JP3764470B1 - 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 that can relieve stress caused by volume change of an active material caused by charge / discharge and can prevent deformation of the negative electrode.
A non-aqueous electrolyte secondary battery negative electrode 10 includes an active material layer 2 containing active material particles 2a. In the active material layer 2, the metal material 4 deposited by electrolytic plating penetrates between the particles. The negative electrode 10 has a number of vertical holes 5 that are open on at least one surface thereof and extend in the thickness direction of the active material layer 2. A pair of current collecting layers 3a and 3b in contact with the electrolytic solution is further provided, and the active material layer 2 is disposed between the current collecting layers 3a and 3b.
[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.

  A metal element that has a metal element that forms an alloy with lithium and a metal element that does not form an alloy with lithium as a constituent element and that does not form an alloy with lithium at the surface that is in contact with the electrolyte of the negative electrode and is connected to the surface facing the positive electrode and the output terminal A negative electrode for a lithium secondary battery with a high content of is proposed (see Patent Document 1). According to this negative electrode, even when a metal element that forms an alloy with lithium is pulverized due to charge and discharge, conductivity is maintained through a metal that does not form an alloy with lithium.

  In Patent Document 1, as a specific structure of the negative electrode, a powdery member containing a metal element that forms an alloy with lithium is used as a metal current collecting member that does not form an alloy with lithium using a binder. A bonded structure and a fired structure have been proposed. It has also been proposed to dispose a metal element that does not form an alloy with lithium on a layer containing a metal element that forms an alloy with lithium. The metal element that does not form an alloy with lithium is formed by plating, for example.

  However, the negative electrode described in Patent Document 1 has a sufficient surface coverage and strength due to the fact that the thickness of the metal layer that does not form an alloy with lithium covering the negative electrode surface is as thin as about 50 nm. Can't get. As a result, the stress due to the volume change caused by the expansion and contraction of the active material due to charge / discharge cannot be sufficiently relaxed, and the negative electrode is significantly deformed. Moreover, when the active material is pulverized due to expansion and contraction, it cannot be effectively prevented from falling off. Therefore, it is not easy to improve the cycle characteristics of the negative electrode.

  Apart from the above-mentioned patent document, a negative electrode for a non-aqueous electrolyte secondary battery having a hole penetrating the active material layer has been proposed (see Patent Document 2). However, in this negative electrode, when the active material is pulverized due to expansion and contraction, it is difficult to maintain conductivity, and the active material may fall off from the side wall of the through hole. is there. Therefore, it is not easy to improve the cycle characteristics of the negative electrode.

JP-A-8-50922 JP 2001-76761 A

  Accordingly, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery that can eliminate the various drawbacks of the above-described conventional technology.

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery including an active material layer containing active material particles.
In the active material layer, a metal material having a low ability to form a lithium compound deposited by electrolytic plating penetrates between the particles, and the active material layer is open in at least one surface of the negative electrode and has a thickness direction of the active material layer. The above object is achieved by providing a negative electrode for a non-aqueous electrolyte secondary battery, characterized in that it has a number of vertical holes extending in the direction.

  The present invention also provides a non-aqueous electrolyte secondary battery comprising the negative electrode.

  According to the present invention, the vertical holes extending in the thickness direction of the active material layer can sufficiently relieve the stress caused by the volume change of the active material due to charging / discharging, so that significant deformation of the negative electrode is effective. Can be prevented. Therefore, the cycle life is significantly increased, and the charge / discharge efficiency is also increased. In addition, since the metal material is deposited between the active material particles in the active material layer, even if the active material particles are pulverized due to charge / discharge, there is an effect that an electrically isolated active material exists. Therefore, sufficient current collecting property can be obtained.

  The present invention will be described below based on preferred embodiments with reference to the drawings. First, the negative electrode of the first embodiment shown in FIG. 1 will be described. The negative electrode 10 of the present embodiment has a first surface 1a and a second surface 1b which are a pair of front and back surfaces in contact with the electrolytic solution. The negative electrode 10 includes an active material layer 2. The active material layer 2 is continuously covered with a pair of current collecting layers 3 a and 3 b formed on each surface of the layer 2. Each of the current collecting layers 3a and 3b includes a first surface 1a and a second surface 1b. As is clear from FIG. 1, the electrode 10 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 layers 3a and 3b have a current collecting function in the negative electrode 10 of the present embodiment. The current collecting layers 3a and 3b are also used to prevent the active material contained in the active material layer 2 from changing in volume due to charge and discharge, being pulverized, and falling off.

  Each of the current collecting layers 3a and 3b is thinner than the current collecting thick film conductor used in the conventional electrode. 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 2 can be continuously coated almost uniformly with the minimum necessary thickness. As a result, the pulverized active material 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 current collecting layers 3a and 3b in the above range are preferably formed by electrolytic plating as will be described later. The two current collecting layers 3a and 3b may have the same thickness or different thicknesses.

  As described above, the two current collecting layers 3a and 3b include the first surface 1a and the second surface 1b, respectively. When the negative electrode 10 of the present embodiment is incorporated in a battery, the first surface 1a and the second surface 1b are surfaces in contact with the electrolytic solution. In contrast, a thick film conductor for collecting current in a conventional electrode does not come into contact with the electrolyte solution when the active material layer is formed on both sides thereof, and the active material layer is not provided on one side. Even if it is formed, only one surface is in contact with the electrolyte. In other words, the negative electrode 10 of the present embodiment does not have the current collecting thick film conductor used in the conventional electrode, and the layers positioned on the outermost surface of the electrode, that is, the current collecting layers 3a and 3b are collected. It has both an electric function and a function to prevent the pulverized active material from falling off.

  Since each of the current collecting layers 3a and 3b including the first surface 1a and the second surface 1b has a current collecting function, when the negative electrode 10 of this embodiment is incorporated in a battery, The current collecting layers 3a and 3b also have an advantage that a lead wire for current extraction can be connected.

  Each current collecting layer 3a, 3b 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 ion secondary battery. Examples of such a metal include an element having a low ability to form a lithium compound. Examples of the element having a low ability to form a lithium compound include copper, nickel, iron, cobalt, and alloys of these metals. Of these metals, it is particularly preferable to use copper or nickel or an alloy thereof. In particular, it is preferable to use a nickel-tungsten alloy because the current collecting layers 3a and 3b can have high strength. The two current collecting layers 3a and 3b may have the same or different 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.

  The active material layer 2 positioned between the current collecting layers 3a and 3b includes active material particles 2a. The active material layer 2 is formed, for example, by applying a conductive slurry containing active material particles 2a.

