Electrode body manufacturing method and power storage device manufacturing method

Abstract

To provide a method for manufacturing an electrode body in which cracks at the edge of an active material layer are suppressed.SOLUTION: A method includes a coating step of coating a slurry containing a binder, an active material, and a solvent onto an electrode current collector to form a coating layer such that an uncoated region is formed around the coating layer, and a drying step of irradiating the coating layer with a laser to dry it and form an active material layer, and the coating step is performed such that a first slurry applied to a central region of the coating layer and a second slurry applied to edge regions around the central region and adjacent to the uncoated region satisfy at least one condition selected from the group consisting of (A) the second slurry has a lower NV value than the first slurry, (B) the second slurry contains a lower tap density of the active material than the first slurry, (C) the second slurry contains a lower binder content than the first slurry, and (D) the second slurry contains a lower glass transition temperature Tg of the binder than the first slurry.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an electrode assembly and a method for manufacturing an electricity storage device. [Background technology]

[0002] Conventionally, a method has been used to manufacture an electrode body in which an active material layer is formed on an electrode current collector by applying a slurry containing a binder, an active material, and a solvent onto an electrode current collector to form a coating layer, and then drying the coating layer.

[0003] For example, Patent Document 1 discloses a method for drying a coating film, in which the coating film is irradiated with far-infrared rays having a wavelength that is highly absorbent for organic solvents, thereby evaporating the organic solvent from the entire coating film and bringing the coating film to a dry state. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 06-063495 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when laser irradiation is applied to dry a coating layer for forming an active material layer, cracks may occur at the edges of the active material layer that is formed.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for manufacturing an electrode body that suppresses the occurrence of cracks at the ends of the formed active material layer, and a method for manufacturing an energy storage device. [Means for solving the problem]

[0007] Means for solving the above problems include the following aspects. <1> a coating step of coating a slurry containing a binder, an active material, and a solvent onto an electrode current collector to form a coating layer, and coating the slurry so that an uncoated region where the slurry is not coated is formed around the coating layer; a drying step of irradiating the coating layer with a laser to dry it and form an active material layer, The method for manufacturing an electrode body, wherein in the coating step, a first slurry coated on a central region of the coating layer and a second slurry coated on an end region around the central region and adjacent to the uncoated region satisfy at least one condition selected from the group consisting of the following (A) to (D): (A) The second slurry has a lower NV value than the first slurry. (B) The tap density of the active material contained in the second slurry is lower than that of the first slurry. (C) The second slurry has a lower binder content than the first slurry. (D) The glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry. <2> the electrode current collector has a carbon coating layer on the surface on which the coating layer is to be formed, <1> A method for manufacturing the electrode assembly according to claim 1. <3> the binder contained in the second slurry has a glass transition temperature Tg of −14° C. or lower; <1> A method for manufacturing the electrode assembly according to claim 1. <4> The active material layer has a pore volume of 0.10 mL / g or more. <1> A method for manufacturing the electrode assembly according to claim 1. <5> <1> ~ <4> a step of welding a seal member to the electrode current collector in the uncoated region of the electrode body obtained by the method for manufacturing an electrode body according to any one of the above items; a step of stacking the electrode assemblies to which the sealing members have been welded to form an electrode stack, and thermally welding the sealing members to each other at end surfaces of the electrode stack; The manufacturing method of the electricity storage device has the above-mentioned. [Effects of the Invention]

[0008] According to the present disclosure, there are provided a method for manufacturing an electrode body and a method for manufacturing an electricity storage device that suppress the occurrence of cracks at the edges of the formed active material layer. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a top view showing a workpiece produced in an example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0011] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified. The term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0012] <Electrode body manufacturing method> The method for manufacturing an electrode assembly according to an embodiment of the present disclosure includes the following coating step and drying step. (Coating step) A coating layer is formed by coating a slurry containing a binder, an active material, and a solvent onto an electrode current collector. Note that in the coating step, the slurry is coated so that an uncoated area is formed around the coating layer where the slurry is not coated. (Drying step) The coating layer is irradiated with a laser to dry it, thereby forming an active material layer. The coating process uses different slurries for a first slurry that is coated on a central region (hereinafter also simply referred to as the "central region") in the coating layer and a second slurry that is coated on edge regions (hereinafter also simply referred to as the "edge regions") around the central region and adjacent to the uncoated region, and the first slurry and the second slurry satisfy at least one condition selected from the group consisting of the following (A) to (D): (A) The second slurry has a lower NV value than the first slurry. (B) The tap density of the active material contained in the second slurry is lower than that of the first slurry. (C) The second slurry has a lower binder content than the first slurry. (D) The glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry.

