JP2011238476A - Laminate, nonaqueous electrolyte secondary battery and laminate manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode which has an active material layer involving just minimum necessities in structure and achieves an excellent adhesion strength of its collector base and active material layer particularly in a nonaqueous electrolyte secondary battery.SOLUTION: A laminate has: a collector base 120; and an active material layer 110 stacked on the collector base. The active material layer 110 includes at least an active material 111, a conductive agent 112, a binding agent 113 and a thickener 114. The active material layer has a volume density of 1.2 g/cmor larger. A laminate manufacturing method includes the steps of: coating the collector base with a composition for active material layer formation including at least an active material 111, a conductive agent 112, a binding agent 113, a thickener 114 and a solvent to form an active material coating film; drying the active material coating film at a temperature between 100°C and 150°C inclusive; re-heating the active material coating film at a temperature between 65°C and 115°C inclusive; and applying a pressure per unit area of 320 kgf/cmor larger on the active material coating film.

Description

  The present invention relates to a laminate in which a layer containing particles is laminated on a base material and a method for producing the same, and in particular, a negative electrode active material capable of occluding lithium ions on a current collector base material such as a copper foil. The present invention relates to a laminate for use in a non-aqueous electrolyte secondary battery including a layer containing substance particles, and a method for manufacturing the same.

With the remarkable spread of portable devices such as digital cameras and notebook computers in recent years, demand for lithium ion secondary batteries, which are a kind of non-aqueous electrolyte secondary batteries, is increasing as a power source.
Lithium ion secondary batteries have high energy density due to their small lithium ion, and can be used for portable electronic devices such as notebook computers, because they use non-aqueous electrolytes and have a high voltage. Research and development for application to next-generation electric industry products such as electric bicycles and electric vehicles are also underway. In addition, since the memory effect is smaller than that of a metal lithium secondary battery, it is also suitable for a device such as a mobile phone that performs recharging.

Examples of such a lithium ion secondary battery include a rectangular type and a cylindrical type, which are enclosed in a metal can, and a laminated type (laminated type) packaged in a flexible film. In the rectangular and cylindrical lithium ion secondary batteries, a positive electrode layer, a separator layer, and a negative electrode layer are wound in a flat shape or a cylindrical shape. In addition, the laminate type has a shape in which positive electrode layers and negative electrode layers are alternately laminated via separator layers.
In any type of lithium ion secondary battery, the positive electrode and the negative electrode layer are layers containing particles called active materials capable of inserting and extracting lithium ions on a sheet-like current collector (current collector base material) ( Active material layer). The positive electrode layer and the negative electrode layer are provided with terminals for taking out a potential difference in each active material as a current. A separator capable of transmitting lithium ions is disposed between the positive electrode layer and the negative electrode layer, and an organic electrolyte is interposed in the whole.

  However, the active material layer of the lithium ion secondary battery has a very large ratio of the active material in order to absorb lithium ions to the maximum extent. Moreover, the active material repeats expansion and contraction by repeating insertion / extraction of lithium ions. Accordingly, there is a problem that the active material is peeled off from the current collecting base material, and this problem is particularly remarkable between the negative electrode active material layer and the negative current collecting base material.

  Conventionally, an active material layer forming slurry containing a binder (binder), a dispersion medium, and a thickening agent in addition to the active material is prepared, and this is applied to a current collector (current collector base material) to form an electrode. It was manufactured (see Patent Document 1). However, a phenomenon called migration occurs in which the binder contained in the slurry is unevenly distributed in the upper layer of the coating film and the amount of the binder in the lower layer of the coating film is reduced. There was a problem that the adhesion strength with the electric base material was remarkably weakened.

  In order to solve such a problem, in order to solve the decrease in the adhesion strength between the current collecting substrate and the coating film (active material layer), in addition to the first polymer in the slurry (negative electrode mixture), A method of adding a second polymer (see Patent Document 2, FIG. 2 (a)) and adhesion for enhancing the adhesion between the negative electrode active material layer containing the binder and the negative electrode current collector substrate A method of providing a layer (see Patent Document 3 and FIG. 2B) has been proposed.

JP-A-4-51459 JP 2003-242967 A JP 2004-200011 A

However, in the method of adding a new polymer to the slurry, it is not preferable to add a material that is not necessary for the active material layer, which is disadvantageous in terms of cost. Further, in the method of providing an adhesion layer, the number of steps for providing the adhesion layer is increased by one step, so that it takes time to manufacture and the productivity is lowered. In any case, it is not preferable that the structure of the active material layer is complicated.
An object of the present invention is to maintain the adhesion strength between the current collecting base material and the active material layer while keeping the configuration of the active material layer to the minimum necessary. More specifically, it is an object to prevent the binder from being unevenly distributed (migration) in the active material layer and to maintain the adhesion strength without degrading the performance of the active material layer.

