JP2012033426A - Method of manufacturing electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode capable of improving adhesive strength between an electrode mixture layer and a collector.SOLUTION: In the method of manufacturing the electrode by drying and remove a solution after applying an electrode mixture which contains an electrode active material, a binder and the solution on the collector, the collector is preheated to 70 to 100°C when the electrode mixture is applied.

Description

  The present invention relates to a battery manufacturing method capable of improving the adhesive strength between an electrode mixture layer and a current collector.

  In recent years, non-aqueous electrolytic secondary batteries with high capacity, high output and high safety have been used as secondary batteries for hybrid cars, electric cars, electric assist bicycles, household secondary battery power supplies and electric tools. These secondary batteries are generally manufactured by preparing an electrode by stirring an electrode mixture, applying it to a current collector, drying and cutting, and assembling the electrode and other members. In this step, an electrode that does not peel off the electrode mixture during cutting or assembly handling is required. When the electrode mixture is peeled off in the cutting or assembling process, the peeled electrode mixture is mixed in the secondary battery, destroying the separator separating the positive electrode and the negative electrode, and causing a short circuit during charge / discharge. In addition, electric charges are unevenly distributed during charging and discharging, and battery performance is significantly reduced.

  Patent Document 1 discloses a method for manufacturing a secondary battery having a step of applying an electrode mixture composed of two or more kinds of binders having different specific gravities, an electrode active material, and a solvent to a current collector. Of the two or more types of binders, many binders having a large specific gravity are present in the vicinity of the current collector, and the adhesion between the electrode mixture layer and the current collector can be improved.

JP 2009-245925 A

  However, since the electrode mixture layer of the electrode of the secondary battery manufactured by the method described in Patent Document 1 contains two or more types of binders, Competition occurs and it is difficult to achieve adhesion as designed. Also, it takes time to determine the optimum binder type and ratio.

  An object of this invention is to provide the manufacturing method of the battery which can improve the adhesive strength of an electrode mixture layer and a collector.

  The method for producing an electrode according to the present invention is a method for producing an electrode in which an electrode mixture containing an electrode active material, a binder and a solvent is applied onto a current collector, and then the solvent is removed by drying. At the time of application, the current collector is preheated to 70 to 100 ° C.

  According to the method of the present invention, a battery having high adhesive strength between the electrode mixture layer and the current collector can be produced.

It is sectional drawing of an example of the electrode manufactured by the method concerning this invention. It is a schematic diagram which shows an example of the apparatus used for the process of apply | coating the electrode mixture in this invention on a collector.

  The method for producing an electrode according to the present invention is a method for producing an electrode in which an electrode mixture containing an electrode active material, a binder and a solvent is applied onto a current collector, and then the solvent is removed by drying. At the time of application, the current collector is preheated to 70 to 100 ° C.

  In the conventional method, drying progresses from the surface of the electrode mixture layer during drying, and the diffusion of the binder accompanying heat conduction is large, so that sufficient adhesive strength cannot be obtained between the electrode mixture layer and the current collector. In the present invention, since the electrode mixture is applied in a state where the current collector is preheated to 70 to 100 ° C., diffusion of the binder accompanying heat conduction can be suppressed in the subsequent drying step. Thereby, since it can dry in the state which binder disperse | distributed uniformly in electrode mixture, the electrode with high adhesive strength of an electrode mixture layer and a collector can be produced.

(Electrode mixture)
The electrode mixture includes an electrode active material, a binder, and a solvent.

As an electrode active material, for example, as a positive electrode active material of a secondary battery, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ , Li-transition metal oxide, Li-transition metal phosphate, Li-transition Examples thereof include metal sulfates and Li metals. These may use only 1 type and may use 2 or more types together. Further, for example, as the negative electrode active material of the secondary battery, graphite, soft carbon, hard carbon, carbon material, silicon, transition metal oxide, Li-transition metal nitride, Li metal, and the like can be given. These may use only 1 type and may use 2 or more types together.

  Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoride (PTFE), fluoropolymer, styrene butadiene copolymer (SBR), polyacrylate, and the like. These may use only 1 type and may use 2 or more types together. However, in the present invention, it is not always necessary to use two or more kinds of binders as in Patent Document 1, and only one kind of binder can be used as the binder.

