JP2015138611A - Method for manufacturing positive electrode for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a positive electrode for a secondary battery capable of providing a secondary battery with excellent performance.SOLUTION: A method for manufacturing a positive electrode for a secondary battery comprises the steps of: preparing a first granulated body using a positive electrode active material, a conductive agent, a thickener, and water; preparing a second granulated body by adding a binder to the first granulated body; cracking the second granulated body with a high-speed stirring granulation device; and providing a positive electrode mixture slurry including a third granulated body obtained by cracking the second granulated body in a positive electrode collector. When the second granulated body is cracked, at least one of the positive electrode active material and the conductive agent arranged inside the second granulated body is exposed.

Description

  The present invention relates to a method for producing a positive electrode for a secondary battery, and more particularly to a method for producing a positive electrode mixture slurry.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-111384) describes a large aggregated particle contained in an aqueous paste after kneading a positive electrode active material powder containing granulated particles with water or an aqueous binder solution to prepare an aqueous paste. It is described that the scouring treatment is carried out while pressure is collapsed, and the resulting scouring paste is applied to a current collecting substrate to a desired thickness and dried.

JP 2010-111384 A

  FIG. 5 is a flowchart showing the main part of a conventional method for producing a positive electrode for a secondary battery in the order of steps. FIG. 6 is a side view schematically showing a positive electrode obtained according to the manufacturing method shown in FIG. FIG. 7 is an image (left side) obtained by observing a cross section of the positive electrode obtained with the microscope according to the manufacturing method shown in FIG. 5 and a distribution diagram (right side) of the binder in the positive electrode mixture layer of the positive electrode.

  In the conventional method for producing a positive electrode for a secondary battery, after mixing the positive electrode active material 1, the conductive agent and the thickener (step S901), water is added to the mixture and kneaded (step S902). The binder 7 is added to the kneaded product and further kneaded (step S903). In this way, a positive electrode mixture slurry is obtained. The obtained positive electrode mixture slurry is applied to a positive electrode current collector 31A such as an aluminum foil and dried. In this way, a positive electrode 931 in which the positive electrode mixture layer 931B is bonded to the positive electrode current collector 31A is obtained.

  In step S901, the thickener is attached to the surface of the conductive agent to obtain the covering 94, but a part of the covering 94 is aggregated without being dispersed in the mixture to form the aggregate 96. When the binder 7 is added in this state, the binder 7 preferentially adheres to the aggregate 96. Therefore, the binder 7 is not uniformly dispersed in the positive electrode mixture slurry. When the positive electrode mixture layer 931B is formed using such a positive electrode mixture slurry, the binder 7 also aggregates without being uniformly dispersed in the formed positive electrode mixture layer 931B (FIG. 7). Therefore, the constituent material of the positive electrode mixture layer 931B may be dropped from the positive electrode current collector 31A without being bonded to the positive electrode current collector 31A, thereby causing a decrease in conductivity of the positive electrode 931 and a decrease in capacity of the secondary battery. .

  Aggregation of the binder 7 can be prevented by adding a dispersant or the like. However, since the added dispersant may coat the positive electrode active material 1 or the like, the reactivity of the positive electrode is lowered. As a result, the IV resistance of the secondary battery is increased at low temperatures. The objective of this invention is providing the manufacturing method of the positive electrode for secondary batteries which can improve the performance of a secondary battery.

  The method for producing a positive electrode for a secondary battery according to the present invention includes a step of producing a first granule using a positive electrode active material, a conductive agent, a thickener and water, and a binder on the first granule. A step of producing a second granulated body by adding, a step of crushing the second granulated body with a high-speed stirring granulator, and a third granulated body obtained by crushing the second granulated body. And a step of providing the positive electrode mixture slurry containing the positive electrode mixture slurry on the positive electrode current collector. By crushing the second granulated body, at least one of the positive electrode active material and the conductive agent disposed inside the second granulated body is exposed.

  The “first granulated body” is formed by adhering positive electrode active materials to each other through a thickener attached to the surface of the conductive agent. The “second granulated body” means a structure in which the first granulated bodies are bonded to each other via a binder. “Crushing” means an operation necessary for releasing the adhesion between the conductive agents present on the surface of the second granulated body.

