JP2008243656A - Electrode for electrochemical element, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method appropriate for mass production in which lithium equivalent to irreversible capacity can be supplemented uniformly in a short time, when using Si and its oxide for an active material, in order to enlarge the capacity of an electrochemical element. <P>SOLUTION: The manufacturing method of an electrode for the electrochemical element includes a first process of continuously installing active material layers for storing and releasing lithium on a conductive current collector, and forming a precursor of the electrode in a hoop state; a second process of forming a plurality of grooves in the active material layer; and a third process of membrane forming lithium on the active material layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an electrode for an electrochemical device including a negative electrode for a non-aqueous electrolyte secondary battery, and more particularly to a technique for accurately replenishing lithium corresponding to an irreversible capacity in a short time.

  In recent years, electronic devices have become increasingly portable and cordless, and as a power source for driving these devices, small and light-weight electrochemical devices (specifically, capacitors and secondary batteries) have high energy density. There is a growing demand. In addition to small-sized consumer applications, technological development for large-sized electrochemical devices that require long-term durability and safety, such as power storage and electric vehicles, has been accelerated. From such a viewpoint, a non-aqueous electrolyte secondary battery having a high voltage and a high energy density, particularly a lithium secondary battery, is expected as a power source for the above-mentioned applications.

The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed therebetween, and a nonaqueous electrolyte. For the positive electrode, lithium cobalt oxide (for example, LiCoO ₂ ) having a high potential with respect to lithium as an active material, excellent safety, and relatively easy synthesis is used. As the separator, a microporous membrane made mainly of polyolefin is used. As the non-aqueous electrolyte, a liquid non-aqueous electrolyte (non-aqueous electrolyte) obtained by dissolving a lithium salt such as LiBF ₄ or LiPF ₆ in an aprotic organic solvent is used.

  For the negative electrode, a carbon material such as graphite is used as an active material. However, since graphite can theoretically store only one lithium atom per six carbon atoms, the theoretical capacity density is 372 mAh / g, irreversible capacity (negative electrode active material during discharge while being stored in the positive electrode active material during charging) In view of the capacity loss due to the lithium that cannot be returned to, it is only about 310 to 330 mAh / g. Furthermore, while it is required to increase the energy of the nonaqueous electrolyte secondary battery, as a negative electrode active material having a high theoretical capacity density, a simple substance of silicon (Si), tin (Sn), or germanium (Ge) alloyed with lithium, These oxides and alloys are expected. Among them, inexpensive Si and its oxide are widely studied.

  However, since Si and its oxides have large irreversible capacities, it is necessary to further add a positive electrode active material corresponding to a loss corresponding to the irreversible capacities, and the battery design capacity does not increase as expected.

Therefore, as a technology for supplementing lithium corresponding to the irreversible capacity, a technology capable of supplementing lithium corresponding to the irreversible capacity by attaching metallic lithium to the surface of the negative electrode mixture layer not facing the positive electrode mixture layer has been proposed. (For example, Patent Document 1). Further, a technique for forming a dispersion-coated lithium powder layer on at least one surface of a positive electrode, a negative electrode, and a separator has been proposed (for example, Patent Document 2). In addition, a lithium metal layer is formed on the negative electrode by a dry film-forming method such as vacuum deposition or ion plating, and stored in a dry atmosphere or in an electrolyte solution to occlude lithium in the negative electrode for the first charge / discharge. A technique for improving the efficiency has been proposed (for example, Patent Document 3).
JP 2002-075454 A JP 2005-317551 A JP 2005-038720 A

  The irreversible capacity of Si and its oxides is at most about 1 to 20 μm in terms of the lithium layer although it is large. In view of this, Patent Document 3 seems to be promising as a technique for uniformly filling the negative electrode with lithium, compared to Patent Document 1 in which a large amount of lithium is locally provided and Patent Document 2 in which dispersibility is questionable. However, since the technique of Patent Document 3 takes time to occlude lithium in the negative electrode active material, the productivity is low and mass production is difficult.

  The present invention has been made in view of the above-described problems, and when Si and its oxide are used as an active material in order to increase the capacity of an electrochemical element, lithium corresponding to an irreversible capacity is uniformly formed in a short time. It is an object to provide a method suitable for mass production that can be compensated for.