  Examples of the solvent include water and 1-methyl-2-pyrrolidone (NMP).

  An electrode mixture is prepared by stirring the electrode active material, binder and solvent with a disperser or stirrer such as a roll mill, ball mill, sand mill, KD mill, high-speed impeller mill, attritor, jet mill, vibrator mill, kneader. can do. The mixing ratio of the electrode mixture is preferably 92 to 99.5 parts by mass of the electrode active material, 0.5 to 8 parts by mass of the binder, and 40 to 110 parts by mass of the solvent. In addition to the electrode active material, the binder, and the solvent, the electrode mixture may include a conductivity imparting agent such as carbon powder and metal powder, and a thickening agent such as carboxymethyl cellulose (CMC).

(Current collector)
As the current collector, a conductive metal foil such as aluminum, copper, nickel, and stainless steel can be used. Although the thickness of a collector is not specifically limited, For example, it can be set as 1-30 micrometers.

(Method for manufacturing electrode)
A cross-sectional view of an example of an electrode manufactured by the method according to the present invention is shown in FIG. In the electrode, the electrode mixture layer 1 is formed on both surfaces of the current collector 2. The thickness of the electrode mixture layer 1 is not particularly limited, and can be appropriately selected according to the battery using the electrode.

  The electrode according to the present invention is manufactured by drying and removing the solvent after the electrode mixture is applied onto the current collector, and the current collector is preliminarily maintained at 70 to 100 ° C. when the electrode mixture is applied. It is heated.

  The method for applying the electrode mixture onto the current collector is not particularly limited, but examples thereof include a roll coater, a gravure coater, a knife coater, a blade coater, an air doctor coater, a curtain coater, a fan mountain coater, a die coater, and a kiss coater. It can apply | coat on a collector using the coating machine of this. Although it does not specifically limit as a thickness of the electrode mixture layer formed by apply | coating an electrode mixture on a collector, For example, it can be set as 20-100 micrometers.

  In this invention, this electrical power collector is preheated at 70-100 degreeC at the time of application | coating of the said electrode mixture. A preheating temperature of the current collector of less than 70 ° C. is not preferable because the effect of improving the adhesive strength between the electrode mixture layer and the current collector cannot be obtained. On the other hand, when the preheating temperature of the current collector exceeds 100 ° C., wrinkles due to thermal expansion may occur, which is not preferable. The preheating temperature of the current collector is preferably 90 to 100 ° C.

  As a method of preheating the current collector to the above range, it is preferable to carry out by bringing a heated roll into contact with the current collector. In order to set the preheating temperature of the current collector at the time of application of the electrode mixture to 70 to 100 ° C, the surface temperature of the roll is preferably 100 to 160 ° C. The surface temperature of the roll is more preferably 140 to 160 ° C.

  The method for heating the roll is not particularly limited. For example, an induction heating type in which a coil inside the roll is energized to induce heating of the roll body, a heating medium circulation type in which a hot solvent is circulated inside the roll, and a roll Examples thereof include an electric heating type in which a resistance heater inside generates heat, a steam heating type in which a roll is filled with steam and heated. Although the material of the said roll is not specifically limited, For example, carbon tool steel, stainless steel, alloy tool steel, etc. are mentioned.

  As the roll, for example, at least one of a backup roll and an infeed roll can be used. Here, the backup roll is a roll that comes into contact with the current collector at a part of the outer periphery, and indicates a backup roll that is disposed to face a coating machine used for application of the electrode mixture. The in-feed rolls are a pair of rolls that come into contact with the current collector in a part of the outer periphery by sandwiching the current collector, and indicate a roll provided in front of the coating machine.

  An example of the apparatus used for the process of apply | coating the electrode mixture in this invention on a collector is shown in FIG. In FIG. 2, first, the current collector 2 is unwound from the unwinding roll 3 and sent to the backup roll 6 via the infeed roll 4 and the guide roll 5. The backup roll 6 is heated to a predetermined temperature. The electrode mixture 1 is applied onto the current collector 2 by a die coater head 7 disposed so as to face the backup roll 6. The temperature of the current collector 2 when the electrode mixture 1 is applied is 70 to 100 ° C. Thereby, the electrical power collector 2 with which the electrode mixture 1 was apply | coated is manufactured. In the apparatus shown in FIG. 2, the backup roll 6 is heated, but the unwinding roll 3, the infeed roll 4, the guide roll 5, and the backup roll 6 in the path for transporting the current collector 2 to the die coater head 7. Any one or more of these may be heated to preheat the current collector 2.