A first invention for solving the above problem is a laminate in which an active material layer is laminated on a current collecting base material, and the active material layer includes at least an active material, a conductive agent, and a binder. And a thickening agent, and the bulk density of the active material layer is 1.2 g / cm ³ or more.
Furthermore, the active material is a negative electrode active material, and the current collecting base material is a copper foil.
Furthermore, the non-aqueous electrolyte secondary battery is characterized in that the laminate is used as a negative electrode layer of a non-aqueous electrolyte secondary battery.

A second invention for solving the above-described problem is a method for manufacturing a laminate in which an active material layer is laminated on a current collecting base material. A step of applying an active material layer-forming composition containing at least an active material, a conductive agent, a binder, a thickener, and a solvent on the current collecting substrate to form an active material coating film; 2. 2. a step of drying the active material coating film at a temperature of 100 ° C. or higher and 150 ° C. or lower; 3. heating the active material coating film again at a temperature of 65 ° C. or higher and 115 ° C. or lower; The method for producing a laminate, wherein the step of applying a pressure of 320 kgf / cm ² or more per unit area to the active material coating is performed in the order of 1 to 4.
Further, the method includes a step of cooling the active material coating film to room temperature between the step 2 and the step 3, wherein the step 2 is performed for 10 minutes to 15 minutes and the step 3 is performed for 60 minutes or more. It is the manufacturing method of the laminated body characterized.
Further, the step 4 is a method for producing a laminate, which is performed while keeping the heat applied in the step 3 at or above the melting point of the binder.

  According to 1st invention, it can be set as the laminated body excellent in the adhesive strength of an active material layer and a current collection base material. Further, since the active materials are close to each other, there are effects of increasing the discharge capacity of the active material per unit volume and improving the cycle characteristics. Therefore, it can be suitably used as a negative electrode layer of a nonaqueous electrolyte secondary battery.

According to the second invention, it is possible to improve the adhesion between the active material layer and the current collecting base material without changing the configuration of the active material layer without adding a new polymer or forming a layer. It was.
By removing the solvent in the drying step and then performing the reheating step, it is considered that the uneven distribution of the binder in the upper and lower layers in the active material coating can be eliminated and the distribution of the negative electrode active material can be made uniform. . And a binder can be pushed in into the space | gap which exists in an active material coating film by pressing an active material coating film with the pressure of 320 kgf / cm < ² > or more per unit area.

In particular, by taking a sufficient time for the reheating step and then pressing at a temperature higher than the melting point of the binder, the temperature of the active material coating becomes constant, and the binder is collected with the active material coating. It is possible to efficiently fill the voids present at the interface with the electric substrate, improve the adhesion between the active material layer and the current collecting substrate, and increase the bulk density of the active material layer.
According to the present invention, there can be obtained a laminate including an active material layer having no uneven distribution of the binder, less voids, and a high bulk density (negative electrode), and in particular, the negative electrode of the nonaqueous electrolyte secondary battery. When used as an electrode layer, it can be expected that the binder reduces the influence of the binder preventing the electrochemical reaction in taking out the electric capacity from the negative electrode active material.

It is sectional drawing which showed typically the laminated body before and behind the process 4 which comprises the manufacturing method of this invention. It is sectional drawing which shows typically the negative electrode layer by a prior art, and the negative electrode layer by this invention. It is explanatory drawing which shows the process of pressing a laminated body with a pneumatic flat plate press. It is explanatory drawing which shows the outline | summary of a manual peel test. It is a cross-sectional photograph of the laminated body before and behind the process 4 which comprises the manufacturing method of this invention.

The present invention will be described based on examples.
<Configuration of laminate>
The laminate of the present invention is a laminate in which an active material layer is laminated on a current collecting substrate, and the active material layer includes at least an active material, a conductive agent, a binder, and a thickener. And the bulk density of the active material layer is 1.2 g / cm ³ or more. Hereinafter, the structure of a laminated body is demonstrated.

