JP2012174554A - Method for manufacturing battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a battery which has high durability against charge/discharge cycles.SOLUTION: In a method for manufacturing a battery according to the present invention, the battery includes an electrode configured such that a mixture layer including an active material 22 and a binder 52 is held by a collector 10. The method for manufacturing the battery includes: a step of preparing a binder solution including the binder 52 and a solvent 54; a step of coating the collector 10 with the binder solution to form a binder solution layer 50 on a surface of the collector 10; and a step of forming a mixture layer by applying a mixture paste 40 including the active material 22 and a solvent 24 from above the binder solution layer 50 to be dried. In the binder solution layer 50, the binder 52 having a glass transition temperature of 10°C or above is used.

Description

  The present invention relates to a battery manufacturing method, and more particularly to a battery manufacturing method including an electrode having a configuration in which a mixture layer containing an active material and a binder is held by a current collector.

  In recent years, lithium-ion batteries, nickel-metal hydride batteries, and other secondary batteries have become increasingly important as power sources for vehicles or as power sources for personal computers and portable terminals. In particular, a lithium secondary battery that is lightweight and has a high energy density is expected to be preferably used as a high-output power source for mounting on a vehicle. In one typical configuration of this type of secondary battery, an electrode having a configuration in which a material (electrode active material) capable of reversibly occluding and releasing lithium ions is held in a conductive member (electrode current collector) is used. Prepare. For example, as a typical example of the electrode active material (negative electrode active material) used for the negative electrode, carbon-based materials such as graphite carbon and amorphous carbon are exemplified. A typical example of the electrode current collector (negative electrode current collector) used for the negative electrode is a sheet-like or foil-like member mainly composed of copper or a copper alloy.

  In producing a negative electrode having such a structure, as one of typical methods for holding a negative electrode active material on a negative electrode current collector, a powder of a negative electrode active material and a binder (binder) are dispersed in an appropriate medium. Examples include a method of forming a layer (negative electrode mixture layer) containing a negative electrode active material by applying a mixture paste to a negative electrode current collector (copper foil or the like) and drying the mixture paste (eg, Patent Documents 1 to 3). ). The binder contained in the negative electrode mixture layer has a role of binding between the negative electrode active materials and between the negative electrode active material and the current collector.

JP 2003-308441 A JP 2003-151555 A JP 2009-238720 A

  In Patent Document 1, in a slurry for forming a negative electrode coating film of a non-aqueous secondary battery, in which the solid content is a carbon material active material and a binder and the medium is water, glass is used as the binder. A technique using an aqueous dispersion emulsion resin having a transition temperature Tg of 10 ° C. to 40 ° C. is described. According to such a technique, it is said that a negative electrode coating film of a non-aqueous secondary battery having excellent adhesion between the negative electrode material and the current collector, little reduction in discharge capacity, and excellent durability against charge / discharge cycles can be formed. . However, simply using a binder having a high glass transition temperature Tg has a problem that the flexibility of the mixture layer is reduced, and cracking and cracking occur in the mixture layer when the electrode is wound. Therefore, the present invention solves the above problems.

  According to the present invention, a method for producing a battery (for example, a lithium secondary battery) including an electrode having a configuration in which a mixture layer containing an active material and a binder is held by a current collector is provided. This manufacturing method includes preparing a binder solution containing a binder and a solvent. In addition, the method includes applying a binder solution to the current collector to form a binder solution layer on the surface of the current collector. Furthermore, it includes a step of forming a mixture layer by applying a mixture paste containing an active material and a solvent from the binder solution layer and drying it. In the binder solution layer, a binder having a glass transition temperature of 10 ° C. or higher is used.

  In the present specification, the “battery” is a term that generally indicates an electricity storage device that can take out electric energy, and is a secondary battery (a lithium ion battery, a metal lithium secondary battery, a nickel hydrogen battery, a nickel cadmium battery, etc. Including so-called storage batteries and electric storage elements such as electric double layer capacitors).

  According to the manufacturing method of this invention, the hardness of a mixture layer becomes hard by using a binder whose glass transition temperature Tg is 10 degreeC or more. For this reason, the volume change of the mixture layer accompanying charging / discharging is suppressed, and the durability of the electrode is improved. In addition, since the mixture paste is supplied over the binder solution layer containing the binder, most of the binder in the binder solution layer applied to the surface of the current collector is close to the surface of the current collector. Although it stays, a part moves to the surface side of mixture paste (application | coating material), and a binder spread | diffuses in mixture paste. Thereby, a mixture layer in which a binder is appropriately present near the surface of the current collector and a part of the binder is widely diffused can be obtained. According to such a configuration, since the binder is appropriately present near the surface of the current collector, the binding strength between the mixture layer and the current collector can be sufficiently ensured. Furthermore, since a mixture layer in which the binder is widely diffused is obtained, even when a binder having a glass transition temperature Tg of 10 ° C. or higher is used, the flexibility of the mixture layer can be secured, and the balance between hardness and flexibility is achieved. It is possible to form an optimal mixture layer with a good peeling. Therefore, according to the present invention, the durability of the electrode is maintained while maintaining the flexibility of the mixture layer (for example, the flexibility of preventing the mixture layer from being cracked or cracked when the electrode is wound). An optimum electrode with improved properties can be obtained. A battery comprising such an electrode can be of higher performance (eg, high cycle life).

  The glass transition temperature Tg of the binder is preferably approximately 10 ° C. or higher (for example, 10 ° C. to 40 ° C.). Thus, by using a binder having a glass transition temperature Tg of 10 ° C. or higher, the hardness of the mixture layer is appropriately increased. Therefore, the volume change of the mixture layer at the time of charging / discharging is suppressed, and the durability of the electrode is improved. On the other hand, a binder having a glass transition temperature Tg that is too high has little merit because it becomes difficult to produce and the durability improving effect accompanying the increase in the glass transition temperature Tg is slowed down. The glass transition temperature Tg of the binder is generally 10 ° C. or higher (eg, 10 ° C. to 40 ° C.), preferably 15 ° C. or higher (eg, 15 ° C. to 40 ° C.), and more preferably 20 ° C. (eg, 20 ° C.). And more preferably 25 ° C. or more (for example, 25 ° C. to 40 ° C.).

