JP2006012556A - Anode for non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a non-aqueous electrolyte secondary battery in which an active material is prevented from falling off and has a high current collecting function.
A negative electrode 1 for a non-aqueous electrolyte secondary battery includes an active material layer 3 and a current collecting surface layer 4a that covers the active material layer 3 and has a large number of fine holes 6 through which an electrolyte can flow. The conductive polymer 5 is interposed between the two layers continuously or discontinuously. The active material layer preferably includes particles of the active material, and the space between the particles is filled with a material having a low ability to form a lithium compound. This negative electrode is for current collection in which a conductive polymer is applied to the surface of an active material layer, and electroplating is performed thereon to cover the active material layer and have a large number of fine holes through which an electrolyte can flow. It is obtained by forming a surface layer.
[Selection] Figure 1

Description

  The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery and a method for producing the same.

  A negative electrode for a non-aqueous electrolyte secondary battery is known in which a metal material having a low lithium compound forming ability is deposited on the surface of an active material layer having a high lithium compound forming ability formed on a current collector. (For example, refer to Patent Documents 1 and 2). According to these patent documents, it is said that a metal material having a low ability to form a lithium compound can suppress the decrease in current collecting ability in the surface direction and suppress the promotion of pulverization on the negative electrode surface where pulverization is most likely to occur. ing.

  However, a metal material having a low ability to form a lithium compound deposited on the surface of the active material layer has a thickness of about 0.02 μm or 0.05 μm, and is 0.2 μm at the maximum. Does not uniformly cover the active material layer, but is only distributed in islands. Therefore, it cannot be said that it is sufficient to suppress pulverization of the active material. Further, when the active material is a material with low electron conductivity such as Si, the current collecting property cannot be said to be sufficient. Furthermore, when these negative electrodes are wound in a spiral shape while facing the positive electrode through a separator, the metal material is easily peeled off.

  Apart from these techniques, a technique for forming a large number of fine holes in a metal foil is known. For example, a method for producing a porous metal foil is proposed in which a porous metal foil electrodeposited on an electrodeposited substrate having a rough surface in which an insulating portion and a conductive portion are dispersed is peeled off from the substrate (patent) Reference 3). However, in this method, it is necessary to roughen the surface of the electrodeposited substrate in advance. Further, there are limits to the repeated use of the electrodeposited substrate, and it is often necessary to perform a roughening treatment.

JP-A-8-50922 JP 2002-289178 A JP 50-141540 A

  Accordingly, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery and a method for manufacturing the same, which can eliminate the various disadvantages of the above-described prior art.

  The present invention includes an active material layer and a current collecting surface layer that covers the active material layer and has a large number of fine pores through which an electrolyte can flow, and a conductive polymer is interposed between both layers continuously or discontinuously. The object is achieved by providing a negative electrode for a non-aqueous electrolyte secondary battery.

  The present invention also provides a current collector having a large number of fine pores that are coated with a conductive polymer on the surface of the active material layer and electrolytically plated thereon to cover the active material layer and allow the electrolyte solution to flow therethrough. The manufacturing method of the negative electrode for non-aqueous-electrolyte secondary batteries characterized by forming the surface layer for water is provided.

  In the negative electrode for a non-aqueous electrolyte secondary battery according to the present invention, the surface of the active material layer is uniformly covered by the surface layer, not in an island shape, so that the active material is effectively removed due to pulverization. Is prevented. Moreover, since a large number of micropores are formed in the surface layer, the flow of the electrolytic solution to the active material layer is not hindered. Further, since the current collecting function is ensured by the surface layer, even if an active material having low electron conductivity is used, sufficient current collecting property is obtained. Furthermore, since the strength of the surface layer is enhanced by the conductive polymer, peeling when the negative electrode is wound and used can be effectively prevented.

  The present invention will be described below based on preferred embodiments with reference to the drawings. FIG. 1 schematically shows the structure of an embodiment of the negative electrode of the present invention. The negative electrode 1 of the present embodiment includes an active material layer 3 including active material particles 2. Each surface of the active material layer 3 is continuously covered with first and second current collecting surface layers 4a and 4b, respectively. The surface of each surface layer 4a, 4b is a surface in contact with the electrolyte. A conductive polymer 5 is interposed between the active material layer 3 and the first surface layer 4a. As is clear from FIG. 1, the negative electrode 1 has a current collector thick film conductor (for example, a metal foil or expanded metal having a thickness of about 12 to 35 μm) that has been used for a conventional electrode. Not done.

  The current collecting surface layers 4a and 4b have a current collecting function in the negative electrode 1 of the present embodiment. The surface layers 4a and 4b are also used to prevent the active material particles 2 contained in the active material layer 3 from falling off due to expansion and / or contraction and pulverization due to electrode reaction. ing. Furthermore, the surface layers 4a and 4b also have a function as a flow path for the electrolytic solution.