<Current collector base>
From the viewpoint of flowing a high current, the conductive material is preferably used as the current collecting base material. Among them, copper, nickel, stainless steel, iron, aluminum and the like can be mentioned. Among them, aluminum and negative electrode current collectors are used as the positive electrode current collector base material in terms of cost and relatively low in terms of metal ionization. Copper is preferred for the substrate.
As the negative electrode current collecting substrate, rolled copper foil is preferable among copper. This is because the copper crystals in the rolled copper foil are lined up in the rolling direction, and the negative electrode layer using this is difficult to break even when stress is applied. This is because there is an advantage of being rich.
Therefore, rolled copper foil was used also in the present invention. However, since the rolled copper foil also has a length limitation due to its manufacturing method, it is also preferable to use an electrolytic copper foil from the advantage that the length is not limited in the production process. For the positive electrode current collector base material, a rolled aluminum foil is preferable for the same reason as the rolled copper foil. Again, since the aluminum crystals are arranged in the rolling direction, the positive electrode layer using the aluminum crystals is not easily broken when stress is applied. Therefore, when forming a laminated body, there exists an advantage that it is rich in a moldability.

<Active material>
Any active material that can occlude and release lithium ions can be used. Specifically, as the positive electrode active material, lithium-containing metal oxides such as LiMn ₂ O ₄ , LiFePO ₄ , LiCoO ₂ , Li ₂ MnO ₃ , LiMnO ₂ , LiFeSiO ₄ , and LiFeVO ₄ that are already known, V ₂ O ₅ , Examples thereof include transition metal oxides such as MoO ₃ and transition metal sulfides such as TiS ₂ and amorphous MoS ₃ .
Examples of the negative electrode active material include carbon-based materials such as amorphous carbon, graphite, natural graphite, and mesocarbon microbeads (MCMB), oxide-based materials such as LiTiO ₄ and SiO ₂ , lithium metal alloys, and lithium metals. It is done.
Among these, artificial graphite and natural graphite are currently widely used industrially, and are preferable for the negative electrode active material because they are inexpensive and easy to handle. Also in the present invention, artificial graphite and natural graphite can be preferably used.

<Binder>
As the binder, a polymer that is chemically stable with respect to the dispersion solvent described later is preferable. For example, resin polymers such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PTFE), aromatic polyamide, rubber polymers such as styrene / butadiene rubber (SBR) and ethylene / propylene rubber, polyvinylidene fluoride ( PVDF) and fluorine-based polymers such as polytetrafluoroethylene.
Among them, the positive electrode layer is a fluorine-based polymer such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene from the viewpoint of improving the adhesion between the current collecting base material and the positive electrode active material and the adhesion between the positive electrode active material. Is preferred.
The negative electrode layer is preferably a fluorine polymer such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene, or a rubber polymer such as styrene / butadiene rubber (SBR) or ethylene / propylene rubber. In particular, SBR has a low melting point (115 ° C.) and can suppress the amount of heat in the reheating step and the pressing step, and an aqueous solvent can be used. SBR was used as the negative electrode binder in the examples of the present invention from the viewpoint that the solvent recovery was unnecessary and the cost could be reduced.

<Conductive agent>
As the conductive agent, a substance that can ensure the conductivity of the electrode material (current collecting base material) and does not cause a chemical reaction in the charge / discharge reaction is preferred. In general, carbon-based materials such as acetylene black, ketjen black, channel black, and furnace black, metal fibers, conductive polymers, carbon fluoride, and metal powder are used. Among these, acetylene black and ketjen black are particularly preferable.

<Thickener>
In the nonaqueous electrolyte secondary battery of the present invention, an active material layer-forming composition in which an active material is dispersed in a solvent is applied onto a current collecting substrate to form an active material coating film. A thickener may be added to adjust the viscosity of the composition. The thickener is preferably a polymer material such as carboxymethyl cellulose (CMC) or polyethylene glycol.

<Solvent>
In order to form the active material layer of the nonaqueous electrolyte secondary battery of the present invention, the composition for forming an active material layer is applied onto a current collecting substrate. The composition for forming an active material layer includes an active material, a conductive agent, a binder, a thickener, and a solvent, and is adjusted in a slurry form. Solvents that can be used to adjust the composition for forming an active material layer include water, water-based solvents obtained by mixing ethanol, N-methylpyrrolidone (NMP), and the like, cyclic amides such as NMP, N, N- Examples thereof include linear amides such as dimethylformamide and N, N-dimethylacetamide, and aromatic hydrocarbons such as toluene and xylene.

<Structure of non-aqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery of the present invention is, for example, a lithium ion secondary battery, and includes a type sealed in a metal can and a laminate type (laminated type) packaged in a flexible film. In the rectangular and cylindrical lithium ion secondary batteries, a positive electrode layer, a separator layer, and a negative electrode layer are wound in a flat shape or a cylindrical shape. In addition, the laminate type has a shape in which positive electrode layers and negative electrode layers are alternately laminated via separator layers.
In any type of lithium ion secondary battery, the positive electrode and the negative electrode layer each have a layer (active material layer) containing particles called an active material capable of inserting and extracting lithium ions on a sheet-like current collecting base material. It is the laminated body laminated | stacked. The positive electrode layer and the negative electrode layer are provided with terminals for taking out a potential difference in each active material as a current. A separator capable of transmitting lithium ions is disposed between the positive electrode layer and the negative electrode layer, and an organic electrolyte is interposed in the whole.