  Since the first granulated body is prepared using the positive electrode active material, the conductive agent, the thickener, and water, the thickener is attached to the surface of the conductive agent together with water to form a covering. Thereby, aggregation of a covering is prevented. Therefore, aggregation of the binder added after that can be prevented. Therefore, it is possible to prevent a decrease in the conductivity of the positive electrode and a decrease in the capacity of the secondary battery.

  Further, in the third granulated body, at least one of the positive electrode active material and the conductive agent arranged inside the second granulated body is exposed. Thereby, the fall of the reactivity of a positive electrode can be prevented. Therefore, an increase in the IV resistance of the secondary battery at a low temperature can be prevented.

  In the present invention, it is possible to prevent a decrease in the conductivity of the positive electrode, a decrease in the capacity of the secondary battery, and an increase in the IV resistance of the secondary battery at a low temperature. Therefore, it is possible to provide a secondary battery excellent in performance.

It is a flowchart which shows the manufacturing method of the positive electrode of one Embodiment of this invention in process order. It is a side view which shows the principal part of the manufacturing method of the positive electrode of one Embodiment of this invention in order of a process. It is sectional drawing which shows the structure of the coating body of one Embodiment of this invention. It is the image (left side) which observed the cross section of the positive electrode of one Embodiment of this invention with the microscope, and the distribution map (right side) of the binder in the positive mix layer of the positive electrode. It is a flowchart which shows the principal part of the manufacturing method of the conventional positive electrode in order of a process. It is a side view which shows typically the positive electrode obtained according to the manufacturing method shown in FIG. It is the image (left side) which observed the cross section of the positive electrode obtained according to the manufacturing method shown in FIG. 5 with the microscope, and the distribution map (right side) of the binder in the positive mix layer of the positive electrode.

  Hereinafter, the manufacturing method of the positive electrode for secondary batteries of the present invention (hereinafter simply referred to as “positive electrode”) will be described with reference to the drawings. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

[Production of positive electrode]
FIG. 1 is a flowchart showing a method for manufacturing a positive electrode according to an embodiment of the present invention in the order of steps. FIG. 2 is a side view showing the main part of the positive electrode manufacturing method of the present embodiment in the order of steps. FIG. 3 is a cross-sectional view showing the configuration of the covering according to the present embodiment. FIG. 4 is an image (left side) obtained by observing a cross section of the positive electrode of the present embodiment with a microscope and a distribution diagram (right side) of the binder in the positive electrode mixture layer of the positive electrode.

  In the manufacturing method of the positive electrode 31, the first granule is produced using the positive electrode active material 1, the conductive agent 3, the thickener 5, and water, so that the thickener 5 adheres to the surface of the conductive agent 3 together with water. Thus, the covering 4 is formed. Thereby, aggregation of the covering 4 is prevented. Therefore, even if the binder 7 is added to the first granulated body, aggregation of the binder 7 in the produced second granulated body 11 can be prevented. Therefore, since the aggregation of the binder 7 can be prevented also in the positive electrode mixture layer 31B formed in the subsequent process (FIG. 4), the constituent materials of the positive electrode mixture layer 31B (the positive electrode active material 1, the conductive agent 3 or the increase). It is possible to prevent the sticky agent 5 and the like from dropping from the positive electrode current collector 31A. As a result, the manufactured positive electrode 31 can prevent a decrease in conductivity. Moreover, if a secondary battery is manufactured using the positive electrode 31, the capacity | capacitance fall of a secondary battery can be prevented.

  Moreover, by crushing the second granulated body 11, at least one of the positive electrode active material 1 and the conductive agent 3 disposed inside the second granulated body 11 is exposed. That is, the third granulated body 21 includes the positive electrode active material 1, the conductive agent 3 or the positive electrode active material 1 and the conductive agent 3 having a surface (exposed surface) that is not covered with the binder 7. If the positive electrode 31 is produced using such a third granulated body 21, a decrease in the reactivity of the positive electrode 31 can be prevented. Therefore, if a secondary battery is manufactured using the positive electrode 31, an increase in the IV resistance of the secondary battery at a low temperature can be prevented.

  As mentioned above, if the positive electrode 31 is manufactured according to the manufacturing method of the positive electrode 31 of this embodiment, the secondary battery excellent in the output characteristic can be provided. Hereinafter, each process will be described.

