JP2013054871A - Secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable secondary battery.SOLUTION: According to the present invention, there is provided a secondary battery having a constitution where an active material layer including at least an electrode active material and an aqueous binder is held on a surface of a collector. In the collector, a surface including the active material layer has a first irregularity 62a having an arithmetic average roughness Raof about 0.3-1 μm and a second irregularity 62b formed on a surface of the first irregularity 62a and having an arithmetic average roughness Raof about 0.01-0.2 μm. The electrode is manufactured by a manufacturing method including the steps of: preparing a collector having a first irregularity 62a having an arithmetic average roughness Raof about 0.3-1 μm; adjusting a pH of an aqueous paste to about 10-13, the aqueous paste being obtained by mixing at least the electrode active material, the aqueous binder, and an aqueous solvent; and coating the aqueous paste having the adjusted pH on the surface of the collector to form an active material layer.

Description

  The present invention relates to a secondary battery and a manufacturing method thereof.

  In the present specification, the “secondary battery” generally refers to a battery that can be repeatedly charged, and includes, for example, a so-called storage battery such as a lithium secondary battery (typically a lithium ion secondary battery), a nickel hydride battery, or the like.

  A lithium ion secondary battery, such as a nickel metal hydride battery, can achieve a relatively high capacity and high output relative to other secondary batteries such as a nickel metal hydride battery. For this reason, in particular, the importance is increasing as a power source (vehicle-mounted power source) for driving a motor coupled to a driving wheel of the vehicle.

  As one typical configuration, a lithium ion secondary battery has an electrode active material layer mainly composed of an electrode active material capable of reversibly occluding and releasing lithium ions (specifically, a positive electrode active material layer and a negative electrode). An active material layer) is provided on the surface of the electrode current collector.

  The electrode active material layer is formed on the surface of the electrode current collector, for example, by applying a paste-like composition to the positive electrode current collector, drying, and rolling as necessary. Here, the paste-like composition includes a slurry-like composition.

  For example, a positive electrode active material layer is formed by previously mixing a positive electrode active material such as a lithium transition metal composite oxide together with a highly conductive material powder (conductive material) and a binder in an appropriate solvent. A paste-like composition is prepared. And the positive electrode active material layer is formed by apply | coating this composition to a positive electrode electrical power collector. In such an electrode, the adhesiveness between the current collector and the active material layer is increased, whereby the current collecting property of the electrode is improved, and the charge / discharge cycle characteristics of the lithium ion secondary battery are improved. On the other hand, when the adhesion between the current collector and the active material layer is poor, the current collecting property of the electrode is lowered.

  As a prior art for improving the adhesiveness between the current collector and the active material layer in such an electrode, for example, Patent Document 1 can be cited. In the technique disclosed in Patent Document 1, the average roughness Ra of the surface of the current collector made of aluminum foil is 0.3 μm or more and 1.5 μm or less, and the maximum height Ry is 0.5 μm or more and 5.0 μm or less. It is disclosed that a roughening treatment is performed. According to Patent Document 1, this configuration increases the surface area of the current collector and improves the adhesion between the active material layer and the current collector.

JP 11-162470 A

  By the way, in the secondary battery, the active material layer applied to the current collector repeatedly expands and contracts with charge and discharge. In addition, secondary batteries used as power sources for vehicles (typically automobiles, in particular hybrid cars, electric cars) are repeatedly charged and discharged at a very high rate compared to household electric appliances, etc. Use is envisaged. In a secondary battery used as a power source for a vehicle, charging and discharging at a high rate are repeated, so that the active material layer applied to the current collector is repeatedly expanded and contracted. For this reason, in the vehicle driving battery, in particular, the active material layer applied to the current collector is easily peeled off from the current collector. On the other hand, as disclosed in Patent Document 1, sufficient adhesion may not be obtained simply by defining the average roughness of the surface of the current collector.

The secondary battery according to the present invention includes a current collector and an active material layer held on the surface of the current collector. Here, the active material layer includes at least an electrode active material and an aqueous binder. And on the surface of the electrical power collector holding the active material layer, it has 1st unevenness | corrugation whose arithmetic mean roughness Ra1 is 0.3 micrometer- ₁ micrometer. Furthermore, the surface of the first unevenness has second unevenness having an arithmetic average roughness Ra ₂ of 0.01 μm to 0.2 μm.

  Here, the “electrode active material” can reversibly occlude and release (typically insertion and removal) chemical species that serve as charge carriers in the secondary battery (for example, lithium ions in the lithium ion secondary battery). Refers to a substance. The “aqueous binder” is a composition that forms an active material layer together with the electrode active material and is a substance that dissolves or disperses in water.

  According to such a secondary battery, finer second irregularities exist on the surface of the larger first irregularities on the current collector surface. The current collector and the active material layer can be bonded in a mechanically strong bonding form by a complicated interface formed by the first unevenness and the second unevenness. Accordingly, a secondary battery having high peel strength between the current collector and the active material layer, improved current collection, and excellent charge / discharge cycle characteristics (typically capacity retention rate) is realized.

In this case, for example, the arithmetic average roughness Ra ₂ of the second unevenness may be 0.01 μm or more and 10% or less of the arithmetic average roughness Ra ₁ of the first unevenness. When the relationship between the first unevenness and the second unevenness is such a form, the current collector and the active material layer can be mechanically and more strongly bonded.

Hereinafter, the above-described special uneven form will be further described. The roughness curve of the surface (cross section) provided with the active material layer of the current collector according to the present invention, when viewed as a waveform, is a rough first unevenness having a low frequency component and a large amplitude, and the first unevenness. It is composed of a high frequency component formed on the surface and fine second irregularities having a small amplitude. This first unevenness can also be regarded as a swell component. In the present invention, such a surface form composed of the first unevenness and the second unevenness is represented by arithmetic average roughness Ra ₁ and Ra ₂ .