  The solvent is removed from the current collector coated with the electrode mixture produced by the above method by drying. The method for drying the current collector coated with the electrode mixture is not particularly limited, and examples thereof include a method of drying in a hot air jet drying furnace. The hot-air spraying type drying furnace has one or more drying chambers, and nozzles for spraying dry air heated to a high temperature are arranged above and below each drying chamber. As a drying temperature, it can be 80-160 degreeC, for example. Moreover, as drying time, it can be 3-15 minutes, for example.

  Hereinafter, although the detail of this invention is demonstrated using an Example, this invention is not limited to these.

(Peel strength test)
About the manufactured electrode, the 180 degree | times peeling test was implemented according to JISK6854-2, and peeling strength was computed. In each example and comparative example, five electrode samples were prepared, the peel strength was measured for each electrode sample, and the average value of the peel strengths was calculated.

Example 1
95 parts by mass of graphite powder (trade name: Carbotron P, manufactured by Kureha Co., Ltd.) as an electrode active material, 1 part by mass of carbon powder (trade name: EC300J, manufactured by Lion Corporation) as a conductivity imparting agent, and fluoropolymer as a binder (Product name: KF polymer, manufactured by Kureha Co., Ltd.) 4 parts by mass were mixed to prepare a mixture. The mixture and 100 parts by mass of 1-methyl-2-pyrrolidone (NMP) with respect to the mixture were stirred with a three-roll mill to prepare an electrode mixture.

  The electrode mixture was applied to the current collector 2 using the apparatus shown in FIG. The current collector 2 was a copper foil having a thickness of 10 μm. The current collector 2 was unwound from the unwinding roll 3 and sent to the backup roll 6 through the infeed roll 4 and the guide roll 5. The surface temperature of the backup roll 6 was 100 ° C. In addition, the heating system of the backup roll 6 was a steam heating system. The electrode mixture was applied on the current collector 2 in a layered form having a thickness of 40 μm by using a die coater head 7 installed facing the backup roll 6. The temperature of the current collector 2 during application of the electrode mixture was 70.9 ° C.

  Thereafter, the current collector 2 to which the electrode mixture was applied was conveyed into a drying furnace. The drying furnace is a hot air jet type, and there are four drying furnaces, the temperature in the first chamber is 100 ° C., the temperature in the second chamber is 110 ° C., the temperature in the third chamber is 120 ° C., The furnace temperature in the fourth chamber was 130 ° C. The length of each drying furnace was 3500 mm. Moreover, the conveyance speed of the electrical power collector 2 which apply | coated the electrode mixture was 1 m / min. This produced an electrode. Five electrodes were prepared (Samples 1 to 5), and the peel strength test was performed. The results are shown in Table 1.

(Example 2)
An electrode was prepared in the same manner as in Example 1 except that the surface temperature of the backup roll 6 was 120 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 88.1 ° C., and a peel strength test was performed. The results are shown in Table 1.

(Example 3)
An electrode was prepared in the same manner as in Example 1 except that the surface temperature of the backup roll 6 was 140 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 92.8 ° C., and a peel strength test was performed. The results are shown in Table 1.

Example 4
An electrode was produced in the same manner as in Example 1 except that the surface temperature of the backup roll 6 was 160 ° C. and the temperature of the current collector 2 at the time of applying the electrode mixture was 100 ° C., and a peel strength test was performed. The results are shown in Table 1.

(Comparative Example 1)
An electrode was prepared in the same manner as in Example 1 except that the backup roll 6 was not heated, the surface temperature of the backup roll 6 was 25 ° C., and the temperature of the current collector 2 was 25.6 ° C. during application of the electrode mixture. A peel strength test was conducted. The results are shown in Table 1.