(Production of first granulated body)
In step S101, the positive electrode active material 1, the conductive agent 3, the thickener 5 and water are mixed. Thereby, a 1st granulated body (for example, a particle size is about 1 mm) is produced.

  When the positive electrode active material 1, the conductive agent 3, and the thickener 5 are wetted with water, granulation starts gradually. In general, the conductive agent 3 has a large specific surface area, and the thickener 5 also functions as an adhesive. Therefore, the thickener 5 is attached to the surface of the conductive agent 3 together with water to form the covering 4. Since the covering 4 is formed in this way, aggregation of the covering 4 can be prevented. In addition, the positive electrode active materials 1 are bonded to each other through the thickener 5 on the surface of the covering 4.

  It is preferable to produce the first granulated body by stirring granulation, and it is more preferred to produce the first granulated body using a high-speed stirring granulator. Thereby, the 1st granule with a uniform particle size is obtained. The high-speed agitation granulator includes a stirring blade (agitator) and a crushing blade (chopper), for example, a trade name “High Speed Mixer” manufactured by Earth Technica Co., Ltd.

The positive electrode active material 1 to be used is a chemical reaction material in the positive electrode 31. As the positive electrode active material 1, a conventionally known material can be used as the positive electrode active material of the nonaqueous electrolyte secondary battery without particular limitation, and a compound containing lithium and one or more metals other than lithium is used. It is preferable to use an oxide containing lithium and one or more transition metals. The positive electrode active material 1 is, for example, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ .

  The conductive agent 3 used is a conductive compound. The addition of the conductive agent 3 can be expected to form an electronic network inside the positive electrode mixture layer 31B. As the conductive agent 3, a conventionally known material can be used as the conductive agent for the positive electrode of the nonaqueous electrolyte secondary battery without any particular limitation, and a carbon material (for example, carbon black such as acetylene black, graphite, carbon fiber) Etc.) are preferred.

  The thickener 5 to be used is a compound that can impart viscosity to the first granulated body by addition. By adding the thickener 5, the applicability of the positive electrode mixture slurry to the positive electrode current collector 31A is improved. As the thickener 5, a conventionally known material can be used as the thickener for the positive electrode of the nonaqueous electrolyte secondary battery without any particular limitation, and CMC (carboxymethylcellulose) is preferably used. CMC also functions as a binder. Therefore, if CMC is used as the thickener 5, the covering 4 is easily formed, and the first granulated body is also easily formed.

(Production of second granulated body)
In step S102, the binder 7 is added to the first granulated body. Thereby, 1st granulation body is adhere | attached through the binder 7, Therefore, the 2nd granulation body 11 is produced.

  The binder 7 is preferably added to the first granulated body in a state of being dispersed in water. For example, it is preferable to add the binder 7 to a solution in which the first granulated body is dispersed. The suspension containing the first granulated body, the binder 7 and water preferably has a solid content of 70% by mass or more and 85% by mass or less. When the solid content is 70% by mass or more, the aggregation of the binder 7 in the suspension can be prevented, so that the aggregation of the binder 7 in the second granulated body 11 can be effectively prevented. If the solid content is 85% by mass or less, since the binder 7 can be prevented from penetrating into the first granulated body, the binder 7 is formed on the surface of the positive electrode active material 1 of the first granulated body. It can prevent adhesion. Therefore, the capacity reduction of the secondary battery can be prevented. “Solid fraction” means the ratio (%) of the mass of the solid to the total of the mass of the liquid and the mass of the solid contained in the suspension. By adjusting the amount of the liquid contained in the suspension, the solid content ratio of the suspension can be adjusted to a desired value. The solid content of the suspension is more preferably 75% by mass or more and 85% by mass or less.

  The production method of the second granulated body 11 is not particularly limited. However, like the first granulated body, it is preferable to produce the second granulated body 11 by stirring granulation, and it is more preferred to produce the second granulated body 11 using a high-speed stirring granulation apparatus.

  The binder 7 to be used is a compound having binding properties. By adding the binder 7, it is possible to effectively prevent the constituent material of the positive electrode mixture layer 31B from dropping off from the positive electrode current collector 31A. As the binder 7, a conventionally known material can be used without particular limitation as a binder for the positive electrode of the nonaqueous electrolyte secondary battery, and for example, PTFE (polytetrafluoroethylene) or the like is preferably used.