  Here, the “arithmetic mean roughness” means that only the reference length L is extracted from the roughness curve of the target surface in the direction of the average line, and the absolute value of the deviation from the average line of the extracted portion to the measurement curve is totaled. The average value. The arithmetic average roughness can be measured by obtaining a roughness curve of a target surface (cross section) with an appropriate surface roughness measuring instrument and calculating a parameter representing the surface roughness from the roughness curve.

Here, in order to calculate the arithmetic average roughness Ra ₁ of the first unevenness, for example, when the fine unevenness (the unevenness corresponding to the second unevenness) having a higher frequency component and a smaller amplitude than the first unevenness is ignored. Good. In order to calculate the arithmetic average roughness Ra ₂ of the fine second unevenness having a high frequency component and small amplitude formed on the surface of the first unevenness, for example, the first unevenness is compared with the second unevenness. Ignore the corresponding swell.

  In a preferred aspect of the secondary battery disclosed herein, the aqueous binder may be at least one binder selected from the group consisting of a fluorine-based resin, polyethylene, and polypropylene. By using these aqueous binders, the active material layer held on the surface of the current collector can be made homogeneous.

  In a preferred embodiment of the secondary battery disclosed herein, the current collector is formed of aluminum or an aluminum alloy. If such a current collector is used, the above-described special uneven form can be formed.

  The electrode active material may be various negative electrode active materials or positive electrode active materials. And the preferable one aspect | mode in the electrode for secondary batteries disclosed here is a positive electrode active material. Among these, a positive electrode active material mainly composed of a lithium transition metal composite oxide having a layered structure can be given.

The method for manufacturing a secondary battery according to the present invention is a method for manufacturing a secondary battery in which an active material layer including at least an electrode active material and an aqueous binder is formed on the surface of a current collector. This method is prepared by preparing a current collector having first irregularities having an arithmetic average roughness Ra ₁ of approximately 0.3 μm to 1 μm, and by mixing at least the electrode active material, the aqueous binder, and an aqueous solvent. It includes adjusting the pH of the paste to about 10 to 13, and applying the aqueous paste having the adjusted pH to the surface of the current collector to form an active material layer.

The method for manufacturing a secondary battery according to the present invention includes the following steps A to C.
Step A is a step of preparing a current collector having first irregularities with an arithmetic average roughness Ra ₁ of approximately 0.3 μm to 1 μm.
Step B is a step of preparing an aqueous paste in which at least the electrode active material, the aqueous binder, and the aqueous solvent are mixed and the pH is adjusted to about 10-13.
Step C is an active material layer containing an electrode active material and an aqueous binder on the surface of the current collector by applying the aqueous paste prepared in Step B to the surface of the current collector prepared in Step A. Is a step of forming.

In this case, the aqueous paste (including the paste-like composition) having a pH adjusted to 10 to 13 is applied to a current collector having first irregularities with an arithmetic average roughness Ra ₁ of about 0.3 μm to 1 μm. Thus, the second unevenness having the arithmetic average roughness Ra ₂ of 0.01 to 0.2 μm can be formed on the surface of the first unevenness.

That is, by applying the aqueous paste to the current collector having the first unevenness having an arithmetic average roughness Ra1 of 0.3 μm to ₁ μm, the surface of the first unevenness of the current collector is corroded by the aqueous paste, and the first A finer second unevenness is formed on the uneven surface. In this case, in the step of forming the active material layer (step of applying the aqueous paste to the current collector), the second unevenness is formed. In this case, the aqueous paste is composed of the first unevenness and the second unevenness. The current collector and the active material layer are mechanically firmly bonded to each other because they are closely adapted to the complex interface of the current collector to be formed.

  This provides a secondary battery having high peel strength between the current collector and the active material layer, improved current collection, and excellent charge / discharge cycle characteristics (typically capacity retention and life). Can do. Since the secondary battery provided here has high peel strength between the current collector and the active material layer, the secondary battery can exhibit good current collection and capacity retention. In this case, the water-based binder may be at least one selected from the group consisting of a fluorine-based resin, polyethylene, and polypropylene. The current collector may be formed of aluminum or an aluminum alloy.

  The electrode active material can be various negative electrode active materials or positive electrode active materials, and more preferably is a positive electrode active material. In a preferred embodiment of the production method disclosed herein, the electrode active material is a lithium transition metal composite oxide having a layered structure. As the lithium transition metal composite oxide having such a layered structure, a material exhibiting an alkalinity of approximately pH 10 or more is easily obtained when lithium ions are eluted in an aqueous solvent. Therefore, it becomes easy to adjust the pH of the aqueous paste to 10-13.

  Such a secondary battery is suitable as a battery mounted on a vehicle such as an automobile. Therefore, according to the present invention, a vehicle including any of the secondary batteries disclosed herein is provided. For this reason, performance suitable as a battery used as a power source (power source) for driving a motor mounted on a vehicle that is particularly required to be charged at a high rate is provided. Therefore, according to the present invention, a vehicle provided with the secondary battery (typically a lithium ion secondary battery) disclosed herein is provided. In particular, a vehicle (for example, an automobile) provided with the lithium ion secondary battery as a power source (typically, a hybrid vehicle or an electric vehicle) is suitably provided.

It is explanatory drawing which shows typically schematic structure of the electrode manufacturing apparatus which concerns on one Embodiment. It is explanatory drawing which shows typically the surface roughness of the positive electrode electrical power collector which concerns on one Embodiment. It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment. It is a longitudinal cross-sectional view which follows the IV-IV line in FIG. It is a figure explaining the 90 degree peeling adhesion strength test method in an Example. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  Hereinafter, the lithium ion secondary battery according to the present embodiment will be described. Here, the positive electrode of a lithium ion secondary battery will be described first. Here, the positive electrode includes a positive electrode current collector and a positive electrode active material layer.