  In a preferred aspect of the battery manufacturing method disclosed herein, the mixture paste is composed of a composition that does not substantially contain the binder. When the binder paste is applied to the mixture paste applied from above the binder solution layer, both binders aggregate together near the current collector, and the active material is likely to slip off in the surface layer portion. Such inconvenience can be avoided.

  In a preferred embodiment of the battery manufacturing method disclosed herein, at least one polymer selected from the group consisting of styrene butadiene rubber, polyacrylate, polyurethane, polyethylene oxide, and polyethylene is used as the binder. These polymers are preferable in that they have a strong binding force and can easily adjust the glass transition temperature Tg to a suitable range.

  In a preferable embodiment of the battery manufacturing method disclosed herein, the binder concentration of the binder solution layer is suitably 5% by mass to 30% by mass, for example, 8% by mass to 20% by mass (for example, 10% by mass). %). If the binder concentration is too smaller than the above range, the mixture paste may be repelled on the binder solution layer and may not be applied to a uniform thickness. On the other hand, if the binder concentration is too larger than the above range, the handling property of the binder solution (for example, the coating property when the binder solution is applied to a current collector (particularly a foil-shaped current collector)) is likely to deteriorate. May be.

  In a preferred embodiment of the battery manufacturing method disclosed herein, the proportion of the binder in the mixture layer is 0.5% by mass to 1% by mass. When the ratio is too larger than the above range, the internal resistance of the battery may increase. On the other hand, when the ratio of the binder is too smaller than the above range, the binding force of the mixture layer is reduced, and the active material is liable to slip off.

  In addition, according to the present invention, a battery (for example, a lithium secondary battery) manufactured by any of the manufacturing methods disclosed herein is provided. As described above, the battery is excellent in that it is constructed by using a higher performance electrode for at least one of the electrodes in which the durability of the electrode is improved while maintaining the flexibility in the mixture layer. It shows battery performance. For example, a battery satisfying at least one (preferably all) of high durability against charge / discharge cycles, excellent input / output characteristics, and excellent production stability can be provided.

  Such a battery is suitable as a battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, there is provided a vehicle including any of the batteries disclosed herein (which may be in the form of an assembled battery in which a plurality of batteries are connected). In particular, since the lightweight and high output can be obtained, the battery is a lithium secondary battery (typically a lithium secondary battery), and the lithium secondary battery is used as a power source (typically a hybrid vehicle or A vehicle (for example, an automobile) provided as a power source of an electric vehicle is preferable.

It is sectional drawing which shows typically the cross section of the electrode which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the electrode which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the electrode which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the electrode which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the cross section of the electrode which concerns on one Embodiment of this invention. It is a figure which shows the manufacture flow of the electrode which concerns on one Embodiment of this invention. It is a figure which shows typically the battery which concerns on one Embodiment of this invention. It is a figure for demonstrating the bending resistance test which concerns on one test example of this invention. It is a graph which shows the relationship between Tg and the minimum core diameter. It is a figure for demonstrating the 90 degree peeling strength test which concerns on one test example of this invention. It is a graph which shows the relationship between Tg and peeling strength. It is a figure which shows typically the laminate cell which concerns on one test example of this invention. It is a graph which shows the relationship between Tg and a capacity | capacitance maintenance factor. It is a side view showing typically a vehicle provided with a battery concerning one embodiment of the present invention. It is sectional drawing which shows the cross section of the conventional electrode typically.

  Embodiments according to the present invention will be described below with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of an electrode body including a positive electrode and a negative electrode, the configuration and manufacturing method of a separator and an electrolyte, The battery and other general technologies related to the construction of the battery, etc.) can be grasped as a design matter of those skilled in the art based on the prior art in the field.

  The electrode manufacturing method disclosed herein is a method for manufacturing an electrode 30 having a configuration in which a mixture layer 20 including an active material 22 and a binder 52 is held by a current collector 10 as shown in FIG. Although not intended to be particularly limited, the present embodiment will be described in more detail below using as an example a case where a negative electrode for a lithium secondary battery (typically a lithium ion secondary battery) is mainly manufactured. .

  As shown in FIG. 1, the negative electrode 30 according to this embodiment has a configuration in which a negative electrode mixture layer 20 including a negative electrode active material 22 and a binder 52 is held by a negative electrode current collector 10.

  As the negative electrode current collector 10 used in the present embodiment, one made of a metal having good conductivity (for example, a metal such as aluminum, nickel, copper, stainless steel or an alloy containing the metal as a main component) is preferably used. be able to. For example, when producing a negative electrode for a lithium secondary battery, it is preferable to use a current collector made of copper (which is composed of copper or an alloy containing copper as a main component (copper alloy)). The shape of the current collector to be used is not particularly limited because it may vary depending on the shape of the battery constructed using the obtained electrode, and various shapes such as a rod shape, a plate shape, a sheet shape, a foil shape, a mesh shape, etc. It can be in the form of The technique disclosed here can be preferably applied to manufacture of an electrode using, for example, a sheet-like or foil-like current collector.

  The negative electrode active material 22 contained in the negative electrode mixture layer 20 is not particularly limited as long as it is the same as that used for a typical lithium ion secondary battery. For example, typical examples of the negative electrode active material used for the negative electrode include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal composite oxide (lithium titanium composite oxide, etc.), lithium transition metal composite nitride, and the like. Is done. In particular, it is preferable to use a negative electrode active material (typically, a negative electrode active material substantially composed of natural graphite (or artificial graphite), which is mainly composed of natural graphite (or artificial graphite). For example, spheroidized natural graphite (or spheroidized artificial graphite) having an average particle diameter in the range of about 5 μm to 30 μm can be preferably used as the negative electrode active material. Carbonaceous powder having amorphous carbon coated on the surface may be used.

