. On the other hand, in the comparative battery, the electrode plate is greatly swollen, and the electronic network in the mixture is cut off, and the cycle characteristics are considered to be deteriorated.
[0033]
In the present embodiment, water is shown as an example of a solvent capable of dispersing and holding the binder, but an organic solvent such as ethanol may also be used.
[0034]
【The invention's effect】
As described above, the electrode plate is produced by the manufacturing method of the present invention, thereby minimizing the deterioration of the binder accompanying the charge / discharge cycle of the battery and keeping the electronic network in the mixture well. A non-aqueous electrolyte secondary battery having excellent life characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Claims (4)

A step of pasting a mixture containing an active material and a binder, applying the mixture onto a conductive support and providing a mixture layer, then drying to prepare an electrode plate; and a step of pressing the electrode plate a step to include the pressure molding after the electrode plate dissolved or dispersed holdable solvent binder to the mixture layer of the solvent step menstrual Ru non-aqueous electrolyte secondary battery plate to be removed A method for producing an electrode plate for a non-aqueous electrolyte secondary battery, wherein the active material is a carbon material . A paste containing a mixture containing an active material and a binder is applied to a conductive support and a mixture layer is provided, followed by drying to prepare a plate, and dissolving or binding the binder to the plate a step of including a dispersion capable of holding the solvent, the production of a glass transition temperature higher than Ru through a step of pressure molding the non-aqueous electrolyte secondary battery plate of the binder electrode plate containing the solvent It is a method , Comprising: The said active material is a carbon material, The manufacturing method of the electrode plate for nonaqueous electrolyte secondary batteries characterized by the above-mentioned . A step of pasting a mixture containing an active material and a binder, applying the mixture onto a conductive support and providing a mixture layer, then drying to prepare an electrode plate; and a step of pressing the electrode plate the method for manufacturing a nonaqueous electrolyte secondary battery plate Ru through the process to include a binder again mixture layer after press molding, the active material is a carbon material, the mixture The non-aqueous electrolyte secondary battery characterized in that the step of re-adding the binder to the layer includes adding a solvent in which the binder is dissolved or dispersed in the mixture layer and then drying the electrode plate. Method for manufacturing an electrode plate . The method for producing an electrode plate for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3 , wherein the active material is graphite having a (002) plane spacing of 0.337 nm or less as measured by XRD.