JP6358470B2 - Method for producing negative electrode for secondary battery - Google Patents

Description

  The present invention relates to a method for producing a negative electrode for a secondary battery.

  In recent years, secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries have become increasingly important as power sources mounted on vehicles using electricity as power sources, or power sources mounted on personal computers, mobile terminals, and other electrical products. Yes. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle.

  In a typical negative electrode of this type of secondary battery, a negative electrode active material layer mainly composed of a negative electrode active material capable of reversibly occluding and releasing chemical species serving as a charge carrier is held on a negative electrode current collector. It has a configuration. The negative electrode active material layer can be generally formed by slurrying a negative electrode active material and a binder with a suitable solvent, applying and drying this negative electrode slurry on a negative electrode current collector, and then pressing (for example, Patent Document 1). In addition, a method for producing a negative electrode by wet powder molding without using a large amount of solvent has been attempted. In wet powder molding, typically, wet granulated particles obtained by granulating a negative electrode active material, a binder, and a small amount of solvent are granulated, and the powder of the wet granulated particles is pressed (rolled) to obtain a negative electrode collector. By forming a film on the current collector, a negative electrode active material layer can be formed on the negative electrode current collector.

JP 2005-129437 A

  By the way, in recent years, a metal-based negative electrode active material made of a simple substance such as Si or Sn or an alloy thereof has attracted attention as a negative electrode active material capable of obtaining a high capacity (for example, Patent Document 1). The metal-based negative electrode active material has a higher theoretical capacity than carbon materials such as graphite, and can contribute to an increase in capacity of the battery, but has a large volume expansion / contraction rate due to charge / discharge. Therefore, cracks (cracks) occur around the metal-based negative electrode active material while charging and discharging are repeated, which can be a factor causing performance deterioration. In order to cope with such a problem, it has been studied to reduce the cracks by using a metal-based negative electrode active material and a carbon material having a relatively small expansion / contraction amount. However, even with such a technique, cracks may occur around the metal-based negative electrode active material depending on the dispersion state of the binder in the negative electrode. This invention provides the negative electrode for secondary batteries excellent in durability.

  The method of manufacturing a negative electrode for a secondary battery proposed here is a granulation method for granulating wet granulated particles containing a metal-based negative electrode active material containing at least one metal element, a carbon material, a binder, and a solvent. Process. The method also includes a step of forming a negative electrode active material layer on the negative electrode current collector by press-molding a powder composed of the wet granulated particles. The granulation step includes a first mixing process of mixing the metal-based negative electrode active material, the binder, and the solvent, and a second mixing process of mixing the carbon material into the obtained mixture after the first mixing process. Mixing process. According to such a manufacturing method, a secondary battery negative electrode having excellent durability, in which cracks are unlikely to occur around the metal-based negative electrode active material even when charging and discharging are repeated, can be obtained.

  The content of the binder with respect to the entire solid content of the wet granulated particles may be 0.5% by mass to 2% by mass. The durability improvement effect mentioned above may be more suitably exhibited, suppressing the raise of battery resistance as it is in the range of content of such a binder.

  The ratio of the content of the metal-based negative electrode active material and the carbon material contained in the wet granulated particles (metal-based negative electrode active material: carbon material) may be 1: 9 to 5: 5 on a mass basis. With such a ratio of the content of the metal-based negative electrode active material and the carbon material, it is possible to effectively suppress the occurrence of cracks due to the volume change of the metal-based negative electrode active material while suppressing an increase in battery resistance. it can. Therefore, both low resistance and improved durability can be realized at a higher level.

  The metal-based negative electrode active material may include at least one metal element of silicon (Si) and tin (Sn) as a constituent element. A metal-based negative electrode active material containing these metal elements has a high theoretical capacity and is useful as a negative electrode active material that contributes to an increase in capacity of a battery. On the other hand, volume change due to charge and discharge is large, and it tends to cause cracks. is there. However, according to the negative electrode manufacturing method of the present invention, the occurrence of cracks can be effectively suppressed even when such a metal negative electrode active material having a large volume change is used. Therefore, the manufacturing method disclosed herein has an advantage that a negative electrode having excellent durability can be obtained while using a useful metal-based negative electrode active material such as Si or Sn.

  In the first mixing process, a first stirring process in which the metal-based negative electrode active material and the binder are stirred together with powder, and after the first stirring process, the solvent is mixed into the obtained powder stirred product. And a second stirring process of stirring. According to such a configuration, the metal-based negative electrode active material and the binder are uniformly mixed with each other, and then the solvent is added. Therefore, the binder can be uniformly and reliably disposed around the metal-based negative electrode active material. . Therefore, generation of cracks around the metal-based negative electrode active material can be more effectively suppressed.

  The first stirring process and the second stirring process are performed using the same stirring device, and the stirring rotational speed of the stirring device in the first stirring process is the stirring rotational speed of the stirring device in the second stirring process. You may set so that it may become larger. In this way, a mixture in which the metal-based negative electrode active material, the binder, and the solvent are uniformly mixed can be stably obtained.

FIG. 1 is a diagram showing a manufacturing flow of a secondary battery negative electrode. FIG. 2 is a diagram showing a flow of the granulation process. FIG. 3 is a diagram schematically showing wet granulated particles obtained in the granulation step. FIG. 4 is a schematic view showing a powder roll press apparatus. FIG. 5 is a diagram schematically showing a battery configuration. FIG. 6 is a view for explaining the wound electrode body. FIG. 7 is a diagram showing a flow of the granulation process of Comparative Example 1.

Hereinafter, an embodiment of a method for manufacturing a negative electrode for a secondary battery proposed here will be described. The embodiments described herein are, of course, not intended to limit the present invention in particular. Each drawing is schematically drawn. For example, the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship.
In the present specification, “secondary battery” refers to a battery that can be repeatedly charged. A “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of charges associated with lithium ions between the positive and negative electrodes.

  As a preferred embodiment of a method for producing a negative electrode for a secondary battery disclosed herein, a method for producing a negative electrode for a lithium ion secondary battery is taken as an example and the flowcharts shown in FIGS. 1 and 2 are referred to. However, the present invention is not intended to be limited to such secondary batteries.