(Comparative Example 2)
An electrode was prepared in the same manner as in Example 1 except that the surface temperature of the backup roll 6 was 60 ° C., and the temperature of the current collector 2 at the time of application of the electrode mixture was 45.2 ° C., and a peel strength test was performed. The results are shown in Table 1.

(Comparative Example 3)
An electrode was produced in the same manner as in Example 1 except that the surface temperature of the backup roll 6 was 80 ° C. and the temperature of the current collector 2 at the time of applying the electrode mixture was 61.7 ° C., and a peel strength test was performed. The results are shown in Table 1.

  It was confirmed that Examples 1 to 4 in which the current collector 2 was preheated to 70 to 100 ° C. were improved by 3 to 31% in comparison with Comparative Example 1 in which preheating was not performed. On the other hand, Comparative Examples 2 and 3 in which the current collector 2 was preheated to less than 70 ° C. had the same peel strength as Comparative Example 1 in which preheating was not performed. Moreover, it was confirmed that the surface temperature of the backup roll 6 is preferably 100 ° C. or higher.

(Example 5)
95 parts by mass of graphite powder (trade name: Carbotron P, manufactured by Kureha Co., Ltd.) as an electrode active material, 1 part by mass of carbon powder (trade name: EC300J, manufactured by Lion Corporation) as a conductivity imparting agent, carboxy as a thickener 1 part by mass of methyl cellulose (CMC) (trade name: SN80C, Nippon Paper Chemicals Co., Ltd.) and 3 parts by mass of styrene butadiene copolymer (trade name: BM-400B, produced by Nippon Zeon Co., Ltd.) as a binder are prepared to prepare a mixture. did. The mixture and 100 parts by mass of water with respect to the mixture were stirred with a high-speed impeller mill to prepare an electrode mixture.

  Using the electrode mixture, the surface temperature of the backup roll 6 was 100 ° C., and the electrode 2 was prepared in the same manner as in Example 1 except that the temperature of the current collector 2 during application of the electrode mixture was 72.0 ° C. A peel strength test was performed. The results are shown in Table 2.

(Example 6)
An electrode was produced in the same manner as in Example 5 except that the surface temperature of the backup roll 6 was 120 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 84.3 ° C., and a peel strength test was performed. The results are shown in Table 2.

(Example 7)
An electrode was produced in the same manner as in Example 5 except that the surface temperature of the backup roll 6 was 140 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 89.9 ° C., and a peel strength test was performed. The results are shown in Table 2.

(Example 8)
An electrode was produced in the same manner as in Example 5 except that the surface temperature of the backup roll 6 was 160 ° C., and the temperature of the current collector 2 at the time of applying the electrode mixture was 99.7 ° C., and a peel strength test was performed. The results are shown in Table 2.

(Comparative Example 4)
An electrode was produced in the same manner as in Example 5 except that the backup roll 6 was not heated, the surface temperature of the backup roll 6 was 25 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 24.8 ° C. A peel strength test was conducted. The results are shown in Table 2.

(Comparative Example 5)
An electrode was produced in the same manner as in Example 5 except that the surface temperature of the backup roll 6 was 60 ° C. and the temperature of the current collector 2 was 44.8 ° C. during application of the electrode mixture, and a peel strength test was performed. The results are shown in Table 2.

(Comparative Example 6)
An electrode was produced in the same manner as in Example 5 except that the surface temperature of the backup roll 6 was set to 80 ° C., and the temperature of the current collector 2 during application of the electrode mixture was set to 60.1 ° C., and a peel strength test was performed. The results are shown in Table 2.

  In comparison with Comparative Example 4 in which no preheating was performed, Examples 5 to 8 in which the current collector 2 was preheated to 70 to 100 ° C. were confirmed to have an improvement in peel strength of 8 to 23%. On the other hand, Comparative Examples 5 and 6 in which the current collector 2 was preheated to less than 70 ° C. had the same peel strength as Comparative Example 4 in which no preheating was performed. Moreover, it was confirmed that the surface temperature of the backup roll 6 is preferably 100 ° C. or higher.