Examples of the active material include silicon-based materials, tin-based materials, aluminum-based materials, and germanium-based materials. In particular, a silicon-based material is preferable. Since the active material layer 2 is covered with the two current collecting layers 3a and 3b, the active material is effectively prevented from being pulverized and falling off due to charge / discharge. Further, since the vertical holes described later are formed, the active material particles 2a can be in contact with the electrolytic solution, so that the electrode reaction is not hindered.

The active material particles 2a preferably have a maximum particle size of 30 μm or less, and more preferably 10 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 0.3 to 2 μm. When the maximum particle size is more than 30 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 laser diffraction / scattering particle size distribution measurement 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 2 can be appropriately adjusted according to the ratio of the amount of the active material to the whole negative electrode and the particle size of the active material, and is not particularly critical in the present embodiment. Generally, the thickness is about 1 to 100 μm, particularly about 3 to 60 μm. The active material layer is preferably formed by applying a conductive slurry containing particles of the active material, as will be described later.

  In the active material layer 2, as shown in FIG. 1, a metal material 4 having a low lithium compound forming ability penetrates between particles contained in the layer. The metal material 4 is deposited between the particles by electrolytic plating. It is preferable that the metal material 4 penetrates over the entire thickness direction of the active material layer 2. The active material particles 2a are preferably present in the permeated material. That is, it is preferable that the active material particles 2a are not substantially exposed on the surface of the negative electrode 10 and are embedded in the current collecting layers 3a and 3b. Thereby, the adhesiveness between the active material layer 2 and the current collecting layers 3a and 3b becomes strong, and the active material is further prevented from falling off. In addition, since electronic conductivity is ensured between the current collecting layers 3a and 3b and the active material through the material 4 that has penetrated into the active material layer 2, it is possible to generate an electrically isolated active material, particularly an active material. Generation of an electrically isolated active material in the deep part of the layer 2 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 metal material 4 having a low ability to form a lithium compound penetrating into the active material layer 2 has conductivity, and examples thereof include metal materials such as copper, nickel, iron, cobalt, and alloys of these metals. Is mentioned. The material may be the same kind of material as the material constituting the current collecting layers 3a and 3b, or may be a different kind of material.

  It is preferable that the metal material 4 having a low ability of forming a lithium compound penetrating into the active material layer 2 penetrates the active material layer 2 in the thickness direction. As a result, the two current collecting layers 3a and 3b are electrically conducted through the metal material 4, and the electron conductivity of the whole negative electrode is further increased. That is, the negative electrode 10 of the present embodiment as a whole has a current collecting function. The permeation of the metal material 4 having a low lithium compound forming ability throughout the thickness direction of the active material layer 2 can be confirmed by electron microscope mapping using the material as a measurement target. A preferable method for infiltrating the metal material 4 having a low lithium compound forming ability into the active material layer 2 will be described later.

  The space between the active material particles 2a in the active material layer 2 is preferably not completely filled with the metal material 4 having a low lithium compound forming ability, but preferably has voids between the particles. Due to the presence of the voids, the stress caused by the volume change of the active material particles 2a caused by charging / discharging is relieved. From this viewpoint, the proportion of voids in the active material layer 2 is preferably about 0.1 to 30% by volume, particularly about 0.5 to 5% by volume. The void ratio can be determined by electron microscope mapping. Since the active material layer 2 is formed by applying and drying a conductive slurry containing the active material particles 2 a, voids are naturally formed in the active material layer 2. Accordingly, in order to set the void ratio within the above range, for example, the particle diameter of the active material particles 2a, the composition of the conductive slurry, and the application conditions of the slurry may be appropriately selected. In addition, after the slurry is applied and dried to form the active material layer 2, the proportion of voids may be adjusted by pressing under appropriate conditions. It should be noted that the voids mentioned here do not include the vertical holes 5 described later.

  The active material layer may contain a conductive carbon material in addition to the active material particles 2a. This further imparts electronic conductivity to the negative electrode 10. 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.

  As shown in FIG. 1, the negative electrode 10 has a number of vertical holes 5 that are open in the surface of the negative electrode 10 and extend in the thickness direction of the active material layer 2 and the current collecting layers 3 a and 3 b. The vertical hole 5 penetrates in the thickness direction of the negative electrode 10. In the active material layer 2, the active material layer 2 is exposed on the wall surface of the vertical hole 5. The roles of the vertical holes 5 can be broadly classified as follows.

  One is the role of supplying the electrolytic solution into the active material layer through the active material layer 2 exposed on the wall surface of the vertical hole 5. In this case, the active material layer 2 is exposed at the wall surface of the vertical hole 5, but the metal material 4 permeates between the active material particles 2 a in the active material layer, so that the particles 2 a may fall off. It is prevented.

  The other is the role of relieving the stress caused by the volume change when the volume of the active material particles 2a in the active material layer changes due to charge / discharge. The relaxation of the stress due to the volume change occurs mainly in the planar direction of the negative electrode 10. That is, the increase in the volume of the active material particles 2 a whose volume has been increased by charging is absorbed by the vertical holes 5 serving as spaces. As a result, significant deformation of the negative electrode 10 is effectively prevented.

Another role of the vertical hole 5 is that the gas generated in the negative electrode can be released to the outside. Specifically, gas such as H ₂ , CO, and CO ₂ may be generated due to moisture contained in a minute amount in the negative electrode. When these gases accumulate in the negative electrode, the polarization increases and causes charge / discharge loss. By forming the vertical hole 5, the gas is released to the outside of the negative electrode through this, so that the polarization caused by the gas can be reduced. Further, as another role of the vertical hole 5, there is a role of heat dissipation of the negative electrode. Specifically, since the specific surface area of the negative electrode is increased by forming the vertical holes 5, the heat generated with the insertion of Li is efficiently released to the outside of the negative electrode. Further, when stress is generated due to the volume change of the active material particles 2a, heat may be generated due to the stress. Since the stress is relieved by forming the vertical hole 5, the generation of heat itself is suppressed.

  From the viewpoint of sufficiently supplying the electrolytic solution into the active material layer and effectively reducing the stress caused by the volume change of the active material particles 2a, the opening of the vertical hole 5 opened on the surface of the negative electrode 10 is opened. The value obtained by dividing the porosity, that is, the total area of the vertical holes 5 by the apparent area of the surface of the negative electrode 10 and multiplying by 100 is preferably 0.3 to 30%, particularly 2 to 15%. For the same reason, the opening diameter of the vertical hole 5 opened on the surface of the negative electrode 10 is preferably 5 to 500 μm, particularly preferably 20 to 100 μm. Also, by setting the pitch of the vertical holes 5 to preferably 20 to 600 μm, more preferably 45 to 400 μm, the electrolyte can be sufficiently supplied into the active material layer, and the stress due to the volume change of the active material particles 2 a Can be effectively mitigated. Further, when attention is paid to an arbitrary portion on the surface of the negative electrode 10, an average of 100 to 250,000, particularly 1000 to 40000, especially 5000 to 20000, vertical holes 5 are opened in a 1 cm × 1 cm square observation field. It is preferable to have holes.

