Electrode for nonaqueous electrolyte secondary battery, method for manufacturing the electrode, and nonaqueous electrolyte secondary battery provided with the electrode

Abstract

An electrode disclosed herein is provided with an electrode current collector in a long strip shape and an electrode active material layer formed on the electrode current collector. A surface portion of the electrode active material layer has a plurality of first grooves extending in a width direction of the electrode current collector and at least one second groove (18) extending in a long side direction of the electrode current collector. The first grooves are formed in a continuous manner from one end portion to the other end portion. Here, in a region where the first grooves and the second groove are formed, the region is equally divided into three layers of an upper layer, an intermediate layer, and a lower layer in a thickness direction of the electrode current collector from a surface of the electrode active material layer, and electrode densities (g / cm 3 ) of the upper layer, the intermediate layer, and the lower layer of the grooves are respectively set as d1, d2, d3, when the electrode is provided with a relationship of 0.8 < (d1 / d3) < 1.1.

Description

Technical Field

[0001] The present invention relates to an electrode for a non-aqueous electrolyte secondary battery, a method for manufacturing the electrode, and a non-aqueous electrolyte secondary battery having the electrode. Background Technology

[0002] Lithium-ion rechargeable batteries and other rechargeable batteries are preferred for use as high-output power sources in vehicles or as power sources for personal computers and mobile terminals due to their lighter weight and higher energy density compared to existing batteries. A typical structure for the positive and negative electrodes (hereinafter referred to as "electrodes" without specific distinction) of such rechargeable batteries is a structure in which an electrode active material layer, primarily composed of electrode active material, is formed on one or both sides of a foil-shaped electrode current collector. This electrode active material layer is formed by dispersing solid components such as electrode active material, binder, and conductive material in a specified solvent, coating the prepared paste-like electrode material onto the surface of the current collector to form a coating film, drying the coating film, and then applying pressure to achieve a specified density and thickness.

[0003] As a type of secondary battery, a battery structure is known that comprises a wound electrode body, obtained by stacking and winding elongated sheet-shaped electrodes (positive and negative electrodes) in a vortex shape with a separator in between. By making the electrode body into a vortex shape, the reaction area of ​​the positive and negative electrodes can be increased, thereby improving the energy density and enabling high output. In addition, to improve the sealing between the positive and negative electrodes and the separator, external pressure is applied to the secondary battery with the wound electrode body. This reduces the resistance of the secondary battery and prevents the electrodes and separator from deviating from their designated positions. On the other hand, since the gap between the electrodes and the separator becomes smaller, the electrolyte becomes more difficult to penetrate, and there is a tendency for the impregnation of non-aqueous electrolytes into the entire wound electrode body to decrease.

[0004] To address the aforementioned problems, Patent Document 1 discloses a battery that improves the electrolyte injection rate and degassing rate by forming multiple grooves, at least one end of which extends to the end of the electrode, in the active material layer of either the positive or negative electrode. The document further discloses that the grooves are formed by pressurizing the dried electrode active material layer with two flat molds or two roller molds with protrusions.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2002-15764 Summary of the Invention

[0008] However, when forming the trench using conventional techniques, the density in the adjacent areas of the trench locally increases (densification) because the mold presses down on the dried electrode active material layer. Furthermore, since the trench is formed by machining the surface of the electrode active material layer, foreign matter generated during this process causes the formed trench to become discontinuous (i.e., unconnected), leading to a reduction in electrode capacity. While the densified trench functions as an injection path for the electrolyte into the electrode, the densified surface of the trench tends to result in low electrolyte impregnation of the entire electrode. Additionally, discontinuous trenches have been found to clog the electrolyte or trap air bubbles, indicating that there is still room for improvement in increasing the electrolyte injection rate.

[0009] The present invention was made in view of the above circumstances, and its main objective is to provide an electrode with excellent electrolyte impregnation properties. Furthermore, another objective is to provide a battery having the electrode and a method for manufacturing the electrode.

[0010] To achieve the above objective, an electrode for a non-aqueous electrolyte secondary battery is provided. The electrode disclosed herein is either a positive or negative electrode, comprising an elongated sheet-shaped electrode current collector and an electrode active material layer formed on the electrode current collector. The surface portion of the electrode active material layer has a plurality of first grooves extending in the width direction of the electrode current collector and at least one second groove extending in the long side direction of the electrode current collector. The first grooves are formed continuously from one end to the other. Here, in the region where the first and second grooves are formed, the electrode active material layer is equally divided into three layers—an upper layer, a middle layer, and a lower layer—from the surface of the electrode active material layer to the thickness direction of the electrode current collector, and the electrode density (g / cm³) of the upper, middle, and lower layers of the electrode active material layer is specified. 3 When d1, d2, and d3 are respectively set, the relationship 0.8 < (d1 / d3) < 1.1 exists.

[0011] According to the above configuration, a first groove is formed on the surface of the electrode active material layer, extending continuously from one end to the other in the width direction of the electrode current collector. A second groove is formed orthogonally to the first groove, extending in the long side direction of the electrode current collector. This allows the electrolyte injected through the first groove to be injected into the entire electrode through the second groove. Furthermore, since the area where the first and second grooves are formed is not densified, the electrolyte impregnation of the electrode is high. By having such grooves on the surface of the electrode active material layer, an electrode with excellent electrolyte impregnation can be provided.

[0012] In a preferred embodiment of the electrode disclosed herein, a plurality of the aforementioned second grooves are formed along the long side direction of the electrode current collector.

[0013] Based on the above configuration, the electrolyte injected through the first tank can be easily injected into the entire electrode. Therefore, it is possible to provide an electrode with further improved electrolyte impregnation.

[0014] To achieve the aforementioned other objective, a non-aqueous electrolyte secondary battery is provided. The non-aqueous electrolyte secondary battery disclosed herein is characterized by having a flat, wound electrode body and a non-aqueous electrolyte. The wound electrode body is formed by winding a positive electrode having a positive active material layer on a strip-shaped positive current collector, a negative electrode having a negative active material layer on a strip-shaped negative current collector, and a separator around a winding axis. At least one of the positive and negative electrodes uses the electrode described above.

[0015] Based on the above configuration, by providing electrodes with the above characteristics, it is possible to provide a non-aqueous electrolyte secondary battery with improved electrolyte impregnation and battery characteristics.

[0016] To achieve the other objective mentioned above, a method for manufacturing an electrode for a non-aqueous electrolyte secondary battery is provided. The electrode manufacturing method disclosed herein is a method for manufacturing an electrode having either a positive or negative electrode current collector and an electrode active material layer, comprising the following steps: a step of preparing a wet powder formed from aggregated particles containing at least an electrode active material, a binder, and a solvent, wherein at least 50% of the aggregated particles of the wet powder are in a pendulum state or a ribbon state in terms of solid, liquid, and gas phases; a step of forming a coating film composed of the wet powder on the electrode current collector in a state of residual gas phase of the coating film; a step of forming a plurality of first grooves extending in a direction orthogonal to the conveying direction on the coating film by conveying the coating film on the electrode current collector and performing embossing using a first roller die; a step of forming at least one second groove extending in the conveying direction on the coating film by performing embossing using a second roller die; a step of drying the coating film formed on the electrode current collector to form an electrode active material layer; and a step of pressurizing the electrode active material layer. Here, the first groove mentioned above is formed continuously from one end to the other in the electrode active material layer after the pressurization process.

[0017] Based on the above configuration, an electrode possessing the aforementioned characteristics can be appropriately fabricated. By forming a groove on a coating film formed in a state with residual gas phase before the drying and pressurization processes, a groove of the desired shape can be formed without densifying the adjacent area of ​​the groove. Furthermore, since it does not involve a process of processing the electrode active material layer after the drying process as in conventional techniques, the electrode capacity is not reduced, and no foreign matter is generated. Thus, a continuous groove from one end to the other can be formed.

[0018] In a preferred embodiment of the electrode manufacturing method disclosed herein, when the wet powder prepared in the process of preparing the aforementioned wet powder is measured by loading the wet powder (g) into a container of a specified volume (mL) without applying force and then measuring the bulk density, the loose bulk density X (g / mL) is defined as the loose bulk density X, and the density calculated from the composition of the wet powder assuming the absence of a gas phase is defined as the true density Y (g / mL), the ratio of the true density Y to the loose bulk density X, Y / X, is 1.2 or higher.

