JP6233653B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a nonaqueous electrolyte secondary battery.

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

  A typical electrode of this type of secondary battery has a structure in which an active material layer mainly composed of an active material capable of reversibly occluding and releasing chemical species as charge carriers is formed on a current collector. It has an electrode. Examples of the active material (negative electrode active material) used for the negative electrode include graphite materials. An example of a current collector (negative electrode current collector) used for the negative electrode is a copper foil. Such a negative electrode active material layer is formed by applying a negative electrode active material layer forming paste prepared by adding a graphite material to a binder and a thickener together with an appropriate aqueous solvent to a negative electrode current collector. Patent document 1 is mentioned as this kind of prior art. Patent Document 1 includes a negative electrode obtained by coating a negative electrode current collector with an aqueous negative electrode mixture paste obtained by mixing graphite particles, carboxyl cellulose (CMC), styrene butadiene rubber, and water. A lithium ion secondary battery is described.

JP 2009-110972 A

  By the way, since the negative electrode active material layer forming paste is applied to the negative electrode current collector as described above, its viscosity has an appropriate range. When the range of the viscosity of the paste for forming a negative electrode active material layer that is preferable from the viewpoint of coating property and stability is exemplified, it is, for example, about 6000 mPa · s to 10000 mPa · s. This viscosity range can be controlled by changing the amount of the thickener in the negative electrode active material layer forming paste. In general, carboxyl cellulose (CMC) is widely used as a thickener. CMC has a function of floating in the aqueous solvent of the negative electrode active material layer forming paste to thicken the paste.

  CMC has the property of swelling and adsorbing on the surface of graphite when it absorbs moisture. When CMC is adsorbed on graphite, the amount of CMC floating in the aqueous solvent of the negative electrode active material layer forming paste decreases accordingly, so that there is a possibility that an appropriate viscosity increase cannot be obtained with respect to the added amount. In this regard, it is possible to add a large amount of CMC in consideration of the amount adsorbed on graphite. However, if a large amount of CMC is added, CMC works as a resistance component, which causes an increase in battery resistance. obtain. It is useful if a small amount of CMC can efficiently increase the viscosity of the negative electrode active material layer forming paste. The present invention solves the above problems.

In order to achieve the above object, according to the present invention, a negative electrode in which a negative electrode active material layer including at least graphite as a negative electrode active material and carboxymethyl cellulose (CMC) as a thickener is formed on a negative electrode current collector is provided. A method for producing a nonaqueous electrolyte secondary battery is provided. This manufacturing method includes a step of preparing a negative electrode active material layer forming paste containing graphite, CMC, and an aqueous solvent.
Here, the graphite has a hydrophilic surface to which oxygen atoms are bonded. The sum of C—O bonds and C═O bonds when the total amount of C—C bonds, C—O bonds and C═O bonds on the graphite surface determined by X-ray photoelectron spectroscopy (XPS) is 100%. The ratio (hereinafter also referred to as “surface hydrophilic group ratio”) is 35.1% to 38.6%. Moreover, when the total solid content of the said negative electrode active material layer forming paste is 100 mass%, content of CMC is 0.48 mass%-0.53 mass%. Furthermore, the viscosity at the shear rate of 1 s ⁻¹ of the negative electrode active material layer forming paste is 6440 mPa · s to 9500 mPa · s.
Further, the method includes a step of 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 viscosity of the paste is a viscosity 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.

  According to this production method, the total amount of C—O bonds and C═O bonds (surface hydrophilic group ratio) on the graphite surface is 35.1% to 38.6%, so that the amount of CMC adsorbed on graphite can be reduced. Reduced compared to the prior art. Therefore, even with a small amount of CMC such as 0.48% by mass to 0.53% by mass, a suitable viscosity of the negative electrode active material layer forming paste can be ensured, and a high-performance nonaqueous electrolyte secondary battery can be obtained. .

  In a preferred embodiment of the production method disclosed herein, before the step of preparing the negative electrode active material layer forming paste, the surface of the graphite is hydrophilized by performing plasma treatment in an oxygen atmosphere. Process. In this way, a suitable hydrophilic surface can be formed by bonding an appropriate amount of oxygen atoms to the surface of graphite.

In a preferred embodiment of the manufacturing method disclosed herein, the specific surface area of the graphite ^is 2.5m ² /g~3.5m 2 / g. When the specific surface area is within such a range, an appropriate amount of oxygen atoms can be efficiently bonded to the surface of the graphite.

  In a preferred aspect of the manufacturing method disclosed herein, in the hydrophilization step, the surface of the graphite is etched using an inert gas before the plasma treatment. In this way, since the active surface of graphite increases, oxygen atoms can be bound more efficiently.

It is a figure which shows the manufacture flow of the battery which concerns on one Embodiment of this invention. It is a figure which shows typically the battery structure which concerns on one Embodiment of this invention. It is a figure for demonstrating the winding electrode body which concerns on one Embodiment of this invention. It is a graph which shows the relationship between a surface hydrophilic group rate and paste viscosity. It is a graph which shows the relationship between a surface hydrophilic group rate and IV resistance. It is a graph which shows the relationship between oxygen plasma processing time and a surface hydrophilic group rate. It is a graph which shows the relationship between the specific surface area of graphite, and a surface hydrophilic group rate. It is a graph which shows the relationship between the amount of CMC addition, and the amount of unadsorbed CMC. It is a graph which shows the relationship between the amount of unadsorbed CMC and paste viscosity. It is a graph which shows the relationship between CMC addition amount and paste viscosity. It is the graph which compared the battery capacity of each example. It is the graph which compared IV resistance of each example.

