Method for manufacturing electrode body and method for manufacturing power storage device

Abstract

The present disclosure provides a method for manufacturing an electrode body and a method for manufacturing a power storage device that can suppress the occurrence of cracks at the end of a formed active material layer. In this method for manufacturing an electrode body, a slurry is applied to an electrode current collector, and a coating layer is formed so as to form an uncoated region. And drying the coating layer to form an active material layer. A first slurry applied to a central region of the coating layer and a second slurry applied to an end region adjacent to the uncoated region around the central region satisfy at least one of the following conditions: (A) a lower NV value of the second slurry than the first slurry, and (B) a lower tap density of an active material contained in the second slurry than the first slurry. (C) the content of the binder in the second paste is lower than the content of the binder in the first paste, and (D) the glass transition temperature of the binder contained in the second paste is lower than the glass transition temperature of the binder contained in the first paste.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an electrode body and a method for manufacturing a power storage device. Background Art

[0002] Conventionally, the following method has been carried out: a coating is formed by applying a slurry containing a binder, an active material, and a solvent onto an electrode current collector, and then the coated layer is dried to manufacture an electrode body having an active material layer formed on the electrode current collector.

[0003] For example, Japanese Patent Laid-Open No. 06-063495 discloses a method for drying a coating film, in which far-infrared rays having a wavelength with high absorbability for an organic solvent are irradiated onto the coating film to evaporate the organic solvent from the entire layer of the coating film, thereby bringing the coating film into a dried state. Summary of the Invention

[0004] However, when laser irradiation is applied to dry the coating layer for forming the active material layer, cracks sometimes occur at the end of the formed active material layer.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing an electrode body and a method for manufacturing a power storage device that can suppress the occurrence of cracks at the end of the formed active material layer.

[0006] Means for solving the above problems include the following aspects.

[0007] <1>A method for manufacturing an electrode body, having a coating step and a drying step,

[0008] 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 coated layer, and the slurry is applied in such a manner that an uncoated area where the slurry is not applied is formed around the coated layer.

[0009] In the drying step, the coated layer is irradiated with laser to dry it and form an active material layer.

[0010] In the coating step, a first slurry applied to a central region of the coated layer and a second slurry applied to an end region around the central region and adjacent to the uncoated area satisfy at least one of the following conditions (A) to (D).

[0011] Condition (A): The NV value of the second slurry is lower than that of the first slurry.

[0012] Condition (B): The tapped density of the active material contained in the second slurry is lower than that of the first slurry.

[0013] Condition (C): The content rate of the binder in the second paste is lower than that in the first paste.

[0014] Condition (D): The glass transition temperature of the binder contained in the second paste is lower than that in the first paste.

[0015] <2>The manufacturing method of the electrode body according to <1>,

[0016] The surface of the electrode current collector on the side where the coating layer is formed has a carbon coating.

[0017] <3>The manufacturing method of the electrode body according to <1>,

[0018] The glass transition temperature of the binder contained in the second paste is -14°C or lower.

[0019] <4>The manufacturing method of the electrode body according to <1>,

[0020] The pore volume of the active material layer is 0.10 mL / g or more.

[0021] <5>A manufacturing method of a power storage device, comprising:

[0022] A step of welding a sealing member to the electrode current collector in the uncoated area of the electrode body obtained by the manufacturing method of the electrode body according to any one of <1> to <4>; and

[0023] A step of laminating the electrode bodies to which the sealing members are welded to form an electrode laminate, and thermally welding the sealing members on the end faces of the electrode laminate to each other.

[0024] According to the present disclosure, there is provided a manufacturing method of an electrode body capable of suppressing cracks from occurring at the end of the formed active material layer, and a manufacturing method of a power storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Hereinafter, the features, advantages, and technical and industrial significance of the exemplary embodiments of the present disclosure will be described with reference to the drawings, where the same reference numerals denote the same elements.