[0019] Based on the above configuration, it is possible to manufacture a groove of the desired shape more appropriately, so as to prevent the adjacent area of ​​the groove from becoming dense and to make the groove continuous from one end to the other.

[0020] In a preferred embodiment of the electrode manufacturing method disclosed herein, a plurality of the second grooves are formed along the conveying direction in the second groove forming step.

[0021] Based on the above configuration, it is possible to appropriately manufacture an electrode that further improves the impregnation of the electrolyte. Attached Figure Description

[0022] Figure 1 This is an explanatory diagram schematically illustrating one embodiment of a lithium-ion secondary battery.

[0023] Figure 2 This is an explanatory diagram schematically illustrating the configuration of a wound electrode body of a lithium-ion secondary battery according to one embodiment.

[0024] Figure 3 This is a schematic cross-sectional view of a wound electrode body of a lithium-ion secondary battery according to one embodiment.

[0025] Figure 4 This is a top view schematically showing an electrode of one embodiment.

[0026] Figure 5 This is a diagram illustrating an electrode according to one embodiment.

[0027] Figure 6A This is a diagram schematically illustrating an example of the groove cross-sectional shape of an electrode in one embodiment.

[0028] Figure 6B This is a diagram schematically illustrating another example of the groove cross-sectional shape of an electrode in one embodiment.

[0029] Figure 7 This is a diagram illustrating the configuration of an electrode in one embodiment as a wound electrode body.

[0030] Figure 8 This is a flowchart illustrating the general steps of an electrode manufacturing method according to one embodiment.

[0031] Figure 9 This is a block diagram schematically illustrating the configuration of an electrode manufacturing apparatus according to one embodiment.

[0032] Figure 10 This is an illustration showing the existence of the solid phase (solid components such as active material particles), liquid phase (solvent), and gas phase (void) in the aggregated particles that constitute wet powder. (A) represents the pendulum state, (B) represents the ribbon state, (C) represents the capillary state, and (D) represents the slurry state.

[0033] Symbol Explanation

[0034] 1. Condensed particles

[0035] 2. Active material particles (solid phase)

[0036] 3. Solvent (liquid phase)

[0037] 4. Voids (Gas Phase)

[0038] 10 electrodes

[0039] 12-electrode current collector

[0040] 16. First slot

[0041] 18. Second slot

[0042] 20. Winded electrode body

[0043] 30 Electrode Materials

[0044] 32 Coating

[0045] 31 Battery casing

[0046] 54 Positive electrode active material layer

[0047] 64 Negative Electrode Active Material Layer

[0048] 70 isolation components

[0049] 100 Electrode Manufacturing Equipment

[0050] 120 Film-forming section

[0051] 130 Coating Processing Department

[0052] 140 Drying Section

[0053] 150 Pressurization Section

[0054] 200 Lithium-ion Secondary Battery Detailed Implementation

[0055] The preferred embodiment of the electrode manufacturing method disclosed herein will be described below, taking as an example an electrode preferably used in a lithium-ion secondary battery, a typical example of a non-aqueous electrolyte secondary battery. It should be noted that, except for matters specifically mentioned herein, anything necessary for implementation can be grasped by those skilled in the art based on existing technology in the field. The electrode manufacturing method disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

[0056] It should be noted that the dimensional relationships (length, width, thickness, etc.) do not reflect the actual dimensional relationships.

[0057] In addition, the description of "A~B (where A and B are arbitrary values)" in this specification refers to A above and B below.

[0058] In this manual, "non-aqueous electrolyte secondary battery" refers to a secondary battery in which the electrolyte is primarily composed of non-aqueous solvents (i.e., organic solvents). "Secondary battery" generally refers to a rechargeable energy storage device, including not only lithium-ion batteries, nickel-metal hydride batteries, and nickel-cadmium batteries (so-called storage batteries, i.e., chemical batteries), but also double-layer capacitors (i.e., physical batteries). Furthermore, in this manual, "lithium-ion secondary battery" refers to a non-aqueous electrolyte secondary battery that utilizes lithium ions as charge carriers and achieves charging and discharging through the migration of lithium ion charge between the positive and negative electrodes. In this manual, when there is no specific distinction between the positive and negative electrodes, they are abbreviated as electrodes.

[0059] Figure 1 The lithium-ion secondary battery 200 shown is constructed by housing a flat, wound electrode body 20 and a non-aqueous electrolyte (not shown) within a sealable box-shaped battery casing 31. The battery casing 31 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin-walled safety valve 33 designed to release internal pressure when the internal pressure of the battery casing 31 rises above a predetermined level. Additionally, the battery casing 31 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte. The positive terminal 42 is electrically connected to a positive current collector 42a. The negative terminal 44 is electrically connected to a negative current collector 44a. The battery casing 31 is preferably made of a high-strength, lightweight, and thermally conductive metallic material; examples of such metallic materials include aluminum and steel.

[0060] 20 winding electrode bodies Figure 1 and Figure 2The electrode typically consists of a strip-shaped positive electrode (hereinafter referred to as positive electrode 50) and a strip-shaped negative electrode (hereinafter referred to as negative electrode 60) overlapped and wound along their long sides, separated by a strip-shaped separator 70. The positive electrode 50 has a configuration in which a positive active material layer 54 is formed on one or both sides of the strip-shaped positive current collector 52 along its long side. The negative electrode 60 has a configuration in which a negative active material layer 64 is formed on one or both sides of the strip-shaped negative current collector 62 along its long side. The wound electrode body 20 disclosed herein is as follows... Figure 2 and Figure 3 The coiled electrode shown is flat and has a pair of curved surfaces (bending portions) 22a and 22b facing each other, and two planar portions 24 formed continuously between the pair of curved surfaces.

[0061] Positive current collector plate 42a and negative current collector plate 44a are respectively joined to the positive current collector exposed portion 56 (i.e., the portion of the positive current collector 52 that does not form a positive active material layer 54) and the negative current collector exposed portion 66 (i.e., the portion of the negative current collector 62 that does not form a negative active material layer 64) formed in such a way that they protrude outward from both ends of the winding axis of the wound electrode body 20.

[0062] As the positive current collector 52, examples include metallic materials with good conductivity such as aluminum, nickel, titanium, and stainless steel. Among these, aluminum (e.g., aluminum foil) is particularly preferred.

[0063] As a positive electrode active material contained in the positive electrode active material layer 54, LiNi can be cited as an example. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 Lithium transition metal complex oxides such as O4 and lithium transition metal phosphate compounds such as LiFePO4.

[0064] The positive electrode active material layer 54 may contain components other than the active material, such as conductive materials and binders. As conductive materials, carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite) may be appropriately used. As binders, for example, polyvinylidene fluoride (PVDF) may be used.

[0065] The positive electrode active material is typically granular. There is no particular limitation on the average particle size of the granular positive electrode active material; below 20 μm is suitable, typically 1 μm to 20 μm. It should be noted that in this specification, "average particle size" refers to the particle size (Dsize) that corresponds to 50% of the cumulative frequency from the smallest particle side in a particle size distribution based on a general laser diffraction scattering method. 50(also known as median particle size).

[0066] The negative current collector 62 is, for example, made of a metallic material with good conductivity, such as copper, copper-based alloys, nickel, titanium, or stainless steel. Copper (e.g., copper foil) is particularly preferred.

[0067] Examples of negative electrode active materials included in the negative electrode active material layer 64 include carbon materials such as graphite, hard carbon, and soft carbon. The negative electrode active material layer 64 may contain components other than the active material, such as binders and thickeners. For example, styrene-butadiene rubber (SBR) can be used as a binder. For example, carboxymethyl cellulose (CMC) can be used as a thickener.

[0068] The negative electrode active material is typically granular. There is no particular limitation on the average particle size of granular negative electrode active materials, but below 50 μm is appropriate, typically below 20 μm, for example, 1 μm to 20 μm.

[0069] From the viewpoint of energy density, the content of the electrode active material in the electrode active material layer 14 (i.e., the ratio of the electrode active material to the total mass of the electrode active material layer) is preferably approximately 50% by mass or more, for example, more preferably 80% to 99% by mass, and even more preferably 85% to 95% by mass. Furthermore, the content of the binder in the electrode active material layer 14 is preferably, for example, 0.1% to 15% by mass, more preferably 1% to 10% by mass. Additionally, when various additives such as thickeners are included, the content of the additives in the electrode active material layer 14 is preferably, for example, 7% by mass or less, more preferably 5% by mass or less.