  In the negative electrode 10 of the present embodiment, the vertical hole 5 penetrates in the thickness direction of the negative electrode 10. However, in view of the role of the vertical hole 5 to sufficiently supply the electrolyte solution into the active material layer and relieve the stress caused by the volume change of the active material particles 2 a, the vertical hole 5 has a thickness of the negative electrode 10. There is no need to penetrate in the direction, as long as it is open at the surface of the negative electrode 10 and reaches at least the active material layer 2.

  As shown in FIG. 1, in the negative electrode 10, the current collecting layers 3 a and 3 b are opened on the first surface 1 a and the second surface 1 b, which are the surfaces of the current collecting layers 3 a and 3 b. (It should be noted that the fine voids 6 are different from the voids formed in the active material layer 2). The fine gap 6 exists in the current collecting layers 3a and 3b so as to extend in the thickness direction of the current collecting layers 3a and 3b. The fine gap 6 is capable of flowing an electrolytic solution. The fine gap 6 has a finer structure than the vertical hole 5 described above. The role of the fine voids 6 assists the role of the vertical holes 5 to sufficiently supply the electrolytic solution into the active material layer. Therefore, the fine gap 6 is not an essential structure in the present invention.

  The fine gap 6 has a width of about 0.1 μm to about 10 μm when the current collecting layers 3a and 3b are observed in cross section. Although it is fine, the fine gap 6 has 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 fine gap 6 is small. The fine gap 6 is preferably formed at the same time when the current collecting layers 3a and 3b are formed by electrolytic plating.

When the 1st surface 1a and the 2nd surface 1b are planarly viewed by electron microscope observation, the average opening area of the fine space | gap 6 in at least one surface is 0.1-50 micrometers ² , Preferably it is 0.1. ～20Myuemu ^2, more preferably from about ² 0.5 to 10 [mu] m. 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 electrolytic solution. Further, the charge / discharge capacity can be increased from the initial stage of charge / discharge.

  Of the first surface 1a and the second surface 1b, when the surface where the average hole area satisfies the above range is viewed in plan by electron microscope observation, the sum of the hole area of the fine gap 6 with respect to the area of the observation field The ratio (this ratio is referred to as the opening ratio) is preferably 0.1 to 20%, more preferably 0.5 to 10%. This reason is the same reason as setting the aperture area of the fine gap 6 within the above range. Furthermore, for the same reason, when the surface of the first surface 1a and the second surface 1b that satisfies the above range of the average aperture area is viewed in plan by electron microscope observation, any observation field of view is taken. It is preferable that 1 to 20,000, particularly 10 to 1,000, especially 30 to 500 fine voids 6 exist in a 100 μm × 100 μm square field of view (this value is referred to as distribution rate). ).

  Next, the preferable manufacturing method of the negative electrode 10 of this embodiment is demonstrated, referring FIG. In this manufacturing method, the current collecting layer 3b is formed by electrolytic plating, the active material layer 2 is then formed thereon, the current collecting layer 3a is further formed thereon by electrolytic plating, and finally the vertical holes 5 are formed. The process of doing is performed. First, a carrier foil 11 is prepared as shown in FIG. The carrier foil 11 is used as a support for manufacturing the negative electrode 10. Further, the manufactured negative electrode 10 is supported before use or during battery assembly processing, and is used for improving the handleability of the negative electrode 10. From these viewpoints, it is preferable that the carrier foil 11 has such strength that no twist or the like is generated in the manufacturing process of the negative electrode 10 and in the transporting process and the battery assembling process after the manufacturing. Therefore, the carrier foil 11 preferably has a thickness of about 10 to 50 μm. As described above, an important role of the carrier foil 11 is a support for manufacturing the negative electrode 10. Therefore, when the strength of the current collecting layer 3b is sufficient, it is not always necessary to manufacture the negative electrode 10 using the carrier foil.

  It is preferable to use a conductive foil as the carrier foil 11. In this case, the carrier foil 11 may not be made of metal as long as it has conductivity. However, the use of the metal carrier foil 11 has an advantage that the carrier foil 11 can be melted and manufactured after the negative electrode 10 is manufactured and recycled. When the metal carrier foil 11 is used, the carrier foil 11 is configured to include at least one metal of Cu, Ni, Co, Fe, Cr, Sn, Zn, In, Ag, Au, Al, and Ti. It is preferable.

  As the carrier foil 11, for example, a foil manufactured by various methods such as a rolled foil and an electrolytic foil can be used without particular limitation. From the viewpoint of controlling the pore size and density of fine voids in the current collecting layer 3b formed on the carrier foil 11, the surface of the carrier foil 11 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 current collecting layer 3b is formed on the rough surface of the carrier foil 11 made of electrolytic foil, it is convenient because it is possible to save the trouble of performing a roughening treatment on the carrier foil separately. The advantage of using a rough surface will be described later. When the current collecting layer 3b is formed on such a rough surface, the surface roughness Ra (JIS B 0601) is 0.05 to 5 μm, particularly 0.2 to 0.8 μm. It is preferable from the point which can form the fine space | gap which has this.

  Next, a release agent is applied to one surface of the carrier foil 11 to perform a release treatment. The release agent is preferably applied to the rough surface of the carrier foil 11. The stripping agent is used for successfully stripping the negative electrode 10 from the carrier foil 11 in the stripping step described later. As the release agent, it is preferable to use an organic compound, and 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. These organic compounds are used by being dissolved in alcohol, water, acidic solvent, alkaline solvent or the like. For example, when CBTA is used, the concentration is preferably 2 to 5 g / 1. The peelability can be controlled by the concentration of the release agent and the coating amount. On the other hand, it is also effective to form an inorganic release layer by chromium, lead, chromate treatment or the like instead of the release layer made of an organic compound. The step of applying the release agent is only performed in order to successfully peel off the negative electrode 10 from the carrier foil 11 in the later-described peeling step (FIG. 2G). Therefore, even if this step is omitted, fine voids can be formed in the current collecting layer 3b.

  Next, as shown in FIG. 2 (b), after applying a release agent (not shown), a coating liquid containing a conductive polymer is applied and dried to form a coating film 12. Since the coating liquid is applied to the rough surface of the carrier foil 11, it tends to accumulate in the recesses on the rough surface. When the solvent volatilizes in this state, the thickness of the coating film 12 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 this manufacturing method, a large number of fine voids are formed in the current collecting layer 3b by utilizing the thickness non-uniformity of the coating film 12.