≪Positive electrode current collector≫
The positive electrode current collector is preferably a conductive member made of a highly conductive metal, like the current collector used for the positive electrode of a conventional lithium ion secondary battery (typically a lithium ion secondary battery). Used. For example, a metal containing aluminum, nickel, titanium, iron or the like as a main component or an alloy thereof can be used, and aluminum or an aluminum alloy is more preferable. There is no restriction | limiting in particular about the shape of a positive electrode electrical power collector, Various things can be considered according to the shape of a lithium ion secondary battery, etc. For example, it may be in various forms such as a bar shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. Typically, a sheet-like positive electrode current collector made of aluminum is used.

≪Positive electrode active material layer≫
The positive electrode active material layer is formed on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and an aqueous binder.

≪Positive electrode active material≫
The positive electrode active material is not particularly limited in its composition and shape as long as it is a positive electrode active material having a property capable of realizing the object of the present invention. A typical positive electrode active material includes a composite oxide containing lithium and at least one transition metal element. For example, cobalt lithium composite oxide (LiCoO ₂ ), nickel lithium composite oxide (LiNiO ₂ ), manganese lithium composite oxide (LiMn ₂ O ₄ ), or nickel-cobalt-based LiNi _x Co _1-x O ₂ ( 0 <x <1), cobalt / manganese-based LiCo _x Mn _1-x O ₂ (0 <x <1), nickel / manganese-based LiNi _x Mn _1-x O ₂ (0 <x <1) and LiNi _x Mn _2-x O 4, as represented by (0 <x <2), a so-called binary lithium-containing composite oxide containing two kinds of transition metal elements, or the general formula:
_{Li (Li a Mn x Co y} Ni z) O 2
(Where a, x, y, and z are real numbers satisfying a + x + y + z = 1)
A so-called ternary lithium-containing composite oxide containing three kinds of transition metal elements may be used.

The positive electrode active material has a general formula of LiMAO ₄ (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and And an anion selected from the group consisting of V.).

Here, in the present invention, as will be described in detail later, from the viewpoint of adjusting the pH of the aqueous paste containing the electrode active material to 10 to 13, the positive electrode active material is a lithium transition metal composite oxide having a layered structure. Preferably there is. For example, the above-mentioned LiCoO ₂ , LiNiO ₂ , Li ₂ MnO ₃ , or a ternary lithium-containing composite oxide such as a nickel / cobalt / manganese system containing three kinds of transition metal elements.

  The compound which comprises such a positive electrode active material can be prepared and provided by a conventionally well-known method, for example. For example, several raw material compounds appropriately selected according to the atomic composition are mixed at a predetermined molar ratio, and the mixture is fired by an appropriate means. Thereby, an oxide suitable as a compound constituting the positive electrode active material can be prepared. The fired product may be pulverized, granulated and classified by an appropriate means. Thereby, the granular positive electrode active material powder substantially comprised by the secondary particle which has a desired average particle diameter and / or particle size distribution can be obtained. In addition, the preparation method itself of a positive electrode active material (lithium containing complex oxide powder etc.) does not characterize this invention at all.

  In addition, when a conductive material is included in the positive electrode active material layer formed on the positive electrode according to the present embodiment, the conductive material is not limited to a specific material, and is conventionally used in this type of secondary battery. Various conductive materials that have been used can be used. For example, carbon materials such as carbon powder and carbon fiber are used as the conductive material. As the carbon powder, various carbon blacks (for example, acetylene black, furnace black, ketjen black), graphite powder, and the like can be used. Among these, you may use together 1 type, or 2 or more types.

≪Water-based binder≫
Furthermore, in the present embodiment, an aqueous paste (typically a composition prepared in a paste or slurry form, hereinafter also referred to as a positive electrode active material layer forming paste) is used as the composition for forming the positive electrode active material layer. Use. For this reason, as a water-based binder (binder) contained in the positive electrode active material layer formed in the positive electrode according to the present embodiment, a polymer material that is dissolved or dispersed in water can be preferably used.

  Cellulose polymers such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), etc .; polyvinyl alcohol (PVA) And the like are exemplified.

  Examples of polymer materials that are dispersed in water (water-dispersible) include vinyl polymers such as polyethylene (PE) and polypropylene (PP); polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), and tetrafluoroethylene. -Fluororesin such as perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer; rubbers such as styrene butadiene rubber (SBR).

  In the present invention, from the viewpoint of easy formation of the active material layer (typically coating), the water-based binder is a fluorine resin such as polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene. It is more preferable to use (PP).

  The “aqueous paste” is a concept indicating a composition using water or a mixed solvent mainly composed of water (aqueous solvent) as a dispersion medium of the electrode active material. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.

Next, a method for manufacturing a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to FIGS. Here, a method for manufacturing a positive electrode will be described in particular. Here, the manufacturing method of the positive electrode includes the following steps A to C.
Step A: A current collector 62 having first irregularities 62a having an arithmetic average roughness Ra1 of 0.3 μm to ₁ μm is prepared.
Step B: An aqueous paste whose pH is adjusted to 10 to 13 is prepared by mixing at least an electrode active material, an aqueous binder, and an aqueous solvent.
Step C: An active material containing an electrode active material and an aqueous binder on the surface of the current collector 62 by applying the aqueous paste prepared in Step B to the surface of the current collector 62 prepared in Step A Form a layer.

≪Process A≫
Specifically, in the process A, the arithmetic average roughness Ra ₁ is 0.3 μm to ₁ μm (the aluminum sheet-like positive electrode current collector 62 having the first unevenness 62 a with 0.3 μm ≦ Ra ₁ ≦ 1.0 μm ( An electrode current collector is prepared, more preferably, Ra ₁ is 0.5 μm or more (0.5 μm ≦ Ra ₁ ), further 0.7 μm or more (0.7 μm ≦ Ra ₁ ), and further Ra ₁ Is preferably 0.9 μm or less (Ra ₁ ≦ 0.9 μm) The thickness of the positive electrode current collector 62 can be about 10 μm to 30 μm including the first unevenness 62a.