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, the term “secondary battery” generally refers to a battery that can be repeatedly charged, a so-called chemical battery with a chemical reaction, such as a lithium ion secondary battery, a nickel hydride battery, or a nickel cadmium battery, and an electric double layer. This term includes so-called physical batteries such as 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.).

  As a preferred embodiment of a method for producing a nonaqueous electrolyte secondary battery disclosed herein, a method for producing a lithium ion secondary battery will be described in detail with reference to the flowchart shown in FIG. However, the present invention is not intended to be limited to such batteries. Hereinafter, the present invention will be described in detail by 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).

  The manufacturing method according to the present embodiment is a method for manufacturing a lithium ion secondary battery including a negative electrode in which a negative electrode active material layer containing graphite and carboxymethyl cellulose (CMC) is formed on a negative electrode current collector. As shown in FIG. 1, this manufacturing method includes a hydrophilization process (step S10), a paste preparation process (step S20), and a negative electrode formation process (step S30). The hydrophilization step is a step of hydrophilizing the surface of the graphite by bonding oxygen atoms to the surface of the graphite. The paste preparation step is a step of preparing a negative electrode active material layer forming paste containing the graphite, CMC, and aqueous solvent. The negative electrode forming step is a step of forming the negative electrode active material layer on the negative electrode current collector by applying the negative electrode active material layer forming paste to the negative electrode current collector. Hereinafter, each process will be described in detail.

<Hydrophilic process>
The hydrophilization step is a step of hydrophilizing the surface of the graphite by bonding oxygen atoms to the surface of the graphite. As graphite (negative electrode active material) used in the production method disclosed herein, natural graphite or artificial graphite is preferred, and natural graphite is more preferred. Further, various graphites such as natural graphite and artificial graphite processed into particles (spherical) (pulverization, spherical molding, etc.) can be used. For example, flaky graphite can be used. The average particle diameter of the graphite is, for example, a median diameter (average particle diameter D ₅₀ : 50% volume average particle diameter) that can be derived from a particle size distribution measured based on a particle size distribution measuring apparatus based on a laser scattering / diffraction method. It is preferable that it is 25 micrometers. The technique disclosed here can be preferably implemented, for example, in an embodiment in which the average particle size of graphite is 10 μm to 25 μm.
As the specific surface area based on a gas adsorption method of graphite (BET specific surface area), approximately 2.5m ² /g~3.5m ² / g (typically 2.5m ² / g~3m ² / g) It is preferable that Within the range of such a specific surface area, oxygen atoms can be efficiently bonded to the surface of graphite in the oxygen plasma treatment. As a method of processing various types of graphite into particles, a conventionally known method (for example, mechanofusion or hybridization) can be employed without particular limitation.

Introduction of oxygen atoms to the surface of the graphite is performed, for example, by supplying a chemical species containing oxygen (for example, oxygen gas (O ₂ ), oxygen radical, oxygen plasma, etc.) to the surface of the graphite. Specifically, plasma treatment, corona discharge treatment, or the like is performed on graphite in an atmosphere containing oxygen gas. A typical example is a treatment method in which plasma treatment is performed in an atmosphere containing oxygen gas.

  When oxygen plasma treatment is performed, the treatment conditions are not particularly limited, but the gas pressure (degree of vacuum) during the plasma treatment is suitably about 10 Pa to 50 Pa, and preferably 20 Pa to 40 Pa ( Typically 30 ± 5 Pa). If the gas pressure is too high, the amount of generated plasma is reduced and the oxygen plasma concentration is lowered. As a result, the amount of oxygen atoms attached to the graphite surface may tend to be lowered. On the other hand, if the gas pressure is too low, a large amount of plasma itself is generated, but the oxygen plasma concentration decreases due to the high degree of vacuum, and as a result, the amount of oxygen atoms attached to the graphite surface may tend to decrease. The oxygen gas flow rate is preferably set within a range of approximately 100 ml / min to 200 ml / min. If the oxygen gas flow rate is too low, the gas may be insufficient and the oxygen plasma concentration may decrease.On the other hand, if the oxygen gas flow rate is too high, the oxygen plasma concentration becomes too high and the movement of the plasma is inhibited. There are cases where oxygen atoms cannot be efficiently bonded to the graphite surface.

  The plasma treatment time is not particularly limited, but is generally 5 minutes or more (for example, 5 to 30 minutes), preferably 10 minutes or more (for example, 10 to 30 minutes, typically 10 to 15 minutes). ). If the treatment time is too short, an appropriate amount of oxygen atoms cannot be bonded to the graphite surface and the hydrophilization treatment may be insufficient. On the other hand, if the treatment time is too long, the increase in the amount of attached oxygen atoms tends to slow down. Therefore, there is not much merit. As RF power at the time of plasma processing, about 100 W to 500 W is appropriate, and preferably 200 W to 400 W.

  In a preferred embodiment, before performing the plasma treatment, the surface of the graphite is etched using an inert gas. Specifically, a plasma etching process, a sputter etching process, or the like is performed on graphite in an atmosphere containing an inert gas. A typical example is a processing method in which a plasma etching process is performed in an atmosphere containing an inert gas. Such etching treatment removes impurities and foreign matter adhering to the surface of the graphite, thereby activating the surface of the graphite. Moreover, since the surface of graphite is roughened and the active surface increases, oxygen atoms can be efficiently introduced into the graphite surface.

