JP2008103231A - Electrode for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that the electrode end part forming active materials is easily damaged by a traveling system or the like and that the active materials are peeled off due to impact from a current collector. <P>SOLUTION: This is an electrode carrying the active materials 2 capable of storing and releasing lithium on the current collector 1. The electrode for a lithium secondary battery is provided in which a first region 21 where a protruded part is regularly formed on at least one face of the current collector and a second region 22 where the protruded part is randomly formed are formed, in which by slitting the current collector 1 in the second region 22 high in adhesiveness of the active materials 2, peeling-off due to the impact from the traveling system is suppressed, and which is superior in yield, and its manufacturing method is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode in which an active material is formed on a current collector having a protrusion, and a lithium secondary battery using the electrode.

  In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as power sources has increased. High energy density and excellent cycle characteristics are desired for batteries used in the above applications.

In response to the above demands, various nonaqueous electrolytes such as organic electrolytes, gel polymer electrolytes obtained by making organic electrolytes non-fluidic using polymers or gelling agents, and lithium ions as charge transfer media. Non-aqueous electrolyte lithium secondary batteries have been developed. As a positive electrode material, a material such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, and the like that exhibits a high reversible potential by reversibly occluding and releasing lithium ions with various electrolytes has been discovered. As the negative electrode material, materials having a low reversible potential such as various carbon bodies such as graphite and carbon have been discovered. Lithium secondary batteries that use these active materials as a positive electrode or a negative electrode and have the positive electrode and the negative electrode arranged opposite to each other via a separator have been developed and mass-produced.

  However, as the functions of portable devices improve, higher energy density is required for power supplies than ever.

  Under such circumstances, Si (silicon) or Sn is used as a high-capacity negative electrode material (hereinafter also referred to as a negative electrode active material) that can form an intermetallic compound with Li and occlude and release lithium to obtain a very high capacity. Attention has been focused on (tin) or alloy materials based on these. 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, the structure of these negative electrode materials greatly changes when lithium ions are occluded and expands. As a result, the active material particles are broken or the active material layer is peeled off from the current collector, resulting in a decrease in electronic conductivity between the active material and the current collector, resulting in a decrease in cycle characteristics. Was.

  In order to solve the problem, a proposal has been made to form an expansion space in the active material layer during occlusion of lithium ions (Patent Document 1).

In Patent Document 1, regular protrusions are formed on a current collector, and an active material patterned in a columnar shape is formed thereon. With this configuration, the voids between the negative active materials formed in a columnar shape can absorb the volume expansion of the active material, and the active material is prevented from peeling from the current collector.
JP 2004-127561 A

  In Patent Document 1, by providing an expansion space in the active material layer, it is possible to absorb the volume expansion during Li occlusion, but since the upper part of the protrusion is formed flat, the active material formed thereon Adhesive strength with the interface decreases. In particular, the electrode end portion is easily damaged by a running system in the manufacturing process and has a problem that the active material is peeled off from the current collector by impact.

  In order to solve the above problems, the present invention provides an electrode carrying an active material capable of occluding and releasing lithium on a current collector, wherein protrusions are regularly formed on at least one surface of the current collector. It has a 1st area | region and the 2nd area | region in which the projection part was formed at random.

  Further, according to the present invention, the active material is grown in a columnar shape on the protrusion of the current collector, the upper portion of the protrusion formed in the first region is flat, and the second region is Compared with the first region, the adhesiveness with the active material is excellent.

  In addition, the second region of the present invention is formed at least at the electrode end in the width direction of the current collector, and suppresses the separation of the active material from the current collector due to an impact and a slit. And has excellent charge / discharge characteristics.

  In the second region of the present invention, the surface roughness Ra of the second region is 0.5 μm or more and 5 μm or less, and the active material is prevented from peeling off.

  Further, the present invention is characterized in that the negative electrode active material is silicon, tin, germanium, or an alloy, oxide, or nitride containing these main components, and by using these materials as the active material of the negative electrode. Excellent high capacity.

  Furthermore, the present invention provides an electrode carrying an active material capable of occluding and releasing lithium on a current collector, the current collector comprising: a first region in which protrusions are regularly formed; and a protrusion A portion having a second region formed at random on at least one surface, and slitting a portion where the second region is formed, thereby suppressing the separation of the active material at the time of slitting, thereby increasing the yield. An excellent manufacturing method is provided.

