JP2005293942A - Method for manufacturing negative electrode for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a negative electrode for secondary batteries having superior coherency and high capacity. <P>SOLUTION: An active material layer on a collector is formed through a process for manufacturing slurry containing at least a carbon material, a metal oxide, and a coupling agent, a process for applying the slurry onto the collector, and a process for drying the slurry. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a negative electrode for a secondary battery, and more particularly to a method for producing a negative electrode for a secondary battery having excellent electrode adhesion.

  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. Secondary batteries are required to be smaller, lighter, have higher capacity, have higher energy density, and have a longer life. In order to satisfy these requirements, various improvements have been made particularly on the electrodes.

  The electrode is composed of an active material layer containing an active material, a conductive agent and a binder, and a current collector. For the purpose of increasing the capacity, for example, the ratio of the binder in the active material layer is small. An electrode having a high proportion of the active material, an electrode using a high-capacity material as the active material, and the like are being studied.

  However, a secondary battery using an electrode with a small binder ratio or an electrode using a high-capacity material has a problem that the active material easily peels off from the electrode during charge and discharge. Such a problem is caused by the volume of the active material changing due to the occlusion and release of lithium ions by the active material during charging and discharging of the secondary battery. An electrode with a small proportion of the binder has a weak adhesion between the active material materials or between the active material and the current collector. In addition, an electrode using a high-capacity material has a large volume change of the active material when the active material absorbs and releases lithium ions. Therefore, these electrodes with a low binder ratio and electrodes using a high-capacity material separate the active material from each other or the active material from the current collector when the volume of the active material changes. There is a difficulty that it becomes easy. For this reason, since the charge / discharge of the secondary battery is repeated, the adhesion between the active material or the adhesion between the active material and the current collector (hereinafter referred to as electrode adhesion) gradually deteriorates. In addition, the capacity of the electrode is lowered. As a result, a secondary battery using such an electrode has a problem that cycle characteristics are deteriorated.

On the other hand, in order to improve the adhesiveness of an electrode, for example, an electrode in which an active material layer is formed on a current collector via a coupling agent layer has been reported (see Patent Document 1). It is described that since this electrode has excellent adhesion of the active material layer to the current collector, it is possible to prevent peeling, dropping and cracking of the active material layer. Moreover, the electrode which processed the active material layer or the active material with the coupling agent is described (refer patent document 2). According to the description of Patent Document 2, this electrode is described as having high charge / discharge efficiency and excellent cycle characteristics.
JP-A-9-237625 (see claim 1, paragraph number 0034) JP 11-354104 A (refer to claim 1, claim 15, paragraph number 0014, paragraph numbers 0039 to 0046)

  Since the coupling agent has an inorganic reactive group and an organic reactive group, the inorganic reactive group is bonded to the inorganic material and the organic reactive group X is bonded to the organic material as shown in FIG. And organic materials adhere to each other. At this time, a strong bond is formed between the inorganic reactive group of the coupling agent and the inorganic material, and a weak bond is formed between the organic reactive group of the coupling agent and the organic material.

  For this reason, when the electrode described in Patent Documents 1 and 2 uses a carbon material as an active material, a weak bond is formed between the organic reactive group of the coupling agent and the carbon material. When the secondary battery is charged / discharged, the carbon material is easily peeled from the electrode, and the secondary battery is repeatedly charged / discharged, whereby the electrode adhesion may gradually deteriorate. Furthermore, a secondary battery using such an electrode has a problem that cycle characteristics are likely to deteriorate.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for producing a high-capacity negative electrode for a secondary battery having excellent electrode adhesion.

  The method for producing a negative electrode for a secondary battery according to the present invention for solving the above-described problem includes a step of producing a slurry in which an active material layer on a current collector contains at least a carbon material, a metal oxide, and a coupling agent. The slurry is formed through a step of applying the prepared slurry onto a current collector and a step of drying the applied slurry.

  According to this invention, since the slurry contains at least a carbon material, a metal oxide, and a coupling agent, the active material layer after drying has a network shape in which the coupling agent and the metal oxide are both strongly bonded. A structure is formed, and a carbon material is included in the network structure. As a result, the negative electrode for a secondary battery in which such an active material layer is formed on the current collector has a high capacity and excellent adhesion.