≪Process B≫
Next, in step B, a positive electrode active material (for example, lithium cobaltate particles), a conductive material (for example, graphite), and an aqueous binder (for example, PTFE) are dispersed in a predetermined aqueous solvent (for example, ion-exchanged water). An aqueous paste (that is, a positive electrode active material layer forming paste) is prepared. If necessary, an additive such as a dispersant may be added. Here, the aqueous paste is adjusted so that the pH is approximately in the range of 10 to 13.

  In the aqueous paste, lithium ions constituting the positive electrode active material are eluted in the aqueous solvent. Thereby, the aqueous paste naturally exhibits alkalinity. In the case where the positive electrode active material is a lithium transition metal composite oxide having a layered structure, the pH of the aqueous paste is generally in the range of 10 to 13 without particularly adjusting the pH.

For example, when the positive electrode active material is a lithium transition metal composite oxide having a spinel structure, the pH of the aqueous paste is only about 9 to 10. When the pH of the aqueous paste does not become sufficiently high as described above, for example, lithium hydroxide may be added to adjust the pH of the aqueous paste to be in the range of 10-13. Conversely, in the case that the pH of the aqueous paste exceeds 13, it may be adjusted so that the pH is equal Komu blown CO ₂ in the aqueous paste is approximately 10 to 13 range.

≪Process C≫
FIG. 1 is a diagram illustrating an electrode manufacturing apparatus 200 that embodies the process C. As shown in FIG. 1, the electrode manufacturing apparatus 200 generally includes an unwinding roll 205, a paste application unit 220, a drying furnace 225, and a winding roll 210. The electrode manufacturing apparatus 200 feeds the positive electrode current collector 62 from the unwinding roll 205 and applies the prepared aqueous paste onto the positive electrode current collector 62 in the paste application unit 220. As a method of applying the aqueous paste in the paste application unit 220, a technique similar to a conventionally known method can be appropriately employed. In the paste application unit 220, for example, the above-mentioned aqueous paste can be suitably applied on the positive electrode current collector 62 by using an appropriate application device such as a slit coater, a die coater, or a gravure coater.

  Here, as shown in FIGS. 2A and 2B, the first unevenness 62a on the surface of the positive electrode current collector 62 coated with the aqueous paste is corroded by the aqueous paste showing alkalinity, and the finer first irregularities 62a. Two irregularities 62b are formed. Here, (a) in FIG. 2 depicts the first unevenness 62 a on the surface of the positive electrode current collector 62. (B) in FIG. 2 depicts fine second unevenness 62b formed on the first unevenness 62a. FIGS. 2A and 2B are schematically depicted, and the actual shapes of the first unevenness 62a and the second unevenness 62b are not necessarily accurately depicted.

Here, the aqueous paste exhibits alkalinity because lithium ions are eluted from the positive electrode active material into the aqueous solvent. In Step C, when the aqueous paste is applied to the metal positive electrode current collector 62, alkali corrosion occurs on the surface of the positive electrode current collector 62 where the aqueous paste touches. Then, the first concave-convex 62a second uneven 62b arithmetic average roughness Ra ₂ of approximately 0.01μm~0.2μm fine on the surface is formed. At this time, the fine second irregularities 62 b are formed by the aqueous paste corroding the positive electrode current collector 62. In the surface roughness of the relationship between the first concave-convex 62a and the second concave-convex 62b, the arithmetic average roughness Ra ₂ of the fine second uneven 62b is 10% or less of the size of and Ra ₁ is 0.01μm or more It is preferable.

  For this reason, the aqueous paste reaches the inside of the fine second unevenness 62b. Further, the aqueous paste forms such fine second irregularities 62 b in the region applied to the positive electrode current collector 62. At this time, since the first unevenness 62a is formed in advance on the positive electrode current collector 62, the second unevenness 62b is formed along the undulation of the first unevenness 62a. As a result, the aqueous paste contacts the positive electrode current collector 62 along a complicated surface shape in which the second unevenness 62b overlaps the first unevenness 62a.

  Next, as shown in FIG. 1, the positive electrode current collector 62 to which the aqueous paste is applied is sent out into the drying furnace 225 in a state where a certain tension is applied by the tension roller 215. Then, evaporation of the aqueous solvent formed on the positive electrode current collector 62 and drying of the aqueous paste (positive electrode active material layer forming paste) are performed simultaneously in the drying furnace 225. The drying temperature is desirably equal to or lower than the melting point of the binder, and is about 50 ° C to 150 ° C, preferably 70 ° C to 90 ° C. The drying time is about 40 seconds to 300 seconds, preferably 50 seconds to 80 seconds. As described above, the aqueous paste is dried in a state in which the first unevenness 62a and the second unevenness 62b are sufficiently spread over the unevenness of different scales to form the active material layer 64. For this reason, the positive electrode current collector 62 and the active material layer 64 come into contact with each other with a larger surface area.

  In particular, in the present embodiment, in the coating process, the first unevenness 62a of the positive electrode current collector 62 is corroded by the aqueous paste, and finer second unevenness 62b is formed on the surface of the first unevenness 62a. At this time, since the second unevenness 62b is formed by contacting the aqueous paste, the aqueous paste is sent to the drying process in a state of being in close contact with the fine unevenness of the second unevenness 62b. For this reason, the positive electrode active material layer 64 formed by drying the aqueous paste and the positive electrode current collector 62 can be bonded more firmly.

  The drying method is not particularly limited as long as it can remove excess volatile components. For example, an appropriate drying device such as a hot air device, various infrared devices, an electromagnetic induction device, or a microwave device can be used.