  According to the current collector, the battery electrode plate, the secondary battery using the current collector, and the manufacturing method thereof according to the present invention, a high-capacity active material is used, and active material peeling at the electrode end face portion that is easily damaged is suppressed. be able to. Moreover, it has the effect that it can prevent peeling of an active material by slitting in a 2nd area | region at the time of manufacture of an electrode. As a result, a lithium secondary battery with excellent cycle characteristics can be provided.

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

(Embodiment)
As shown in FIG. 3, the electrode for the lithium secondary battery of the present embodiment includes a sheet-like current collector 1 and an active material 2 formed on the surface of the current collector 1.

  The active material 2 is not shown, and only the current collector 1 is seen from the surface as shown in FIG. The current collector 1 has a longitudinal direction and a width direction as indicated by arrows in FIG. On the surface of the current collector 1, as shown in FIG. 1, a first region 21 in which a first protrusion 11 is formed at the center in the width direction and second protrusions 12 are formed at both ends in the width direction. There is a second region 22.

  The width | variety of the 1st area | region 21 changes with uses of a battery, and is not specifically limited. For example, it is 60 to 65 mm. The width | variety of the 2nd area | region 22 is a width | variety required on manufacture, for example, is 0.25-5 mm, More preferably, it is 0.5-2.5 mm. Further, the first region and the second region may be formed continuously in the width direction, or a region between the first region and the second region, for example, a region without a protrusion ( There may be a third region).

  FIG. 2 is a cross-sectional view of the current collector 1 taken along the line AA in FIG. For easy understanding, the current collector 1 is displayed in a state before slitting, that is, in a state where a plurality of current collectors 1 are continuous in the width direction.

  As is apparent from FIGS. 1 and 2, the first region 21 and the second region 22 have different protrusion shapes and protrusion dispositions. In the first region 21, the protrusions 11 are formed relatively regularly, whereas in the second region 22, the protrusions 12 are formed relatively irregularly (randomly).

  In addition, the protrusions 11 and 12 are usually formed on both surfaces of the current collector 1 as shown in FIG. 2, but the present invention is also effective when formed on only one surface.

  The current collector 1 is preferably a metal containing at least one element selected from copper, nickel, and iron, and an alloy material containing these as a main component can also be used. Of these, copper or a copper alloy is particularly preferable because it has excellent flexibility and stretchability and does not react with lithium. For example, in the case of copper, electrolytic copper foil, electrolytic copper alloy foil, electrolytic copper foil that has been subjected to roughening treatment in advance, rolled copper foil that has been subjected to roughening treatment, and the like can be used.

  The thickness of the current collector 1 can be any thickness, but is preferably 5 μm to 100 μm, and particularly preferably 8 μm to 35 μm. This is because when the thickness is 100 μm or more, the strength of the current collector is ensured, but the current collector volume occupies the whole battery, and it is not expected to increase the capacity of the battery. On the other hand, if the thickness is less than 5 μm, the strength cannot be ensured and the current collector is wrinkled or broken.

  Next, the purpose of regularly arranging and forming the first protrusions 11 is to provide a space in the active material layer by the shadow of the protrusions of the current collector when the active material layer is formed by a vapor phase method or the like. It is in. The shadow effect due to the current-projecting protrusions is particularly prominent when the active material layer is formed by an oblique incidence gas phase method, as represented by oblique vapor deposition. In this way, by increasing the space ratio of the active material layer, the expansion of the active material layer at the time of lithium occlusion can be absorbed.

  Although there is no restriction | limiting in particular in the pattern shape of the 1st processus | protrusion 11 of this invention, 10-20 micrometers square is preferable for the convex part 11, and the width | variety of a recessed part has a preferable about 10 micrometers. Therefore, the period in which the first protrusions 11 are formed is 20 to 30 μm. This period may be the same or different in the width direction and the longitudinal direction, but it is desirable that both are within this range. When the width of the concave portion is wide, the shadow effect due to the current collector projection is lost, and when the width of the concave portion is narrow, the space ratio of the active material particles is small. Further, the top of the protrusion 11 is flat, and the cross-sectional shape is preferably a columnar shape, a polygonal shape, a cylindrical shape, a cone shape, a trapezoidal shape, or the like. By flattening the tops of the protrusions in this way, the active material particles can grow in a columnar shape in the vertical direction with the protrusions 11 as nuclei, and the particles can be prevented from growing thick. A pattern having these shapes can be easily produced by a combination of a resist method and a plating method.

