JP3575131B2 - Method for producing electrode sheet for battery - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an electrode sheet for a battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras and notebook computers, demand for small-sized and high-capacity batteries has increased. Among these, most of the secondary batteries are nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is as low as about 1.2 V, and it is difficult to improve the energy density. 2. Description of the Related Art In recent years, lithium ion secondary batteries using various carbonaceous materials capable of doping and undoping of lithium ions for a negative electrode have been proposed and are being actively developed.
[0003]
There are various methods for manufacturing an electrode sheet used for such a lithium ion secondary battery and the like. Generally, a paste-like electrode agent is applied to one surface of a current collector and dried. Next, the electrode agent is similarly applied to the opposite surface (uncoated surface) of the current collector, and drying is performed. Next, heat treatment is performed, and finally, pressure is applied to the electrode sheet using a press or the like to produce the electrode sheet.
[0004]
In such a conventional manufacturing method, since the pressing pressure is applied only after the heat treatment, there has been a problem that the electrode agent is separated from the current collector in the electrode winding step which is a subsequent step. When peeling occurs, there is a problem in that fragments, powders, etc. of the electrode agent generated at the time of peeling enter between the electrode sheets or between the separators and the like, causing the wound electrode to be distorted or causing a short circuit of the wound electrode. .
[0005]
[Problems to be solved by the invention]
The present invention is to solve the drawbacks of the conventional manufacturing method described above, and to make it difficult for the electrode material to be peeled off in an electrode winding step which is a subsequent step, and to improve the yield during battery manufacturing. It is.
[0006]
[Means for Solving the Problems]
The present invention has the following configuration to solve the above problems. That is, in the method for producing an electrode sheet for a battery manufactured by applying an electrode agent to a current collector, at least a step of applying the electrode agent to the current collector, drying the applied electrode agent, performing a pressing step, and performing a heat treatment is performed. A method for producing an electrode sheet for a battery characterized by having the above.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
As the current collector that can be used in the present invention, a metal foil, a metal fabric, a metal mesh, or the like can be used, but a current collector having a small electric resistance is preferable. As the current collector for a lithium ion secondary battery, a metal foil is most desirable, and specifically, an aluminum foil, a copper foil, a stainless steel foil, or the like can be preferably used.
[0008]
The battery electrode sheet in the present invention has a configuration in which an electrode agent is provided on one or both surfaces of a current collector. Specifically, an active agent and a binder are mixed, and a paste is formed with a solvent. The electrode agent prepared as described above is applied to one or both surfaces of the current collector and dried.
[0009]
The electrode agent used in the present invention was prepared by mixing the active agent and the binder as described above and preparing the paste in a solvent. It is more preferable to increase conductivity. The active agent of the electrode agent includes a negative electrode and a positive electrode, and will be described below.
[0010]
The active material of the negative electrode material is not particularly limited, and those generally used as the active material of the negative electrode material can also be used in the present invention. Among them, as the lithium ion secondary battery, Preferably, a carbonaceous material is used. The carbonaceous material is not particularly limited, and any material can be used as long as it is capable of doping and undoping lithium ions. Specifically, natural graphite, artificial graphite, various cokes, mesophase carbon, various carbon fibers, resin fired bodies, and the like can be used.
[0011]
Various forms of the carbonaceous material such as a powder form and a fibrous form can be used. The carbon fiber is not particularly limited, and generally is obtained by firing an organic substance. PAN-based carbon fiber obtained from polyacrylonitrile (PAN), pitch-based carbon fiber obtained from pitch such as coal or petroleum, cellulosic carbon fiber obtained from cellulose, vapor-grown carbon obtained from gas of low molecular weight organic matter Fibers and the like can be used, and in addition, carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol, and the like can also be used. Among the carbon fibers, when used as a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt, PAN-based carbon fibers, pitch-based carbon fibers, and vapor-grown carbon fibers are preferable. Further, PAN-based carbon fibers can be preferably used in that the doping of alkali metal ions, particularly lithium ions, is good.