(Disintegration of second granule)
In step S103, the second granulated body 11 is crushed with a high-speed stirring granulator. Thereby, at least one of the positive electrode active material 1 and the conductive agent 3 arranged in the second granulated body 11 is exposed, and the third granulated body 21 is obtained.

  The shearing force of the high-speed agitation granulator has a sufficient magnitude for releasing the adhesion between the conductive agents 3 on the surface of the second granulated body 11. On the other hand, when the second granulated body 11 is crushed using an apparatus having a shearing force smaller than that of the high-speed stirring granulator, it is difficult to release the adhesion between the conductive agents 3 on the surface of the second granulated body 11. Moreover, since the adhesive force between the positive electrode active material 1 and the conductive agent 3 is large, the bond between the positive electrode active material 1 and the conductive agent 3 is not released by the shearing force of the high-speed stirring granulator. As mentioned above, if the 2nd granulation body 11 is crushed with a high-speed stirring granulation apparatus, the 3rd granulation body 21 can be obtained efficiently.

  More preferably, the second granulated body 11 is put into a high-speed stirring granulator together with water and crushed. Thereby, the positive mix slurry containing the 3rd granulated body 21 is obtained.

(Coating / Drying)
Subsequently, in step S104, the positive electrode mixture slurry is applied to the positive electrode current collector 31A and then dried. Thereby, the positive electrode 31 in which the positive electrode mixture layer 31B is provided on the positive electrode current collector 31A is obtained. As a method of applying the positive electrode mixture slurry to the positive electrode current collector 31A, a conventionally known method can be used without particular limitation as a method of applying the positive electrode mixture slurry of the nonaqueous electrolyte secondary battery. Further, as the positive electrode current collector 31A, a conventionally known configuration can be used without particular limitation as the positive electrode current collector of the nonaqueous electrolyte secondary battery.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
(Preparation of positive electrode mixture slurry)
As a positive electrode active material, a powder made of a lithium-containing transition metal composite oxide containing Li and three transition metal elements (Co, Ni, and Mn) was prepared. Using a high speed mixer (manufactured by Earth Technica Co., Ltd.), the positive electrode active material, acetylene black (conductive agent), CMC sodium salt (thickener) and water were mixed to obtain a first granulated body.

  Next, the 1st granule, PTFE (binder), and water were mixed using the said high speed mixer, and the 2nd granule was obtained. The amount of water was adjusted so that the solid content of the suspension containing the first granulated body, PTFE, and water was 80% by mass.

  Subsequently, the second granule contained in the suspension was pulverized using the high speed mixer. In this way, a positive electrode mixture slurry containing the third granulated body was obtained.

(Preparation of positive electrode)
The positive electrode mixture slurry was applied to both surfaces of the Al foil so that one end in the width direction of the Al foil (positive electrode current collector) was exposed. The coating amount of the positive electrode mixture slurry was 30 mg / cm ² . Thereafter, the positive electrode mixture slurry was dried. Thus, a positive electrode hoop having a positive electrode exposed portion was obtained.

(Preparation of negative electrode)
As the negative electrode active material, scaly graphite (particle size D50 = 10 μm) was prepared. The negative electrode active material, SBR (Styrene-butadiene rubber) (binder) and CMC sodium salt (thickener) were mixed to obtain a negative electrode mixture slurry.

The negative electrode mixture slurry was applied to both surfaces of the Cu foil so that one end in the width direction of the Cu foil (negative electrode current collector) was exposed. The coating amount of the negative electrode mixture slurry was 18 mg / cm ² . Thereafter, the negative electrode mixture slurry was dried. In this way, a negative electrode hoop having a negative electrode exposed portion was obtained.

(Production of wound electrode body)
A separator (width: 59.5 mm, thickness: 25 μm) made of PE (polyethylene) was prepared. Next, the positive electrode, the separator, and the negative electrode were arranged so that the positive electrode exposed portion and the negative electrode exposed portion protruded from the separator in opposite directions in the width direction of the Al foil. Then, the winding axis | shaft (not shown) was arrange | positioned so that it might become parallel with respect to the width direction of Al foil, and the positive electrode, the separator, and the negative electrode were wound using the winding axis | shaft. Thus, a wound electrode body was obtained.