  Each of the surface layers 4a and 4b is thinner than the thick film conductor for current collection used in conventional electrodes. Specifically, a thin layer of about 0.3 to 10 μm, particularly about 0.4 to 8 μm, particularly about 0.5 to 5 μm is preferable. As a result, the active material layer 3 can be continuously coated almost uniformly with the minimum necessary thickness. As a result, the pulverized active material particles 2 can be prevented from falling off. In addition, by making such a thin layer and not having a thick film conductor for current collection, the proportion of the active material in the whole negative electrode becomes relatively high, and per unit volume and per unit weight. Energy density can be increased. In the conventional electrode, the ratio of the thick film conductor for current collection to the entire electrode is high, so there is a limit to increasing the energy density. The thin surface layers 4a and 4b in the above range are preferably formed by electrolytic plating as described later. The two surface layers 4a and 4b may have the same thickness or different thicknesses.

  When the negative electrode 1 of this embodiment is incorporated in a battery, the surface of each surface layer 4a, 4b becomes a surface in contact with the electrolyte and participates in the electrode reaction. In contrast, a thick film conductor for collecting current in a conventional electrode is not in contact with the electrolyte solution when the active material layer is formed on both sides thereof, and does not participate in the electrode reaction. Even when an active material layer is formed on one side, only one side is in contact with the electrolyte. That is, the negative electrode 1 of the present embodiment does not have the current collecting thick film conductor used in the conventional electrode, and the layers located on the outermost surface of the electrode, that is, the surface layers 4a and 4b are used for the electrode reaction. In addition to being involved, it has both a current collecting function and a function to prevent the active material from falling off.

  Since each of the surface layers 4a and 4b has a current collecting function, when the negative electrode 1 of this embodiment is incorporated in a battery, a lead wire for current extraction is provided on any of the surface layers 4a and 4b. There is an advantage that it can be connected.

  Each surface layer 4a, 4b is comprised from the material which can become a collector of a non-aqueous-electrolyte secondary battery. In particular, it is preferably made of a material that can be a current collector of a lithium secondary battery. Examples of such a metal include a material having a low ability to form a lithium compound. Specific examples include copper, nickel, iron, cobalt, and alloys of these metals. Of these metals, it is particularly preferable to use copper and nickel or an alloy thereof. The two surface layers 4a and 4b may have the same or different constituent materials. “Lithium compound forming ability is low” means that lithium does not form an intermetallic compound or solid solution, or even if formed, lithium is in a very small amount or very unstable.

  Each surface layer 4a, 4b is formed with a large number of fine holes 6 extending in the thickness direction of the surface layer. The fine holes 6 are opened on the surface of the surface layer. The fine hole 6 extends while being bent. A part of the numerous fine holes 6 extends in the thickness direction of the surface layer and reaches the active material layer 3. The micro holes 6 are capable of flowing an electrolytic solution. By forming the fine holes 6, the electrolytic solution can sufficiently penetrate into the active material layer 3, and the reaction with the active material particles 2 occurs sufficiently. The fine holes 6 are fine ones having a width of about 0.1 μm to about 10 μm when the surface layer is observed in cross section. Although fine, the fine holes 6 have a width that allows the electrolyte solution to penetrate. However, since the nonaqueous electrolytic solution has a smaller surface tension than the aqueous electrolytic solution, it can sufficiently penetrate even if the width of the micropore 6 is small. The fine holes 6 can be formed by a method described later. In particular, with respect to the first surface layer 4a, the fine holes 6 are successfully formed due to the presence of the conductive polymer 5 described later.

In a plan view the surface layer 4a, the surface of 4b electron microscopy, the average opening area of the micropores 6 is 0.1 to 50 [mu] m ^2, preferably 0.1 to 20 [mu] m ^2, more preferably 0. It is about 5 to 10 μm ² . By setting the opening area within this range, it is possible to effectively prevent the active material from falling off while ensuring sufficient permeation of the non-aqueous electrolyte. Further, the charge / discharge capacity can be increased from the initial stage of charge / discharge. From the viewpoint of more effectively preventing the active material particles 2 from falling off, the average pore area is 0.1 to 50%, particularly 0.1 to 20% of the maximum cross-sectional area of the active material particles 2. Preferably there is. The maximum cross-sectional area of the active material particle 2 is the maximum cross-sectional area when the particle diameter (D ₅₀ value) of the active material particle 2 is measured and the particle is regarded as a sphere having a diameter of D ₅₀ value. Say.

  When the surfaces of the surface layers 4a and 4b are viewed in plan by electron microscope observation, the ratio of the total area of the micropores 6 to the area of the observation field (this ratio is referred to as the aperture ratio) is 0.1-20. %, Preferably 0.5 to 10%. The reason for this is the same as that for setting the area of the fine holes 6 within the above range. Furthermore, for the same reason, when the surfaces of the surface layers 4a and 4b are viewed in plan by electron microscope observation, any observation field of view is 1 to 10,000 within a square field of view of 100 μm × 100 μm, particularly 10 It is preferable that 500, especially 10 to 100, fine holes 6 exist.

