JP2005063929A - Negative electrode for non-aqueous electrolyte secondary battery, its manufacturing method, and non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for a non-aqueous electrolyte secondary battery with high current collecting characteristics, improved cycle life, and high energy density, prevented from dropping of an active material, of which, the current collecting characteristics of the active material are secured even if charge and discharge are repeated. <P>SOLUTION: The negative electrode for the non-aqueous electrolyte secondary battery is provided with a pair of surface layers for the current collection having a surface contacting the surface with the electrolytic solution, and at least one layer of the active material interposed between the surface layers, containing particles of the active material high in a forming ability of a lithium compound. The material structuring the surface layer for current collection is permeated across the whole region in the thickness direction of the active material layer, and both surface layers are electrically conducted, and the whole electrode has a current collecting function as one integral body. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery. More specifically, the current collecting property is high, the active material is prevented from falling off due to absorption and desorption of lithium ions, and the cycle life is improved. It is related with the negative electrode which can obtain a high nonaqueous electrolyte secondary battery. Moreover, this invention relates to the manufacturing method of this negative electrode, and the nonaqueous electrolyte secondary battery using this negative electrode.

  In general, graphite is used as a negative electrode active material of a lithium ion secondary battery. Currently, Sn-based alloys and Si-based alloys having a capacity potential 5 to 10 times that of graphite are being actively developed. For example, a conductive metal foil such as a copper foil is used as a current collector, and a mixture of active material particles containing silicon or a silicon alloy and a conductive metal powder such as copper or a copper alloy is not formed on the surface of the current collector. A negative electrode for a lithium secondary battery obtained by sintering in an oxidizing atmosphere has been proposed (see Patent Document 1).

Japanese Patent Laid-Open No. 2002-260637

  However, in this negative electrode, since the active material particles are exposed to the electrolytic solution, the active material particles easily fall off due to expansion and contraction of the active material particles due to absorption and desorption of lithium ions. Cycle life is likely to decrease. Moreover, since the collector in this negative electrode is comparatively thick, such as 10-100 micrometers, the ratio of the active material to the whole negative electrode is low, and it is not easy to raise an energy density resulting from it.

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

  As a result of intensive studies, the inventors have sandwiched the active material layer between two surface layers that also function as a current collector, thereby preventing the active material from falling off due to lithium absorption and desorption. It was found that the proportion of the active material in the entire electrode can be increased while maintaining the electric function.

  The present invention has been made based on the above knowledge, and includes at least a pair of current collecting surface layers whose surfaces are in contact with an electrolytic solution, and active material particles having a high ability to form a lithium compound interposed between the surface layers. The object is achieved by providing a negative electrode for a non-aqueous electrolyte secondary battery comprising a single active material layer.

  Further, in the present invention, as a preferable method for producing the negative electrode, a thin release layer is formed on one surface of a carrier foil, and a metal material having a low ability to form a lithium compound is electrolytically plated thereon to form one current collecting surface layer. Then, a conductive slurry containing active material particles is applied on the current collecting surface layer to form an active material layer, and a metal material having a low lithium compound forming ability is electroplated on the active material layer. Forming the other current collecting surface layer, and thereafter separating and separating the carrier foil from the one current collecting surface layer. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery Is to provide.

  Further, the present invention provides another method for producing the negative electrode, in which a carrier resin having a large number of cation exchange groups on the surface is treated with a metal ion-containing liquid to form a metal salt of the cation exchange group, The metal salt is reduced to form a film of the metal serving as a catalyst nucleus on the surface of the carrier resin, and a metal material having a low ability to form a lithium compound is electroplated on the film to form one current collecting surface layer. And forming an active material layer by applying a conductive slurry containing active material particles on the current collecting surface layer, and electrolyzing a metal material having a low lithium compound forming ability on the active material layer. Plating to form the other current collecting surface layer, and thereafter separating the carrier resin from the one current collecting surface layer by peeling or dissolving, for a non-aqueous electrolyte secondary battery A method for producing a negative electrode is provided.

  Furthermore, the present invention provides a non-aqueous electrolyte secondary battery comprising the negative electrode.

  In the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the active material is not exposed on the surface of the electrode and is embedded in the surface layer for current collection, so there is an electrically isolated active material. Can be effectively prevented, and sufficient current collecting property can be obtained. In addition, the surface layer prevents the active material from falling off, and the current collecting property of the active material is ensured even when charging and discharging are repeated. Furthermore, the secondary battery using this negative electrode has a low deterioration rate even if charging / discharging is repeated, and the cycle life is greatly prolonged, and the charging / discharging efficiency is also increased. In particular, when the conductive metal foil layer as the core material, that is, the current collector used in the conventional negative electrode is not used, the proportion of the active material in the entire negative electrode can be made higher than that of the conventional negative electrode. As a result, a secondary battery having a high energy density per unit volume and unit weight can be obtained.

  Hereinafter, the negative electrode for a nonaqueous electrolyte secondary battery of the present invention will be described based on preferred embodiments thereof. First, the first embodiment will be described. The negative electrode of the present embodiment includes an active material layer containing active material particles and a pair of current collecting surface layers disposed on each surface of the layer.

  The current collecting surface layer has a current collecting function in the electrode of the present embodiment. The surface layer is also used to prevent the active material contained in the active material layer from falling off due to the expansion and contraction of the active material due to absorption and desorption of lithium ions. The surface layer is made of a metal that can be a current collector of a non-aqueous electrolyte secondary battery. In particular, it is preferably made of a metal that can be a current collector of a lithium secondary battery. An example of such a metal is a metal material having a low lithium compound forming ability. 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 may have the same constituent material or may be different. “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 is thinner than the current collector used in a conventional electrode. Specifically, a thin layer of about 0.3 to 10 μm, particularly about 1 to 5 μm is preferable. Thereby, the ratio of the active material to the whole negative electrode becomes relatively high, and the energy density per unit volume and unit weight can be increased. In the conventional negative electrode, since the ratio of the current collector in the entire negative electrode was high, there was a limit to increasing the energy density. The thin surface layer in the above range is preferably formed by electrolytic plating as will be described later. The two surface layers may have the same thickness or may be different.