  As the inert gas, a rare gas such as argon (Ar), xenon (Xe), helium (He), or krypton (Kr) can be appropriately employed. Of these, the use of Ar is preferable. The etching treatment time is preferably about 1 minute or longer (for example, 1 minute to 30 minutes, for example, 5 minutes or longer, typically 5 minutes to 10 minutes). If the treatment time is too short, the effect of improving the bonding efficiency of oxygen atoms by the etching process may be insufficient. On the other hand, if the treatment time is too long, the effect of improving the bonding efficiency of oxygen atoms tends to slow down. There is not much merit. The inert gas flow rate is preferably about 100 ml / min to 200 ml / min.

<Paste preparation process>
The paste preparation step is a step of preparing a negative electrode active material layer forming paste. The negative electrode active material layer forming paste disclosed herein is a material mainly composed of the graphite, CMC, and an aqueous solvent for dispersing the graphite and CMC. The CMC has a function of floating in the aqueous solvent of the negative electrode active material layer forming paste and thickening the paste. Further, the graphite has a hydrophilic surface to which oxygen atoms are bonded by the oxygen plasma treatment described above. That is, oxygen atoms bonded to the graphite surface are present on the graphite surface in the form of C—O bonds (which can typically react with moisture in the air to become C—OH) or C═O bonds. A hydrophilic surface appears in graphite due to the charge bias (polarity) of C—O bonds and C═O bonds.

  The graphite used in the negative electrode active material layer forming paste disclosed herein is 100% of the total amount of C—C bonds, C—O bonds, and C═O bonds on the graphite surface determined by X-ray photoelectron spectroscopy. In this case, the total ratio of C—O bonds and C═O bonds (surface hydrophilic group ratio) is 35.1% to 38.6%.

  Here, X-ray photoelectron spectroscopy (XPS) irradiates the sample surface with X-rays and measures the energy of the emitted photoelectrons to determine the constituent elements and the electronic state of the sample surface. It is a method of analysis. Since a spectrum obtained by XPS shows a pattern specific to a substance and a peak intensity proportional to the quantity of the substance, qualitative and quantitative analysis of the substance is possible. Using such XPS, the C—C bond, C—O bond and C═O bond on the graphite surface are quantitatively analyzed, and the total amount of C—C bond, C—O bond and C═O bond is 100%. In this case, by calculating the total ratio of C—O bonds and C═O bonds, it can be used as an index of the abundance ratio of hydrophilic functional groups (C—O groups and C═O groups) on the graphite surface. .

  The graphite disclosed here has a C—O bond and a C—O bond when the total amount of C—C bond, C—O bond and C═O bond on the graphite surface determined by the X-ray photoelectron spectroscopy is 100%. The total proportion of C═O bonds (surface hydrophilic group ratio) is suitably 35.1% to 38.6%. By imparting a hydrophilic surface to the graphite so that the surface hydrophilic group ratio is 35.1% to 38.6%, the graphite is easily adapted to the aqueous solvent. Therefore, when the negative electrode active material layer forming paste is prepared, the aqueous solvent preferentially adheres to graphite, so that CMC is hardly adsorbed on graphite. As a result, the amount of CMC that is unadsorbed and floats in the aqueous solvent of the negative electrode active material layer forming paste increases, so that a sufficient paste viscosity can be expressed even with a small amount of CMC.

  From the viewpoint of suppressing adsorption of CMC, the surface hydrophilic group ratio is preferably 35.5% or more, more preferably 36% or more, and particularly preferably 37% or more. On the other hand, since the surface hydrophilic group ratio is too large, insertion / extraction of charge carriers (here, lithium ions) is inhibited by hydrophilic functional groups (C—O group and C═O group). The reaction resistance may increase. From the viewpoint of suppressing an increase in reaction resistance, the total ratio of the C—O bond and the C═O bond is preferably 38.6% or less, and particularly preferably 38% or less (eg, 37.8% or less). .

  The content of CMC in the negative electrode active material layer forming paste is approximately 0.48 mass when the total solid content of the negative electrode active material layer forming paste (the total solid content excluding the aqueous solvent) is 100 mass%. % To 0.53 mass% (preferably 0.48 mass% to 0.51 mass%) is appropriate. According to the aspect of the present invention, by setting the surface hydrophilic group ratio of the graphite surface to 35.1% or more, even with a small amount of CMC such as 0.48% by mass to 0.53% by mass, the negative electrode active material The viscosity of the layer forming paste can be effectively increased. If the amount of CMC is too small, the viscosity of the paste is not sufficiently increased, and handling, stability, coating property, coating film uniformity and the like are impaired, which may cause various problems. On the other hand, if the amount of CMC is too large, CMC works as a resistance component, and thus the internal resistance of the battery may increase.

The negative electrode active material layer forming paste disclosed here has a viscosity of 6440 mPa · s to 9500 mPa · s (preferably 6500 mPa · s to 9000 mPa · s, more preferably 7000 mPa · s to 8500 mPa · s) at a shear rate of 1 s ^−1. S, particularly preferably 7500 mPa · s to 8500 mPa · s). Typically, the viscosity is a viscosity measured by using a commercially available rheometer to shear the negative electrode active material layer forming paste at a shear rate of 1 s ⁻¹ . The paste for forming a negative electrode active material layer disclosed herein has a viscosity of 6440 mPa · s to 9500 mPa · s, so that stability and coating suitable for applying the paste to the negative electrode current collector are provided. Showing gender.