  The active material layer 3 positioned between the surface layers 4a and 4b includes active material particles 2 having a high lithium compound-forming ability. The active material layer 3 is formed, for example, by applying a conductive slurry containing the active material particles 2. Since the active material layer 3 is continuously covered with the surface layers 4a and 4b, the active material particles 2 are effectively prevented from falling off due to absorption and desorption of lithium ions. Since the active material particles 2 can be in contact with the electrolyte solution through the fine holes 6, the electrode reaction is not hindered.

  Examples of the active material include silicon-based materials, tin-based materials, aluminum-based materials, and germanium-based materials. Particularly preferable particles 2 include, for example, a) particles of silicon or tin, b) particles of at least silicon or tin and carbon, c) particles of silicon or tin and metal, and d) silicon or tin and metal. And compound particles of silicon or tin and metal and mixed particles of metal particles, and f) particles in which the surface of silicon or tin particles is coated with metal. B), c), d), d), f) and f) particles of silicon-based material caused by lithium absorption / desorption compared to the case of b) using silicon or tin particles. There is an advantage that the conversion is further suppressed. Further, there is an advantage that electron conductivity can be imparted to silicon which is a semiconductor and has poor electron conductivity.

The active material particles 2 have a maximum particle size of preferably 50 μm or less, more preferably 20 μm or less. Moreover, when the particle diameter of the particle 2 is expressed by a D ₅₀ value, it is preferably 0.1 to 8 μm, particularly preferably 1 to 5 μm. If the maximum particle size is more than 50 μm, the particles 2 are likely to fall off, and the life of the negative electrode 1 may be shortened. There is no particular limitation on the lower limit of the particle size, and the smaller the better. In view of the method for producing the particles 2, the lower limit is about 0.01 μm. The particle size of the particle 2 is measured by a laser diffraction / scattering particle size distribution measuring device or an electron microscope.

  If the amount of the active material relative to the whole negative electrode 1 is too small, it is difficult to sufficiently improve the energy density of the battery. Conversely, if the amount is too large, the active material tends to fall off. Considering these, the amount of the active material is preferably 5 to 80% by weight, more preferably 10 to 50% by weight, and still more preferably 20 to 50% by weight with respect to the entire negative electrode 1. The thickness of the active material layer 3 can be appropriately adjusted according to the ratio of the amount of the active material to the whole negative electrode, and is not particularly critical in the present embodiment. Generally, it is about 1 to 100 μm, particularly about 3 to 40 μm.

  In the active material layer 3, the space between the active material particles 2 is preferably filled with a material having a low lithium compound forming ability. In particular, it is preferable that a material having a low ability to form a lithium compound penetrates the entire active material layer 3 in the thickness direction. The active material particles 2 are preferably present in the permeated material. That is, it is preferable that the active material particles 2 are not substantially exposed on the surface of the negative electrode 1 and are embedded in the surface layers 4a and 4b. This further prevents the active material from falling off. In addition, since electronic conductivity is ensured between the surface layers 4a and 4b and the active material through the material that has penetrated into the active material layer 3, it is possible to generate an electrically isolated active material, in particular, the active material layer 3 The generation of an electrically isolated active material in the deep part of the substrate is effectively prevented, and the current collecting function is maintained. As a result, functional degradation as a negative electrode is suppressed. In addition, the life of the negative electrode can be extended. This is particularly advantageous when a material that is a semiconductor and has poor electron conductivity, such as a silicon-based material, is used as the active material.

  The material having a low ability to form a lithium compound that has permeated throughout the thickness direction of the active material layer 3 is preferably the same type of material as that of the surface layers 4a and 4b. However, if the lithium compound forming ability is low, a material different from the material constituting the surface layers 4a and 4b may be used.

  The material having a low lithium compound forming ability preferably penetrates the active material layer 3 in the thickness direction. Accordingly, the two surface layers 4a and 4b are electrically connected through the material, and the electron conductivity of the negative electrode 1 as a whole is further increased. That is, the negative electrode 1 of the present embodiment as a whole has a current collecting function. The penetration of the material having a low ability to form a lithium compound throughout the thickness direction of the active material layer 3 can be obtained by electron microscope mapping using the material as a measurement target. A preferred method for infiltrating a material having a low lithium compound forming ability into the active material layer 3 will be described later.

  As described above, the surface layers 4a and 4b are also made of a material having a low ability to form a lithium compound. However, the material and a material having a low ability to form a lithium compound penetrating into the active material layer 3 are used. May be the same or different.

  The active material layer 3 preferably contains conductive carbon material or conductive metal material particles (not shown) in addition to the active material particles 2. Thereby, the negative electrode 1 is further provided with electronic conductivity. From this viewpoint, the amount of the conductive carbon material or conductive metal material particles contained in the active material layer 3 is 0.1 to 20% by weight, particularly 1 to 10% by weight, based on the active material layer 3. Is preferred. For example, particles such as acetylene black and graphite are used as the conductive carbon material. The particle diameter of these particles is preferably 40 μm or less, and particularly preferably 20 μm or less from the viewpoint of further imparting electron conductivity. The lower limit of the particle size of the particles is not particularly limited and is preferably as small as possible. In view of the method for producing the particles, the lower limit is about 0.01 μm.