  As for two surface layers, those surfaces have constituted the outermost surface in the electrode of this embodiment. When the negative electrode of the present embodiment is incorporated in a battery, the surfaces of the two surface layers are in contact with the electrolytic solution and participate in the electrode reaction. In contrast, the current collector in the conventional negative electrode does not contact the electrolyte and does not participate in the electrode reaction when the active material layer is formed on both sides, and the active material on one side. Even when the layer is formed, only one surface is in contact with the electrolyte. That is, in the negative electrode of the present embodiment, the current collector used in the conventional negative electrode, that is, the conductive metal foil layer as the core material disposed in the central portion in the thickness direction of the negative electrode does not exist, and the outermost surface of the negative electrode The layer located on the surface, that is, the surface layer is involved in the electrode reaction, and also has a current collecting function, and further functions to prevent the active material from falling off.

  Since each of the two surface layers has a current collecting function, when the negative electrode of this embodiment is incorporated in a battery, a lead wire for current extraction can be connected to either surface layer. There are advantages.

  Each current collecting surface layer is formed with a large number of fine voids extending in the thickness direction of the surface layer. The fine gap extends while bending. A part of the numerous fine voids extends in the thickness direction of the surface layer and reaches the active material layer. By forming the fine voids, the non-aqueous electrolyte can sufficiently penetrate into the active material layer, and the reaction with the active material particles sufficiently occurs. The fine void is a fine one having a width of about 0.1 μm to about 10 μm when the cross section of the surface layer is observed. Although fine, the fine gap has a width that allows the non-aqueous electrolyte to penetrate. However, since the non-aqueous electrolyte has a smaller surface tension than the aqueous electrolyte, it can sufficiently penetrate even if the width of the fine gap is small. The fine voids can be formed by various methods described later.

Open area of the microvoids in a plan view by a surface layer electron microscopy, 0.1 to 100 [mu] m ² on average, to be particularly 1 to 30 [mu] m ² or so, a sufficient penetration of the non-aqueous electrolyte It is preferable from the viewpoint that the active material layer can be effectively prevented from falling off while ensuring. For the same reason, when the surface layer is viewed in plan by electron microscope observation, no matter what observation field is taken, 1 to 30, particularly 3 to 10 fine voids in a 100 μm × 100 μm square field range. Is preferably present (this value is referred to as a distribution ratio). Further, for the same reason, when the surface layer is viewed in plan by electron microscope observation, the ratio of the total area of the fine voids to the area of the observation field (this ratio is referred to as the area ratio) is 0.1 to 10%. In particular, 1 to 5% is preferable.

  The active material layer sandwiched between the two surface layers includes active material particles having a high lithium compound forming ability. Examples of the active material include silicon-based materials, tin-based materials, aluminum-based materials, and germanium-based materials. Since the active material layer is covered with the two surface layers, the active material is effectively prevented from falling off due to absorption and desorption of lithium ions.

The active material particles preferably have a maximum particle size of 50 μm or less, and more preferably 20 μm or less. Moreover, when the particle diameter of the particle 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 are likely to fall off, and the life of the electrode 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, the lower limit is about 0.01 μm. The particle size of the particles is measured by microtrack and electron microscope observation (SEM observation).

  If the amount of the active material relative to the whole negative electrode 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 whole negative electrode.

  The thickness of the active material layer can be appropriately adjusted according to the ratio of the amount of the active material to the entire negative electrode and the particle size of the active material, and is not particularly critical in the present embodiment. Generally, it is about 1 to 100 μm, particularly about 3 to 40 μm. The active material layer is preferably formed by applying a conductive slurry containing particles of the active material, as will be described later.

  The total thickness of the negative electrode including the surface layer and the active material layer is preferably 2 to 50 μm, particularly preferably about 10 to 50 μm.

  In the active material layer, it is preferable that the material constituting the current collecting surface layer penetrates over the entire thickness direction of the active material layer. The active material particles are preferably present in the permeated material. In other words, the active material particles are preferably not exposed on the surface of the electrode but embedded in the surface layer. Thereby, the adhesion between the active material layer and the surface layer becomes strong, and the active material is further prevented from falling off. In addition, since electronic conductivity is ensured between the surface layer and the active material through the material that has penetrated into the active material layer, an electrically isolated active material is generated, particularly in the deep part of the active material layer. It is effectively prevented that an isolated active material is generated, 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 electrical conductivity, such as a silicon-based material, is used as the active material. The material constituting the current collecting surface layer preferably penetrates the active material layer in the thickness direction and is connected to both surface layers. As a result, the two surface layers are electrically conducted through the material, and the electron conductivity of the negative electrode as a whole is further increased. That is, the negative electrode of the present embodiment has a current collecting function as a whole. The fact that the material constituting the current collecting surface layer permeates over the entire thickness direction of the active material layer and the two surface layers are connected to each other can be determined by electron microscope mapping using the material as a measurement target. A preferred method for allowing the material constituting the current collecting surface layer to penetrate into the active material layer will be described later.

  The active material particles in the active material layer are not completely filled with the constituent material of the surface layer, but preferably there are voids between the particles. Note that it is different from the fine voids formed in the layer). The presence of the voids relieves stress caused by the active material particles absorbing and desorbing lithium and expanding and contracting. From this viewpoint, the void ratio in the active material layer is preferably about 5 to 30% by volume, particularly about 5 to 9% by volume. The void ratio can be determined by electron microscope mapping. As will be described later, since the active material layer is formed by applying and drying a conductive slurry containing particles of the active material, voids are naturally formed in the active material layer. Therefore, in order to set the void ratio within the above range, for example, the particle diameter of the active material particles, the composition of the conductive slurry, and the application conditions of the slurry may be appropriately selected. Alternatively, the slurry may be applied and dried to form an active material layer, and then pressed under appropriate conditions to adjust the void ratio.

  The active material layer preferably contains a conductive carbon material in addition to the active material particles. This further imparts electronic conductivity to the negative electrode. From this viewpoint, the amount of the conductive carbon material contained in the active material layer is preferably 0.1 to 20% by weight, particularly 1 to 10% by weight. 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.

  Next, details of the active material will be described. When the silicon-based material or tin-based material described above is used as the active material, the silicon-based material or tin-based material particles include, for example, a) silicon simple substance or tin simple particles, and b) at least silicon or tin. Mixed particles of carbon, c) mixed particles of silicon or tin and metal, d) compound particles of silicon or tin and metal, e) mixed particles of compound particles of silicon or tin and metal, and metal particles F) Particles in which the surface of particles of silicon alone or tin alone are 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 electronic conductivity can be imparted to silicon which is a semiconductor and has poor electrical conductivity.