  There is no restriction | limiting in particular as a conductive polymer, 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. The conductive polymer 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 coating liquid containing a conductive polymer 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.

  In this manufacturing method, the mechanism by which the current collecting layer 3b having a large number of fine voids is formed on the carrier foil 11 is considered as follows. The carrier foil 11 on which the coating film 12 is formed is subjected to an electrolytic plating process to form a current collecting layer 3b on the coating film 12 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 constituting the coating film 12 has electronic conductivity, although not as much as metal. Accordingly, the coating film 12 has different electron conductivity depending on its thickness. As a result, when a metal is deposited on the coating film 12 containing a conductive polymer by electrolytic plating, a difference occurs in the deposition rate according to the electron conductivity, and the current collection layer 3b is finely divided by the difference in the deposition rate. A void 6 is formed. That is, a portion where the electrodeposition rate is low, in other words, a portion where the coating film 12 is thick is likely to become the fine void 6. As described above, it is not essential in the present invention to form fine voids in the current collecting layer. Therefore, in the case where fine voids are not formed in the current collecting layer, the coating liquid containing a conductive polymer is used. A coating process is unnecessary.

  As described above, the pore diameter and density of the fine voids 6 can be controlled by the surface roughness Ra of the rough surface of the carrier foil 11. In addition to this, the concentration of the conductive polymer contained in the coating liquid can also be controlled. It is possible to control the pore size and density of the fine voids 6. For example, when the concentration of the conductive polymer is low, the pore diameter tends to be small and the existence density tends to be small. Conversely, when the concentration of the conductive polymer is high, the pore diameter tends to increase. From this viewpoint, the concentration of the conductive polymer in the coating solution is preferably 0.05 to 5% by weight, particularly 1 to 3% by weight.

The plating bath and plating conditions for forming the current collecting layer 3b are appropriately selected according to the constituent material of the current collecting layer 3b. When the current collecting layer 3b is made of, for example, copper, a copper sulfate bath or a copper pyrophosphate 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 50 A / dm ² .
・ CuSO ₄ .5H ₂ O 150-350 g / l
・ H ₂ SO ₄ 50-250 g / l
The release agent layer and the conductive polymer layer composed of an organic agent can be formed by dipping in addition to coating.

  Next, as shown in FIG. 2D, an active material layer 2 is formed on the current collecting layer 3b by applying a conductive slurry containing particles of the active material. In addition to the active material particles, the slurry contains 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), styrene butadiene rubber (SBR) 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. A dilution solvent is added to these to form a slurry.

  The active material layer 2 is formed by drying the slurry coating. The formed active material layer 2 has a large number of minute spaces between particles. The carrier foil 11 on which the active material layer 2 is formed is immersed in a plating bath containing a metal material having a low lithium compound forming ability to perform electrolytic plating. By immersing in the plating bath, the plating solution enters the minute space in the active material layer 2 and reaches the interface between the active material layer 2 and the current collecting layer 3b. Under this condition, electrolytic plating is performed (hereinafter, this plating is also referred to as penetration plating). As a result, a metal material having a low ability to form a lithium compound is formed on the inside of (a) the active material layer 2 and (b) the inner surface side of the active material layer 2 (that is, the surface side facing the current collecting layer 3b). The material is deposited and permeates throughout the thickness direction of the active material layer 2.

The conditions of the osmotic plating are important in order to deposit a metal material having a low lithium compound forming ability in the active material layer 2. For example, when copper is used as a metal material having a low lithium compound forming ability, 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, and the concentration of chlorine is 30 ppm or less. The liquid 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, a metal material having a low lithium compound forming ability is deposited over the entire thickness direction of the active material layer 2. A particularly important condition is the current density during electrolysis. If the current density is too high, precipitation inside the active material layer 2 does not occur, and precipitation occurs only on the surface of the active material layer 2.

  Next, the current collecting layer 3 a is formed on the active material layer 2. Incidentally, since the active material layer 2 includes the active material particles 2a and the like, the surface thereof is rough. Therefore, if the same means as the means for forming the current collecting layer 3b on the rough surface of the carrier foil 11 made of electrolytic foil is employed to form the current collecting layer 3a, the current collecting layer 3a also has a large number of fine elements. It is also possible to form the gap 6. That is, a coating liquid containing a conductive polymer is applied to the surface of the active material layer 2 and dried to form a coating film. Next, using the same conditions as those for forming the current collecting layer 3b, as shown in FIG. 2E, the current collecting layer 3a is formed on the coating film by electrolytic plating. As described above, it is not essential in the present invention to form fine voids in the current collecting layer. Therefore, in the case where fine voids are not formed in the current collecting layer, the coating liquid containing a conductive polymer is used. A coating process is unnecessary.

  Next, as shown in FIG. 2 (f), the vertical holes 5 penetrating both the current collecting layers 3a and 3b and the active material layer 2 are formed by a predetermined drilling process. There is no restriction | limiting in particular in the formation method of the vertical hole 5. FIG. For example, the vertical holes 5 can be formed by laser processing. Alternatively, drilling can be performed mechanically with a needle or punch. When both are compared, it is easier to obtain a negative electrode with good cycle characteristics and charge / discharge efficiency when laser processing is used. This is because, in the case of laser processing, the metal material dissolved and re-solidified by processing covers the surface of the active material particles present on the wall surface of the vertical hole 5, thereby preventing the active material from being directly exposed, thereby This is because the substance is prevented from falling off the wall surface of the vertical hole 5. In addition, as another forming means of the vertical hole 5, it is also possible to form the vertical hole 5 by using sandblasting or using a photoresist technique. The vertical holes 5 are preferably formed so as to exist at substantially equal intervals. This is because the entire electrode can react uniformly.

  Finally, as shown in FIG. 2G, the carrier foil 11 is peeled and separated from the current collecting layer 3b. Thereby, the negative electrode 10 is obtained. In FIG. 2 (g), the conductive polymer coating 12 is drawn so as to remain on the current collecting layer 3b side. However, the coating film 12 is on the carrier foil 11 side depending on the thickness and type of the conductive polymer. Or may remain on the current collecting layer 3b side. Or it may remain in both of them. As described above, the negative electrode 10 may be supported on the carrier foil 11 without being peeled off from the carrier foil 11 before use.

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.

  Next, a second embodiment of the negative electrode of the present invention will be described with reference to FIG. For points that are not particularly described with respect to the second embodiment, the description detailed with respect to the first embodiment is applied as appropriate. In FIG. 4, the same members as those in FIGS.

  The negative electrode 10 of the present embodiment has two negative electrode precursors 20 and a metal lithium layer 7 as its basic constituent members. The metallic lithium layer 7 is sandwiched between the negative electrode precursors 20.