[0013] According to the manufacturing method of the electrode assembly according to the embodiment of the present disclosure, the occurrence of cracks in the edge regions of the active material layer is suppressed. This effect is presumably achieved for the following reasons.

[0014] Conventionally, a method has been used to manufacture an electrode assembly in which an active material layer is formed on an electrode current collector by applying a slurry containing a binder, an active material, and a solvent onto an electrode current collector to form a coating layer, and then drying the coating layer. From the perspective of improving the drying efficiency of the coating layer, drying using laser irradiation has been attempted. However, when laser irradiation is performed during drying, cracks may occur at the edges of the formed active material layer. The reason for this is thought to be as follows: During the drying process, the electrode current collector in the uncoated region surrounding the coating layer is also irradiated with the laser, causing the electrode current collector to heat excessively, and heat is applied from the heated electrode current collector to the edge region of the coating layer. As a result, the solvent rapidly evaporates in the edge region of the coating layer, and the generated gas cannot completely escape from within the coating layer, causing pressure from the gas to be applied, resulting in cracks in the active material layer.

[0015] In contrast, in the manufacturing method of the electrode body according to an embodiment of the present disclosure, the first slurry applied to the central region of the coating layer and the second slurry applied to the edge region satisfy at least one condition selected from the group consisting of (A) to (D). When condition (A) is satisfied, the second slurry has a lower nonvolatile content (NV) than the first slurry, meaning that the second slurry in the edge regions has a higher solvent content, which balances the drying with the central region and suppresses cracking in the edge regions of the active material layer.

[0016] When condition (B) is satisfied, the tap density of the active material contained in the second slurry is lower than that of the first slurry, and therefore the pore volume of the formed active material layer is larger in the edge regions, which allows gas generated by evaporation of the solvent to pass more easily through the edge regions, thereby suppressing cracking in the edge regions of the active material layer.

[0017] When condition (C) is satisfied, the second slurry has a lower binder content than the first slurry, and therefore the pore volume of the formed active material layer is larger in the edge regions, which allows gas generated by evaporation of the solvent to pass through more easily in the edge regions, thereby suppressing cracking in the edge regions of the active material layer.

[0018] When condition (D) is satisfied, the glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry, and therefore the edge regions of the formed active material layer are more flexible. As a result, even if pressure is applied to the edge regions from the gas generated by evaporation of the solvent, the flexibility of the layer absorbs the pressure, and cracks in the edge regions of the active material layer are suppressed.

[0019] As described above, according to the method for manufacturing an electrode assembly according to an embodiment of the present disclosure, the occurrence of cracks in the edge regions of the active material layer is suppressed.

[0020] Hereinafter, each step of the method for manufacturing an electrode assembly according to an embodiment of the present disclosure will be described.

[0021] (coating process) In the coating step, a slurry containing a binder, an active material, and a solvent is applied onto an electrode current collector to form a coating layer. Note that in the coating step, the slurry is applied so as to form an uncoated region around the coating layer where the slurry is not applied.

[0022] In the coating step, different slurries are used: a first slurry is coated on the central region of the coating layer, and a second slurry is coated on the edge regions around the central region and adjacent to the uncoated regions. The first slurry and the second slurry satisfy at least one condition selected from the group consisting of the following (A) to (D):

[0023] The first slurry and the second slurry may satisfy two or more conditions selected from the group consisting of the following (A) to (D), or may satisfy only one condition selected from the group consisting of the following (A) to (D).

[0024] Furthermore, the central region of the coating layer to which the first slurry is applied and the edge regions to which the second slurry is applied are not particularly limited in size, as long as the edge regions are arranged around the central region and the regions adjacent to the uncoated regions all constitute the edge regions. However, it is preferable that the area of the edge regions is 20% or less of the total area of the coating layer. For example, if the coating layer is rectangular, it is preferable that the width of the edge regions is 10% or less of the length of one side of the coating layer (i.e., the sum of the widths of the edge regions at both ends is 20% or less of the length of one side of the coating layer).

