Method for manufacturing electrode for lithium ion battery

Abstract

This invention provides a method for manufacturing an electrode for lithium-ion batteries, resulting in an electrode for lithium-ion batteries with an anisotropy of surface roughness (Ro) of the active material layer surface below a certain value. Specifically, a first xy orthogonal coordinate is set on the surface of the active material layer, and the arithmetic mean roughness of the surface of the active material layer measured in the x-axis direction of the first xy orthogonal coordinate is set as Ro. ax The arithmetic mean roughness of the surface of the active material layer, measured along the y-axis in the first orthogonal xy coordinate system, is set as R. ay At this time R ax -R ax The absolute value is less than 0.2 μm. Furthermore, a second xy orthogonal coordinate is defined by rotating the first xy orthogonal coordinate 45° within the plane formed by its x-axis and y-axis. The arithmetic mean roughness of the surface of the active material layer measured along the x-axis direction of the second xy orthogonal coordinate is set as R. ax Let R be the arithmetic mean roughness of the surface of the active material layer measured along the y-axis in the second orthogonal xy coordinate system. ay ′, at this time R ax ′-R ay The absolute value of ′ is less than 0.2μm.

Description

[0001] This application is a divisional application of the patent application with application number 201980008747.2, filed on January 7, 2019, and with the title “Electrode for lithium ion battery and lithium ion battery”. TECHNICAL FIELD

[0002] The present application relates to a manufacturing method of an electrode for a lithium ion battery. BACKGROUND

[0003] Lithium ion batteries, as a representative of secondary batteries, have been indispensable in modern society. In addition, with the high performance of various electrical / electronic devices, and the like, development for further large capacity, safety improvement, production cost reduction, and the like has been continuously ongoing.

[0004] For example, in Patent Literature 1, a lithium ion battery positive electrode is described, in which a positive electrode active material having a layer structure represented by a composition formula: Li x (Ni y M 1-y )O z (In the formula, M is Mn and Co, x is 0.9 to 1.2, y is 0.3 to 0.9, and z is 1.8 to 2.4) is coated on the surface of a current collector to produce the lithium ion battery positive electrode, and the surface roughness (R zjis ) measured by scanning with a measurement length of 4 mm is 10 μm or less.

[0005] In addition, in Patent Literature 2, a lithium ion battery is described, which includes a positive electrode including a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions, a negative electrode including a negative electrode active material, and an electrolyte, in which the lithium ion battery, the arithmetic mean value of the surface roughness of the positive electrode, Ra, after performing a charge and discharge process is 155 to 419 nm, or the arithmetic mean value of the surface roughness of the negative electrode, Ra, is 183 to 1159 nm.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Publication No. 2011-187178

[0009] Patent Literature 2: Japanese Patent Application Publication No. 2005-108810 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] Generally, an active material formed on a current collector such as a metal foil is calendered, and wound to manufacture an electrode (for example, a positive electrode) of a lithium ion battery.

[0012] However, in the past, for example, there have been cases where the electrode is broken in the transport of the electrode after calendering for winding, or cases where a defect occurs at the time of winding (for example, cases where winding is not good due to wrinkles or stripe patterns occurring in the electrode). These are problems in terms of deterioration in yield, reduction in productivity, and the like.

[0013] The present application is made in view of such circumstances. That is, one of the objects of the present application is to suppress breakage of an electrode and winding defects in the production of an electrode for a lithium ion battery.

[0014] Means for solving the problem

[0015] The present inventors have conducted intensive studies in order to solve the above problem, and as a result, the following provided invention was made, and it was found that the above problem could be solved.

[0016] According to the present application, there is provided an electrode for a lithium ion battery, the electrode for a lithium ion battery comprising: a current collector; and an active material layer formed on a surface of the current collector, the active material layer containing active material particles and a binder resin, wherein a first xy orthogonal coordinate is set on a surface of the active material layer, an arithmetic mean roughness of the surface of the active material layer measured in an x-axis direction of the first xy orthogonal coordinate is set as R ax an arithmetic mean roughness of the surface of the active material layer measured in a y-axis direction of the first xy orthogonal coordinate is set as R ay , and at this time, the absolute value of R ay - R ay is 0.2 μm or less, a second xy orthogonal coordinate is set such that the first xy orthogonal coordinate is rotated by 45° in a plane formed by the x-axis and the y-axis thereof, an arithmetic mean roughness of the surface of the active material layer measured in an x-axis direction of the second xy orthogonal coordinate is set as R ax ', an arithmetic mean roughness of the surface of the active material layer measured in a y-axis direction of the second xy orthogonal coordinate is set as R ay ', and at this time, the absolute value of R ax '- R ay ' is 0.2 μm or less.

[0017] Further, according to the present application, there is provided a lithium ion battery comprising the above-described electrode for a lithium ion battery.

