JP5676173B2 - Method for producing negative electrode for secondary battery - Google Patents

Description

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

  With the widespread use of mobile terminals such as mobile phones and laptop computers, the role of secondary batteries that serve as the power source has become important. These secondary batteries are required to have a small size, a light weight, and a high capacity, which are resistant to deterioration even after repeated charging and discharging.

  For the negative electrodes of these secondary batteries, carbon materials such as graphite and hard carbon capable of occluding and releasing lithium ions have been put into practical use from the viewpoint of high energy density, good charge / discharge cycle characteristics, and high safety. Yes. However, the current capacity of the secondary battery is insufficient to satisfy the demands of high-capacity high-speed communication such as mobile phones and high-speed communication of color moving images, and further higher energy density of the negative electrode is necessary.

  Various attempts have been made to increase the capacity of a negative electrode using a carbon material as a base. As a method for improving the capacity, for example, Patent Document 1 discloses a technique for increasing the capacity by adding aluminum, lead, and silver having a small particle size to a carbon material as a lithium ion storage and release aid. ing. Patent Document 2 discloses that a metal oxide containing Sn or the like is used as a negative electrode material. It is said that a negative electrode with high capacity and good cycle characteristics can be obtained by adding and mixing a metal or metal oxide to such a carbon negative electrode material. The technique of adding aluminum or the like with a small particle diameter disclosed in Patent Document 1 to a carbon material is difficult to uniformly disperse metal particles in the carbon material, and the metal is localized in the negative electrode. As a result, when the charge / discharge cycle is repeated, there is a problem in that the charge / discharge state of the electrode becomes non-uniform due to local concentration of the electric field, causing deformation of the electrode, peeling of the active material from the current collector and the like. For this reason, it has been difficult to maintain a high level of cycle characteristics. SnBxPyOz (x is 0.4 to 0.6, y is 0.6 to 0.4) metal oxide amorphous material disclosed in Patent Document 2 has a large irreversible capacity in the first charge / discharge and sufficient energy density of the battery It had the subject that it was difficult to make it high.

  These conventional techniques have a common problem that a high operating voltage cannot be obtained. The reason is that, when a metal and a carbon-based material are mixed, a plateau peculiar to the metal is formed at a voltage higher than carbon in the discharge curve, so that the operating voltage is lower than when only carbon is used as the negative electrode. . Lithium secondary batteries have a lower limit voltage depending on their use. Therefore, when the operating voltage is lowered, the usable area is narrowed. As a result, it is difficult to increase the capacity in the area where the battery is actually used.

  In order to solve these problems, a negative electrode has been proposed in which an active material layer made of a Si-based alloy or the like is formed on the surface of a carbon layer by vacuum film formation (Patent Document 3, Patent Document 4, and Patent Document 5).

JP-A-9-259868 Republished patent WO96 / 33519 JP 7-296798 A JP 7-326342 A JP 2001-283833 A

  However, the conventional technique for forming an active material layer made of a Si-based alloy or the like on the surface of the carbon layer by vacuum film formation has the following problems.

  In the above-described laminated negative electrode in which a layer made of an active material such as silicon is formed on the surface of the carbon layer by vacuum film formation, the first carbon layer is generally composed of an active material such as graphite and a binder as an organic solvent. The dispersed paint is applied to a conductive substrate and dried to form a coating film containing an active material.

  When a battery is fabricated and charged / discharged using a negative electrode in which a layer made of a metal or a semiconductor is formed on the first layer by vacuum film formation, the initial capacity is large. Since the expansion / contraction rate of this layer was larger than that of the first layer, the cycle efficiency was greatly deteriorated because the second layer was peeled off or micronized.

  Further, when a hardly evaporating substance such as Si having a very high melting point is vacuum deposited on the surface of the carbon layer, the radiant heat from the evaporation source is very large. If the material of the negative electrode layer absorbs this radiant heat in a large amount, the binder contained in the negative electrode layer may be seriously damaged, which may adversely affect the charge / discharge cycle characteristics of the battery. In order to suppress the amount of radiant heat, various devices are required, such as flowing a refrigerant through the apparatus and increasing the traveling speed of negative electrode equipment (copper foil, etc.), which complicates the apparatus configuration. Increasing the traveling speed of the negative electrode equipment (such as copper foil) can reduce the effect of radiant heat, but the amount of adhesion to the equipment is reduced, making it difficult to obtain the desired film thickness. In vacuum film formation such as vacuum deposition, CVD, and sputtering, the film formation rate is slower than in conventional coating methods, and thus it takes a long time to obtain a negative electrode film thickness of several microns.

  Further, when mass production is attempted, a large amount of active material adheres in the chamber, so that there is a problem in process such as frequent cleaning. For these reasons, it is conceivable that the yield on the characteristics of the battery deteriorates.

  From the above, in order to obtain stable cycle characteristics, it is extremely important to select the constituent material of the second layer that suppresses expansion and contraction as much as possible, and the selection of the manufacturing method thereof.

  The present invention has been made in view of the above circumstances, and in view of the problems of the prior art of a laminated composite negative electrode in which a thin film layer of metal or semiconductor is formed on a carbon layer, high charge and discharge efficiency and The object is to obtain a high battery capacity while maintaining good cycle characteristics.

According to the present invention, the current collector, the first layer mainly composed of carbon, and the second layer mainly composed of a film material having lithium ion conductivity are laminated in this order. A method for producing a negative electrode for a secondary battery, comprising : forming a first layer by applying a coating solution containing carbon as a main component and containing a binder to the current collector; and Li: Forming a second layer by applying a coating liquid containing Si alloy particles and a binder to the surface of the first layer and then drying the coating liquid, and the Li An average particle size of the Si alloy particles is 80% or less of the thickness of the second layer. A method for producing a negative electrode for a secondary battery is provided.

  According to the present invention, since the negative electrode has a configuration in which one or more particles selected from metal particles, alloy particles, and metal oxide particles are bound by the binder, the second layer is the first layer. It adheres firmly to the layer and improves the mechanical strength of the multilayer film.