[0025] (A) The second slurry has a lower NV value than the first slurry. The second slurry has a lower nonvolatile content (NV) than the first slurry, which results in a higher solvent content in the edge regions of the second slurry, which balances the drying with the central region and suppresses cracking in the edge regions of the active material layer.

[0026] The NV value (non-volatile content) can be controlled by adjusting the amount of solvent in the first slurry and the second slurry. When condition (A) is satisfied, the binder, active material, and solvent contained in the first slurry and the second slurry may be made of different materials, but it is preferable that they are all made of the same material.

[0027] The NV value (non-volatile content) of the first slurry is preferably, for example, more than 74 mass %, more preferably 75 mass % or more, and the upper limit is preferably 80 mass % or less. The NV value (non-volatile content) of the second slurry is, for example, preferably 74% by mass or less, and more preferably 73% by mass or less, with the lower limit being preferably 70% by mass or more.

[0028] The NV value of the slurries (first slurry and second slurry) is measured by heating the slurry to be measured for 2 hours at a temperature equal to the volatilization temperature of the solvent contained therein plus 20°C, measuring the mass before and after heating, and calculating the NV value using the formula (mass after heating) / (mass after heating) × 100 (mass%).

[0029] (B) The tap density of the active material contained in the second slurry is lower than that of the first slurry. Because the active material contained in the second slurry has a lower tap density than the active material contained in the first slurry, the pore volume of the formed active material layer is larger in the edge regions, which allows gas generated in the edge regions to pass through more easily, thereby suppressing cracking in the edge regions of the active material layer.

[0030] The tap density of the active material can be controlled by adjusting the shape of the active material contained in the first slurry and the second slurry, etc. For example, when aggregated particles (i.e., secondary particles formed by aggregation of primary particles) are used as the active material, the tap density can be controlled by adjusting the degree of aggregation, the number of aggregated primary particles, etc. When condition (B) is satisfied, the binder and solvent contained in the first slurry and the second slurry may be different in material, but are preferably the same in material. Also, when condition (B) is satisfied, the active materials contained in the first slurry and the second slurry may be different in material, but are preferably the same in material but with different tap densities (for example, different degrees of aggregation when aggregated particles are used).

[0031] The tap density of the active material contained in the first slurry is preferably, for example, more than 1.80 g / ml, more preferably 1.90 g / ml or more, and preferably 2.00 g / ml or less as the upper limit. The tap density of the active material contained in the second slurry is preferably 1.80 g / ml or less, more preferably 1.75 g / ml or less, for example, and the lower limit thereof is preferably 1.50 g / ml or more.

[0032] The tap density of the active material contained in the slurries (first slurry and second slurry) can be measured by the method specified in JIS K1469:2003 using a general tapping type density measuring device.

[0033] (C) The second slurry has a lower binder content than the first slurry. Because the second slurry has a lower binder content than the first slurry, the pore volume of the formed active material layer is larger in the edge regions, which allows gas generated in the edge regions to pass through more easily, thereby suppressing cracking in the edge regions of the active material layer.

[0034] The binder content can be controlled by adjusting the amount of binder contained in the first slurry and the second slurry. When condition (C) is satisfied, the binder, active material, and solvent contained in the first slurry and the second slurry may be made of different materials, but it is preferable that they are all made of the same material.

[0035] The binder content of the first slurry is preferably, for example, more than 1.15 mass %, more preferably 1.3 mass % or more, and the upper limit is preferably 1.5 mass % or less. The binder content of the second slurry is preferably, for example, 1.15% by mass or less, and more preferably 1.0% by mass or less, with the lower limit being preferably 0.8% by mass or more.

[0036] (D) The glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry. The second slurry contains a binder with a lower glass transition temperature Tg than the first slurry, which results in a more flexible edge region of the active material layer, which absorbs pressure from gas generated in the edge region and prevents cracks in the edge region of the active material layer.

[0037] The glass transition temperature Tg of the binder can be controlled by selecting the type of binder contained in the first slurry and the second slurry. In other words, when condition (D) is satisfied, it is preferable that the first slurry and the second slurry contain binders of different materials. When condition (D) is satisfied, the active material and the solvent contained in the first slurry and the second slurry may be made of different materials, but it is preferable that they are made of the same material.