[0026] Figure 1 It is a top view of a workpiece manufactured in the example. DETAILED DESCRIPTION

[0027] Hereinafter, an embodiment as an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiment and do not limit the scope of the invention.

[0028] In the numerical ranges described intermittently in this specification, the upper limit value or the lower limit value described in one numerical range may also be replaced with the upper limit value or the lower limit value of another numerically intermittent range. In addition, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may also be replaced with the value shown in the examples.

[0029] Each component may also contain a plurality of corresponding substances.

[0030] When referring to the amounts of the respective components in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of these multiple substances present in the composition.

[0031] A "process" is not only an independent process, but also included in this term even when it cannot be clearly distinguished from other processes as long as the intended function of the process can be achieved.

[0032] Method for manufacturing an electrode body

[0033] The method for manufacturing an electrode body according to an embodiment of the present disclosure has a coating process and a drying process as shown below.

[0034] (Coating process) A slurry containing a binder, an active material, and a solvent is coated on an electrode current collector to form a coating layer. Furthermore, in the coating process, the slurry is coated in such a manner that an uncoated area where the slurry is not coated is formed around the coating layer.

[0035] (Drying process) The coating layer is irradiated with laser light to dry it and form an active material layer.

[0036] Moreover, in the coating process, the first slurry coated on the central region (hereinafter also simply referred to as the "central region") of the coating layer and the second slurry coated on the end region (hereinafter also simply referred to as the "end region") around the central region and adjacent to the uncoated area are different. The first slurry and the second slurry satisfy at least one of the following conditions (A) to (D).

[0037] Condition (A): The NV value of the second slurry is lower than that of the first slurry.

[0038] Condition (B): The tapped density of the active material contained in the second slurry is lower than that of the first slurry.

[0039] Condition (C): The content rate of the binder in the second slurry is lower than that of the first slurry.

[0040] Condition (D): The glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry.

[0041] The manufacturing method of an electrode body according to an embodiment of the present disclosure can suppress the generation of cracks in the end region of the active material layer. Furthermore, it is speculated that the effect is caused by the following reasons.

[0042] Conventionally, the following method has been carried out: a coating is formed by coating a slurry containing a binder, an active material, and a solvent on an electrode current collector, and then the coating is dried to manufacture an electrode body having an active material layer formed on the electrode current collector. Moreover, from the viewpoint of improving the drying efficiency of the coating layer and the like, drying by laser irradiation has been attempted. However, if laser irradiation is performed during drying, cracks sometimes occur at the ends of the formed active material layer. The reason is considered as follows. In the drying process, by irradiating the laser also on the electrode current collector in the uncoated area around the coating layer, the electrode current collector is overheated, and heat is also applied to the end region of the coating layer from the heated electrode current collector. Therefore, it is considered that the solvent rapidly vaporizes in the end region of the coating layer, and the generated gas cannot be completely discharged from the coating layer, and the pressure generated by the gas is applied, resulting in cracks in the active material layer.

[0043] In contrast, in the manufacturing method of the electrode body according to the embodiment of the present disclosure, the first slurry coated on the central region of the coating layer and the second slurry coated on the end region satisfy at least one condition selected from the conditions (A) to (D).

[0044] When the condition (A) is satisfied, the NV value (Nonvolatile content, non-volatile component content rate) of the second slurry is lower than that of the first slurry, that is, the solvent content rate of the second slurry in the end region is high. Therefore, the balance with the drying in the central region is achieved, and cracks in the end region of the active material layer are suppressed.

[0045] When the condition (B) is satisfied, the tapped density of the active material contained in the second slurry is lower than that of the first slurry. Therefore, the pore volume of the formed active material layer becomes larger in the end region. As a result, the gas generated by the evaporation of the solvent in the end region becomes easy to pass through, and cracks in the end region of the active material layer are suppressed.

