JP2007052960A - Method of manufacturing electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an electrode which is easy to be manufactured and has a high capacity and a superior charge and discharge cycle characteristics in which occurrence of wrinkles caused by expansion and shrinkage occurring during charge and discharge cycles can be suppressed in the electrode used for the lithium-ion secondary battery. <P>SOLUTION: This manufacturing method of the electrode is arranged so that the manufacturing method has a process for installing an intermediate layer that is mutually soluble with an electrolytic solution so as to cover a current collector on a sheet-state surface of the current collector having conductivity and having a plurality of protrusions on the surface, a process in which at least a part of the plurality of protrusions of the current collector are made to be exposed by removing a part of the surface of the intermediate layer, and a process in which an active material layer is installed at the exposed part of the protrusions. It is easy to be manufactured, and when a battery is constituted by using this electrode, a space is formed for moderating the expansion and shrinkage at the time of charging and discharging, thus occurrence of wrinkle on the electrode is suppressed, and the electrode having the high capacity and superior charge and discharge cycle characteristics and the lithium-ion secondary battery using it are realized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode manufacturing method, and more particularly to a manufacturing method suitable for manufacturing an electrode for a lithium ion secondary battery.

  In recent years, alloy-based negative electrode materials containing elements such as Si (silicon) and Sn (tin) have attracted attention as negative electrode active materials for increasing the capacity of nonaqueous electrolyte secondary batteries. For example, the theoretical discharge capacity of Si is about 4199 mAh / g, which is about 11 times the theoretical discharge capacity of graphite.

  However, these alloy-based negative electrode materials expand due to a large change in structure when occlusion of lithium ions. As a result, the active material particles are broken or the active material layer is peeled off from the current collector, whereby the electronic conductivity between the active material and the current collector is lowered, and as a result, battery characteristics such as cycle characteristics are lowered.

  In the negative electrode using the above-mentioned material as an active material, several techniques for suppressing the destruction of the active material layer and the decrease in conductivity that occur with expansion are disclosed (for example, Patent Document 1, Patent Document) 2, see Patent Document 3).

  Patent Document 1 discloses that a columnar structure can be formed by forming an active material thin film on a current collector having an uneven surface. Thereby, the cycle characteristics are improved by relieving stress due to expansion and contraction of the active material. As a method for forming irregularities on a current collector, it is disclosed that fine copper plating is performed after applying particulate copper on a metal foil by plating.

  Patent Document 2 discloses a battery electrode in which a thin film made of a metal alloyed with Li or an alloy containing the metal is formed on a current collector made of a material that is not alloyed with Li. In this example, an uneven negative electrode active material layer is formed in a predetermined pattern on a current collector by applying a photoresist method and a plating technique. Thereby, the space | gap is ensured between negative active materials.

Patent Document 3 discloses that an active material layer is formed on an adhesive resin layer made of a pattern-coated organic titanium compound, a silane coupling agent, or the like. This shows that the adhesive force and electrical connection between the current collector and the active material layer can be compatible and the cycle characteristics are improved. By applying this, the unevenness of the resin material can be formed on the substrate through a coating process, a cured process (patterning), a removing process, and an active material forming process. An active material layer having columnar particles can be formed by forming an active material layer thereover.
JP 2002-319408 A JP 2002-279972 A Japanese Patent Laid-Open No. 11-73947

  However, it is complicated to produce the voids between the columnar active material particles by the above-described conventional method because it is complicated, and the active material is also stacked in the recesses of the current collector. There is a problem that the electric body is easily deformed.

  In view of such circumstances, the present invention provides a simple method for manufacturing an electrode that improves the cycle characteristics of a high-performance active material having a large expansion / contraction rate by not stacking an excess active material in the recess of the current collector. The purpose is to do.

In order to solve the conventional problems, the method for producing an electrode of the present invention includes:
A step of providing an intermediate layer compatible with the electrolyte solution so as to cover the current collector on the surface of the sheet-shaped current collector having conductivity and having a plurality of convex portions on the surface;
Removing a part of the surface of the intermediate layer to expose at least some of the plurality of convex portions of the current collector; and
And a step of providing an active material layer on the exposed convex portion.

  In this manufacturing method, since the plurality of convex portions of the current collector are exposed and the other portions are covered with the intermediate layer, the active material layer can be formed only on the exposed surfaces of the plurality of convex portions. . In addition, there is no excess active material in the portion where the active material layer is not formed, that is, the portion covered with the intermediate layer, and the intermediate layer is compatible with the organic electrolyte when the battery is configured. Thus, it is possible to easily obtain an electrode that secures a sufficient space for absorbing the expansion and contraction.