  In order to achieve the above object, the method for producing an electrode for an electrochemical device according to the present invention comprises continuously providing an active material layer that occludes and releases lithium on a conductive current collector, and provides a precursor for the electrode. The method includes a first step of forming a hoop, a second step of forming a plurality of grooves in the active material layer, and a third step of forming lithium on the active material layer. .

  Further, as one embodiment of the electrode for an electrochemical element obtained by the method for producing an electrode for an electrochemical element described above, the electrode for an electrochemical element of the present invention has an activity of occluding and releasing lithium on a conductive current collector. A material layer is arranged, and random cracks are formed on the surface of the active material layer.

  By forming a plurality of grooves in the active material layer in the second step, a new active surface is formed in the depth direction of the active material layer, and the surface area that can be supplemented with lithium is increased. By forming lithium uniformly on the active material layer in this state, the reactivity between the active material layer and lithium is increased, so that lithium can be compensated in a short time.

  According to the present invention, lithium equivalent to the irreversible capacity can be uniformly compensated in a short time, so that a high-capacity electrochemical device using Si and its oxide as an active material can be mass-produced and provided with high accuracy. become.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  According to a first aspect of the present invention, there is provided a first step in which an active material layer for inserting and extracting lithium is continuously provided on a conductive current collector, and a precursor of an electrode is formed in a hoop shape; The present invention relates to a method for manufacturing an electrode for an electrochemical element, comprising a second step of forming a plurality of grooves and a third step of forming lithium on an active material layer. Hereinafter, description will be made using a negative electrode for a nonaqueous electrolyte secondary battery as an example of an electrode for an electrochemical element.

  FIG. 1 is a schematic view showing an example of a first step corresponding to the first invention. In the vacuum vessel 16 decompressed by the vacuum pump 17, the current collector 19 is run from the unwinding roll 11 toward the winding roll 15, and the material evaporated by the vapor deposition source 13 below the film forming rolls 14a and 14b. Is deposited on the current collector 19 to form an active material layer. In FIG. 1, the area where the active material layer is provided is controlled by providing the mask 12, and the active material layer is made oxide by flowing oxygen from the oxygen nozzle 18.

By forming a plurality of grooves in the active material layer in the precursor obtained in the first step as the second step, a new active surface can be formed in the depth direction of the active material layer and lithium can be supplemented. Increases surface area. In this state, the lithium is uniformly formed on the active material layer as the third step, whereby the reactivity between the active material layer and lithium is increased, so that lithium can be compensated in a short time. Note that a specific method for forming the plurality of grooves in the active material layer will be described in detail later.

According to a second invention, in the first invention, the active material layer contains at least silicon, tin, or germanium. Lithium metal or carbon material can be used as the active material for the negative electrode for nonaqueous electrolyte secondary batteries. Among them, active materials containing silicon, tin, or germanium have high capacity and high reactivity with lithium. Therefore, it is preferable because lithium can be rapidly occluded in the active material layer in the third step. Specific examples of these active materials include, for example, Si, SiO _x (0.05 <x <1.95) for silicide, or any of these for B, Mg, Ni, Ti, Mo, Co, An alloy or compound in which a part of Si is substituted with at least one element selected from the group consisting of Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn, Alternatively, a solid solution or the like can be used. As the tin compound, Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (0 <x <2), SnO ₂ , SnSiO ₃ , LiSnO, or the like can be applied. These active materials may be used individually by 1 type, and may be used in combination of 2 or more type.

  According to a third invention, in the first invention, the second step is a step of causing the precursor to travel by applying tension while bringing the precursor into contact with a part of the peripheral surface of at least one roll. And

  FIG. 2 is a schematic diagram showing an example of second and third steps corresponding to the third invention. In the vacuum container 28 decompressed by the vacuum pump 29, the precursor 23 having an active material layer travels from the unwinding roll 21 toward the winding roll 22, and active in the crack processing unit 24 in which the crack processing roll 30 is disposed. Cracks are formed in the material layer (second step). Next, lithium evaporated by the vapor deposition source 26 is deposited on the active material layer below the film forming roll 25 (third step). In FIG. 3, by providing the mask 27, the area for depositing lithium is controlled.

  As shown in FIG. 2, the crack can be continuously formed in the entire active material layer by setting the second step to the configuration of the third invention. In particular, if the active material layer is hard as in the structure of the second invention, the entire negative electrode can be bent as shown in FIG. 2 without damaging the current collector, and excessive compression or This is preferable because cracks can be efficiently formed without applying shear stress.