  Here, the average particle diameter of the metal particles, metal alloy particles, or metal oxide particles contained in the second layer is desirably 80% or less of the thickness of the second layer from the viewpoint of film thickness control accuracy. . By carrying out like this, the target film thickness can be controlled suitably and generation | occurrence | production of the unevenness | corrugation on the surface of a 2nd layer can be suppressed. Concavity and convexity are particularly noticeable when the film thickness is, for example, 5 μm or less. If the unevenness is too large, damage to the separator increases, and as a result, there is a possibility of causing a short circuit with the positive electrode. In addition, when a third layer such as lithium is vacuum-deposited on the second layer, which will be described later, it is difficult to form a uniform film thickness if the uneven portion is large. There is a problem that becomes larger. If the unevenness of a layer made of a highly active substance such as lithium is large, there will be many random active sites, and dendrites are likely to be generated. Problem arises.

  When the second layer includes metal particles, the group consisting of Si, Ge, Sn, In, and Pb from the viewpoints of high theoretical active material energy density, easy conduction of lithium ions, dispersibility in the binder, and the like. It is preferable to include one or more elements selected from

  The alloy particles contained in the second layer preferably contain one or more elements selected from the group consisting of Si, Ge, Sn, In and Pb, specifically, Li: Si alloy. An alloy with lithium such as Li: Ge alloy, Li: Sn alloy, Li: In alloy, Li: Pb alloy is particularly preferable.

  When the second layer contains metal oxide particles, Si, Ge, Sn, In, and Pb are used from the viewpoints of high theoretical active material energy density, easy conduction of lithium ions, dispersibility in the binder, and the like. It is preferable to consist of one or two or more materials selected from the group consisting of oxides.

  The metal particles and the like may be used alone without containing carbonaceous matter, or those having a surface coated with a carbonaceous layer or those coated with a metal layer on the surface of carbonaceous particles may be used as appropriate.

  The particles constituting the second layer may have any of a configuration mainly composed of metal particles, a configuration mainly composed of alloy particles, and a configuration mainly composed of metal oxide particles. “Mainly” means, for example, that the particles constitute 80% by mass or more of the entire particles contained in the second layer. In the present invention, when the particles constituting the second layer are mainly composed of metal particles, it is more preferable in terms of initial capacity and the like. On the other hand, when the particles constituting the second layer are mainly composed of metal oxide particles, it is more preferable in terms of cycle characteristics and the like.

  The negative electrode for a secondary battery of the present invention may be configured to further include a third layer having lithium ion conductivity on the second layer. By doing so, the initial capacity can be improved.

  In the secondary battery negative electrode of the present invention, the first layer is formed by binding a carbonaceous material with a binder, and is included in the binder contained in the first layer and the second layer. Any of the binders may be a fluorine-containing resin. When such a configuration is adopted, since the binder of the first layer and the second layer is both a fluorine-containing resin, stress due to expansion and contraction associated with insertion and extraction of lithium can be reduced, peeling of the negative electrode and fine powder Can be effectively suppressed.

  In the present invention, any coating method such as extrusion coater, reverse roller, doctor blade, etc. may be adopted as the coating method of the coating liquid, and when coating films are formed by lamination, these coating methods are combined appropriately. For example, a lamination method such as a simultaneous multilayer coating method or a sequential multilayer coating method can be employed.

In the present invention, it is possible to provide a lithium secondary battery having a higher capacity and excellent charge / discharge cycle characteristics by using a negative electrode having a multilayer structure in which a third layer is provided on the second layer. In the present invention, the substance constituting the third layer is not particularly limited as long as it is lithium or a compound containing lithium, but preferably metal lithium, lithium alloy, lithium nitride, Li _3-x M _x N (M = Co, Ni, Cu) and mixtures thereof. Since such a material can electrochemically release a large amount of lithium, it can supplement the irreversible capacity of the negative electrode and improve the charge / discharge efficiency of the battery. A part of lithium contained in the third layer is doped into the second layer made of a film material having lithium ion conductivity, thereby increasing the lithium ion concentration of the second layer and increasing the number of carriers. Therefore, the lithium ion conductivity is further improved. Thereby, the resistance of the battery can be reduced, and the effective capacity of the battery is further improved. In addition, since such an ion conductive film exists uniformly on the negative electrode, the electric field distribution between the positive electrode and the negative electrode becomes uniform. For this reason, local concentration of the electric field does not occur, and even if a cycle passes, damage such as separation of the active material from the current collector does not occur, and stable battery characteristics can be obtained.

  In the present invention, the substance constituting the third layer preferably has an amorphous structure. Since the amorphous structure is structurally isotropic compared to the crystal, it is chemically stable and hardly causes a side reaction with the electrolytic solution. For this reason, the lithium contained in the third layer is efficiently used to compensate for the irreversible capacity of the negative electrode.

  Further, in the present invention, when the third layer is formed, an effect may be obtained by any of a vacuum film forming method such as a vapor deposition method, a CVD method and a sputtering method, and a wet method such as a coating method. When these film forming methods are used, a uniform amorphous layer can be formed on the entire negative electrode. In particular, when a vacuum film forming method is adopted, it is not necessary to use a solvent, so that a side reaction is unlikely to occur and a higher-purity layer can be produced, and lithium contained in the third layer is efficiently irreversible for the negative electrode. Used to make up for capacity.

  A buffer layer may be provided between the first layer containing carbon as a main component and the second layer, or between the second layer and the third layer. The buffer layer has a role of increasing adhesion between layers, adjusting lithium ion conductivity, and preventing local electric field, and is a thin film containing metal, metal oxide, carbon, semiconductor, etc. Can do.

1 is an example of a schematic cross-sectional structure of secondary battery negative electrodes according to Examples 1 to 3 and Comparative Examples 1 to 3 of the present invention. It is an example of the schematic cross-section of the secondary battery negative electrode which concerns on Example 4-Example 8 and Comparative Example 4-Comparative Example 6 of this invention. It is an example which shows the outline of the copper foil in which the patterned graphite layer which concerns on Example 1- Example 8 and Comparative Example 1- Comparative Example 6 of this invention was formed. An outline of the copper foil when the patterned second layer 3a is formed on the patterned graphite layer according to Examples 1 to 3 and Comparative Examples 1 to 3 of the present invention. It is an example to show. A patterned second layer 3a and a patterned third layer 4a are formed on the patterned graphite layer according to Examples 4 to 8 and Comparative Examples 4 to 6 of the present invention. It is an example which shows the outline of the copper foil in the case of being done. It is an example of schematic structure of the vacuum evaporation system for producing the 2nd layer 3a and the 3rd layer 4a of the secondary battery negative electrode which concern on the comparative example 1- comparative example 6 and the Example 4-8.