[0018] Effects of the Invention

[0019] According to the present application, breakage of an electrode and winding defects can be suppressed in the production of an electrode for a lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0020] The above objects as well as other objects, features and advantages will become more apparent from the following description taken in conjunction with the accompanying drawings.

[0021] Figure 1 is a diagram schematically showing a structure (particularly, a layer structure) of an electrode for a lithium ion battery.

[0022] Figure 2 is a diagram for explaining arithmetic average roughness R ax , R ay、 , R ax ' and R ay '.

[0023] Figure 3 is a diagram for explaining "anisotropy of surface roughness" in a surface of an electrode for a lithium ion battery.

[0024] Figure 4 is a diagram schematically showing one aspect of a manufacturing method of an electrode for a lithium ion battery. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings.

[0026] In all the drawings, the same reference numerals are applied to the same constituent elements, and the description will be appropriately omitted.

[0027] In order to avoid the trouble, the following cases are assumed: (i) a case where the same constituent elements are present in a plurality of the same drawings, in which case the reference numerals are attached to only one of them, not to all of them; (ii) particularly in Figure 2 Hereinafter, the reference numerals will not be reattached to the same constituent elements. Figure 1

[0028] All the drawings are ultimately for the purpose of explanation. The shape, size ratio, etc. of each member in the drawings do not necessarily correspond to those of the actual article.

[0029] In the present specification, the notation of "a ~ b" in the description of a numerical range means a to b inclusive, unless otherwise specified. For example, the so-called "1 to 5 mass%", means 1 mass% or more and 5 mass% or less.

[0030] In the notation of a group (radical) in the present specification, the notation of "with or without substitution" includes both a group without a substituent (unsubstituted group) and a group with a substituent. For example, the so-called "alkyl group" includes not only an alkyl group without a substituent (unsubstituted alkyl group), but also an alkyl group with a substituent (substituted alkyl group).

[0031] <ELECTRODE FOR A LITHIUM ION BATTERY>

[0032] Figure 1 ​This illustrates an example of an electrode for a lithium-ion battery according to this embodiment.

[0033] exist Figure 1 In the lithium-ion battery electrode 1 (hereinafter referred to as "electrode 1"), at least: a current collector 2; and an active material layer 3 formed on at least one side of the surface.

[0034] Alternatively, active material layers 3 can be provided on both sides of the current collector 2.

[0035] Figure 2 (A) and Figure 2 (B) is a top-view diagram of electrode 1 with the active material layer 3 of electrode 1 as the upper surface. Additionally, Figure 2 Electrode 1 of (A) and Figure 2 (B) Electrode 1 is the same as electrode 1.

[0036] exist Figure 2 In (A), a first xy orthogonal coordinate system is set as shown on its left (in addition, in the case that electrode 1 is rectangular, the x-axis is typically set in the long side direction and the y-axis is set in the short side direction). The arithmetic mean roughness of the surface of the active material layer 3, measured in the x-axis direction of this first xy orthogonal coordinate system, is set as R. ax Let the arithmetic mean roughness of the surface of the active material layer 3, measured along the y-axis in this coordinate system, be R. ay At that time, R ax -R ay absolute value (R) ax With R ay The absolute value of the difference is less than 0.2 μm.

[0037] exist Figure 2 In (B), a second xy orthogonal coordinate is set as shown on its left. This second xy orthogonal coordinate is obtained by rotating the aforementioned first xy orthogonal coordinate by 45° within the plane formed by its x-axis and y-axis. Furthermore, the arithmetic mean roughness of the surface of the active material layer 3, measured along the x-axis direction of this second xy orthogonal coordinate, is set as R. ax Let R be the arithmetic mean roughness of the surface of the active material layer 3 measured along the y-axis in this coordinate system. ay At ′, R ax ′-R ay The absolute value of ′ (R ax ′ and R ay The absolute value of the difference between the two is also less than 0.2 μm.

[0038] Here, R ax R ay R ax ′ and R ayThe values of R, R, R, and R are values obtained by measurement based on JIS B0601:2013. As a measurement device, for example, a device "VR-3000" manufactured by KLA-Tencor Corporation can be used.

[0039] In addition, in the measurement, in order to eliminate the arbitrariness of the measurement results of the measurement position, for example, measurement can be performed at 5 points of the center of gravity 1 point of the electrode, and 2 points each of which is apart from the center of gravity by ±5 mm in the x-axis direction in the 1st xy coordinates, and 2 points each of which is apart from the center of gravity by ±5 mm in the y-axis direction. Also, the average value of the measurement results of the 5 points can be adopted as R ax , R ay , R ax , and R ay in this specification.

[0040] The physical meanings of "the absolute value of R ax -R ay is 0.2 μm or less" and "the absolute value of R ax -R ay is 0.2 μm or less" are supplemented.