That is, the negative electrode active material layer forming paste having a viscosity at a shear rate of 1 s ⁻¹ having a predetermined value or more is excellent in stability at the time of standing (when left at room temperature without performing an operation such as stirring). 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 precipitating. 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.

Moreover, the negative electrode active material layer forming paste having a viscosity at a shear rate of 1 s ⁻¹ of a predetermined value or less has high fluidity and good coatability. 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 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 higher. A high performance negative electrode can be formed.

  As the aqueous solvent used in the negative electrode active material layer forming paste, 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, particularly preferably 98% by mass or more) of the aqueous solvent is water. A particularly preferred example is an aqueous solvent substantially consisting of water.

  As long as the object of the present invention can be achieved, the negative electrode active material layer forming paste can contain various polymer materials dispersed in water that can function as a binder. Examples of polymer materials dispersed in water that can function as a binder include vinyl acetate copolymers, styrene butadiene block copolymers (SBR), acrylic acid-modified SBR resins (SBR latex), rubbers such as gum arabic, Or, polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoro Examples thereof include fluorine resins such as ethylene copolymer (ETFE). Among these, a styrene butadiene block copolymer (SBR) can be preferably used. In addition, such a polymer material may be used individually by 1 type, and may be used in combination of 2 or more type.

  Although not particularly limited, the ratio of graphite to the total solid content (total solid content excluding the aqueous solvent) of the negative electrode active material layer forming paste is approximately 90% by mass or more (eg, 90% by mass to 99.5%). % By mass), preferably 95% by mass or more, more preferably 98% by mass or more, and particularly preferably 98.5% by mass or more. According to this embodiment, since the amount of CMC used can be reduced as compared with the conventional one, the composition ratio of graphite can be increased accordingly. Increasing the composition ratio of graphite can increase the capacity and energy density of the battery. 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%).

  The solid content of the negative electrode active material layer forming paste is preferably about 40% by mass or more, and is preferably in the range of 40% by mass to 70% by mass, preferably 50% by mass to 65% by mass. Yes, more preferably 55% by mass to 60% by mass. When the solid content is within such a range, a negative electrode active material layer-forming paste having a desired viscosity can be suitably prepared.

  The negative electrode active material layer forming paste disclosed here can be typically prepared by kneading the above graphite (typically in powder form), CMC, a binder and an aqueous solvent. Preferably, first, graphite powder, CMC, and an aqueous solvent are mixed, and then a binder is further added and kneaded. The aqueous solvent may be added in small portions in a plurality of times. 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 such a procedure and kneading them together, the negative electrode active material layer forming paste having the aforementioned viscosity can be suitably prepared.

<Negative electrode forming step>
The negative electrode forming step is a step of forming a negative electrode active material layer on the negative electrode current collector by applying a negative electrode active material layer forming paste to the negative electrode current collector. The operation of applying the negative electrode active material layer forming paste to the 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.

  Thus, a negative electrode (negative electrode sheet) having a configuration in which a negative electrode active material layer containing graphite and CMC is held on the negative electrode current collector can be obtained. Such a negative electrode is preferable as a component of various types of batteries or a component of an electrode body incorporated in the battery because the amount of CMC in the negative electrode active material layer is smaller than that of the conventional and higher performance. Can be used.

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

  Other materials and members constituting the lithium ion secondary battery including the negative electrode obtained by the method disclosed herein may be the same as those conventionally used for the same type of battery, and are not particularly limited. Hereinafter, other components will be described with reference to the schematic diagrams shown in FIGS. 2 and 3. FIG. 2 is a cross-sectional view of a lithium ion secondary battery 100 according to an embodiment of the present invention. FIG. 3 is a diagram showing an electrode body 40 housed in the lithium ion secondary battery 100. In the lithium ion secondary battery 100, a negative electrode (negative electrode sheet) 60 manufactured by applying the above-described method is used as the negative electrode (negative electrode sheet) 60.

  A lithium ion secondary battery 100 according to an embodiment of the present invention is configured in a flat rectangular battery case (that is, an exterior container) 20 as shown in FIG. As shown in FIGS. 2 and 3, in the lithium ion secondary battery 100, a flat wound electrode body 40 is housed in a battery case 20 together with a liquid electrolyte (electrolytic solution) 80.

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

  As shown in FIG. 2, a positive terminal 23 and a negative terminal 24 for external connection are formed on the lid 22. A thin safety valve 30 configured to release the internal pressure when the internal pressure of the battery case 20 rises above a predetermined level and a liquid injection port 32 are formed between both terminals 23 and 24 of the lid 22. Has been. In FIG. 2, the liquid injection port 32 is sealed with a sealing material 33 after the liquid injection.

  As shown in FIG. 3, the wound electrode body 40 includes a long sheet-like positive electrode (positive electrode sheet 50) and a long sheet-like negative electrode (negative electrode sheet 60) similar to the positive electrode sheet 50 in total. Long sheet separators (separators 72 and 74).