(Preparation of electrolyte)
EC (ethylene carbonate), EMC (methyl ethyl carbonate), and DEC (diethyl carbonate) were mixed so that the volume ratio was 3: 5: 2 to obtain a mixed solvent. LiPF ₆ was added to this mixed solvent so that the concentration became 1.0 mol / L. In this way, an electrolytic solution was obtained.

(Sealing)
An outer case having a diameter of 18 cm and a height of 650 mm was prepared. After putting the wound electrode body and the electrolyte into the outer case, the outer case was sealed. Thus, the nonaqueous electrolyte secondary battery of Example 1 (theoretical capacity is 1.0 Ah, 18650 cylindrical lithium ion secondary battery) was obtained.

<Examples 2-7, Comparative Examples 1-3>
In Example 2, according to the method described in Example 1 except that the first granulated body and the second granulated body were produced using a planetary mixer (Inoue Seisakusho Co., Ltd.), non-water An electrolyte secondary battery was manufactured.

  In Examples 3 to 7, non-aqueous electrolyte secondary batteries were manufactured according to the method described in Example 1 except that the solid content rate of the suspension was the value shown in Table 1.

In Comparative Example 1, a nonaqueous electrolyte secondary battery was manufactured according to the method shown in FIG.
In Comparative Example 2, a nonaqueous electrolyte secondary battery was manufactured according to the method described in Example 1 except that the second granulated body was pulverized using the planetary mixer.

  In Comparative Example 3, a nonaqueous electrolyte secondary battery was manufactured according to the method described in Example 2 except that the second granulated body was crushed using the planetary mixer.

(Measurement of peel strength)
The positive electrode was taken out from the non-aqueous electrolyte secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3. Next, based on the method described in JIS Z0237 (2000), the strength necessary for the positive electrode mixture layer to peel from the positive electrode current collector was measured by a 90 ° peel strength test. The results are shown in “Peel strength” in Table 1. Higher peel strength means that the positive electrode mixture layer is more difficult to peel from the positive electrode current collector.

(Measurement of IV resistance at low temperature)
The nonaqueous electrolyte secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were discharged at −15 ° C. with a current of 0.4 C for 10 seconds, and then the voltage was measured. Change the current to 0.8C, 1.2C, 1.6C, 2.0C, 2.4C, 2.8C, 3.2C, 3.6C, 4.0C, 4.4C, 4.8C, and so on The voltage was measured according to the method. A current vs voltage line was created using the 12 voltages measured, and the slope of the line was taken as the IV resistance at low temperature. The results are shown in Table 1, “IV Resistance at Low Temperature”. It means that it is excellent in performance, so that IV resistance in low temperature is small.

(Discussion)
In Comparative Examples 1 to 3, the peel strength was small, and the IV resistance at low temperature was large. The following can be considered as the reason. In Comparative Example 1, the positive electrode mixture slurry was prepared by the method shown in FIG. 5, and the peel strength was extremely small. In Comparative Examples 2 and 3, the second granulated body was crushed using the planetary mixer.

On the other hand, in Examples 1-5, peeling strength was large and IV resistance in low temperature was small.
In Example 1 and Example 2, the first granulated body and the second granulated body were produced using different apparatuses, but the results were not significantly different. From this, it was found that the type of apparatus used for producing the first granulated body and the second granulated body is not particularly limited.

  In Examples 4 to 6, the peel strength was large and the IV resistance at low temperature was small compared to Examples 3 and 7. From this, it was found that the solid content of the suspension is preferably 70% by mass or more and 85% by mass or less.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Positive electrode active material, 3 Conductive agent, 4,94 Cover body, 5 Thickener, 7 Binder, 11 2nd granule, 21 3rd granule, 31,931 positive electrode, 31A Positive electrode collector, 31B, 931B Positive electrode mixture layer, 96 aggregate.

Claims (1)

Producing a first granulated body using a positive electrode active material, a conductive agent, a thickener and water;
Producing a second granulated body by adding a binder to the first granulated body;
Crushing the second granulated body with a high-speed stirring granulator;
Providing a positive electrode mixture slurry containing a third granulated body obtained by crushing the second granulated body on a positive electrode current collector,
A method for producing a positive electrode for a secondary battery in which at least one of a positive electrode active material and a conductive agent disposed inside the second granule is exposed by crushing the second granule.