[0012]
In the case of using carbon fibers, it is desirable to use milled carbon fibers because the number of manufacturing steps is smaller than in the case of using long fibers. The milled carbon fiber preferably has a diameter of 0.1 to 1000 μm, more preferably 3 to 10 μm, and an average length of preferably 5 μm or more and less than 1 mm, more preferably 7 μm or more and less than 100 μm. Things.
[0013]
When the milled carbon fiber is used as the negative electrode active material, it is more preferable to perform high-temperature heat treatment beforehand in order to improve cycle life characteristics.
[0014]
As the activator of the electrode agent for the positive electrode used in the present invention, inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals, polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, polythiophene and the like Examples of the positive electrode used in ordinary secondary batteries include a conjugated polymer, a crosslinked polymer having a disulfide bond, and thionyl chloride. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, transition metal oxides and transition metal chalcogens such as cobalt, manganese, molybdenum, vanadium, chromium, iron, copper, and titanium are used. It is preferably used.
[0015]
Among them, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiyNi _1- xMexO ₂ (selected from Me: Ti, V, Mn, Fe), Li _1-x-a AxNi _1-y-b ByO ₂ (However, A is at least one kind of alkali or alkaline earth metal element, and B is at least one kind of transition metal element) can be preferably used because of high voltage and high energy density. In _particular, in _{Li 1-x-a AxNi 1} -y-b ByO 2, 0 <x ≦ 0.1,0 ≦ y ≦ 0.3, -0.1 ≦ a ≦ 0.1, -0.15 ≦ b ≦ 0.15 (however, when A and B consist of two or more elements, x is the total number of moles of all transition metal elements excluding Ni, y is the alkali or alkaline earth metal excluding Li, When y = 0, A contains one or more kinds of alkaline earth metals), whereby a positive electrode active agent having excellent characteristics can be obtained. In this case, the type, number, and composition of A and B may be changed, or a positive electrode active agent in which x, y, a, and b are changed may be used. Among them, A is preferably Mg or Sr, and B is Co or Fe.
[0016]
The binder of the electrode agent is not particularly limited, and may be any of a thermoplastic resin and a thermosetting resin, and is not particularly limited. Further, it can be used in the form of a solution or an emulsion. The amount of addition is usually 0.01 to 40 wt% in the electrode material. Specific examples include various epoxy resins, cellulose resins, organofluorine poly and copolymers, acrylic resins, organic chlorinated resins, polyamides, polyimides, and polycarbonates. Among them, polyvinylidene fluoride, polytetrafluoroethylene, propylene hexafluoride polymer and copolymer are preferable because they are excellent in binding power, chemical stability, coating property and the like.
[0017]
In many cases, a material having low conductivity is used as the positive electrode material, and in that case, it is preferable to use a conductive material. It is desirable that the negative electrode material is also used to reduce the resistance value of the negative electrode sheet and reduce the loss of the entire battery. In this case, the conductive agent is not particularly limited, and various materials can be used. Among them, various carbonaceous materials can be preferably used. In particular, it is desirable that the material has good conductivity and does not have characteristics of an active agent as much as possible. Specifically, pyrolytic carbon such as artificial graphite, acetylene black, and Ketjen black, vapor-grown carbon, mesophase Examples include carbon, coke, and fired organic materials. The conductive agent has a function of assisting the electrical connection between the active agents, and the particle size of the conductive agent is desirably the same size as the active agent or smaller than the active agent. The addition amount of the conductive agent is not limited, but is 0.5 to 30 wt%, and more preferably 0.7 to 20 wt%. If it is less than 0.5 wt%, the effect on conductivity is poor, and if it exceeds 20 wt%, the capacity per unit weight of the electrode tends to decrease.
[0018]
The method for producing a battery electrode sheet of the present invention will be described below using a negative electrode sheet as an example. Using a milled carbon fiber as the active agent for the negative electrode agent, polyvinylidene fluoride as the binder, and carbon black as the conductive agent in a predetermined weight ratio, add a solvent to the mixture and mix and disperse well with a kneading machine. An electrode agent paste is used. One side of a copper foil as a current collector is coated using a commercially available coater having a drying zone and a roll press, and dried at a predetermined temperature. After similarly coating and drying the opposite surface of the current collector, a predetermined pressure is applied by, for example, a roll press. Next, heat treatment is performed at a predetermined temperature. Next, a predetermined pressure is applied again by the roll press.