  A fourth invention is characterized in that, in the third invention, the traveling direction of the precursor is changed by 90 ° or more by arranging a plurality of rolls so that the rotation axes thereof are non-parallel. .

  FIG. 3 is a schematic view showing a characteristic portion according to an example of a second step corresponding to the fourth invention. By arranging the crack processing roll 30 of the crack processing portion 24 in the process of FIG. 2 as shown in FIG. 3, a new crack can be formed in the active material layer each time the direction of the roll changes. In the second invention, cracks were generated only in one direction. However, in the fourth invention, cracks can be generated in multiple directions in a single process, further improving the reactivity with lithium. It is preferable because it is possible.

  The fifth invention is characterized in that, in the first invention, the second step is a step of pressing at least one blade against the active material layer.

FIG. 4 is a schematic diagram showing an example of second and third steps corresponding to the fifth invention. The crack processing unit 24 of FIG. 2 is a cutter processing unit 32 having a cutter blade 31, and the cutter blade 31 is pressed with a constant load against the active material layer of the precursor 23 pressed against the lower roll with the tension during traveling. A groove can be formed in the active material layer. As shown in FIG. 4, by making the second step as in the fifth aspect, the depth and number of grooves can be arbitrarily adjusted, so convenience is increased.

  According to a sixth invention, in the first invention, the second step is a step of polishing the surface of the active material layer.

  FIG. 5 is a schematic view showing an example of second and third steps corresponding to the sixth invention. The crack processing unit 24 in FIG. 2 is used as a polishing processing unit 34 having a polishing paper 33, and the polishing paper 33 is pressed against the active material layer of the precursor 23 pressed against the lower roll with a running tension by a constant load. A random groove can be formed in the active material layer. By making the second step as in the sixth aspect of the invention, it is preferable because many fine grooves can be formed in the entire active material layer, and the surface area to be filled with lithium is remarkably increased.

  A seventh invention is characterized in that an active material layer that occludes and releases lithium is disposed on a conductive current collector, and random cracks are formed on the surface of the active material layer. The present invention relates to an electrode for an electrochemical element. Specifically, those having cracks in multiple directions as in the fourth invention and those having cracks by polishing as in the sixth invention are applicable, but the depth of the crack is particularly about 5 to 10 μm. The electrode provided at a depth of 5 can be compensated uniformly for lithium in an irreversible capacity in a short time, and thus can be an electrode for an electrochemical device having excellent characteristics.

  In the above description, the method of performing the second step continuously with the third step in the vacuum vessel has been described. However, after performing only the second step in the atmosphere, the third step is performed in the vacuum vessel. Even if the process is performed, the process is complicated, but the same result is obtained.

  Non-aqueous electrolyte secondary battery negative electrode binders include, for example, PVDF, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester , Polyacrylic acid ethyl ester, polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, Hexafluoropolypropylene, styrene butadiene rubber, carboxymethyl cellulose and the like can be used. Two types selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene A copolymer of the above materials may be used. Two or more selected from these may be mixed and used. Examples of the conductive agent contained in the electrode include natural graphite and artificial graphite graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and other carbon blacks, carbon fibers and metal fibers. Conductive fibers such as carbon fluoride, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, organic conductive materials such as phenylene derivatives, etc. Is used.

  There is no limitation in particular about the preparation methods of the negative electrode for nonaqueous electrolyte secondary batteries, and various electrode plate forming methods can be used.

However, when lithium is deposited on the negative electrode by vacuum deposition, substances other than the active material in the negative electrode (
For example, when a binder, a conductive material, etc.) are present, diffusion of lithium into the negative electrode active material is hindered, and the lithium occlusion rate tends to be slow. Therefore, it is better for the negative electrode to have as few substances as possible other than the active material, and the case of only the active material is more preferable because the diffusion becomes the fastest. Examples of the method of forming the negative electrode using only the active material include dry film forming methods such as vacuum deposition, sputtering, and ion plating.

  For the current collector, a long porous conductive substrate or a nonporous conductive substrate is used. As a material used for the conductive substrate, for example, stainless steel, nickel, copper, or the like is used. The thickness of these current collectors is not particularly limited, but is preferably 1 to 500 μm, and more preferably 5 to 40 μm. By setting the current collector thickness within the above range, it is possible to reduce the weight while maintaining the strength of the electrode plate.