  FIG. 1 is a cross-sectional view of the negative electrode of the nonaqueous electrolyte secondary battery according to this embodiment, and shows an example in which the negative electrode layer is composed of a first layer 2a and a second layer 3a.

  The copper foil 1a serving as a current collector acts as an electrode for taking out the current to the outside of the battery or taking in the current from the outside into the battery during charging and discharging. The current collector may be a conductive metal foil, and other than copper, for example, aluminum, stainless steel, gold, tungsten, molybdenum, or the like can be used.

  The carbon negative electrode that is the first layer 2a is a negative electrode member that occludes or releases Li during charging and discharging. This carbon negative electrode is carbon that can store Li, and examples thereof include graphite, fullerene, carbon nanotube, DLC (diamond-like carbon), amorphous carbon, hard carbon, or a mixture thereof.

  The second layer 3a is a negative electrode member having lithium ion conductivity, and is dispersed by adding one or more of metal particles, metal alloy particles or metal oxide particles and at least a binder and mixing them, It is formed by applying and drying a coating liquid. Examples of the lithium ion conductive negative electrode member include silicon, tin, germanium, lead, indium, boron oxide, phosphorus oxide, aluminum oxide, and complex oxides thereof. These may be used alone or in combination of one or more. it can. Further, lithium, lithium halide, lithium chalcogenide, or the like may be added thereto to increase lithium ion conductivity. The second layer may be provided with conductivity by adding an electron conduction aid (conductivity imparting material). The electron conduction aid is not particularly limited, but it is a powder made of a metal powder such as aluminum powder, nickel powder, copper powder, or a material having good electrical conductivity such as carbon powder generally used in batteries. Can be used. The binder of the second layer is not particularly limited. For example, polyvinyl alcohol, ethylene / propylene / diene terpolymer, styrene / butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, tetrafluoro An ethylene-hexafluoropropylene copolymer or the like is used.

  As shown in FIG. 1, the present invention is not limited to the structure in which the first carbon negative electrode layer and the second negative electrode layer are formed on both surfaces of the current collector. In the present invention, the negative electrode layer is formed only on one surface of the current collector. Also good. Moreover, when forming a negative electrode layer on both surfaces, the negative electrode material and structure of each surface are not necessarily the same.

  An example of the negative electrode structure when the third layer 4a is formed on the second layer 3a is shown in FIG.

The third layer 4a is a negative electrode member made of lithium or a lithium-containing compound. Examples of such a material include lithium metal, lithium alloy, lithium nitride, Li _3-x M _x N (M = Co, Ni, Cu) and a mixture thereof, and these may be used alone or in combination of one or more. Can do.

  As shown in FIG. 2, the present invention is not limited to the configuration in which the first carbon negative electrode layer, the second layer 3a, and the third layer 4a are formed on both surfaces of the current collector. In the present invention, only one surface of the current collector is used. A negative electrode layer may be formed. Moreover, when forming a negative electrode layer on both surfaces, the negative electrode material and structure of each surface are not necessarily the same.

The positive electrode that can be used in the lithium secondary battery of the present invention includes a composite oxide that is Li _x MO ₂ (where M represents at least one transition metal), such as Li _x CoO ₂ , Li _x NiO. _{2, Li x Mn 2 O 4} , Li x MnO 3, Li x Ni y C 1-y O 2 , etc., conductive materials such as carbon black, a binder such as polyvinylidene fluoride (PVDF) N-methyl A material obtained by dispersing and kneading a solvent such as -2-pyrrolidone (NMP) on a substrate such as an aluminum foil can be used.

  Moreover, as a separator which can be used in the lithium secondary battery of the present invention, a polyolefin film such as polypropylene or polyethylene, or a porous film such as a fluororesin can be used.

Moreover, as electrolyte solution, cyclic carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl Linear carbonates such as carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2- Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, di Oxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, Aprotic organic solvents such as propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, etc. are used alone or in admixture of two or more. Dissolve the lithium salt to be dissolved. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lithium of lower aliphatic carboxylic acid carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides and the like. Further, a polymer electrolyte may be used instead of the electrolytic solution.

  The shape of the battery is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a coin shape. Further, the outer packaging of the battery is not particularly limited, and examples thereof include a metal can and a metal laminate type.

( Reference Example 1)
Reference Example 1 will explain the present invention in more detail. The configuration of the battery according to this reference example is the same as that shown in FIG. 1, and has a configuration in which a first layer 2a and a second layer 3a are stacked on a copper foil 1a serving as a current collector. Yes. Graphite was used as a main component as the carbon negative electrode of the first layer 2a. The second layer was mainly formed by dispersing Si powder in a binder, and was formed by a coating method. Hereafter, the manufacturing method of this battery is demonstrated.

  First, as shown in FIG. 3, a copper foil 20 having a length of about 2000 m and a thickness of 10 μm is used for a negative electrode current collector as a flexible support, and a first layer 2 a made of graphite is formed thereon with a thickness of about 50 μm. Deposited. The first layer 2a made of graphite is made of a graphite powder mixed with polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone as a binder and a conductive material, and is made into a paste on both sides of a copper foil. A film was formed by a coating method using a blade. The pattern of the graphite application part is shown in FIG. On the surface side of the copper foil, there is an uncoated portion having a left end portion of 7 m and a right end portion of 6.42 m. The graphite coating part is formed with a width of 0.16 m from the position of the left end part 7 m and a pitch method 0.43 m pitch (coating part: 0.41 m, space: 0.02 m), and there are 4620 graphite coating parts. . On the other hand, there is an uncoated portion having a left end portion of 7 m and a right end portion of 6.48 m on the back surface side. The graphite application part is formed at a pitch of 0.43 m (application part: 0.35 m, space: 0.08 m) from the position of the left end part 7 m, and there are 4620 graphite application parts.