  The height of the surface protrusion 11 of the current collector is preferably 1 to 20 μm, and particularly preferably 3 to 10 μm. This is because stress relaxation becomes insufficient when the protrusion height is smaller than 1 μm. This is because when the height of the protrusion is 20 μm or more, the volume of the protrusion in the entire battery increases, and it is not possible to increase the capacity of the battery.

  However, the active material layer formed on the current collector having these has a problem that the adhesion strength with the current collector interface is weak and is easily peeled off by impact or the like.

  In contrast, a current collector having random protrusions can increase the adhesion strength between the active material layer and the current collector interface. The present invention is characterized in that the second region 22 having such high adhesion is provided at the end in the width direction of the current collector, and the active material is peeled off from the current collector interface due to damage caused by the running system and the slit. Can be suppressed. Thereby, the outstanding charging / discharging characteristic is acquired.

  As a method of forming the second region 22 in which the second protrusions 12 are randomly formed, it can be easily produced by wet etching. The etchant when using copper as the current collector is an acid such as dilute sulfuric acid + aqueous peroxide solution. Etching is performed in a circular shower process to form protrusions with Ra of about 0.1 to 1.0 μm. I can do it. Also, the first region 21 is protected with a resist, and dry etching such as sand blasting or the like in which ceramic powder such as alumina or zirconia having a particle size of about several μm to several tens of μm is sprayed on the second region 22 with compressed air A protrusion having a Ra of about 0.5 to 5 μm can be molded.

  When the current collector surface roughness Ra of the second region 22 is less than 0.5 μm, the adhesion with the active material 2 is reduced and peeling is likely to occur. Further, in order to increase Ra, it is necessary to increase the thickness of the current collector 1. For a current collector having a thickness of 35 μm or less, it is difficult to process Ra to 5 μm or more by a sandblast method or the like. Therefore, Ra is preferably 0.5 μm or more and 5 μm or less. By providing such surface roughness, the adhesion strength between the current collector interface and the active material can be increased. The surface roughness Ra is defined in Japanese Industrial Standard (JISB 0601-1994), and can be measured by, for example, a surface roughness meter.

  Next, FIG. 3 shows a schematic view of a cross section of an electrode in which an active material 2 is formed on the current collector 1.

  When a substrate having a protrusion is used when forming a thin film, the vapor pressure is high at the tip of the protrusion and the vapor pressure is low at the protrusion, and a vapor pressure distribution is generated on the surface of the substrate. For this reason, when using the board | substrate which has a processus | protrusion, it tends to grow in columnar shape by using the front-end | tip part of a processus as a nucleus.

  Further, in the embodiment of the present invention, a space is generated between the pillars grown in the active material layer 2 by the shadow of the protrusion 11 of the first region 21 of the current collector 1, and this shadow effect is oblique. This is particularly noticeable when the active material layer 2 is formed by an obliquely incident vapor phase method represented by vapor deposition.

  Thus, by increasing the space ratio in the active material layer, it is possible to absorb the expansion of the active material layer during lithium storage.

  In the second region 22 of the current collector 1, the interval between the protrusions adjacent to each other, the height of the protrusions, and the depth of the valley recesses are randomly arranged. The center-to-center distance (that is, the period) is preferably in the range of 0.1 to 6 μm, the protrusion height of the convex portion is in the range of 0.5 to 20 μm, and the surface roughness Ra is in the range of 0.5 to 5 μm. The period may be the same or different in the width direction and the longitudinal direction, but it is desirable that both are within this range. With such a surface shape, when the active material layer 2 grows, a distribution occurs in the space between the pillars. Further, when the Ra of the second region 22 is in the range of 0.5 μm to 5 μm, the protrusions are formed. The distance between the projections is sufficiently smaller than the height of the columns, and the active material layer 2 comes into contact with each other and inhibits when the active material layer 2 grows in a columnar shape. Therefore, the columnar particles cannot grow thick.

