JP2015141773A - Method for manufacturing secondary battery negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of avoiding poor coating of a paste for forming a negative electrode active material layer, thereby manufacturing a secondary battery negative electrode excellent in quality stability.SOLUTION: A method for manufacturing a secondary battery negative electrode provided by the present invention includes: preparing a paste for forming a negative electrode active material layer, the paste including a negative electrode material and an aqueous solvent for dispersing the negative electrode material, and having a viscosity α at a shear rate: 1 sof more than 1,000 mPa s and less than 30,000 mPa s, and a viscosity β at a shear rate: 1,000 sof less than 1,300 mPa s; and applying the paste for forming a negative electrode active material layer to a negative electrode collector to form a negative electrode active material layer on the negative electrode collector.

Description

  The present invention relates to a method for producing a negative electrode for a secondary battery. Specifically, the present invention relates to a method for manufacturing a negative electrode for a secondary battery in which a negative electrode active material layer is formed on a negative electrode current collector.

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

  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 as charge carriers is formed on a negative electrode current collector. A negative electrode having the above structure. Such a negative electrode active material layer is sometimes abbreviated as a paste or slurry-like composition prepared by adding an appropriate solvent together with a binder or a thickener (hereinafter referred to as “negative electrode active material layer forming paste”). .) Is applied to the negative electrode current collector (typically, coating and drying). Patent document 1 is mentioned as a prior art regarding the manufacturing method of the said negative electrode.

JP 2013-045714 A

  By the way, in order to efficiently manufacture the negative electrode, it is desirable to reduce the solvent by highly solidifying the paste so that the negative electrode active material layer forming paste can be easily dried. However, when the negative electrode active material layer forming paste is highly solid differentiated, the viscosity of the paste is remarkably increased. For this reason, there are cases where the coating property when the paste is applied to the negative electrode current collector is impaired, or the piping of the coating apparatus is clogged.

  The present invention has been made in view of the above points, and its main purpose is to manufacture a negative electrode for a secondary battery that can avoid poor coating of the negative electrode active material layer forming paste and has excellent quality stability. Is to provide a method.

In order to achieve the above object, the present invention provides a method for producing a negative electrode for a secondary battery in which a negative electrode active material layer is formed on a negative electrode current collector. The production method disclosed herein includes a negative electrode active material and an aqueous solvent in which the negative electrode active material is dispersed, and a viscosity α at a shear rate of 1 s ⁻¹ is 1000 mPa · s <α <30000 mPa · s, In addition, the method includes preparing a negative electrode active material layer forming paste having a viscosity β of β <1300 mPa · s at a shear rate of 1000 s ⁻¹ . Further, the method includes applying the negative electrode active material layer forming paste to a negative electrode current collector to form a negative electrode active material layer on the negative electrode current collector. Here, the above-mentioned viscosities α and β are viscosities that can be measured by a commercially available shear viscometer. For example, by using a cone plate viscometer such as a standard rheometer or E type viscometer in the field, the viscosity can be easily measured under the conditions of the shear rate range as described above.

  The negative electrode active material layer forming paste disclosed above has viscosity characteristics as described above. As a result, it is excellent in stability at the time of standing and handling property, and hardly causes defects such as streaks during coating. Therefore, if the paste having the above configuration is used, a higher performance negative electrode can be produced while preventing the occurrence of coating failure.

It is a figure which shows typically the secondary battery which concerns on one Embodiment of this invention. It is a graph which shows the relationship between a shear rate and a viscosity. It is a graph which shows the relationship between a shear rate and a viscosity. It is a graph which shows the relationship between a shear rate and a viscosity. It is a graph which shows the relationship between a shear rate and a viscosity. It is a graph which shows the relationship between a shear rate and a viscosity.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
In the present specification, “secondary battery” generally refers to a battery that can be repeatedly charged, and involves a chemical reaction such as a lithium secondary battery (typically a lithium ion battery), a nickel metal hydride battery, or a nickel cadmium battery. This term includes so-called chemical batteries and so-called physical batteries such as electric double layer capacitors. In the present specification, the “electrode active material” refers to an active material capable of reversibly occluding and releasing (typically inserting and removing) a chemical species that serves as a charge carrier in a secondary battery. Moreover, the viscosity of the paste mentioned in this specification has shown the value of the viscosity measured at normal temperature. Here, “normal temperature” refers to a temperature range of 15 to 35 ° C., and typically refers to a temperature range of 20 to 30 ° C. (for example, 25 ° C.).