[0038] The glass transition temperature Tg of the binder contained in the first slurry is, for example, preferably higher than −14° C., and more preferably not lower than −13° C. The upper limit is preferably not higher than −5° C. The glass transition temperature Tg of the binder contained in the second slurry is, for example, preferably −14° C. or lower, more preferably −15° C. or lower, and even more preferably −20° C. or lower. The lower limit is preferably −30° C. or higher.

[0039] The glass transition temperature Tg of the binder contained in the slurries (first slurry and second slurry) can be measured by differential scanning calorimetry (DSC).

[0040] In the manufacturing method of an electrode assembly according to an embodiment of the present disclosure, the electrode current collector used may have a carbon coating layer on at least the surface on which the coating layer is formed. Alternatively, the electrode current collector may have a carbon coating layer on both sides. An electrode current collector having a carbon coating layer is more likely to be heated by laser irradiation, which makes cracks more likely to occur in the edge regions of the active material layer. However, in the manufacturing method of an electrode assembly according to an embodiment of the present disclosure, the first slurry applied to the central region of the coating layer and the second slurry applied to the edge regions satisfy at least one condition selected from the group consisting of (A) to (D) above, thereby suppressing cracks in the edge regions of the active material layer.

[0041] (drying process) In the drying step, the coating layer is irradiated with a laser to dry it and form an active material layer.

[0042] The laser output and input heat amount are not particularly limited, and are appropriately selected within a range that allows the solvent in the slurry to evaporate.

[0043] An active material layer is formed through a drying process. The active material layer preferably has a pore volume of 0.10 mL / g or more. In particular, in the edge region formed by the second slurry, the pore volume is preferably 0.15 mL / g or more, and more preferably 0.20 mL / g or more. When the pore volume is within the above range, the active material layer has an appropriate amount of gap, allowing gas to pass through easily.

[0044] The pore volume can be adjusted by the tap density of the active material contained in the slurry, the binder content in the slurry, and the like.

[0045] Next, each component contained in the slurry will be described.

[0046] · Negative electrode active material layer Examples of the negative electrode active material include graphite-based carbons such as natural graphite, artificial graphite, and amorphous-coated graphite. The proportion of graphite in the graphite-based carbon is generally 50% by mass or more, preferably 80% by mass or more. Examples of the binder contained in the negative electrode active material include rubbers such as styrene-butadiene copolymer (SBR), and vinyl halide resins such as polyvinylidene fluoride (PVdF). The negative electrode active material layer may further contain other components such as a thickening agent. Examples of the thickening agent include celluloses such as carboxymethyl cellulose (CMC).

[0047] · Positive electrode active material layer Examples of the positive electrode active material include lithium nickel cobalt manganese composite oxide (hereinafter sometimes simply referred to as "LNCM"). The simplest LNCM has the following general formula: LiNi x Co y Mn z O2 (where x, y, and z in the formula satisfy 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). In addition to Li, Ni, Co, and Mn, LNCM may contain other additive elements such as transition metal elements other than Ni, Co, and Mn, and typical metal elements other than Li. LNCM has a layered crystal structure. LNCM should exceed 50% by mass of the entire positive electrode active material, for example, and may account for 80 - 100% by mass. The positive electrode active material may be composed of only LNCM. Examples of other positive electrode active materials include lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel manganese composite oxide, and the like.

[0048] Examples of the binder contained in the positive electrode active material layer include vinyl halide resins such as polyvinylidene fluoride (PVdF). The positive electrode active material layer may further contain other components, such as a conductive material, etc. Examples of the conductive material include non-graphitizable carbon, easily graphitizable carbon such as carbon black, and graphite.

[0049] The solvent contained in the slurry is, for example, water.

[0050] (Method of manufacturing an electricity storage device) The electrode assembly obtained by the electrode assembly manufacturing method according to the embodiment of the present disclosure is used in an electricity storage device. A method for manufacturing an energy storage device includes, for example, a step of welding a sealing member to an electrode current collector in an uncoated area of an electrode body, a step of stacking the electrode bodies with the sealing member welded thereto to form an electrode stack, and a step of thermally welding the sealing members together at the end faces of the electrode stack, thereby obtaining an energy storage device.