  As shown in FIG. 1, the manufacturing method disclosed herein is a granulation method for granulating wet granulated particles containing a metal-based negative electrode active material containing at least one metal element, a carbon material, a binder, and a solvent. A granulation step (step S100) and a pressing step (step S200) for forming a negative electrode active material layer on the negative electrode current collector by press-molding a powder composed of wet granulated particles. Hereinafter, each process will be described in detail.

<Granulation process>
The granulation step of Step S100 is a step of granulating wet granulated particles containing a metal-based negative electrode active material, a carbon material, a binder, and a solvent.

The metal-based negative electrode active material used for the wet granulated particles may be any material that contains at least one metal element as a constituent element. Preferable examples include a metal-based negative electrode active material mainly composed of a material containing at least one metal element of silicon (Si) and tin (Sn). Examples of the material containing Si as a constituent element include a simple metal element of Si, an oxide containing Si as a constituent element (for example, SiO _x ), and an alloy containing Si as a constituent element. Examples of the material containing Sn as a constituent element include a single metal of Sn, an oxide containing Sn as a constituent element (for example, SnO _x ), and an alloy containing Sn as a constituent element. Examples of constituent elements other than Si and Sn in the alloy include Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, In, Al, and Li. These materials are preferable in that they have a high theoretical capacity and can contribute to an increase in battery capacity. Alternatively, a metal-based negative electrode active material mainly containing an oxide (lithium titanate) containing lithium and titanium as constituent metal elements may be used. One kind selected from such materials may be used alone, or two or more kinds may be used in combination. The “metal” in the present specification may also include a semimetal such as Si. The “alloy” in the present specification means a mixture of two or more metals at a microscopic level, and the alloy structure includes, for example, a solid solution, an intermetallic compound, or the coexistence thereof. Things can be included. Although the property of the said metal type negative electrode active material is not specifically limited, For example, the average particle diameter (D50 diameter) based on a laser diffraction / scattering method is about 1 micrometer-50 micrometers (typically 5 micrometers-20 micrometers, preferably 8 micrometers-12 micrometers) The powder form (particulate form) can be preferably used. The production method disclosed herein can be more suitably applied to a metal-based negative electrode active material having such an average particle size.

  Carbon materials used for wet granulated particles include so-called graphitic materials, non-graphitizable carbon materials (hard carbon), graphitizable carbon materials (soft carbon), and combinations of these. Any carbon material can be suitably used. A carbon material containing a graphite structure (layered structure) at least partially is preferable. In addition, various graphites such as natural graphite and artificial graphite are processed into particles (pulverized, spherically shaped, etc.) (eg, spheroidized graphite obtained by spheroidizing Flake Graphite graphite), and various graphites are made of amorphous carbon. Coated (coated); etc. can be used. Alternatively, carbon powders such as acetylene black (AB), oil furnace black, graphitized carbon black, carbon black, and ketjen black may be used. One kind selected from such carbon materials may be used alone, or two or more kinds may be used in combination. The carbon material disclosed herein may be one that can occlude and release charge carriers (functions as a negative electrode active material) or one that can function as a conductive material. In a preferred embodiment, the carbon material functions as a negative electrode active material and can also function as a conductive material. The property of the carbon material is not particularly limited. For example, the average particle diameter (D50 diameter) based on the laser diffraction / scattering method is about 1 μm to 50 μm (typically 5 μm to 20 μm, preferably 8 μm to 12 μm). (Particulate) can be preferably used. The production method disclosed herein can be more suitably applied to a carbon material having such an average particle size.

  The binder used in the wet granulated particles is one that can adhere to the surface of the individual metal negative electrode active material and carbon material particles, and further bind the metal negative electrode active material and carbon material particles together. There is no limit. For example, it is preferable to use a material mainly composed of polyimide (PI), polyamideimide (PAI), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polyacrylic acid and derivatives thereof. it can. One kind selected from such polymer materials may be used alone, or two or more kinds may be used in combination. Among these, polyimide (PI), polyvinyl alcohol (PVA), and derivatives thereof are preferable because they can firmly bind the metal negative electrode active material and the carbon material particles with a relatively small addition amount. Moreover, it is preferable at the point which can improve the binding property of a negative electrode active material layer and a negative electrode electrical power collector, and can implement | achieve the negative electrode which does not produce interface peeling easily.

  As the solvent used for the wet granulated particles, either an aqueous solvent or a non-aqueous solvent can be used. Typically, water or a mixed solvent mainly composed of water is preferably used. As a solvent component other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water.

  As shown in FIG. 2, the granulation process disclosed herein is obtained after the first mixing process (step S110) in which the metal-based negative electrode active material, the binder, and the solvent described above are mixed, and the first mixing process. And a second mixing process (step S120) for mixing the carbon material with the obtained mixture.

(First mixing process)
In the first mixing process of step S110, the metal-based negative electrode active material, the binder, and the solvent described above are mixed. In this embodiment, the first mixing process may include a first stirring process (step S112) and a second stirring process (step S114).

  In the first stirring process of step S112, the metal-based negative electrode active material and the binder are stirred with powder. In the first stirring treatment, it is preferable that the metal-based negative electrode active material powder and the binder powder are sufficiently mixed until they are in a uniformly mixed state. The stirring time of the first stirring treatment may vary depending on the apparatus configuration and stirring conditions, but is usually about 1 to 30 seconds, preferably 3 to 10 seconds, more preferably 5 to 8 seconds. It is. In the first stirring treatment, the metal-based negative electrode active material and the binder are stirred with each other, so that a powder stirred product in which the metal-based negative electrode active material powder and the binder powder are uniformly mixed can be obtained.