  Although not intended to be particularly limited, the present invention will be described in detail below, taking as an example a negative electrode (negative electrode sheet) for a lithium ion secondary battery mainly having a copper foil-shaped negative electrode current collector (copper foil). explain.

  The manufacturing method of the electrode for lithium ion secondary batteries which concerns on this embodiment manufactures the negative electrode (negative electrode sheet) which has the negative electrode active material layer formed by apply | coating and drying the paste for negative electrode active material layer formation on a negative electrode collector. It is a method to do.

  The negative electrode active material layer forming paste disclosed herein is a material mainly composed of a negative electrode active material powder and an aqueous medium for dispersing the powder, as in the conventional paste material of this type. .

  As the negative electrode active material powder that is the main component of the solid content of the paste, one or more of materials conventionally used in lithium ion secondary batteries can be used without particular limitation. Preferable examples include carbon-based materials such as natural graphite, artificial graphite, graphite, and amorphous carbon. As such a material (typically in particulate form), for example, a material powder prepared by a conventionally known method can be used as it is. For example, a material powder substantially composed of particles having an average particle diameter (D50 diameter) based on a laser diffraction / scattering method in the range of about 5 μm to 20 μm (preferably 8 μm to 15 μm) is preferably used as the negative electrode active material. Can do.

The negative electrode active material layer forming paste can contain various polymers that function as binders and thickeners as long as the object of the present invention can be achieved. Preferable examples of the polymer functioning as the binder include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and the like. Moreover, carboxymethylcellulose (CMC) is illustrated as a suitable example of the polymer which functions as a thickener. By dispersing and kneading these polymers together with the negative electrode active material powder in an appropriate aqueous solvent, a negative electrode active material layer forming paste can be prepared.
Although not particularly limited, the content ratio of the negative electrode active material powder in the total solid content excluding the aqueous solvent of the negative electrode active material layer forming paste is approximately 90% by mass or more (for example, 90% by mass to 99.5% by mass). %), And preferably 95% by mass or more (for example, 95% by mass to 99% by mass). The binder content in the entire solid content is suitably about 0.1% by mass or more (for example, 0.1% by mass to 1% by mass), preferably 0.5% by mass or more ( For example, 0.5 mass% to 0.8 mass%).

  As the aqueous solvent in which the negative electrode active material powder is dispersed, those used in conventional paste materials of this type can be used without particular limitation. 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.

The negative electrode active material layer forming paste suitably used for the negative electrode manufacturing method disclosed herein has a viscosity α at a shear rate of 1 s ⁻¹ of 1000 mPa · s <α <30000 mPa · s (preferably 3000 mPa · s). ≦ α ≦ 25000 mPa · s, for example 6000 mPa · s ≦ α ≦ 15000 mPa · s), and the viscosity β when the shear rate is 1000 s ⁻¹ is β <1300 mPa · s (for example, 500 mPa · s ≦ β <1300 mPa · s). s, preferably β ≦ 1150 mPa · s, for example β ≦ 1000 mPa · s). Typically, the above-mentioned viscosities α and β are viscosities measured by using a commercially available rheometer to shear the paste material under any of the above shear rate conditions. The negative electrode active material layer forming paste used in the negative electrode manufacturing method disclosed herein has a viscosity such that 1000 mPa · s <α <30000 mPa · s and β <1300 mPa · s. When it is applied to a current collector, it exhibits suitable stability, handling properties and coating properties.

That is, the negative electrode active material layer forming paste having a viscosity α at a shear rate of 1 s ⁻¹ of 1000 mPa · s <α is stable when left standing (when left at room temperature without performing stirring or the like). Therefore, when the paste is applied to the negative electrode current collector, a good dispersion state can be maintained without the solid content in the paste being settled. For this reason, various problems caused by the solid content in the paste being settled (for example, uneven distribution of the negative electrode active material and binder, increase in internal resistance, and decrease in adhesion between the negative electrode active material layer and the negative electrode current collector). Can be prevented. Further, by setting the viscosity α at a shear rate of 1 s ⁻¹ to α <30000 mPa · s, the handleability of the paste is improved, so that the paste is applied to a pipe (for example, a coating part such as a die coater, a tank to a coater). Inconveniences such as clogging in the liquid feeding part) can be avoided.
Furthermore, the negative electrode active material layer forming paste in which the viscosity β at a shear rate of 1000 s ⁻¹ is β <1300 mPa · s has high fluidity (easy to pass through a narrow narrow channel such as a die coater), and has a coating property. It is good. Therefore, when the paste is applied to the negative electrode current collector, streaks and thickness unevenness can be prevented from occurring on the coated surface.
That is, according to the above configuration, since the paste has good stability, handling properties and coating properties, the negative electrode active material layer is difficult to peel off from the negative electrode current collector while avoiding the occurrence of poor coating, and the internal resistance is low. Lower performance negative electrodes can be produced.