  The mixture paste used in the method disclosed herein can be an aqueous paste in which such a negative electrode active material is dispersed in an aqueous solvent. Further, the negative electrode mixture layer 20 disclosed herein may be formed using such an aqueous paste. Here, the “aqueous solvent” is a concept indicating water or a mixed solvent mainly composed of water. As the solvent other than water constituting the 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 about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water. Although it does not specifically limit, solid content concentration (nonvolatile content, ie, the ratio of mixture layer formation component) of mixture paste may be about 40-60 mass%, for example.

  The above-mentioned mixture paste is a material used as a mixture paste for forming a mixture layer in the production of a general negative electrode in addition to the negative electrode active material 22 and the aqueous solvent 24. The material which does not receive can be contained as needed. Representative examples of such materials include various polymer materials that can function as a thickener for a mixture paste. As such a polymer material, a polymer material conventionally used as a thickening agent in preparing an aqueous mixture paste can be appropriately selected and used. The use of a polymeric material that is substantially insoluble in organic solvents and that dissolves or disperses in water is preferred. For example, as a water-soluble (water-soluble) polymer material, carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP), etc. Of cellulose derivatives.

  The mixture paste does not contain SBR as a so-called binder (binder) 52. That is, the mixture paste is composed of a paste-like composition that does not substantially contain the binder 52 that is susceptible to migration. In the method disclosed herein, as shown in FIG. 2, a binder solution layer 50 including a binder 52 is applied to the surface of the current collector 10, and the mixture paste is supplied over the binder solution layer 50 ( (See FIG. 3). For this reason, the portion near the surface of the current collector 10 contains a large amount of the binder 52. Hereinafter, the configuration and forming method of the binder solution layer 50 will be described.

  As shown in FIG. 2, the binder solution layer contains a binder 52 and a solvent 54. Such a binder solution layer can be typically formed by applying a binder solution prepared by adding and mixing the binder 52 to an appropriate solvent 54 to the surface of the current collector 10. The solvent constituting the binder solution can be appropriately selected in consideration of the combination with the binder material to be used. From various viewpoints such as reduction of environmental load, reduction of material cost, simplification of equipment, reduction of waste, improvement of handling property, use of an aqueous solvent is preferable. As the aqueous solvent, 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. The binder solution layer is not limited to an aqueous solvent, and may be a solvent solvent (a binder dispersion medium is mainly an organic solvent). As the non-aqueous solvent, for example, N-methylpyrrolidone (NMP) can be used.

  The binder 52 contained in the binder solution can be used without particular limitation as long as the glass transition temperature Tg is 10 ° C. or higher. For example, when the binder solution layer 50 is formed using an aqueous solvent (a solution using water or a mixed solvent containing water as a main component as a binder dispersion medium), the glass transition temperature Tg is 10 ° C. as the binder. The polymer which is the above and is dispersed or dissolved in water can be preferably used. Examples of the polymer that is dispersed or dissolved in water include styrene butadiene rubber (SBR). Here, the styrene-butadiene rubber is a copolymer containing styrene and 1,3-butadiene, and the copolymerization mode is not particularly limited. Further, it may be a modified SBR obtained by copolymerizing an unsaturated carboxylic acid or an unsaturated nitrile compound. Other examples of the polymer that is dispersed or dissolved in water include polyacrylate (acrylic ester homopolymer or copolymer), polyurethane, polyethylene oxide, polyethylene, and the like. Such binders may be used alone or in combination of two or more.

  The glass transition temperature Tg of the styrene butadiene rubber (SBR) can be adjusted, for example, by changing the styrene / butadiene copolymer ratio, adding an additive, adding a crosslinking agent, and the like. The styrene / butadiene copolymer ratio in SBR can be, for example, about 1/1 or less (typically 1/5 to 1/1), and about 1/2 or less (typically 1/4 to 1). / 2). Thereby, the glass transition temperature Tg can be easily adjusted to a suitable range. The glass transition temperature Tg can be measured using a commercially available differential scanning calorimeter (DSC) apparatus.

  The glass transition temperature Tg of the binder 52 is preferably approximately 10 ° C. or higher (for example, 10 ° C. to 40 ° C.). Thus, by using a binder having a glass transition temperature Tg of 10 ° C. or higher, the hardness of the mixture layer 20 is appropriately increased. Therefore, the volume change of the mixture layer during charge / discharge is appropriately suppressed, and the durability of the electrode 30 is improved. On the other hand, a binder having a glass transition temperature Tg that is too high has little merit because it becomes difficult to produce and the durability improving effect accompanying the increase in the glass transition temperature Tg is slowed down. The glass transition temperature Tg of the binder is generally 10 ° C. or higher (eg, 10 ° C. to 40 ° C.), preferably 15 ° C. or higher (eg, 15 ° C. to 40 ° C.), and more preferably 20 ° C. (eg, 20 ° C.). And more preferably 25 ° C. or more (for example, 25 ° C. to 40 ° C.).

  The binder concentration in the binder solution is suitably about 5% by mass to 30% by mass, and preferably 8% by mass to 20% by mass (for example, 10% by mass). If the binder concentration is too smaller than the above range, the mixture paste 40 may be repelled on the binder solution layer 50 and may not be applied to a uniform thickness. On the other hand, when the binder concentration is too larger than the above range, the handling property of the binder solution (for example, the coating property when the binder solution is applied to the current collector 10 (particularly the foil-shaped current collector)) decreases. May be easier.

  The operation of kneading (adding and mixing) the binder 52 and the solvent 54 can be performed using, for example, an appropriate kneading apparatus (a planetary mixer, a homodisper, a clear mix, a fill mix, or the like). In particular, it is preferable to knead using a planetary mixer (preferably a biaxial planetary mixer). By using a planetary mixer, a binder solution in which the binder 52 is uniformly dispersed can be prepared.