[0051] The energy storage device obtained by the energy storage device manufacturing method according to the embodiment of the present disclosure is suitable for use in, for example, a lithium-ion battery. The battery includes, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. This energy storage device may be a solid-state battery with a solid electrolyte or a liquid battery with a liquid electrolyte, but a liquid battery is preferred. Alternatively, the energy storage device may be a bipolar battery having a positive electrode active material layer and a negative electrode active material layer on both sides of a current collector that functions as a positive electrode current collector and a negative electrode current collector. The positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. The separator is an electrically insulating porous film. The separator electrically isolates the positive electrode and the negative electrode. The battery according to the embodiment of the present disclosure may also be a liquid-based battery further including an electrolyte. A nonaqueous electrolyte is particularly preferred. Examples of applications of batteries include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). [Example]

[0052] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples in any way.

[0053] (Experimental Method) As shown in Fig. 1, a rectangular electrode foil 2 having sides of 100 mm was coated with a central 80 mm region, leaving 10 mm on each end (i.e., uncoated regions). Specifically, a 60 mm region on one end (right side in Fig. 1) of the coated region was designated as a first slurry region 4 to which slurry 1 was applied, and a 20 mm region on the other end (left side in Fig. 1) was designated as a second slurry region 6 to which slurry 2 was applied. In each of the examples and comparative examples, the first slurry region 4 of the electrode foil 2 was coated with slurry 1 shown in Table 1, and the second slurry region 6 was coated with slurry 2 shown in Table 1, to prepare a workpiece.

[0054] The workpiece was irradiated with a laser (i.e., the entire surface was irradiated) in an irradiation range equal to the size of the workpiece (i.e., 100 mm × 100 mm) to dry the slurry on the workpiece. For each example and comparative example, the output of the irradiated laser was increased (i.e., the time required for drying to be completed was shortened), and the limit time (seconds) at which drying could be completed without cracking was measured for each of the first slurry region 4 where slurry 1 was applied and the second slurry region 6 where slurry 2 was applied.

[0055] The results for the first slurry region and the second slurry region are shown in Table 1. The shorter the critical time, the more effectively cracking is suppressed.

[0056] [Table 1]

[0057] From the results shown in Table 1, in Comparative Example 1, cracks occurred due to overheating of the second slurry region by electrical heat from the current collecting foil side. In Example 1, slurry 2 having a lower NV value than slurry 1 was used, and cracking at the edge was suppressed compared to Comparative Example 1. In Example 2, Slurry 2, which has a lower binder content than Slurry 1, was used, and cracking at the edges was suppressed compared to Comparative Example 1. In Example 3, Slurry 2 containing an active material with a lower tap density than Slurry 1 was used, and cracking at the edges was suppressed compared to Comparative Example 1. In Examples 4 and 5, Slurry 2 containing a binder with a lower Tg than Slurry 1 was used, and cracking at the edges was suppressed compared to Comparative Example 1. [Explanation of symbols]

[0058] 2 electrode foil, 4 first slurry region, 6 second slurry region

Claims

1. a coating step of coating a slurry containing a binder, an active material, and a solvent onto an electrode current collector to form a coating layer, and coating the slurry so that an uncoated region where the slurry is not coated is formed around the coating layer; a drying step of irradiating the coating layer with a laser to dry it and form an active material layer, A method for manufacturing an electrode body, wherein in the coating step, a first slurry coated on a central region of the coating layer and a second slurry coated on an end region around the central region and adjacent to the uncoated region satisfy at least one condition selected from the group consisting of the following (A) to (D): (A) The second slurry has a lower NV value than the first slurry. (B) The tap density of the active material contained in the second slurry is lower than that of the first slurry. (C) The second slurry has a lower binder content than the first slurry. (D) The glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry.

2. The method for manufacturing an electrode assembly according to claim 1 , wherein the electrode current collector has a carbon coating layer on the surface on which the coating layer is formed.

3. The method for manufacturing an electrode assembly according to claim 1 , wherein the binder contained in the second slurry has a glass transition temperature Tg of −14° C. or lower.

4. The method for manufacturing an electrode assembly according to claim 1 , wherein the active material layer has a pore volume of 0.10 mL / g or more.

5. a step of welding a seal member to the electrode current collector in the uncoated region of the electrode body obtained by the electrode body manufacturing method according to any one of claims 1 to 4; a step of stacking the electrode assemblies to which the sealing members have been welded to form an electrode stack, and thermally welding the sealing members to each other at end surfaces of the electrode stack; The manufacturing method of the electricity storage device has the above-mentioned.

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