The viscosities α and β can be adjusted, for example, by changing the content of the thickener contained in the paste, the oil absorption of the negative electrode active material, the solid content of the paste, and the like. The content of the thickener in the entire solid content of the negative electrode active material layer forming paste is appropriately 0.2% by mass to 0.7% by mass, preferably 0.3% by mass to 0.5% by mass. Further, the oil absorption amount of the negative electrode active material is suitably about 40 × 10 ⁻⁵ (m ³ / kg) to 60 × 10 ⁻⁵ (m ³ / kg), preferably 40 × 10 ^−5. (M ³ / kg) to 45 × 10 ⁻⁵ (m ³ / kg). Here, the amount of oil absorption of the negative electrode active material is linseed oil as a reagent, titrated on the negative electrode active material to be inspected with a constant speed burette, and the change in viscosity characteristics is measured with a torque detector. The amount of linseed oil added per unit mass of the negative electrode active material corresponding to 70% of the generated maximum torque is taken as the oil absorption amount. As the measuring device, for example, an oil absorption measuring device of Asahi Research Institute, Ltd. can be used. Moreover, as a solid content rate of a paste, it is preferable to set it as 50 mass% or more in general, For example, the range of 50 mass%-70 mass% is suitable, Preferably it is 55 mass%-65 mass%, More preferably Is 58 mass% to 62 mass%. A negative electrode active material layer forming paste having the above-mentioned viscosities α and β is preferably prepared within the range of the content of such a thickener, the oil absorption amount of the negative electrode active material, and the solid content rate of the paste. Can do.

  The negative electrode active material layer forming paste disclosed herein can be typically prepared by kneading the negative electrode active material powder, a binder, a thickener, and an aqueous solvent. Preferably, first, the negative electrode active material powder and the thickener are mixed in a powder state. Next, the aqueous solvent may be added to the powder mixture a plurality of times and added and kneaded (solid kneaded) in small portions, and then a binder may be added and kneaded. The apparatus used for the kneading is not particularly limited, and examples thereof include a planetary mixer, an extrusion kneader such as a disper, a ball mill, and a kneader, and a mixer. By mixing various paste materials in this order and kneading them together, the negative electrode active material layer forming paste having the aforementioned viscosity α, β can be suitably prepared.

Then, the process of providing the negative electrode active material layer forming paste to a negative electrode collector, and forming a negative electrode active material layer on this collector is performed. The operation of applying the negative electrode active material layer forming paste to the negative electrode current collector can be performed in the same manner as in the case of producing a conventional negative electrode for a lithium ion secondary battery. For example, using a suitable coating apparatus (a die coater, a slit coater, a comma coater, etc.), a predetermined amount of the negative electrode active material layer forming paste is applied to the negative electrode current collector to a uniform thickness. Then, the aqueous solvent in the negative electrode active material layer forming paste is removed by volatilizing the aqueous solvent in the negative electrode active material layer forming paste in a drying furnace. The negative electrode active material layer is formed by removing the aqueous solvent from the negative electrode active material layer forming paste. Thus, a negative electrode (negative electrode sheet) in which a negative electrode active material layer is formed on a negative electrode current collector can be obtained. In addition, after drying, the thickness and density of a negative electrode active material layer can be suitably adjusted by performing an appropriate press process (for example, roll press process) as needed. The coating amount (weight per unit area) of the negative electrode active material layer forming paste is preferably about 5 mg / cm ² (solid basis) or less per side, more preferably 4 mg / cm ² or less.

  Other materials and members constituting the lithium ion secondary battery including the negative electrode manufactured by the method disclosed herein may be the same as those conventionally provided in the same type of battery, and are not particularly limited. Hereinafter, other components will be described, but the present invention is not intended to be limited to such embodiments.