The operation of applying the binder solution to the current collector surface 10 can be suitably performed using a conventionally known appropriate application device (slit coater, die coater, comma coater, gravure coater, etc.). In the technique disclosed herein, a method of applying the binder solution on the current collector 10 includes a method of applying the binder solution on the current collector 10 with a gravure coater. Thereby, the binder solution layer 50 having a uniform thickness can be formed. The coating amount of the binder solution is not particularly limited, but if the coating amount is too large, the binder 52 is concentrated in the vicinity of the current collector 10 and the interface resistance between the current collector 10 and the mixture layer 20 tends to increase. If the coating amount is too small, the binder 52 may be insufficient on the surface of the mixture layer 20 and the active material may easily slip off. From the viewpoint of uniformly dispersing the binder, usually at suitably about per side of the coating amount of current collector ^{0.04mg / cm 2 ~0.2mg / cm 2} ( solids basis), for example it is preferable to ^{0.06mg / cm 2 ~0.15mg / cm 2} ( based on solids).

  In addition, it is preferable that the binder solution layer 50 is provided so as to include at least a range in which the negative electrode mixture layer 20 is formed on the surface of the negative electrode current collector 10. For example, when the negative electrode mixture layer 20 is formed only on one side of the negative electrode current collector 10 (may be a part of the single side or the entire range), the single-sided negative electrode mixture layer In the embodiment in which the binder solution layer 50 is formed over a range in which 20 is formed, and when the negative electrode mixture layer 20 is formed on both sides of the negative electrode current collector 10, the negative electrode mixture layer 20 on both sides is formed. It is preferable to employ a mode in which the binder solution layer 50 is provided over a range in which is formed.

  The operation of applying the mixture paste 40 from above the binder solution layer 50 can be performed in the same manner as the operation of forming the binder solution layer 50 by applying the binder solution to the surface of the current collector 10. The application amount of the mixture paste 40 is not particularly limited, and may be appropriately changed depending on the shape and application of the negative electrode and the battery. Thus, in the manufacturing method of this embodiment, as shown in FIG. 3, before the binder solution layer 50 is sufficiently dried, the mixture paste 40 is supplied in layers. That is, the state is called “wet on wet”. At this time, it is desirable that the binder solution layer 50 and the mixture paste 40 be maintained in a two-layer state with a certain degree of stability when the mixture paste 40 is supplied in layers. From such a viewpoint, immediately after coating (before drying), the ratio of the thickness of the binder solution layer to the mixture paste (coating material) (binder solution layer: mixture paste coating material) is approximately 1: 5. It is preferable to supply the mixture paste 40 so as to overlap the binder solution layer 50 so as to be ˜1: 100. Moreover, it is preferable that the surface tension of the binder solution layer 50 is higher than the surface tension of the mixture paste 40 supplied to be superimposed on the binder solution layer 50.

  After applying the mixture paste, the coating material is dried (at this time, an appropriate drying accelerating means (such as a heater) may be used as necessary). The solvent of the mixture paste and the solvent of the binder solution layer Remove. At that time, convection occurs in the mixture paste (coating material). For example, as shown in FIG. 4, most of the binder (SBR) 52 in the binder solution layer 50 applied to the surface of the current collector 10 is collected. Although it remains near the surface of the electric body 10, a part moves to the surface side of the mixture paste (application), and the binder 52 diffuses into the mixture paste (application). Thereby, as shown in FIG. 5, the negative electrode mixture layer 20 in which the binder (SBR) 52 is appropriately present near the surface of the current collector 10 and a part of the binder 52 is widely diffused is obtained. Can do. That is, the negative electrode mixture layer 20 in which the binder (SBR) 52 is uniformly distributed as a whole can be formed.

  Although it does not specifically limit as said drying temperature, When a solvent is water, about 70 to 180 degreeC is suitable, for example, it is preferable to set it as 120 to 160 degreeC (for example, 150 degreeC). In this embodiment, since it is not necessary to consider the segregation (migration) of the binder 52 due to convection when setting the drying temperature, the drying temperature can be set higher as described above.

  A negative electrode having a target thickness can be obtained by pressing the laminate (negative electrode) thus obtained in the thickness direction as desired. As a method for performing the pressing, a conventionally known roll pressing method, flat plate pressing method, or the like can be appropriately employed.

  Although not particularly limited, the proportion of the negative electrode active material in the entire negative electrode mixture layer is preferably about 50% by mass or more (typically 90 to 99% by mass), preferably about 95 to 99% by mass. It is preferable that Further, the ratio of the binder in the entire negative electrode mixture layer is preferably about 5% by mass or less, for example, about 1% by mass or less (for example, about 0.5 to 1% by mass, for example, 0.8% by mass). It is preferable. When the ratio of the binder is more than the above range, the internal resistance of the battery may increase. On the other hand, when the ratio of the binder is too smaller than the above range, the binding force of the mixture layer is reduced, and the active material is liable to slip off. Further, in a composition containing a negative electrode mixture layer forming component (for example, a thickener) other than the negative electrode active material and the binder, the total content ratio of these arbitrary components (ratio to the total negative electrode mixture layer forming component) is about 3 It is preferable to set it as mass% or less, and it is more preferable to set it as about 2 mass% or less (for example, about 0.5-2 mass%). The total content of the optional components may be about 1.5% by mass or less (for example, about 0.5 to 1.5% by mass).

  A preferred embodiment for producing an electrode (for example, a negative electrode for a lithium secondary battery) by the production method disclosed herein will be described below with reference to process cross-sectional views shown in FIGS. 2 to 5 and a flowchart shown in FIG. It is as follows. That is, first, a current collector (for example, copper foil) 10 is prepared (prepared) (step S100). On the other hand, a binder solution containing the binder 52 and the solvent 54 is prepared (step S110). And the binder solution prepared by step S110 is apply | coated to the single side | surface or both surfaces of the electrical power collector 10, and the binder solution layer 50 is formed (step S120, FIG. 2). Next, the mixture paste 40 containing the active material 22 and the solvent 24 is applied on the binder solution layer 50 formed in step S120 (FIGS. 3 and 4), and the applied material is dried to mix the mixture layer 20. (Step S130, FIG. 5). Thereafter, the whole is pressed or cut into a desired size as necessary, and an electrode 30 having a desired thickness and size is obtained.