  Therefore, in the second region 22 of the current collector 1, the columnar particles of the active material layer 2 grow more densely and the space ratio becomes smaller than in the first region 21. As a result, in the second region 22, the adhesion strength between the current collector 1 and the active material method 2 is increased, and peeling is suppressed.

  As described above, the period of the protrusions in the second region is smaller than the period in which the protrusions 11 in the first region 21 are formed. If the protrusion 11 of the first region 21 is formed over the entire surface of the current collector 1, there will be a problem when slitting, and if the protrusion 12 of the second region 22 is formed over the entire surface, the characteristics of the active material 2 cannot be secured. . Therefore, it is necessary to form protrusions with different periods in the first and second regions.

The active material used in the present invention is not particularly limited as long as it absorbs and releases lithium ions, but in the case of a negative electrode material, silicon, glutanium, tin alone or an alloy thereof, silicon oxide, silicon nitride, tin oxide These oxides and nitrides are preferable for obtaining a high energy density. In addition, these materials are preferably amorphous or low crystalline from the viewpoints of reactivity with lithium and high durability in repeated charge and discharge. Here, low crystallinity refers to a region where the crystal grain size is 50 nm or less. The grain size of the crystal grain is calculated by the Scherrer equation from the half-value width of the peak having the highest intensity in the diffraction image obtained by X-ray diffraction analysis. The term “amorphous” means that the diffraction image obtained by X-ray diffraction analysis has a broad peak in the range of 2θ = 15 to 40 °. In the case of a positive electrode material, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are preferable for obtaining a high energy density. These materials are preferably crystalline from the viewpoints of reactivity with lithium and high durability in repeated charge and discharge.

  Next, a method for forming the active material layer 2 will be described. As a method for forming the active material layer 2 by a vacuum process, a vapor deposition method, a sputtering method, a CVD method, or the like can be used. Among these, the vapor deposition method is particularly desirable from the viewpoint of efficiently forming the active material layer. As the vapor deposition method, electron beam vapor deposition may be used, or resistance heating vapor deposition may be performed. When depositing oxide or nitride of silicon or tin, oxide or nitride may be used as an evaporation material, and oxygen gas or nitrogen gas or these gases may be used while evaporating silicon or tin. Reactive vapor deposition may be performed by directing an ionized or radicalized product.

  The thickness of the active material layer 2 is usually in the range of 5 μm to 40 μm, although it depends on the required capacity. When the active material layer 2 is less than 5 μm, the proportion of the active material in the entire battery decreases, and the energy density of the battery decreases. Further, when the active material layer 2 exceeds 40 μm, the stress at the interface between the current collector and the active material layer increases, and even when the configuration of the present invention is used, the current collector is deformed.

  FIG. 4 is a schematic diagram showing a method for producing an electrode plate according to the present invention when using a vapor deposition method. In the vacuum chamber 4 evacuated by the exhaust pump 3, the long current collector 1 unwound from the unwinding roll 5 runs along the peripheral surfaces of the transport roller 6 and the cylindrical can 7. It is wound on a winding roll 8. In the meantime, the active material vapor is supplied from the evaporation source 9, and the active material layer 2 is formed on the surface of the current collector 1 by the vapor that has passed through the opening of the mask 10. Thereafter, the current collector 1 formed with the active material layer 2 can be manufactured by being wound by the winding roll 8.

  Next, the slit process which cleaves a collector into multiple pieces is demonstrated using FIG.

  The current collector on which the active material layer 2 that is the raw fabric 31 is formed is sent out by the transport roller 32 and cut into a predetermined electrode width by a slit blade provided with a plurality of blades. Conventionally, during this slitting process, the electrode end portion has been damaged due to friction with the running system, and the active material has been separated from the current collector by impact.

  On the other hand, in the embodiment of the present invention, the electrode end portion is the second region 22 in which the second protrusions 12 are randomly formed, thereby improving the adhesion with the active material 2 and performing the slit process. In addition, it is possible to suppress peeling from the current collector. At this time, the width of the second region 22 where the friction with the traveling system is generated is preferably about 0.5 mm to 10 mm, more preferably about 1 mm to 5 mm in order to ensure the stability of traveling.