  In particular, when the silicon-based particles or tin-based particles are composed of at least mixed particles of silicon or tin and carbon, the cycle life is improved and the negative electrode capacity is increased. The reason is as follows. Carbon, particularly graphite used in negative electrodes for non-aqueous electrolyte secondary batteries, contributes to the absorption and desorption of lithium, has a negative electrode capacity of about 300 mAh / g, and has a very large volume expansion during occlusion of lithium. It is small. On the other hand, silicon is characterized by having a negative electrode capacity of about 4200 mAh / g, which is 10 times or more that of graphite. On the other hand, the volume expansion of silicon during lithium occlusion reaches about 4 times that of graphite. Therefore, when silicon or tin and carbon such as graphite are mixed and pulverized at a predetermined ratio using a mechanical milling method or the like to obtain a homogeneously mixed powder having a particle size of about 0.1 to 1 μm, lithium occlusion The volume expansion of silicon or tin at the time is relaxed by graphite, the cycle life is improved, and a negative electrode capacity of about 1000 to 3000 mAh / g is obtained. The mixing ratio of silicon or tin and carbon is preferably such that the amount of silicon or tin is 10 to 90% by weight, particularly 30 to 70% by weight, especially 30 to 50% by weight. On the other hand, the amount of carbon is preferably 90 to 10% by weight, particularly 70 to 30% by weight, and particularly preferably 70 to 50% by weight. If the composition is within this range, the capacity of the battery and the life of the negative electrode can be increased. In this mixed particle, a compound such as silicon carbide is not formed.

  When the silicon-based particles or the tin-based particles are composed of b) particles, the particles may be a mixed particle of three or more elements including other metal elements in addition to silicon or tin and carbon. As metal elements, Cu, Ag, Li, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn, In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr, One or more kinds of elements selected from the group consisting of Pd and Nd can be mentioned (hereinafter these elements are collectively referred to as additive metals).

  When the silicon-based particles or tin-based particles are the mixed particles of silicon or tin and metal of c), examples of the metal contained in the mixed particles include one or more of the aforementioned additive metals. Of these additive metals, Cu, Ag, Ni, Co, and Ce are preferable, and Cu, Ag, and Ni are preferably used from the viewpoint of excellent electronic conductivity and low ability to form a lithium compound. In addition, when Li is used as the additive metal, metallic lithium is included in the active material in advance, and advantages such as reduction in irreversible capacity, improvement in charge / discharge efficiency, and improvement in cycle life due to reduction in volume change rate occur. preferable. In the mixed particles of silicon or tin and metal of c), the amount of silicon or tin is preferably 30 to 99.9% by weight, particularly 50 to 95% by weight, and particularly preferably 85 to 95% by weight. On the other hand, the amount of the added metal is preferably 0.1 to 70% by weight, particularly 5 to 50% by weight, particularly 5 to 15% by weight. If the composition is within this range, the capacity of the battery and the life of the negative electrode can be increased.

  The mixed particles of silicon or tin and metal of c) can be produced, for example, by the method described below. First, silicon particles or tin particles and metal particles of added metal are mixed, and these particles are mixed and pulverized simultaneously by a pulverizer. As a pulverizer, an attritor, a jet mill, a cyclone mill, a paint shaker, a fine mill, or the like can be used. The particle size of these particles before pulverization is preferably about 20 to 500 μm. By mixing and pulverization by a pulverizer, particles in which silicon or tin and the added metal are uniformly mixed are obtained. The particle size of the particles obtained by appropriately controlling the operating conditions of the pulverizer is, for example, 40 μm or less. As a result, mixed particles of c) are obtained.

  When the silicon-based particles or tin-based particles are the compound particles of silicon or tin and metal of d), the compound includes silicon or an alloy of tin and metal, and 1) a solid solution of silicon or tin and metal 2) Of the intermetallic compound of silicon or tin and metal, or 3) Of the silicon single phase or tin single layer, metal single phase, solid solution of silicon or tin and metal, or intermetallic compound of silicon or tin and metal Any of a composite composed of two or more phases. As the metal, the same metal as the additive metal contained in the mixed particles of silicon or tin and metal of c) can be used. The composition of silicon or tin and metal in the compound particles of d) is 30 to 99.9% by weight of silicon or tin and 0.1 to 70% by weight of metal as with the mixed particles of c). It is preferable that A more preferable composition is selected in an appropriate range depending on the method for producing compound particles. For example, when the compound is a binary alloy of silicon or tin and metal, and the alloy is manufactured using a rapid cooling method described later, the amount of silicon or tin is preferably 40 to 90% by weight. On the other hand, the amount of the added metal is preferably 10 to 60% by weight.

  When the compound is a ternary or higher alloy of silicon or tin and a metal, B, Al, Ni, Co, Sn, Fe, Cr, Zn, In, A small amount of an element selected from the group consisting of V, Y, Zr, Nb, Ta, W, La, Ce, Pr, Pd and Nd may be contained. Thereby, the additional effect that pulverization is suppressed is produced. In order to further enhance this effect, these elements are preferably contained in an alloy of silicon or tin and metal in an amount of 0.01 to 10% by weight, particularly 0.05 to 1.0% by weight.

  D) When the compound particles of silicon or tin and metal are alloy particles, the alloy particles are produced, for example, by a rapid cooling method described below, so that the crystallites of the alloy are finely sized and homogeneously dispersed. By doing so, it is preferable from the viewpoint that pulverization is suppressed and electron conductivity is maintained. In this rapid cooling method, first, a raw material melt containing silicon or tin and an additive metal is prepared. The raw material is made into molten metal by high frequency melting. The ratio of silicon or tin to the additive metal in the molten metal is in the range described above. The temperature of the molten metal is preferably 1200 to 1500 ° C., particularly 1300 to 1450 ° C., in relation to the rapid cooling conditions. An alloy is obtained from this molten metal using a mold casting method. That is, the molten metal is poured into a copper or iron mold to obtain a rapidly cooled silicon alloy or tin alloy ingot. The ingot is pulverized and sieved, and for example, those having a particle size of 40 μm or less are provided for the present invention.

Instead of this mold casting method, a roll casting method can also be used. That is, the molten metal is injected onto the peripheral surface of a copper roll that rotates at high speed. The rotation speed of the roll is preferably 500 to 4000 rpm, particularly 1000 to 2000 rpm from the viewpoint of quenching the molten metal. When the rotational speed of the roll is expressed as a peripheral speed, it is preferably 8 to 70 m / sec, particularly 15 to 30 m / sec. By rapidly cooling the molten metal having a temperature in the above range using a roll rotating at a speed in the above range, the cooling rate becomes 10 ² K / sec or higher, particularly 10 ³ K / sec or higher. The injected molten metal is rapidly cooled in a roll to become a thin body. The thin body is pulverized and sieved and, for example, one having a particle size of 40 μm or less is provided for the present invention. Instead of this rapid cooling method, a desired atomization method can be obtained by spraying an inert gas such as argon at a pressure of 5 to 100 atm on a molten metal at 1200 to 1500 ° C. and atomizing and rapidly cooling the gas. Further, as another method, an arc melting method or mechanical milling can be used.