[0041] According to both of the absolute value of R ax -R ay is 0.2 μm or less and the absolute value of R ax -R ay is 0.2 μm or less, it can be said that the "anisotropy of the surface roughness" of the active material layer 3 is small enough. If explained in more detail, it is as follows.

[0042] The so-called arithmetic mean roughness is an index indicating the roughness of a certain surface when scanning the surface in one dimension. The so-called R ax -R ay is 0.2 μm or less in the 1st xy orthogonal coordinates means that the roughness in the "longitudinal direction" (x direction) and the roughness in the "lateral direction" (y direction) of the surface of the active material layer 3 are the same degree. According to only this index, it seems that the "anisotropy of the surface roughness" of the active material layer 3 is small at a glance.

[0043] However, if only R ax and R ay are measured in the 1st xy orthogonal coordinates, in practice, even in a case where there is anisotropy in the surface roughness (although the surface roughness is large in measurement in a certain direction, the surface roughness is small in measurement in another direction), the absolute value of R ax -R ay is sometimes calculated to be small enough. For example Figure 3 The case schematically shown in FIG. 1A corresponds to this case.

[0044] Thus, in the present embodiment, in addition to the arithmetic average roughness of the longitudinal and lateral directions of the surface of the active material layer 3 being defined, the arithmetic average roughness of the "diagonal direction" is also defined. That is, by also defining the absolute value of the difference between the arithmetic surface roughness of each of the x and y directions in the above-mentioned second xy orthogonal coordinate (R ax ′-R ay ′) to be 0.2 μm or less, the "anisotropy" of the roughness in all directions on the surface of the active material layer 3 is defined to be small.

[0045] As described above, in the electrode 1, since the absolute value of R ax -R ay and the absolute value of R ax ′-R ay ′ are 0.2 μm or less (the anisotropy of the roughness in all directions on the surface of the active material layer 3 is small), the breaking of the electrode, the uneven winding of the electrode in the manufacture of the electrode of the lithium ion battery is suppressed.

[0046] The inventors of the present application have investigated the reasons for the breaking of the electrode, the poor winding of the electrode in the manufacture of the electrode of the lithium ion battery from various viewpoints.

[0047] The inventors of the present application have particularly investigated the fact that certain unevenness of the surface of the electrode is one of the reasons for the breaking of the electrode, the poor winding of the electrode. Through the investigation, the following insight was obtained: if the anisotropy is present in the surface roughness of the active material layer, the tendency to easily cause poor winding is present. The reason for this is presumed to be because, if the anisotropy is present in the surface roughness, the stress of the surface of the electrode or the inside of the electrode is not uniformly relaxed, and the tendency to easily cause deformation, wrinkles, striped patterns, and the like is present.

[0048] The inventors of the present application have solved the problem based on the above-mentioned insight by newly involving the electrode for a lithium ion battery in which the "anisotropy" of the surface roughness of the active material layer is small.

[0049] In other words, the inventors of the present application have newly designed the electrode for a lithium ion battery in which both the absolute value of R ax -R ay and the absolute value of R ax ′-R ay ′ are 0.2 μm or less. Furthermore, by the electrode of the new design, the breaking of the electrode, the poor winding of the electrode in the manufacture of the electrode of the lithium ion battery has been successfully suppressed.

[0050] For example, by appropriately selecting the raw material of the active material layer 3 and the like, and by using the specific manufacturing method (putting effort into the pressing method) described later, it is possible to obtain the electrode 1 in which the absolute value of R ax -R ay and the absolute value of Rax | R | -R ay | R | -R

[0051] In addition, in the case where the electrode 1 has the active material layer on both the front and back surfaces, with respect to at least one of the active material layers, the absolute value of R ax | R | -R ay | R | -R ax | R | -R ay | R | -R ax | R | -R ay | R | -R ax | R | -R ay | R | -R

[0052] | R | -R ax | R | -R ay | R | -R ax | R | -R ay | R | -R ax | R | -R ay | R | -R ax | R | -R ay | R | -R

[0053] The structure and material of the electrode 1 will be described below.

[0054] The electrode 1 is a positive electrode or a negative electrode for a lithium ion battery.

[0055] First, the case where the electrode 1 is a positive electrode for a lithium ion battery will be described.

[0056] (Collector 2 of the positive electrode)

[0057] As the collector 2 of the positive electrode, any substance having electrical conductivity can be used. For example, aluminum, stainless steel, nickel, titanium, or alloys thereof, or the like can be used. Among these, aluminum is preferred from the viewpoints of price, ease of procurement, electrochemical stability, and the like. In addition, the shape of the collector is not particularly limited, and can be in the form of a foil, a flat plate, a mesh, or the like. The thickness of the collector is preferably in the range of 0.001 to 0.5 mm (1 to 500 μm), more preferably 5 to 100 μm, and further preferably 0.01 to 0.02 mm (10 to 20 μm).