[0070] The average thickness (average film thickness) of each single side of the positive electrode active material layer 54 and the negative electrode active material layer 64 is not particularly limited, and can be 10 μm to 300 μm or less, for example, 20 μm to 150 μm or less. The thickness of the positive electrode current collector 52 and the negative electrode current collector 62 can be approximately 5 μm to 20 μm, and preferably 8 μm to 15 μm.

[0071] As the separator 70, examples include porous sheets (membranes) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet can be a single-layer structure or a multi-layered structure (e.g., a three-layer structure with PP layers laminated on both sides of a PE layer). The separator 70 may be provided with a heat-resistant layer (HRL).

[0072] Figure 4 This is a schematic top view of the electrodes disclosed herein. Figure 5 This is a diagram illustrating the electrode. Figure 4The symbol X in the figure represents the direction of the long side of the electrode, and the symbol Y represents the direction of the width of the electrode. Figure 5 In this diagram, the symbol X represents the long side direction of the electrode, and the symbol Z represents the thickness direction of the electrode. Electrode 10 includes an electrode current collector 12 and an electrode active material layer 14 formed on the electrode current collector 12. The electrode 10 disclosed herein is as follows... Figure 4 As shown, the surface of the electrode active material layer 14 has a first groove 16 extending in the width direction (Y direction) of the electrode current collector 12 and a second groove 18 extending in the long side direction (X direction).

[0073] Multiple first grooves 16 are formed continuously from one end to the other in the width direction (Y direction). Considering their effect as electrolyte injection paths, the first grooves 16 are preferably formed such that at least one exists in each planar portion 24 during the construction of the wound electrode body 20. The first grooves 16 can be formed at a certain interval (spacing) or at different intervals (spacings). When the first grooves 16 are formed at different intervals, for example, since the circumference is shorter at the winding start side than at the winding end side during the construction of the wound electrode body 20, considering the above aspects, the interval of the first grooves 16 can be narrowed at the position corresponding to the winding start side of the wound electrode body 20 (i.e., the number of first grooves 16 formed increases), and the interval widens as it reaches the winding end side (i.e., the number of first grooves 16 formed decreases). By adjusting the interval of the first grooves 16 in this way, a wound electrode body 20 with appropriate electrolyte injection can be constructed.

[0074] When the average film thickness of the electrode active material layer 14 is set to t1 (μm) and the depth of the trench is set to t2 (μm), the first trench 16 is preferably a trench depth t2 that is 15% or more (e.g., 15% to 95%, typically 20% to 80%) of the average film thickness t1. It should be noted that the average film thickness of the electrode active material layer refers to the average film thickness of the portion of the electrode active material layer in which no trench is formed.

[0075] Furthermore, it is preferable that the groove depth t2 (μm) remains even when the wound electrode body 20 is constructed by winding the electrode 10. This is not particularly limited depending on the type of wound electrode body 20 being manufactured, but when the wound electrode body 20 is constructed and housed in the lithium-ion secondary battery 200, it is more preferable that the groove depth t2 (μm) exists even when a predetermined restraint load σ (N) is applied from both sides of the wide surface of the battery casing 31. For example, by applying the restraint load σ (N), the groove depth t2 (μm) in the electrode active material layer 14 and the thickness d (μm) of the separator 70 change respectively. The groove depth Δt when the restraint load σ (N) is applied is a value calculated from the Young's modulus G of the electrode active material layer 14, the groove depth t2 (μm) before the restraint load σ (N) is applied, and the restraint load σ (N), and is expressed as Δt2 = (σt2 / G). Furthermore, the thickness Δd of the spacer when the restraint load σ(N) is applied is a value calculated from the Young's modulus E of the spacer 70, the thickness d before the restraint load σ(N) is applied, and the restraint load σ(N), and is expressed as Δd = (σd / E). In this case, if the groove depth t2(μm) is greater than (Δt2 + Δd), a groove will remain. Therefore, a groove depth t2(μm) that satisfies t2 > (Δt2 + Δd) is preferred. That is, a groove depth t2(μm) that satisfies t2 > (Gσd / E(G - σ)) is preferred.

[0076] When the opening width of the first groove 16 is set to w1 (μm) and the bottom width is set to w2 (μm), the opening width w1 and the bottom width w2 can be the same length or different lengths. There is no particular limitation on the opening width w1 and the bottom width w2, but they can be 40μm to 250μm or 50μm to 200μm.

[0077] The cross-sectional shape of the first groove 16 is preferably a groove that remains in the bends 22a and 22b of the wound electrode body 20. More preferably, it is a groove that remains in the bends 22a and 22b from the beginning of the winding of the wound electrode body 20 to one turn (hereinafter also referred to as the innermost circumference 26). Figure 6A and Figure 6B A diagram illustrating the cross-sectional shape of the groove. Figure 6A and Figure 6B In this context, the symbol X represents the direction of the long side of the electrode, and the symbol Z represents the direction of the electrode's thickness. For example... Figure 5 , Figure 6A and Figure 6BAs shown, the cross-sectional shape of the first groove 16 formed in the electrode active material layer 14 can be approximately the same as the groove width w1 at the opening and the groove width w2 at the bottom (e.g., a rectangle), or the groove width w1 at the opening and the groove width w2 at the bottom can be different (e.g., a trapezoid), or the groove width w2 at the bottom can be 0 μm (e.g., an inverted triangle). Furthermore, when having an inverted triangle cross-sectional shape, it is preferable to form it with an angle θ of 90 degrees or more. It should be noted that the cross-sectional shape does not need to be formed only by straight lines; for example, it can also be a circular cross-sectional shape (e.g., a semicircle).

[0078] As the cross-sectional shape of the groove, when constructing the wound electrode body 20 as described above, it is preferable that the groove exists in the bending portions 22a and 22b. Figure 7 This diagram schematically illustrates the innermost circumference 26 of the wound electrode body 20 when the electrode 10 is constructed as a wound electrode body 20. When the radius of the inner circumference of the curved portion from the start of winding the electrode body 20 to the first turn is set as r, and the radius of the outer circumference is set as (r+t1), the circumference of the inner circumference of the curved portion is πr, and the circumference of the outer circumference is π(r+t1). The difference between the circumference of the inner circumference πr and the circumference of the outer circumference π(r+t1) is represented by πt1. When the curved portion has n grooves, the groove width w1 of each groove is reduced by (πt1 / n). Similarly, the difference between the bottom groove width w2 and the circumference of the outer circumference π(r+t1) is represented by π(t1-t2), and the groove width w2 of each groove is reduced by (π(t1-t2) / n). Therefore, the cross-sectional shape of the first groove 16 only needs to satisfy the relationship w1>(πt1 / n) and / or satisfy the relationship w2>(π(t1-t2) / n).

[0079] like Figure 6A As shown, when the cross-sectional shape of the groove is such that w1 < w2, as... Figure 7 When winding in this way, the opening side can be completely closed (i.e., w1 = 0), leaving only space on the bottom side. Even in this case, as long as there is space for injecting non-aqueous electrolyte, it functions as an injection path. That is, when manufacturing the wound electrode body 20, the cross-sectional shape of the groove with the opening closed (i.e., w1 = 0) can also be used.

[0080] The second groove 18 only needs to exist at least once on the surface of the electrode active material layer 14, extending in the long side direction (X direction) of the electrode current collector 12. The second groove 18 can exist in the center of the current collector in the width direction (Y direction) or at the end. From the viewpoint of shortening the liquid injection time, it is preferable to have one in the center where non-aqueous electrolytes are more difficult to penetrate. By forming at least one second groove 18, the non-aqueous electrolyte that penetrates through the first groove 16 penetrates the entire electrode 10 at a faster rate, thereby improving the impregnation of the electrode 10.

[0081] Multiple second grooves 18 may exist. When multiple second grooves 18 exist, they may be formed at a certain interval (spacing) or at different intervals (spacing). When formed at different intervals, for example, they may be formed such that more grooves exist at the ends relative to the central portion in the width direction of the electrode 10.