  The negative electrode precursor 20 includes a current collecting layer 3 and an active material layer 2 disposed on one surface of the current collecting layer 3. As shown in FIG. 4, the metal lithium layer 7 is sandwiched between the negative electrode precursors 20 so that the active material layers 2 of the negative electrode precursors 20 face each other and the current collecting layer 3 faces outward. .

  The metallic lithium layer 7 interposed between the two active material layers 2 constitutes a local battery with the active material (negative electrode active material) in the presence of the non-aqueous electrolyte. Thereby, metallic lithium chemically reacts with an active material located in the vicinity of the metallic lithium layer 7 to form a lithiated product. Alternatively, lithium reacts with the active material due to a lithium concentration gradient to form a lithiated product. Thus, the metal lithium layer 7 acts as a lithium supply source. As a result, even if lithium is consumed due to a reaction with the electrolyte during charge / discharge cycles or long-term storage, the lithium depletion problem is solved because lithium is supplied from the lithiated product. Thereby, the lifetime of the negative electrode 10 is extended. The metallic lithium layer 7 is not exposed on the surface of the negative electrode 10 and is located inside the negative electrode 10, and lithium reacts with the active material to form a lithiated product, causing internal short circuit and ignition There is little risk of formation of lithium dendrites. In the metallic lithium layer 7 after the reaction of lithium, there is a lithium compound that has undergone volume expansion due to a reaction between lithium and the active material.

  It should be noted that the reaction between the lithium metal and the active material occurs without charging the negative electrode 10 in the battery. This phenomenon was first discovered by the present inventors. The reaction between metallic lithium and the active material occurs before the battery is installed, so that the active material has already increased in volume before the battery is installed. Therefore, even if the negative electrode 10 is subsequently incorporated into the battery and charged and discharged, the expansion rate of the negative electrode 10 resulting from charging and discharging is extremely small. As a result, the negative electrode 10 of the present embodiment has a very advantageous effect that deformation due to the volume change of the active material due to charge / discharge is extremely difficult to occur.

  The amount of metallic lithium is preferably 0.1 to 70%, particularly 5 to 30%, based on the saturation reversible capacity of the active material, because the capacity recovery characteristics are improved.

  Next, a preferred method for producing the negative electrode 10 shown in FIG. 4 will be described with reference to FIG. In addition, about the point which is not demonstrated especially regarding this manufacturing method, the description regarding the manufacturing method shown in FIG.2 and FIG.3 is applied suitably. First, the negative electrode precursor 20 is manufactured. For the production of the negative electrode precursor 20, a carrier foil 11 is prepared as shown in FIG. Next, if necessary, a release agent is applied on one surface of the carrier foil 11 to perform a release treatment. Further, as shown in FIG. 5B, a coating liquid 12 containing a conductive polymer is applied and dried to form a coating film 12. Next, as shown in FIG. 5C, the current collecting layer 3 is formed by depositing the coating film 12 and electrodepositing the constituent material of the current collecting layer 3 by electrolytic plating. On the current collecting layer 3, as shown in FIG. 5D, an active material layer 2 is formed by applying a conductive slurry containing active material particles. After the coating film of the slurry is dried and the active material layer 2 is formed, the carrier foil 11 on which the active material layer 2 is formed is immersed in a plating bath containing a metal material having a low lithium compound forming ability. Perform osmotic plating.

  Thus, the negative electrode precursor 20 provided with the current collecting layer 3 and the active material layer 2 in this order on the carrier foil 11 is formed. Using this pair, as shown in FIG. 5 (e), the metal lithium foil 30 is sandwiched between the negative electrode precursors 20 so that the active material layers 2 in each negative electrode precursor 20 face each other. Thereby, the metallic lithium foil 30 and the two negative electrode precursors 20 are integrated by bonding. In this case, these three members can be bonded together by an operation in which the metallic lithium foil 30 and the negative electrode precursors 20 are simply overlapped and pressed. In order to strengthen the bonding, these three members may be bonded using a conductive adhesive material such as a conductive paste. Alternatively, the carrier foil may be separated and removed in advance before the pair of negative electrode precursors 20 are bonded together.

  Next, as shown in FIG. 5 (f), one carrier foil 11 is peeled from the current collecting layer 3 to expose the current collecting layer 3. When one of the current collecting layers 3 is exposed, as shown in FIG. 5G, a vertical drilling that penetrates both the current collecting layers 3 and 3, both the active material layers 2 and 2, and the metal lithium foil 30 by a predetermined drilling process. Hole 5 is formed. Finally, as shown in FIG. 5 (h), the other carrier foil 11 is peeled off from the other current collecting layer 3. Thereby, the intended negative electrode 10 is obtained.

  Next, third to fifth embodiments of the negative electrode of the present invention will be described with reference to FIGS. Regarding points that are not particularly described with respect to the third to fifth embodiments, the description in detail regarding the first and second embodiments is applied as appropriate. Moreover, in FIGS. 6-9, the same code | symbol is attached | subjected to the same member as FIGS. 1-5.

  In the negative electrode 10 of the third embodiment shown in FIG. 6, one active material layer 2 and one metal lithium layer 7 are interposed between the pair of current collecting layers 3a and 3b. And many vertical holes 5 which penetrate the negative electrode 10 in the thickness direction are formed. The active material layer 2 and the current collecting layer 3a adjacent thereto correspond to the negative electrode precursor 20 in the negative electrode of the second embodiment. A fine gap (not shown) is formed in the current collecting layer 3a adjacent to the active material layer 2 as necessary. On the other hand, no fine voids are formed in the current collecting layer 3b adjacent to the metal lithium layer 7.

  A negative electrode 10 according to the fourth embodiment shown in FIG. 7 includes a pair of negative electrode precursors 20 including an active material layer 2 and a current collecting layer 3 adjacent thereto. Moreover, the electroconductive foil 8 with which the metal lithium layer 7 was distribute | arranged on each surface is also provided. The conductive foil 8 in which the metal lithium layer 7 is arranged on each surface is formed between the negative electrode precursors 20 so that the active material layers 2 of the negative electrode precursors 20 face each other and the current collecting layer 3 faces outward. It is pinched. A fine gap (not shown) is formed in the current collecting layer 3 as necessary. Furthermore, a number of vertical holes 5 that penetrate the negative electrode 10 in the thickness direction are formed.

  The negative electrode 10 of the embodiment shown in FIG. 7 is higher in strength than the negative electrode of the embodiment shown in FIG. This is advantageous when a battery of the jelly roll type is manufactured. From this viewpoint, the thickness of the conductive foil 8 is preferably 5 to 20 μm. The conductive foil 8 is generally composed of a metal foil. Examples of the material constituting the conductive foil 8 include a metal material having a low lithium compound forming ability. As such a material, the material similar to the material demonstrated previously as the current collection layer 3 or the metal material 4 used for osmotic plating can be used. From the viewpoint of increasing the strength, it is also effective to use a stainless steel foil or a high strength rolled alloy foil.