[0058] (Active material layer 3 of the positive electrode)

[0059] The surface of the active material layer 3 needs to satisfy the above-described roughness requirements. On the other hand, as for the chemical material, composition, etc. of the active material layer 3, the prior art can be appropriately used.

[0060] In the case where the electrode 1 is a positive electrode, the active material layer 3 preferably contains positive electrode active material particles. In addition, a binder resin, a conductive aid, etc. are preferably further contained. Of course, components other than these can also be contained.

[0061] The following describes components that the active material layer 3 can contain in the case where the electrode 1 is a positive electrode.

[0062] • Positive electrode active material particles

[0063] The positive electrode active material particles are not particularly limited as long as they are positive electrode active material particles that can be used in a positive electrode of a lithium ion secondary battery. For example, lithium-transition metal composite oxides such as lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt composite oxides, lithium-nickel-aluminum composite oxides, lithium-nickel-cobalt-aluminum composite oxides, lithium-nickel-manganese-cobalt composite oxides, lithium-nickel-manganese-aluminum composite oxides, and lithium-nickel-cobalt-manganese-aluminum composite oxides; transition metal sulfides such as TiS2, FeS, and MoS2; transition metal oxides such as MnO, V2O5, V6O 13

[0064] In the present embodiment, the positive electrode active material particles preferably contain at least one compound selected from the group consisting of lithium-cobalt oxides, lithium-manganese oxides, lithium-nickel oxides, and lithium-iron phosphates. Thereby, an increase in charge-discharge capacity when used as a lithium ion battery, etc. can be expected.

[0065] The average particle diameter of the positive electrode active material particles is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 5 μm or more. In addition, the average particle diameter is preferably 80 μm or less, more preferably 40 μm or less, and further preferably 20 μm or less. A suitable particle diameter is selected from the viewpoint of input-output characteristics and electrode production.

[0066] Here, the average particle diameter refers to the particle diameter at 50% of the cumulative value (median diameter: D50) in the particle size distribution (volume basis) by the laser diffraction scattering method. 50 ​). By being set to a numerical range, side reactions during charge and discharge are suppressed, and a decrease in charge and discharge efficiency is suppressed.

[0067] The content of the positive electrode active material particles is preferably 85 parts by mass or more and 99.4 parts by mass or less, more preferably 90.5 parts by mass or more and 98.5 parts by mass or less, and further preferably 90.5 parts by mass or more and 97.5 parts by mass or less, based on 100 parts by mass of the entire active material layer 3. This allows sufficient occlusion and release of lithium.

[0068] • Binder resin

[0069] The binder resin can be appropriately selected from publicly known binder resins and is not particularly limited. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and the like, which are commonly used binder resins, can be used. These binder resins are mixed with other components using an appropriate solvent (typically, an organic solvent such as N-methylpyrrolidone (NMP)).

[0070] The content of the binder resin is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 0.5 parts by mass or more and 5.0 parts by mass or less, and further preferably 1.0 parts by mass or more and 5.0 parts by mass or less, based on 100 parts by mass of the entire active material layer 3. If the content of the binder resin is within the above range, the balance between the coatability of the electrode slurry, the adhesion of the binder, and the battery characteristics is more excellent. In addition, if the content of the binder resin is below the above upper limit value, the proportion of the electrode active material becomes large, and the capacity per electrode mass becomes large, and thus is preferred. If the content of the binder resin is above the above lower limit value, electrode peeling is suppressed, and thus is preferred.

[0071] • Conductive aid

[0072] The conductive aid is not particularly limited as long as it is a conductive aid that improves the conductivity of the electrode. For example, carbon black, Ketjen black, acetylene black, natural graphite, artificial graphite, carbon fibers, and the like can be given. These conductive aids can be used alone as one kind or in combination as two or more kinds.

[0073] The content of the conductive aid is preferably 0.5 parts by mass or more and 5.0 parts by mass or less, more preferably 1.0 parts by mass or more and 4.5 parts by mass or less, and further preferably 1.5 parts by mass or more and 4.5 parts by mass or less, based on 100 parts by mass of the entire active material layer 3. If the content of the conductive aid is within the above range, the balance between the coatability of the electrode slurry, the adhesion of the binder, and the battery characteristics is more excellent. In addition, if the content of the conductive aid is below the above upper limit, the proportion of the electrode active material becomes large, and the capacity per electrode mass becomes large, and thus is preferred. If the content of the conductive aid is above the above lower limit, the conductivity of the electrode becomes more excellent, and thus is preferred.

[0074] • Density of active material layer 3

[0075] The density of the active material layer 3 is not particularly limited, and is typically 2.0 g / cm 3 or more, and preferably 3.0 g / cm 3 or more. In addition, from the viewpoint of ease of production and the like, it is typically 4.0 g / cm 3 or more, and preferably 3.5 g / cm 3 or more. If it is within this numerical range, the discharge capacity at the time of use at a high discharge rate is improved, and thus is preferred.