  A cross-sectional structure of the electrode 30 thus formed is schematically shown in FIG. The electrode 30 has a configuration in which the mixture layer 20 including the active material 22 and the binder 52 is held by the current collector 10. The mixture layer 20 is formed by using a binder 52 having a glass transition temperature Tg of 10 ° C. or more and applying and drying the mixture paste 40 on the binder solution layer 50 including the binder 52. It is.

  Here, in the conventional mode in which the binder solution layer 50 is not formed, it is necessary to bind the mixture layer 20 and the current collector 10 depending on only the binder contained in the mixture paste 40. As shown in the schematic cross-sectional view shown in FIG. 15, the binder 52 convects during drying, and migration that segregates in the surface layer portion of the mixture layer 20 occurs. As a result, the binder 52 in the vicinity of the current collector 10 is insufficient, and the binding strength between the current collector 10 and the composite material layer 20 tends to decrease. In addition, when there is a bias in the distribution of the binder 52 as described above, the hardness becomes too flexible at a portion where the binder 52 is relatively large (in the vicinity of the surface layer portion), so that the volume change of the mixture layer at the time of charging / discharging occurs. As a result, the durability of the electrode as a whole decreases. Moreover, since the hardness becomes too hard in a portion where the binder 52 is relatively small (in the vicinity of the current collector), it can be a factor that causes cracks and cracks at the time of winding from that portion. Such an event becomes particularly noticeable when a hard binder 52 having a glass transition temperature Tg of 10 ° C. or higher is used.

  On the other hand, according to the electrode 30 having the configuration shown in FIG. 1, the mixture paste 40 is supplied over the binder solution layer 50, whereby the binder solution layer 50 applied to the surface of the current collector 10 Although most of the binder 52 stays near the surface of the current collector 10, a part of the binder 52 moves to the surface side of the mixture paste (application) 40, and the binder 52 diffuses into the mixture paste 40. Thereby, the mixture layer 20 in which the binder 52 is appropriately present near the surface of the current collector 10 and a part of the binder 52 is diffused widely can be obtained. According to such a configuration, the binder 52 is appropriately present near the surface of the current collector 10, so that the binding strength between the mixture layer 20 and the current collector 10 can be sufficiently ensured. Furthermore, in the binder solution layer 50, by using the binder 52 having a glass transition temperature Tg of 10 ° C. or higher, the optimal mixture layer 20 having a balance between hardness and flexibility can be obtained without uneven distribution of the binder 52. Can be formed. Therefore, according to this configuration, while maintaining the flexibility in the mixture layer 20 (for example, the flexibility that can prevent the mixture layer 20 from being cracked or cracked when the electrode 30 is wound) An optimal electrode 30 with improved durability of the electrode 30 is obtained. A battery including such an electrode 30 can have a higher performance (for example, a higher cycle life).

  Note that the mixture paste in the technology disclosed herein may be a composition containing only the active material, thickener and solvent, or the active material, thickener and In addition to the solvent, the binder (a glass transition temperature of 10 ° C. or higher) may be included. In a preferred embodiment, the mixture paste is substantially composed of only the active material, the thickener and the solvent (that is, the mixture paste is composed of a composition containing substantially no binder). If the binder paste is applied to the mixture paste applied from above the binder solution layer, both binders aggregate near the current collector, and the active material tends to slip off at the surface layer portion. Such a disadvantage can be avoided when the composition is composed only of a thickener and a solvent.

  Since the electrode (in this case, the negative electrode) thus obtained has high performance as described above, the constituent elements of the battery of various forms or the constituent elements of the electrode body incorporated in the battery (for example, the negative electrode) Can be preferably used. For example, a negative electrode manufactured by any of the methods disclosed herein, a positive electrode (which may be a positive electrode manufactured by applying the present invention), an electrolyte disposed between the positive and negative electrodes, Can be preferably used as a component of a lithium secondary battery including a separator that separates the positive and negative electrodes (can be omitted in a battery using a solid or gel electrolyte). 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.

  Hereinafter, an embodiment of a lithium secondary battery constructed using the negative electrode (negative electrode sheet) 30 manufactured by applying the above-described method will be described with reference to a schematic diagram shown in FIG. Although not intended to be particularly limited, a lithium secondary battery (lithium ion secondary battery) in a form in which a wound electrode body (rolled electrode body) and a non-aqueous electrolyte are housed in a box-shaped container will be described below. The following battery will be described as an example. In the lithium secondary battery 100, the negative electrode (negative electrode sheet) 30 manufactured using the above-described electrode manufacturing method is used as the negative electrode (negative electrode sheet) 30. Note that the electrode manufacturing method disclosed here is not limited to the negative electrode 30, and can also be applied to the positive electrode 70.

  As shown in the drawing, the lithium secondary battery 100 according to the present embodiment includes a case 82 made of metal (a resin or a laminate film is also suitable). The case (outer container) 82 includes a flat cuboid case main body 84 having an open upper end, and a lid 86 that closes the opening. On the upper surface (that is, the lid body 86) of the case 82, a positive electrode terminal 72 that is electrically connected to the positive electrode 70 of the electrode body 80 and a negative electrode terminal 74 that is electrically connected to the negative electrode 30 of the electrode body are provided. In the case 82, for example, a long sheet-like positive electrode (positive electrode sheet) 70 and a long sheet-like negative electrode (negative electrode sheet) 30 are laminated together with a total of two long sheet-like separators (separator sheets) 76. A flat wound electrode body 80 produced by winding and then crushing the resulting wound body from the side direction and kidnapping is housed.