  A preferred method for manufacturing the negative electrode 10 of the embodiment shown in FIG. 7 is as follows. First, as shown to Fig.8 (a), the electroconductive foil 8 is prepared and the metal lithium layer 7 is formed in each surface. The metallic lithium layer 7 can be formed by a known thin film forming means, for example, a vacuum evaporation method. Separately, according to the negative electrode manufacturing method of the first embodiment shown in FIG. 2, a negative electrode precursor 20 composed of the active material layer 2 and the current collecting layer 3 adjacent thereto is manufactured in advance, and FIG. ), The conductive foil 8 on which the metal lithium layer 7 is formed is sandwiched between a pair of negative electrode precursors 20. The negative electrode precursor 20 is supported by the carrier foil 11. When sandwiching, the active material layers 2 in the negative electrode precursors 20 face each other, and the current collecting layer 3 faces outward. Next, as shown in FIG. 8C, one carrier foil 11 is peeled from the current collecting layer 3 to expose the current collecting layer 3. When one of the current collecting layers 3 is exposed, as shown in FIG. 8D, both current collecting layers 3 and 3, both active material layers 2 and 2, both metal lithium layers 7 and 7 and A vertical hole 5 penetrating the conductive foil 8 is formed. Finally, as shown in FIG. 8 (e), the other carrier foil 11 is peeled and separated from the other current collecting layer 3. Thereby, the intended negative electrode 10 is obtained.

  The negative electrode 10 of the embodiment shown in FIG. 9 has a current collector 9 unlike the negative electrodes of the embodiments described so far. The negative electrode 10 has the active material layer 2 on the current collector 9. Since the negative electrode 10 of the present embodiment includes the current collector 9, it is not necessary to provide a current collector layer on the active material layer 2. The active material layer 2 includes particles 2a of the active material, and the metal material 4 having a low lithium compound forming ability penetrates between the particles 2a. The negative electrode 10 has a large number of vertical holes 5 that are open in the surface of the active material layer 2 and extend in the thickness direction of the active material layer 2.

  The current collector 9 may be the same as that conventionally used as a current collector for a negative electrode for a nonaqueous electrolyte secondary battery. The current collector is preferably composed of a metal material 4 having a low ability to form a lithium compound. Examples of such metallic materials are as already described. In particular, it is preferably made of copper, nickel, stainless steel or the like. The thickness of the current collector 9 is not critical in the present embodiment, but is preferably 10 to 30 μm in consideration of the balance between maintaining the strength of the negative electrode 10 and improving the energy density.

  The negative electrode 10 of this embodiment can be manufactured by a method similar to the method for manufacturing the negative electrode of the first embodiment. First, a slurry containing the active material particles 2 a is applied to one surface of the current collector 9 to form a coating film. The current collector 9 on which the coating film is formed is immersed in a plating bath containing a metal material having a low ability to form a lithium compound to perform electrolytic plating. Thereby, the active material layer 2 is formed. Finally, a number of vertical holes 5 extending in the thickness direction of the active material layer 2 are formed in the active material layer 2 by drilling the active material layer 2.

  In the negative electrode 10 of the present embodiment, the active material layer 2 is formed only on one side of the current collector 9, but instead, the active material layer 2 is formed on both sides of the current collector 9, and each active material layer 2 is formed. Vertical holes 5 may be formed in the material layer 2. Further, the vertical hole 5 may pass through the current collector 9.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment, A various change is possible. For example, in the negative electrode of the embodiment shown in FIG. 9, expanded metal may be used as the current collector.

  In addition, the negative electrode precursor 20 is superimposed on each surface of a current collector thick film conductor called a current collector that has been used for conventional electrodes, and a vertical hole is formed through these in the thickness direction. You may comprise a negative electrode.

  Moreover, in the negative electrode of the embodiment shown in FIGS. 4 and 6, the vertical hole 5 may not be formed in the metal lithium layer 7. Similarly, in the negative electrode of the embodiment shown in FIG. 7, the vertical holes 5 do not have to be formed in the metal lithium layer 7 and the conductive foil 8.

  In addition, the negative electrode of each of the above embodiments can be used alone, or the negative electrode can be used as a negative electrode precursor, and a plurality of the negative electrode precursors can be stacked. In the latter case, it is also possible to interpose a conductive foil (for example, a metal foil) serving as a core material between adjacent negative electrode precursors.

  In each of the above-described embodiments, the current collecting layer 3 (3a, 3b) has a single layer structure. However, instead of this, a multi-layer structure including two or more layers of different materials may be used. For example, when the current collecting layer 3 (3a, 3b) has a two-layer structure of an inner layer made of nickel and an outer layer made of copper, significant deformation of the negative electrode due to the volume change of the active material can be more effectively prevented. it can.

  Further, when the material of the current collecting layer 3 (3a, 3b) and the metal material having a low ability to form a lithium compound penetrating into the active material layer 2 are different, the material penetrates into the active material layer 2 The metal material having a low lithium compound forming ability may exist up to the boundary between the active material layer 2 and the current collecting layer 3 (3a, 3b). Or the metal material with low formation ability of a lithium compound may comprise a part of current collection layer 3 (3a, 3b) beyond the said boundary part. On the contrary, the constituent material of the current collection layer 3 (3a, 3b) may exist in the active material layer 2 beyond the said boundary part.

  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]
The negative electrode shown in FIG. 1 was manufactured according to the method shown in FIG. First, 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 current collecting 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 current collecting layer was formed to a thickness of 9 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 current collecting layer to a thickness of 20 μm to form an active material layer. The active material particles were made of Si, and the average particle size was D ₅₀ = 2 μm. The composition of the slurry was active material: acetylene black: styrene butadiene rubber = 98: 2: 1.7.

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, 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. Thus, a current collecting layer made of copper was formed on the active material layer. This current collecting layer was formed to a thickness of 8 μm. After lifting from the plating bath, it was washed with pure water for 30 seconds and dried in the air.

Next, the YAG laser was irradiated toward the current collecting layer formed on the active material layer, and vertical holes were regularly formed. The vertical hole was formed so as to penetrate both the current collecting layers and the active material layer located between them. The diameter of the vertical holes was 25 μm, and the pitch was 100 μm (10000 holes / cm ² ).

  Finally, the carrier foil and the current collecting layer in contact with 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 current collecting layers. The external appearance of the obtained negative electrode before use and after one cycle is shown in FIG. Moreover, the scanning electron micrograph of the surface of the obtained negative electrode and a longitudinal cross section is shown in FIG. As a result of observation with a scanning electron microscope, it was confirmed that the current collecting layer on the side peeled from the carrier foil had, on average, 30 fine holes in a 100 μm × 100 μm square range.