[0076] • Thickness of active material layer 3

[0077] The thickness of the active material layer 3 is not particularly limited, and can be appropriately set in correspondence with the desired characteristics. For example, it can be set to be thick from the viewpoint of energy density, and can be set to be thin from the viewpoint of output characteristics. The thickness of the active material layer 3 can be appropriately set, for example, in the range of 10 to 250 μm, preferably 20 to 200 μm, more preferably 100 to 150 μm, and further preferably 120 to 130 μm.

[0078] (Method for manufacturing)

[0079] In obtaining the electrode for lithium ion batteries (for example, the positive electrode) of the present embodiment, the method for manufacturing is not limited, and an electrode satisfying the provisions related to the surface roughness and the like described above can be obtained by any method.

[0080] For example, (i) first, an electrode slurry in which the positive electrode active material particles, the binder resin, and the conductive aid are dispersed or dissolved in a suitable solvent (typically, an organic solvent such as N-methylpyrrolidone) is prepared; (ii) next, the electrode slurry is applied to one side or both sides of the current collector 2, and is dried to provide the active material layer 3; (iii) thereafter, the active material layer 3 formed on the current collector 2 and the current collector 2 are subjected to pressing (roll pressing or the like), whereby the electrode for lithium ion batteries of the present embodiment can be obtained.

[0081] Here, according to the inventor's insights of the present invention, in order to obtain R ax -R ay The absolute value is less than 0.2 μm and R ax ′-R ay For lithium-ion battery electrodes with an absolute value of ′ less than 0.2 μm, it is desirable to focus on the pressing process described in (iii) above. For further information, please refer to... Figure 4 Please provide an explanation.

[0082] Figure 4 This schematically illustrates an example of a pressing process (roll pressing). Electrode 1 (not explicitly shown in the figure, but comprising a current collector 2 and an active material layer 3) is held between two opposing rollers 10, separated by a buffer film 5. The held electrode 1 and the buffer film 5 are pressed together by the rotation of the two rollers 10. Figure 4 Forces, etc. (indicated by arrows), from Figure 4 The material is fed from the left to the right. At this time, the active material layer 3 on the surface of electrode 1 is compressed and / or flattened by being pressed by roller 10 through buffer film 5.

[0083] In addition, Figure 4 In this embodiment, a buffer film 5 exists on both sides of electrode 1, but this is not mandatory. For example, in electrode 1, if the active material layer 3 exists only on one side of current collector 2, it is also possible to have the buffer film 5 exist only on the side of current collector 2.

[0084] According to the inventor's understanding of the present invention, by applying pressure to the active material layer 3 through the buffer film 5 during the pressing process (rolling), R can be obtained. ax -R ay The absolute value is less than 0.2 μm and R ax ′-R ay Electrodes for lithium-ion batteries with an absolute value of less than 0.2 μm.

[0085] R can be made by focusing on such manufacturing methods. ax -R ay The absolute value and R ax ′-R ay The reason for estimating the absolute value of ′ to be less than 0.2 μm is as follows.

[0086] Roll forming, frequently used in the manufacture of lithium-ion batteries, has the advantage of easily applying high pressure. However, since the contact area between the roller and the electrode is a line rather than a surface, it is believed that stress can be easily applied in a specific direction, which relates to the anisotropy of surface roughness. In addition, in recent years, due to the demand for higher capacity, there has been a trend of increasing rolling pressure, suggesting a tendency to apply even more stress.

[0087] On the other hand, it is considered that if the active material layer 3 is rolled with the buffer film 5 interposed therebetween, the buffer film 5 becomes "sacrificial" and thus the stress is mitigated. Thus, it is considered that the anisotropy of the surface roughness is reduced.

[0088] As the buffer film 5, from the viewpoint of the stress mitigation described above, a buffer film of a certain degree of softness and deformability is preferably selected.

[0089] If the handleability, operability, and the like are also taken into account, for example, an aluminum film is selected as the buffer film 5. Here, the "aluminum film" refers not only to a film made of pure aluminum but also to a film made of an alloy of aluminum and another metal element or the like.

[0090] In addition, the synthetic resin film is also preferably selected from the viewpoint of softness and deformability. As the synthetic resin film, a polyester film (PET film or the like), a polyolefin film (polyethylene film, polypropylene film), and other publicly known various synthetic resin films can be used.

[0091] Further, as another viewpoint related to the selection of the buffer film 5, a buffer film 5 of a material softer than the hardness of the positive electrode active material particles contained in the active material layer 3 is considered to be selected.

[0092] The buffer film 5 preferably has a surface (a surface in contact with the electrode 1) of a certain degree of flatness. The arithmetic mean roughness of the surface of the buffer film 5 in contact with the electrode 1 is, for example, 0.1 to 2.0 μm, preferably 0.5 to 1.5 μm, and more preferably 0.6 to 0.8 μm. It is considered that by satisfying this numerical range, the surface of the active material layer 3 can be further smoothed.