  As described above, the negative electrode sheet 30 has a configuration in which the negative electrode mixture layer 20 mainly composed of the negative electrode active material is provided on both surfaces of the long sheet-like negative electrode current collector 10. Similarly to the negative electrode sheet, the positive electrode sheet 70 has a configuration in which a positive electrode mixture layer mainly composed of a positive electrode active material is provided on both surfaces of a long sheet-like positive electrode current collector. At one end of these electrode sheets 30 and 70 in the width direction, an electrode mixture layer non-formed portion where the electrode mixture layer is not provided on any surface is formed.

  In the lamination, the positive electrode sheet 70 and the negative electrode mixture layer non-formed portion of the positive electrode sheet 70 and the negative electrode mixture layer non-formed portion of the negative electrode sheet 30 protrude from both sides of the separator sheet 76 in the width direction. The negative electrode sheet 30 is overlaid with a slight shift in the width direction. As a result, in the lateral direction with respect to the winding direction of the wound electrode body 80, the electrode mixture layer non-formed portions of the positive electrode sheet 70 and the negative electrode sheet 30 are respectively wound core portions (that is, the positive electrode mixture layer forming portion of the positive electrode sheet 70). And a portion where the negative electrode mixture layer forming portion of the negative electrode sheet 30 and the two separator sheets 76 are wound tightly). A positive electrode lead terminal 78 and a negative electrode lead terminal 79 are respectively attached to the protruding portion (that is, the portion where the positive electrode mixture layer is not formed) 70A and the negative electrode side protruding portion (that is, the portion where the negative electrode mixture layer is not formed) 30A. Are electrically connected to the positive terminal 72 and the negative terminal 74 described above.

The positive electrode sheet 70 can be formed by applying a positive electrode mixture layer mainly composed of a positive electrode active material for a lithium secondary battery on a long positive electrode current collector. As the positive electrode current collector, an aluminum foil or other metal foil suitable for the positive electrode is preferably used. As the positive electrode active material, one kind or two or more kinds of substances conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include lithium transition metal composite oxides containing lithium and one or more transition metal elements as constituent metal elements such as LiMn ₂ O ₄ , LiCoO ₂ , and LiNiO ₂ as main components. . The negative electrode sheet 30 may be formed by applying a negative electrode mixture layer mainly composed of a negative electrode active material for a lithium secondary battery on a long negative electrode current collector. For the negative electrode current collector, a copper foil (a foil-like member mainly composed of copper or a copper alloy) or other metal foil suitable for the negative electrode is preferably used. As the negative electrode active material, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. Preferable examples include carbon materials such as graphite carbon and amorphous carbon, lithium transition metal composite oxides (lithium titanium composite oxides, etc.), lithium transition metal composite nitrides, and the like.

  Moreover, as a suitable example of the separator sheet 76 used between the positive and negative electrode sheets 70 and 30, a sheet made of a porous polyolefin-based resin can be cited. When a solid electrolyte or a gel electrolyte is used as the electrolyte, a separator may not be necessary (that is, in this case, the electrolyte itself can function as a separator).

Then, the wound electrode body 80 is accommodated in the main body 84 from the upper end opening of the case main body 84 and an electrolytic solution containing an appropriate electrolyte is disposed (injected) in the case main body 84. The electrolyte is lithium salt such as LiPF _6, for example. For example, a nonaqueous electrolytic solution obtained by dissolving a suitable amount (for example, concentration 1M) of a lithium salt such as LiPF _{6 in} a mixed solvent of diethyl carbonate and ethylene carbonate (for example, a mass ratio of 1: 1) can be used.

  Thereafter, the opening is sealed by welding or the like with the lid 86, and the assembly of the lithium secondary battery 100 according to the present embodiment is completed. The sealing process of the case 82 and the arrangement (injection) process of the electrolyte may be the same as the technique used in the production of the conventional lithium secondary battery, and do not characterize the present invention. In this way, the construction of the lithium secondary battery 100 according to this embodiment is completed.

  The lithium secondary battery 100 constructed in this way is constructed using at least one electrode (here, the negative electrode) using the electrode produced using the above-described electrode production method, and thus has excellent battery performance. Is shown. For example, by constructing a battery using the above electrode, at least one (preferably all) of high capacity maintenance ratio after charge / discharge cycle, excellent input / output characteristics, and excellent production stability is satisfied. The lithium secondary battery 100 can be provided.

  Hereinafter, the present invention will be described in more detail based on test examples, but the present invention is not intended to be limited to the specific examples. In this test example, negative electrode sheets were produced using binders having different glass transition temperatures Tg. Styrene butadiene rubber (SBR) was used as the binder. The glass transition temperature Tg of the SBR was controlled by changing the styrene / butadiene copolymer ratio.

[Preparation of negative electrode sheet]
<Example 1>
SBR (binder) having a glass transition temperature Tg of 30 ° C. was added to the binder solution layer to prepare a negative electrode sheet. That is, the SBR (binder) and water (solvent) were mixed to prepare a binder solution having a binder concentration of about 10% by mass. The binder solution layer 50 was formed by applying this binder solution on both sides of a long sheet-like copper foil (negative electrode current collector; thickness 10 μm). Here, a gravure coater was used for application of the binder solution, and the application amount (weight per unit area) was adjusted to be about 1.28 g / m ² (solid content basis) per one side of the current collector.

Further, natural graphite powder (negative electrode active material) having an average particle size of 10 μm and carboxymethyl cellulose (CMC, thickener) have a mass ratio of these materials of 98.2: 1 and a solid content of about 50 mass. % And mixed with water (solvent) to prepare a mixture paste. The mixture paste was applied from above the binder solution layer 50 formed and dried to obtain a negative electrode sheet 30 in which the negative electrode mixture layer 20 was provided on both surfaces of the negative electrode current collector 10. The coating amount of the mixture paste was adjusted to be about 16 mg / cm ² (solid content basis). The drying conditions were 120 ° C. and 20 seconds. After drying, the negative electrode mixture layer was pressed so as to have a density of about 1.5 g / cm ³ . The blending ratio of final natural graphite powder (negative electrode active material), CMC (thickener) and SBR (binder) is adjusted to be natural graphite: CMC: SBR = 98.2: 1: 0.8 did.