  A conductive polymer 5 is interposed between the active material layer 3 and the first surface layer 4a. The conductive polymer 5 has a function of successfully forming a large number of micropores 6 in the first surface layer 4a (this will be described in detail later). Furthermore, the inventors have studied that the strength and flexibility of the first surface layer 4a are improved by interposing the conductive polymer 5 between the active material layer 3 and the first surface layer 4a. The result turned out. This effectively prevents the first surface layer 4a from being peeled off by the distortion generated due to the winding when the negative electrode 1 is wound in a spiral shape facing the positive electrode through the separator. This is advantageous in that it can be prevented.

  The interposition position of the conductive polymer 5 varies depending on how much a material having a low ability to form a lithium compound penetrates into the active material layer 3. For example, when the material having a low lithium compound forming ability penetrates the entire active material layer 3 and reaches the upper surface of the active material layer 3, the conductive polymer 5 is impregnated with the penetrated lithium compound. Between the first surface layer 4a and the material having a low forming ability. When the material with low lithium compound forming ability does not completely fill the active material layer 3 and there is no material with low lithium compound forming ability on the upper surface of the active material layer 3 and its vicinity, The conductive polymer 5 is interposed between the active material layer 3 and the first surface layer 4 a in a state where a part of the conductive polymer 5 is present in the active material layer 3.

  There is no restriction | limiting in particular in the kind as the conductive polymer 5, A conventionally well-known thing can be used. Examples thereof include polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). In particular, it is preferable to use a lithium ion conductive polymer as the conductive polymer 5. The conductive polymer 5 is preferably a fluorine-containing conductive polymer. This is because the fluorine-containing polymer has high thermal and chemical stability and excellent mechanical strength. Considering these, it is particularly preferable to use polyvinylidene fluoride, which is a fluorine-containing polymer having lithium ion conductivity.

  The conductive polymer 5 may be continuously present over the entire area between the two layers with a thickness sufficient to completely separate the active material layer 3 and the first surface layer 4a. Or you may exist discontinuously between both layers. The amount of the conductive polymer 5 is determined appropriately from the viewpoint of forming the desired micropores 6 in the first surface layer 4a and from the viewpoint of imparting desired strength and flexibility to the first surface layer 4a. Is done.

  The total thickness of the negative electrode 1 having the above configuration is preferably about 2 to 50 μm, particularly about 10 to 50 μm in consideration of maintaining the strength of the negative electrode 1 and increasing the energy density.

  Next, the preferable manufacturing method of the negative electrode 1 shown in FIG. 1 is demonstrated, referring FIG. First, a carrier foil 10 is prepared as shown in FIG. There are no particular restrictions on the material of the carrier foil 10. The carrier foil 10 is preferably conductive. In this case, the carrier foil 10 may not be made of metal as long as it has conductivity. However, the use of the metal carrier foil 10 has an advantage that the carrier foil 10 can be melted and made into a foil and recycled after the negative electrode 1 is manufactured. Considering the ease of recycling, the material of the carrier foil 10 is preferably the same as the material of the second surface layer 4b formed by electrolytic plating described later. Since the carrier foil 10 is used as a support for manufacturing the negative electrode 1, it is preferable that the carrier foil 10 has a strength such that no twist or the like occurs in the manufacturing process. Therefore, the carrier foil 10 preferably has a thickness of about 10 to 50 μm.

  The carrier foil 10 can be manufactured by, for example, electrolysis or rolling. By manufacturing by rolling, carrier foil 10 with low surface roughness can be obtained. On the other hand, by producing the carrier foil 10 by electrolysis, the production from the carrier foil 10 to the production of the negative electrode 1 can be performed in-line. Performing in-line is advantageous from the viewpoint of stable production of the negative electrode 1 and reduction of production costs. When the carrier foil 10 is produced by electrolysis, the rotating drum is used as a cathode, and electrolysis is performed in an electrolytic bath containing metal ions such as copper and nickel to deposit metal on the drum peripheral surface. The carrier foil 10 is obtained by peeling the deposited metal from the drum peripheral surface.

  From the viewpoint of controlling the hole diameter and density of the fine holes 6 formed in the second surface layer 4b, the surface of the carrier foil 10 is preferably somewhat uneven. Each surface of the rolled foil is smooth due to its manufacturing method. On the other hand, one surface of the electrolytic foil is a rough surface, and the other surface is a smooth surface. A rough surface is a precipitation surface at the time of manufacturing electrolytic foil. Therefore, if the rough surface of the electrolytic foil is used as the electrodeposition surface, it is easy to separately carry out the roughening treatment on the carrier foil 10. When such a rough surface is used as an electrodeposited surface, the surface roughness Ra is 0.05 to 5 μm, particularly 0.2 to 0.8 μm, so that micropores having a desired diameter and density can be easily obtained. It is preferable because it can be formed.