  The method for producing a negative electrode for a secondary battery of the present invention is the above-described production method of the present invention, wherein the slurry is mixed by adding a solvent to a mixture of at least a carbon material, a metal oxide, and a coupling agent, Alternatively, it is produced by adding at least a carbon material and a metal oxide to a solvent and mixing them.

  According to this invention, since the carbon material, the metal oxide, and the coupling agent are dispersed in the slurry, the active material layer formed from such a slurry has a network structure in which the coupling agent and the metal oxide are combined. In this structure, the carbon material is dispersed therein, and the coupling state between the metal oxide, the carbon material, the current collector, and the coupling agent is improved. As a result, the obtained negative electrode for a secondary battery has a high capacity and excellent adhesion.

  The method for producing a negative electrode for a secondary battery of the present invention is the above-described production method of the present invention, wherein the mass ratio (carbon material: metal oxide) of the carbon material and metal oxide contained in the slurry is 1: 9-9. : 1.

  According to this invention, since the ratio between the carbon material and the metal oxide is within the above range, the coupling state between the metal oxide, the carbon material, and the current collector, and the coupling agent is improved. . As a result, the obtained negative electrode for a secondary battery has excellent adhesion.

  The manufacturing method of the negative electrode for secondary batteries of this invention is the manufacturing method of the said invention. WHEREIN: The said coupling agent exists in the range of 0.1-5 mass% with respect to the active material layer formed through the said drying process. It is contained in the slurry so that

  According to this invention, since the amount of the coupling agent is within the above range, the active material layer does not become too hard, and thus it is easy to handle and a negative electrode for a secondary battery excellent in adhesion can be manufactured.

  The manufacturing method of the negative electrode for secondary batteries of this invention is (1) The said coupling agent contains 1 type (s) or 2 or more types among a vinyl group, an epoxy group, an amino group, a methacryl group, and a mercapto group, (2 It is preferable that the coupling agent contains an alkoxy group.

  According to the method for manufacturing a negative electrode for a secondary battery of the present invention, a high capacity negative electrode for a secondary battery having excellent adhesion can be obtained. As a result, in the secondary battery using the obtained secondary battery negative electrode, even when charging and discharging are repeated, the adhesiveness of the secondary battery negative electrode is hardly deteriorated, and therefore, the capacity is hardly deteriorated. Therefore, the secondary battery using the obtained negative electrode for a secondary battery can realize excellent cycle characteristics.

  The method for producing a negative electrode for a secondary battery according to the present invention includes a step (slurry production step) of producing a slurry in which an active material layer on a current collector contains at least a carbon material, a metal oxide, and a coupling agent. It is formed through a step of applying the applied slurry on the current collector (application step) and a step of drying the applied slurry (drying step).

  As shown in FIG. 1, the negative electrode for a secondary battery produced by the method for producing a negative electrode for a secondary battery of the present invention comprises a current collector 4 and an active material layer 5 formed on the current collector 4. It is configured. The active material layer 5 includes a carbon material 1 and a metal oxide 2, and has a structure in which the current collector 4, the carbon material 1, and the metal oxide 2 are bonded with a silane coupling agent.

  Hereinafter, a method for producing such a negative electrode for a secondary battery will be described in detail with respect to the slurry preparation step, the coating step, and the drying step.

<Slurry production process>
The slurry production step is a step of producing a slurry containing at least the carbon material 1, the metal oxide 2, and the coupling agent. The slurry is prepared by adding a solvent to the carbon material 1, the metal oxide 2, and the coupling agent and mixing them, and adding a conductivity-imparting agent and a binder as necessary. Alternatively, the slurry is prepared by adding the carbon material 1, the metal oxide 2 and the coupling agent to a solvent and mixing them, and adding a conductivity-imparting agent and a binder as necessary.

  The mixing method is not particularly limited as long as the carbon material 1, the metal oxide 2, the coupling agent, and the like can be uniformly dispersed in the slurry. For example, they can be mixed using a homogenizer or the like. Thus, the slurry in which the carbon material 1, the metal oxide 2, the coupling agent, and the like are uniformly dispersed is used as a material for forming the active material layer 5.