  According to the production method of the present invention, it is possible to easily obtain an electrode that secures a sufficient space between the columnar particles to absorb the expansion and contraction of the active material, and the battery performance of the battery using the electrode, in particular, Cycle characteristics can be improved.

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

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view of a negative electrode according to the present invention. In FIG. 1, the negative electrode 10 includes a current collector 11 having a plurality of convex portions 12 on the surface, an intermediate layer 14 compatible with the electrolytic solution, and a negative electrode active material 13 formed only on the upper surface of the convex portion 12. Become.

  An example of a method for producing the negative electrode 10 will be described with reference to FIG. In FIG. 2, the same components as those in FIG. That is, the intermediate layer 14 compatible with the electrolytic solution is formed on the surface of the current collector 11 (FIG. 2A) having a plurality of convex portions 12 on the surface so as to cover the current collector 11 (FIG. 2 ( b)). Next, the surface of the intermediate layer 14 is removed, and at least a part of the convex portion 12 is exposed (FIG. 2C). At this time, it is preferable to remove the current collector 11 in parallel with the macroscopic surface. Moreover, as shown in FIG.2 (c), it is preferable to remove the convex part 12 similarly. By doing so, the height of the exposed convex portion 12 can be made equal to the height of the intermediate layer 14. Thereafter, the negative electrode active material 13 is formed on the exposed surface of the convex portion 12 (FIG. 2D).

  As the current collector 11, a metal foil that is not alloyed with lithium, such as copper, nickel, platinum, or gold, which has been subjected to a roughening treatment in which metal particles are dispersed and electrodeposited in an electrolytic solution, and an alloy foil thereof are used. I can do it. Of these, copper foil or copper alloy foil is preferable from the viewpoint of low cost and high electrical conductivity.

  The height of the convex portion 12 is preferably 1 μm or more. This is because, depending on the thickness of the negative electrode active material 13 formed on the upper portion, if the thickness is less than 1 μm, the effect of relaxing the stress may not be sufficiently obtained. The upper limit of the height of the convex portion 12 is not particularly limited. If the height of the convex part 12 becomes high, as a result, the ratio of the collector which occupies for a negative electrode will become high, and the capacity | capacitance as a negative electrode will fall. Therefore, the upper limit of the height is determined in consideration of a practical capacity.

  In order to further enhance the effect of the present invention, the ratio of the thickness (t) of the negative electrode active material 13 formed on the upper surface of the convex portion 12 and the average distance (X) between adjacent negative electrode active materials 13 ( X / t) is preferably 2 or more. The distance between adjacent negative electrode active materials 13 refers to the shortest distance connecting the side surface of the negative electrode active material 13 and the adjacent negative electrode active material 13. When the negative electrode active material 13 occludes lithium ions and expands, the expansion at the junction with the upper surface of the convex portion 12 is smaller than that of other portions, so that the negative electrode active material 13 expands in a fan shape. When the value of X / t is smaller than 2, when the negative electrode active material 13 formed on the convex portion 12 expands, the adjacent negative electrode active materials 13 collide with each other. As a result, stress is applied to the current collector, and in the worst case, the current collector is broken. The upper limit of X / t may be determined in consideration of the practical capacity and the ratio of the active material in the negative electrode.

As the negative electrode active material 13, a material generally used as a negative electrode of a lithium ion battery can be used. In particular, when a material having a large expansion when occlusion of lithium ions is used, the effect of the present application is great. Examples of the material having a large expansion include a material containing at least one selected from the group consisting of Si, Sn, SiO _x (0 <X <2), and SnO _x (0 <X <2). Examples thereof include Si simple substance, Sn simple substance, alloys such as Ni ₃ Sn ₄ and Mg ₂ Sn, solid solutions, and compounds such as SiB ₄ and SiB ₆ .

  As the intermediate layer 14, for example, in the case of a lithium battery, at least one selected from the group consisting of organic monomers, organic oligomers, and polymers thereof having a melting point of 0 ° C. or higher and 200 ° C. or lower can be used. Further, at least one selected from the group consisting of carbonate monomers, carbonate oligomers and polymers thereof can also be used. As such a material, for example, ethylene carbonate (EC), which is a cyclic carbonate, or a polycarbonate oligomer material having a degree of polymerization of about 10 to 100 can be used. As a method for forming the intermediate layer 14, various thin film forming methods and coating methods such as spin coating are used.