  In the second stirring process of step S114, after the first stirring process, a solvent is mixed with the obtained powder stirred product and stirred. In the second agitation treatment, the powder agitation is moistened with a solvent and agglomerated into spherical particles by applying a rotational motion of agitation. That is, a granular mixture composed of a metal-based negative electrode active material, a binder, and a solvent is obtained. In the second stirring treatment, stirring is preferably performed until the granular mixture is spheroidized to a certain size. The stirring time of the second stirring treatment may vary depending on the apparatus configuration and stirring conditions, but is usually about 5 seconds to 60 seconds, preferably 8 seconds to 30 seconds, more preferably 10 seconds to 20 seconds. It is.

  The first stirring process and the second stirring process may be performed using the same stirring apparatus or different stirring apparatuses, but it is preferable to use the same stirring apparatus from the viewpoint of productivity. . The stirring apparatus for performing stirring is not particularly limited. For example, the stirrer may have a rotating stirrer (a stirring blade such as a disper blade or a turbine blade, a stirring blade), and may be mixed and granulated by stirring the stirrer. Examples of such a stirring device include mechanical stirring devices such as a planetary mixer, a food processor, a homomixer, a Henschel mixer, a super mixer, a propeller stirrer, and a high-speed mixer.

  In a preferred embodiment, the same stirring apparatus is used for the first stirring process and the second stirring process, and the stirring rotational speed of the stirring apparatus in the first stirring process is set higher than the stirring rotational speed of the stirring apparatus in the second stirring process. Also set larger. By setting the rotational speed of the first stirring process to be larger than the rotational speed of the second stirring process, a powder stirred product in which the metal-based negative electrode active material and the binder are more uniformly mixed can be obtained efficiently. In addition, by setting the rotation speed of the second stirring process to be smaller than the rotation speed of the first stirring process, the powder agitated material moistened with the solvent is easily spheroidized, and the granular mixture can be stably obtained. . Although not particularly limited, the rotation speed of the first stirring process is suitably about 2000 rpm to 5000 rpm, preferably 2500 rpm to 4000 rpm, and more preferably 2600 rpm to 3000 rpm. The stirring speed of the second stirring treatment is generally about 300 rpm to 1800 rpm, preferably 500 rpm to 1500 rpm, and more preferably 800 rpm to 1000 rpm.

(Second mixing process)
In the second mixing process of step S120, after the first mixing process, a carbon material is mixed with the obtained granular mixture (a mixture of a metal-based negative electrode active material, a binder, and a solvent). In this embodiment, the second mixing process includes a third stirring process (step S122) and a fourth stirring process (step S124).

  In the third stirring process in step S122, the granular mixture obtained in the first mixing process and the carbon material are stirred and mixed at a low speed. In the third stirring treatment, it is desirable to stir at a relatively small number of revolutions so that the granular mixture and the carbon material are sufficiently mixed. By mixing the granular mixture and the carbon material in this way, wet granulated particles containing a metal-based negative electrode active material, a carbon material, a binder, and a solvent can be obtained. The third stirring process may be performed using the same stirring apparatus as the second stirring process described above or may be performed using a different stirring apparatus, but from the viewpoint of productivity, the same stirring apparatus may be used. preferable. As a stirring rotation speed of the stirring apparatus in the third stirring treatment, it is appropriate to set the rotation speed to approximately 300 rpm to 1800 rpm, preferably 500 rpm to 1500 rpm, and more preferably 800 rpm to 1000 rpm. The stirring time of the third stirring treatment may vary depending on the apparatus configuration and stirring conditions, but is usually about 5 seconds to 60 seconds, preferably 8 seconds to 30 seconds, more preferably 10 seconds to 20 seconds. It is.

  In the fourth stirring process of step S124, the wet granulated particles obtained by the third stirring process are stirred at a high speed, thereby preventing secondary aggregation of the wet granulated particles and separating them from each other. The fourth stirring process may be performed using the same stirring apparatus as the third stirring process described above or may be performed using a different stirring apparatus, but the same stirring apparatus may be used from the viewpoint of productivity. preferable. As a stirring rotation speed of the stirring device in the fourth stirring treatment, it is appropriate to set it to approximately 2000 rpm to 5000 rpm, preferably 2500 rpm to 4000 rpm, and more preferably 2600 rpm to 3000 rpm. The stirring time of the fourth stirring treatment may vary depending on the apparatus configuration and stirring conditions, but is usually about 0.5 to 8 seconds, preferably 1 to 5 seconds, more preferably 1 second to 3 seconds.

  In this way, wet granulated particles containing a metal-based negative electrode active material, a carbon material, a binder, and a solvent can be granulated.

  FIG. 3 schematically shows an example of the wet granulated particle 10 formed through the granulation step. As shown in FIG. 3, the wet granulated particle 10 disclosed herein includes at least a metal-based negative electrode active material 12, a carbon material 14, a binder 16, and a solvent. In the wet granulated particles 10, binders 16 adhere to the particle surfaces of the individual metal-based negative electrode active materials 12 and carbon materials 14, and between the particles of the metal-based negative electrode active materials 12 and carbon materials 14 are bound by the binders 16. It may be an embodiment in which they are coupled together. In a preferred embodiment, the binder 16 is not uniformly dispersed in the wet granulated particles 10 but is unevenly distributed around the metal-based negative electrode active material 12. That is, the amount of the binder 16 present around the metallic negative electrode active material 12 is greater than the amount of the binder 16 present around the carbon material 14.

  Here, in the conventional manufacturing method, the components of the metal-based negative electrode active material, the carbon material, and the binder are simultaneously charged into the stirrer from the beginning to granulate wet granulated particles. However, according to the knowledge of the present inventor, when the respective components are simultaneously added and stirred from the beginning, the binder is uniformly dispersed between the particles of the metallic negative electrode active material and the carbon material in the wet granulated particles. Therefore, depending on the amount of binder added, the amount of the binder that binds the metal-based negative electrode active material may be insufficient, and the binding strength of the metal-based negative electrode active material may decrease. When the binding strength of the metal-based negative electrode active material is reduced, cracks (cracks) occur around the metal-based negative electrode active material while charging and discharging are repeated, and the battery performance deteriorates. In order to cope with this problem, if the binder addition amount is increased to increase the binding strength of the metal-based negative electrode active material, the excess binder acts as a resistance component, which increases the internal resistance of the battery. obtain.