  The carbon material 1 is an active material that occludes and releases lithium ions, and is used to improve the capacity of the secondary battery negative electrode. Examples of the carbon material 1 include powder or particles such as artificial graphite, natural graphite, amorphous graphite, carbon fiber, carbon nanotube, and fullerene. Note that these powders or particles do not need to be specially treated in advance, and can be used as they are. The average particle diameter of the carbon material 1 is usually 1 to 50 μm. In addition, in this application, a particle size means D50 which is a particle size corresponding to 50% of the integrated distribution measured with the particle size distribution analyzer.

The metal oxide 2 is an active material that absorbs and releases lithium ions, and is used to improve the capacity of the negative electrode for a secondary battery. Examples of the metal oxide 2 include silicon oxide and tin oxide particles or powder. Specifically, SiO, Li _x SiO _y (0 <x ≦ 4, 0 <y ≦ 2), SnO, Li _x SnO _y (0 <x ≦ 4, 0 <y ≦ 2), SiFe _b O _c ( 0 <b ≦ 1, 0 <c ≦ 2), SiNi _b O _c (0 <b ≦ 1, 0 <c ≦ 2), SnCo _b O _c (0 <b ≦ 4, 0 <c ≦ 2), SiCu Examples thereof include particles or powders such as _b O _c (0 <b ≦ 4, 0 <c ≦ 2), SiFe _b O _c (0 <b ≦ 4, 0 <c ≦ 2), and among others, SiO, Li _x SiO It is preferable to use _y (0 <x ≦ 4, 0 <y ≦ 2), SnO or Li _x SnO _y (0 <x ≦ 4, 0 <y ≦ 2). The average particle diameter of the metal oxide 2 is usually 0.1 to 50 μm. Moreover, in order to improve the capacity | capacitance of the negative electrode for secondary batteries, the metal oxide 2 can also be made to contain a material with high lithium occlusion ability.

  The weight ratio of carbon material 1 to metal oxide 2 (carbon material: metal oxide) is preferably in the range of 1: 9 to 9: 1. By setting the weight ratio of the carbon material 1 and the metal oxide 2 within the above range, the bonding state between the carbon material 1, the metal oxide 2, and the current collector 4 and the coupling agent can be maintained. . When the weight ratio of the carbon material 1 and the metal oxide 2 is outside the above range, the bonding state between the carbon material 1, the metal oxide 2 and the current collector 4 and the coupling agent is deteriorated. Adhesiveness of the negative electrode for a secondary battery may be deteriorated.

  The coupling agent has an inorganic reactive group and an organic reactive group. In the present invention, the organic reactive group of the coupling agent is bonded to the carbon material 1, and the inorganic reactive group of the coupling agent is bonded to the metal oxide 2 and the current collector 4, respectively. The adhesion between the objects 2 and the adhesion between the current collector 4 and the carbon material 1 and the metal oxide 2 can be improved. Examples of the coupling agent include a silane coupling agent, a titanate coupling agent, and an aluminum coupling agent. Among them, it is preferable to use a silane coupling agent.

  The coupling agent preferably includes an alkoxy group that is an inorganic reactive group, and includes one or more of a vinyl group, an epoxy group, an amino group, a methacryl group, and a mercapto group that are organic reactive groups. preferable.

  Suitable coupling agents include, for example, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ- Examples include methacryloxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltris (β-methoxyethoxy) silane and N-phenyl-γ-aluminopropyltrimethoxysilane.

  The coupling agent is preferably contained in the slurry so as to be in the range of 0.1 to 5% by mass with respect to the active material layer 5 formed through the drying step. By preparing the slurry so that the coupling agent is within the above range, the adhesion of the obtained negative electrode for the secondary battery is improved, and the secondary battery negative electrode is made easier to handle when producing the secondary battery. be able to. When the coupling agent is contained in the slurry so as to be less than 0.1% by mass with respect to the active material layer 5 formed through the drying step, the obtained negative electrode for the secondary battery is a metal oxide, carbon Since the bonding state between the material and the current collector and the coupling agent is deteriorated, adhesion may be deteriorated. Moreover, when the coupling agent is contained in the slurry so as to exceed 5 mass% with respect to the active material layer 5 formed through the drying step, the active material layer 5 is hard in the obtained negative electrode for a secondary battery. Therefore, it may be difficult to wind the secondary battery when manufacturing the secondary battery, and it may be difficult to handle the negative electrode for the secondary battery.