  Next, chemical mechanical polishing (CMP) can be used as a method of removing the surface of the intermediate layer 14 and exposing at least a part of the convex portion 12. At this time, the height of the convex portion can be changed by changing the polishing amount. As the CMP slurry, a slurry for polishing copper wiring in a semiconductor manufacturing process can be used.

  As a method for forming the negative electrode active material 13 on the surface of the exposed convex portion 12 and intermediate layer 14, a sputtering method, a vacuum deposition method, a laser ablation method, an ion plating method, a CVD (Chemical Vapor Deposition) method, or the like is used. A dry thin film process can be used. In these methods, since the vapor pressure of the intermediate layer 14 in vacuum is high, the negative electrode active material 13 hardly adheres to the surface of the intermediate layer 14, and thus the negative electrode active material 13 is mainly exposed on the surface of the convex portion 12. Accumulates and grows selectively.

  The negative electrode according to the present invention obtained as described above, and a positive electrode in which a positive electrode active material layer containing lithium cobaltate, which is a positive electrode active material that absorbs and releases lithium ions, is formed on a positive electrode current collector such as aluminum. Is sandwiched between separators made of porous polypropylene or the like, placed in a bag made of aluminum laminate or the like, and a lithium ion conductive electrolyte or polymer electrolyte is added to produce a lithium ion battery.

  In the lithium ion battery thus obtained, stress due to negative electrode expansion is relieved, wrinkles and cutting of the electrode plate are suppressed, and reliability is obtained because of less cycle deterioration.

  Hereinafter, the present invention will be described in more detail by way of specific examples. In addition, this invention is not limited to the Example shown below.

Example 1
The negative electrode 10 shown in FIG. 1 was produced by the following method. The current collector 11 is made of a roughened copper foil having a size of 20 mm × 20 mm, a substrate thickness of 35 μm, an average surface roughness Ra = 1 μm, and a maximum height Rmax = 6 μm of the convex portion 12, and an intermediate layer 14 is formed on the surface. For this purpose, the current collector was fixed on the stage of a spin coater, rotated at 1000 rpm (rpm) in a dry atmosphere (dew point = −25 ° C.) at 20 ° C., and melted by heating to 60 ° C. As a result, an EC layer having a thickness of about 1 μm was formed on the back surface of the current collector, and this was repeated seven times to form an intermediate layer having a thickness of 7 μm.

  Next, in order to polish the surface and expose the convex portion 12 of the current collector, the current collector 11 is affixed and fixed on the Si wafer, and chemical mechanical polishing (CMP) is used. The height of the part was changed (CMP polishing apparatus is TRCP500 manufactured by Technorise Co., Ltd., and CMP slurry is CL-1200 manufactured by Seimi Chemical Co., Ltd.).

Further, a SiO _0.3 film 13 as a negative electrode active material layer was formed thereon by an electron beam (EB) evaporation method with a thickness of 1 μm. Deposition conditions were EB power: 500 mA, degree of vacuum: 4 × 10 ⁻³ Pa, oxygen flow rate: 10 SCCM, film formation time: 1 hour (film formation apparatus manufactured by Shinko Seiki Co., Ltd.).

The negative electrode active material 13 made of SiO _0.3 thus formed was formed on the upper surface of the convex portion 12 and was not formed on the intermediate layer 14.

(Comparative Example 1)
Next, as Comparative Example 1, a negative electrode 30 having no projection as shown in FIG. In the electrode manufacturing method, an electrolytic copper foil having a thickness of 20 mm × 20 mm and a thickness of 35 μm was used as the current collector 31, and a SiO _0.3 film 33 as a negative electrode active material layer was formed thereon by an EB vapor deposition method with a thickness of 1 μm. . Deposition conditions were EB power: 500 mA, degree of vacuum: 4 × 10 ⁻³ Pa, oxygen flow rate: 10 SCCM, film formation time: 1 hour (the film formation apparatus was manufactured by Shinko Seiki Co., Ltd.).