[0093] The thickness of the buffer film 5 is not particularly limited, but from the viewpoint of the operability and the like, it is, for example, 10 to 100 μm, preferably 10 to 50 μm, and more preferably 15 to 25 μm.

[0094] In the Figure 4 , the conveyance speed of the electrode 1 (corresponding to the linear speed of the rotation of the roll 10) is not particularly limited, and is typically 1 to 100 m / min, and preferably 2 to 50 m / min.

[0095] In addition, the pressure of the rolling is not particularly limited, and is typically 0.7 to 2.5 [t / cm], and preferably 1.3 to 1.7 [t / cm].

[0096] In addition, as the method of pressing, a method other than the rolling shown in Figure 4 is also applicable, as a matter of course. Among them, the rolling is preferred in terms of easiness of application of a large pressure, easiness of continuous production, and the like.

[0097] The above describes the case where the electrode 1 is a positive electrode for a lithium ion battery.

[0098] Next, the case where the electrode 1 is a negative electrode for a lithium ion battery is described. With regard to the drawings, reference is made to the same figures as for the positive electrode (s). Figure 1

[0099] (Collector 2 of the negative electrode)

[0100] In the case where the electrode 1 is a negative electrode for a lithium ion battery, the collector 2 thereof can use any material having conductivity. As the material, copper, stainless steel, nickel, titanium, alloys thereof, and the like can be used, and the thickness and the like are as described with regard to the collector 2 of the positive electrode.

[0101] (Active material layer 3 of the negative electrode)

[0102] The active material layer 3 of the negative electrode preferably contains negative electrode active material particles. In addition, a binder resin, a conductive aid, and the like can be contained as needed.

[0103] As the negative electrode active material particles, graphite, amorphous carbon, silicon, silicon oxide, lithium metal, and the like are preferably selected, but as long as the material can occlude and release lithium, it is not limited to these.

[0104] As the average particle diameter (lower limit) of the negative electrode active material particles, 1 μm is preferable, 2 μm is more preferable, and 5 μm is further preferable from the viewpoint of input / output characteristics and electrode production. In addition, as the average particle diameter (upper limit), 80 μm is preferable, and 40 μm is more preferable. Here, the average particle diameter refers to the particle diameter (median diameter: D50) at 50% of the cumulative value in the particle size distribution (volume basis) by laser diffraction scattering method. 50 By setting the numerical range, the side reaction at the time of charge and discharge is suppressed, and thus the decrease in charge and discharge efficiency is suppressed.

[0105] As the binder resin and the conductive aid that can be contained in the active material layer 3 of the negative electrode, the same as can be used in the active material layer 3 of the positive electrode described above can be used. In addition, as the binder resin, styrene butadiene rubber and the like can also be used. In addition, as the solvent at the time of coating, instead of using water, an organic solvent can also be used.

[0106] The amount of each component in the negative electrode is appropriately adjusted from the viewpoint of the performance of the battery, manufacturing adaptability, adhesion to the collector, and the like.

[0107] (Lithium ion battery)

[0108] The lithium ion battery of the present embodiment has the electrode for a lithium ion battery described above.

[0109] ​Generally, a lithium ion battery has a positive electrode and a negative electrode. In the lithium ion battery of the present embodiment, at least one of the positive electrode and the negative electrode is composed of the electrode having a small anisotropy in surface roughness as described above. In other words, even if one of the positive electrode and the negative electrode is the electrode having a small anisotropy in surface roughness and the other is not the electrode having a small anisotropy in surface roughness, the lithium ion battery can be the lithium ion battery of the present embodiment. Of these, preferably, at least the positive electrode is composed of the electrode having a small anisotropy in surface roughness.

[0110] The lithium ion battery of the present embodiment, as one aspect, has an electrolyte, a separator, an outer container, and the like in addition to the positive electrode and the negative electrode. These will be described.

[0111] (Electrolyte)

[0112] The electrolyte generally uses a non-aqueous electrolyte containing a lithium salt.

[0113] As examples of the lithium salt, for example, LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiC4F9SO3, Li(CF3SO2)2N, lithium lower aliphatic acid carboxylate, and the like can be given.

[0114] As a solvent for dissolving the lithium salt, a publicly known solvent can be used without particular limitation. For example, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), and vinylene carbonate (VC); lactones such as γ-butyrolactone and γ-valerolactone; ethers such as trimethoxy methane, 1,2-dimethoxy ethane, diethyl ether, tetrahydrofuran, and 2-methyl tetrahydrofuran; sulfoxides such as dimethyl sulfoxide; alkylene oxides such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing solvents such as acetonitrile, nitromethane, formamide, and dimethylformamide; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate; phosphoric acid triesters; diethylene glycol dimethyl ethers; triethylene glycol dimethyl ethers; sulfolanes such as sulfolane and methyl sulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; and sulfonic acid lactones such as 1,3-propane sultone, 1,4-butane sultone, and naphthalene sulfonic acid lactone can be given. These can be used singly or in combination of two or more.