<Separator>
As the separator, a porous sheet polymer that transmits lithium ions and does not change in quality by the organic electrolyte is preferable. For example, olefin-based sheet polymers such as polyethylene (PE) and polypropylene (PP), and sheet polymers such as polyimide and polyaramid are preferred. These sheet polymers differ depending on the use of the non-aqueous electrolyte secondary battery, but a thickness of 40 to 60 μm is preferable for large-scale industries such as automobiles. Further, these sheet-like polymers preferably have a pore size of 1 μm or less, and a porosity of 20 to 80%.
A nonwoven fabric can also be used as the separator. Examples of the nonwoven fabric that can be used as the separator include conventionally known ones such as cotton, rayon, acetate, nylon, polyester, polyolefin resin, polyimide, and aramid. These nonwoven fabrics may be used alone or in combination of two or more.
The bulk density of the nonwoven fabric is not particularly limited. The porosity of the nonwoven fabric is preferably 30 to 90%. Moreover, the thickness of a nonwoven fabric should just be the same grade as the layer by which electrolyte solution is hold | maintained, and 5-200 micrometers is preferable. When the thickness of the nonwoven fabric is 5 μm or less, the electrolyte solution is better retained. If the thickness of the nonwoven fabric is 200 μm or less, the internal resistance becomes smaller.

<Organic electrolyte>
As the organic electrolytic solution that can be used in the nonaqueous electrolyte secondary battery of the present invention, known organic electrolytic solutions can be used.
Solvents for such organic electrolytes include ethers such as diethyl ether and ethylene glycol phenyl ether, amides such as formamide and N-ethylformamide, sulfides such as dimethyl sulfoxide and sulfolane, ethylene carbonate, propylene carbonate Organic solvents such as carbonates such as γ-butyrolactone and NMP can be used. More preferably, a carbonate system such as ethylene carbonate or propylene carbonate is used. These solvents may be used alone or in combination of two or more.
Lithium salt is used for the electrolyte contained in these organic electrolytes, and LiClO ₄ , LiPF ₆ , LiCl, LiBF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ are used as the lithium salt. Etc. are used. Of these, LiPF ₆ is preferred because of its particularly good withstand voltage characteristics.

<Positive electrode layer>
The laminate of the present invention can be particularly preferably used as a negative electrode layer of a nonaqueous electrolyte secondary battery. At this time, the laminate of the present invention can also be used as the positive electrode layer. For example, LiMn ₂ O ₄ , LiFePO ₄ , LiCoO ₂ , LiFeVO ₄ , LiFeSiO ₄ , Li ₂ MnO ₃ can be used as the positive electrode active material. A laminate using can be preferably used.

<Method for producing laminate>
Next, the manufacturing method of the laminated body of this invention is demonstrated.

<Coating process>
<Adjustment of coating solution>
The active material layer is laminated on the current collecting base material to produce the laminate of the present invention. For forming the active material layer, first, an active material, a conductive agent and a binder are dispersed in a solvent and kneaded to prepare a composition for forming an active material layer (coating liquid) as a slurry.
The conductive agent added to the composition for forming an active material layer is 0.5 parts by mass or more and 20 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the active material.
Further, the binder is preferably 5 parts by mass or more and 20 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the active material. This is because when the binder is equal to or higher than the above upper limit, the ratio of the active material is reduced, resulting in a decrease in battery capacity. When the binder is lower than the upper limit, the adhesiveness between the active materials and between the active material and the current collecting substrate is reduced. It will lead to deterioration.
Further, the concentration of the active material in the composition for forming an active material layer is preferably 30% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 55% by mass or less. This is because aggregation of the active material occurs above the upper limit, and sedimentation of the active material occurs below the lower limit.

The adjustment of the composition for forming an active material layer used in the present invention is not particularly limited by the mixing method and mixing order of materials. A highly dispersed slurry can be obtained by using a ball mill, bead mill, sand mill, disper, ultrasonic disperser, homogenizer, planetary mixer or the like for kneading.
Moreover, it is also possible to add a thickener according to a required viscosity.