  When the active material particles are mixed particles of silicon or tin and metal compound particles of e) and metal particles, the compound particles are the same particles as the compound particles of d) described above. Can be used. On the other hand, as the metal particles, the same metal particles as those used for the mixed particles of c) described above can be used. The metal element contained in the compound particle and the metal element constituting the metal particle may be the same or different. In particular, when the metal element contained in the compound particle is nickel, copper, silver or iron and the metal element constituting the metal particle is nickel, copper, silver or iron, a network of these metals in the active material layer A structure is easily formed. As a result, advantageous effects such as improvement of electron conductivity and prevention of falling off due to expansion and contraction of the active material particles are exhibited, which is preferable. From this viewpoint, it is preferable that the metal element contained in the compound particle and the metal element constituting the metal particle are the same type. The active material particles of e) are first obtained by the same method as the production method of the compound particles of d) described above, and the compound particles and the metal particles are mixed with c) described above. It is obtained by mixing according to the method for producing particles. The ratio of silicon or tin and metal in the compound particles can be the same as the ratio of both in the compound particles of d) described above. Further, the ratio of the compound particles to the metal particles can be the same as the ratio of the silicon or tin particles to the metal particles in the mixed particles in (c) described above. Except for these points, the explanation in detail regarding the mixed particles of c) or the compound particles of d) is applied as appropriate to the points not particularly explained regarding the active material particles of e).

  In the case where the silicon-based particles or tin-based particles are particles in which metal is coated on the surface of the silicon simple substance or tin simple particles (this particle is referred to as a metal-coated particle), the coated metal is described above. The additive metal contained in the particles of (c) and d), for example, the same as copper is used (except for Li). The amount of silicon or tin in the metal-coated particles is preferably 70 to 99.9% by weight, particularly 80 to 99% by weight, especially 85 to 95. On the other hand, the amount of the coating metal including copper is preferably 0.1 to 30% by weight, particularly 1 to 20% by weight, particularly 5 to 15% by weight. The metal-coated particles are produced using, for example, an electroless plating method. In this electroless plating method, first, a plating bath in which silicon particles or tin particles are suspended and containing a coating metal such as copper is prepared. In this plating bath, silicon particles or tin particles are electrolessly plated to coat the surface of the silicon particles or tin particles with the coating metal. The concentration of silicon particles or tin particles in the plating bath is preferably about 400 to 600 g / l. When electrolessly plating copper as the coating metal, it is preferable to contain copper sulfate, Rochelle salt or the like in the plating bath. In this case, the concentration of copper sulfate is preferably 6 to 9 g / l, and the concentration of Rochelle salt is preferably 70 to 90 g / l from the viewpoint of controlling the plating rate. For the same reason, the pH of the plating bath is preferably 12 to 13, and the bath temperature is preferably 20 to 30 ° C. As the reducing agent contained in the plating bath, for example, formaldehyde or the like is used, and the concentration thereof can be about 15 to 30 cc / l.

  The active material particles have an oxygen concentration of 3 wt% or less, particularly 2 wt% or less, regardless of the active material particles in any of the above-mentioned forms (i) to (f). It is preferable. As a result, deterioration due to oxidation of the active material particles is effectively prevented, and the life of the negative electrode can be extended. As is apparent from this reason, the lower the oxygen concentration, the better. For the same reason, it is preferable that the active material particles have a silicon or tin concentration at the outermost surface of 1/2 or more, particularly 4/5 or more of the oxygen concentration at the outermost surface (however, F) except for particles). The concentration of oxygen is measured by a gas analysis method that involves combustion of the sample to be measured. The oxygen concentration distribution is measured by various surface state analyzers such as an X-ray photoelectron spectrometer (ESCA) and an Auger electron spectrometer (AES).

  Next, the preferable manufacturing method of the negative electrode of this embodiment is demonstrated, referring FIG. First, a carrier foil 1 is prepared as shown in FIG. There are no particular restrictions on the material of the carrier foil 1. For example, copper foil can be used. Since the carrier foil 1 is used as a support for manufacturing the negative electrode of the present embodiment, it is preferable that the carrier foil 1 has such strength that no twist or the like occurs in the manufacturing process. Therefore, the carrier foil 1 preferably has a thickness of about 10 to 50 μm.

  The carrier foil 1 is preferably produced by electrolysis. Specifically, using a rotating drum as a cathode, electrolysis is performed in an electrolytic bath containing metal ions such as copper to deposit metal on the drum peripheral surface. The carrier foil 1 is obtained by peeling the deposited metal from the drum peripheral surface.

  Next, a thin release layer 2 is formed on one surface of the carrier foil 1 as shown in FIG. When the carrier foil 1 is manufactured by electrolysis, the carrier foil 1 has a smooth glossy surface on one side and a matte surface with an uneven surface on the other side. The glossy surface is the surface facing the drum peripheral surface, and the matte surface is the precipitation surface. In this production method, the release layer 2 may be formed on either the glossy surface or the matte surface. For forming the release layer 2, for example, nitrogen-containing compounds and sulfur-containing compounds described in paragraphs [0037] to [0038] of JP-A No. 11-317574, paragraphs [0020] to [0020] of JP-A No. 2001-140090, and the like. And a mixture of the sulfur-containing compound and copper fine particles. Further, the peeling layer may be formed by performing chromate treatment or nickel plating treatment.

  After the release layer 2 is formed, one surface layer 3a is formed on the release layer by electroplating a metal material having a low ability to form a lithium compound, as shown in FIG. 1 (c). The conditions for electrolytic plating can be the same as the conditions for forming the other surface layer 3b described later. By this electrolytic plating, the fine voids described above can be easily formed in the surface layer 3a. Subsequently, as shown in FIG. 1 (d), an active material layer 4 is formed on the surface layer 3 a by applying a conductive slurry containing active material particles. The surface of the surface layer 3a to which the conductive slurry is applied is a precipitation surface, that is, a mat surface, and the surface roughness is high. By applying the conductive slurry to the surface of the surface layer 3a in such a surface state, there is an advantage that the adhesion between the active material particles and the surface layer 3a is improved.