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

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

  The positive electrode active material layer 53 is prepared by, for example, preparing a positive electrode active material layer forming paste in which the above-described positive electrode active material particles, a conductive material, and a binder are mixed in a solvent, and applying (coating and drying) the positive electrode current collector 52. And is formed by rolling. At this time, as the solvent for the positive electrode active material layer forming paste, both an aqueous solvent and a non-aqueous solvent (for example, N-methylpyrrolidone (NMP)) can be used. Examples of the conductive material include carbon materials such as carbon powder and carbon fiber. As the conductive material, one kind selected from such conductive materials may be used alone, or two or more kinds may be used in combination. As the carbon powder, carbon powders such as various carbon blacks (for example, acetylene black (AB), oil furnace black, graphitized carbon black, carbon black, graphite, ketjen black) and graphite powder can be used. As the binder, polymers such as polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyacrylonitrile (PAN) can be preferably used.

  As shown in FIG. 3, the negative electrode sheet 60 includes a strip-shaped negative electrode current collector 62 and a negative electrode active material layer 63. For the negative electrode current collector 62, for example, a metal foil suitable for the negative electrode can be suitably used. In this embodiment, a strip-shaped copper foil is used for the negative electrode current collector 62 as described above. On one side of the negative electrode current collector 62 in the width direction, an uncoated portion 61 is set along the edge. The negative electrode active material layer 63 is held on both surfaces of the negative electrode current collector 62 except for the uncoated portion 61 set on the negative electrode current collector 62. As described above, the negative electrode active material layer 63 contains graphite, CMC, and a binder as the negative electrode active material. Since the method for producing the negative electrode sheet is as described above, the description thereof is omitted.

  As shown in FIG. 3, the separators 72 and 74 are members that separate the positive electrode sheet 50 and the negative electrode sheet 60. In this example, the separators 72 and 74 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 72 and 74, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. Moreover, you may further form the layer of the particle | grains which have insulation on the surface of the sheet | seat material comprised with this resin. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). ). In this example, the width b1 of the negative electrode active material layer 63 is slightly wider than the width a1 of the positive electrode active material layer 53, as shown in FIG. Furthermore, the widths c1 and c2 of the separators 72 and 74 are slightly wider than the width b1 of the negative electrode active material layer 63 (c1, c2> b1> a1).

  In this embodiment, the wound electrode body 40 is flatly bent in one direction orthogonal to the winding axis WL, as shown in FIG. In the example shown in FIG. 3, the uncoated portion 51 of the positive electrode current collector 52 and the uncoated portion 61 of the negative electrode current collector 62 are spirally exposed on both sides of the separators 72 and 74, respectively. In this embodiment, as shown in FIG. 2, intermediate portions of the uncoated portion 51 are gathered together and welded to current collecting tabs 25 and 26 of electrode terminals (internal terminals) arranged inside the battery case 20. Is done. Reference numerals 25a and 26a in FIG. 2 indicate the welding locations.

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

As the electrolytic solution (non-aqueous electrolytic solution) 80, the same non-aqueous electrolytic solution conventionally used for lithium ion secondary batteries can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which a supporting salt is contained in a suitable nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,3-dioxolane, and the like. One kind or two or more kinds selected from the group can be used. Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. Lithium salts can be used.

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

  In the lithium ion secondary battery 100 constructed in this way, the negative electrode includes a small amount of CMC as described above, and is formed using a negative electrode active material layer forming paste having a suitable viscosity. It shows excellent battery performance. For example, by constructing a battery using the negative electrode, a lithium ion secondary battery satisfying at least one (preferably all) of excellent input / output characteristics, high energy density, and good production stability. 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.

<< Test Example 1 >>
In this example, a negative electrode active material layer forming paste was prepared using graphite and CMC having oxygen atoms bonded to the surface of graphite. Then, the viscosity of the negative electrode active material layer forming paste was evaluated. A specific method will be described below.

<Hydrophilic treatment of graphite surface>
A graphite powder (average particle size 20 μm) was prepared, the surface was modified by Ar etching, and then the surface of graphite was hydrophilized by performing plasma treatment in an oxygen atmosphere. The plasma treatment of graphite was performed using a general plasma treatment apparatus. Here, in Examples 1 to 10, the amount of oxygen atoms bonded to the surface of graphite is different. The amount of oxygen atoms bound to the surface of the graphite was controlled by changing the Ar etching time, the oxygen plasma processing time, and the gas pressure in the chamber. In Example 10, graphite not subjected to oxygen plasma treatment was used as it was.

The graphite surface of each example was measured by X-ray photoelectron spectroscopy (XPS), and the C—C bond, C—O bond, and C═O bond on the graphite surface were quantitatively analyzed. The results are shown in Table 1. The “surface hydrophilic group ratio” in Table 1 shows C—O when the total amount of C—C bonds, C—O bonds and C═O bonds on the graphite surface determined by XPS is 100%. The total proportion of bonds and C═O bonds is shown. The XPS measurement conditions and measurement apparatus are as follows.
Measuring apparatus: Scanning X-ray photoelectron spectrometer (u-XPS) Quantera II (manufactured by ULVAC-PHI Co., Ltd.)
X-ray source used: mono-AlKα ray (1486.6 eV)
Photoelectron extraction angle: 35 °
X-ray beam diameter: about 100 μm
Neutralizing gun conditions: 1.0 V, 20 μA

<Preparation of negative electrode active material layer forming paste>
The graphite powder of each example, CMC as a thickener, and SBR as a binder were kneaded with water so that the mass ratio of these materials was 98.8: 0.5: 0.7, and the negative electrode active A material layer forming paste was prepared. The solid content rate of the negative electrode active material layer forming paste was adjusted to 58 mass%. The viscosity of the obtained negative electrode active material layer forming paste was measured at a shear rate of 1 s ⁻¹ after adjusting the liquid temperature to 25 ° C. using a commercially available rheometer (manufactured by Toki Sangyo Co., Ltd .: RE115H). . The results are shown in Table 1 and FIG. FIG. 4 is a graph showing the relationship between the surface hydrophilic group ratio and the paste viscosity.