<Coating method>
As for the coating method of the produced active material layer forming composition, a general wet material coating method is adopted, and it is applied in accordance with physical properties such as viscosity of the active material layer forming composition in a slurry form. Work is possible. Examples include gravure coating, micro gravure coating, die coating, dip coating, slit coating, comma coating, lip coating, and direct coating. In general, the thickness of the active material coating film is preferably 0.01 mm or more and 1 mm or less, more preferably 0.03 mm or more and 0.2 mm or less.

<Drying process>
The drying process is not particularly limited as long as no solvent remains in the active material layer. For example, hot air drying, hot air drying, vacuum drying, far infrared drying, ultraviolet drying, electron beam drying in a small drying oven or the like. Constant temperature and high humidity drying is preferred. These drying methods may be performed singly or in combination of two or more.
In hot air drying, the air volume, the angle per wind, the distance from the outlet, etc. affect the drying efficiency, so these conditions are appropriately selected.
Furthermore, when coating and drying are continuously performed by a roll-to-roll method, drying may be performed by roll support, floating, or the like, or a combination of these may be performed.
The residual solvent occupies as little as possible in the active material coating film after the drying step, preferably 1% by mass or less, and more preferably 0.5% by mass or less.

<Reheating process>
<Cooling after drying process>
After the heating step, the active material coating film is gradually cooled to room temperature. As the process, it is preferable to cool at room temperature. For example, it is preferable to cool in a constant temperature and high humidity chamber having a temperature of 20 ° C. or higher and less than 30 ° C. for 2 hours or longer.
By passing through this process, the active material coating film temperature at the time of a press process becomes uniform as a whole, and the active material layer of the bulk density without a nonuniformity can be formed.

<Reheating>
Heating methods that can be performed in the reheating process include hot air heating in a small drying oven, hot air heating, vacuum heating in a sealed container, far infrared heating, ultraviolet irradiation heating, electron beam heating, constant temperature and high humidity. Heating is preferred, and these heating methods may be performed alone or in combination of two or more. In the reheating step, in order to uniformly raise the temperature of the active material coating film to near the melting point of the binder, a heating method using an oven or a hot plate in which the temperature is constant is preferable.
In hot air drying, the air volume, the angle per wind, the distance from the outlet, etc. affect the drying efficiency, so these conditions are appropriately selected.
The reheating time is preferably 30 minutes or more, and more preferably 1 hour or more. The reheating temperature varies depending on the binder contained in the active material coating, so the appropriate temperature is different. However, from the viewpoint of softening the binder by reheating and pushing it into the voids of the active material, etc. 115 ° C. or lower, more preferably higher than the melting point of the binder.

<Pressing process>
In order to improve the energy density per unit area, the active material coating film is pressed after reheating or while reheating. Examples of the press include a metal roll press method, a rubber roll press method, and a flat plate press method.
The bulk density of the active material coating, i.e. the active material layer after pressing is preferably laminate when a positive electrode layer is in the range of 1.0 g / cm ² or more 3.8 g / cm ² or less, the negative electrode In the case of an electrode layer, it is preferably 1.0 g / cm ² or more and 2.5 g / cm ² or less. If the bulk density is above this range, there are almost no voids in the active material layer, the organic electrolyte cannot penetrate into the active material layer, resulting in a decrease in battery performance, and below this range, This is because the binder hardly exists in the vicinity of the current collecting base material, which causes poor adhesion between the active material layer and the current collecting base material.
The pressing step is preferably performed in a state in which the temperature of the active material coating film is maintained at or above the melting point of the binder contained in the active material coating film. Although it is possible to perform pressing after the reheating step and before the temperature of the active material coating film is lowered, it is most preferable to perform pressing while heating after a predetermined time in the reheating step. This is because the pressing can be performed in a state where the binder is uniformly melted at the melting point by performing the pressing while performing the heating in the reheating step, so that the binder can efficiently sink into the voids.

<Method for making secondary battery>
The positive electrode layer and the negative electrode layer prepared as described above are combined with a separator and laminated or wound so that the positive electrode layer and the negative electrode layer do not touch the positive electrode layer / separator / negative electrode layer. It is sealed with an organic electrolyte in a container such as a mold, cylinder, or laminate mold. Thereby, a nonaqueous electrolyte secondary battery is produced. At the time of production, the work is performed in a dry room having a low dew point (-50 ° C. or lower) atmosphere, a glove box in which argon gas occupies 95 parts by mass or more and 100 parts by mass or less, and water is contained in a non-aqueous electrolyte secondary battery. It is indispensable not to be sealed in.