  Next, a release agent is applied to one surface of the carrier foil 10 to perform a release treatment. For the reasons described above, the release agent is preferably applied to the rough surface of the carrier foil 10. The release agent is used for successfully peeling the carrier foil 10 and the second surface layer 4b in the peeling step described later. The peeling process is performed by, for example, a chromium plating process, a nickel plating process, a lead plating process, a chromate process, or the like. Moreover, the peeling process using the peeling agent which consists of organic compounds can also be performed. As the organic compound, it is particularly preferable to use a nitrogen-containing compound or a sulfur-containing compound. Examples of nitrogen-containing compounds include benzotriazole (BTA), carboxybenzotriazole (CBTA), tolyltriazole (TTA), N ′, N′-bis (benzotriazolylmethyl) urea (BTD-U), and 3-amino. Triazole compounds such as -1H-1,2,4-triazole (ATA) are preferably used. Examples of the sulfur-containing compound include mercaptobenzothiazole (MBT), thiocyanuric acid (TCA), 2-benzimidazolethiol (BIT), and the like. The peelability can be controlled by the concentration of the release agent and the coating amount. The step of applying the release agent is only performed in order to successfully release the carrier foil 10 and the second surface layer 4b in the release step described later. Therefore, even if this step is omitted, the second surface layer 4b having the fine holes 6 can be formed.

  Next, as shown in FIG. 2B, after applying a release agent (not shown), a coating liquid containing a conductive polymer is applied and dried to form a coating film of the conductive polymer 11. Or after apply | coating a coating liquid, you may peel-process the application surface of this coating liquid with a peeling agent. The coating liquid is obtained by dissolving a conductive polymer in a volatile organic solvent. As the organic solvent, for example, when polyvinylidene fluoride is used as the conductive polymer, N-methylpyrrolidone or the like can be used. Since the coating liquid is applied to the rough surface of the carrier foil 10, it tends to accumulate in the recesses on the rough surface. When the solvent volatilizes in this state, the thickness of the coating film becomes non-uniform. That is, the thickness of the coating film corresponding to the concave portion of the rough surface is large, and the thickness of the coating film corresponding to the convex portion is small. In the present manufacturing method, as described below, a large number of micropores are formed in the second surface layer 4b by utilizing the nonuniformity of the thickness of the coating film.

  The carrier foil 10 on which the coating film of the conductive polymer 11 is formed is subjected to an electrolytic plating process, so that the second surface layer 4b is formed on the coating film as shown in FIG. This state is shown in FIG. 3 which is an enlarged view of the main part of FIG. The conductive polymer 11 has electronic conductivity although not as much as a metal. Therefore, the coating film of the conductive polymer 11 has different electron conductivity depending on its thickness. As a result, when a metal is deposited on the coating film containing the conductive polymer 11 by electrolytic plating, a difference occurs in the deposition rate according to the electron conductivity, and the difference in the deposition rate causes the second surface layer 4b to be deposited. Fine holes 6 are formed. That is, a portion where the electrodeposition rate is low, in other words, a portion where the coating film of the conductive polymer 11 is thick is likely to become the fine holes 6.

As conditions for forming the second surface layer 4b by electrolytic plating, for example, when copper is used as a material having a low ability to form a lithium compound, when a copper sulfate-based solution is used, the copper concentration is 30 to 100 g / l. The concentration of sulfuric acid is 50 to 200 g / l, the concentration of chlorine is 30 ppm or less, the liquid temperature is 30 to 80 ° C., and the current density is 1 to 100 A / dm ² . When using a copper pyrophosphate solution, the concentration of copper is 2 to 50 g / l, the concentration of potassium pyrophosphate is 100 to 700 g / l, the liquid temperature is 30 to 60 ° C., the pH is 8 to 12, and the current density is 1. ~10A / dm ² and it may be set.

  Next, as shown in FIG. 2D, an active material layer 3 is formed on the second surface layer 4b by applying a conductive slurry containing active material particles. The slurry contains active material particles, conductive carbon material or conductive metal material particles, a binder, a diluting solvent, and the like. Among these components, polyethylene (PE), ethylene propylene diene monomer (EPDM), polyvinylidene fluoride (PVDF) and the like are used as the binder. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used. The amount of the active material in the slurry is preferably about 14 to 40% by weight. The amount of the conductive carbon material or conductive metal material particles is preferably about 0.4 to 4% by weight. The amount of the binder is preferably about 0.4 to 4% by weight. Moreover, it is preferable that the quantity of a dilution solvent shall be about 60 to 85 weight%.