<Example 2>
A negative electrode sheet according to Example 2 was produced in the same manner as in Example 1 except that SBR having a glass transition temperature Tg of 10 ° C. was used.

<Example 3>
A negative electrode sheet according to Example 3 was produced in the same manner as in Example 1 except that SBR having a glass transition temperature Tg of −5 ° C. was used.

<Example 4>
A negative electrode sheet according to Example 4 was produced in the same manner as in Example 1 except that SBR having a glass transition temperature Tg of −20 ° C. was used.

<Example 5>
A negative electrode sheet according to Example 5 was produced in the same manner as in Example 1 except that SBR having a glass transition temperature Tg of −40 ° C. was used.

<Example 6>
SBR (binder) having a glass transition temperature Tg of 30 ° C. was added to the mixture paste to prepare a negative electrode sheet. That is, natural graphite powder (negative electrode active material) having an average particle size of 10 μm, carboxymethylcellulose (CMC, thickener), and the above SBR (binder) have a mass ratio of these materials of 98.2: 1: 0. The mixture paste was prepared by mixing with water (solvent) so that the solid content was about 50% by mass. A negative electrode in which a negative electrode mixture layer 20 is provided on both surfaces of the negative electrode current collector 10 by applying this mixture paste to both surfaces of a long sheet-like copper foil (negative electrode current collector; thickness 10 μm) and drying the resulting mixture paste. A sheet 30 was obtained. The coating amount of the mixture paste was adjusted to be about 16 mg / cm ² (solid content basis). The drying conditions were 120 ° C. and 20 seconds. After drying, the negative electrode mixture layer was pressed so that the density was about 1.5 gcm ⁻³ .

<Example 7>
A negative electrode sheet according to Example 7 was produced in the same manner as in Example 6 except that SBR having a glass transition temperature Tg of 10 ° C. was used.

<Example 8>
A negative electrode sheet according to Example 8 was produced in the same manner as in Example 6 except that SBR having a glass transition temperature Tg of −5 ° C. was used.

<Example 9>
A negative electrode sheet according to Example 9 was produced in the same manner as in Example 6 except that SBR having a glass transition temperature Tg of −20 ° C. was used.

<Example 10>
A negative electrode sheet according to Example 10 was produced in the same manner as in Example 6 except that SBR having a glass transition temperature Tg of −40 ° C. was used.

  The performance of the negative electrode sheets produced in Examples 1 to 10 was evaluated by the following bending resistance test and 90 ° peel test.

[Flexibility test]
This was performed according to JIS-K5600-5-1. That is, as shown in FIG. 8, the cylindrical mandrel 65 was sandwiched between the negative electrode sheets 30, bent 180 ° so that the negative electrode mixture layer was on the outside, and the negative electrode mixture layer was observed for cracks and cracks. A test was conducted by changing the core diameter of the mandrel 65 to a small one, and the minimum core diameter at which cracks and cracks started to occur was measured. It can be said that the smaller the minimum core diameter, the better the bending resistance (flexibility). The results are shown in Table 1 and FIG. FIG. 9 is a graph showing the relationship between the glass transition temperature Tg (° C.) and the minimum core diameter (mm).

  As shown in Table 1 and FIG. 9, in Examples 6 to 10 in which the binder was added to the mixture paste, when the TBR of SBR was increased to 10 ° C. or more, the bending resistance (flexibility) was significantly lowered. (Example 6 and Example 7). On the other hand, according to Examples 1 to 5 in which the same amount of binder was added to the binder solution layer, the bending resistance (flexibility) did not change even when the SBR Tg was 10 ° C. or more (Examples 4 and 5). . From the above, it was confirmed that good flexibility of the negative electrode sheet can be maintained by using a binder having a glass transition temperature of 10 ° C. or higher in the binder solution layer.

[90 ° peel test]
This was performed according to JIS-K6854-1. That is, as shown in FIG. 10, the surface on the negative electrode mixture layer 20 side is fixed on the base 66 with the double-sided tape 67 and the polyethylene tape 68, and the negative electrode current collector 10 is fixed to the surface of the negative electrode mixture layer 20. The film was pulled in a vertical direction and continuously peeled off at about 60 mm at a speed of 20 mm per minute. And the minimum value of the load in the meantime was measured as peeling strength [N / m], and the adhesiveness of the negative electrode collector 10 and the negative mix layer 20 was evaluated. The results are shown in Table 1 and FIG. FIG. 11 is a graph showing the relationship between glass transition temperature Tg (° C.) and peel strength (N / m).

As shown in Table 1 and FIG. 11, in Examples 6 to 10 where the binder was added to the mixture paste, the peel strength tended to decrease as the Tg of SBR increased.
On the other hand, in Examples 1 to 5 in which the same amount of binder was added to the binder solution layer, the peel strength tended to increase as the Tg of SBR increased. In particular, by setting Tg to 10 ° C. or higher, an extremely high peel strength of 14 N / m could be achieved (Examples 4 and 5). From the above, it was confirmed that the peel strength is remarkably improved by using a binder having a glass transition temperature of 10 ° C. or higher in the binder solution layer.

  Furthermore, the lithium secondary battery for a test was produced using the negative electrode sheet produced by the separately prepared Examples 1-10, and the performance was evaluated by the charge / discharge cycle test. The test lithium secondary battery was produced as follows.