Example 1
<Preparation of negative electrode active material layer forming composition>
The following materials are kneaded at a ratio of active material: conductive agent: binder: thickener = 85: 15: 1.5: 1.5, and diluted with a solvent so that the solid content becomes 55% by mass. A negative electrode active material layer forming composition was obtained.
Binder: SBR (styrene butadiene rubber) (melting point 115 ° C., BM-400B: manufactured by Nippon Zeon)
Thickener: CMC (Carboxymethylcellulose) (CMC Daicel <Ammonium> manufactured by Daicel Chemical)
Conductive agent: Acetylene black negative electrode active material: Carbon (M1-001, Nippon KMFC graphitized product, manufactured by JFE Chemical)
Solvent: water
<Formation of negative electrode active material layer>
A negative electrode active material layer forming composition prepared by cutting a copper foil (thickness: 10 μm) as a negative electrode current collecting substrate into a width of 15 cm and a length of 50 cm, and adjusting the center of the copper foil with a YA-C applicator having a slit clearance of 300 μm. The product was applied over a width of 10 cm and a length of 40 cm to form a negative electrode active material coating (coating process).
The negative electrode active material coating film was placed in an oven together with the copper foil and dried at 100 ° C. for 15 minutes (drying step).
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm. The temperature in the membrane was measured with a temperature sensor.
The cut specimen was put into the oven again and heated at 115 ° C. for 60 minutes (FIG. 1 (a)) (reheating step).
The test piece taken out from the oven was immediately sandwiched between stainless plates, and a pressure of 320 kgf / cm ² was maintained for 10 minutes with a pneumatic flat plate press (see FIG. 1B and FIG. 3) (pressing step). The temperature in the film immediately after the pressing step was 115 ° C. Thus, a laminate of Example 1 in which the negative electrode active material layer was laminated on the copper foil was obtained.

(Example 2)
The same negative electrode active material forming composition as that prepared in Example 1 was used, and the same procedure as in Example 1 was carried out except that the drying step was performed at 150 ° C. for 10 minutes and the reheating step was performed at 65 ° C. for 60 minutes. The laminate of Example 2 was obtained. The temperature in the film immediately after the pressing step was 65 ° C.

(Comparative Example 1)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 100 ° C. for 15 minutes in the same manner as in Example 1.
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm. The body.

(Comparative Example 2)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 150 ° C. for 10 minutes in the same manner as in Example 2.
After drying, the film was allowed to cool to room temperature, and the part where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cmm and a length of 5 cm. The body.

(Comparative Example 3)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 100 ° C. for 15 minutes in the same manner as in Example 1.
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm.
The cut specimen was placed in an oven again and heated at 115 ° C. for 60 minutes in the same manner as in Example 1 to obtain a laminate of Comparative Example 3.

(Comparative Example 4)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 150 ° C. for 10 minutes in the same manner as in Example 2.
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm.
The cut specimen was placed in the oven again and heated at 65 ° C. for 60 minutes in the same manner as in Example 2 to obtain a laminate of Comparative Example 4.

(Comparative Example 5)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 100 ° C. for 15 minutes in the same manner as in Example 1.
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm.
The test piece was sandwiched between stainless plates, and a pressure of 320 kgf / cm ² was held for 10 minutes with a pneumatic flat plate press. The temperature in the film immediately after the pressing step was 25 ° C. Thus, a laminate of Comparative Example 5 in which the negative electrode active material layer was laminated on the copper foil was obtained.

(Comparative Example 6)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 100 ° C. for 15 minutes in the same manner as in Example 1.
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm.
The cut specimen was put into the oven again and heated at 115 ° C. for 60 minutes in the same manner as in Example 1.
The test piece taken out from the oven was immediately sandwiched between stainless plates, and maintained at a pressure of 80 kgf / cm ² for 10 minutes with a pneumatic flat plate press. The temperature in the film immediately after the pressing step was 115 ° C. Thus, a laminate of Comparative Example 6 in which the negative electrode active material layer was laminated on the copper foil was obtained.

(Example 3)
Using the same negative electrode active material forming composition prepared in Example 1, the coating process was performed in the same manner as in Example 1, and the drying process was performed at 100 ° C. for 15 minutes in the same manner as in Example 1.
After drying, the film was allowed to cool to room temperature, and the portion where the negative electrode active material coating film was formed was cut out together with the copper foil so as to have a width of 5 cm and a length of 5 cm.
The cut specimen was placed in the oven again and heated at 115 ° C. for 5 minutes.
The test piece taken out from the oven was immediately sandwiched between stainless plates, and a pressure of 320 kgf / cm ² was maintained for 10 minutes with a pneumatic flat plate press. The temperature in the film immediately after the pressing step was 115 ° C. Thus, a laminate of Example 3 in which the negative electrode active material layer was laminated on the copper foil was obtained.