[0046] When the condition (C) is satisfied, the binder content rate of the second slurry is lower than that of the first slurry. Therefore, the pore volume of the formed active material layer becomes larger in the end region. As a result, the gas generated by the evaporation of the solvent in the end region becomes easy to pass through, and cracks in the end region of the active material layer are suppressed.

[0047] 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. Therefore, in the formed active material layer, the end region becomes a softer layer. As a result, even when pressure is applied to the end region from the gas generated by the evaporation of the solvent, the pressure is absorbed by its softness, suppressing cracks in the end region of the active material layer.

[0048] As described above, according to the method for manufacturing an electrode body of an embodiment of the present disclosure, generation of cracks in the end region of the active material layer can be suppressed.

[0049] Hereinafter, the method for manufacturing an electrode body of an embodiment of the present disclosure will be described step by step.

[0050] Coating step

[0051] In the coating step, a slurry containing a binder, an active material, and a solvent is coated on the electrode current collector to form a coating layer. Furthermore, in the coating step, the slurry is coated in such a manner that an uncoated region where the slurry is not coated is formed around the coating layer.

[0052] In the coating step, the first slurry coated on the central region of the coating layer and the second slurry coated on the end region around the central region and adjacent to the uncoated region use different slurries. Moreover, the first slurry and the second slurry satisfy at least one of the following conditions (A) to (D).

[0053] Furthermore, in the first slurry and the second slurry, two or more of the following conditions (A) to (D) may be satisfied, or only one of the following (A) to (D) may be satisfied.

[0054] In addition, in the coating layer, the central region where the first slurry is coated and the end region where the second slurry is coated, as long as the end region is arranged around the central region and all the regions adjacent to the uncoated region constitute the end region, its range is not particularly limited. However, the area of the end region is preferably 20% or less with respect to the entire area of the coating layer. For example, when the coating layer is rectangular, it is preferable that the length of the amplitude of the end region is 10% or less with respect to the length of one side of the coating layer (that is, the total width of the end regions existing at both ends is 20% or less with respect to the length of one side of the coating layer).

[0055] Condition (A): The NV value of the second slurry is lower than that of the first slurry

[0056] Since the NV value (Nonvolatile content) of the second paste is lower than that of the first paste, the solvent content of the second paste in the end region becomes higher. As a result, the balance with the drying in the central region is achieved, and cracks in the end region of the active material layer are suppressed.

[0057] Furthermore, the NV value (Nonvolatile content) can be controlled by adjusting the amount of solvent in the first paste and the second paste.

[0058] When condition (A) is satisfied, the binder, active material, and solvent contained in the first paste and the second paste may have different materials, but it is preferably the same material.

[0059] The NV value (Nonvolatile content) of the first paste is preferably, for example, more than 74% by mass, and more preferably 75% by mass or more. Furthermore, as the upper limit value, it is preferably 80% by mass or less.

[0060] The NV value (Nonvolatile content) of the second paste is preferably, for example, 74% by mass or less, and more preferably 73% by mass or less. Furthermore, as the lower limit value, it is preferably 70% by mass or more.

[0061] The NV value of the paste (the first paste and the second paste) is calculated as follows. The paste to be measured is heated at a temperature of the evaporation temperature of the contained solvent + 20°C for 2 hours. The mass of the paste before and after heating is measured. The NV value of the paste (the first paste and the second paste) is calculated by the formula (mass after heating) / (mass before heating) × 100 (% by mass).

[0062] Condition (B): The tapped density of the active material contained in the second paste is lower than that of the first paste.

[0063] Since the tapped density of the active material contained in the second paste is lower than that of the active material contained in the first paste, the pore volume of the formed active material layer becomes larger in the end region. As a result, the gas generated in the end region becomes easier to pass through, and cracks in the end region of the active material layer are suppressed.

[0064] Furthermore, the tapped density of the active material can be controlled by adjusting the shape of the active material contained in the first paste and the second paste, etc. For example, when using aggregated particles (i.e., secondary particles aggregated from primary particles) as the active material, the tapped density can be controlled by adjusting the degree of aggregation and / or the number of aggregated primary particles, etc.