[0082] The dimensions of the second tank 18 can be appropriately set from the viewpoint of improving electrolyte impregnation and shortening injection time, and are not particularly limited. The tank depth t3 (μm) of the second tank 18 is preferably, for example, at least 1% (e.g., 1% to 70%, typically 5% to 40%) of the average film thickness t1. As mentioned above, the cross-sectional shape of the tank can be rectangular, trapezoidal, inverted triangular, or semi-circular, similar to that of the first tank 16. The tank width is not particularly limited and can be 40 μm to 250 μm, or 50 μm to 200 μm.

[0083] Here, refer to Figure 5 The upper, middle, and lower layers in this specification will be described. Here, the region where the first groove 16 is formed will be described, and the same applies to the region where the second groove 18 is formed. The region where the first groove 16 is formed is divided into three equal layers: an upper layer, a middle layer, and a lower layer. These layers are located sequentially along the thickness direction (Z direction) from the interface between the electrode active material layer 14 and the electrode current collector 12, namely the lower layer, the middle layer, and the upper layer. For example, the lower layer refers to the position from the interface between the electrode active material layer 14 and the electrode current collector 12 along the thickness direction (Z direction) up to approximately 33% of the thickness of the electrode active material layer 14. Similarly, the middle and upper layers are located at their respective positions after dividing the thickness of the electrode active material layer 14 into three equal parts. Furthermore, the electrode density (g / cm³) of the upper, middle, and lower layers in the region where the first groove 16 is formed is described. 3 Let d1, d2, and d3 be respectively. It should be noted that in this specification, "the area with the groove" refers to the area formed by drawing vertical lines along the thickness direction (Z direction) of the electrode active material layer 14, assuming that the width w1 of the opening and the width w2 of the bottom are the same length, as shown in the figure. When the width w1 of the opening and the width w2 of the bottom are different lengths, it refers to the area formed by drawing vertical lines along the thickness direction (Z direction) of the electrode active material layer 14, assuming that the longer of the width w1 of the opening and the width w2 of the bottom are different lengths.

[0084] Furthermore, the electrode densities of the upper, middle, and lower layers can be obtained, for example, by multiplying the true density of the electrode by the fill rate of that range (i.e., any one of the upper, middle, and lower layers). The true density of the electrode is, for example, a value calculated based on the density and proportion of the constituent components. The fill rate of that range can be calculated, for example, by binarizing the cross-sectional observation of the electrode active material layer using a scanning electron microscope (SEM). Specifically, the cross-sectional image is binarized using ImageJ, an open-source and public-domain image processing software, by setting the solid phase portion present in that range to white and the gas phase (void) portion to black. Thus, the area of ​​the solid phase portion (white portion) can be set as S1, and the area of ​​the void portion (black portion) can be set as S2, calculated by "S1 / (S1+S2)×100".

[0085] For the electrode 10 disclosed herein, the electrode densities of the upper and lower layers of the grooved region have a relationship of 0.8 < (d1 / d3) < 1.1. More preferably, the electrode densities of the upper and lower layers of the grooved region have a relationship of 0.9 < (d1 / d3) < 1.08, and even more preferably, a relationship of 0.95 < (d1 / d3) < 1.08. When there is no difference in electrode density between the upper and lower layers, the value of (d1 / d3) is 1. That is, in the electrode 10 disclosed herein, as a characteristic, although grooves are formed, the difference in electrode density between the upper and lower layers of the groove is small (i.e., (d1 / d3) is close to 1). The electrode 10 described above can be suitably implemented by using a gas-phase controlled wetted powder as described later. Although not particularly limited, by forming the groove in a thin film state with a suitable solvent (liquid phase) and gas phase, the active material (solid phase) can move to the part where the gas phase is slightly reduced, and densification (local density increase) can be suppressed.

[0086] Based on the above configuration, since the formed groove is not densified, the impregnation of the electrode 10 can be appropriately improved.

[0087] The non-aqueous electrolyte can be the same as that used in conventional lithium-ion secondary batteries. Typically, a solution containing an auxiliary salt (supporting salt) in an organic solvent (non-aqueous solvent) can be used. As the non-aqueous solvent, there are no particular limitations on the use of organic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones. Specifically, for example, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene monofluorocarbonate (MFEC), ethylene difluorocarbonate (DFEC), methyl monofluorodifluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC) are preferred non-aqueous solvents. One such non-aqueous solvent can be used alone, or two or more can be used in appropriate combinations. As the auxiliary salt, for example, lithium salts such as LiPF6, LiBF4, and LiClO4 can be used appropriately. The concentration of the auxiliary salt is not particularly limited, but is preferably around 0.7 mol / L to 1.3 mol / L.

[0088] It should be noted that, as long as the effect of the present invention is not significantly impaired, the above-mentioned non-aqueous electrolyte may contain components other than the above-mentioned non-aqueous solvent and auxiliary salt, such as gas generators, film forming agents, dispersants, thickeners and other additives.

[0089] <Methods for manufacturing electrodes>

[0090] like Figure 8 As shown, the electrode manufacturing method disclosed herein generally includes the following six steps: (1) a step of preparing a wetted powder (electrode material) (S1); (2) a step of forming a coating film composed of the wetted powder (S2); (3) a step of forming a first groove (S3); (4) a step of forming a second groove (S4); (5) a step of drying the coating film to form an electrode active material layer (S5); and (6) a step of pressurizing the electrode active material layer (S6). The method is characterized in that the first and second grooves are formed on the coating film before the drying step. Therefore, the other steps are not particularly limited and can be configured in the same way as conventional manufacturing methods. Each step will be described below.

[0091] Figure 9 This is a block diagram schematically illustrating a simplified configuration of the electrode manufacturing apparatus of the electrode manufacturing method disclosed herein. Figure 9The electrode manufacturing apparatus 100 shown typically includes: a film-forming section 120, which forms a coating 32 made of electrode material 30 on the surface of the electrode current collector 12 while conveying it along its long side from a supply chamber (not shown); a coating processing section 130, which forms a first groove 16 and a second groove 18 on the surface of the coating 32; a drying section 140, which appropriately dries the coating 32 to form an electrode active material layer 14; and a pressurizing section 150, which pressurizes the dried electrode active material layer 14 with an appropriate pressure. These components are arranged sequentially along a predetermined conveying path.

[0092] <Preparation Process>

[0093] Electrode material 30 can be prepared by mixing the aforementioned electrode active material, binder, other additives, and other solid materials with a solvent using a conventionally known mixing apparatus. The solid components (i.e., solid materials other than the solvent) can be appropriately selected from the aforementioned materials. Examples of such mixing apparatus include planetary mixers, ball mills, roller mills, kneaders, and homogenizers.

[0094] Electrode material 30 can be obtained in the form of paste, slurry, and granules, but granules, especially granules in a wet state containing a small amount of solvent (wet powder), are suitable for the purpose of forming an electrode active material layer on the electrode current collector 12 in the electrode manufacturing apparatus 100 disclosed herein. It should be noted that the classification of the morphology of wet powders in this specification adopts the four classifications described in Capes CE's "Particle Size Enlargement" (Elsevier Scientific Publishing Company, 1980), which are now known, and the wet powders disclosed herein have been clearly defined. Specifically, as described below.

[0095] The existence forms (filling states) of the solid components (solid phase), solvent (liquid phase), and voids (gas phase) in the aggregated particles that constitute wet powder can be classified into four types: "pendulum state", "cable state", "capillary state" and "slurry state".

[0096] Here, as Figure 10As shown in (A), the "pendulum state" is a state in which the solvent (liquid phase) 3 exists discontinuously, bridging the active material particles (solid phase) 2 in the condensed particles 1. The active material particles (solid phase) 2 can exist in a continuously connected state. As shown, the content of solvent 3 is relatively low, resulting in most of the voids (gas phase) 4 present in the condensed particles 1 existing continuously, forming interconnecting pores that communicate with the outside. Thus, the following characteristic can be observed: in the pendulum state, a continuous layer of solvent covering the entire outer surface of the condensed particles 1 is not visible during electron microscopy (SEM observation).

[0097] In addition, such as Figure 10 As shown in (B), the "ribbon state" is a state in which the solvent content in the condensed particles 1 is relatively higher than that in the pendulum state, and it is a state in which the solvent (liquid phase) 3 is continuously present around the active material particles (solid phase) 2 in the condensed particles 1. However, since the amount of solvent is still very small, the active material particles (solid phase) 2 exist in an interconnected (continuous) state, just like in the pendulum state. On the other hand, although the proportion of connecting pores in the voids (gas phase) 4 present in the condensed particles 1 that are connected to the outside is slightly reduced, the proportion of discontinuous isolated voids tends to increase, but the presence of connecting pores is confirmed.