  Thereafter, the electrode plate 35 cut into a predetermined electrode width by the slit blade 33 is taken up by the take-up roll 34, whereby a plurality of electrode plates 35 can be manufactured in a single film forming process. .

  The negative electrode plate slit to have a predetermined electrode width is wound or laminated so as to face the positive electrode through a separator. As the separator, a separator made of polypropylene (manufactured by Celgard, thickness 20 μm) or the like can be used.

The positive electrode plate is made of, for example, a powdered material such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ as active material and acetylene black (AB) on a current collector of a rolled Al foil having a thickness of 15 μm, and polyvinylidene fluoride (PVDF). ) And the like, and those that have been kneaded with an organic binder, applied and dried, and then rolled can be used.

  Thereafter, the electrolytic solution is injected to form a wound battery, a laminated battery, or the like as shown in FIG. The structure of the battery is that the negative electrode plate is connected to the positive electrode plate via a separator containing an electrolytic solution in which lithium hexafluorophosphate is dissolved in a mixed solvent of cyclic carbonates such as ethylene carbonate and chain carbonates such as dimethyl carbonate. It is done by facing. Batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape can be manufactured.

  Through these series of steps, the space of the active material layer formed in the first region 21 of the negative electrode plate is used as an expansion space necessary when the negative electrode plate expands during charging. Accordingly, the stress of the negative electrode active material can be relaxed, so that a short circuit between the positive electrode and the negative electrode can be suppressed, and further, the manufacturing process is performed by slitting in the region 22 where the current collector and the active material 2 have strong adhesion. The active material can be prevented from being peeled off at the same time, and a battery with a high yield can be obtained.

  This invention provides the manufacturing method which suppresses the fall of the yield by peeling of the active material in a slit process, when forming an active material by a thin film process. The electrode plate obtained by the production method of the present invention is not limited to the battery industry field and can be applied to all electrochemical devices.

The schematic plan view showing the electrical power collector 1 which concerns on one Embodiment of this invention. Sectional drawing showing the electrical power collector 1 which concerns on one Embodiment of this invention Schematic cross-sectional view of an electrode with an active material film formed on a current collector Schematic diagram showing an example of negative electrode plate manufacturing equipment The schematic diagram which shows an example of the slit process in manufacture of the electrode concerning one Embodiment of this invention. The figure which shows the longitudinal section of the cylindrical battery schematically

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current collector 2 Active material 3 Exhaust pump 4 Vacuum tank 5 Unwinding roll 6 Conveyance roller 7 Can 8 Winding roll 9 Deposition source 10 Mask 11 1st protrusion 12 2nd protrusion 21 1st area | region 22 2nd area Area 30 Slit device 31 Material 32 Transport roller 33 Slit blade 34 Winding roll 35 Electrode plate 41 Positive electrode 42 Negative electrode 43 Positive electrode lead 44 Negative electrode lead 45 Upper insulating ring 46 Lower insulating ring 47 Between electrodes 48 Sealing plate 49 Insulating packing 50 Electrode plate group

Claims (8)

An electrode carrying an active material capable of occluding and releasing lithium on a current collector,
The current collector has a first region in which protrusions are regularly formed and a second region in which protrusions are randomly formed on the same surface. electrode. 2. The electrode for a lithium secondary battery according to claim 1, wherein an upper portion of the protrusion formed in the first region is flat. 2. The electrode for a lithium secondary battery according to claim 1, wherein the second region is formed at least in a width direction of the current collector. 2. The electrode for a lithium secondary battery according to claim 1, wherein the surface roughness Ra of the second region is 0.5 μm or more and 5 μm or less. 5. The electrode for a lithium secondary battery according to claim 1, wherein the active material grows in a columnar shape with a protruding portion of the current collector as a nucleus. 6. 6. The electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material is silicon, tin, germanium, or an alloy, oxide, or nitride containing these main components. . The lithium secondary battery using the electrode for lithium secondary batteries in any one of Claims 1-6. An electrode carrying an active material capable of occluding and releasing lithium on a current collector,
The current collector has, on at least one surface, a first region in which protrusions are regularly formed and a second region in which protrusions are randomly formed, and the second region is formed. A method for producing an electrode for a lithium secondary battery, comprising slitting the formed portion.

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