  As shown in FIG. 1, the positive electrode sheet 66 (positive electrode) in which the positive electrode active material layer 64 is formed on the positive electrode current collector 62 is wound around a winding roll 210. The positive electrode sheet 66 may be pressed (compressed) as necessary. As a pressing (compression) method, conventionally known compression methods such as a roll pressing method and a flat plate pressing method can be employed. Thereby, the thickness of the positive electrode active material layer 64 can be adjusted. In adjusting the thickness of the positive electrode active material layer 64, the thickness may be measured with a film thickness measuring instrument, and may be compressed a plurality of times until a desired thickness is obtained by adjusting the press pressure.

The positive electrode sheet (positive electrode) 66 obtained by the above manufacturing method is formed by two unevennesses in which the interface form between the positive electrode current collector 62 and the active material layer 64 is different in scale. Preferably, the cathode current collector 62 which holds the positive electrode active material layer 64 has an arithmetic average roughness Ra ₁ has a first irregularity 62a approximately 0.3Myuemu～1myuemu, further on the surface of the first concave-convex 62a the arithmetic average roughness Ra ₂ has a second concave-convex 62b of approximately 0.01 to 0.2 [mu] m. The positive electrode current collector 62 and the positive electrode active material layer 64 are in contact with each other with a complicated and wide surface area composed of the first unevenness 62a and the second unevenness 62b. Higher adhesion and stronger adhesion can be ensured between the positive electrode current collector 62 and the positive electrode active material layer 64.

  Next, an embodiment of a lithium ion secondary battery constructed using the positive electrode will be described. First, a negative electrode, a separator and the like suitable for use in combination with the positive electrode (positive electrode sheet 66) described above will be described. The negative electrode can have the same configuration as before. As a negative electrode current collector constituting such a negative electrode, for example, a copper material, a nickel material, or an alloy material mainly composed of them is preferably used. The shape of the negative electrode current collector can be the same as the shape of the positive electrode. Typically, a sheet-like copper negative electrode current collector is used.

The negative electrode active material contained in the negative electrode active material layer formed on the negative electrode may be any material that can occlude and release lithium. For example, carbon materials such as graphite, lithium titanium oxide (Li ₄ Examples thereof include oxide materials such as Ti ₅ O ₁₂ ), metals such as tin, aluminum (Al), zinc (Zn), and silicon (Si), or metal materials composed of metal alloys mainly composed of these metal elements. . A typical example is the amount of powdery carbon material made of graphite or the like. For example, graphite particles can be preferably used.

  The negative electrode active material layer formed on the negative electrode can contain, in addition to the negative electrode active material, for example, one or more materials that can be blended in the positive electrode active material layer, if necessary. As such materials, various materials that can function as binders (binders), dispersants, and the like as listed as constituent materials of the positive electrode active material layer can be used as well. The binder is not limited to a water-based one, and a solvent-based binder such as polyvinylidene fluoride (PVDF) can also be used.

  The negative electrode according to the present embodiment is a paste-like composition (hereinafter referred to as negative electrode active material layer formation) in which a negative electrode active material, a binder, and the like are dispersed in an appropriate solvent (water, organic solvent, etc.) similar to the conventional one. Preparation paste). The prepared negative electrode active material layer forming paste is applied to the negative electrode current collector, dried, and then compressed (pressed) to form the negative electrode current collector and the negative electrode active material formed on the negative electrode current collector A negative electrode provided with a layer can be produced.

  Moreover, as a separator used with a positive electrode and a negative electrode, the separator similar to the past can be used. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. As a constituent material of such a porous sheet, polyolefin resins such as polyethylene (PE), polypropylene (PP), and polystyrene are preferable.

  In particular, a porous structure such as a PE sheet, a PP sheet, a two-layer structure sheet in which a PE layer and a PP layer are laminated, and a three-layer structure sheet in which one PE layer is sandwiched between two PP layers. A polyolefin sheet can be suitably used. When a solid electrolyte or a gel electrolyte is used as the electrolyte, a separator may not be necessary (that is, in this case, the electrolyte itself can function as a separator).

  As the electrolyte, the same electrolyte as a non-aqueous electrolyte (typically, an electrolytic solution) conventionally used in lithium ion secondary batteries can be used without particular limitation. Such a non-aqueous electrolyte typically has a composition in which a suitable non-aqueous solvent (organic solvent) contains a lithium salt that can function as an electrolyte. As the electrolyte, a lithium salt conventionally used in lithium ion secondary batteries can be appropriately selected and used.

Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiBF ₄ , LiCF ₃ SO _{3 and the} like. Such electrolytes can be used alone or in combination of two or more. A particularly preferred example is LiPF ₆ . Examples of the non-aqueous solvent include carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC). Such non-aqueous solvents can be used alone or in combination of two or more.

  Hereinafter, although one form of a lithium ion secondary battery provided with the said positive electrode sheet (positive electrode) 66 is demonstrated with reference to drawings, it is not intending to limit this invention to this embodiment. That is, as long as the positive electrode according to the present embodiment is employed, the shape (outer shape and size) of the lithium ion secondary battery to be constructed is not particularly limited. The battery outer case may have a rectangular shape, a cylindrical shape, or a small button shape. Moreover, the thin sheet | seat type comprised by a laminated film etc. may be sufficient as an exterior. In the following embodiment, a rectangular battery will be described.

  In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show the same effect | action, and the overlapping description may be abbreviate | omitted. Moreover, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.

  FIG. 3 is a perspective view schematically showing the lithium ion secondary battery according to the present embodiment. 4 is a longitudinal sectional view taken along line IV-IV in FIG. As shown in FIGS. 3 and 4, the lithium ion secondary battery 10 according to this embodiment includes the above-described constituent materials (active material for each positive and negative electrode, current collector for each positive and negative electrode, separator, etc.). And a battery case 15 having a rectangular shape (typically a flat rectangular parallelepiped shape) that accommodates the electrode body 50 and a suitable non-aqueous electrolyte (typically, an electrolyte).