(Adhesion evaluation 1)
The laminates prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were attached to a flat stainless steel plate with an adhesive tape to fix the four corners. An adhesive tape (Scotch Mending Tape 230-3-12, 12 mm width, manufactured by Sumitomo 3M Limited) was applied to the negative electrode active material layer, and the tape was peeled in the direction of 180 ° C. by hand (see FIG. 4). By observing the appearance of the peeled adhesive tape and the negative electrode active material layer, the adhesion between the negative electrode active material layer and the copper foil was evaluated according to the following criteria. The results are shown in Table 1 (Adhesion evaluation 1) column.

◯: When the adhesive tape is peeled 180 ° by hand, only the surface of the negative electrode active material layer adheres to the adhesive surface of the adhesive tape, and the copper foil is not exposed in the laminate.
X: When the adhesive tape was peeled 180 ° by hand, the negative electrode active material layer adhered to the adhesive surface of the adhesive tape, and even a slight exposure of the copper foil was observed in the laminate.

  The laminated body of Example 1 and Example 2 which performed the press process through the reheating process in addition to the drying process resulted in the negative electrode active material layer and the copper without exposing the copper foil as a result of (Adhesion Evaluation 1). It was confirmed that the adhesion strength with the foil was high.

(Adhesion evaluation 2)
Using the cross-cut guide (Cortech Co., Ltd., 1 mm width), the laminated body created in Examples 1-3 and Comparative Examples 1-6 is 100 mm of 1 mm x 1 mm so that copper foil may not be damaged with a razor. The negative electrode active material layer was cut so as to form individual grids, and adhered to a flat stainless steel plate with an adhesive tape, and the four corners were fixed.
An adhesive tape (Scotch Mending Tape 230-3-12, 12 mm width, manufactured by Sumitomo 3M Limited) was applied to the cut-out negative electrode active material layer, and the tape was peeled in the direction of 180 ° C. (horizontal direction) by hand. . At this time, the number of cells of the negative electrode active material layer peeled off from the copper foil was investigated, and the adhesion evaluation was quantified. The results are shown in Table 1 (Adhesion evaluation 2) column. The number of (adhesion evaluation 2) described in Table 1 is an average value for four samples prepared under the same conditions.

As a result of (Adhesiveness Evaluation 2), the laminates of Example 1 to Example 3 in which the pressing process was performed through the reheating process in addition to the drying process had a very small number of peeled cells, and the negative electrode active material layer It was confirmed that the adhesion strength between the copper foil and the copper foil was high, and the result of (Adhesion Evaluation 1) was confirmed.
From the results of (Adhesiveness Evaluation 1) and (Adhesiveness Evaluation 2), the film was allowed to cool once after the drying step, passed through a reheating step, and the temperature in the film immediately after the pressing step was maintained at 65 ° C. or higher in the state of 320 kgf. It can be seen that a laminate having high adhesion strength between the negative electrode active material layer and the copper foil was obtained by performing the pressing step at / cm ² .
In particular, Example 1 and Example 2 in which the reheating process time was 60 minutes were shown to exhibit very good adhesion.

(Bulk density measurement)
About the negative electrode active material layer of the laminated body produced in Examples 1-3 and Comparative Examples 1-6, the bulk density measurement was performed according to JISR1628. The results are shown in Table 1. The bulk density described in Table 1 is an average value for four samples prepared under the same conditions.

(Press temperature measurement)
The temperature in the film immediately after the pressing step of the laminates prepared in Examples 1 to 3 and Comparative Examples 1 to 6 was confirmed by a temperature sensor. The results are shown in Table 1.

The bulk densities of the negative electrode active material layers of Examples 1 to 3 are comparative examples 1 and 2 in which neither reheating nor pressing is performed by performing a pressing process at 320 kgf / cm ² after the reheating process. It can be seen that the bulk density is about 1.5 times that of the negative electrode active material layers of Comparative Examples 3 and 4 that were performed but not subjected to the pressing step, and the density was significantly increased.
Moreover, although the comparative example 5 which performed only the press without passing through a reheating process has high bulk density compared with the comparative examples 1 and 2, it cannot be said enough, but has passed the reheating process, but in a press process. It turns out that the bulk density of the comparative example 6 with little pressurization pressure is also low.
Although the reheating process and the pressing process have passed, Example 3 with a short reheating time has a slightly lower bulk density than Examples 1 and 2 that have passed a sufficient reheating time.
And when Example 1 and Example 2 which passed sufficient reheating time are compared, Example 2 in which reheating temperature was low and became temperature lower than melting | fusing point of a binder at the time of a press is described in Example 1. It can be seen that the bulk density is slightly lower than that.