  On the other hand, according to the present embodiment, after mixing the metal-based negative electrode active material, the binder, and the solvent (first mixing process in step S110), the obtained mixture and the carbon material are mixed (first in step S120). Therefore, after the metallic negative electrode active material and the binder are in contact with each other, the carbon material is charged. Thus, by bringing the metal-based negative electrode active material and the binder into contact with each other prior to the introduction of the carbon material, the binder is preferentially disposed around the metal-based negative electrode active material in the wet granulated particles. Therefore, a binder is preferentially disposed around the metal negative electrode active material even in the negative electrode active material layer obtained by pressing the wet granulated particles, and the binding strength of the metal negative electrode active material is effectively increased. Rise. As a result, even if the metal-based negative electrode active material repeatedly expands and contracts, cracks are less likely to occur around the metal-based negative electrode active material. Therefore, according to this configuration, it is possible to manufacture a highly durable secondary battery in which the occurrence of the cracks is suppressed. Such a secondary battery may have, for example, a low internal resistance and a high post-cycle capacity retention rate.

  As the properties of the wet granulated particles 10 granulated in the granulation step, for example, the average particle size may be about 100 μm or more. From the viewpoint of forming a homogeneous negative electrode active material layer, the average particle size of the wet granulated particles 10 is preferably 200 μm or more, more preferably 300 μm or more, and even more preferably 400 μm or more. Moreover, the average particle diameter of the wet granulated particles 10 is approximately 1000 μm or less, for example, 800 μm or less, preferably 600 μm or less. The technique disclosed here can be preferably implemented, for example, in an embodiment where the wet granulated particles 10 have an average particle size of 100 μm or more and 1000 μm or less (for example, 350 μm or more and 500 μm or less).

  In the present specification, unless otherwise specified, the “average particle size” means a particle size at an integrated value of 50% in a particle size distribution measured based on a particle size distribution measuring apparatus based on a laser scattering / diffraction method, that is, 50%. It shall mean the volume average particle diameter. Here, the particle diameter at the integrated value of 50%, that is, the 50% volume average particle diameter is appropriately referred to as “D50”. More specifically, it is a 50% volume average particle diameter measured dry using a laser diffraction / scattering type particle size distribution measuring device without dispersing particles with compressed air.

  The ratio (mass basis) between the content of the metal-based negative electrode active material contained in the wet granulated particles and the content of the carbon material is not particularly limited. From the viewpoint of improving durability, the content of the carbon material is preferably equal to or greater than the content of the metal-based negative electrode active material. The technique disclosed here can be preferably implemented in an aspect in which the mass ratio of the metal-based negative electrode active material and the carbon material is 1: 9 to 5: 5. The mass ratio between the metal-based negative electrode active material and the carbon material is 1 from the viewpoint of better exhibiting the effect of combining the metal-based negative electrode active material and the carbon material (that is, achieving both higher capacity and improved durability). : 5 to 5: 5, preferably 1: 4 to 5: 6, more preferably 1: 3 to 5: 7, and 1: 2 to 5: 8 (for example 1: 2 to 3: 7) is more preferable.

  The binder content (ratio) with respect to the total solid content of the wet granulated particles is not particularly limited. From the viewpoint of improving durability, the binder content is generally 0.5% by mass or more, preferably 0.8% by mass or more, more preferably 1% by mass or more, and further preferably 1.2% by mass. That's it. Further, from the viewpoint of suppressing an increase in resistance, the binder content is generally 2% by mass or less, preferably 1.8% by mass or less, and more preferably 1.5% by mass or less.

  The wet granulated particles disclosed herein can be appropriately selected solid fraction (NV) depending on the purpose, but from the viewpoint of drying efficiency and the like, it is usually 70% by mass or more (for example, 70% by mass to 70% by mass). 95 mass%) is suitable, preferably 75 mass% or more (for example, 75 mass% to 90 mass%), more preferably 78 mass% or more (for example, 78 mass% to 85 mass%).

<Pressing process>
The pressing step of Step S200 is a step of forming a negative electrode active material layer on the negative electrode current collector by press-molding the powder composed of the wet granulated particles described above. Copper or a copper alloy is used as the negative electrode current collector. For example, a strip-shaped electrolytic copper foil can be suitably used as the negative electrode current collector. Although it does not specifically limit as thickness of a negative electrode collector, From a viewpoint of high intensity | strength and low resistance, 6 micrometers-20 micrometers are suitable in general, Preferably they are 8 micrometers-15 micrometers (for example, 10 micrometers). In this embodiment, the negative electrode active material layer is formed by a powder roll forming method.

  FIG. 4 is a perspective view schematically showing a powder roll forming apparatus 90 used in the negative electrode manufacturing method disclosed herein. The powder roll forming apparatus 90 includes a first roll 92 (hereinafter also referred to as a supply roll 92) and a second roll 94 (hereinafter also referred to as a transfer roll 94). There is a gap having a predetermined width between the supply roll 92 and the transfer roll 94. The outer peripheral surface of the supply roll 92 and the outer peripheral surface of the transfer roll 94 are opposed to each other. The supply roll 92 and the transfer roll 94 rotate in opposite directions as indicated by arrows in FIG.

  Next to the transfer roll 94, a third roll 96 (hereinafter also referred to as a backup roll 96) is disposed as a conveying device for the negative electrode current collector 62. The outer peripheral surface of the transfer roll 94 and the outer peripheral surface of the backup roll 96 are opposed to each other. The transfer roll 94 and the backup roll 96 rotate in opposite directions as indicated by arrows in FIG.

  Partition walls 98 are provided at both ends in the width direction of the supply roll 92 and the transfer roll 94. The partition wall 98 holds the powder of the wet granulated particles 10 on the supply roll 92 and the transfer roll 94, and the negative electrode active material layer formed on the negative electrode current collector 62 depending on the distance between the two partition walls 98. It plays the role of defining the width of 63.