  As shown in Table 1 and FIG. 4, the paste viscosity tended to increase as the surface hydrophilic group ratio of graphite increased. As the surface hydrophilic group ratio increases, the amount of CMC adsorbed on the graphite decreases. Therefore, the amount of CMC floating in the negative electrode active material layer forming paste increases, and the viscosity of the paste is effectively increased. Is done. In the case of the negative electrode active material layer forming paste tested here, a favorable paste viscosity of 6440 mPa · s to 9500 mPa · s can be achieved by setting the surface hydrophilic group ratio to 35.1% to 38.6%. It was. In particular, by setting the surface hydrophilic group ratio to 36.8% to 37.8%, an extremely good paste viscosity of 7300 mPa · s to 8700 mPa · s could be achieved. From this result, it was confirmed that a suitable paste viscosity can be achieved even with a small amount of CMC by setting the surface hydrophilic group ratio to 35.1% to 38.6%.

<< Test Example 2 >>
In this example, the negative electrode active material layer forming paste was prepared by adding the minimum CMC necessary to achieve a viscosity of 8000 mPa · s in the above-described negative electrode active material layer forming paste preparation processes of Examples 1 to 10. . Specifically, as shown in Table 2, the negative electrode active material layer forming paste was prepared by varying the amount of CMC added between 0.48 mass% and 0.63 mass%. The viscosity of the paste in each example was constant at 8000 mPa · s. And the lithium ion secondary battery was constructed | assembled using the paste for negative electrode active material layer formation of each example, and IV resistance of this battery was evaluated.

<Preparation of negative electrode sheet>
The negative electrode sheet was produced as follows. The negative electrode active material layer forming paste of each example was applied on a copper foil (negative electrode current collector) and dried to form a negative electrode active material layer. Next, the negative electrode active material layer was rolled to prepare a negative electrode sheet.

<Preparation of positive electrode sheet>
The positive electrode sheet was produced as follows. LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as the positive electrode active material, AB as the conductive material, and PVdF as the binder so that the mass ratio of these materials becomes 93: 4: 3. Was kneaded with NMP to prepare a positive electrode active material layer forming paste. This paste was applied onto an aluminum foil (positive electrode current collector) and dried to form a positive electrode active material layer. Next, the positive electrode active material layer was rolled to produce a positive electrode sheet.

<Construction of lithium ion secondary battery>
A rolled body is produced by winding a positive electrode sheet and a negative electrode sheet into a circular shape through two separators, and is flattened by pressing and rolling the wound body from the lateral direction. An electrode body was produced. The wound electrode body was housed in a battery case (a square case was used here) together with a non-aqueous electrolyte, and the opening of the battery case was hermetically sealed. Here, a porous sheet having a three-layer structure of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) was used as the separator. Further, the volume ratio of ethylene carbonate and dimethyl carbonate and ethyl methyl carbonate, 3: 3: blended with 4, using the electrolytic solution of LiPF ₆ dissolved 1.1 mol. In this way, a lithium ion secondary battery for evaluation test was constructed.

<Measurement of IV resistance>
Further, in order to evaluate the input / output characteristics of the lithium ion secondary battery for evaluation test, IV resistance was measured here. The IV resistance was calculated by the following procedure.
Procedure 1: The SOC is adjusted to 60% by SOC adjustment.
Procedure 2: After Procedure 1, discharge at a current value of 0.8 C and discharge treatment for 10 seconds.
Here, the measured current value measured in the procedure 2 is divided by the voltage drop value ΔV that is a value obtained by subtracting the voltage value at the time of 10 seconds from the initial voltage value in the procedure 2, and the value is divided into the IV resistance value. did. The results are shown in Table 2 and FIG. FIG. 5 is a graph showing the relationship between the surface hydrophilic group ratio and the IV resistance. “IV resistance” in Table 2 and FIG. 5 is a relative value when the IV resistance value of Example 10 is 100.

  As shown in Table 2 and FIG. 5, in Examples 4 to 9, the surface hydrophilic group ratio of graphite is 35.1% to 38.6%, and the amount of CMC added is 0.48% by mass to It is set to 0.53 mass%. Such samples had lower IV resistance and better battery performance than Examples 1 to 3 and Example 10. In contrast, in Examples 1 to 3 and Example 10, the surface hydrophilic group ratio of graphite is 23.3% to 33.6%, and the amount of CMC added is 0.57% by mass to 0.63. It is set to mass%. In such a sample, the IV resistance tends to increase because it is necessary to increase the amount of CMC added to increase the paste viscosity. From this result, the surface hydrophilic group ratio of graphite is 35.1% to 38.6%, and the addition amount of CMC is 0.48% by mass to 0.53% by mass. It was confirmed that a battery could be constructed.