  On the first layer made of carbon, a second layer 3a mainly made of silicon is formed to a thickness of about 3 μm by a coating method using a doctor blade. A Si powder having an average particle size of 1 μm and a conductivity-imparting material are mixed and dispersed in polyvinylidene fluoride dissolved in N-methylpyrrolidone to prepare a coating liquid, and then the coating liquid is formed on the first layer 2a composed of the graphite layer. It was applied in the same manner as above and dried at 130 ° C.

Next, from the copper foil on which this negative electrode layer is formed, the width is 0.04 m per piece, and the longitudinal direction is 0.43 m (surface coated part 0.41 m, surface uncoated part 0.02 m, back coated part 0.35 m, back uncoated part 0.08 m) The negative electrode was cut out so that 4620 × 4 negative electrodes could be made. A second layer containing Si was uniformly formed (same film thickness) on all the graphite layers (first layer 2a). The uncoated part was used as a terminal extraction part. In this way, the laminated negative electrode (FIGS. 1 and 4) used in Reference Example 1 was produced.

  These negative electrodes are combined with a positive electrode obtained by dispersing and kneading lithium cobaltate, a conductive agent, polyvinylidene fluoride, etc. with N-methyl-2-pyrrolidone on an aluminum foil. Battery).

In addition, the polypropylene nonwoven fabric was used for the separator. A mixed solvent (mixing volume ratio: EC / DEC = 30/70) mainly containing ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF ₆ having a concentration of 1 mol / L was dissolved was used as the electrolytic solution. .

The battery using the negative electrode of Reference Example 1 was subjected to a charge / discharge cycle test. The voltage range of the charge / discharge test was 3 to 4.3V. The results of the reference examples are shown in Table 1 (Comparative examples are shown in Table 2). The initial charge / discharge efficiency of Comparative Example 1 is 82.6%, while that of Reference Example 1 is 90.1%. From this result, the initial charge / discharge efficiency of Reference Example 1 is the second in vacuum deposition. It turns out that it is higher than the comparative example 1 which formed the layer (Si).

When the discharge capacity of one cycle is assumed to be 100%, the ratio of the discharge capacity of 500 cycles to that (discharge capacity ratio: C500 / C1) maintains 80% or more of the initial capacity after 500 cycles. Much better than Example 1 (51.5%). The reason why Reference Example 1 has better charge / discharge efficiency and cycle characteristics than Comparative Example 1 is that in Reference Example 1, the binder (PVDF) present in the first layer 2a is not damaged by heat, This is thought to be due to the reduction in the adhesive strength with the current collector and the decomposition of the binder itself. Further, the second layer 3a is firmly adhered to the first layer 2a due to the action of the adhesive force of the binder contained in the second layer 3a, and it becomes difficult to peel off, and the peeling and pulverization due to expansion and contraction can be suppressed. It is thought that it was because of.

The net film formation time (time required for double-sided coating) of the second layer 3a is about 2.7 hours with a copper foil of 2000 m, and the film formation time of Comparative Example 1 (time required for double-sided vapor deposition: 67 hours). In this reference example 1 in which the film was formed on the copper foil 2000 m, the manufacturing time of the negative electrode (second layer 3a) was about 1/25.

From the evaluation results in Reference Example 1, the secondary battery including the negative electrode according to the present invention can realize a significant reduction in the production time of the negative electrode in mass production, has high initial charge / discharge efficiency, and stable cycle characteristics. Proven to be.

(Example 2)
A negative electrode was produced in the same manner as in Reference Example 1 except that the active material contained in the second layer 3a was a Li: Si alloy, and battery characteristics were evaluated. The results are shown in Table 1. The initial charge / discharge efficiency of Comparative Example 2 is 84.4%, while that of Example 2 is 92.4%. From this result, the initial charge / discharge efficiency of Example 2 is the second in vacuum deposition. It turns out that it is higher than the comparative example 2 which formed the layer 3a (Li: Si alloy).

  When the discharge capacity of one cycle is assumed to be 100%, the ratio of the discharge capacity of 500 cycles to that (discharge capacity ratio: C500 / C1) maintains 80% or more of the initial capacity after 500 cycles. Much better than Example 2 (57.1%). The reason why Example 2 has better charge / discharge efficiency and cycle characteristics than Comparative Example 2 is that in Example 2, the binder (PVDF) present in the first layer 2a is not damaged by heat, This is thought to be due to the reduction in the adhesive strength with the current collector and the decomposition of the binder itself. In addition, the adhesive force of the binder contained in the first layer 2a and the second layer 3a works, and the second layer 3a firmly adheres to the first layer 2a and is difficult to peel off. This is thought to be due to the fact that it was possible to suppress the conversion.

  The net film formation time of the second layer 3a (time required for double-sided application) is about 2.7 hours for a copper foil of 2000 m, and the film formation time of Comparative Example 2 (time required for double-sided vapor deposition: 67 hours). The production time of the negative electrode (second layer 3a) was about 1/25 in the present Example 2 in which the film was formed on the copper foil 2000m, much less than the above.

  From the evaluation results in Example 2, the secondary battery including the negative electrode according to the present invention can realize a significant reduction in the production time of the negative electrode in mass production, has high initial charge / discharge efficiency, and stable cycle characteristics. Proven to be.

( Reference Example 3)
A negative electrode was produced in the same manner as in Reference Example 1 except that the active material contained in the second layer 3a was SiO _x , and battery characteristics were evaluated. The results are shown in Table 1.

The initial charge / discharge efficiency of Comparative Example 3 is 74.3%, while that of Reference Example 3 is 89.1%. From this result, the initial charge / discharge efficiency of Reference Example 3 is the second in vacuum deposition. it can be seen that higher than Comparative example 3 in which a layer 3a (SiO _x).

When the discharge capacity of one cycle is 100%, the ratio of the discharge capacity of 500 cycles to that (discharge capacity ratio: C500 / C1) retains 80% of the initial capacity even after 500 cycles. Much better than 3 (failed after 220 cycles). The reason why Reference Example 3 has better charge / discharge efficiency and cycle characteristics than Comparative Example 3 is that, in Reference Example 3, the binder (PVDF) present in the first layer 2a is not damaged by heat, This is thought to be due to the reduction in the adhesive strength with the current collector and the decomposition of the binder itself. In addition, the adhesive force of the binder contained in the first layer 2a and the second layer 3a works, and the second layer 3a firmly adheres to the first layer 2a and is difficult to peel off. This is thought to be due to the fact that it was possible to suppress the conversion.