[0098] The banded state is a state between the pendulum state and the capillary state. In the banded state I, which is close to the pendulum state (i.e., the state with less solvent) and the banded state II, which is close to the capillary state (i.e., the state with more solvent), the banded state I still includes the state in which the solvent layer cannot be seen on the outer surface of the condensed particles 1 in electron microscopy.

[0099] like Figure 10 As shown in (C), the "capillary state" is characterized by an increased solvent content in condensed particles 1, with the solvent amount in condensed particles 1 approaching saturation. A sufficient amount of solvent 3 continuously exists around active material particles 2, resulting in active material particles 2 existing in a discontinuous state. Due to the increased solvent amount, almost all voids (e.g., 80 vol% of the total void volume) in condensed particles 1 exist as isolated voids, and the proportion of voids in condensed particles 1 also decreases.

[0100] like Figure 10 As shown in (D), the "slurry state" is the state in which the active material particles 2 are already suspended in the solvent 3, and thus cannot be called aggregated particles. There is almost no gas phase.

[0101] Wet powder film formation using wetted powder has been known for a long time, but in previous wetted powder film formation methods, the wetted powder was continuously formed as a liquid phase throughout the entire powder. Figure 10 The “capillary state” is shown in (C).

[0102] In contrast, the wet powder disclosed herein is a wet powder formed by at least 50% aggregated particles 1 in the above-described pendulum state or cord state (especially cord state I). Preferably, it has a morphological feature of (2) a layer composed of the above-described solvent that is not visible under an electron microscope covering the entire outer surface of the aggregated particles, achieved by controlling the gas phase.

[0103] Hereinafter, a wetted powder having the above-disclosed (1) and (2) requirements will be referred to as a "vapor-controlled wetted powder".

[0104] It should be noted that the gas-phase controlled wetted powder disclosed herein preferably has at least 50% of its aggregated particles having the above-mentioned requirements (1) and (2).

[0105] Vapor-phase controlled wetting powder can be manufactured using conventional capillary-state wetting powder manufacturing processes. That is, wetting powder as an electrode material (electrode composite material) can be manufactured by adjusting the amount of solvent and solid components (active material particles, binder resin, etc.) in a manner that increases the proportion of the gas phase more than in the past, specifically by forming a large number of continuous voids (connecting pores) from the inside to the outside of the aggregated particles.

[0106] In addition, in order to achieve liquid bridges between active substances with minimal solvent, it is preferable that the surface of the powder material used has appropriate affinity with the solvent used.

[0107] As a preferred gas-phase controlled wetted powder disclosed herein, the following wetted powder is preferably selected: the three-phase state observed by an electron microscope is a pendulum state or a banded state (especially a banded state I), and the "ratio of true density Y to loose bulk density X: Y / X" calculated from the loose bulk density X (g / mL) and the true density Y (g / mL) of the raw material matrix is ​​1.2 or more, preferably 1.4 or more (and further 1.6 or more), and preferably 2 or less, wherein the loose bulk density X is the measured bulk density obtained by loading the obtained wetted powder into a container of a specified volume without applying force and leveling it, and the true density Y of the raw material matrix is ​​the density calculated from the composition of the wetted powder assuming the absence of a gas phase.

[0108] The target wet powder can be manufactured by wet granulation using the materials described above. Specifically, for example, wet powder (i.e., an aggregate of agglomerated particles) is manufactured by mixing the materials using a stirred granulator (such as a planetary mixer). Such a stirred granulator typically includes a cylindrical mixing container, rotating blades housed inside the mixing container, and a motor connected to the rotating blades (also called paddles) via a rotating shaft.

[0109] In preparation step S1, among the aforementioned materials, the materials other than the solvent (solid components) are first pre-mixed and subjected to solvent-free dry dispersion treatment. This results in a highly dispersed state of the solid components. Subsequently, preferably, a solvent and other liquid components (e.g., liquid binders) are added to the dispersed mixture for further mixing. This allows the production of a moist powder obtained by properly mixing the solid components.

[0110] Specifically, electrode active materials and various additives (binder resins, thickeners, conductive materials, etc.) as solid components are added to the mixing container of a stirred granulator. A driving motor rotates the blades at a speed of approximately 2000 rpm to 5000 rpm for 1 to 60 seconds (e.g., 2 to 30 seconds) to create a mixture of the solid components. Next, an appropriate amount of solvent, measured to be at least 70%, more preferably 80% or more (e.g., 85 to 98%) of solid content, is added to the mixing container, and stirred granulation is performed. Without particular limitation, the rotating blades are further rotated at a speed of approximately 100 rpm to 1000 rpm for approximately 1 to 60 seconds (e.g., 2 to 30 seconds). This allows the materials in the mixing container to be mixed with the solvent to create a wet granulated body (wet powder). It should be noted that the agglomeration of the wet powder can be prevented by intermittently stirring for approximately 1 to 5 seconds at a speed of approximately 1000 rpm to 3000 rpm. The particle size of the obtained granules can be, for example, 50 μm or more (e.g., 100 μm to 300 μm).

[0111] For the gas-phase controlled wetted powder disclosed herein, the solid, liquid and gas phases form a pendulum state or a band state (preferably band I state), with a solvent content so low that the solvent layer is not visible on the outer surface of the condensed particles during electron microscopy (e.g., solvent fraction of about 2 to 15%, or 3 to 8%), while the gas phase portion is relatively large.

[0112] To achieve this form, various treatments and operations that increase the gas phase can be introduced in the aforementioned preparation step S1. For example, excess solvent can be evaporated by exposing the granules to a dry gas atmosphere (air or inactive gas) approximately 10 to 50 degrees Celsius higher than room temperature during or after stirring granulation. Furthermore, to promote the formation of aggregated particles in a pendulum or banded state with low solvent content, compression granulation with strong compression can be used to allow active material particles and other solid components to adhere to each other. For example, a compression granulator can be used where powdered raw materials are fed vertically between a pair of rollers while compression is applied between the rollers.

[0113] <Film Forming Process>

[0114] In the manufacturing method disclosed herein, a coating film 32 is formed in the gaseous phase (void) state of the residual electrode material 30. The coating film 32 formed from the electrode material 30 can be formed, for example, in a manner such as... Figure 9 The film-forming process is carried out in the film-forming section 120 shown schematically. As shown, the film-forming section 120 continuously includes a plurality of transfer rollers. In this example, it includes a first transfer roller 122 opposite to the supply roller 121, a second transfer roller 123 opposite to the first transfer roller, and a third transfer roller 124 opposite to the second transfer roller and also opposite to the support roller 125.

[0115] By adopting this configuration, the gaps G1 to G4 between the rollers can be made to have different dimensions, thus forming a suitable coating film while maintaining the interconnected pores of the wet powder. This will be described in detail below.

[0116] In the film-forming section 120, the outer peripheral surface of the supply roller 121 and the outer peripheral surface of the first transfer roller 122 are opposite to each other. This pair of supply rollers 121 and first transfer rollers 122 are as follows: Figure 9 The arrows indicate that the rotation is in the opposite direction. Furthermore, the supply roller 121 and the first transfer roller 122 have a gap G1 with a predetermined width (thickness) corresponding to the desired thickness of the coating 32 formed on the electrode current collector 12. The thickness of the coating 32, composed of the electrode material 30 attached to the surface of the first transfer roller 122, can be controlled according to the size of the gap G1. Additionally, by adjusting the size of the gap G1, the force compressing the electrode material 30 passing between the supply roller 121 and the first transfer roller 122 can also be adjusted. Therefore, by obtaining a larger gap size, film formation can be performed while maintaining the electrode material 30 (specifically, each condensed particle) in a gaseous state.

[0117] The second transfer roller 123 and the third transfer roller 124 form a film by adjusting the gas phase state of the electrode material 30 compressed by the supply roller 121 and the first transfer roller 122. The second transfer roller 123 and the third transfer roller 124... Figure 9 The arrows indicate that the rollers rotate in the opposite direction. In addition, a second gap G2 is provided between the first transfer roller 122 and the second transfer roller 123, and a third gap G3 is provided between the second transfer roller 123 and the third transfer roller 124. By adjusting the gaps G2 and G3, a coating film 32 with the desired thickness and gas phase state can be manufactured.