  The slurry contains active material particles, conductive carbon material particles, a binder, a diluting solvent, and the like. Among these components, the particles of the active material and the particles of the conductive carbon material are as described above. As the binder, polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene propylene diene monomer (EPDM) or the like is used. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used. The amount of the active material particles in the slurry is preferably about 14 to 40% by weight. The amount of the conductive carbon 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 an active material layer is formed, as shown in FIG. 1 (e), a metal material having a low ability to form a lithium compound is electroplated on the active material layer to collect the other current collector. The surface layer 3b for use is formed. As conditions for electrolytic plating, for example, when using copper, when using a copper sulfate solution, the concentration of copper 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 temperature may be 30 to 80 ° C. and the current density may be 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. By appropriately adjusting these electrolytic conditions, the surface layer 3b is formed. Further, the material constituting the surface layer 3b penetrates over the entire thickness direction of the active material layer 4 so that the surface layers 3a and 3b are electrically connected. Further, the numerous fine voids described above are easily formed in the surface layer 3b. This state is shown in FIG. 2A, which is a schematic diagram showing an enlarged main part of FIG. In FIG. 2A, reference numeral 5 represents active material particles, and reference numeral 6 represents conductive carbon material or conductive metal material particles. Reference numeral 7 represents a fine void in the surface layers 3 a and 3 b, and reference numeral 8 represents a void in the active material layer 4.

  The method of forming the fine voids 7 in the surface layers 3a and 3b by electrolytic plating is a method in which an external force is not applied as compared with the formation of the fine voids by press working described later, so that the surface layers 3a and 3b and eventually the negative electrode are damaged. There is an advantage that there is no. Further, regarding the formation of the fine void 7, the surface layer 3b is easier to form than the surface layer 3a. The reason is as follows. Since the active material layer 4 is a layer containing particles of the active material as described above, the surface of the active material layer 4 has a micro uneven shape. That is, the active site where plating is likely to grow and the site that is not so are mixed. When electrolytic plating is performed on the active material layer in such a state, uneven growth occurs in the plating, and the particles of the constituent material of the surface layer 3b grow in a polycrystalline form. When crystal growth proceeds and adjacent crystals collide with each other, a void is formed in that portion. The fine voids 7 are formed by a large number of voids formed in this way. According to this method, the structure of the fine gap 7 becomes extremely fine.

  After the surface layer 3b is formed as shown in FIG. 1 (e), the active material layer 4 may be pressed together with the surface layers 3a and 3b to generate fine voids 7 in the surface layers 3a and 3b. From the viewpoint of obtaining sufficient electron conductivity, the consolidation by press working is such that the total thickness of the active material layer 4 and the surface layers 3a and 3b after the press work is 90% or less, preferably 80% before the press work. It is preferable to carry out the following. For the press working, for example, a roll press machine can be used. The active material layer 4 after the press working preferably has 5 to 30% by volume of voids as described above. Due to the presence of the voids, when the volume expands due to occlusion of lithium during charging, the stress due to the volume expansion is relaxed. Such a gap may be controlled by controlling the press working conditions as described above. The value of this void can be obtained by electron microscope mapping as described above.

  In this manufacturing method, the active material layer 4 may be pressed before the surface layer 3b is formed on the active material layer 4 (this press processing is performed in the sense of distinguishing from the above-described pressing). Called press working). By performing the pre-pressing process, peeling between the active material layer 4 and the surface layer 3a is prevented, and the active material particles are prevented from being exposed on the surface of the surface layer 3b formed later. As a result, it is possible to prevent the deterioration of the cycle life of the battery due to the dropping of the active material particles. The conditions for the pre-pressing are such that the thickness of the active material layer 4 after the pre-pressing is 95% or less, particularly 90% or less of the thickness of the active material layer 4 before the pre-pressing. preferable.

Finally, as shown in FIG. 1 (f), the carrier foil 1 is peeled and separated from the surface layer 3a. Thereby, the negative electrode 10 is obtained. FIG. 2 (b), which is a schematic diagram showing an enlarged main part of FIG. 1 (f), shows this peeling process. When peeling, the peeling layer 2 may remain on the carrier copper foil 1 side or may remain on the surface layer 3a side depending on the thickness and the type of the peeling treatment agent. Or it may remain in both of them. In any case, since the thickness of the release layer 2 is extremely thin, there is no influence on the performance of the obtained negative electrode.
Etc.

  1 is a schematic diagram, the surface layers 3a and 3b are clearly separated from the active material layer 4, and the negative electrode 10 is represented as a three-layer structure. However, in practice, as shown in FIG. 2, it should be noted that the constituent materials of the surface layers 3a and 3b penetrate into the active material layer 4 and the surface layers 3a and 3b are connected to each other. It is.

  According to this manufacturing method, the negative electrode which can use both surfaces of an electrode for an electrode reaction is obtained only by performing formation operation of an active material layer once. In the conventional negative electrode, in order to use both surfaces of the electrode for the electrode reaction, it is necessary to form active material layers on both surfaces of the current collector. In other words, it was necessary to perform the operation of forming the active material layer twice. Therefore, according to this production method, the production efficiency of the negative electrode is greatly improved.

  In addition, according to the present manufacturing method, the carrier foil 1 is not peeled until the negative electrode is incorporated into the battery, and the carrier foil 1 is peeled off immediately before the incorporation, so that the thin film is easily wrinkled and is difficult to roll. There is also an advantage that the negative electrode can be transported with good handling properties.

The negative electrode of the present embodiment thus obtained is used with a known positive electrode, separator, and non-aqueous electrolyte solution to form a non-aqueous 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. The lithium salt, for _{example, 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.

  As another method of manufacturing the negative electrode of the present embodiment, the following method can also be employed. First, a carrier resin having a large number of cation exchange groups on the surface is treated with a metal ion-containing liquid to produce a metal salt of the cation exchange group. Examples of the carrier resin having a cation exchange group include those obtained by treating the surface of a polyimide resin with an aqueous alkali solution such as sodium hydroxide or potassium hydroxide to open an imide ring to generate a large number of carboxyl groups. Can be mentioned. The concentration of the alkaline aqueous solution is suitably about 3 to 10 mol / l. The treatment temperature of the alkaline aqueous solution may be about 20 to 70 ° C., and the treatment time may be about 3 to 10 minutes. The polyimide resin treated with the aqueous alkali solution is preferably neutralized with an acid. Details of ring-opening and formation of a metal film by alkali treatment of polyimide resin are described in JP-A-2001-73159.