  After the slurry coating is dried and the active material layer 3 is formed, the carrier foil 10 on which the active material layer 3 is formed is immersed in a plating bath and electrolyzed, as shown in FIG. Plating is performed. The plating bath includes, for example, a metal material having a low lithium compound forming ability. The space between the active material particles contained in the active material layer 3 by this electrolytic plating is filled with the deposited metal material, and the metal material penetrates throughout the thickness direction of the active material layer 3 (hereinafter referred to as this Plating is called penetration plating). The osmotic plating is preferably performed to such an extent that all the active material particles contained in the active material layer 3 are not completely embedded, and some of the active material particles are exposed above the plating surface.

For example, when Ni is used for the permeation plating, a Watt bath or a sulfamic acid bath having the following composition can be used as a plating bath. When these plating baths are used, the bath temperature is preferably about 40 to 70 ° C., and the current density is preferably about 0.5 to 20 A / dm ² .
・ NiSO ₄・ 6H ₂ O 150 ~ 300g / l
・ NiCl ₂ .6H ₂ O 30-60 g / l
・ H ₃ BO ₃ 30-40 g / l

  Next, as shown in FIG. 2 (f), a coating solution containing the conductive polymer 5 is applied to the surface of the active material layer 3 that has been subjected to permeation plating. As this conductive polymer 5, the same kind or different kind of the conductive polymer 11 used previously can be used. The surface of the active material layer 3 subjected to the osmotic plating has an uneven shape by plating. In addition, since some particles of the active material are exposed on the surface, the uneven shape is more prominent. When a coating liquid containing the conductive polymer 5 is applied to the surface of the active material layer 3 in such a surface state to form a coating film, the surface unevenness of the active material layer 3 is formed on the coating film. A difference in thickness according to the shape occurs. As a result, the coating film of the conductive polymer 5 has different electron conductivity depending on its thickness. In this state, as shown in FIG. 2 (g), when the first surface layer 4a is formed by performing electroplating on the coating film to deposit a metal, depending on the electronic conductivity of the coating film. A difference occurs in the electrodeposition rate, and micropores 6 are formed in the first surface layer 4a due to the difference in the electrodeposition rate. The conditions for forming the first surface layer 4a by electrolytic plating can be the same as those for the second surface layer 4b. The constituent material of the first surface layer 4a may be the same as or different from the material of the previous infiltration plating.

  Finally, as shown in FIG. 2 (h), both are peeled at the interface between the carrier foil 10 and the second surface layer 4b. Thereby, the intended negative electrode 1 is obtained. In FIG. 2 (h), the coating film of the conductive polymer 11 is drawn so as to remain on the second surface layer 4b side, but in some cases, the coating film of the conductive polymer 11 on the carrier foil 10 side. May remain, or both. As a result of studies by the present inventors, it was found that the strength and flexibility of the second surface layer 4b increase as the degree of the coating film of the conductive polymer 11 remaining on the second surface layer 4b side increases. . In order to leave the coating film of the conductive polymer 11 on the second surface layer 4b side, as described above, after forming the release layer on the surface of the carrier foil 10, the coating film of the conductive polymer 11 is formed thereon. It is advantageous to form

The negative electrode 1 thus obtained is used with a known positive electrode, separator, and nonaqueous electrolyte solution to form a nonaqueous electrolyte secondary battery. The positive electrode is prepared by suspending a positive electrode active material and, if necessary, a conductive agent and a binder in an appropriate solvent to prepare a positive electrode mixture, applying this to a current collector, drying it, then rolling and pressing, and further cutting. It is obtained by punching. As the positive electrode active material, conventionally known positive electrode active materials such as lithium nickel composite oxide, lithium manganese composite oxide, and lithium cobalt composite oxide are used. As the separator, a synthetic resin nonwoven fabric, polyethylene, polypropylene porous film, or the like is preferably used. In the case of a lithium secondary battery, the nonaqueous electrolytic solution is a solution in which a lithium salt that is a supporting electrolyte is dissolved in an organic solvent. Examples of the lithium _{salt, LiBF 4, LiC1O 4, LiA1Cl} 4, LiPF 6, LiAsF 6, LiSbF 6, LiSCN, LiC1, LiBr, LiI, etc. _{LiCF 3 SO 3, LiC 4 F} 9 SO 3 are exemplified.

  The present invention is not limited to the embodiment. For example, the negative electrode 1 of the above embodiment does not have a current collecting thick film conductor that does not allow electrolyte to permeate, but the negative electrode of the present invention has such a current collecting thick film conductor. It may be what you are doing. For example, as shown in FIG. 4, an active material layer 3 containing active material particles 2 is formed on at least one surface of a thick film conductor 7 for current collection that does not allow electrolyte to permeate. You may comprise negative electrode 1 'in which the surface layer 4a is formed. Also in this embodiment, the conductive polymer 5 is continuously or discontinuously interposed between the active material layer 3 and the surface layer 4a. Also in this negative electrode 1 ', the same effect as the negative electrode 1 of the embodiment shown in FIG. In the negative electrode 1 ′, the active material layer 3 is formed only on one surface of the thick film conductor 7 for current collection. However, an active material layer may be formed on the other surface as necessary.