  For example, the positive electrode (positive electrode sheet) 50 may have a configuration in which a positive electrode active material layer 54 is formed on a sheet-like positive electrode current collector 52 (for example, an aluminum foil), as shown in FIG. For the positive electrode current collector 52, for example, a strip-shaped aluminum foil having a thickness of about 15 μm is used. A positive electrode active material layer non-forming portion 52 a is set along an edge portion on one side in the width direction of the positive electrode current collector 52. In the illustrated example, the positive electrode active material layer 54 is held on both surfaces of the positive electrode current collector 52 except for the positive electrode active material layer non-forming portion 52 a set in the positive electrode current collector 52. The positive electrode active material layer 54 is a composition in which a positive electrode active material and various additives such as a conductive material, a binder, and a thickener added as necessary are mixed in an appropriate solvent (positive electrode active material layer formation). The paste is applied to the positive electrode current collector 52, and the solvent is dried and compression molded.

  As the positive electrode active material, a material used as a positive electrode active material of a lithium ion secondary battery can be used. As an example of a positive electrode active material, an oxide (lithium transition metal) containing lithium and one or more transition metal elements (particularly at least one transition metal element of Ni, Co, and Mn) as constituent metal elements A positive electrode active material mainly composed of an oxide). For example, a conductive material such as acetylene black (AB) can be mixed with the positive electrode active material. In addition to the positive electrode active material and the conductive material, various polymers such as PVdF, SBR, and CMC can be added. A positive electrode active material layer forming paste can be prepared by dispersing and kneading these in an appropriate dispersion medium. The positive electrode active material layer 54 is formed by applying this paste to the positive electrode current collector 52, drying it, and pressing it to a predetermined thickness.

  The negative electrode sheet 60 includes a strip-shaped negative electrode current collector 62 and a negative electrode active material layer 64. For the negative electrode current collector 62, for example, a strip-shaped copper foil having a thickness of about 10 μm is used. On one side in the width direction of the negative electrode current collector 62, a negative electrode active material layer non-formation part 62a is set along the edge. The negative electrode active material layer 64 is held on both surfaces of the negative electrode current collector 62 except for the negative electrode active material layer non-forming portion 62 a set in the negative electrode current collector 62. The negative electrode active material layer 64 includes a negative electrode active material, a thickener, a binder, and the like. The formation method of the negative electrode active material layer 64 is as described above.

  Moreover, as a suitable example of the separator sheet 70 used between the positive and negative electrode sheets 50 and 60, one made of a porous polyolefin-based resin can be cited. For example, a porous separator sheet made of synthetic resin (for example, made of polyolefin such as polyethylene) can be suitably used. 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).

The wound electrode body 20 having such a configuration is accommodated in the case main body 32 of the battery case 30, and an appropriate nonaqueous electrolytic solution is disposed (injected) into the case main body 32. As the non-aqueous electrolyte accommodated in the case body 32 together with the wound electrode body 20, the same non-aqueous electrolyte as that used in a conventional lithium ion secondary battery 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. For example, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3: 4: 3 contains LiPF ₆ as a supporting salt at a concentration of about 1 mol / liter. A nonaqueous electrolyte solution can be used.

  The non-aqueous electrolyte is housed in the case body 32 together with the wound electrode body 20, and the opening of the case body 32 is sealed with the lid body 34, thereby constructing the lithium ion secondary battery 100 according to the present embodiment ( Assembly) is completed. In addition, the sealing process of the case main body 32 and the arrangement | positioning (injection) process of electrolyte solution can be performed similarly to the method currently performed by manufacture of the conventional lithium ion secondary battery. Moreover, there is no restriction | limiting in particular about the structure of the said battery case 30, a magnitude | size, material (For example, it can be metal or a product made from a laminate film), etc.

  The secondary battery constructed in this way exhibits excellent battery performance because it is constructed using a negative electrode having a negative electrode active material layer with low battery resistance and good adhesion as described above. Is. For example, by constructing a battery using the negative electrode, a secondary satisfying at least one (preferably all) of good cycle characteristics, excellent output characteristics, high durability, and good production stability. A battery can be provided.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to this specific example.

  A negative electrode for a lithium ion secondary battery according to the present invention was prepared, and a tensile test of the negative electrode active material layer in the negative electrode was performed to evaluate the peel strength. Moreover, the lithium ion secondary battery was constructed | assembled using this negative electrode, and IV resistance of this battery was evaluated. A specific method will be described below.