(Comparative Example 2)
Furthermore, as Comparative Example 2, a negative electrode 40 having no convex part and patterned only with an active material as shown in FIG. 4 was produced. In the electrode production method, an electrolytic copper foil having a size of 20 mm × 20 mm and a thickness of 35 μm was used as the current collector 41, and a resist made of 2.3.5 trimethylphenol was applied to the surface to form a resist. RY-3315 manufactured by Hitachi Chemical Co., Ltd. was used as the resist. Next, ultraviolet light is irradiated through a quartz mask patterned by arranging 10 μm squares on one side (light quantity: 50 mJ / cm ² ), and immersed in an aqueous sodium carbonate solution (0.8 wt%, 25 ° C.) for 10 seconds to pattern the resist. went. It was then formed by EB vapor deposition in a thickness of 1μm to _{SiO 0.3} film 43 serving as the negative electrode active material layer thereon. Deposition conditions were EB power: 500 mA, degree of vacuum: 4 × 10 ⁻³ Pa, oxygen flow rate: 10 SCCM, film formation time: 1 hour (the film formation apparatus was manufactured by Shinko Seiki Co., Ltd.).

Next, it was immersed in an aqueous sodium hydroxide solution (2.0 wt%, 50 ° C.) for 10 seconds, and lift-off was performed to remove the resist and the SiO _0.3 film thereon. Thereafter, in order to completely remove sodium hydroxide, it was taken out by being immersed in pure water for 10 minutes and dried in the atmosphere.

(Comparative Example 3)
Further, as Comparative Example 3, a negative electrode 50 in which a SiO _0.3 film 53 is formed on a current collector 51 of a roughened copper foil having convex portions 52 having an average surface roughness Ra = 1 μm as shown in FIG. Produced. The SiO _0.3 film as the negative electrode active material layer was formed by EB vapor deposition with a thickness of 1 μm. Deposition conditions were EB power: 500 mA, degree of vacuum: 4 × 10 ⁻³ Pa, oxygen flow rate: 10 SCCM, film formation time: 1 hour (the film formation apparatus was manufactured by Shinko Seiki Co., Ltd.).

(Production of battery)
Next, a positive electrode to be combined with the negative electrodes prepared in Example 1 and Comparative Examples 1 to 3 was prepared as follows. First, a 20 mm × 20 mm platinum foil having a thickness of 50 μm is used as the substrate 12, and then LiCoO ₂ is used as the first active material 13, and a sputtering method (200 W power, Ar / O ₂ = 3/1 is 20 SCCM at a thickness of 2 μm. , 20 mTorr), and further heat-treated in a tube furnace at 800 ° C. for 2 hours in the atmosphere to obtain a positive electrode.

As an electrolytic solution, 1 mol / l LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and diethylene carbonate (mixing volume ratio = 1: 2) was used.

  As the separator, a polypropylene separator (thickness 20 μm) manufactured by Celgard was used.

The positive electrode and the negative electrodes of Examples and Comparative Examples 1 to 3 are combined so that the active materials oppose each other, a separator is disposed between the positive electrode and the negative electrode, and laminated, and then an aluminum laminate bag The electrolyte solution was injected at 1 cm ³ , the electrolyte solution inlet of the bag was sealed by heat sealing, the bag was sandwiched between 2 mm-thick glass plates, and fixed with clips to prepare a model cell.

(Evaluation)
The cycle characteristics of the obtained model cell were obtained as follows. Charging is performed at a current of 0.1 mA up to 4.2 V, and subsequent discharging is performed at a current of 0.1 mA up to 3.0 V. This charge / discharge cycle was performed 200 times, and the cycle characteristic was determined by multiplying the value obtained by dividing the discharge capacity of the first cycle by the discharge capacity of the 200th cycle by 100. The discharge capacity at the first cycle of the produced model cell was approximately 0.5 mAh. Furthermore, after 200 cycles of the charge and discharge, the aluminum laminate bag was opened, the negative electrode was taken out, and the presence or absence of wrinkles on the negative electrode current collector was examined. The results are shown in Table 1.

  As is clear from Table 1, Example 1 had higher cycle characteristics than Comparative Examples 1 to 3, and no negative electrode current collector was found. This is considered to be because the space of the current collector relaxed the stress due to the volume expansion of the active material in Example 1. In Comparative Example 2, the active material was formed directly on the current collector although it had space, and in Comparative Example 3, there was no space, so stress relaxation was considered insufficient. Further, in Comparative Example 1 having no space, many wrinkles were generated on the current collector, and cutting of the current collector was observed.