  The produced metal salt is reduced with a reducing agent. Examples of the reducing agent include sodium borohydride, hypophosphorous acid and a salt thereof. By the reduction, the metal film serving as a catalyst nucleus is formed on the surface of the carrier resin. Next, electrolytic plating is performed on the coating to form one current collecting surface layer. Subsequently, a conductive slurry containing active material particles is applied on the surface layer to form an active material layer. Further, the active material layer is further electrolytically plated to form the other current collecting surface layer. Thereafter, the carrier resin is peeled off or the carrier resin is dissolved using an organic solvent to separate the carrier resin from one of the current collecting surface layers. Thereby, the negative electrode of the present embodiment is obtained. Note that the description regarding the manufacturing method shown in FIG. 1 described above is appropriately applied to points that are not particularly described regarding the present manufacturing method.

  As still another method of this production method, the following method can also be used. When this method is used, a negative electrode having the surface layers 3a and 3b in which many fine holes are formed can be obtained. The micropores, combined with the microvoids, further ensure the circulation of the non-aqueous electrolyte to the active material layer. For convenience, in the following description, the surface layer 3a is referred to as a first surface layer, and the surface layer 3b is referred to as a second surface layer.

  First, the coated body is coated on one surface of the carrier foil by a predetermined means. It is preferable that the carrier foil is subjected to a pretreatment such as acid cleaning before coating to keep its surface clean. The covering is used to form a large number of micropores in the first surface layer by making the electron conductivity of the formation surface of the first surface layer in the carrier foil nonuniform. The covering is preferably formed to have a thickness of 0.001 to 1 μm, particularly 0.002 to 0.5 μm, especially 0.005 to 0.2 μm. This is because by setting the thickness to such a level, the covering covers the surface of the carrier foil discontinuously, for example, in an island shape. Forming the covering discontinuously is advantageous from the viewpoint of easily forming micropores.

  The covering is made of a material different from the constituent material of the first surface layer. Accordingly, the first surface layer can be successfully peeled from the carrier foil in the peeling step described later. In particular, the covering is a material different from the constituent material of the first surface layer, and Cu, Ni, Co, Mn, Fe, Cr, Sn, Zn, In, Ag, Au, C, Al, Si, It is preferable that at least one element of Ti and Pd is included.

  There is no restriction | limiting in particular in the formation method of a coating body. For example, the formation method of the covering can be selected in relation to the formation method of the first surface layer. Specifically, when the first surface layer is formed by electrolytic plating, it is preferable from the viewpoint of manufacturing efficiency and the like that the covering is also formed by electrolytic plating. However, the coating can be formed by other methods such as electroless plating, sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), sol-gel, or ion plating.

When forming a covering by electrolytic plating, an appropriate plating bath and plating conditions are selected according to the constituent material of the covering. For example, when the covering is made of tin, a plating bath having the following composition or a tin fluoride bath can be used. When this plating bath is used, the bath temperature is preferably about 15 to 30 ° C., and the current density is preferably about 0.5 to 10 A / dm ² .
・ SnSO ₄ 30-70 g / l
・ H ₂ SO ₄ 60-150 g / l
・ Cresol sulfonic acid 70-100g / l

  As described above, the covering is used to make the electron conductivity of the surface of the carrier foil where the first surface layer is formed nonuniform. Therefore, if the electronic conductivity of the constituent material of the covering is greatly different from the electronic conductivity of the carrier foil, the electronic conductivity of the surface of the carrier foil on which the first surface layer is formed is immediately non-uniform by forming the covering. It becomes a state. For example, it is a case where carbon is used as a constituent material of the covering. On the other hand, when a material having the same electronic conductivity as the carrier foil, for example, various metal materials such as tin, is used as a constituent material of the covering, the first surface may be formed depending on the formation of the covering. The electronic conductivity of the layer forming surface does not immediately become uneven. Therefore, in the case of forming a covering from such a material, it is preferable that the carrier foil on which the covering is formed is exposed to an oxygen-containing atmosphere, for example, air, in a dry state. This oxidizes the surface of the covering (and the exposed surface of the carrier foil 1). By this operation, the electronic conductivity of the surface on which the first surface layer is formed becomes nonuniform. When electrolytic plating described later is performed in this state, a difference occurs in the electrodeposition rate between the surface of the covering and the exposed surface of the carrier foil, and micropores can be easily formed. The degree of oxidation is not critical in the present invention. For example, the inventors have found that it is sufficient to leave the carrier foil on which the covering is formed in the atmosphere for about 10 to 30 minutes. However, forcibly oxidizing the carrier foil on which the covering is formed is not prevented.

  The reason why the carrier foil on which the covering is formed is dried when it is exposed to an oxygen-containing atmosphere is to efficiently oxidize. For example, when the covering is formed by electrolytic plating, the carrier foil is lifted from the plating bath, dried using a dryer or the like, and then left in the atmosphere for a predetermined time. When a dry method such as a sputtering method or various vapor deposition methods is used as a method for forming the covering, a drying operation is not necessary, and it may be left in the atmosphere after the formation of the covering.

  After oxidizing the covering, a release layer is formed thereon. The formation of the release layer is as described above. The formation process of a peeling layer is only performed in order to peel the 1st surface layer from carrier foil successfully in the peeling process mentioned later. Therefore, even if this step is omitted, the first surface layer having a large number of fine holes can be formed.

On the release layer, the constituent material of the first surface layer is electrodeposited by electrolytic plating to form the first surface layer. Many fine holes are formed in the formed first surface layer. The plating bath and plating conditions are appropriately selected according to the constituent material of the first surface layer. For example, when the first surface layer is made of Ni, a Watt bath or a sulfamic acid bath having the following composition can be used as the plating bath. When using a watt bath, the bath temperature is preferably about 40 to 70 ° C., and the current density is preferably about 0.5 to 20 A / dm ² . When the sulfamic acid bath is used, the bath temperature is about 40 to 60 ° C., and the current density can be the same as that of the watt bath.
・ 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, an active material layer is formed on the first surface layer. The active material layer is formed, for example, by applying a paste containing active material particles or conductive material particles.

A coating liquid containing carbonaceous material particles, such as a paste, is applied onto the active material layer. This coating solution is applied for the purpose of forming micropores in the second surface layer. For example, acetylene black can be used as the carbonaceous material. The carbonaceous material has an average particle diameter D ₅₀ (measured by the combined use of laser diffraction scattering and scanning electron microscope observation) of 2 to 200 nm, particularly about 10 to 100 nm. This is preferable because it can be easily formed. The thickness for applying the coating solution on the active material layer is preferably about 0.001 to 1 μm, particularly about 0.05 to 0.5 μm. Next, the constituent material of the second surface layer is electrodeposited on the coating film by electrolytic plating to form the second surface layer. The conditions for electrolytic plating can be the same as the plating conditions for the first surface layer described above. The formed second surface layer has a large number of micropores.