  Hereinafter, the present invention will be described based on examples.

Example 1
The precursor 23 was produced by the method shown in FIG. Specifically, a strip-shaped copper foil (thickness 30 μm, average surface roughness Ra = 0.125 μm, manufactured by Hitachi Cable) is used as the current collector 19, and the inside of the vacuum vessel 16 is set to an argon atmosphere with a pressure of 3.5 Pa. , Si (scrap silicon: purity 99.999%) is used as the evaporation source 13, the electron beam from the electron beam generator is polarized by the polarization yoke and irradiated to the evaporation source 13. While generating Si vapor from the vapor deposition unit that unitizes the generator, this Si vapor is applied to both surfaces of the current collector 19 from the opening of the mask 12 so that the film formation rate is 2 nm / second, A precursor 23 (thickness: 50 μm) having active material layers on both surfaces of the current collector 19 was produced.

  Next, cracks were formed in the active material layer of the precursor 23 using the apparatus shown in FIG. Specifically, by using a roll having a diameter of 5 mm as the roll 30 and running the negative electrode while applying a tension of 0.5 kgf / cm per width while contacting the precursor 23, the active material layer has an average of 7 μm from the surface. A crack having a depth was formed. The crack depth was measured from the depth at which lead was detected by cutting out a part of the precursor 23 and staining the crack with lead, observing the distribution of lead in the thickness direction by energy dispersive elemental analysis. .

(Example 2)
The same method as in Example 1 except that the precursor 23 having an active material layer made of SiO _0.6 formed by introducing oxygen from the oxygen nozzle 18 shown in FIG. 1 and reacting Si and O ₂ was used. The product manufactured in step 2 is referred to as Example 2. The crack depth in Example 2 was 8 μm.

(Example 3)
The method for forming cracks in the active material layer of the precursor 23 was the same as in Example 1 except that the method shown in FIG. 2 was changed to the method shown in FIG. Specifically, the arrangement of the rollers 30 (5 mm in diameter) of the crack processing unit 24 shown in FIG. 2 is arranged so that the traveling direction of the precursor 23 changes, and 0.5 kgf per width while the precursor 23 abuts. Cracks were formed in the active material layer by running the negative electrode while applying a tension of / cm. The average depth of the cracks formed in a mesh shape was 6 μm. This is Example 3.

Example 4
The method for forming cracks in the active material layer of the precursor 23 was the same as in Example 1 except that the method shown in FIG. 2 was changed to the method shown in FIG. Specifically, the active material layer of the precursor 23 is made to have a groove (average depth) in the active material layer by running the negative electrode while a plurality of cutter blades 31 (arranged at 5 mm width intervals) in the cutter processing unit 32 are in contact with each other. 4 μm) was formed. This is Example 4.

(Example 5)
The method for forming cracks in the active material layer of the precursor 23 was the same as in Example 1 except that the method shown in FIG. 2 was changed to the method shown in FIG. Specifically, the surface of the active material layer is obtained by running the negative electrode while bringing the active material layer of the precursor 23 into contact with the polishing paper 33 (3M water resistant sandpaper No. 2000, manufactured by 3M Company) in the polishing processing unit 34. Cracks having a random appearance (average depth 2 μm) were formed. This is Example 5.

(Comparative Example 1)
Comparative Example 1 is the same as Example 1 except that no cracks were formed in the same precursor as in Example 1.

(Comparative Example 2)
Comparative Example 2 is the same as Example 2 except that no cracks were formed in the same precursor as in Example 2.

  Lithium was deposited on the active material layer of the precursor 23 of each example produced as described above by the method shown in FIGS. Specifically, metallic lithium (manufactured by Honjo Metal) is used as the vapor deposition source 26, which is placed on a tungsten board, lithium is evaporated by resistance heating, and the vapor deposition range is adjusted by the mask 27, while the precursor 23 An amount of lithium corresponding to 12 μm was deposited on the active material layer in terms of the thickness of the foil. The lithium deposition rate was set to a desired value by changing the temperature at which the deposition source 26 was heated.