[Example 2]
The negative electrode shown in FIG. 4 was manufactured according to the method shown in FIG. First, 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 current collecting 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 current collecting 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 current collecting layer to a thickness of 15 μm to form an active material layer. The active material particles were made of Si, and the average particle size was D ₅₀ = 2 μm. The composition of the slurry was active material: acetylene black: styrene butadiene rubber = 98: 2: 1.7.

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. After lifting from the plating bath, it was washed with pure water for 30 seconds and dried in the air. Thus, a negative electrode precursor supported on the carrier foil was obtained.
・ NiSO ₄・ 6H ₂ O 250g / l
・ NiCl ₂・ 6H ₂ O 45g / l
・ H ₃ BO ₃ 30g / l

  A metal lithium foil having a thickness of 25 μm prepared separately from the negative electrode precursor was sandwiched between a pair of negative electrode precursors. The sandwiching was performed so that the active material layers in each negative electrode precursor face each other. Thus, each negative electrode precursor and metallic lithium were bonded and integrated.

Next, one carrier foil was peeled from the current collecting layer to expose the current collecting layer. The exposed current collecting layer was irradiated with a YAG laser to regularly form vertical holes penetrating each negative electrode precursor and the metal lithium foil. The diameter of the vertical holes was 25 μm, and the pitch was 100 μm (10000 holes / cm ² ). Finally, the other carrier foil and the current collecting layer were peeled off to obtain a target negative electrode. The amount of metallic lithium in the negative electrode was 30% with respect to the saturation reversible capacity of the active material.

Example 3
The negative electrode shown in FIG. 6 was manufactured. First, a negative electrode precursor supported by a carrier foil was obtained by the same operation as in Example 2. Next, apart from the negative electrode precursor, a metal lithium layer having a thickness of 10 μm was formed on one surface of a copper foil (current collecting layer) having a thickness of 5 μm by a vacuum deposition method. This copper foil and the negative electrode precursor manufactured previously were bonded together and integrated. The bonding was performed so that the metal lithium layer in the copper foil and the active material layer in the negative electrode precursor were in contact with each other.

Next, the YAG laser was irradiated toward the copper foil, and vertical holes penetrating the copper foil, the metal lithium layer, and the negative electrode precursor were regularly formed. The diameter of the vertical holes was 25 μm, and the pitch was 100 μm (10000 holes / cm ² ). Finally, the carrier foil and the current collecting layer were peeled off to obtain a target negative electrode. The amount of metallic lithium in the negative electrode was 25% with respect to the saturation reversible capacity of the active material.

Example 4
The negative electrode shown in FIG. 7 was manufactured according to the method shown in FIG. First, a negative electrode precursor supported by a carrier foil was obtained by the same operation as in Example 2. Separately from the negative electrode precursor, a metal lithium layer having a thickness of 10 μm was formed on each surface of a copper foil having a thickness of 10 μm by a vacuum deposition method. Next, this copper foil was sandwiched between a pair of negative electrode precursors previously produced. The sandwiching was performed such that the active material layers in each negative electrode precursor face each other and the current collecting layer faced outward. As a result, the copper foil having the metal lithium layer on each surface and the respective negative electrode precursors were bonded and integrated.

Next, one carrier foil was peeled from the current collecting layer to expose the current collecting layer. The exposed current collecting layer was irradiated with a YAG laser, and vertical holes penetrating the copper foil having each negative electrode precursor and a metal lithium layer on each surface were regularly formed. The diameter of the vertical holes was 25 μm, and the pitch was 100 μm (10000 holes / cm ² ). Finally, the other carrier foil and the current collecting layer were peeled off to obtain a target negative electrode. The amount of metallic lithium in the negative electrode was 25% with respect to the saturation reversible capacity of the active material.

Example 5
In the same manner as in Example 4, a pair of negative electrode precursors was obtained. The negative electrode precursor was irradiated with a YAG laser toward the surface where the active material layer was exposed, and vertical holes penetrating the negative electrode precursor were regularly formed. The diameter of the vertical holes was 25 μm, and the pitch was 100 μm (10000 holes / cm ² ).

  Next, a copper foil having a metal lithium layer on both sides obtained by the same operation as in Example 4 was sandwiched between a pair of negative electrode precursors in which vertical holes were formed. The sandwiching was performed such that the active material layers in each negative electrode precursor face each other and the current collecting layer faced outward. Thereby, the copper foil having the metal lithium layer on each surface and the respective negative electrode precursors were superposed and integrated. Finally, the carrier foil and the current collecting layer were peeled off to obtain a target negative electrode. The amount of metallic lithium in the negative electrode was 27% with respect to the saturation reversible capacity of the active material.

Example 6
In Example 5, a negative electrode was obtained in the same manner as in Example 5 except that the diameter of the vertical holes was 15 μm and the pitch was 100 μm (10000 holes / cm ² ).

Example 7
In Example 5, a negative electrode was obtained in the same manner as in Example 5 except that the diameter of the vertical holes was 25 μm and the pitch was 200 μm (2500 holes / cm ² ).

Example 8
A negative electrode was obtained in the same manner as in Example 5 except that the diameter of the vertical holes was 50 μm and the pitch was 100 μm (10000 holes / cm ² ).

Example 9
In Example 5, a negative electrode was obtained in the same manner as in Example 5 except that the diameter of the vertical holes was 50 μm and the pitch was 200 μm (2500 holes / cm ² ).

Example 10
In Example 5, a negative electrode was obtained in the same manner as in Example 5 except that the diameter of the vertical holes was 100 μm and the pitch was 300 μm (1111 holes / cm ² ).

Example 11
In Example 5, a negative electrode was obtained in the same manner as in Example 5 except that the diameter of the vertical holes was 250 μm and the pitch was 1000 μm (100 holes / cm ² ).

Example 12
In Example 5, the negative electrode precursor was prepared in the same manner as in Example 5 except that a copper pyrophosphate bath having the following composition was used and osmotic plating was performed on the active material layer under the following conditions. Obtained.
<Composition of copper pyrophosphate bath>
・ K ₄ P ₂ O ₇ 450 g / l
・ Cu ₂ P ₂ O ₇・ 3H ₂ O 105g / l
・ KNO ₃ 15g / l
<Penetration plating conditions>
・ Current density: 3 A / dm ²
・ Bath temperature: 55 ℃
-PH: 8.2
・ Anode: DSE electrode

Example 13
In Example 10, a negative electrode was obtained in the same manner as in Example 5 except that mechanical punching by a punch was used instead of the YAG laser as a method for forming the vertical hole.