  A solvent is added in order to mix the carbon material 1, the metal oxide 2, a coupling agent, etc. uniformly. As the solvent, N-methyl-2-pyrrolidone (NMP), a fluororesin, or the like can be used, and what is previously mixed with a binder described later is used as a carbon material 1, a metal oxide 2, a coupling agent, and the like. In addition, they may be mixed.

  The conductivity-imparting agent can be used as an optional component in order to improve the conductivity of the negative electrode for a secondary battery. As the conductivity-imparting agent, any electron conductive material that does not cause a chemical change in the secondary battery constituted by the obtained negative electrode for a secondary battery can be used without particular limitation. For example, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder, metal fiber, polyphenylene derivative, polyacetylene, etc. Alternatively, two or more kinds of electron conductive materials can be used. The conductivity-imparting agent is, for example, 0.01% from the viewpoint of improving the conductivity of the secondary battery negative electrode with respect to the active material layer 5 formed through the drying step, while not deteriorating the adhesion of the secondary battery negative electrode. It is added to ˜50 mass%, preferably 0.4 to 10 mass%.

  The binder can be used as an optional component in order to further improve the adhesion of the secondary battery negative electrode. Binders include polyacrylic acid, carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, diacetyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, polypropylene, styrene butadiene rubber (SBR), ethylene propylene rubber (EPDM), sulfonated ethylene propylene rubber (sulfonated EPDM), fluororubber, polybutadiene and polyethylene oxide, among these, polyacrylic acid, carboxymethylcellulose, polytetrafluoro Ethylene or polyvinylidene fluoride (PVDF) is preferred. The viewpoint of making the secondary battery negative electrode easy to handle when producing the secondary battery while improving the adhesion of the secondary battery negative electrode to the active material layer 5 formed through the drying step. From 1 to 20% by mass, preferably 2 to 8% by mass.

<Application process>
The application step is a step of applying the slurry prepared in the above-described slurry preparation step onto the current collector 4.

  The current collector 4 is used to take out or supply current when charging / discharging the secondary battery, and a metal foil is usually used. The material of the metal foil is not particularly limited as long as it is conductive, and examples thereof include copper, nickel, iron, cobalt, and stainless steel. The thickness of the current collector 4 is preferably 5 μm or more and 30 μm or less.

  As a method of applying the slurry onto the current collector 4, a doctor blade method, spray coating, or the like can be used.

<Drying process>
A drying process is a process of drying the slurry apply | coated on the electrical power collector 4, and forming a coupling | bonding between each of the carbon material 1, the metal oxide 2, and the electrical power collector 4, and a coupling agent.

  As a method for drying the slurry, a known drying method such as vacuum drying or heat drying can be used. After drying the slurry, the active material layer 5 is pressed to a desired density to produce a secondary battery negative electrode. Furthermore, you may perform a drying process after that.

  The active material layer 5 is formed on the current collector 4 through the slurry preparation process, the application process, and the drying process described above.

  The active material layer 5 includes the carbon material 1 and the metal oxide 2 and is considered to have a structure in which the carbon material 1 is included in a network structure including the coupling agent and the metal oxide 2. The active material layer 5 may be formed on one side of the current collector 4 or may be formed on both sides.

  In such an active material layer 5, the bonding state of each of the carbon material 1, the metal oxide 2 and the current collector 4 and the coupling agent is taken as an example when a silane coupling agent is used as the coupling agent. This will be described in detail.

  The inorganic reactive group of the silane coupling agent contained in the slurry is hydrolyzed to form hydroxyl groups (OH groups) with water present in the atmosphere or in the slurry, or with water present on the surface of the current collector 4. This hydroxyl group (OH group) is hydrogen-bonded to the surface of the inorganic material (the surface of the current collector 4 or the metal oxide 2). At the same time, the silane coupling agent is partially condensed into an oligomer state. By drying this slurry, a dehydration condensation reaction occurs from the hydroxyl group of the hydrogen-bonded silane coupling agent and the surface of the inorganic material (the surface of the current collector 4 or metal oxide 2) to form a strong bond. Is done.

  Therefore, according to the method for manufacturing a negative electrode for a secondary battery of the present invention, a slurry containing at least a silane coupling agent, a carbon material 1 and a metal oxide 2 is prepared, and this slurry is applied on a current collector. Since the drying process is performed, the hydroxyl group (OH group) of the oligomerized silane coupling agent 3 forms a strong bond with the dispersed metal oxide 2 as shown in FIG. It is thought that it has a structure spread to. The hydroxyl group (OH group) of the silane coupling agent 3 forms a strong bond with the current collector 4.