[0118] The support roller 125 serves to transfer the electrode current collector 12 to the third transfer roller 124. The third transfer roller 124 and the support roller 125 are as follows: Figure 9 The arrow indicates that it rotates in the opposite direction. In addition, a fourth gap G4 with a predetermined width (thickness) is provided between the third transfer roller 124 and the support roller 125, and the thickness of the coating film 32 formed on the electrode current collector 12 can be controlled according to the size of the gap G4.

[0119] The supply roller 121, the first transfer roller 122, the second transfer roller 123, the third transfer roller 124, and the support roller 125 are connected to their respective independent drive devices (motors) (not shown), and therefore can rotate at different speeds. Specifically, the first transfer roller 122 rotates faster than the supply roller 121, the second transfer roller 123 rotates faster than the first transfer roller 122, the third transfer roller 124 rotates faster than the second transfer roller 123, and the support roller 125 rotates faster than the third transfer roller 124.

[0120] Roller film formation can be achieved by gradually increasing the rotational speed between the rotating rollers along the current collector conveying direction (travel direction).

[0121] The gap dimensions are set such that the first gap G1 is relatively the largest, and the second gap G2, the third gap G3, and the fourth gap G4 gradually decrease in size (G1 > G2 > G3 > G4). Since the gaps G1 to G4 are set to gradually decrease along the conveying direction (travel direction) of the electrode current collector 12, film formation can be performed while adjusting the state of the gas phase (void) of the coating 32. The dimensions (widths) of each gap G1 to G4 are not particularly limited; they can be set to a gap size such that the average film thickness of the coating 32 is 10 μm to 300 μm (e.g., 20 μm to 150 μm).

[0122] Partitions (not shown) may be provided at both ends of the supply roller 121 and the first transfer roller 122 in the width direction. The partitions can hold the electrode material 30 on the supply roller 121 and the first transfer roller 122, and the width of the coating 32 formed on the electrode current collector 12 is defined by the distance between the two partitions. The electrode material 30 is supplied between the two partitions through a feed port (not shown) or the like.

[0123] The dimensions of the supply roller 121, the first transfer roller 122, the second transfer roller 123, the third transfer roller 124, and the support roller 125 are not particularly limited and can be the same as those of conventional film-forming apparatuses; for example, their diameters can be 50 mm to 500 mm respectively. The diameters of these supply rollers 121, the first to third transfer rollers 122, 123, 124, and the support roller 125 can be the same or different. Furthermore, the width of the coating 32 formed can be the same as that of conventional film-forming apparatuses and can be appropriately determined based on the width of the electrode current collector 12 to which the coating 32 is to be formed.

[0124] The material of the outer peripheral surfaces of the supply roller 121, the first transfer roller 122, the second transfer roller 123, the third transfer roller 124, and the support roller 125 can be the same as the material of the rotating rollers in conventional film-forming apparatuses, for example, SUS steel, SUJ steel, etc. For the material of the outer peripheral surfaces of the supply roller 121 and the first to third transfer rollers 122, 123, 124 that are in direct contact with the electrode material 30, in order to prevent the generation of metal foreign matter, ceramics such as zirconium oxide, alumina, chromium nitride, aluminum nitride, titanium dioxide, and chromium oxide are more preferred.

[0125] It should be explained that Figure 10 Although the arrangement of the supply roller 121, the first transfer roller 122, the second transfer roller 123, the third transfer roller 124 and the support roller 125 is shown as an example, the arrangement of each roller is not limited thereto.

[0126] <First tank forming process>

[0127] The formation of the first groove 16 of the coating 32 extending in a direction orthogonal to the conveying direction can, for example, be achieved by using a method such as Figure 9 The process is performed using the first embossing roller 132A and the support roller 132B shown. The first embossing roller 132A has a protrusion that extends parallel to the axis of rotation along its outer circumferential surface.

[0128] In the electrode manufacturing method disclosed herein, a first groove forming step S3 is performed on a coating film 32 formed in a state of residual voids (gas phase). The average porosity (gas phase ratio) of the coating film 32 is preferably at least 1% or more, for example, it can be 1% to 55%, typically 5% to 55%. By forming the first groove 16 in a state of residual gas phase, the ductility is improved, and therefore the coating film 32 can be given the desired groove with a smaller load than before. In addition, even when a load is applied to form the first groove 16, the first groove 16 can be formed on the surface of the coating film 32 without causing a local increase in density (densification).

[0129] It should be noted that, in this specification, the "average porosity (vapor phase ratio) of the coating" can be calculated, for example, by cross-sectional observation of the electrode active material layer based on electron microscopy (SEM). The cross-sectional image is binarized using ImageJ, a well-known image processing software that is open-source and in the public domain, by setting the solid or liquid phase portion to white and the vapor phase (void) portion to black. Thus, the area of ​​the portion containing the solid or liquid phase (white portion) can be set as S1, and the area of ​​the void portion (black portion) as S2, and "S2 / (S1+S2)×100" can be calculated. This is taken as the porosity of the coating before drying. Multiple cross-sectional SEM images are obtained (e.g., 5 or more), and the average of the above porosity is taken as the "average porosity (vapor phase ratio) of the coating" before drying. It should be noted that the "average porosity (vapor phase ratio) of the coating" does not include the depressions (i.e., macroscopic voids) formed during the unevenness formation process.

[0130] The first embossing roller 132A has a protrusion extending parallel to the rotation axis for forming a predetermined pattern on the surface of the coating film 32. The support roller 132B is a roller that supports the conveyed electrode current collector 12 while being conveyed along the conveying direction. The first embossing roller 132A and the support roller 132B are arranged in opposite positions. The coating film 32 on the electrode current collector 12 passes through the gap between the first embossing roller 132A and the support roller 132B, thereby transferring the protrusion of the first embossing roller 132A to the surface of the coating film 32, thereby forming a first groove 16 on the surface of the coating film 32. The linear pressure of the first embossing roller 132A can vary depending on the desired groove depth and other factors, and is therefore not particularly limited, but can be set approximately 15 N / cm to 75 N / cm, for example, 25 N / cm to 65 N / cm.

[0131] The first groove 16 needs to be a continuous groove from one end to the other in the width direction of the electrode current collector 12. That is, the first groove 16 needs to be a groove that is not discontinuous from one end to the other due to the generation of foreign matter or poor groove formation. A continuous groove from one end to the other in the width direction of the electrode current collector 12 can be achieved by the electrode manufacturing method disclosed herein.

[0132] The first groove 16 can be formed at a certain interval or at different intervals. Preferably, when constructing the wound electrode body 20, it is formed such that at least one first groove 16 exists in the planar portion 24. Since it varies depending on the circumference of the constructed wound electrode body 20, there is no particular limitation, but when the first groove 16 is formed at a certain interval, it is preferably 10 μm to 5 mm, more preferably 50 μm to 4 mm, and even more preferably 100 μm to 3 mm. When the first groove 16 is formed at different intervals, it is preferable to adjust the interval so that more first grooves 16 are formed in the region corresponding to the winding start side of the wound electrode body 20.

[0133] <Second tank forming process>

[0134] In the second groove forming process S4, a second groove 18 extending along the conveying direction is formed on the coating 32 that was applied to the first groove 16 in the first groove forming process S3. The formation of the second groove 18 can be performed, for example, by using a second embossing roller 134A and a support roller 134B as shown in the figure. The second embossing roller 134A has a protrusion perpendicular to the rotation axis along its outer peripheral surface. The linear pressure of the second embossing roller 134A is not particularly limited, as it can vary depending on the desired groove depth and shape, and can generally be set to approximately 15 N / cm to 75 N / cm, for example, 25 N / cm to 65 N / cm.

[0135] It is acceptable to form at least one second groove 18, or multiple second grooves 18 may be formed. When multiple second grooves 18 are formed, they may be formed at a certain interval (spacing) or at different intervals (spacing). When formed at a certain interval, the spacing is 500 μm or more, and more preferably 1 mm or more.

[0136] By utilizing the electrode manufacturing method disclosed herein to form grooves, it is possible to form continuous grooves from one end to the other without densifying the grooves. While not particularly limited, the reasons are as follows.