[0115] (Separator)

[0116] As the separator, a publicly known separator can be used.

[0117] The separator can be made of resin-based porous membranes, woven fabrics, non-woven fabrics, etc. As the resin component, polyolefin resins such as polypropylene and polyethylene, polyester resins, acrylic resins, styrene resins, or nylon resins can be used. Polyolefin-based microporous membranes are particularly preferred due to their excellent ion permeability and ability to physically separate the positive and negative electrodes.

[0118] Alternatively, a layer containing inorganic particles may be formed in the partition as needed. Examples of such inorganic particles include insulating oxides, nitrides, sulfides, and carbides. TiO2 and / or Al2O3 are preferred.

[0119] (outer container)

[0120] For the outer container, known components can be used. However, a flexible film is preferred from the viewpoint of battery weight reduction.

[0121] As a flexible film, it can be used where a resin layer is provided on the front and back sides of a metal layer that serves as a substrate. The metal layer can be a barrier metal that prevents electrolyte leakage and the intrusion of external moisture; aluminum, stainless steel, etc., can be used.

[0122] The embodiments of the present invention have been described above, but these are merely examples, and various structures other than those described can be employed. Furthermore, the present invention is not limited to the embodiments described above; modifications and improvements within the scope of achieving the objectives of the present invention are also included in the present invention.

[0123] Example

[0124] The embodiments of the present invention will be described in detail based on examples and comparative examples. However, the present invention is not limited to these examples.

[0125] <Examples 1-3: Manufacturing of Electrodes (Positive Electrodes)>

[0126] 1. Preparation of slurry for the formation of active substance layers

[0127] (1) Preparation of the slurry in Example 1

[0128] First, mix the following materials evenly at the ratio shown.

[0129] • Positive electrode active material: lithium nickel oxide particles (D 50 :8μm) and lithium manganese oxide particles (D 50 A mixture of 12 μm and 12 μm in a mass ratio of 3:7…93% by mass

[0130] • Conductive additives: Carbon black…3% by mass

[0131] • Binder resin: PVDF (polyvinylidene fluoride)... 4 mass%

[0132] Further, a solvent NMP (N-methyl-2-pyrrolidone) was mixed in the mixture to prepare a positive electrode slurry.

[0133] (2) Preparation of the slurry of Example 2

[0134] The positive electrode slurry was prepared in the same manner as in the above (1), except that lithium nickel oxide and lithium manganese oxide were mixed at a mass ratio of 7:3 as the positive electrode active material.

[0135] (3) Preparation of the slurry of Example 3

[0136] The positive electrode slurry was prepared in the same manner as in the above (1), except that only lithium nickel oxide was used as the positive electrode active material.

[0137] 2. Coating of the slurry onto the current collector, and rolling

[0138] The positive electrode slurry prepared in the above 1. was coated on both sides of an aluminum base material (thickness: about 15 μm) serving as the current collector, and dried to obtain an active material layer-uncompressed positive electrode.

[0139] The active material layer-uncompressed positive electrode was compressed using a rolling device such as a roll press (roll diameter: 200 mm, number of rolls: 2, roll gap: 0.2 mm). Figure 4 The compression was performed at a force of 1.6 t / cm from both sides through a buffer film (aluminum base material, thickness: 20 μm, surface roughness (arithmetical mean roughness): 0.7 μm) as described above (roll speed: 3 m / min). Transportation speed: 3 m / min).

[0140] Here, as the buffer film, an aluminum base material (thickness: 20 μm, surface roughness (arithmetical mean roughness): 0.7 μm) was used.

[0141] Thus, an electrode (positive electrode) for a lithium ion battery was obtained. The density of the active material layer was 3.4 g / cc or more.

[0142] 3. Measurement of surface roughness

[0143] First, the electrode (positive electrode) for a lithium ion battery obtained in the above 2. was cut into a rectangle of a total of 10 cm x 5 cm in length to obtain an electrode for measurement of surface roughness.

[0144] The surface roughness of the surface (the surface on which the active material layer was coated and compressed) of the electrode for measurement was measured. That is, R ax , R ay , R ax ' and R ayvalues of R ax , R ay , R ax , and R ay were measured. The measurement was performed at the center of the electrode for measurement and at four points around the center, for a total of five points, using a measuring device VR-3000 manufactured by KANSAI CHEMICAL CO., LTD., in accordance with the provisions of JIS B0601:2013, as described above, and the average of the five points was taken as R ax , ay , ax , ay .

[0145] [Manufacture of (positive electrode)]

[0146] In the above "2. Coating of slurry onto current collector, and roll-pressing", except that a buffer film was not used, electrodes (positive electrodes) for lithium ion batteries were obtained in the same manner as in Examples 1 to 3 (i.e., using the same positive electrode slurry and current collector).