  In the above embodiment, the micropores are formed in each of the surface layers 4a and 4b formed on each surface of the active material layer 3. Instead, the micropores are formed only in one surface layer. It is not necessary to form micropores in the other surface layer.

  In the manufacturing method described above, after the active material layer 3 is formed, the active material layer 3 is subjected to osmotic plating. However, instead of forming the active material layer 3, the osmotic plating is not performed. Alternatively, a coating film of the conductive polymer 5 may be formed on the surface of the active material layer 3, and then the first surface layer 4a may be formed by electrolytic plating. In this case, the formation of the first surface layer 4a and the permeation plating on the active material layer 3 can be performed simultaneously by forming the conductive polymer coating film discontinuously. This method is advantageous from the viewpoint of the manufacturing method because the plating step is reduced by one step.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
A copper carrier foil (thickness 35 μm) obtained by electrolysis was acid-washed at room temperature for 30 seconds. Subsequently, it was washed with pure water at room temperature for 30 seconds. Subsequently, the carrier foil was immersed in a 3.5 g / l CBTA solution maintained at 40 ° C. for 30 seconds. In this way, peeling treatment was performed. After the peeling treatment, the substrate was pulled up from the solution and washed with pure water for 15 seconds.

A coating solution having a concentration of 2.5% by weight in which polyvinylidene fluoride was dissolved in N-methylpyrrolidone was applied to the rough surface of the carrier foil (surface roughness Ra = 0.5 μm). After the solvent was volatilized and a coating film was formed, electrolytic plating was performed by immersing the carrier foil in an H ₂ SO ₄ / CuSO ₄ plating bath. Thus, a second surface layer made of copper was formed on the coating film. The composition of the plating bath was 250 g / l for CuSO _{4 and} 70 g / l for H ₂ SO ₄ . The current density was 5 A / dm ² . The second surface layer was formed to a thickness of 5 μm. After lifting from the plating bath, it was washed with pure water for 30 seconds and dried in the air.

Next, a slurry containing negative electrode active material particles was applied on the second surface layer to a thickness of 15 μm to form an active material layer. The active material particles were an alloy having a composition of Si 80 wt% -Ni 20 wt%, and the average particle diameter was D ₅₀ = 1.5 μm. The composition of the slurry was active material: Ni powder: acetylene black: polyvinylidene fluoride = 60: 34: 1: 5.

After the active material layer was formed, the carrier foil was immersed in a Watt bath having the following bath composition, and nickel was infiltrated into the active material layer by electrolysis. The current density was 5 A / dm ² , the bath temperature was 50 ° C., and the pH was 5. A nickel electrode was used as the anode. A DC power source was used as the power source. This infiltration plating was performed to such an extent that some active material particles were exposed from the plating surface. After lifting from the plating bath, it was washed with pure water for 30 seconds and dried in the air.
・ NiSO ₄・ 6H ₂ O 250g / l
・ NiCl ₂・ 6H ₂ O 45g / l
・ H ₃ BO ₃ 30g / l

Next, a coating solution having a concentration of 2.5% by weight in which polyvinylidene fluoride was dissolved in N-methylpyrrolidone was applied to the surface of the active material layer. After the solvent was volatilized and a coating film was formed, electrolytic plating was performed by immersing the carrier foil in a Cu-based plating bath. The composition of the plating bath was 200 g / l for H ₃ PO _{4 and} 200 g / l for Cu ₃ (PO ₄ ) ₂ .3H ₂ O. The plating conditions were a current density of 5 A / dm ² and a bath temperature of 40 ° C. Thereby, the 1st surface layer which consists of copper was formed on the coating film. The first surface layer was formed to a thickness of 3 μm. After lifting from the plating bath, it was washed with pure water for 30 seconds and dried in the air.

  Finally, the second surface layer and the carrier foil were peeled off to obtain a negative electrode for a non-aqueous electrolyte secondary battery in which an active material layer was sandwiched between a pair of surface layers. As a result of qualitative analysis by IR and NMR, it was confirmed that polyvinylidene fluoride was adhered to the outer surface of the second surface layer in this negative electrode. Moreover, it was confirmed by the cross-sectional observation of the negative electrode with a scanning electron microscope that polyvinylidene fluoride is interposed between the active material layer and the first surface layer. Furthermore, as a result of observing the surface layer with a scanning electron microscope, it was confirmed that the first surface layer had, on average, 50 fine holes in a 100 μm × 100 μm square range. About the 2nd surface layer, it confirmed that 30 micropores existed on the average.

[Comparative Example 1]
A slurry similar to the slurry used in Example 1 was used on each surface of a copper foil (thickness 35 μm) obtained by electrolysis, and this was applied to a thickness of 15 μm to form an active material layer. The copper foil on which the active material layer was formed was immersed in a Cu-based plating bath to perform electrolytic plating. The composition of the plating bath and the plating conditions were the same as in Example 1. Thus, a thin copper layer having a thickness of 0.05 μm was formed on the surface of the active material layer. In this way, a negative electrode for a non-aqueous electrolyte secondary battery was obtained. As a result of observation with a scanning electron microscope, the thin copper layer was not continuously coated on the surface of the active material, but was distributed in islands. Moreover, the hole which can be called a micropore did not exist.