The net film formation time (time required for double-sided coating) of the second layer 3a is about 2.7 hours for a copper foil of 2000 m, and the film formation time of Comparative Example 3 (time required for double-sided vapor deposition: 67 hours). In this reference example 3 in which the film was formed on the copper foil 2000 m, the manufacturing time of the negative electrode (second layer 3a) was about 1/25.

From the evaluation results in Reference Example 3, the secondary battery including the negative electrode according to the present invention can realize a significant reduction in the production time of the negative electrode in mass production, has high initial charge / discharge efficiency, and stable cycle characteristics. Proven to be.

(Comparative Example 1)
As Comparative Example 1, a laminated negative electrode in which a Si layer (second layer 3a) was formed by vacuum deposition on a copper foil current collector (FIG. 3) on which a carbon negative electrode was formed as in Reference Example 1. Produced.

  A schematic internal configuration of the vacuum film forming apparatus used in Comparative Example 1 is shown in FIG. Basically, it comprises a traveling mechanism of the copper foil 1a and a moving mechanism of the movable shielding mask 9 provided for forming the copper foil 1a and an undeposited portion for taking out the terminal. The movable shielding mask 9 has a width of 2 cm for the front surface of the copper foil 1a and a width of 8 cm for the back surface. From unwinding to unwinding of the copper foil 1a, the unwinding roller 5 for unwinding the copper foil 1a, the close contact and synchronization of the copper foil 1a sent from the unwinding roller 5 and the movable shielding mask 9 are synchronized. It is comprised from the can roller 8 for raising the precision of the film-forming to perform, and the winding roller 6 for winding up the copper foil 1a sent from the can roller 8. FIG. In addition, a position detector 7 is provided between the unwinding roller 5 and the can roller 8 so that an uncoated portion in a vacuum can be accurately detected and patterning by the movable shielding mask 9 can be accurately performed. It is. The distance between the evaporation source 10 and the lowermost portion of the can roller 8 was 25 cm. The gap between the movable shielding mask 9 and the copper foil 1a was set to 1 mm or less. The movable shielding mask 9 moves so as to shield the uncoated portion in synchronism with the copper foil 1a during film formation (from right to left in the figure). When the film formation for the first pitch is completed, it returns so as not to block the evaporated substance (from left to right in the figure), and it is installed so as to block the uncoated portion of the second electrode pitch. By repeating this, patterning by vacuum film formation on all the graphite layers becomes possible.

First, a Si layer (thickness 3 μm) is formed by patterning on the patterned graphite layer on the surface side of the copper foil 1a by vacuum deposition. As the initial installation state of the copper foil 1a, the winding core of the copper foil 1a previously produced was attached to the unwinding roller 5 shown in FIG. The copper foil 1 a was moved along the can roller 8, and the tip of the copper foil 1 a was attached to the take-up roller 6. All or a part of the rollers were driven to give an appropriate tension to the copper foil 1a and brought into close contact with the can roller 8 on the evaporation source 10 without causing the copper foil 1a to sag or bend. The vacuum evacuation apparatus 11 was operated to evacuate the vacuum chamber to a vacuum of 1 × 10 ⁻⁴ Pa, and then film formation was performed.

  By driving all the rollers, the copper foil 1a and the movable shielding mask 9 are run at an arbitrary speed while being synchronized, Si is continuously evaporated from the evaporation source 10, and the graphite on the surface side of the copper foil 1a. A Si layer was formed on the layer. The traveling speed of the copper foil 1a is 1 m / min, and the traveling film forming speed is 3 μm · m / min. After film formation, Ar gas was introduced into the chamber using the gas introduction valve 12, the chamber was opened, and the copper foil 1a taken up by the take-up roller 6 was taken out.

Next, an active material made of Si was formed by patterning on the patterned graphite layer on the back side of the copper foil 1a by vacuum deposition. As the initial installation state of the copper foil 1a, the winding core of the copper foil 1a previously produced was attached to the unwinding roller 5 shown in FIG. The copper foil 1 a was moved along the can roller 8, and the tip of the copper foil 1 a was attached to the take-up roller 6. All or a part of the rollers were driven to give an appropriate tension to the copper foil 1a and brought into close contact with the can roller 8 on the evaporation source 10 without causing the copper foil 1a to sag or bend. After the vacuum evacuation device 11 was operated and the inside of the vacuum chamber was evacuated to a vacuum of 1 × 10 ⁻⁴ Pa, film formation was performed. By driving all the rollers, the copper foil 1a and the movable shielding mask 9 are run at an arbitrary speed while being synchronized, Si is continuously evaporated from the evaporation source, and the graphite layer on the surface side of the copper foil 1a A Si layer was formed on the substrate. After film formation, Ar gas was introduced into the chamber using the gas introduction valve 12, the chamber was opened, and the copper foil 1a taken up by the take-up roller 6 was taken out.

A battery having the same configuration as that of Reference Example 1 was produced using the negative electrode produced using the vacuum deposition method in this manner (FIGS. 1 and 4). The results are shown in Table 2. It was confirmed that the characteristics of Comparative Example 1 were inferior to Reference Example 1. The reason for this is considered that the binder (PVDF) present in the first layer 2a is damaged by radiant heat during vacuum deposition of Si, leading to a decrease in adhesive strength with the current collector, decomposition of the binder itself, and the like. It is done. Moreover, it is thought that it is also caused by pulverization and peeling of the deposited Si layer itself.

(Comparative Example 2)
A battery was produced in the same manner as in Comparative Example 1 except that the active material contained in the second layer 3a was a Si: Li alloy, and the battery characteristics were evaluated. The results are shown in Table 2. The reason why the characteristics of Comparative Example 2 are inferior to those of Example 2 is that the binder (PVDF) present in the first layer 2a is damaged by radiant heat during the vacuum deposition of the Li: Si alloy, and adheres to the current collector. This is thought to be caused by a decrease in force and decomposition of the binder itself. Moreover, it is thought that the vaporized Li: Si alloy layer itself is pulverized or peeled off.