[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) as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder Were mixed in N-methylpyrrolidone (NMP) so that the mass ratio of these materials was 90: 5: 5 to prepare a positive electrode mixture paste. The positive electrode mixture layer was provided on one side of the positive electrode current collector by applying the positive electrode mixture paste in a band shape on one side of a long sheet-like aluminum foil (positive electrode current collector; thickness 15 μm) and drying. A positive electrode sheet 70 was produced. The coating amount of the positive electrode mixture paste was adjusted to be about 320 g / m ² (solid content basis). Moreover, after drying, it pressed so that the density of a positive mix layer might be set to about 2.8 g / cm < ³ >.

[Production of lithium secondary battery]
The positive electrode sheet obtained above was punched out to 5 cm × 5 cm to produce a positive electrode. Moreover, the negative electrode sheet concerning each Examples 1-10 prepared separately was punched out into 5 cm x 5 cm, and the negative electrode was produced. An aluminum lead is attached to the positive electrode, a nickel lead is attached to the negative electrode, and they are opposed to each other through a separator (a polypropylene (PP) -polyethylene (PE) -polypropylene (PP) three-layer structure). The lithium secondary battery (laminate cell) 60 shown in FIG. 12 was constructed by inserting it into a laminate bag together with the nonaqueous electrolyte. In FIG. 12, reference numeral 61 indicates a negative electrode, reference numeral 62 indicates a positive electrode, reference numeral 63 indicates a separator impregnated with an electrolytic solution, and reference numeral 64 indicates a laminate bag. In addition, as a non-aqueous electrolyte solution, LiPF ₆ as a supporting salt is approximately mixed in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4. The one contained at a concentration of 1 mol / liter was used. In this way, a lithium secondary battery was assembled.

[Measurement of initial capacity]
Each of the lithium secondary batteries using the negative electrode sheet according to each of Examples 1 to 10 was charged at 25 ° C. with a constant current and constant voltage method with a current of 1 C and a voltage of 4.1 V until the total charging time was 3 hours. . After 10 minutes of rest, the charged battery was discharged at 25 ° C. to a constant current and a constant voltage of 1/3 C until the total discharge time was 3 hours, and the discharge capacity at this time was defined as the initial capacity. .

[Charge / discharge cycle test]
Moreover, the charging / discharging pattern which repeats charging / discharging was provided with respect to each of each lithium secondary battery, and the charging / discharging cycle test was done. Specifically, after charging at a constant current of 2C so that the charging depth (SOC) of each battery is 90% of the initial capacity, discharging is performed at a constant current of 2C so as to be 30% of the initial capacity, The charging / discharging cycle which rests for 10 minutes was repeated 1000 times continuously. Then, the discharge capacity after the charge / discharge cycle test is obtained by the same method as the above initial capacity, and the capacity retention rate after the charge / discharge cycle test (= [charge / discharge cycle] Discharge capacity after test / initial capacity] × 100) was calculated. The results are shown in Table 1 and FIG. FIG. 13 is a graph showing the relationship between the glass transition temperature Tg (° C.) and the capacity retention rate (%).

  As shown in Table 1 and FIG. 13, in Examples 1 to 3 and Examples 8 to 10 in which the TBR of SBR was −40 ° C., −20 ° C., and −5 ° C., the capacity retention rate after repeating the charge / discharge cycle There was not much difference. On the other hand, in Examples 4, 5 and Examples 9 and 10 in which the TBR of SBR was 10 ° C. and 30 ° C., Example 4 and Example 5 in which the binder was added to the binder solution layer were the examples 9 and Compared to Example 10, the capacity retention rate was significantly increased. From the above, it was confirmed that the capacity retention rate after the charge / discharge cycle was remarkably improved by using a binder having a glass transition temperature of 10 ° C. or higher in the binder solution layer.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment is only an illustration and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

  Any of the batteries 100 disclosed herein may have performance suitable as a battery mounted on a vehicle, and may be particularly excellent in durability against charge / discharge cycles. Therefore, according to the present invention, as shown in FIG. 14, a vehicle 1 including any of the batteries 100 disclosed herein is provided. In particular, a vehicle (for example, an automobile) including the battery 100 as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is provided.

  As a preferable application target of the technology disclosed herein, a secondary that can be used in a charge / discharge cycle including a high-rate discharge of 50 A or more (for example, 50 A to 250 A), or even 100 A or more (for example, 100 A to 200 A). Batteries: Large capacity type with a theoretical capacity of 1Ah or more (more than 3Ah), and used in charge / discharge cycles including high rate charge / discharge of 10C or more (for example 10C to 50C) and even 20C or more (for example 20C to 40C) Secondary battery;

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Negative electrode collector 20 Negative electrode mixture layer 22 Negative electrode active material 24 Solvent 30 Negative electrode sheet 40 Mixture paste 50 Binder solution layer 52 Binder 54 Solvent 70 Positive electrode sheet 72 Positive electrode terminal 74 Negative electrode terminal 76 Separator sheet 78 Positive electrode lead terminal 79 Negative electrode lead terminal 80 Electrode body 82 Battery case 84 Case body 86 Cover body 100 Battery

Claims (5)

A method for producing a battery comprising an electrode having a configuration in which a mixture layer containing an active material and a binder is held by a current collector,
Preparing a binder solution comprising the binder and a solvent;
Applying the binder solution to the current collector to form a binder solution layer on the surface of the current collector; and
Forming a mixture layer from above the binder solution layer by applying and drying a mixture paste containing the active material and a solvent;
Including
In the binder solution layer, a binder having a glass transition temperature of 10 ° C. or higher is used.   The battery manufacturing method according to claim 1, wherein the mixture paste is composed of a composition that does not substantially contain the binder.   The battery manufacturing method according to claim 1 or 2, wherein at least one polymer selected from the group consisting of styrene butadiene rubber, polyacrylate, polyurethane, polyethylene oxide, and polyethylene is used as the binder.   The battery manufacturing method as described in any one of Claims 1-3 whose binder density | concentration of the said binder solution layer is 5 mass%-30 mass%. The battery manufacturing method as described in any one of Claims 1-4 whose ratio of the said binder to the said mixture layer is 0.5 mass%-1 mass%.

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