[Performance evaluation]
Using the negative electrodes obtained in Examples and Comparative Examples, non-aqueous electrolyte secondary batteries were produced by the following method. The maximum negative electrode discharge capacity, the battery capacity, and the capacity retention rate at 50 cycles of this battery were measured and calculated by the following methods. These results are shown in Table 1 below.

[Production of non-aqueous electrolyte secondary battery]
The negative electrodes obtained in Examples and Comparative Examples were used as working electrodes, LiCoO ₂ was used as a counter electrode, and both electrodes were opposed to each other through a separator. A non-aqueous electrolyte secondary battery was produced by a conventional method using a mixed solution (1: 1 volume ratio) of LiPF ₆ / ethylene carbonate and dimethyl carbonate as the non-aqueous electrolyte.

[Maximum negative electrode discharge capacity]
The discharge capacity per active material weight in the cycle where the maximum capacity was obtained was measured. The unit is mAh / g.

[Capacity maintenance rate at 50 cycles]
The discharge capacity at the 50th cycle was measured, and the value was divided by the maximum negative electrode discharge capacity and multiplied by 100.

  As is clear from the results shown in Table 1, the battery using the negative electrode of Example 1 had either the maximum negative electrode discharge capacity or the capacity retention rate at 50 cycles compared to the battery using the negative electrode of Comparative Example 1. It can be seen that is excellent.

It is a schematic diagram which shows the structure of one Embodiment of the negative electrode of this invention. It is process drawing which shows the manufacturing method of the negative electrode shown in FIG. It is a schematic diagram which expands and shows the principal part of FIG.2 (c). It is a schematic diagram which shows the structure of other embodiment of the negative electrode of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Active material particle 3 Active material layer 4a 1st surface layer 4b 2nd surface layer 5 Conductive polymer 6 Micropore 7 Thick film conductor for current collection which does not permeate | transmit electrolyte solution 10 Carrier foil

Claims (13)

  An active material layer, and a current collecting surface layer that covers the active material layer and has a large number of fine pores through which an electrolyte can flow, and that a conductive polymer is interposed between both layers continuously or discontinuously. A negative electrode for a non-aqueous electrolyte secondary battery.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the active material layer includes particles of an active material, and a space between the particles is filled with a material having a low lithium compound forming ability. Each surface of the active material layer is covered with the current collecting surface layer, the conductive polymer is interposed between one current collecting surface layer and the active material layer, and does not allow the electrolytic solution to pass therethrough. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode does not have a thick film conductor for collecting current.   3. The non-aqueous solution according to claim 1, wherein the active material layer is formed on at least one surface of a thick film conductor for collecting current that does not allow electrolyte to permeate, and the surface layer for collecting current is formed thereon. Negative electrode for electrolyte secondary battery.   The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the current collecting surface layer has a thickness of 0.3 to 10 µm.   6. The non-aqueous electrolyte 2 according to claim 1, wherein the number of the fine holes opened on the surface of the current collecting surface layer is 1 to 10,000 within a range of 100 μm × 100 μm. Negative electrode for secondary battery.   The nonaqueous electrolytic solution according to any one of claims 2 to 6, wherein a material having a low ability to form a lithium compound penetrates throughout the thickness direction of the active material layer, and the entire electrode has a current collecting function. Negative electrode for secondary battery.   A conductive polymer is applied to the surface of the active material layer, and electroplating is performed thereon to form a current collecting surface layer that covers the active material layer and has a large number of micropores through which the electrolyte can flow. A method for producing a negative electrode for a nonaqueous electrolyte secondary battery.   The slurry containing active material particles is applied to form the active material layer, and then the active material layer is infiltrated with a plating solution containing a material having a low ability to form a lithium compound to perform electrolytic plating. 9. The manufacturing method according to claim 8, wherein the material is filled with a material having a low ability to form a lithium compound, and then the conductive polymer is applied to form the current collecting surface layer thereon.   On the carrier foil, a first current collecting surface layer having a large number of fine holes through which electrolyte can be circulated by a predetermined means is formed, and the active material layer is formed thereon, and then the conductive material is formed on the surface. The manufacturing method of Claim 8 or 9 which coats a conductive polymer, forms the 2nd surface layer for current collection on it, and peels the surface layer for 1st current collection and carrier foil after that.   The manufacturing method according to claim 10, wherein a conductive polymer is coated on the carrier foil, and then electrolytic plating is performed on the conductive polymer coated surface to form a first current collecting surface layer.   9. The active material layer is formed on at least one surface of a thick-film current collector that does not allow electrolyte to permeate, the conductive polymer is coated on the surface, and the current collecting surface layer is further formed thereon. Or the manufacturing method of 9. A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

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