Example 9
95 parts by mass of LiCoO ₂ (trade name: Selion, manufactured by AGC Seimi Chemical Co., Ltd.) as an electrode active material, 1 part by mass of carbon powder (trade name: EC300J, manufactured by Lion Corporation) as a conductivity imparting agent, fluorine as a binder 4 parts by mass of a polymer (trade name: KF polymer, manufactured by Kureha Co., Ltd.) was mixed to prepare a mixture. The mixture and 100 parts by mass of 1-methyl-2-pyrrolidone (NMP) with respect to the mixture were stirred with a three-roll mill to prepare an electrode mixture.

  The electrode mixture was applied to the current collector 2 using the apparatus shown in FIG. The current collector 2 was an aluminum foil having a thickness of 20 μm. The current collector 2 is unwound from the unwinding roll 3 and sent to the backup roll 6 via the infeed roll 4 and the guide roll 5. The surface temperature of the backup roll 6 was 140 ° C. In addition, the heating system of the backup roll 6 is a steam heating system. The electrode mixture was applied on the current collector 2 in a layered form having a thickness of 70 μm by using a die coater head 7 installed facing the backup roll 6. The temperature of the current collector 2 during application of the electrode mixture is 70.9 ° C. Then, it dried similarly to Example 1, the electrode was produced, and the peeling strength test was done. The results are shown in Table 3.

(Example 10)
An electrode was prepared in the same manner as in Example 9 except that the surface temperature of the backup roll 6 was set to 160 ° C., and the temperature of the current collector 2 during application of the electrode mixture was set to 85.3 ° C., and a peel strength test was performed. The results are shown in Table 3.

(Comparative Example 7)
An electrode was prepared in the same manner as in Example 9 except that the backup roll 6 was not heated, the surface temperature of the backup roll 6 was 25 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 25.1 ° C. A peel strength test was conducted. The results are shown in Table 3.

(Comparative Example 8)
An electrode was prepared in the same manner as in Example 9 except that the surface temperature of the backup roll 6 was set to 60 ° C., and the temperature of the current collector 2 during application of the electrode mixture was set to 41.0 ° C., and a peel strength test was performed. The results are shown in Table 3.

(Comparative Example 9)
An electrode was produced in the same manner as in Example 9 except that the surface temperature of the backup roll 6 was set to 80 ° C., and the temperature of the current collector 2 during application of the electrode mixture was set to 46.7 ° C., and a peel strength test was performed. The results are shown in Table 3.

(Comparative Example 10)
An electrode was prepared in the same manner as in Example 9 except that the surface temperature of the backup roll 6 was 100 ° C. and the temperature of the current collector 2 at the time of applying the electrode mixture was 54.2 ° C., and a peel strength test was performed. The results are shown in Table 3.

(Comparative Example 11)
An electrode was produced in the same manner as in Example 9 except that the surface temperature of the backup roll 6 was 120 ° C., and the temperature of the current collector 2 during application of the electrode mixture was 66.1 ° C., and a peel strength test was performed. The results are shown in Table 3.

  It was confirmed that Examples 9 and 10 in which the current collector 2 was preheated to 70 to 100 ° C., compared with Comparative Example 7 in which no preheating was performed, had an improvement in peel strength of 6 to 11%. Moreover, the improvement of peeling strength was confirmed also about Examples 9 and 10 also with respect to Comparative Examples 8 to 11 in which the current collector 2 was preheated to less than 70 ° C.

  The electrode produced according to the present invention can be used for a non-aqueous electrolyte secondary battery, but is not limited to this and can be applied to other batteries.

1 Electrode mixture (layer)
2 Current collector 3 Unwinding roll 4 Infeed roll 5 Guide roll 6 Backup roll 7 Die coater head

Claims (5)

In the method for producing an electrode in which an electrode mixture containing an electrode active material, a binder and a solvent is applied onto a current collector, and then the solvent is removed by drying
The manufacturing method of the electrode by which the said collector is preheated at 70-100 degreeC at the time of application | coating of the said electrode mixture.   The method for producing an electrode according to claim 1, wherein the preheating is performed by bringing a heated roll into contact with the current collector.   The electrode manufacturing method according to claim 2, wherein the roll has a surface temperature of 100 to 160 ° C. 4.   The method for producing an electrode according to claim 2, wherein the roll is at least one of a backup roll and an infeed roll.   The electrode manufactured by the method as described in any one of Claim 1 to 4.

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