  In the deposition step of the manufacturing method disclosed herein, first, the powder of the wet granulated particles 10 is passed through a gap between the rotating supply roll 92 and the rotating transfer roll 94 to form a coating film. Specifically, first, the powder of the wet granulated particles 10 is supplied between the rotating supply roll 92 and the rotating transfer roll 94. When the powder of the wet granulated particles 10 is supplied between the supply roll 92 and the transfer roll 94, the powder of the wet granulated particles 10 is transferred to the supply roll 92 and the transfer roll 94 by the rotation of the supply roll 92 and the transfer roll 94. Carried into the gap between. The powder of the wet granulated particles 10 is pressed through a gap between the supply roll 92 and the transfer roll 94 to form a coating film. That is, the wet granulated particles 10 are integrated while the powder of the wet granulated particles 10 is crushed by the supply roll 92 and the transfer roll 94, and is stretched to form a coating film.

  Subsequently, the coating film is attached to the transfer roll 94 and conveyed. The coating film adhering to the transfer roll 94 is conveyed by the rotation of the transfer roll 94. Subsequently, the coating film transported as described above is transferred onto the negative electrode current collector 62 transported by the backup roll 96 to form a negative electrode active material layer 63 made of a coating film. The coating film adhering to the surface of the transfer roll 94 comes into contact with the negative electrode current collector 62 conveyed by the backup roll 96 with a certain pressure, whereby the coating film is transferred to the negative electrode current collector 62. Thereby, the negative electrode active material layer 63 is formed on the negative electrode current collector 62. If necessary, a step of drying the formed negative electrode active material layer 63 may be performed.

  In this way, a negative electrode having a configuration in which the negative electrode active material layer 63 is held by the negative electrode current collector 62 can be obtained.

  Here, the negative electrode active material layer is generally formed by slurrying a negative electrode active material and a binder with an appropriate solvent, applying and drying the negative electrode slurry on a current collector, and then pressing the slurry. In such a method, when the negative electrode slurry applied on the negative electrode current collector is dried, the binder in the vicinity of the negative electrode current collector moves to the surface of the slurry applied product by convection and segregates on the surface of the slurry applied product (migration). To do. As a result, the adhesion between the negative electrode active material layer and the negative electrode current collector is lowered, and the negative electrode active material layer may be peeled off while being repeatedly charged and discharged. In addition, the amount of solvent in the slurry for the negative electrode is large (typically, the solid content is 55% by mass or less), and it takes time to dry the slurry applied product, which causes a problem that the production efficiency is lowered. On the other hand, in the powder roll forming method disclosed here, the powder of the wet granulated particles 10 is pressed by rotating rolls 92 and 94 to form the negative electrode active material layer 63. Typically, the wet granulated particle 10 powder is supplied between a pair of rolls 92 and 94 rotating in opposite directions, and the wet granulated particle 10 powder is pressed between the pair of rolls 92 and 94. Thus, the negative electrode active material layer 63 is formed. According to such a powder roll forming method, the negative electrode active material layer 63 can be formed with a small amount of solvent, so that the drying time can be shortened as compared with the conventional method. Further, since convection does not occur during drying, binder segregation (migration) cannot occur, and the problem that the negative electrode active material layer 63 peels off from the negative electrode current collector 62 can be solved. Furthermore, since a high-density negative electrode active material layer can be obtained by increasing the solid content ratio of the wet granulated particles, the pressing step after drying as in the case of using a conventional negative electrode slurry (the negative electrode active material layer) The step of adjusting the density becomes unnecessary. Therefore, according to the powder roll forming method disclosed herein, it is possible to efficiently form a negative electrode for a secondary battery with better adhesion between the negative electrode active material layer 63 and the negative electrode current collector 62 than in the past. Can do.

  Since such a negative electrode has higher performance because cracks do not easily occur around the metal-based negative electrode active material even after repeated charge and discharge as described above, the constituent elements of the secondary battery in various forms or the secondary battery It can be preferably used as a component (negative electrode) of the electrode body incorporated in the.

  For example, a negative electrode obtained by any of the methods disclosed herein, a positive electrode, an electrolyte disposed between the positive and negative electrodes, and a separator (solid or gel-like) that typically separates the positive and negative electrodes. It can be omitted in a battery using an electrolyte.) And can be preferably used as a component of a lithium ion secondary battery. Structure (for example, metal casing or laminate film structure) and size of an outer container constituting such a battery, or structure of an electrode body (for example, a wound structure or a laminated structure) having a positive / negative electrode current collector as a main component There is no particular restriction on the etc.

<Lithium ion secondary battery>
Hereinafter, an embodiment of a lithium ion secondary battery constructed using a negative electrode (negative electrode sheet) manufactured by applying the above-described method will be described with reference to schematic diagrams shown in FIGS. 5 and 6. FIG. 5 is a cross-sectional view of a lithium ion secondary battery 100 according to an embodiment of the present invention. FIG. 6 is a diagram showing an electrode body 40 housed in the lithium ion secondary battery 100. In this lithium ion secondary battery 100, a negative electrode (negative electrode sheet) 60 manufactured by applying the above-described method using wet granulated particles is used as the negative electrode (negative electrode sheet) 60.

  A lithium ion secondary battery 100 according to an embodiment of the present invention is configured in a flat rectangular battery case (that is, an exterior container) 20 as shown in FIG. As shown in FIGS. 5 and 6, in the lithium ion secondary battery 100, a flat wound electrode body 40 is housed in a battery case 20 together with a liquid electrolyte (electrolytic solution) 80.

<Battery case>
The battery case 20 has a box-shaped (that is, a bottomed rectangular parallelepiped) case body 21 having an opening at one end (corresponding to an upper end portion in a normal use state of the battery 100), and is attached to the opening. It is comprised from the cover body (sealing board) 22 which consists of a rectangular-shaped plate member which plugs up an opening part. The material of the battery case 20 may be the same as that used in the conventional lithium ion secondary battery, and is not particularly limited. A battery case 20 mainly composed of a lightweight and highly heat conductive metal material is preferable, and aluminum or the like is exemplified as such a metal material.

