JP2005116376A - Electrode and its manufacturing method, and secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a secondary battery in which there is no fracture in a pressurization process and the work efficiency in a winding and turning process is improved and its manufacturing method, and a secondary battery using the electrode. <P>SOLUTION: When an electrode active material layer is formed on both sides of a current collector 1, the length of an electrode active material layer 2a formed on a first face arranged at opposed positions through the current collector 1 is made longer than the electrode active material layer 2b formed on a second face, and the distance d<SB>1</SB>, d<SB>2</SB>in the longitudinal direction of the current collector between the end parts of the two electrode active material layers arranged at the opposed positions are respectively made 1-5 mm and 5-100 mm. Therefore, when applying pressurization for reducing the gap of the electrode active material layers, concentration of pressure on a specific part of the current collector is eliminated and defect by fracture can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrode mainly used for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a manufacturing method thereof, and a secondary battery including the electrode as a constituent element.

  A secondary battery as a small power source is indispensable for a portable communication terminal represented by a mobile phone or a notebook personal computer. In addition, the demand for downsizing and weight reduction of the entire device tends to increase, and in order to meet this demand, secondary batteries with small size and high performance have been developed and put into practical use.

  Lithium-ion batteries are expected to achieve the highest voltage and energy density among the secondary batteries so far, and even now, studies on improving characteristics and downsizing are actively promoted. Yes.

  A lithium ion secondary battery has, as main components, a positive electrode active material layer, a negative electrode active material layer, a positive electrode and a negative electrode, and a positive and negative electrode formed on a sheet-like current collector made of a conductor. It has an intervening separator and electrolyte. In lithium ion secondary batteries currently in practical use, the positive electrode uses an electrode active material, a powder mainly composed of lithium cobalt oxide, and the negative electrode uses a carbon-based material powder as an electrode active material. It has been. In addition, a porous film made of a polymer material such as polyethylene or polypropylene is used for the separator.

  FIG. 2 is a perspective view showing an example of a configuration in which a positive electrode and a negative electrode are overlapped and wound with a separator interposed therebetween. In FIG. 2, 4a is a positive electrode, 4b is a negative electrode, 6a is a positive current extraction tab, 6b is a negative current extraction tab, 5 is a separator, and 7 is a winding element.

  In this example, first, a strip-shaped conductor is prepared as a current collector, and positive and negative electrode active material layers (not shown) are formed on the current collector surface to produce a positive electrode 4a and a negative electrode 4b. Then, the separator 5 is interposed between the positive electrode and the negative electrode, and is wound into a flat shape to form a winding element 7.

  As described above, the lithium ion secondary battery has a feature of high energy density. However, with the recent development of electronic devices, it is required to further increase the energy density. For this purpose, it is necessary to increase the electrode active material layer. However, a simple increase leads to an increase in the size of the battery. Therefore, the porosity of the electrode active material layer is reduced.

  The electrode active material layer is formed by applying a paste containing a mixture of electrode active material powder, a polymer material to be a binder, and a solvent for dissolving the polymer material to the surface of the current collector, and removing the solvent by drying. It is common to do. And since the electrode active material layer after drying has a space | gap as much as the part which removed the solvent, in order to reduce a porosity, it is effective to pressurize using a roll etc.

  However, on the other hand, in order to improve the working efficiency in the process of winding the electrode, the electrode surface is provided with a portion where the electrode active material layer is not formed, such as a winding start portion, on both sides of the current collector. If the formation start ends of the two electrode active material layers provided coincide with each other, the pressure propagated from the electrode active material layer is concentrated, and the current collector may break at this portion, which increases the manufacturing cost. .

  In order to prevent such breakage, the formation start end and the formation end end of the two electrode active material layers facing each other through the current collector are arranged to be biased. According to such a method, the pressure applied to the current collector through the electrode active material layer at the time of pressurization does not concentrate in a narrow range, so that a certain effect is exhibited in preventing the breakage. .

  In Patent Document 1, an active material is intermittently applied to one surface of a current collecting core material, dried and solidified to form an electrode mixture portion, and an application start position is formed on the other surface of the current collecting core material. At a position 1-5 mm away from the application end portion of the electrode mixture portion on one side and closer to the application start end portion, and at a position 1-5 mm away from the application start end portion of the electrode mixture portion on one side to the non-application side The active material is intermittently applied in a state set to be dried and solidified to form an electrode mixture portion, and the boundary between the electrode mixture portion on the opposite side is the boundary between the starting end of the electrode mixture portion and the uncoated portion. A technique is disclosed in which the current collecting core is backed up at the mixture application terminal portion facing the terminal portion.

  FIG. 3 is a schematic diagram of a cross section of an electrode according to the prior art disclosed in Patent Document 1. As shown in FIG. In FIG. 3, 8 is a current collector, 9a is an electrode active material layer formed on one surface, 9b is an electrode active material layer formed on the other surface, 10a and 10b are raised portions, and 11 is an electrode. The raised portions 10a and 10b are inevitably generated due to an increase in pressure at the start of application inside the die used for applying the paste for forming the electrode active material layer.