  The case 15 includes a box-shaped case main body 30 in which one of the narrow surfaces in the flat rectangular parallelepiped shape is an opening 20, and the opening 20 is attached (for example, welded) to the opening 20. And a lid 25 for closing. As a material constituting the case 15, the same material as that used in a general lithium ion secondary battery can be used as appropriate, and there is no particular limitation. For example, a metal (for example, aluminum, steel, etc.) container, a synthetic resin (for example, a polyolefin resin, a high melting point resin such as a polyamide resin, etc.), or the like can be preferably used. The case 15 according to the present embodiment is made of, for example, aluminum.

  The lid body 25 is formed in a rectangular shape that matches the shape of the opening 20 of the case body 30. Further, the lid body 25 is provided with a positive electrode terminal 60 and a negative electrode terminal 70 for external connection, respectively, and a part of these terminals 60, 70 protrudes from the lid body 25 toward the outside of the case 15. It is formed to do. As in the case of the conventional lithium ion secondary battery, the lid 25 has a safety valve (not shown) for discharging the gas generated inside the case 15 to the outside of the case 15 when the battery is abnormal. Is provided. The safety valve can be used without any limitation as long as it has a mechanism that opens and discharges gas to the outside of the case 15 when the pressure inside the case 15 exceeds a predetermined level.

  In the present embodiment, as shown in FIG. 4, the lithium ion secondary battery 10 includes a wound electrode body 50. The electrode body 50 is accommodated in the case main body 30 in a posture in which the winding axis is laid down (that is, in the direction in which the opening 20 is positioned in the lateral direction with respect to the winding axis). The electrode body 50 includes a positive electrode sheet (positive electrode) 66 having a positive electrode active material layer 64 formed on the surface of a long sheet-like positive electrode current collector 62 and a long sheet-like negative electrode current collector (electrode current collector). A negative electrode sheet (negative electrode) 76 having a negative electrode active material layer (electrode active material layer) 74 formed on the surface of 72 is overlapped with two long separator sheets 80 and wound, and the obtained electrode body 50 is wound. It is formed into a flat shape by crushing it from the side direction and causing it to be ablated.

  Further, in the wound positive electrode sheet 66, the positive electrode current collector 62 is exposed without forming the positive electrode active material layer 64 at one end portion along the longitudinal direction. On the other hand, the wound negative electrode Also in the sheet 76, the negative electrode current collector 72 is exposed at one end portion along the longitudinal direction without forming the negative electrode active material layer 74. A positive electrode terminal 60 is joined to the exposed end of the positive electrode current collector 62, and is electrically connected to the positive electrode sheet 66 of the wound electrode body 50 formed in the flat shape. Similarly, the negative electrode terminal 70 is joined to the exposed end portion of the negative electrode current collector 72 and is electrically connected to the negative electrode sheet 76. The positive and negative electrode terminals 60 and 70 and the positive and negative electrode current collectors 62 and 72 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The material and the member constituting the wound electrode body 50 having the above configuration are the same as the electrode body of the conventional lithium ion secondary battery except that the positive electrode disclosed here (the positive electrode sheet 66) is adopted as the positive electrode. There are no particular restrictions.

  The positive electrode sheet 66 is produced as described above. On the other hand, the negative electrode sheet 76 is produced by forming a negative electrode active material layer 74 on a long negative electrode current collector (for example, a long copper foil) 72. That is, a negative electrode active material layer forming paste is prepared by dispersing a negative electrode active material (for example, graphite) and a binder (for example, PVDF) in an organic solvent (for example, NMP). The prepared paste is applied to the negative electrode current collector 72, dried, and then compressed (pressed) to form the negative electrode active material layer 74. In addition, the formation method itself of the negative electrode active material layer 74 may be the same as the conventional one, and does not characterize the present invention. Therefore, detailed description is omitted.

  In the present embodiment, the produced positive electrode sheet 66 and negative electrode sheet 76 are stacked and wound together with two separators (for example, porous polyolefin resin) 80. Thereby, the wound electrode body 50 is accommodated in the case main body 30 so that the winding axis of the obtained wound electrode body 50 lies sideways. Then, a non-aqueous electrolyte such as a mixed solvent of EC and DMC (for example, a mass ratio of 1: 1) containing an appropriate amount (for example, a concentration of 1M) of an appropriate supporting salt (for example, a lithium salt such as LiPF6) is injected. Then, the lithium ion secondary battery 10 of this embodiment can be constructed by mounting and sealing the lid body 25 on the opening 20 of the case body 30. For sealing the opening 20 of the case body 30, for example, the lid body 25 may be welded to the case body 30. In this case, welding is preferably performed by laser welding, for example.

In the above-described embodiment, as shown in FIG. 2, the surface of the positive electrode current collector 62 holding the positive electrode active material layer 64 has the first unevenness 62a having an arithmetic average roughness Ra ₁ of about 0.3 μm to 1 μm. and, further, the surface of the first concave-convex 62a, the arithmetic average roughness Ra ₂ has the second concave-convex 62b of approximately 0.01 to 0.2 [mu] m. Thus, the 1st unevenness | corrugation 62a and the 2nd unevenness | corrugation 62b are applied with respect to the positive electrode of a lithium ion secondary battery. This form is not limited to the positive electrode, and can be applied to the negative electrode of a lithium ion secondary battery, for example. Moreover, although lithium ion secondary battery 10 was illustrated in embodiment mentioned above, this invention is not restricted to a lithium ion secondary battery, With respect to the electrodes (positive electrode and negative electrode) of secondary batteries, such as a nickel-hydrogen battery. Can also be applied.

  Hereinafter, as some specific examples, a secondary battery (here, a lithium ion secondary battery) was constructed by the manufacturing method described above, and its performance was evaluated.