[0019]
As described above, the manufacturing method of the present invention is characterized in that the heat treatment is performed after pressing, but the pressing step is further divided into two or more times, and at least one heat treatment is performed during the pressing step. Is preferably applied. The press is not necessarily limited to a roll press, but a roll press is preferable for trial use in mass production.
[0020]
Regarding one press step, there is no problem even if there are a plurality of press rolls and one step is a multi-stage press. In the present invention, the heat treatment may be performed during any one of the pressing steps as long as it is performed during a plurality of pressing steps.
[0021]
The heat treatment is preferably performed at a temperature higher than the temperature at the time of drying in order to increase the binding force between the current collector and the electrode agent. The drying temperature is preferably, for example, about 80 to 120 ° C, and the heat treatment temperature after pressing is preferably about 130 to 220 ° C.
[0022]
The pressure at the time of pressing is not particularly limited, but is preferably in a range of 500 kg / cm ² or more and 3000 kg / cm ² or less. If it is less than 500 kg / cm ² , the density of the electrode agent is low, and therefore the amount of the electrode sheet stored in the battery can is small, and as a result, the battery capacity tends to be small. If it exceeds 3000 kg / cm ² , mechanical deformation of the current collector may occur. In order to maintain the flatness of the electrode sheet, the pressure at the time of pressing is more preferably in the range of 500 kg / cm ² or more and 2000 kg / cm ² or less.
[0023]
In the conventional manufacturing method, since the heat treatment was performed only before applying pressure, it is presumed that the contact area (or binding area) between the current collector and the electrode agent was reduced. In the manufacturing method of the present invention, the contact area can be sufficiently increased by applying pressure before heat treatment is performed, the binding between the current collector and the electrode agent is improved, and peeling during entrainment occurs. It is presumed that it became difficult. Further, in the manufacturing method of the present invention, by applying pressure again after the heat treatment, the thickness of the electrode material expanded by the heat treatment can be regulated to a predetermined thickness, so that the amount of the wound electrode body stored in the battery can can be reduced. No battery power can be maintained.
[0024]
【Example】
Example 1, Comparative Example 1
An example in which an electrode sheet for a lithium ion secondary battery is formed using a roll coater will be described below. As an active agent for the negative electrode, a PAN-based milled carbon fiber MLD-30 manufactured by Toray and subjected to a heat treatment at 1300 ° C. is used. As a binder, polyvinylidene fluoride manufactured by Kureha Chemical Industry Co., Ltd. An electrode material paste for a negative electrode sheet is obtained by mixing and dispersing N-methylpyrrolidone as a solvent in a mixture of “Denka Black” (acetylene black) manufactured by Chemical Industry at a weight ratio of 90: 5: 5, respectively, using a kneader. And A copper foil having a thickness of 10 μm, which is a current collector, was caused to travel, the electrode agent paste was applied to one surface of the current collector, and then wound up through a drying zone set at a temperature of 90 ° C. The opposite side was similarly coated with an electrode agent paste, dried, and then roll-pressed at a pressure of 1300 kg / cm ² . Next, after passing through a heat treatment zone set at a temperature of 200 ° C., roll pressing was performed at a pressure of 700 kg / cm ² to obtain a negative electrode sheet having a thickness of about 60 μm.
[0025]
As the active agent for the positive electrode agent, commercially available LiCoO ₂ , “Denka Black” manufactured by Denki Kagaku Kogyo as a conductive agent, and polyvinylidene fluoride manufactured by Kureha Chemical Co., Ltd. as a binder at a weight ratio of 80: 5: 15. Then, a mixture obtained by adding N-methylpyrrolidone as a solvent to a paste for a positive electrode material by sufficiently mixing and dispersing with a kneader was used, and a 20 μm-thick aluminum foil was produced by the same production method as that for producing a negative electrode sheet. A positive electrode sheet having a thickness of about 100 μm was obtained on both surfaces of the substrate.