  When the second surface layer is formed by electrolytic plating, the plating solution penetrates into the active material layer and reaches the interface between the first surface layer and the active material layer that has been previously formed. Electroplating is performed under conditions. As a result, (b) the inside of the active material layer, (b) the outer surface side of the active material layer (that is, the surface side in contact with the plating solution) and (c) the inner surface side of the active material layer (that is, the first surface layer) The metal material is deposited on the facing surface side). As a result, the second surface layer is formed, and the material constituting the second surface layer penetrates over the entire thickness direction of the active material layer and reaches the previously formed first surface layer. . A part thereof enters a part of the fine holes of the first surface layer.

  Finally, the previously formed first surface layer is peeled from the carrier foil. Thereby, the negative electrode of the present invention is obtained.

  Next, a second embodiment of the present invention will be described with reference to FIG. The present embodiment will be described only with respect to differences from the first embodiment, and the description detailed with respect to the first embodiment is applied as appropriate to points that are not particularly described. In FIG. 3, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals.

  As shown in FIG. 3, the negative electrode of the present embodiment includes a conductive metal foil layer 9 as a core material at the center in the thickness direction. Active material layers 4 and 4 are respectively formed on each surface of the metal foil layer 9. Furthermore, current collecting surface layers 3a and 3b for covering the active material layers 4 and 4 are formed.

  In each of the active material layers 4, 4, the material constituting the current collecting surface layers 3 a, 3 b penetrates over the entire thickness direction of each active material layer 4, 4. The active material particles 5 are not exposed on the surface of the electrode and are embedded in the surface layers 3a and 3b. The material constituting each surface layer 3 a, 3 b penetrates each active material layer 4, 4 in the thickness direction and is connected to the metal foil layer 9. As a result, the surface layers 3a and 3b are electrically connected to the metal foil layer 9, and the electron conductivity of the whole negative electrode is further increased. That is, the negative electrode of the present embodiment also has a current collecting function as a whole, as with the negative electrode of the first embodiment.

  The thicknesses of the surface layers 3a and 3b and the active material layers 4 and 4 in this embodiment can be the same as those in the first embodiment. The thickness of the metal foil layer 9 is preferably 5 to 40 μm, particularly preferably 10 to 20 μm, from the viewpoint of increasing the energy density by suppressing the thickness of the entire negative electrode. From the same viewpoint, the thickness of the whole negative electrode is preferably 10 to 100 μm, particularly preferably 20 to 60 μm.

  The outline of the manufacturing method of the negative electrode of this embodiment is as follows. First, a conductive slurry containing active material particles is applied to each surface of the metal foil layer 9 to form active material layers. The metal foil layer 9 may be manufactured in advance, or may be manufactured in-line as one step in the negative electrode manufacturing process of the present embodiment. When the metal foil layer 9 is manufactured in-line, it is preferably manufactured by electrolytic deposition. After the slurry coating is dried and an active material layer is formed, the metal foil layer 9 on which the active material layer is formed is immersed in a plating bath containing a conductive material having a low lithium compound forming ability, Under the state, electrolytic plating with the conductive material is performed on the active material layer to form the surface layers 3a and 3b. By using this method, a large number of fine voids can be easily formed in the surface layers 3a and 3b. Further, the conductive material constituting the surface layers 3 a and 3 b penetrates over the entire thickness direction of the active material layer, and both surface layers are electrically connected to the metal foil layer 9.

  The present invention is not limited to the embodiment. For example, in the first embodiment, the material constituting the current collecting surface layer penetrates the active material layer in the thickness direction, and both surface layers are electrically connected. Both surface layers do not have to be electrically connected to the extent that can be sufficiently secured. The same applies to the second embodiment.

  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. Unless otherwise specified, “%” means “% by weight”.

[Examples 1 and 2]
(1) Formation of release layer An electrolytic copper foil having a thickness of 35 μm was used as a carrier foil. This carrier foil was washed in a pickling solution 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 g / l carboxybenzotriazole solution kept at 40 ° C. for 30 seconds to form a release layer as shown in FIG. Further, it was washed with pure water at room temperature for 15 seconds.

(2) Formation of first surface layer A carrier foil is immersed in a nickel plating bath having the following bath composition for electrolysis, and as shown in FIG. A layer was formed. The first surface layer was formed on the release layer formed on the glossy surface side of the carrier foil. The current density was 5 A / dm ² and the bath temperature was 50 ° C. A nickel electrode was used as the anode. A DC power source was used as the power source. The film thickness of the first surface layer was 3 μm in Example 1 and 1 μm in Example 2.

Nickel plating bath composition NiSO ₄ · 6H ₂ O 250g / L
NiCl ₂ · 6H ₂ O 45g / L
H ₃ BO ₃ 30g / L

(3) Formation of active material layer After the formation of the first surface layer, it was washed with pure water for 30 seconds and then dried in the air. Next, a slurry containing active material particles was applied onto the first surface layer to form an active material layer having a thickness of 15 μm as shown in FIG. As active material particles, alloy powder having a composition of Si 80% -Ni 20% with an average particle diameter D ₅₀ of 1.5 μm was used. The slurry contained active material particles, nickel powder, acetylene black, and polyvinylidene fluoride (hereinafter referred to as PVdF). The slurry composition was active material: nickel powder: acetylene black: PVdF = 60: 34: 1: 5.

(4) Formation of Second Surface Layer As shown in FIG. 1 (e), a second surface layer made of an ultrathin nickel foil was formed on the active material layer by electrolysis. The electrolysis conditions were the same as the conditions for forming the first surface layer. However, electrolysis was performed so that the film thickness was 3 μm.

(5) Peeling of the electrode The electrode thus obtained was peeled from the carrier foil as shown in FIG. 1 (f) to obtain a negative electrode of the present invention. An electron micrograph of the cross section of the negative electrode obtained in Example 1 is shown in FIG.