  In Examples 8 and 9, the surface hydrophilic group ratio of graphite is 38.4% to 38.6%, and the amount of CMC added is set to 0.48% by mass. In such a sample, although the amount of CMC added was smaller than those in Examples 4 to 7, the IV resistance tended to increase. In Examples 8 and 9, since there are many hydrophilic functional groups (C—O groups and C═O groups) on the graphite surface, the insertion and release of lithium ions is inhibited by the hydrophilic functional groups. It is estimated that the reaction resistance has increased. From the viewpoint of suppressing an increase in reaction resistance, the surface hydrophilic group ratio of graphite is preferably 37.8% or less.

  In order to confirm the influence of the treatment conditions (treatment time, gas pressure, specific surface area of graphite, etc.) on plasma surface treatment of graphite on the surface hydrophilic group ratio, the following tests were conducted.

<< Test Example 3 >>
In this example, the hydrophilic treatment was performed by varying the Ar etching treatment time and the oxygen plasma treatment time between 0 minutes and 30 minutes in the above-described hydrophilic treatment treatment of graphite. The gas pressure was constant at 30 Pa. The specific surface area of graphite was constant at 2.5 m ² / g. And the surface hydrophilic group rate of the graphite after a process was measured. The results are shown in Table 3 and FIG. Table 3 shows the surface hydrophilic group ratio when the Ar etching treatment time and the oxygen plasma treatment time are varied between 0 minutes and 30 minutes. FIG. 6 is a graph showing the relationship between the oxygen plasma treatment time and the surface hydrophilic group ratio.

  As shown in Table 3 and FIG. 6, the surface hydrophilic group ratio tended to increase as the Ar etching treatment time increased. Further, the surface hydrophilic group ratio tended to increase as the oxygen plasma treatment time increased. However, it was found that the surface hydrophilic group ratio converges to a substantially constant value (37.8 to 39) when the treatment time exceeds 10 minutes in both the Ar etching treatment time and the oxygen plasma treatment time.

<< Test Example 4 >>
In this example, the hydrophilic treatment was performed by changing the gas pressure during the Ar etching treatment and the oxygen plasma treatment to 10 Pa, 30 Pa, and 50 Pa in the above-described graphite hydrophilization treatment process. The Ar etching treatment time and the oxygen plasma treatment time were fixed at 10 minutes each. The specific surface area of graphite was constant at 2.5 m ² / g. And the surface hydrophilic group rate of the graphite after a process was measured. The results are shown in Table 4.

  As shown in Table 4, when the gas pressure was 30 Pa, the surface hydrophilic group ratio was maximized, and the treatment conditions were such that oxygen atoms were most easily bonded. From the viewpoint of efficiently bonding oxygen atoms, the gas pressure during the plasma treatment is preferably set to 30 ± 5 Pa.

<< Test Example 5 >>
In this example, the hydrophilic process of the graphite described above, the specific surface area of graphite varied in the range of 2.5m 2 ^/ g~4m 2 ^{/ g} was subjected to a hydrophilic treatment. The Ar etching treatment time and the oxygen plasma treatment time were fixed at 10 minutes each. The gas pressure was constant at 30 Pa. And the surface hydrophilic group rate of the graphite after a process was measured. The results are shown in FIG. FIG. 7 is a graph showing the relationship between the specific surface area of graphite and the surface hydrophilic group ratio.

As shown in FIG. 7, the surface hydrophilic group ratio tended to increase as the specific surface area of graphite decreased. In the case of the graphite used here, a surface hydrophilic group ratio of 35.1% or more could be achieved by setting the specific surface area to 3.5 m ² / g or less. From the viewpoint of coupling efficiently oxygen atom, the specific surface area of graphite is preferably to 3.5 m ² / g or less (eg 2.5m ² /g~3.5m ² / g).

  Further, in order to confirm the effect of unadsorbed CMC suspended in the negative electrode active material layer forming hot water paste on the paste viscosity, the following test was performed.

<< Test Example 6 >>
In this example, the amount of CMC added was 0.3% by mass, 0.5% by mass, and 0.7% by mass in the negative electrode active material layer forming paste preparation process of Examples 4, 6, 7, and 10 described above. %, A negative electrode active material layer forming paste was prepared. Then, the viscosity of the paste was measured at a shear rate of 1 s- ¹ . Moreover, after diluting the negative electrode active material layer forming paste with water, the graphite on which CMC was adsorbed was precipitated using an ultracentrifuge, and the supernatant liquid on which unadsorbed CMC was suspended was collected. Then, the amount of unadsorbed CMC contained in the supernatant was calculated by non-dispersive infrared gas analysis. The results are shown in Table 5 and FIGS. FIG. 8 is a graph showing the relationship between the amount of CMC added and the amount of unadsorbed CMC. FIG. 9 is a graph showing the relationship between the amount of unadsorbed CMC and the paste viscosity. FIG. 10 is a graph showing the relationship between the amount of CMC added and the paste viscosity. Here, the amount of unadsorbed CMC is shown in terms of the ratio of the amount of unadsorbed CMC to the amount of CMC added (= [unadsorbed CMC amount / CMC added amount] × 100).