[0065] When condition (B) is satisfied, the binders and solvents contained in the first slurry and the second slurry may also be made of different materials, but are preferably made of the same material. Additionally, when condition (B) is satisfied, the active materials contained in the first slurry and the second slurry may also be made of different materials. However, as the materials, those of the same type with different tapped densities (for example, different degrees of aggregation in the case of using aggregated particles) are preferred.

[0066] The tapped density of the active material contained in the first slurry is preferably, for example, more than 1.80 g / ml, and more preferably 1.90 g / ml or more. Furthermore, as the upper limit value, it is preferably 2.00 g / ml or less.

[0067] The tapped density of the active material contained in the second slurry is preferably, for example, 1.80 g / ml or less, and more preferably 1.75 g / ml or less. Furthermore, as the lower limit value, it is preferably 1.50 g / ml or more.

[0068] The tapped density of the active material contained in the slurries (the first slurry and the second slurry) can be measured using a general tapping-type density measuring device by the method specified in JIS K1469:2003.

[0069] Condition (C): The second slurry has a lower binder content rate than the first slurry

[0070] By the second slurry having a lower binder content rate than the first slurry, the pore volume of the formed active material layer becomes larger in the end region. As a result, the gas generated in the end region becomes easier to pass through, suppressing cracks in the end region of the active material layer.

[0071] Furthermore, the binder content rate can be controlled by adjusting the amounts of the binders contained in the first slurry and the second slurry.

[0072] When condition (C) is satisfied, the binders, active materials, and solvents contained in the first slurry and the second slurry may also be made of different materials, but are preferably made of the same material.

[0073] The binder content rate of the first slurry is preferably, for example, more than 1.15 mass%, and more preferably 1.3 mass% or more. Furthermore, as the upper limit value, it is preferably 1.5 mass% or less.

[0074] The binder content rate of the second slurry is preferably, for example, 1.15 mass% or less, and more preferably 1.0 mass% or less. Furthermore, as the lower limit value, it is preferably 0.8 mass% or more.

[0075] Condition (D): The second slurry has a lower glass transition temperature Tg of the binder than the first slurry

[0076] Since the glass transition temperature Tg of the binder contained in the second slurry is lower than that of the first slurry, in the formed active material layer, the end region becomes a softer layer. As a result, even when pressure is applied by the gas generated in the end region, the pressure can be absorbed by its softness, suppressing cracks in the end region of the active material layer.

[0077] Furthermore, the glass transition temperature Tg of the binder can be controlled by selecting the types of binders contained in the first slurry and the second slurry. That is, when the condition (D) is satisfied, it is preferable to include binders of different materials in the first slurry and the second slurry.

[0078] When the condition (D) is satisfied, the active materials and solvents contained in the first slurry and the second slurry may have different materials, but it is preferable that they are all of the same material.

[0079] The glass transition temperature Tg of the binder contained in the first slurry is, for example, preferably more than -14°C, and more preferably -13°C or higher. Furthermore, as the upper limit value, it is preferably -5°C or lower.

[0080] 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 further preferably -20°C or lower. Furthermore, as the lower limit value, it is preferably -30°C or higher.

[0081] The glass transition temperature Tg of the binder contained in the slurry (the first slurry and the second slurry) can be determined by differential scanning calorimetry (DSC: Differential Scanning Calorimetry).

[0082] Furthermore, in the method for manufacturing an electrode body according to an embodiment of the present disclosure, the electrode current collector used may have a carbon coating on at least the surface on the side where the coating layer is formed. Alternatively, it may have a carbon coating on both sides. The electrode current collector having a carbon coating is more easily heated by laser irradiation, and as a result, cracks are likely to occur in the end region of the active material layer. However, in the method for manufacturing an electrode body according to an embodiment of the present disclosure, the first slurry coated on the central region of the coating layer and the second slurry coated on the end region of the coating layer satisfy at least one of the conditions (A) to (D) selected above. Therefore, cracks in the end region of the active material layer are suppressed.