From the above, by performing a pressing process at 320 kgf / cm ² for a certain time while maintaining a temperature equal to or higher than the melting point of the binder for a long time of 1 hour, the negative electrode active material coating film (negative electrode active material layer) is formed. This is probably because the voids that were present were filled with the binder. Since the negative electrode active materials are closer to each other in the negative electrode active material layer due to the increase in bulk density, when such a laminate is used as the negative electrode layer of a non-aqueous electrolyte secondary battery, the discharge capacity As a result, favorable results such as an increase in cycle characteristics and an improvement in cycle characteristics are brought about.

(Cross section observation)
About the laminated body created in Examples 1-3 and Comparative Examples 1-6, the cross section of the negative electrode active material layer was observed in SEM, and the following references | standards evaluated. The results are shown in Table 1.

○: No voids are observed (the voids in the negative electrode active material layer are filled with a binder, and the negative electrode active materials are close to each other)
X: A space | gap is observed (the space | interval of negative electrode active materials is comparatively separated)

FIG. 5A is an SEM image of a cross section of the laminate of Example 1. FIG. No voids were observed in the cross sections of the negative electrode active material layers of Examples 1 to 3. By passing through a pressing process at 320 kgf / cm ² , it was confirmed that the voids present in the negative electrode active material layer were filled with the binder.
FIG. 5B is an SEM image of the laminate of Comparative Example 3. Gaps were observed in the cross sections of the negative electrode active material layers of Comparative Examples 1 to 4, 6 as shown in the image of FIG. For this reason, the bulk density is low, and the negative electrode active materials or the negative electrode active material and the copper foil are not sufficiently connected by the binder, so that the adhesion is low.

As mentioned above, according to the manufacturing method of the laminated body of this invention, a negative electrode active material coating film (negative electrode active material) is performed by performing the press process by 320 kgf / cm < ² > for a fixed time, keeping the temperature near melting | fusing point of a binder. It was shown that the voids present in the layer) were filled with the binder, the bulk density of the negative electrode active material layer was increased, and the adhesion between the negative electrode active material layer and the current collecting substrate was improved.
Further, the bulk density is 1.2 g / cm ³ or more, and by using such a laminate as a negative electrode layer of a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary has a large discharge capacity and good cycle characteristics. A battery can be obtained.

DESCRIPTION OF SYMBOLS 100 Laminate 110 Active material layer 111 Active material 112 Conductive agent 113 Binder 114 Thickener 115 Void 116 Aggregation of active material 120 Current collecting base material 200 Negative electrode layer 210 Negative electrode active material layer 211 Negative electrode active material 213 Binder 216 Adhesion layer 217 Second polymer 220 Copper foil 300 Pneumatic flat plate press 301 Lower plate 302 Upper plate 303 Strut 304 Compressed air supply pipe 305 Pressure gauge 306 Stainless steel plate 307 Press machine operating direction 308 Pressing direction 401 Adhesive tape 402 Peeling direction

Claims (6)

A laminate in which an active material layer is laminated on a current collecting substrate,
The active material layer includes at least an active material, a conductive agent, a binder, and a thickener,
The active material layer has a bulk density of 1.2 g / cm ³ or more.   The laminate according to claim 1, wherein the active material is a negative electrode active material, and the current collecting base material is a copper foil.   A non-aqueous electrolyte secondary battery comprising the laminate according to claim 1 or 2 as a negative electrode layer of a non-aqueous electrolyte secondary battery. A method for producing a laminate in which an active material layer is laminated on a current collecting substrate,
The active material layer is
1. A step of applying an active material layer forming composition containing at least an active material, a conductive agent, a binder, a thickener, and a solvent on the current collecting base material to form an active material coating film;
2. Drying the active material coating film at a temperature of 100 ° C. or higher and 150 ° C. or lower;
3. Heating the active material coating film again at a temperature of 65 ° C. or higher and 115 ° C. or lower;
4). Applying a pressure of 320 kgf / cm ² or more per unit area to the active material coating;
Is performed in the order of 1 to 4, a method for manufacturing a laminate.   A step of cooling the active material coating film to room temperature is provided between the step 2 and the step 3, wherein the step 2 is performed for 10 minutes to 15 minutes and the step 3 is performed for 60 minutes or more. The manufacturing method of the laminated body of Claim 4.   5. The method for manufacturing a laminate according to claim 4, wherein the step 4 is performed while maintaining the heat applied in the step 3 at or above the melting point of the binder.