[0137] In conventional techniques, grooves are formed by pressing a mold with protrusions onto a dried coating (electrode active material layer). Alternatively, grooves are formed by machining the surface of the dried coating using laser processing or by cutting the surface of the electrode active material layer with a rotary tool. When forming grooves using laser processing, controlling the thinning portion of the coating (typically the end in the width direction of the current collector) is very difficult when aiming to form a continuous groove from one end to the other, posing a risk of penetrating the current collector. When forming grooves using a rotary tool, a relatively large load is applied to the dried, hardened active material layer during cutting, which may cause cracks or fissures in the electrode, and it is difficult to form grooves of the desired size.

[0138] That is, for the groove formed using conventional techniques, the bottom of the groove and the adjacent area of ​​the groove are densified, and the groove becomes discontinuous due to foreign matter generated when processing the surface of the electrode active material layer.

[0139] In contrast, in the electrode manufacturing method disclosed herein, as described above, the first and second groove forming steps are performed on a coating film 32 composed of wetted powder (vapor-controlled wetted powder) in a pendulum state or a ribbon state (preferably ribbon I state). The aforementioned coating film 32 is as follows... Figure 10 As shown in (A) and (B), there are many gas phases 4, which form interconnected pores within the coating film 32. Additionally, the active material particles 2 are bridged together by the solvent 3, i.e. Figure 10 In the case of (C), the capillary state is different, and the active material particles 2 are not completely covered by the solvent 3. Therefore, during the formation processes of the first and second tanks, the gas phase 4 of the coating film 32 is difficult to isolate under applied pressure. Furthermore, due to the low resistance between the active material particles 2 and the solvent 3, the active material particles 2 are easy to move. As a result, the coating film 32, composed of gas-phase controlled wetted powder, exhibits excellent spreadability.

[0140] As described above, by performing a trench forming process (first trench forming process S3 and second trench forming process S4) on the coating 32 with excellent ductility before the drying process S5, the desired trench can be formed with a smaller load. Furthermore, the trenches formed by the first trench forming process disclosed herein, while having a certain degree of high density, are formed with residual connecting holes, and form a continuous trench from one end to the other. Therefore, the electrode having the first trench 16 and the second trench 18 exhibits excellent electrolyte impregnation.

[0141] The first and second groove forming processes can be implemented in a manner that increases the surface area of ​​the coating film 32. In particular, in the coating film 32 formed using vapor-phase controlled wetting of powder, the average surface area of ​​the reference region (Lcm×Bcm, where L and B are integers of 3 or more) measured at n (n is an integer of 5 or more) distinct points in the coating film can reach 1.05×L×Bcm. 2 The above (preferred size 1.1×L×Bcm) 2 above).

[0142] Furthermore, the coating processing unit 130 may further include a mechanism for adjusting the film thickness and vapor phase state of the coating 32 using a pressure roller 136A and a support roller 136B. The pressure roller 136A is a roller used to compress the coating 32 by pressing it in the film thickness direction, and the support roller 136B is a roller used to support and convey the incoming electrode current collector 12 in the conveying direction. The pressure roller 136A and the support roller 136B are positioned opposite each other. The coating 32 formed (film-forming) on ​​the incoming electrode current collector 12 can be pressurized and compressed to a degree that, for example, does not produce isolated voids. Therefore, the vapor phase state of the coating 32 can be adjusted in a manner more suitable for implementing unevenness formation. The appropriate pressure of the pressure roller 136A and the support roller 136B can vary depending on the thickness and density of the target coating (electrode active material layer), and is therefore not particularly limited. For example, it can be set to 0.01MPa to 100MPa, or approximately 0.1MPa to 70MPa.

[0143] <Drying Process>

[0144] like Figure 9 As shown, the electrode manufacturing apparatus 100 of this embodiment has a drying chamber 142 equipped with a heater (not shown) disposed downstream of the coating processing section 130 in the conveying direction as a drying section 140. The drying section 140 dries the coating 32 formed on the electrode current collector 12 to form an electrode active material layer. The drying method is not particularly limited; for example, hot air drying, infrared drying, etc., are examples.

[0145] The drying temperature (temperature inside the drying oven) in the drying process S4 varies depending on the type of solvent used and the solid content of the coating 32 (the proportion of solid components in the electrode material), and therefore is not particularly limited. For example, it is preferably set to 80°C or higher, typically 100°C or higher, and further to 120°C or higher. The upper limit of the drying temperature is not particularly limited, but from the viewpoint of preventing oxidation of the electrode current collector 12, it is preferably set to 200°C or lower, typically 190°C or lower, and further to 180°C or lower.

[0146] From the perspective of improving productivity, the conveying speed in the drying process S5 is preferably set to 1 m / min or more, and more preferably 3 m / min or more. If the conveying speed is too fast, cracks are easily generated in the coating film 32. Therefore, from the above perspective, it can be set to 15 m / min or less, 10 m / min or less, or 8 m / min or less.

[0147] Generally, when conventional coatings made of paste-like electrode materials are dried at high temperatures (e.g., 100°C or higher) and high conveying speeds (e.g., 8 m / min or higher), a phenomenon occurs where the binder with low density segregates to the surface side, i.e., migration. When this migration occurs, the adhesion between the electrode current collector 12 and the electrode active material layer 14 decreases, and the electrode active material layer 14 is easily peeled off from the electrode current collector 12 during the manufacturing process and repeated charge-discharge cycles. In contrast, in the electrode manufacturing method disclosed herein, the electrode active material layer manufactured using gas-phase controlled wetting powder is divided into two layers, an upper layer and a lower layer, in an even direction from the surface of the active material layer to the thickness of the electrode current collector, and the concentrations (mg / L) of the binder resin in the upper and lower layers are set as C1 and C2, respectively, with a relationship of 0.8 ≤ (C1 / C2) ≤ 1.2. That is, the electrode active material layer 14 can be an electrode active material layer 14 in which binder segregation (migration) is less likely to occur between the upper and lower layers.

[0148] By using vapor-phase controlled wetting powder as electrode material 30, the solid content can be significantly increased compared to coatings made of slurry electrode materials. Therefore, even by shortening the drying process S5 (e.g., by setting a higher temperature in the drying oven and a faster conveying speed in drying process S5), migration can be suppressed. Thus, according to the electrode manufacturing method disclosed herein, durable (high-quality) electrodes for secondary batteries can be manufactured without sacrificing productivity.

[0149] <Pressure Process>

[0150] After the drying process S5, a pressing process S6 is performed in the pressing section 150 to adjust the unit area weight and electrode density of the electrode active material layer 14. The pressing process S6 can be performed using a rolling mill or a flat calender as the pressing device 152, and is carried out according to conventionally known methods.

[0151] The pressurization performed here is performed in a manner similar to the pressurization of the first and second grooves formed in step S3 and step S4. The pressurization pressure varies depending on the thickness of the coating 32 and the groove depths of the first and second grooves 16, and is therefore not particularly limited. For example, in roll pressing based on a rolling mill, a linear pressure of approximately 1 ton / cm to 5 ton / cm is preferably set. In the case of pressurization based on a flat calender, for example, a pressure of approximately 100 to 500 MPa is preferably set. By adjusting the pressurization pressure to the above-mentioned levels, an electrode 10 with grooves that improve electrolyte impregnation can be appropriately manufactured.

[0152] Thus, a strip-shaped electrode for manufacturing secondary batteries is obtained. The strip-shaped electrode manufactured in this way can be used in the construction of the non-aqueous electrolyte secondary batteries disclosed herein.

[0153] The electrode 10 thus manufactured and the lithium-ion secondary battery 200 constructed using the electrode 10 can be used for various applications. Preferred applications include power supplies for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The lithium-ion secondary battery 200 can also be used in the form of a battery pack consisting of multiple batteries connected in series and / or in parallel.

[0154] The following describes embodiments related to the electrode manufacturing method disclosed herein, but it is not intended to limit the technology disclosed herein to the solutions shown in these embodiments.

[0155] <Example 1>

[0156] A gas-phase controlled wetted powder, which can be preferably used as a positive electrode material, is prepared, and then a positive electrode active material layer is formed on a copper foil using the prepared wetted powder (positive electrode material).

[0157] In this experimental example, the average particle size (D) based on laser diffraction scattering was used. 50 LiNi is a 20 μm lithium transition metal oxide. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is used as the positive electrode active material, polyvinylidene fluoride (PVDF) is used as the binder, acetylene black is used as the conductive material, and NMP is used as the non-aqueous solvent.