D ₃ is the distance between the formation start end and the formation end end of the electrode active material layers facing each other through the current collector, that is, the amount of deviation. In addition, the arrow in FIG. 3 shows the moving direction of the electrical power collector at the time of apply | coating a paste, and is apply | coated to the up-and-down surface in FIG.

  Even with the technique disclosed in Patent Document 1, a certain degree of effect is recognized in reducing defects in the pressurizing process. However, as shown in FIG. 3, the electrode active material layer 9b becomes unnecessarily thick at the end portion and the material is used more than necessary only by shifting the formation position of the electrode active material layer in the same direction by 1 to 5 mm. As a result, there is a problem that a local mismatch of the balance between the positive electrode and the negative electrode occurs.

  In addition, providing the portion where the electrode active material layer is not formed contributes to improving the efficiency of the process of winding the electrode as described above, but as disclosed in Patent Document 1, When both of the deviation amounts are 1 to 5 mm, particularly when the folded element has a folded portion as shown in FIG. 2, the length of the portion where the electrode active material layer is not formed is insufficient. It may not be fully expressed.

JP 2002-134102 A

  Accordingly, an object of the present invention is to provide an electrode for a secondary battery, a method for manufacturing the same, and a secondary battery using the electrode, in which there is no breakage in the pressurizing process and the working efficiency of the winding process is improved. There is.

  The present invention has been made as a result of reexamining the arrangement of electrode active material layers on both sides of a current collector in order to solve the above-described problems.

  That is, the present invention provides an electrode having an electrode active material layer forming portion and an electrode active material layer non-forming portion on the first and second surfaces facing each other in a current collector made of a strip-shaped conductive material. One end portion of the electrode active material layer forming portion of the other side of the electrode active material layer forming portion on the second surface at a position facing the current collector is opposite to the other end portion. The electrode on the second surface at a position where the other end of the electrode active material layer forming portion of the first surface is opposed to the current collector is disposed 5 to 100 mm offset to the side The electrode is characterized in that the electrode is formed so as to be deviated by 1 to 5 mm on the one end side from the other end of the active material layer forming portion.

  Moreover, this invention forms in said 1st surface in the manufacturing method of the electrode which forms an electrode active material layer discontinuously in the 1st surface and 2nd surface which oppose in the collector which consists of a strip | belt-shaped conductor. From the position where the electrode active material layer is displaced by 5 to 100 mm on the other end side from one end of the electrode active material layer on the second surface formed at the position facing the current collector. 1-5 mm deviation from the other end portion of the electrode active material layer on the second surface formed at a position facing the current collector through the current collector. The method for producing an electrode is characterized in that the formation is finished at the above-mentioned position.

  Moreover, this invention forms in said 1st surface in the manufacturing method of the electrode which forms an electrode active material layer discontinuously in the 1st surface and 2nd surface which oppose in the collector which consists of a strip | belt-shaped conductor. The electrode active material layer is located at a position offset by 1 to 5 mm from the one end of the second surface electrode active material layer formed at the position facing the current collector to the other end. 5-100 mm deviation from the other end of the electrode active material layer on the second surface formed at a position opposite to the current collector through the current collector. The method for producing an electrode is characterized in that the formation is finished at the above-mentioned position.

  The present invention also provides a secondary battery comprising a winding element formed by winding the positive electrode and the negative electrode having the above structure together with a separator interposed therebetween.

  In the electrode of the present invention, the electrode active material layer forming portion and the electrode active material layer non-forming portion are provided on both sides of the current collector, and the formation start end or formation end of the electrode active material layer facing each other through the current collector Since the positions of the ends are deviated from each other, it is possible to extremely reduce the failure to break in the pressing process.

  In the winding process, even when the radius of curvature is small as in the case of folding, the electrode of the present invention can be dealt with by providing a part where the electrode active material layer non-formed part is elongated. Efficiency is improved and the occurrence of defects can be suppressed.

FIG. 1 is a diagram schematically showing a cross section of an example of an electrode according to the best mode for carrying out the present invention. In FIG. 1, 1 is a current collector, 2a is an electrode active material layer formed on the first surface, 2b is an electrode active material layer formed on the second surface, and 3 is an electrode. The deviation amounts d ₁ and d ₂ are set to 1 to 5 mm and 5 to 100 mm, respectively. In particular, d ₂ can be appropriately adjusted depending on the winding diameter of the electrode, the number of windings, and the like.

  In addition, the material used for the current collector is not particularly limited as long as it has conductivity, and various metal foils, flexible polymer sheets in which conductive powder is dispersed, and the like are used. It is done. In selecting the material, it is needless to say that it does not cause a chemical reaction with the electrolytic solution and is insoluble in the solvent constituting the electrolytic solution.

  Moreover, as a positive electrode active material, if it is a lithium ion secondary battery, lithium-cobalt composite oxide etc. are used with conductive carbon materials, such as a graphite, As a negative electrode active material, graphite, coke, activated carbon Etc. are used.

  In order to apply these electrode active materials to the surface of the current collector, the material is prepared into a powder having an appropriate particle size, and then mixed with a binder such as polyvinylidene fluoride, for example, a solvent such as N-methyl-2-pyrrolidone. Then, a method of applying as a paste is used.