  As shown in Table 5 and FIG. 8, the surface hydrophilic group ratio of graphite increases in the order of Example 10, Example 4, Example 6, and Example 7. It was confirmed that the amount of unadsorbed CMC showed an increasing tendency as the surface hydrophilic group ratio of graphite increased. Further, as shown in FIG. 9, there is a certain correlation between the amount of unadsorbed CMC and the paste viscosity. For example, when the CMC addition amount was the same, it was confirmed that the paste viscosity showed an increasing tendency as the amount of unadsorbed CMC increased in the order of Example 10, Example 4, Example 6, and Example 7. Furthermore, as shown in FIG. 10, it was confirmed that the paste viscosity increased effectively even with a small amount of CMC in accordance with the increase in the surface hydrophilic group ratio of graphite in the order of Example 10, Example 4, Example 6, and Example 7. . From this, it was confirmed that by adding a hydrophilic group to graphite, it is possible to reduce the amount of CMC added while ensuring a suitable paste viscosity.

<< Test Example 7 >>
In this example, a negative electrode sheet was prepared in the same procedure as described above <Preparation of negative electrode sheet> using the negative electrode active material layer forming pastes of Examples 4, 6, 7, and 10 described above. However, the addition amount of CMC was changed to 0.7 mass%, 0.6 mass%, 0.6 mass%, and 0.5 mass% in the order of Example 10, Example 4, Example 6, and Example 7. The SBR (binder) content was fixed at 0.7% by mass, and the total mass of graphite, CMC and SBR was adjusted to 100% by mass. And the lithium ion secondary battery was constructed | assembled using this negative electrode sheet | seat, and battery capacity and IV resistance were measured.

The battery capacity was measured in the following procedures 1 to 3 at a temperature of 25 ° C. and a voltage range of 3.0 V to 4.1 V.
Procedure 1: Discharge to 3.0 V at a constant current of 1 C, then discharge at constant voltage for 2 hours and rest for 10 seconds.
Procedure 2: Charge to 4.1V with a constant current of 1 C, then charge at a constant voltage for 2.5 hours and rest for 10 seconds.
Procedure 3: Discharge to 3.0 V at a constant current of 0.5 C, then discharge at a constant voltage for 2 hours, and stop for 10 seconds.
The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 was defined as the battery capacity.

The results are shown in FIG. 11 and FIG. FIG. 11 is a graph comparing the battery capacities of the examples.
Here, the battery capacity of Example 10 is shown as a relative value with 100 as the battery capacity. FIG. 12 is a graph comparing the IV resistance of each example. Here, the IV resistance of Example 10 is shown as a relative value with 100 as the value.

  As shown in FIG. 11, the batteries according to Example 4, Example 6, and Example 7 were able to increase the composition ratio of graphite by the amount of addition of CMC, so that the battery capacity increased compared to the battery according to Example 10. did. Further, as shown in FIG. 12, the batteries according to Example 4, Example 6, and Example 7 had a smaller amount of CMC added than Example 10, and therefore, good results were obtained with respect to IV resistance.

  Although the lithium ion secondary battery according to one embodiment of the present invention has been described above, the secondary battery according to the present invention is not limited to any of the above-described embodiments, and various modifications can be made.

  For example, in the above-described embodiment, the case of imparting hydrophilicity to graphite by oxygen plasma treatment has been illustrated, but the method of hydrophilization is not limited to this. For example, oxygen atoms may be bonded to the surface of graphite by heat-treating graphite in an oxygen atmosphere. However, as in the above-described embodiment, it is preferable to make the graphite hydrophilic by oxygen plasma treatment from the viewpoint of effectively increasing the surface hydrophilic group ratio.

  As described above, the present invention can contribute to improving the performance of a battery (for example, a lithium ion secondary battery). The present invention is suitable for a lithium ion secondary battery for a vehicle driving power source such as a driving battery for a hybrid vehicle or an electric vehicle. That is, for example, the lithium ion secondary battery can be suitably used as a vehicle driving power source for driving a motor (electric motor) of a vehicle such as an automobile. The power source for driving the vehicle may be an assembled battery in which a plurality of secondary batteries are combined.

20 battery case 40 wound electrode body 50 positive electrode sheet 52 positive electrode current collector 53 positive electrode active material layer 60 negative electrode sheet 62 negative electrode current collector 63 negative electrode active material layers 72 and 74 separator 80 electrolyte solution 100 lithium ion secondary battery

Claims (4)

A method for producing a non-aqueous electrolyte secondary battery comprising a negative electrode in which a negative electrode active material layer containing graphite and carboxymethylcellulose (CMC) is formed on a negative electrode current collector, comprising:
A step of preparing a negative electrode active material layer forming paste containing graphite, CMC, and an aqueous solvent;
Here, the graphite has a hydrophilic surface to which oxygen atoms are bonded,
The sum of C—O bonds and C═O bonds when the total amount of C—C bonds, C—O bonds and C═O bonds on the graphite surface determined by X-ray photoelectron spectroscopy (XPS) is 100%. The proportion is between 35.1% and 38.6%,
When the total solid content of the negative electrode active material layer forming paste is 100% by mass, the content of CMC is 0.48% by mass to 0.53% by mass,
The negative electrode active material layer forming paste has a viscosity at a shear rate of 1 s ⁻¹ of 6440 mPa · s to 9500 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 non-aqueous electrolyte secondary battery. Before the step of preparing the negative electrode active material layer forming paste,
The manufacturing method according to claim 1, further comprising a hydrophilization step of hydrophilizing the surface of the graphite by performing a plasma treatment in an oxygen atmosphere. The specific surface area of the graphite ^is 2.5m ² /g~3.5m 2 / g, The process according to claim 2. The manufacturing method according to claim 2 or 3, wherein in the hydrophilization step, the surface of the graphite is etched using an inert gas before the plasma treatment.

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