[0083] Drying process

[0084] In the drying process, laser is irradiated on the coating layer to dry it and form an active material layer.

[0085] There is no particular limitation on the output power and input heat of the laser, and they can be appropriately selected within the range of evaporating the solvent in the slurry.

[0086] The active material layer is formed by undergoing a drying process. Furthermore, the pore volume of the active material layer is preferably 0.10 mL / g or more. Particularly in the end region formed from the second slurry, the pore volume is preferably 0.15 mL / g or more, and more preferably 0.20 mL / g or more.

[0087] With the pore volume in the above range, the active material layer has an appropriate gap, and gas can easily pass through.

[0088] Furthermore, the pore volume can be adjusted by the tapped density of the active material contained in the slurry, the binder content rate in the slurry, and the like.

[0089] Next, each component contained in the slurry will be described.

[0090] · Negative electrode active material layer

[0091] As the negative electrode active material, for example, graphite-based carbon such as natural graphite, artificial graphite, and amorphous-coated graphite is exemplified. In the graphite-based carbon, the proportion of graphite is approximately 50% by mass or more, and preferably 80% by mass or more.

[0092] As the binder contained in the negative electrode active material, for example, rubber-like substances such as styrene-butadiene copolymer (SBR) and vinylidene fluoride resins such as polyvinylidene fluoride (PVdF) are exemplified.

[0093] The negative electrode active material layer may further contain other components, such as a thickener. As the thickener, for example, cellulose-based substances such as carboxymethyl cellulose (CMC) are exemplified.

[0094] · Positive electrode active material layer

[0095] As the positive electrode active material, lithium nickel cobalt manganese composite oxide (hereinafter sometimes simply referred to as "LNCM") can be cited. The simplest LNCM is represented by the following general formula: LiNi x Co y Mn z O2 (where x, y, and z in the formula are 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). In addition to Li, Ni, Co, and Mn, LNCM may further 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 can exceed 50% by mass of the entire positive electrode active material, for example, accounting for 80 - 100% by mass. The positive electrode active material may also be composed only of LNCM.

[0096] As other positive electrode active materials, for example, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel manganese composite oxide, etc. can be cited.

[0097] As the binder contained in the positive electrode active material layer, for example, vinyl halide resins such as polyvinylidene fluoride (PVdF) are exemplified.

[0098] The positive electrode active material layer may further contain other components such as a conductive material. As the conductive material, for example, non-graphitizable carbon, graphitizable carbon such as carbon black, graphite, etc. can be cited.

[0099] As the solvent contained in the slurry, for example, water can be cited.

[0100] Manufacturing method of the power storage device

[0101] The electrode body obtained by the manufacturing method of the electrode body of the embodiment of the present disclosure is used for a power storage device.

[0102] The power storage device is manufactured, for example, through the following first process and second process. In the first process, for the electrode body, a sealing member is welded to the electrode current collector in the uncoated area. In the second process, the electrode bodies with the sealing members welded are stacked to form an electrode stack, and the sealing members at the ends of the electrode stack are heat-welded to each other.

[0103] The power storage device obtained by the manufacturing method of the power storage device of the embodiment of the present disclosure is suitably used for, for example, a lithium-ion battery. The battery has, for example, a negative electrode, a positive electrode, a separator, and an electrolyte. The power storage device may be a solid battery having a solid electrolyte or a liquid battery having a liquid electrolyte, but a liquid battery is preferred. In addition, it may also 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 having the functions of 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 to the positive electrode current collector. The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material layer fixed to the negative electrode current collector. The separator is an electrically insulating porous membrane. The separator electrically isolates the positive electrode and the negative electrode. The battery of the embodiment of the present disclosure may also be a liquid system battery further having an electrolyte. A non-aqueous electrolyte is particularly preferred.

[0104] As battery applications, for example, power sources for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), battery electric vehicles (BEV), etc. can be cited.