<Sample 1>
The positive electrode was produced by the following procedure.
First, the positive electrode active material, the conductive material, and the thickener were dispersed in water with the following composition, and then the binder was added so that PTFE was 2 parts by weight to prepare a positive electrode aqueous paste. Moreover, the pH of the positive electrode aqueous paste produced here was 12.5.
Positive electrode active material: Lithium nickel manganese cobalt composite oxide 100 parts by weight Conductive material: Denka black powder 4 parts by weight (solid content weight)
Thickener: Carboxymethylcellulose 1 part by weight (solid content weight)
Binder: PTFE aqueous dispersion 2 parts by weight (solid content weight)

Next, an aluminum foil having a thickness of 15 μm and an arithmetic average roughness Ra ₁ of 0.5 μm was prepared as the positive electrode current collector 62, and a predetermined amount of the above positive electrode aqueous paste was applied to both surfaces of the positive electrode current collector 62. And dried at 95 ° C. for 1 minute. After drying, the coated material was pressed to produce a positive electrode sheet 66 having a positive electrode active material layer 64. Refer to FIG. 5 for the positive electrode sheet 66.

Although not shown, the negative electrode was produced by the following procedure.
Natural graphite is used as the negative electrode active material and weighed so that the mass ratio of styrene butadiene rubber (SBR) as the binder and carboxymethyl cellulose (CMC) as the thickener is 98: 1: 1. Next, these weighed materials were dispersed in ion-exchanged water to prepare a negative electrode active material layer forming paste. And after apply | coating this paste on both surfaces of 10-micrometer-thick copper foil predeterminedly and drying, it pressed and produced the negative electrode sheet.

The non-aqueous electrolyte is prepared by dissolving 1 mol / L LiPF ₆ in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) in a volume ratio of 3: 5: 2. Using.

The positive electrode sheet and the negative electrode sheet obtained as described above are rolled together with two separator sheets (polypropylene porous separator) to obtain a wound electrode body. The obtained wound electrode body was crushed into a flat shape and housed in a cylindrical container together with the non-aqueous electrolyte described above to constitute a lithium ion secondary battery with a theoretical capacity of 1000 mAh.
<Sample 2>
As a current collector, the arithmetic average roughness Ra _1, except that an aluminum foil 0.84 .mu.m, and a battery in the same manner as Sample 1.
<Sample 3>
A battery was constructed in the same manner as Sample 1, except that a positive electrode aqueous paste was prepared in the same manner as Sample 1 and then the pH was adjusted to 10 to 11 (here, pH 10.6) by blowing CO ₂ into the paste. did.

<Sample 4>
As a current collector, the arithmetic average roughness Ra _1, except that an aluminum foil 0.12 .mu.m, and a battery in the same manner as Sample 1.
<Sample 5>
As a current collector, the arithmetic average roughness Ra _1, except that aluminum foil was used 1.4 [mu] m, and a battery in the same manner as Sample 1.
<Sample 6>
A positive electrode aqueous paste was prepared in the same manner as in Sample 1, and then a battery was constructed in the same manner as Sample 1 except that the paste was blown with CO ₂ to adjust the pH to below 10 (here, pH 9.3).
<Sample 7>
A positive electrode aqueous paste was prepared in the same manner as in Sample 1, and then a battery was constructed in the same manner as in Sample 1 except that lithium hydroxide was added to the paste to adjust the pH higher than 13 (here, pH 13.7).

The pH of the positive electrode aqueous pastes of Examples and Comparative Examples obtained above, the peel strength of the positive electrode active material layer from the current collector, and the battery capacity of the obtained battery were measured and are shown in Table 1 below. Further, the cross section of the positive electrode is observed with an SEM, and the surface roughness Ra ₂ of finer irregularities (the irregularities corresponding to the second irregularities 62b (see FIG. 2)) formed on the surface of the positive electrode current collector 62 is obtained. The measured values are shown in Table 1 below.

Incidentally, sample 5 has an arithmetic average roughness Ra ₁ of the current collector was employed 1.4μm and too large, the coating weight of the positive electrode aqueous paste is not stable, it was not possible to obtain a suitable cathode. Further, in Sample 7, the pH of the positive electrode aqueous paste used was too high, the current collector was corroded greatly by the application of the positive electrode aqueous paste, the coating weight was not stable, and an appropriate positive electrode could not be obtained.

  FIG. 5 is a diagram showing a 90-degree peel adhesion strength test method. As shown in FIG. 5, the positive electrode peel strength was measured according to a 90-degree peel adhesion strength test method (JIS K 6854-1). Here, the sample 120 is affixed to the positive electrode active material layer 64 on one side of the positive electrode sheet 66 with an adhesive tape 105 (No. 3303N) manufactured by Nitto Denko, and cut into a size of 15 mm wide × 120 mm long. For the cut sample 120, the adhesive tape 105 is peeled off by 40 mm from one end. Next, a Nitto Denko double-sided tape (No. 501F) is applied to the stage 115. The sample 120 is stuck on the double-sided tape 110 with the adhesive tape 105 facing down. Next, the 40 mm portion from which the sample 120 has been peeled is fixed to the chuck 125. Then, the chuck 125 is pulled at 90 ° with respect to the stage 115, and the tensile load is measured. A Minebea universal testing machine was used to pull the chuck 125. The pulling speed was 20 m / min. The obtained tensile load (N) was divided by the width (15 mm) of the sample 120 to obtain the peel strength N / m.

  In addition, the battery capacity was measured by charging a battery to 4.1 V at 2 A and discharging to 3.0 V at 2 A, 1000 cycles at 25 ° C., and then measuring the battery embedding. The capacity retention rate after the charge / discharge cycle was calculated. The capacity retention rate was “discharge capacity after 1000 cycles” / “initial discharge capacity” × 100 (%).