Example 14
In Example 10, a negative electrode was obtained in the same manner as in Example 5 except that the hole was formed by using a sandblast method instead of the YAG laser as a method for forming the vertical hole.

Example 15
A negative electrode shown in FIG. 9 was produced. A slurry containing negative electrode active material particles was applied to one surface of an 18 μm thick electrolytic copper foil to a thickness of 20 μm to form an active material layer. The active material particles were made of Si, and the average particle size was D ₅₀ = 2 μm. The composition of the slurry was active material: acetylene black: styrene butadiene rubber = 98: 2: 1.7. Next, nickel plating was performed on the active material layer. The conditions for the infiltration plating were the same as in Example 1. The active material layer thus obtained was irradiated with a YAG laser to form vertical holes regularly. The diameter of the vertical holes was 25 μm, and the pitch was 100 μm (10000 holes / cm ² ).

[Comparative Example 1]
A slurry similar to the slurry used in Example 1 was applied to each surface of a copper foil (thickness 35 μm) obtained by electrolysis so as to have a film thickness of 15 μm to form an active material layer. A negative electrode for a liquid secondary battery 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 discharge capacity after 1 cycle of this battery, the irreversible capacity after 1 cycle, the capacity maintenance rate after 100 cycles, the charge / discharge efficiency after 100 cycles, and the negative electrode thickness change rate 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 (positive electrode), and both electrodes were opposed via 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. Two types of batteries having a capacity ratio of the positive electrode to the negative electrode of 1: 1 and 1: 2 were prepared. A battery having a capacity ratio of 1: 1 between the positive electrode and the negative electrode was used to measure the discharge capacity after one cycle and the irreversible capacity after one cycle. A battery having a capacity ratio of 1: 2 between the positive electrode and the negative electrode was used to measure the capacity retention rate after 100 cycles, the charge / discharge efficiency after 100 cycles, and the rate of change in thickness of the negative electrode.

[Discharge capacity after one cycle]
The discharge capacity per unit weight and per unit volume was measured. The discharge capacity per unit weight was based on the weight of the active material (Si). The discharge capacity per unit volume was based on the volume of the negative electrode. However, the expansion of the negative electrode during charging was not considered.

[Irreversible capacity after one cycle]
Irreversible capacity (%) = (1−initial discharge capacity / initial charge capacity) × 100
That is, it indicates the capacity remaining in the active material after being charged but not discharged.

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

[Charge / discharge efficiency after 100 cycles]
Charge / discharge efficiency after 100 cycles (%) = discharge capacity after 100 cycles / charge capacity after 100 cycles × 100

[Negative electrode thickness change rate]
Using an HS displacement cell manufactured by Hosen Co., Ltd., the thickness change of the negative electrode accompanying charging in one cycle was measured. In this displacement cell, the total thickness change of negative electrode + separator + positive electrode LiCoO ₂ is measured. However, since the positive electrode hardly expands due to charge and discharge and the contribution ratio of the change in thickness of the negative electrode is large, the thickness change being measured can be regarded substantially as the change in thickness of the negative electrode. The negative electrode thickness change rate is calculated from the following equation.
Negative electrode thickness change rate (%) = [(Thickness in one cycle charge state) − (Thickness before charging) / Thickness before charging] × 100

  As is clear from the results shown in Table 1, it can be seen that the battery using the negative electrode of each example has a high discharge capacity and a small irreversible capacity. Furthermore, it turns out that a capacity | capacitance maintenance factor and charging / discharging efficiency are high. Furthermore, it turns out that the thickness change rate of a negative electrode is small.

It is a schematic diagram which shows the cross-sectional structure of 1st Embodiment of the negative electrode of this invention. It is process drawing which shows an example of the manufacturing method of the negative electrode shown in FIG. It is a schematic diagram which shows the state in which a current collection layer and a fine space | gap are formed. It is a schematic diagram which shows the cross-sectional structure of 2nd Embodiment of the negative electrode of this invention. It is process drawing which shows an example of the manufacturing method of the negative electrode shown in FIG. It is a schematic diagram which shows the cross-section of 3rd Embodiment of the negative electrode of this invention. It is a schematic diagram which shows the cross-section of 4th Embodiment of the negative electrode of this invention. It is process drawing which shows an example of the manufacturing method of the negative electrode shown in FIG. It is a schematic diagram which shows the cross-section of 5th Embodiment of the negative electrode of this invention. 2 is a photograph showing the appearance of the negative electrode obtained in Example 1 before use and after one cycle. 2 is an enlarged scanning electron micrograph showing the surface and vertical cross section of the negative electrode obtained in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Surface 2 Active material layer 3, 3a, 3b Current collection layer 4 Metal material with low lithium compound formation ability 5 Vertical hole 6 Fine void 7 Metal lithium layer 8 Conductive foil 10 Negative electrode 20 Negative electrode precursor 30 Metal lithium foil

Claims (16)

In the negative electrode for a non-aqueous electrolyte secondary battery provided with an active material layer containing active material particles,
In the active material layer, a metal material having a low ability to form a lithium compound deposited by electrolytic plating penetrates between the particles, and the active material layer is open in at least one surface of the negative electrode and has a thickness direction of the active material layer. A negative electrode for a non-aqueous electrolyte secondary battery, characterized in that it has a number of vertical holes extending in the vertical direction. It further comprises a current collecting layer in contact with the electrolytic solution, and the active material layer is disposed inside the current collecting layer,
The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the vertical hole extends in a thickness direction of the current collecting layer and the active material layer.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2, comprising a pair of the current collecting layers and the active material layer interposed between the current collecting layers.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3, wherein the thickness of at least one of the pair of current collecting layers is 0.3 to 10 μm.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 4, wherein each of the pair of current collecting layers has a thickness of 0.3 to 10 μm.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 3, further comprising a pair of the current collecting layers, and the active material layer and the metal lithium layer interposed between the current collecting layers.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 6, comprising a pair of the active material layers, wherein the metal lithium layer is interposed between the active material layers.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 7, comprising a pair of the metal lithium layers, and a conductive foil interposed between the metal lithium layers.   The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein a hole area ratio of the vertical holes opened on the surface of the negative electrode is 0.3 to 30%.   The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 9, wherein an opening diameter of the vertical hole formed on the surface of the negative electrode is 5 to 500 µm.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the vertical hole penetrates in the thickness direction of the negative electrode.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the vertical hole is formed by laser processing.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the vertical hole is formed by mechanical perforation.   A negative electrode for a non-aqueous electrolyte secondary battery, wherein the negative electrode according to claim 1 is used as a negative electrode precursor, and a plurality of the negative electrode precursors are laminated.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 14, wherein a conductive foil is interposed between the negative electrode precursors adjacent to each other. A non-aqueous electrolyte secondary battery comprising the negative electrode according to claim 1.