  Furthermore, the organic reactive group X of the silane coupling agent 3 is bonded to the carbon material 1, and the bond between the organic reactive group X and the carbon material 1 is the bond between the silane coupling agent 3 and the metal oxide 2. The bond is weaker than the bond between the silane coupling agent 3 and the current collector 4. However, since the carbon material 1 has a structure included in the network structure composed of the silane coupling agent 3 and the metal oxide 2, the carbon material 1 is difficult to peel from the negative electrode for the secondary battery, and the secondary battery It is thought that the adhesiveness of the negative electrode for use is improved.

  As described above, according to the method for manufacturing a negative electrode for a secondary battery of the present invention, the active material layer 5 includes the carbon material 1 and the metal oxide 2 that are high-capacity materials. The negative electrode has a high capacity. Moreover, since the active material layer 5 has a structure in which the carbon material 1 is included in a network structure composed of a coupling agent and the metal oxide 2, the obtained negative electrode for a secondary battery has a high capacity. In addition to being excellent in adhesion. Therefore, the secondary battery using the secondary battery negative electrode obtained by the present invention is excellent in that the capacity of the secondary battery negative electrode is hardly deteriorated because the adhesion of the secondary battery negative electrode is maintained even after repeated charge and discharge. Cycle characteristics can be realized.

  Such a secondary battery is, for example, after laminating the positive electrode and the above-described negative electrode for a secondary battery via a separator, or after winding the laminated one, and containing the electrolyte in a container. Manufactured by sealing.

  The shape of the secondary battery is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a coin shape. Moreover, as a material of a container, the flexible film etc. which consist of a laminated body of a metal can or a synthetic resin and metal foil are mentioned.

The positive electrode is produced by applying a positive electrode active material, a conductivity-imparting agent, and a binder dispersed and kneaded to a current collector to form a positive electrode active material layer. As the positive electrode active material, for _{example, LiCoO 2, LixCo 1-y} M y O 2, Li 2 NiO 2, LixMnO 2, LixMnF 2, LixMnS 2, LixMn 1-y M y O 2, LixMn 1-y M y O _{2, LixMn 1-y M y} O 2-z F z, LixMn 1-y M y O 2-z S z, LixMn 2 O 4, LixMn 2 F 4, LixMn 2 S 4, LixMn 2-y M y O _{4, LixMn 2-y M y} O 4-z F z and _{LixMn 2-y M y O 4} -z S z (0 <x ≦ 1.5,0 <y <1.0, Z ≦ 1.0, M represents at least one or more transition metals.). At this time, the thickness of the positive electrode active material layer is usually 10 to 500 μm. In addition, the thing similar to what was used with the manufacturing method of the negative electrode for secondary batteries of the above-mentioned this invention can be used for a conductive provision agent, a binder, and a collector.

  The separator is provided between the negative electrode and the positive electrode, and one having insulation and ion conductivity is used. Examples of such a separator include polyolefin porous films such as polypropylene and polyethylene.

  Examples of the electrolyte solution include 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 carbonate ( EMC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-ethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylform Amide, dioxolane, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- One or more solvents selected from aprotic organic solvents such as oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methyl-2-pyrrolidone (NMP) The lithium salt that dissolves in these solvents is dissolved and used.

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 , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl and imides. Further, a polymer electrolyte may be used instead of the electrolytic solution.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

Example 1
Artificial graphite, which is a carbon material, silicon oxide (SiO), which is a metal oxide, carbon black, which is a conductivity-imparting agent, polyvinylidene fluoride (PVDF), which is a binder, and N-, which is a coupling agent. β- (Aminoethyl) -γ-aminopropyltrimethoxysilane was mixed and N-methyl-2-pyrrolidone (NMP) as a solvent was added to prepare a slurry. This slurry was applied onto a current collector made of copper foil using a doctor blade method. At this time, the carbon material is 9.2% by weight, the metal oxide is 79.3% by weight, the coupling agent is 5% by weight, and the conductivity imparting agent is 0.5% by weight with respect to the weight of the slurry excluding the solvent. The binder was 6% by mass.