[0026]
The obtained positive and negative electrode sheets according to the present invention were slit to a width of 54 mm for the positive electrode and a width of 56 mm for the negative electrode, and after welding the leads, these positive and negative electrode sheets were made of Ube Industries, Ltd. A spiral wound electrode was obtained by a winding machine together with a separator made of the same.
[0027]
Insulating plates were arranged above and below the obtained wound electrode, inserted into a battery can, and then a predetermined amount of an electrolyte was injected. Then, a positive electrode cap was placed and sealed to obtain a lithium ion secondary battery. The electrolyte used was one in which 1 mol of lithium hexafluorophosphate was dissolved in an electrolyte in a mixed solvent of polycarbonate and dimethyl carbonate.
[0028]
100 spiral wound electrodes were manufactured by the same manufacturing method as described above. In this case, the number of defective windings or the short-circuiting of the wound electrodes was three.
[0029]
As a comparative example, the manufacturing process of Example 1 was the same as Example 1 except that the pressing step before the heat treatment step was omitted, the pressing step after the heat treatment was performed only once, and the pressure at the time of this pressing was 1300 kg / cm ^2. Similarly, positive and negative electrode sheets were manufactured, and a lithium ion secondary battery of Comparative Example 1 was obtained in the same manner as in Example 1.
[0030]
100 spiral wound electrodes were manufactured by the same manufacturing method as described above. In this case, the number of winding defects or the number of winding electrode short-circuits was 27.
The cycle life tests of the batteries of Example 1 and Comparative Example 1 were performed under the conditions of a charging current of 1 A, a constant current and constant voltage charging of 4.2 V at a charging time of 2.5 hours, a discharging current of 0.5 A and a final voltage of 2.5 V. It was carried out in.
[0031]
As a result of a cycle life test of the batteries of Example 1 and Comparative Example 1, the capacity of the battery of Comparative Example 1 was 1290 mAh at the fifth cycle, and the capacity retention after 500 cycles was 61%. The battery of Example 1 had a capacity at the fifth cycle of 1320 mAh and a capacity retention after 500 cycles of 74%, and was a battery excellent in battery capacity and cycle life. As a result of disassembling the battery after the cycle life test and examining the positive and negative electrode sheets, some of the positive and negative electrode sheets of Comparative Example 1 were separated from the current collector, but the positive and negative electrode sheets of Example 1 were removed. No peeling occurred on the sheet.
[0032]
Further, as shown in Example 1, peeling of the electrodes during winding was reduced as compared with Comparative Example 1, and the yield during manufacturing was able to be improved.
[0033]
【The invention's effect】
According to the method for manufacturing a battery electrode sheet of the present invention, before applying heat treatment to the electrode sheet, peeling of the electrode agent from the current collector by applying pressure is less likely to occur. The yield can be improved. There is also an effect that the cycle life characteristics can be improved. Furthermore, in the manufacturing method of the present invention, by applying pressure again after the heat treatment, a large battery capacity can be maintained without reducing the storage amount of the electrode sheet in the battery can.

Claims (7)

In the manufacturing method of an electrode sheet for a battery produced by coating an electrode material on the current collector, coating an electrode material on the current collector, and dried, and the pressing process, during the two or more pressing process And a method for producing an electrode sheet for a battery , comprising the heat treatment step . The method for producing a battery electrode sheet according to claim 1, wherein the temperature of the heat treatment is higher than a drying temperature. The method for producing a battery electrode sheet according to claim 1, wherein the electrode sheet is for a lithium ion secondary battery. The method according to claim 1, wherein the electrode sheet is used as a negative electrode, and the active agent is carbon fiber. The method for producing an electrode sheet for a battery according to claim 4 , wherein the carbon fiber is obtained from polyacrylonitrile. The method for producing an electrode sheet for a battery according to claim 4 , wherein the carbon fibers are milled carbon fibers. The method for producing an electrode sheet for a battery according to claim 1, wherein the electrode agent comprises a conductive agent.