  As shown in FIG. 5, the lid 22 is formed with a positive terminal 23 and a negative terminal 24 for external connection. A thin safety valve 30 configured to release the internal pressure when the internal pressure of the battery case 20 rises above a predetermined level and a liquid injection port 32 are formed between both terminals 23 and 24 of the lid 22. Has been. In FIG. 5, the liquid injection port 32 is sealed with a sealing material 33 after the liquid injection.

<Winded electrode body>
As shown in FIG. 6, the wound electrode body 40 includes a long sheet-like positive electrode (positive electrode sheet 50) and a long sheet-like negative electrode (negative electrode sheet 60) similar to the positive electrode sheet 50 in total. Long sheet separators (separators 72 and 74).

<Positive electrode sheet>
The positive electrode sheet 50 includes a strip-shaped positive electrode current collector 52 and a positive electrode active material layer 53. For the positive electrode current collector 52, for example, a metal foil suitable for the positive electrode can be suitably used. In this embodiment, an aluminum foil is used as the positive electrode current collector 52. An uncoated portion 51 is set along an edge on one side in the width direction of the positive electrode current collector 52. In the illustrated example, the positive electrode active material layer 53 is held on both surfaces of the positive electrode current collector 52 except for the uncoated portion 51 set on the positive electrode current collector 52. The positive electrode active material layer 53 includes positive electrode active material particles, a conductive material, and a binder.

  As the positive electrode active material, a material capable of occluding and releasing lithium ions is used, and one or more of materials conventionally used in lithium ion secondary batteries (for example, oxides having a layered structure or oxides having a spinel structure) are used. Are used without any particular limitation. Examples thereof include lithium-containing transition metal oxides such as lithium nickel composite oxide, lithium cobalt composite oxide, and lithium manganese composite oxide. Examples of the binder include polyvinylidene fluoride (PVDF). Examples of the conductive material include carbon black such as acetylene black (AB) and other carbon materials such as graphite.

<Negative electrode sheet>
As shown in FIG. 6, the negative electrode sheet 60 includes a strip-shaped negative electrode current collector 62 and a negative electrode active material layer 63. On one side of the negative electrode current collector 62 in the width direction, an uncoated portion 61 is set along the edge. The negative electrode active material layer 63 is held on both surfaces of the negative electrode current collector 62 except for the uncoated portion 61 set on the negative electrode current collector 62. As described above, the negative electrode active material layer 63 includes a metal-based negative electrode active material, a carbon material, and a binder. Since the method for producing the negative electrode sheet is as described above, the description thereof is omitted.

<Separator>
As shown in FIG. 6, the separators 72 and 74 are members that separate the positive electrode sheet 50 and the negative electrode sheet 60. In this example, the separators 72 and 74 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 72 and 74, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. Moreover, you may further form the layer of the particle | grains which have insulation on the surface of the sheet | seat material comprised with this resin. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). ). In this example, the width b1 of the negative electrode active material layer 63 is slightly wider than the width a1 of the positive electrode active material layer 53, as shown in FIG. Furthermore, the widths c1 and c2 of the separators 72 and 74 are slightly wider than the width b1 of the negative electrode active material layer 63 (c1, c2>b1> a1).

<Attaching the wound electrode body>
In this embodiment, the wound electrode body 40 is flatly bent in one direction orthogonal to the winding axis WL, as shown in FIG. In the example shown in FIG. 6, the uncoated portion 51 of the positive electrode current collector 52 and the uncoated portion 61 of the negative electrode current collector 62 are spirally exposed on both sides of the separators 72 and 74, respectively. In this embodiment, as shown in FIG. 5, the intermediate part of the uncoated part 51 is gathered and welded to current collecting tabs 25 and 26 of electrode terminals (internal terminals) arranged inside the battery case 20. Is done. 25a and 26a in FIG. 5 have shown the said welding location.

  Then, the wound electrode body 40 is accommodated in the main body 21 from the upper end opening of the case main body 21, and the opening is sealed by welding with the lid body 22 or the like. Further, the electrolytic solution 80 is disposed (injected) into the case body 21 from the injection port 32.

<Electrolytic solution (nonaqueous electrolytic solution)>
As the electrolytic solution (non-aqueous electrolytic solution) 80, the same non-aqueous electrolytic solution conventionally used for lithium ion secondary batteries can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane, and the like. One kind or two or more kinds selected from the group can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. Lithium salts can be used. As an example, a non-solvent containing LiPF ₆ at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (eg, volume ratio 3: 4: 3). A water electrolyte may be mentioned.

  Then, the liquid injection port 32 is sealed with the sealing material 33, and the assembly of the lithium secondary battery 100 which concerns on this embodiment is completed. The sealing process of the case 20 and the placement (injection) process of the electrolytic solution may be the same as the method used in the manufacture of the conventional lithium ion secondary battery, and do not characterize the present invention. In this way, the construction of the lithium ion secondary battery 100 according to this embodiment is completed.

  As described above, the lithium secondary battery 100 constructed as described above has a binder disposed preferentially around the metal negative electrode active material even with a small amount of binder as described above. Since cracks are less likely to occur in the surroundings, excellent battery performance can be exhibited. For example, a secondary battery satisfying at least one (preferably all) of cycle characteristics, high capacity, excellent input / output characteristics, and excellent productivity can be provided.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “%” is based on mass unless otherwise specified.

<Granulation of wet granulated particles>
(Examples 1-5)
In Examples 1-5, after mixing each component of a metal type negative electrode active material and a binder previously, the wet granulation particle | grains were granulated by the sequential method which mixes a carbon material. Specifically, silicon powder as a metal-based negative electrode active material and polyimide resin powder as a binder are put into a food processor and stirred for 5 seconds at a rotation speed of 2600 rpm (first stirring process in the first mixing step). Then, ion-exchanged water as a solvent was added and stirred for 10 seconds at a rotation speed of 800 rpm (second stirring process in the first mixing step). Next, the amorphous carbon-coated graphite powder as a carbon material was charged, stirred for 10 seconds at a rotation speed of 800 rpm (third stirring process in the second mixing step), and further stirred for 3 seconds at a rotation speed of 2600 rpm (in the second mixing step). Fourth stirring process). Thus, negative electrode wet granulated particles having an average particle size of 400 μm were obtained. The solid content rate of the negative electrode wet granulated particles was adjusted to 78%. Table 1 shows the binder content and the ratio (mass basis) of the content of the metal-based negative electrode active material and the carbon material to the total solid content of the negative electrode wet granulated particles used in each example.