(Example 2)
Next, the result of having performed the same evaluation as in Example 1 with the same structure as that of the negative electrode in Example 1 and changing the height of the convex portion is shown. The height of the convex portion was adjusted by adjusting the polishing amount in Example 1. For confirmation of the surface shape, the intermediate layer was dissolved with dimethyl carbonate, and then measured using a laser microscope VK-8550 manufactured by Keyence Corporation. Others were the same as in Example 1. The results are shown in Table 2.

  Accordingly, it was found that if the height of the convex portion is 1 μm or more, the cycle characteristics are particularly effective. This is presumably because the stress applied to the substrate due to the expansion of the active material deposited on the convex portion is reduced by increasing the convex portion.

(Example 3)
Next, with the same structure as the negative electrode of Example 1, the average distance (X) between adjacent negative electrode active materials was changed, the same evaluation as in Example 1 was performed, and the thickness of the negative electrode active material (t ) And X. The distance between adjacent negative electrode active materials was determined by using a current collector having a different surface roughness and changing the polishing amount. For confirmation of the surface shape, the intermediate layer was dissolved with dimethyl carbonate, and then measured using a laser microscope VK-8550 manufactured by Keyence Corporation. Others were the same as in Example 1. The results are shown in Table 3.

  As is apparent from Table 3, characteristics were improved when X / t was 2 or more.

  In Examples 1 and 2, a mixed solvent of ethylene carbonate and diethyl carbonate was used as the electrolytic solution. However, the present invention is not limited to this, and propylene carbonate or γ-butyl lactone, dimethyl carbonate, and methyl ethyl are used. The same effect can be obtained even if a mixed solvent of carbonate is used.

  Further, in Examples 1 and 2, EC and polycarbonate oligomer were used as the intermediate layer, but the present invention is not limited thereto, and ethylene acrylic acid copolymer oligomer having a polymerization degree of 10 to 100, ethylene methacrylic acid The same effect can be obtained by using a copolymer oligomer, an ethylene methyl methacrylate copolymer oligomer, a polyester oligomer, a polycaprolactone oligomer, or a polyvinyl alcohol oligomer.

  In the negative electrode produced by the manufacturing method of the present invention, the current collector is provided with a plurality of convex portions, the negative electrode active material is formed only on the upper surface of the convex portions, and the active material is present on the current collector other than the plurality of convex portions. Since the space that is not formed can be provided with certainty, the concentration of stress due to the volume change of the active material can be alleviated, and the occurrence of wrinkling and cutting of the current collector can be prevented and the deterioration of cycle characteristics can be suppressed. Is possible. For this reason, by using the electrode according to the manufacturing method of the present invention, it is possible to produce a high-capacity lithium secondary battery excellent in reliability such as cycle characteristics.

Schematic cross-sectional view of the negative electrode in Embodiment 1 of the present invention Schematic cross-sectional view showing an example of a method for manufacturing a negative electrode in Embodiment 1 of the present invention Schematic sectional view of a negative electrode in Comparative Example 1 of the present invention Schematic sectional view of the negative electrode in Comparative Example 2 of the present invention Schematic sectional view of the negative electrode in Comparative Example 3 of the present invention

Explanation of symbols

10, 30, 40, 50 Negative electrode 11, 31, 41, 51 Current collector 12, 52 Current collector convex portion 13, 33, 43, 53 Negative electrode active material 14 Intermediate layer

Claims (7)

A step of providing an intermediate layer compatible with the electrolytic solution so as to cover the current collector on the surface of the sheet-shaped current collector having conductivity and having a plurality of convex portions on the surface;
Exposing at least some of the plurality of convex portions of the current collector by removing a portion of the surface of the intermediate layer;
Providing an active material layer on the exposed protrusions;
A method for producing an electrode, comprising: The current collector has a surface roughness Ra of 0.1 μm or more and 3 μm or less,
The method for producing an electrode according to claim 1. Using chemical mechanical polishing as a method of exposing at least some of the plurality of convex portions of the current collector;
The method for producing an electrode according to claim 1. The current collector is a copper foil or a copper alloy foil.
The manufacturing method of the electrode of Claim 1. The intermediate layer includes at least one selected from the group consisting of organic monomers, organic oligomers, and polymers thereof,
The manufacturing method of the electrode in any one of Claim 1 to 4. The intermediate layer includes at least one selected from the group consisting of carbonate monomers, carbonate oligomers, and polymers thereof.
The manufacturing method of the electrode in any one of Claim 1 to 4. The active material layer includes at least one selected from the group consisting of Si, Si oxide and Si alloy,
The manufacturing method of the electrode in any one of Claim 1 to 6.

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