[Examples 3 and 4]
An ultrathin copper foil as the first surface layer was formed by electrolysis. The bath composition was as follows. The current density was 20 A / dm ² and the bath temperature was 40 ° C. A dimensionally stabilized anode was used as the anode. A DC power source was used as the power source. The film thickness of the first surface layer was 3 μm in Example 3 and 1 μm in Example 4. The first surface layer was then treated with a 1 g / l benzotriazole solution maintained at 25 ° C. for 10 seconds for the purpose of rust-proofing the first surface layer. A negative electrode was obtained in the same manner as Example 1 except for these.
Copper plating bath composition CuSO ₄ · 5H ₂ O 250g / L
H ₂ SO ₄ 70 g / L

Example 5
A slurry similar to the slurry used in Example 1 was coated on each surface of an electrolytic copper foil having a thickness of 35 μm so as to have a thickness of 15 μm, and dried to form an active material layer. Subsequently, it was immersed in a nickel plating bath having the same bath composition as in Example 1 to perform electrolysis, and each surface layer made of an ultrathin nickel foil was formed as shown in FIG. The electrolysis conditions were the same as in Example 1. The thickness of each surface layer was 3 μm. In this way, the negative electrode shown in FIG. 3 was obtained.

[Comparative Example 1]
A slurry having a mixing ratio (weight ratio) of graphite powder (average particle diameter D ₅₀ = 10 μm): acetylene black (average particle diameter D ₅₀ = 40 nm): PVdF: N-methylpyrrolidone = 16: 2: 2: 80 was prepared. . The slurry was applied to each surface of a 35 μm thick copper foil and dried to form an active material layer. Next, roller pressing was performed at a pressure of 0.5 t / cm. The thickness of one side of the active material layer after press working was 40 μm. In this way, a negative electrode was obtained.

[Comparative Example 2]
A slurry similar to the slurry used in Example 1 was applied to each surface of a 35 μm-thick copper foil so as to have a thickness of 15 μm and dried to form an active material layer. In this way, a negative electrode was obtained.

[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 nonaqueous electrolyte secondary battery was produced by a conventional method using a mixed solution (1: 1 volume ratio) of LiPF ₆ / ethylene carbonate and diethyl carbonate as a nonaqueous 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.

[Battery capacity]
The volume was calculated from the thickness and area of the negative electrode, and the capacity per unit volume was calculated. The capacity of the battery using the electrode of Comparative Example 1 as the negative electrode was taken as 100, and the capacity of other batteries was displayed in relative terms.

[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 shown in Table 1, the secondary battery using the electrode obtained in each example has a maximum negative electrode discharge capacity, a battery capacity and 50% higher than the secondary battery using the electrode obtained in each comparative example. It can be seen that the capacity retention rate during the cycle is high. Although not shown in the table, as a result of observation with an electron microscope, in the negative electrodes of Examples 1 to 4, the constituent material of the surface layer penetrated throughout the thickness direction of the active material layer, and both surface layers were electrically It was confirmed that it was electrically connected. In the negative electrode of Example 5, it was confirmed that the constituent material of the surface layer penetrated over the entire region in the thickness direction of the active material layer and was electrically connected to the copper foil. Furthermore, in the negative electrodes of Examples 1 to 5, it was confirmed that many fine voids extending in the thickness direction of the surface layer were formed in the surface layer.

FIG. 1A to FIG. 1F are process diagrams showing an example of a method for producing a negative electrode of the present invention. 2 (a) and 2 (b) are schematic views showing enlarged main parts of FIGS. 1 (e) and 1 (f), respectively. It is a schematic diagram which shows the structure of the negative electrode of the 2nd Embodiment of this invention. 2 is an electron micrograph of a cross section of the negative electrode obtained in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carrier copper foil 2 Release layer 3a, 3b Current collecting surface layer 4 Active material layer 5 Active material particle 6 Conductive carbon material and conductive metal material particle 7 Fine void 8 Void 9 Metal foil layer 10 Negative electrode

Claims (13)

  A pair of current collecting surface layers whose surfaces are in contact with the electrolytic solution, and at least one active material layer including active material particles having a high lithium compound-forming ability, disposed between the surface layers. A negative electrode for a non-aqueous electrolyte secondary battery.   The material constituting the current collecting surface layer penetrates over the entire thickness direction of the active material layer, and both surface layers are electrically connected, and the entire electrode has a current collecting function as a whole. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the current collecting surface layer has a thickness of 0.3 to 10 µm.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the particles of the active material are particles of a silicon-based material or a tin-based material.   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 is made of a metal material having a low ability to form a lithium compound.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material layer is formed by applying a conductive slurry containing particles of the active material.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the current collecting surface layer is formed by electrolytic plating.   The nonaqueous electrolytic solution according to any one of claims 1 to 7, wherein the current collecting surface layer has a large number of fine voids extending in a thickness direction of the surface layer and allowing the nonaqueous electrolytic solution to permeate. Negative electrode for secondary battery.   9. The non-aqueous electrolyte secondary battery according to claim 1, wherein a conductive metal foil layer as a core material is not provided at a central portion in the thickness direction, and the total thickness is 2 to 50 μm. Negative electrode.   The current collector is provided with a conductive metal foil layer as a core material in a central portion in the thickness direction, the active material layer is formed on each surface of the metal foil layer, and further covers each active material layer The negative electrode for nonaqueous electrolyte secondary batteries in any one of Claims 1-8 in which the surface layer for each is formed, and the whole thickness is 10-100 micrometers. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1,
A thin release layer is formed on one surface of the carrier foil, and a metal material having a low ability to form a lithium compound is electrolytically plated thereon to form one current collecting surface layer, and an active layer is formed on the current collecting surface layer. A conductive slurry containing material particles is applied to form an active material layer, and a metal material having a low ability to form a lithium compound is electroplated on the active material layer to form the other current collecting surface layer. Then, after that, the carrier foil is peeled and separated from the one surface layer for current collection. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1,
A carrier resin having a large number of cation exchange groups on the surface is treated with a metal ion-containing liquid to form a metal salt of the cation exchange group, and the metal salt is reduced to form a catalyst nucleus on the surface of the carrier resin. The metal film is formed, and a metal material having a low ability to form a lithium compound is electroplated on the film to form one current collecting surface layer, and active material particles are formed on the current collecting surface layer. An active material layer is formed by applying a conductive slurry containing, and the other surface layer for current collection is formed on the active material layer by electroplating a metal material having a low ability to form a lithium compound. Thereafter, the carrier resin is separated from the one surface layer for current collection by peeling or dissolving, and the method for producing a negative electrode for a non-aqueous electrolyte secondary battery. A nonaqueous electrolyte secondary battery comprising the negative electrode for a nonaqueous electrolyte secondary battery according to claim 1.