(Comparative Example 1)
In Comparative Example 1, wet granulated particles were granulated by a batch method in which the components of the metal-based negative electrode active material, the carbon material, and the binder were simultaneously mixed. Specifically, as shown in FIG. 7, silicon powder as a metal-based negative electrode active material, amorphous carbon-coated graphite powder as a carbon material, and polyimide-based resin powder as a binder are put into a food processor and rotated. The mixture was stirred at several 2600 rpm for 5 seconds. Next, ion-exchanged water as a solvent was added and stirred for 10 seconds at a rotation speed of 800 rpm, and further stirred for 3 seconds at a rotation speed of 2600 rpm. Thus, negative electrode wet granulated particles having an average particle size of 400 μm were obtained. The solid content rate of the negative electrode wet granulated particles was adjusted to 78%. Table 1 shows the binder content to the total solid content of the wet granulated particles used in Comparative Example 1, and the ratio (mass basis) of the content of the metal-based negative electrode active material and the carbon material.

<Preparation of negative electrode sheet>
The negative electrode wet granulated particles in each example were pressed using a powder roll molding apparatus shown in FIG. 4 and transferred onto a long sheet-like copper foil (negative electrode current collector), whereby a negative electrode current collector was obtained. A negative electrode sheet having a negative electrode active material layer provided on the body was produced. The negative electrode sheet was cut into a substantially rectangular shape to obtain a negative electrode for an evaluation test cell.

<Preparation of positive electrode sheet>
Lithium nickel manganese cobaltate (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) powder as a positive electrode active material, acetylene black (AB) powder as a conductive material, and polyvinylidene fluoride (PVdF) as a binder Then, N-methylpyrrolidone as a solvent was put into a food processor and stirred to granulate positive electrode wet granulated particles. The positive electrode wet granulated particles are pressed using a powder roll press shown in FIG. 4 and transferred onto a long sheet-like aluminum foil (positive electrode current collector). A positive electrode sheet provided with a positive electrode active material layer was prepared. Such a positive electrode sheet was cut into a substantially rectangular shape to obtain a positive electrode of an evaluation test cell.

<Construction of evaluation test cell>
The positive electrode and the negative electrode were laminated with a separator interposed therebetween so that the electrode active material layers face each other, and were accommodated in a laminate film (exterior member) together with the electrolytic solution. As the separator for the evaluation test cell, a microporous sheet having a total thickness of 24 μm and having a three-layer structure (PP / PE / PP) in which both sides of polyethylene (PE) are sandwiched between polypropylene (PP) was used. . Thus, an evaluation test cell (laminate cell) was constructed.

<Evaluation of evaluation test cell>
The performance of the evaluation test cell was evaluated based on the initial resistance, the post-cycle capacity retention rate, and the post-cycle resistance increase rate as output characteristics. Next, with respect to the evaluation test cell constructed as described above, the measurement of the initial resistance, the measurement of the capacity retention rate after cycling, and the rate of increase in resistance after cycling will be described in this order.

<Measurement of initial resistance>
In order to evaluate the output characteristics of the evaluation test cell, the initial IV resistance was measured here. The IV resistance was calculated by the following procedure.
Procedure 1: The SOC is adjusted to 60% by SOC adjustment.
Procedure 2: After Procedure 1, discharge at a current value of 0.8 C and discharge treatment for 10 seconds.
Here, the measured current value measured in the procedure 2 is divided by the voltage drop value ΔV that is a value obtained by subtracting the voltage value at the time of 10 seconds from the initial voltage value in the procedure 2. The value was obtained as an IV resistance value (initial resistance). The results are shown in the corresponding column of Table 1.

<Measurement of capacity retention after cycle>
About the cell for evaluation tests, the charge / discharge pattern which repeats charging / discharging by 2C was provided, and the cycle test was done. Specifically, a charge / discharge cycle of charging to SOC 85% with a constant current of 2C and then discharging to SOC 20% with a constant current of 2C was performed 100 times continuously. The post-cycle capacity retention rate was calculated by (discharge capacity at the 100th cycle / initial capacity) × 100. The results are shown in the corresponding column of Table 1.
The initial capacity and the discharge capacity at the 100th cycle were measured by the following procedures 1 to 3 for a battery for evaluation test at a temperature of 25 ° C.
Procedure 1: After reaching 3.0V by constant current discharge of 1C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.
Procedure 2: After reaching 4.1 V by constant current charging at 1 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.
Procedure 3: After reaching 3.0 V by constant current discharge of 0.5 C, discharge at constant voltage discharge for 2 hours, and then stop for 10 seconds.
Here, the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 was defined as the battery capacity.

<Measurement of resistance increase after cycling>
For the evaluation test cell, the IV resistance after the cycle test was performed in the same procedure as the measurement of the initial resistance. Then, the resistance increase rate after the cycle was calculated by [(IV of the 100th cycle−initial resistance) / initial resistance] × 100. The results are shown in the corresponding column of Table 1.

  As shown in Table 1, the battery of Comparative Example 1 in which the metallic negative electrode active material, the carbon material and the binder were mixed at the same time had a capacity retention rate after cycling of less than 90% and a resistance increase rate after cycling of 10%. % And lacked durability. In contrast, the battery according to Example 2 in which the metal-based negative electrode active material and the binder were first mixed and then the carbon material was mixed, compared with Comparative Example 1, the initial resistance, the post-cycle capacity retention rate, and Good results were obtained for any post-cycle resistance rise rate. In Example 2, since the generation of cracks was suppressed by preferentially arranging the carbon material around the metal-based negative electrode active material, it was possible to suppress a decrease in capacity and an increase in resistance due to the charge / discharge cycle. Guessed. From this result, it was confirmed that a battery having excellent durability can be obtained by mixing the components of the metal-based negative electrode active material and the binder first and then mixing the carbon material.