(Comparative Example 3)
A battery was produced in the same manner as in Comparative Example 1 except that the active material contained in the second layer 3a was SiO _x , and the battery characteristics were evaluated. The results are shown in Table 2. The reason why the characteristics of Comparative Example 3 are inferior to those of Reference Example 3 is that the binder (PVDF) present in the first layer 2a is damaged by radiant heat during the vacuum deposition of SiO _x , and the adhesive strength with the current collector is reduced. This is thought to be caused by a decrease and decomposition of the binder itself. Moreover, it is thought that the vaporized SiO _x layer itself is pulverized or peeled off.

( Reference Example 4)
In this reference example, the negative electrode having a three-layer structure in which the Li layer as the third layer 4a is further formed on the second layer 3a in the configuration of the negative electrode shown in the reference example 1 (FIGS. 2 and 5). This is an example. The materials for the current collector, the first layer 2a, and the second layer 3a and the production method thereof are the same as those in Reference Example 1.

  The copper foil with the negative electrode formed up to the second layer 3a is set in the vacuum vapor deposition apparatus shown in Comparative Example 1, the metal Li is set in the evaporation source, and the copper foil is run at a traveling vapor deposition rate of 12 μm · m / min. The Li layer as the third layer 4a was formed to 2 μm on the negative electrode layer (FIG. 5). “Μm · m / min” refers to the film thickness formed while the copper foil travels 1 meter per minute. For example, at a traveling deposition rate of “12 μm · m / min”, a film having a thickness of 12 μm is formed while the copper foil is traveling for 1 meter per minute.

The results are shown in Table 3. The initial charge / discharge efficiency of Comparative Example 4 is 83.3%, while that of Reference Example 4 is 93.9%. From this result, the initial charge / discharge efficiency of Reference Example 4 is the second by vacuum deposition. It turns out that it is higher than the comparative example 4 which formed layer 3a (Si). In addition, by providing the third layer 4 a made of a lithium layer, the charge / discharge efficiency was further higher than that of the two-layered negative electrode of Reference Example 1.

When the discharge capacity of one cycle is assumed to be 100%, the ratio of the discharge capacity of 500 cycles to that (discharge capacity ratio: C500 / C1) maintains 80% or more of the initial capacity after 500 cycles. Much better than Example 4 (55.8%). The reason why Reference Example 4 has better charge / discharge efficiency and cycle characteristics than Comparative Example 4 is that in Reference Example 4, the binder (PVDF) present in the first layer 2a is not damaged by heat, This is thought to be due to the reduction in the adhesive strength with the current collector and the decomposition of the binder itself. In addition, the adhesive force of the binder contained in the first layer 2a and the second layer 3a works, and the second layer 3a firmly adheres to the first layer 2a and is difficult to peel off. This is thought to be due to the fact that it was possible to suppress the conversion.

  The net film formation time of the second layer 3a (time required for double-sided coating) is about 2.7 hours for a copper foil of 2000 m, and the film formation time of the second layer of Comparative Example 4 (time required for double-sided vapor deposition) : 67 hours).

From the evaluation results in Reference Example 4, the secondary battery including the negative electrode according to the present invention can realize a significant reduction in the production time of the negative electrode in mass production, has high initial charge / discharge efficiency, and stable cycle characteristics. Proven to be.

(Example 5)
This example is an example of a negative electrode having a three-layer structure in which the Li layer as the third layer 4a is further formed on the second layer 3a in the structure of the negative electrode shown in Example 2 (FIGS. 2 and 5). ). The materials for the current collector, the first layer 2a, and the second layer 3a and the production method thereof are the same as in Example 2.

  The copper foil with the negative electrode formed up to the second layer 3a is set in the vacuum vapor deposition apparatus shown in Comparative Example 1, metal Li is set in the evaporation source, and the traveling vapor deposition rate is 12 μm · m / min. On the negative electrode layer of the copper foil, 2 μm of the Li layer as the third layer 4a was formed (FIG. 5).

The results are shown in Table 3. The initial charge / discharge efficiency of Comparative Example 5 is 85.8%, while that of Example 5 is 94.5%. From this result, the initial charge / discharge efficiency of Example 5 is the second by vacuum deposition. It turns out that it is higher than the comparative example 5 which formed layer 3a (Li: Si). In addition, by providing the third layer 4a made of a lithium layer, the charge / discharge efficiency was higher than that of the two-layered negative electrode of Example 2.

  When the discharge capacity of one cycle is assumed to be 100%, the ratio of the discharge capacity of 500 cycles to that (discharge capacity ratio: C500 / C1) maintains 80% or more of the initial capacity after 500 cycles. Much better than Example 5 (59.4%). The reason why Example 5 has better charge / discharge efficiency and cycle characteristics than Comparative Example 5 is that in Example 5, the binder (PVDF) present in the first layer 2a is not damaged by heat, This is thought to be due to the reduction in the adhesive strength with the current collector and the decomposition of the binder itself. In addition, the adhesive force of the binder contained in the first layer 2a and the second layer 3a works and the second layer 3a is firmly adhered to the first layer 2a and is difficult to peel off. This is thought to be due to the fact that it was possible to suppress the conversion.

  The net film formation time (time required for double-sided coating) of the second layer 3a is about 2.7 hours for a copper foil of 2000 m, and the film formation time of the second layer of Comparative Example 5 (required for double-sided vapor deposition). Time: 67 hours).

  From the evaluation results in Example 5, the secondary battery including the negative electrode according to the present invention can realize a significant reduction in the production time of the negative electrode in mass production, has high initial charge / discharge efficiency, and stable cycle characteristics. Proven to be.

( Reference Example 6)
In this reference example, an example of a negative electrode having a three-layer structure in which the Li layer as the third layer 4a is further formed on the second layer 3a in the configuration of the negative electrode shown in the reference example 3 (FIGS. 2 and 2). 5). The constituent materials and the manufacturing method of the current collector, the first layer 2a, and the second layer 3a are the same as in Reference Example 3.