  Next, the present invention will be described in more detail with specific examples.

  First, the manufacturing method of a positive electrode is demonstrated. Here, lithium carbonate and cobalt carbonate were mixed so that the molar ratio of lithium to cobalt was 1: 1, and baked in air at 900 ° C. for 5 hours. The fired body was pulverized using a mortar to obtain a fired powder having an average particle size of 15 μm. Further, the obtained fired powder and lithium carbonate powder were mixed so that the weight ratio was 95/5.

  The mixed powder, graphite as a conductive material, and polyvinylidene fluoride as a binder are weighed and mixed at a weight ratio of 91/6/3, dispersed in N-methyl-2-pyrrolidone, and positive electrode active The material layer forming paste was obtained. This paste was applied to an aluminum foil having a thickness of 20 μm prepared as a current collector to form an electrode active material layer.

  In the coating process, first, the paste was applied to the first surface so as to form a repeated pattern in which the length of the electrode active material layer forming portion was 420 mm and the length of the electrode active material layer non-forming portion was 6 mm. The amount of paste applied was adjusted so that the thickness of the electrode active material layer after drying was 110 μm.

Next, the paste was applied to the second surface so that d ₁ and d ₂ in FIG. 1 were 3 mm and 60 mm, respectively. Also on the second surface side, the amount of paste applied was adjusted so that the thickness of the electrode active material layer after drying was 110 μm. Subsequently, the sheet | seat which formed the electrode active material layer on both surfaces of the electrical power collector was pressurized using the roll, and the whole thickness was 160 micrometers.

  Next, the manufacturing method of a negative electrode is demonstrated. Here, a carbon material having an average particle size of 20 μm obtained by firing and pulverizing a phenol resin in an inert gas stream and a polyvinylidene fluoride as a binder are weighed and mixed so that the weight ratio is 90/10. And dispersed in N-methyl-2-pyrrolidone to obtain a paste for forming a negative electrode active material layer. Subsequent steps were performed in the same manner as in the case of the positive electrode to obtain a negative electrode. The metal foil used for the current collector is a copper foil having a thickness of 20 μm.

  The positive electrode and the negative electrode thus obtained were not broken at all, and it was found that pressure concentration did not occur at a specific location of the current collector in the pressurizing step. Therefore, it is clear that the productivity and reliability of the secondary battery can be improved by the present invention.

  Moreover, in the said Example, although the lithium ion secondary battery was demonstrated, it is applicable also to electrochemical cells, such as another secondary battery and the electric double layer capacitor which has the same structure.

The cross-sectional schematic diagram of the example of the electrode which concerns on the best form for implementing this invention. The perspective view which shows the example of the structure which piled up and wound the positive electrode and the negative electrode through the separator. The schematic diagram of the cross section of the electrode by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,8 Current collector 2a Electrode active material layer 2b formed on the first surface Electrode active material layer 3,11 formed on the second surface Electrode 4a Positive electrode 4b Negative electrode 5 Separator 6a Positive electrode current extraction tab 6b Negative electrode current the electrode active material layer 10a formed on the other surface electrode active material layer 9b formed on the take-out tab 7 spirally wound element 9a one aspect, 10b protruding portion d _1, d _2, d ₃ bias amount

Claims (4)

  In the electrode having the electrode active material layer forming portion and the electrode active material layer non-forming portion on the opposing first surface and second surface of the current collector made of a strip-shaped conductive material, the electrode active material layer on the first surface One end of the formation portion is biased 5 to 100 mm closer to the other end than the one end of the electrode active material layer formation portion on the second surface at the position facing the current collector. And the other end portion of the electrode active material layer forming portion of the first surface is a portion of the electrode active material layer forming portion of the second surface at a position facing through the current collector. The electrode is characterized in that it is arranged with a deviation of 1 to 5 mm on the one end side with respect to the other end.   In the electrode manufacturing method in which the electrode active material layer is formed discontinuously on the first and second surfaces facing each other in the current collector made of a strip-shaped conductor, the electrode active material layer formed on the first surface is: Formation is started from a position deviated by 5 to 100 mm on the other end side from one end of the electrode active material layer on the second surface formed at a position facing through the current collector; and The formation is finished at a position deviated from the other end of the second surface electrode active material layer formed at the position facing the current collector by 1 to 5 mm toward the one end. A method for manufacturing an electrode.   In the electrode manufacturing method in which the electrode active material layer is formed discontinuously on the first and second surfaces facing each other in the current collector made of a strip-shaped conductor, the electrode active material layer formed on the first surface is: Starting from a position that is offset by 1 to 5 mm on the other end side from one end of the electrode active material layer on the second surface formed at a position facing through the current collector, and The formation is finished at a position that is offset by 5 to 100 mm toward the one end side of the other end part of the electrode active material layer on the second surface formed at a position facing through the current collector. A method for manufacturing an electrode.   A secondary battery comprising a winding element formed by winding the positive electrode and the negative electrode having the structure according to claim 1 together with a separator interposed therebetween.

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