  When Examples 1 to 3 were compared, the initial resistance tended to increase as the binder content increased. In the case of the battery used here, by setting the binder content to 1% by mass or less, an extremely low initial resistance of 1.5 mΩ could be realized. From the viewpoint of reducing the initial resistance, the binder content is suitably 2% by mass or less, preferably 1% by mass or less. In addition, when Examples 2, 4, and 5 are compared, with respect to the content ratio of the metal-based negative electrode active material and the carbon material, as the ratio of the carbon material increases, the initial resistance, the capacity retention rate after cycling, and the resistance after cycling increase The rate showed good results. From this result, from the viewpoint of improving the initial resistance and durability, the ratio of the content of the metal negative electrode active material and the carbon material (metal negative electrode active material: carbon material) is preferably 1: 9 to 5: 5, 1: 9-3: 7 are more preferable.

  As mentioned above, although the manufacturing method of the negative electrode for secondary batteries which concerns on one Embodiment of this invention was demonstrated, the negative electrode manufacturing method which concerns on this invention is not limited to any embodiment mentioned above, A various change is possible. is there.

  For example, in the above-described embodiment, the case where the wet granulated particles are granulated by the stirring granulation method (the method of agglomerating the spherical particles by applying a rotational motion) is illustrated, but the present invention is not limited thereto. Any granulation method may be used as long as each component can be mixed and granulated. For example, wet granulated particles may be granulated by a fluidized bed granulation method, a rolling granulation method, or the like. Even in such a case, the binder can be preferentially disposed around the metallic negative electrode active material by bringing the metallic negative electrode active material and the binder into contact with each other before introducing the carbon material. Can be obtained. However, as in the above-described embodiment, it is preferable to granulate wet granulated particles using the stirring granulation method from the viewpoint of stably obtaining wet granulated particles.

  Further, in the above-described embodiment, a case where a granular mixture of a metal-based negative electrode active material, a binder, and a solvent is formed in the second stirring treatment, and a carbon material is mixed with this granular mixture is illustrated. It is not limited to this. For example, spheronization may be performed in the third stirring treatment, and wet granulated particles containing a metal-based negative electrode active material, a carbon material, a binder, and a solvent may be granulated. According to the present invention, regardless of the spheroidization timing, the binder is preferentially disposed around the metallic negative electrode active material by bringing the metallic negative electrode active material and the binder into contact with each other before introducing the carbon material. The above-described effects can be obtained. However, as in the above-described embodiment, it is more efficient to form a granular mixture of a metallic negative electrode active material, a binder, and a solvent, and to mix a carbon material into the granular mixture so that the binder is more efficient around the metallic negative electrode active material. It is preferable from the viewpoint of arranging well.

  In the above-described embodiment, the wet granulated particles are roll-pressed to form a coating film, and the coating film is transferred onto the negative electrode current collector to form the negative electrode active material layer. The method for forming the active material layer is not limited to this. For example, the wet granulated particles may be deposited on the negative electrode current collector and then press-molded to form the negative electrode active material layer. However, as in the above-described embodiment, it is more effective to roll press wet granulated particles to form a coating film and transfer the coating film onto the negative electrode current collector to form the negative electrode active material layer. It is preferable from the viewpoint.

  The type of secondary battery is not limited to the above-described lithium ion secondary battery, and may be batteries having various contents with different electrode body constituent materials and electrolytes. Further, the size and other configurations of the battery can be appropriately changed depending on the application (typically for in-vehicle use).

  The secondary battery including the negative electrode manufactured by the manufacturing method proposed here has a negative electrode that is less prone to cracking and excellent in durability. For this reason, it is preferably used in applications where durability is required. As such an application, for example, a power source (drive power source) for a motor mounted on a vehicle can be cited. The type of vehicle is not particularly limited, and examples thereof include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, motorbikes, electric assist bicycles, electric wheelchairs, electric railways, and the like. It is done. Such secondary batteries may be used in the form of an assembled battery formed by connecting a plurality of them in series and / or in parallel.

DESCRIPTION OF SYMBOLS 10 Wet granulated particle 12 Metal type negative electrode active material 14 Carbon material 16 Binder 100 Secondary battery

Claims (6)

Wet granulated particles comprising a metal-based negative electrode active material having at least one metal element as a constituent element, a carbon material, a binder, and a solvent , wherein the particles have a solid content of 70% by mass or more A granulation process for granulating
Forming a negative electrode active material layer on the negative electrode current collector by press molding a powder composed of the wet granulated particles,
In the granulation step,
A first mixing process of mixing the metal-based negative electrode active material, the binder, and the solvent;
The manufacturing method of the negative electrode for secondary batteries including the 2nd mixing process which mixes the said carbon material with the obtained mixture after the said 1st mixing process.   The manufacturing method of Claim 1 whose content of the said binder with respect to the whole solid content of the said wet granulated particle is 0.5 mass%-2 mass%.   The ratio of the content of the metal-based negative electrode active material and the carbon material contained in the wet granulated particles (metal-based negative electrode active material: carbon material) is 1: 9 to 5: 5 on a mass basis. 3. The production method according to 1 or 2.   The said metal type negative electrode active material is a manufacturing method as described in any one of Claims 1-3 which contains at least one metal element of silicon (Si) and tin (Sn) as a structural element. In the first mixing process,
A first stirring treatment of stirring the metal-based negative electrode active material and the binder between powders;
The manufacturing method as described in any one of Claims 1-4 with which the 2nd stirring process which mixes the said solvent with the obtained stirring thing and stirs after the said 1st stirring process. Performing the first stirring process and the second stirring process using the same stirring apparatus; and
The manufacturing method according to claim 5, wherein the stirring rotation speed of the stirring device in the first stirring process is set to be larger than the stirring rotation speed of the stirring apparatus in the second stirring process.

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