  For the purpose of producing a negative electrode active material layer forming paste, graphite powder (negative electrode active material) and CMC powder (thickening agent) were mixed with a planetary mixer. Next, pure water as an aqueous solvent was added in a plurality of times, kneaded, and further mixed with SBR (binder) to obtain a target negative electrode active material layer forming paste. Here, in Examples 1 to 19, the content of CMC contained in the paste, the oil absorption of graphite, and the solid content of the paste are different. Moreover, in Examples 1-19, content of SBR was made constant with 0.7 mass% when the sum total of graphite, CMC, and SBR was 100 mass%. The viscosity of the negative electrode active material layer forming paste of each example was measured by using a commercially available rheometer (MCR301 manufactured by Anton Paar), adjusting the liquid temperature to 25 ° C., and changing the shear rate. The results are shown in Table 1 and FIGS. FIG. 2 is a graph showing the relationship between the shear rate and the viscosity in Examples 1 to 3, FIG. 3 is a graph showing the relationship between the shear rate and the viscosity in Examples 3 and 11, and FIG. 17 is a graph showing the relationship between the shear rate and the viscosity of FIG. 17, FIG. 5 is a graph showing the relationship between the shear rate and the viscosity of Examples 5 and 11, and FIG. 6 is a graph showing the relationship between the shear rate and the viscosity of Examples 12 and 13. It is a graph which shows a relationship.

  The negative electrode active material layer forming paste of each example was collected in a test tube and allowed to stand for 3 days, and then the solid content of the supernatant was measured. And the difference with the solid content rate immediately after paste preparation was computed. The results are shown in the corresponding column of Table 2. Here, it can be said that the smaller the change (difference) in the solid content rate, the higher the stability (a good dispersion state is maintained).

In addition, the negative electrode active material layer forming paste of each example was applied to both sides of a long sheet-like copper foil (thickness 10 μm, negative electrode current collector) in a band shape using a die coater and dried, whereby a negative electrode current collector A negative electrode sheet having negative electrode active material layers provided on both sides of the body was produced. The coating amount of the negative electrode active material layer forming paste was adjusted so as to be about 4 mg / cm ² (based on solid content) per side. And the coating property at the time of apply | coating the said paste to copper foil was confirmed visually. The results are shown in the corresponding column of Table 2. Here, the coating of the paste was performed smoothly, “○” when there was no unevenness on the coating film surface, paste stuck in the coating part of the die coater, or unevenness on the coating surface. The thing was described as "x".

  The peel strengths of the negative electrode sheets of Examples 1, 6, 9, 11-16, and 18 were measured. Specifically, the negative electrode sheet is placed on a measuring table, the surface of the negative electrode active material layer is fixed to a jig with a double-sided tape, and the jig is perpendicular to the surface of the negative electrode current collector (with a peeling angle of 90 ± 5). )) And peeled off continuously at a speed of 0.5 mm per second. And the average value of the load while a negative electrode active material layer peeled from a negative electrode electrical power collector was made into peeling strength. The results are shown in the corresponding column of Table 2.

Furthermore, an evaluation cell (design capacity 20 mAh) was constructed using the negative electrode sheets of Examples 1, 6, 9, 11-16, and 18, and the IV resistance of the battery was evaluated. Specifically, the negative electrode sheet and the two positive electrode sheets of each example are alternately laminated so that the positive electrode active material layer and the negative electrode active material layer face each other, and a separator (PP (polypropylene) / A porous sheet in which PE (polyethylene) / PP (polypropylene) was laminated was used. This electrode body was inserted into a laminate bag together with a non-aqueous electrolyte to construct a test lithium ion secondary battery (laminate cell). As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4, and LiPF ₆ as a supporting salt is used. What was contained at a concentration of about 1 mol / liter was used.

  After each cell for evaluation was adjusted to a charged state (SOC 60%) of about 60% of the initial capacity, discharge was performed for 2 seconds at a current value of 3C in an environmental atmosphere of −30 ° C., and 2 seconds after the start of discharge. Later voltage values were measured and IV resistance was calculated. The results are shown in the corresponding column of Table 2.