[0158] First, a solid component consisting of 90 parts by mass of the above-mentioned positive electrode active material, 2 parts by mass of PVDF, and 8 parts by mass of acetylene black is added to a mixing granulator (planetary mixer or high-speed mixer) for mixing.

[0159] Specifically, the mixing blades were set to rotate at 4500 rpm in a stirred granulator with mixing blades, and the mixture was stirred and dispersed for 15 seconds to obtain a powder material mixture composed of the above-mentioned solid components. NMP was added as a solvent to the obtained mixture to achieve a solid content of 90% by weight, and the mixture was stirred and granulated at 300 rpm for 30 seconds for compounding. Then, it was stirred at 4500 rpm for 2 seconds for micronization. This produced the wet powder (positive electrode material) of this experimental example.

[0160] Next, the gas-phase controlled wetted powder (positive electrode material) obtained above is supplied to the film forming section of the electrode manufacturing apparatus to form a coating film on the surface of a separately prepared positive electrode current collector made of aluminum foil with an average film thickness of 100 μm.

[0161] The coating is conveyed to the coating processing unit, where it is transferred using an embossing roller to form multiple first grooves and second grooves orthogonal to the first grooves. The first grooves are formed with a depth of 80 μm and a spacing of 2.5 mm. The second groove is formed as a single groove with a depth of 50 μm. The coating is then dried in the drying unit to obtain an electrode having an electrode (positive electrode) active material layer on an aluminum foil.

[0162] <Comparative Example 1>

[0163] As a comparison, an electrode without grooves was prepared. Specifically, the electrode material was mixed in the same manner as in Example 1, and a coating was formed on the surface of a separately prepared positive current collector made of aluminum foil. The coating was dried in a drying section to obtain an electrode having an electrode (positive electrode) active material layer on the aluminum foil.

[0164] <Comparative Example 2>

[0165] As a comparison, the first and second grooves were formed on the dried and pressurized electrode using a rotary cutter, with the same groove size as in Example 1. Specifically, the electrode material was mixed as in Example 1, and a coating was formed on the surface of a separately prepared positive current collector made of aluminum foil. The coating was dried in a drying section to obtain an electrode having an electrode (positive electrode) active material layer on the aluminum foil. A plurality of first grooves and second grooves orthogonal to the first grooves were formed on the surface of the electrode using a rotary cutter. It should be noted that the depth and spacing of the grooves were the same as in Example 1.

[0166] The surfaces of the electrodes of Example 1 and Comparative Example 2 were observed using a scanning electron microscope (SEM). The groove in Example 1 was formed continuously from one end to the other. On the other hand, the groove in Comparative Example 2 had foreign matter remaining at multiple locations, resulting in a discontinuous groove.

[0167] The impregnation properties of the electrolyte were tested in Examples 1, 1, and 2. Specifically, the electrodes of each example were clamped together with two glass slides along their thickness direction, confining both ends of the long side of the current collector, to prepare the sample. At 25°C, a portion of the unconstrained part (the lower side in the width direction) of each glass slide was immersed in a non-aqueous electrolyte, and the penetration of the non-aqueous electrolyte was observed. It should be noted that the non-aqueous electrolyte was a solution obtained by dissolving LiPF6 (as an auxiliary salt) at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a 1:1:1 volume ratio.

[0168] The time for the non-aqueous electrolyte to be immersed in the entire electrode was 1 minute and 30 seconds in Example 1, 40 minutes in Comparative Example 1, and 22 minutes in Comparative Example 2. In Example 1, the non-aqueous electrolyte was injected into the entire tank after 10 seconds of immersion, and it was observed that the non-aqueous electrolyte was immersed in the entire tank. In Comparative Example 2, although a tank was formed, the immersion time of the non-aqueous electrolyte was much longer than that in Example 1. It is speculated that this is because foreign matter was generated at multiple locations in the tank of Comparative Example 2, making the tank discontinuous and thus less effective as an injection path. In addition, it is speculated that because the tank was densified, it was difficult to immerse the non-aqueous electrolyte in the tank.

[0169] That is, the surface portion of the electrode active material layer has a plurality of first grooves extending in the width direction of the current collector and at least one second groove extending in the long side direction. The first grooves are formed continuously from one end to the other. The region where the first and second grooves are formed is divided into three layers—an upper layer, an intermediate layer, and a lower layer—equally in the direction from the surface of the electrode active material layer to the thickness of the electrode current collector. The electrode density (g / cm³) of the upper layer, the intermediate layer, and the lower layer of the groove is specified. 3 An electrode with a relationship of 0.8 < (d1 / d3) < 1.1 when d1, d2, and d3 are respectively set as d3 can be said to be an electrode with appropriately improved impregnation.

[0170] The present invention has been described in detail above with specific examples, but these are merely illustrative and do not limit the scope of protection claimed. The technology contained in the scope of protection includes various modifications and alterations to the specific examples described above.

Claims

1. An electrode for a secondary battery, either of a positive electrode and a negative electrode of a nonaqueous electrolyte secondary battery, comprising an electrode current collector in a long sheet shape, and an electrode active material layer formed on the electrode current collector, the electrode active material layer is formed of a wet powder having a solid content rate of 85% to 98% by weight, a plurality of first grooves extending in a width direction of the electrode current collector and a plurality of second grooves extending in a longitudinal direction of the electrode current collector and formed in a manner orthogonal to the first grooves are provided in a surface portion of the electrode active material layer, the first grooves are formed in a manner continuous from one end portion to another end portion, at least one of the second grooves is formed in a central portion in the width direction of the electrode current collector, wherein, In the region where the first groove and the second groove are formed, the thickness direction from the surface of the electrode active material layer to the electrode current collector is equally divided into three layers of an upper layer, an intermediate layer, and a lower layer, and the electrode densities of the upper layer, the intermediate layer, and the lower layer of the first groove are respectively d1, d2, and d3, and the electrode density has a relationship of 0.8 < (d1 / d3) < 1.1 3 .

2. The electrode for a secondary battery according to claim 1, wherein a plurality of the second grooves are formed in the longitudinal direction of the electrode current collector.

3. A nonaqueous electrolyte secondary battery characterized by comprising: A nonaqueous electrolyte secondary battery comprising a flat-shaped wound electrode body in which a positive electrode having a positive electrode active material layer on a long sheet-shaped positive electrode current collector and a negative electrode having a negative electrode active material layer on a long sheet-shaped negative electrode current collector, and a separator are wound around a winding axis, and a nonaqueous electrolyte, at least one of the positive electrode and the negative electrode uses the electrode according to claim 1 or 2.

4. A manufacturing method of an electrode for a nonaqueous electrolyte secondary battery, the electrode having an electrode current collector and an electrode active material layer of either of a positive electrode and a negative electrode, the manufacturing method comprising the following steps: a step of preparing a wet powder formed of agglomerated particles containing at least an electrode active material, a binder resin, and a solvent, wherein a solid phase, a liquid phase, and a gas phase of at least 50% or more of the agglomerated particles of the wet powder in number form a pendulum state or a cord state, a solid content rate of the wet powder being 85% to 98% by weight; a step of forming a coating film composed of the wet powder on the electrode current collector in a state in which a gas phase remains in the coating film using the wet powder; a step of forming a plurality of first grooves extending in a direction orthogonal to a conveyance direction on the coating film on the electrode current collector by conveyance of the coating film using a first roll die to perform concave-convex transfer; a step of forming at least one second groove extending in the conveyance direction on the coating film on which the first grooves are formed by performing concave-convex transfer using a second roll die; a step of drying the coating film formed on the electrode current collector to form an electrode active material layer; and a step of applying pressure to the electrode active material layer; wherein the first grooves are formed in a manner continuous from one end portion to another end portion in the electrode active material layer after the step of applying pressure. For the wet powder prepared in the step of preparing the wet powder, a bulk density obtained by measuring a wet powder charged in a container of a prescribed volume in a manner scraped flat without applying a force is set as a loose bulk density X, and a density calculated from a composition of the wet powder assuming that there is no gas phase is set as a true density Y, 5. The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 4, wherein a ratio Y / X of the true density Y to the loose bulk density X is 1.2 or more, a unit of the wet powder is g, a unit of the volume is mL, and a unit of the density is g / mL. ​ 6. The method for producing an electrode for a nonaqueous electrolyte secondary battery according to claim 4 or 5, wherein In the second groove forming step, a plurality of the second grooves are formed in the conveyance direction.

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