As shown in Sample 4 and Sample 5 in Table 1, an electrode having a high peel strength of the positive electrode active material layer can be obtained even if the large unevenness provided on the current collector represented by Ra ₁ is too large or too small. I found that there was no. And as shown in Sample 6 and Sample 7, even if Ra ₁ with large irregularities is in an appropriate range, if the fine irregularities represented by Ra ₂ are not of an appropriate size, the peel strength of the positive electrode active material layer It was found that a high electrode could not be obtained.

Positive samples 1-3, and large irregularities suitable surface roughness Ra ₁ on the surface of the current collector, there is a more suitable surface roughness Ra ₂ fine irregularities, the positive electrode active material layer is complex It was confirmed that the interface was firmly bonded to the current collector.

Moreover, when the positive electrode paste having a high pH is applied to the current collector, the coated surface of the current collector is corroded. The degree of corrosion depends on the positive electrode paste pH. At this time, it is easy to stably obtain an appropriate surface roughness Ra ₂ at a pH of about 10 to 13. Then, by adjusting the pH of the positive electrode paste to an appropriate range, it is possible to collect fine irregularities having an appropriate surface roughness Ra ₂ corresponding to the second irregularities 62b without requiring a special roughening process. It can be formed on the surface of the body.

The secondary batteries (samples 1 to 3) disclosed herein have first irregularities on the surface of the positive electrode current collector 62 holding the positive electrode active material layer 64 with an arithmetic average roughness Ra ₁ of about 0.3 μm to 1 μm. having 62a, further, the surface of the first concave-convex 62a, the arithmetic average roughness Ra ₂ has a second concave-convex 62b of approximately 0.01 to 0.2 [mu] m. In this case, the capacity maintenance rate is greatly improved. This is considered to originate from the improved adhesion between the current collector and the electrode active material layer. The secondary battery disclosed herein is expected to improve the high rate characteristics, rapid charge / discharge characteristics, and the like of the lithium ion secondary battery. That is, in the above embodiment, due to the presence of the second unevenness 62b, the positive electrode current collector 62 and the positive electrode active material layer 64 are finely adhered, and the contact area is widened. For this reason, not only the effect that the peel strength between the positive electrode current collector 62 and the positive electrode active material layer 64 is improved, but also the resistance required for charge transfer between the positive electrode active material layer 64 and the positive electrode current collector 62 is reduced. it is conceivable that.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

  According to the technique disclosed here, a secondary battery in which the current collector and the electrode active material layer are firmly bonded can be provided without requiring a special roughening treatment of the current collector. This secondary battery has excellent durability between the current collector and the active material layer, and the contact area has been increased, so that the lithium ion has good durability with reduced performance degradation (for example, reduced capacity retention rate). A secondary battery such as a secondary battery can be provided. Therefore, according to the present invention, as shown in FIG. 6, the lithium ion secondary battery 10 (which may be in the form of an assembled battery formed by connecting a plurality of the batteries 10 in series) is provided as a power source. A vehicle 1000 (typically, an automobile including an electric motor such as an automobile, particularly a hybrid automobile or an electric automobile) can be provided.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 15 Battery case 20 Opening part 25 Cover body 30 Case main body 50 Winding electrode body 60 Positive electrode terminal 62 Positive electrode current collector (electrode current collector)
64 Positive electrode active material layer (electrode active material layer)
66 Positive electrode sheet (positive electrode)
70 Negative electrode terminal 72 Negative electrode current collector (electrode current collector)
74 Negative electrode active material layer (electrode active material layer)
76 Negative electrode sheet (negative electrode)
80 Separator 105 Adhesive tape 110 Double-sided tape 115 Stage 120 Sample 125 Chuck 200 Electrode manufacturing apparatus 205 Unwinding roll 210 Winding roll 215 Tension roller 220 Paste application part 225 Drying furnace 1000 Vehicle

Claims (10)

A current collector,
An active material layer held on the surface of the current collector,
here,
The active material layer includes at least an electrode active material and an aqueous binder,
On the surface of the current collector holding the active material layer, the arithmetic mean roughness Ra ₁ has first irregularities of 0.3 μm to ₁ μm,
Wherein the first roughened surface of the arithmetic average roughness Ra ₂ has a second unevenness of 0.01 to 0.2 [mu] m, the secondary battery. 2. The secondary battery according to claim 1, wherein the arithmetic average roughness Ra ₂ of the second unevenness is 0.01 μm or more and 10% or less of the arithmetic average roughness Ra ₁ of the first unevenness.   The secondary battery according to claim 1, wherein the water-based binder is at least one binder selected from the group consisting of a fluorine-based resin, polyethylene, and polypropylene.   The secondary battery according to any one of claims 1 to 3, wherein the current collector is formed of aluminum or an aluminum alloy.   The secondary battery according to any one of claims 1 to 4, wherein the electrode active material is a lithium transition metal composite oxide having a layered structure.   A vehicle provided with the secondary battery as described in any one of Claim 1-5. Step A for preparing a current collector having first irregularities with an arithmetic average roughness Ra ₁ of 0.3 μm to ₁ μm;
Step B for preparing an aqueous paste having a pH adjusted to 10 to 13 by mixing at least the electrode active material, the aqueous binder, and an aqueous solvent;
By applying the aqueous paste prepared in Step B to the surface of the current collector prepared in Step A, the surface of the current collector includes the electrode active material and the aqueous binder. A method for manufacturing a secondary battery, comprising: step C of forming an active material layer.   The method for manufacturing a secondary battery according to claim 7, wherein the water-based binder is at least one binder selected from the group consisting of a fluorine-based resin, polyethylene, and polypropylene.   The method for manufacturing a secondary battery according to claim 7 or 8, wherein the current collector is formed of aluminum or an aluminum alloy.   The method for manufacturing a secondary battery according to any one of claims 7 to 9, wherein the electrode active material is a lithium transition metal composite oxide having a layered structure.

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