As shown in Tables 1 and 2, the negative electrode active material layer forming pastes of Examples 4, 8 to 10 and 12 have a viscosity α of 1000 mPa · s or less at a shear rate of 1 s ⁻¹ . In such a sample, the change in the solid content of the supernatant after the paste was allowed to stand for 3 days was large, and the stability of the paste was lacking. In addition, the negative electrode active material layer forming pastes of Examples 2, 3, 7, 17, and 19 have a viscosity α of 3000 mPa · s or more when the shear rate is 1 s ⁻¹ , and the shear rate is 1000 s ⁻¹ . The viscosity β is 1300 mPa · s or more. In such a sample, although the stability of the paste was relatively good, the coating property when the paste was applied to the negative electrode current collector was lacking. In contrast, the negative electrode active material layer forming pastes of Examples 1, 6, 11, 13 to 16, and 18 have a viscosity α of 1000 mPa · s <α <30000 mPa · s when the shear rate is 1 s ⁻¹ . And, the viscosity β when the shear rate is 1000 s ⁻¹ is β <1300 mPa · s. In such a sample, both the stability and the coating property of the paste are good, and the battery manufactured using the paste has good adhesion between the negative electrode active material layer and the negative electrode current collector, and has an internal resistance. Was also low. From this result, by using the negative electrode active material layer forming paste with 1000 mPa · s <α <30000 mPa · s and β <1300 mPa · s, the battery resistance is lower and the negative electrode active material layer is difficult to peel off, It was confirmed that a battery having excellent durability could be constructed.

  In addition, as shown in Table 1 and Table 2, Examples 1-3 differ in the solid content rate of a paste mutually. In this case, the higher the solid content of the paste, the higher the viscosity of the paste at high shear (see FIG. 2), and the coatability tends to deteriorate. On the other hand, in Example 11, although the solid content rate is the same as Example 3, the viscosity of the paste at the time of high shear is kept low by adjusting the oil absorption amount of graphite and the content of CMC ( (See FIG. 3). In Example 11, compared with Example 3, the coatability is good even at a high solid content rate.

  Examples 9, 13, and 17 have different CMC contents. In this case, the higher the CMC content, the higher the viscosity of the paste at the time of high shear (see FIG. 4), and the coatability tends to deteriorate. From the viewpoint of coatability, the CMC content is preferably less than 0.6% by mass (for example, 0.5% by mass or less). Further, the smaller the CMC content, the lower the paste viscosity at the time of high shear, and the lower the stability at rest (the difficulty of settling). From the standpoint of stability during standing, the content of CMC is preferably more than 0.2% by mass (for example, 0.3% by mass or more).

In Examples 5 and 11, the oil absorption of graphite is different from each other. In this case, the larger the oil absorption amount of graphite, the higher the viscosity of the paste at the time of high shear (see FIG. 5), and the coatability tends to deteriorate. From the viewpoint of coatability, the oil absorption of graphite is preferably less than 56.2 × 10 ⁻⁵ m ³ / kg (for example, 50 × 10 ⁻⁵ m ³ / kg or less).

  In Examples 12 and 13, the solids content of the paste is different from each other. In this case, the smaller the solid content of the paste, the lower the viscosity of the paste at the time of low shear (see FIG. 6), and the stability at rest (hardness of settling) tends to deteriorate. From the standpoint of stability during standing, the solid content of the paste is preferably more than 59% by mass (for example, 60% by mass or more).

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here. For example, the type of 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 negative electrode for a secondary battery according to the present invention includes a negative electrode active material layer that is difficult to peel from the negative electrode current collector and has excellent adhesion. Due to such characteristics, the secondary battery including the negative electrode for the secondary battery according to the present invention can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Accordingly, a vehicle (typically an automobile, particularly a hybrid automobile, an electric automobile, etc.) having such a secondary battery (which may be in the form of an assembled battery formed by connecting a plurality of such batteries in series) as a power source. A motor vehicle equipped with an electric motor).

20 wound electrode body 50 positive electrode sheet 52 positive electrode current collector 54 positive electrode active material layer 60 negative electrode sheet 62 negative electrode current collector 64 negative electrode active material layer 70 separator sheet 100 lithium ion secondary battery

Claims (1)

A method for producing a negative electrode for a secondary battery in which a negative electrode active material layer is formed on a negative electrode current collector,
A negative electrode active material and an aqueous solvent in which the negative electrode active material is dispersed, the viscosity α when the shear rate is 1 s ⁻¹ is 1000 mPa · s <α <30000 mPa · s, and the shear rate is 1000 s ⁻¹ . Preparing a negative electrode active material layer forming paste having a viscosity β of β <1300 mPa · s, and
Applying the negative electrode active material layer forming paste to a negative electrode current collector to form a negative electrode active material layer on the negative electrode current collector;
A method for producing a negative electrode for a secondary battery, comprising:

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