  The copper foil with the negative electrode formed up to the second layer 3a was set in the vacuum vapor deposition apparatus shown in Comparative Example 1, and the metal Li was set in the evaporation source and the copper was deposited at a traveling vapor deposition rate of 12 μm · m / min. On the negative electrode layer of the foil, 2 μm of the Li layer as the third layer 4a was formed (FIG. 5).

The results are shown in Table 3. The initial charge / discharge efficiency of Comparative Example 6 is 66.2%, while that of Reference Example 6 is 92.3%. From this result, the initial charge / discharge efficiency of Reference Example 6 is the second in vacuum deposition. it can be seen that higher than Comparative example 6 to form a layer 3a (SiO _x). In addition, by providing the third layer 4 a made of a lithium layer, the charge / discharge efficiency was further higher than that of the two-layered negative electrode of Reference Example 3.

When the discharge capacity of one cycle is assumed to be 100%, the ratio of the discharge capacity of 500 cycles to that (discharge capacity ratio: C500 / C1) maintains 80% or more of the initial capacity after 500 cycles. Much better than Example 6 (failure after 230 cycles). The reason why Reference Example 6 has better charge / discharge efficiency and cycle characteristics than Comparative Example 6 is that in Reference Example 6, the binder (PVDF) present in the first layer 2a is not damaged by heat, This is thought to be due to the reduction in the adhesive strength with the current collector and the decomposition of the binder itself. In addition, the adhesive force of the binder contained in the first layer 2a and the second layer 3a works, and the second layer 3a firmly adheres to the first layer 2a and is difficult to peel off. This is thought to be due to the fact that it was possible to suppress the conversion.

  Furthermore, the net film formation time of the second layer 3a (time required for double-sided coating) is about 2.7 hours for a copper foil of 2000 m, and the film formation time of the second layer of Comparative Example 6 (for double-sided vapor deposition). Time required: 67 hours).

From the evaluation results in Reference Example 6, the secondary battery including the negative electrode according to the present invention can realize a significant reduction in the production time of the negative electrode in mass production, has high initial charge / discharge efficiency, and stable cycle characteristics. Proven to be.

(Comparative Example 4)
In this comparative example 4, in the negative electrode configuration shown in comparative example 1, an example of a negative electrode having a three-layer structure in which a Li layer as the third layer 4a is further formed on the second layer 3a (FIG. 2, FIG. FIG. 5) is shown. The materials of the current collector, the first layer 2a, and the second layer 3a and the production method thereof are the same as those in Comparative Example 1.

  The copper foil with the negative electrode formed up to the second layer 3a was set in the vacuum vapor deposition apparatus shown in Comparative Example 1, and the metal Li was set in the evaporation source and the copper was deposited at a traveling vapor deposition rate of 12 μm · m / min. On the negative electrode layer of the foil, 2 μm of the Li layer as the third layer 4a was formed (FIG. 5).

Table 4 shows the results. The reason why the characteristics of Comparative Example 4 are inferior to those of Reference Example 4 is that the binder (PVDF) present in the first layer 2a is damaged by radiant heat during the vacuum deposition of the second layer 3a (Si), and the current collection This is thought to be due to a decrease in the adhesive strength with the body and the decomposition of the binder itself. Moreover, it is thought that it is also caused by pulverization and peeling of the deposited Si layer itself.

(Comparative Example 5)
In this comparative example, an example of a negative electrode having a three-layer structure in which the Li layer as the third layer 4a is further formed on the second layer 3a in the configuration of the negative electrode shown in the comparative example 2 (FIG. 2, FIG. 5). The constituent materials and manufacturing methods of the current collector, the first layer 2a, and the second layer 3a are the same as those in Comparative Example 2.

  The copper foil with the negative electrode formed up to the second layer 3a is set in the vacuum vapor deposition apparatus shown in Comparative Example 1, the metal Li is set in the evaporation source, and the copper foil is run at a traveling vapor deposition rate of 12 μm · m / min. The Li layer as the third layer 4a was formed to 2 μm on the negative electrode layer (FIG. 5).

  The results are shown in Table 4. The reason why Comparative Example 5 is inferior to Example 5 is that the binder (PVDF) present in the first layer 2a is damaged by radiant heat during the vacuum deposition of the second layer 3a (Li: Si), This is thought to be due to a decrease in the adhesive strength with the current collector and the decomposition of the binder itself. Moreover, it is thought that the vapor deposition Li: Si layer itself is pulverized or peeled off.

(Comparative Example 6)
In this comparative example, an example of a negative electrode having a three-layer structure in which the Li layer as the third layer 4a is further formed on the second layer 3a in the configuration of the negative electrode shown in the comparative example 3 (FIG. 2, FIG. 5).

  The materials for the current collector, the first layer 2a, and the second layer 3a and the production method thereof are the same as those in Comparative Example 3.

  The copper foil with the negative electrode formed up to the second layer 3a was set in the vacuum vapor deposition apparatus shown in Comparative Example 1, and the metal Li was set in the evaporation source and the copper was deposited at a traveling vapor deposition rate of 12 μm · m / min. On the negative electrode layer of the foil, 2 μm of the Li layer as the third layer 4a was formed (FIG. 5).

The results are shown in Table 4. The reason why Comparative Example 6 is inferior to Reference Example 6 is that the binder (PVDF) present in the first layer 2a is damaged by radiant heat during the vacuum deposition of the second layer 3a (SiO _x ). This is thought to be due to a decrease in the adhesive strength with the electric body and the decomposition of the binder itself. Moreover, it is thought that the vaporized SiO _x layer itself is pulverized or peeled off.

( Reference Example 7)
In this reference example, in the configuration of the negative electrode shown in Reference Example 4, the average particle diameter of Si particles contained in the second layer 3a (thickness: 3 μm) is changed, and further the Li layer as the third layer 4a The example of the negative electrode (FIG. 2, FIG. 5) of the three-layer structure which formed (2 micrometers) is shown. The manufacturing method of the current collector, the first layer 2a, and the second layer 3a is the same as in Reference Example 1.

  The copper foil with the negative electrode formed up to the second layer 3a is set in the vacuum vapor deposition apparatus shown in Comparative Example 1, the metal Li is set in the evaporation source, and the copper foil is run at a traveling vapor deposition rate of 12 μm · m / min. The Li layer as the third layer 4a was formed to 2 μm on the negative electrode layer (FIG. 5).