[0147] The values of R ax , R ay , R ax , and R ay for the Examples and Comparative Examples, and the absolute values of R ax -R ay and R ax '-R ay ' are collectively described in Table 1 below.

[0148] [Evaluation: Presence or absence of wrinkles and stripe patterns]

[0149] The surfaces of the electrodes of each of the Examples and Comparative Examples obtained by the above procedures 1. and 2. were observed, and evaluated for the presence or absence of wrinkles and stripe patterns. An electrode for which wrinkles and stripe patterns were not at all confirmed was set to "none", and an electrode for which wrinkles and stripe patterns were confirmed was set to "yes".

[0150] The evaluation results are shown in Table 1.

[0151] [Evaluation: Winding property]

[0152] The electrodes of each of the Examples and Comparative Examples obtained by the above procedures 1. and 2. were wound. At this time, an electrode that could be wound neatly without gaps and deformation was set to "good", and an electrode that was not wound neatly due to the presence of gaps and deformation, or an electrode that was broken, was set to "poor".

[0153] The evaluation results are shown in Table 1.

[0154] [Table 1]

[0155]

[0156] As shown in Table 1, R ax -Ray whose absolute value is 0.2 μm or less and R ax ′-R ay ′ whose absolute value is 0.2 μm or less of Examples 1 to 3 were confirmed to have no wrinkles and stripe patterns, and good results were obtained in terms of winding properties.

[0157] That is, by the electrode for lithium ion batteries of the present embodiment, deterioration of the yield is suppressed, and in addition, improvement of the productivity can be achieved.

[0158] On the other hand, R ax -R ay whose absolute value and R ax ′-R ay ′ whose absolute value exceeds 0.2 μm, wrinkles and stripe patterns were observed, and in addition, the winding properties were poor.

[0159] In the special comparative example 2, although R ax ′-R ay ′ whose absolute value was 0.04 μm (i.e., the same level as Examples 1 to 3), and in addition, R ax -R ay whose absolute value was also 0.22 μm (a value close to 0.2 μm), but in terms of wrinkles, stripe patterns, and winding properties, the results were inferior to those of Examples 1 to 3. It was found that it is important in solving the problem to set both R ax -R ay whose absolute value and R ax ′-R ay ′ whose absolute value to 0.2 μm or less.

[0160] This application claims priority from Japanese Application No. 2018-005486 filed on January 17, 2018, the disclosure of which is incorporated herein in its entirety.

Claims

1. A method for manufacturing an electrode for a lithium ion battery, characterized by comprising: an electrode collector; and an active material layer formed on a surface of the electrode collector, wherein the active material layer contains active material particles and a binder resin, and wherein the method comprises: a step of providing the active material layer containing the active material particles, the binder resin, and a conductive aid on one or both surfaces of the electrode collector; and a pressing step of pressing the active material layer formed on the electrode collector together with the electrode collector, wherein the pressing step compresses and / or flattens the electrode having the electrode collector and the active material layer by being pressed through a buffer film, and wherein an arithmetic mean roughness of a surface of the buffer film that contacts the electrode is 0.1 to 2.0 μm.

2. The method for manufacturing an electrode for a lithium ion battery according to claim 1, wherein the step of providing the active material layer on one or both surfaces of the electrode collector is a coating step of coating an electrode slurry in which the active material particles, the binder resin, and the conductive aid are dispersed or dissolved in a solvent on one or both surfaces of the electrode collector, and drying the electrode slurry to provide the active material layer.

3. The method for manufacturing an electrode for a lithium ion battery according to claim 1 or 2, wherein the pressing step is a roll pressing step of roll pressing the active material layer formed on the electrode collector together with the electrode collector, and wherein the roll pressing step is performed by sandwiching the electrode having the electrode collector and the active material layer through the buffer film by two rolls disposed to face each other. A first xy orthogonal coordinate is set on the surface of the active material layer, and an arithmetic mean roughness of the surface of the active material layer measured in the x-axis direction of the first xy orthogonal coordinate is set as R ax An arithmetic mean roughness of the surface of the active material layer measured in the y-axis direction of the first xy orthogonal coordinate is set as R ay At this time, the absolute value of R ax - R ay is 0.2 μm or less, The arithmetic mean roughness of the surface of the active material layer measured in the x-axis direction of the second xy orthogonal coordinate is set to R ax The arithmetic mean roughness of the surface of the active material layer measured in the y-axis direction of the second xy orthogonal coordinate is set to R ay ax ay The absolute value of R​​ 4. The method for manufacturing an electrode for a lithium ion battery according to claim 1, wherein the buffer film is an aluminum film.

5. The method for manufacturing an electrode for a lithium ion battery according to claim 1 or 2, wherein a pressure of 0.7 to 2.5 [t / cm] is applied to the electrode collector and the active material layer in the pressing step. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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