  Whether or not lithium after deposition was occluded in the active material layer of the precursor 23 was evaluated by NMR. Specifically, when a peak of 265 ppm corresponding to metallic lithium is measured, lithium that has not been occluded in the active material layer is present on the active material layer, so that it is “x”. When it was not measured, since all the lithium was occluded in the active material layer, “◯” was given. The unit of the vapor deposition rate was represented by the vapor deposition amount (μm / second) converted into the thickness of the lithium foil per unit time. The results of vapor deposition at various vapor deposition rates for the precursor 23 of each example are shown in Table 1.

リチウムの蒸着速度が０．０５μｍ／秒という比較的遅い蒸着速度の場合、第１の工程を施さなくても、蒸着したリチウムがすべて活物質層内に吸蔵され、ＮＭＲで金属リチウ
ムが確認されなかった。しかしリチウムの蒸着速度を０．１〜０．２μｍ／秒まで速めると、前駆体２３の活物質層の表面に、金属リチウムの存在が確認された。

In the case of a relatively slow deposition rate of 0.05 μm / sec, the deposited lithium is all occluded in the active material layer and no metallic lithium is confirmed by NMR even if the first step is not performed. It was. However, when the deposition rate of lithium was increased to 0.1 to 0.2 μm / second, the presence of metallic lithium was confirmed on the surface of the active material layer of the precursor 23.

  On the other hand, when the first step was performed as in each example, all the deposited lithium was occluded in the active material layer even when the deposition rate of lithium was 0.2 μm / second. In particular, in Example 3 in which deep cracks were formed in a plurality of directions, all the deposited lithium was occluded even when the deposition rate was increased to 1.0 μm / second.

  It goes without saying that the same effect can be obtained even when the production method of the present invention is applied to a negative electrode precursor having an active material layer made of graphite.

  A non-aqueous electrolyte secondary battery using a negative electrode produced by the production method of the present invention has a large capacity and excellent characteristics, so a drive source for electronic devices such as notebook computers, mobile phones, and digital still cameras, Furthermore, it is useful for power storage and electric vehicle power sources that require high output.

The conceptual diagram which shows an example of the 1st process of this invention Schematic diagram showing an example of the second and third steps of the present invention The schematic diagram which shows the characteristic part which concerns on an example of the 2nd process of this invention. Schematic diagram showing an example of the second and third steps of the present invention Schematic diagram showing an example of the second and third steps of the present invention

Explanation of symbols

11 Unwinding roll 12 Mask 13 Deposition source 14a Film forming roll A
14b Deposition roll B
DESCRIPTION OF SYMBOLS 15 Winding roll 16 Vacuum container 17 Vacuum pump 18 Oxygen nozzle 19 Current collector 21 Unwinding roll 22 Winding roll 23 Negative electrode 24 Crack processing part 25 Film forming roll 26 Deposition source 27 Mask 28 Vacuum container 29 Vacuum pump 30 For crack processing Roll 31 Cutter blade 32 Cutter processing unit 33 Abrasive paper 34 Abrasion processing unit

Claims (7)

A method for producing an electrode for an electrochemical device comprising an active material layer that occludes and releases lithium on a conductive current collector,
A first step of continuously providing the active material layer on the current collector and forming a precursor of the electrode in a hoop shape;
A second step of forming a plurality of grooves in the active material layer;
A third step of depositing lithium on the active material layer;
The manufacturing method of the electrode for electrochemical elements characterized by including. The method for producing an electrode for an electrochemical element according to claim 1, wherein the active material layer contains at least silicon, tin, or germanium. The electrochemical device according to claim 1, wherein the second step is a step of running the precursor by applying a tension while bringing the precursor into contact with a part of a peripheral surface of at least one roll. Electrode manufacturing method. 4. The electrochemical device according to claim 3, wherein a plurality of rolls are arranged such that their rotational axes are non-parallel, so that the traveling direction of the precursor is changed by 90 ° or more. Electrode manufacturing method. The method for manufacturing an electrode for an electrochemical element according to claim 1, wherein the second step is a step of pressing at least one blade against the active material layer. The method for producing an electrode for an electrochemical element according to claim 1, wherein the second step is a step of polishing the surface of the active material layer. An electrode for an electrochemical device comprising an active material layer that occludes and releases lithium on a conductive current collector,
An electrode for an electrochemical element, wherein random cracks are formed on the surface of the active material layer.

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