  Next, after drying this slurry and evaporating N-methyl-2-pyrrolidone (NMP) to form an active material layer, the density of this active material layer was adjusted to 1.3 to 1.5 g / cc. Pressed. Furthermore, in order to accelerate the dehydration condensation reaction of the coupling agent, the negative electrode for a secondary battery was produced by holding at 120 ° C. for 10 hours.

(Examples 2-7 and Comparative Examples 1-3)
In Example 1, for the secondary batteries of Examples 2 to 7 and Comparative Examples 1 to 3, in the same manner as in Example 1 except that the carbon material, the metal oxide, and the coupling agent were mixed in the ratio shown in Table 1. A negative electrode was produced.

(Peel strength test)
The negative electrodes for secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 were cut into 20 mm × 5 mm, and the surface on which the active material layer was formed at the longitudinal direction of these secondary battery negative electrodes was 10 mm. In this way, it was bent at 90 °. This negative electrode for secondary battery was fixed with double-sided tape as shown in FIG. Then, these negative electrodes for secondary batteries were pulled up perpendicularly to the fixed surface, and the maximum value of the force required to peel the double-sided tape from the secondary battery negative electrode was defined as the peel strength. The results of this peel strength test are shown in Table 1.

  From the results in Table 1, it was found that the peel strength was improved when the weight ratio of the carbon material to the metal oxide was 1: 9 to 9: 1. The reason is considered that a good network structure was formed between the coupling agent and the metal oxide.

  Moreover, sufficient peel strength was not obtained for the negative electrode for secondary batteries in which the coupling agent was less than 0.1% by mass with respect to the active material layer containing the coupling agent. Furthermore, the negative electrode for secondary batteries in which the coupling agent was within 5% by mass with respect to the active material layer containing the coupling agent was able to be wound well when producing the secondary battery.

(Cycle characteristic test)
Cylindrical secondary batteries were prepared by combining the negative electrodes for secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 3 with the positive electrode, and charging and discharging of the secondary batteries were repeated until the capacity retention rate became 80% or less. It was. At this time, when charging / discharging the secondary battery for the first time, a current value that can be charged in 1 hour and discharged in 1 hour was adopted. LiCoO ₂ was used as the positive electrode active material. Further, the electrolytic solution was a mixture of ethyl carbonate containing LiPF ₆ and (EC) and diethyl carbonate (DEC).

  The results of the cycle characteristics are shown in Table 1. As a result of the above-mentioned peel strength test, an electrode having a small peel strength could not obtain good cycle characteristics.

It is an expanded sectional view showing an example of the negative electrode for secondary batteries of the present invention. In the negative electrode for secondary batteries of this invention, it is the schematic diagram which showed a mode that the electrical power collector, each of the carbon material, and the metal oxide, and the coupling agent couple | bonded. In the conventional electrode, it is the schematic diagram which showed a mode that both the electrical power collector and the carbon material and the coupling agent couple | bonded. It is the schematic which showed the mode of the peel strength test in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carbon material 2 Metal oxide 3 Coupling agent 4 Current collector 5 Active material layer

Claims (6)

  A step of producing a slurry in which the active material layer on the current collector contains at least a carbon material, a metal oxide, and a coupling agent; a step of applying the produced slurry onto the current collector; and the applied slurry A method for producing a negative electrode for a secondary battery, comprising:   The slurry is prepared by adding and mixing a solvent to a mixture of at least a carbon material, a metal oxide, and a coupling agent, or mixing at least a carbon material and a metal oxide in a solvent. The manufacturing method of the negative electrode for secondary batteries of Claim 1 characterized by the above-mentioned.   The mass ratio (carbon material: metal oxide) of the carbon material and the metal oxide contained in the slurry is within a range of 1: 9 to 9: 1. The manufacturing method of the negative electrode for secondary batteries.   The said coupling agent is contained in a slurry so that it may exist in the range of 0.1-5 mass% with respect to the active material layer formed through the said drying process. The manufacturing method of the negative electrode for secondary batteries of Claim 1.   5. The secondary according to claim 1, wherein the coupling agent contains one or more of a vinyl group, an epoxy group, an amino group, a methacryl group, and a mercapto group. A method for producing a negative electrode for a battery. The said coupling agent contains an alkoxy group, The manufacturing method of the negative electrode for secondary batteries of any one of Claims 1-5 characterized by the above-mentioned.

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