The results are shown in Table 4. When the average particle size of Si contained in the second layer 3a is 2.4 μm or less (80% or less of the thickness of the second layer 3a), the initial charge / discharge efficiency is as high as 90% or more, and charge / discharge is repeated 500 cycles. Even so, the discharge capacity ratio (C500 / C1) maintains 80% or more of the initial capacity. On the other hand, when the average particle size of Si contained in the second layer 3a is 2.5 μm or more (exceeding 80% of the thickness of the second layer 3a), the initial charge / discharge efficiency is 80% or less, and the charge / discharge is 500%. The cycle could not be repeated, causing a short circuit or failure. In the present Reference Example 7, when the average particle size of Si is 2.5 μm or more (exceeding 80% of the thickness of the second layer 3a), the reason for the occurrence of the short circuit is that the irregularities on the surface of the second layer 3a are large. As a result, it is considered that a short circuit occurred with the positive electrode.

From the evaluation results in Reference Example 7, in the negative electrode for secondary battery according to the present invention, the average particle diameter of the active material (metal) particles contained in the second layer 3a is 80% of the thickness of the second layer 3a. The following proved to be preferable.

( Reference Example 8)
In this reference example, in the configuration of the negative electrode shown in Reference Example 6, the average particle diameter of the SiO _x particles contained in the second layer 3a (thickness: 3 μm) was changed, and Li 3 as the third layer 4a was further changed. The example of the negative electrode (FIG. 2, FIG. 5) of the three-layer structure in which the layer (2 micrometers) was formed is shown. The method for producing the current collector, the first layer 2a, and the second layer 3a is the same as in Reference Example 7.

  The copper foil with the negative electrode formed up to the second layer 3a is set in the vacuum vapor deposition apparatus shown in Comparative Example 1, the metal Li is set in the evaporation source, and the copper foil is run at a traveling vapor deposition rate of 12 μm · m / min. The Li layer as the third layer 4a was formed to 2 μm on the negative electrode layer (FIG. 5).

The results are shown in Table 5. When the average particle diameter of SiO _x contained in the second layer 3a is 2.4 μm or less (80% or less of the thickness of the second layer 3a), the initial charge / discharge efficiency is as high as 80% or more, and charge / discharge is performed 500 cycles. Even if it repeats, the discharge capacity ratio (C500 / C1) maintains 88% or more of the initial capacity. On the other hand, when the average particle diameter of SiO _x contained in the second layer 3a is 2.5 μm or more (exceeding 80% of the thickness of the second layer 3a), the initial charge / discharge efficiency falls below 80%, 500 cycles could not be repeated and a short circuit or failure occurred on the way. In this reference example 8, when the average particle diameter of SiO _x is 2.5 μm or more (exceeding 80% of the thickness of the second layer 3a), the reason for the occurrence of the short circuit is the unevenness of the surface of the second layer 3a. This is thought to be due to a short circuit with the positive electrode as a result.

From the evaluation results in the present Reference Example 8, in the negative electrode for secondary battery according to the present invention, the average particle diameter of the active material (metal oxide) particles contained in the second layer 3a is the thickness of the second layer 3a. It proved to be preferable to be 80% or less.

  As described above, the negative electrode according to the present invention is a negative electrode having a configuration in which one or more particles selected from metal particles, alloy particles, and metal oxide particles are bound by a binder. This layer firmly adheres to the first layer, and the mechanical strength of the multilayer film is improved. Therefore, a high battery capacity can be obtained while maintaining high charge / discharge efficiency and good cycle characteristics with a simple manufacturing method.

  The negative electrode manufacturing method according to the present invention includes a second method in which at least one of metal particles, alloy particles, and metal oxide particles is dispersed in a solution in which a binder is dissolved, and the coating liquid is applied and dried. Since a layer is formed, a high-capacity secondary battery with less thermal damage such as a binder and excellent cycle characteristics can be realized than a conventional multilayered negative electrode manufactured by vacuum film formation.

  In the present invention, if the average particle size of the metal particles, alloy particles, or metal oxide particles contained in the second layer is 80% or less of the thickness of the second layer, the film thickness can be easily controlled. Thus, it becomes possible to produce a secondary battery that does not cause a short circuit. Further, by forming the second layer of the negative electrode by employing the coating method, the film formation rate is significantly higher than when the conventional vacuum film formation method is used, and the negative electrode manufacturing time can be greatly shortened.

DESCRIPTION OF SYMBOLS 1a Copper foil 2a 1st layer 3a 2nd layer 4a 3rd layer 5 Unwinding roller 6 Winding roller 7 Position detector 8 Can roller 9 Movable shielding mask 10 Evaporation source 11 Vacuum exhaust apparatus 12 Gas introduction valve 20 Copper foil

Claims (4)

A negative electrode for a secondary battery in which a current collector, a first layer mainly composed of carbon, and a second layer mainly composed of a film-like material having lithium ion conductivity are laminated in this order. A manufacturing method comprising:
Forming the first layer by applying a coating solution containing carbon as a main component and containing a binder to the current collector ;
Forming a second layer by applying a coating liquid containing Li: Si alloy particles and a binder to the surface of the first layer and then drying the coating liquid;
Including
The method for producing a negative electrode for a secondary battery, wherein the Li: Si alloy particles have an average particle size of 80% or less of the thickness of the second layer.   2. The method for producing a negative electrode for a secondary battery according to claim 1, wherein the particles constituting the second layer are mainly Li: Si alloy particles. 3.   3. The method for manufacturing a negative electrode for a secondary battery according to claim 1, further comprising a step of forming a third layer having lithium ion conductivity on the second layer. The manufacturing method of the negative electrode for secondary batteries. In the manufacturing method of the negative electrode for secondary batteries of Claim 3,
After the coating liquid containing the carbonaceous material and the binder is applied to the surface of the current collector, the first layer is formed by drying the coating liquid containing the carbonaceous material and the binder. ,
A method for producing a negative electrode for a secondary battery, wherein a fluorine-containing resin is used as both the binder contained in the first layer and the binder contained in the second layer.

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