[0105] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited to these examples.

[0106] Experimental method

[0107] As Figure 1 shown, for the rectangular electrode foil 2 with one side being 100 mm, 10 mm is left at each end (i.e., as the uncoated area), and the central 80 mm area is used as the coating area for the slurry. Specifically, one end side in the coating area (Figure 1 A range of 60 mm on the right side (in the figure) is defined as the first slurry region 4 for coating slurry 1, and a range of 20 mm on the other end side ( Figure 1 the left side in the figure) is defined as the second slurry region 6 for coating slurry 2. In each of the examples and comparative examples, slurry 1 shown in Table 1 was coated on the first slurry region 4 of the electrode foil 2, and slurry 2 shown in Table 2 was coated on the second slurry region 6 to fabricate workpieces.

[0108] The workpieces were irradiated with laser (i.e., full irradiation) within an irradiation range equal to the size of the workpieces (i.e., 100 mm × 100 mm) to dry the slurry on the workpieces. For the workpieces in each of the examples and comparative examples, the output power of the irradiated laser was increased (i.e., the time required to complete drying was shortened), and the limit time (seconds) for drying without generating cracks was measured for the first slurry region 4 coated with slurry 1 and the second slurry region 6 coated with slurry 2, respectively.

[0109] The results for the first slurry region and the second slurry region are shown in Tables 1 and 2, respectively. The shorter the limit time, the more effectively crack generation can be suppressed.

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] According to the results shown in Table 2, in Comparative Example 1, cracks were generated due to overheating caused by heat transfer from the current collector foil side to the second slurry region.

[0115] In Example 1, slurry 2 with a lower NV value than slurry 1 was used, and cracks at the ends could be suppressed compared to Comparative Example 1.

[0116] In Example 2, slurry 2 with a lower binder content ratio than slurry 1 was used, and cracks at the ends could be suppressed compared to Comparative Example 1.

[0117] In Example 3, slurry 2 containing an active material with a lower tapped density than slurry 1 was used, and cracks at the ends could be suppressed compared to Comparative Example 1.

[0118] In Examples 4 and 5, slurry 2 containing a binder with a lower Tg than slurry 1 was used, and cracks at the ends could be suppressed compared to Comparative Example 1.

Claims

1. A manufacturing method of an electrode body, comprising a coating step and a drying step, In the coating step, a slurry containing a binder, an active material, and a solvent is coated on an electrode current collector to form a coating layer, and the slurry is coated in such a manner that an uncoated area where the slurry is not coated is formed around the coating layer. In the drying step, the coating layer is irradiated with laser to be dried to form an active material layer. In the coating step, the first slurry coated on the central region of the coating layer and the second slurry coated on the end region around the central region and adjacent to the uncoated area satisfy at least one of the following conditions (A) to (D): Condition (A): The non-volatile content ratio (NV value) of the second slurry is lower than that of the first slurry. Condition (B): The tapped density of the active material contained in the second slurry is lower than that of the first slurry. Condition (C): The content ratio of the binder in the second slurry is lower than that of the first slurry. Condition (D): The glass transition temperature of the binder contained in the second slurry is lower than that of the first slurry.

2. The manufacturing method of the electrode body according to claim 1, The surface of the electrode current collector on the side where the coating layer is formed has a carbon coating.

3. The manufacturing method of the electrode body according to claim 1, The glass transition temperature of the binder contained in the second slurry is -14°C or lower.

4. The manufacturing method of the electrode body according to claim 1, The pore volume of the active material layer is 0.10 mL / g or more.

5. A manufacturing method of a power storage device, comprising: A step of welding a sealing member to the electrode current collector in the uncoated area of the electrode body obtained by the manufacturing method of the electrode body according to any one of claims 1 to 4; and A step of laminating the electrode bodies with the sealing members welded thereto to form an electrode laminate, and heat-welding the sealing members on the end faces of the electrode laminate to each other.

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