Method for manufacturing an active material layer for a battery, an active material layer for a battery, and a battery

Abstract

To provide a method for manufacturing an active material layer for batteries that can reduce the resistance of a battery while suppressing a reduction in battery capacity. [Solution] A step of preparing an active material layer containing a binder and an active material, and a step of applying a femtosecond laser to the active material layer with a heat output of 0.04 J / mm². 2 More than 0.32J / mm 2 A method for manufacturing an active material layer for a battery, comprising an irradiation step performed under the following conditions.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing an active material layer for batteries, an active material layer for batteries, and a battery. [Background technology]

[0002] Conventionally, in liquid-based batteries using an electrolyte, an active material layer containing a binder and active material has been used.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte battery comprising an electrode group, an outer material, and a non-aqueous electrolyte, wherein the electrode group comprises a positive electrode, a negative electrode, and a separator, the positive electrode having a positive electrode current collector and a positive electrode layer formed on the positive electrode current collector containing a positive electrode active material and a binder, the negative electrode having a negative electrode current collector and a negative electrode layer formed on the negative electrode current collector containing a negative electrode active material and a binder, the separator being interposed between the positive electrode layer and the negative electrode layer and wound together with the positive electrode and the negative electrode, and at least one of the positive electrode layer and the negative electrode layer having multiple penetration promoting portions formed on the surface side so as to connect both long sides (S) and having less binder on the surface side of the other region (R) and promoting the penetration of the non-aqueous electrolyte from the surface side of the region (R). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-171020 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Patent Document 1 discloses a method for forming a region with less binder on the surface of the electrode layer using a CW laser in a battery using a non-aqueous electrolyte. However, laser irradiation can remove active material from the electrode layer, reducing the amount of active material and consequently lowering the battery capacity.

[0006] Furthermore, in batteries, the permeability of the electrolyte to the active material layer affects the battery's resistance. Therefore, it is desirable to reduce the battery's resistance by improving the permeability of the electrolyte to the active material layer.

[0007] This disclosure is made in view of the above circumstances and aims to provide a method for manufacturing a battery active material layer that can reduce the resistance of a battery while suppressing a reduction in the battery capacity, a battery active material layer, and a battery having the battery active material layer. [Means for solving the problem]

[0008] The means for solving the above problems include the following embodiments. <1> A step of preparing an active material layer containing a binder and active material, A femtosecond laser is applied to the active material layer with a heat output of 0.04 J / mm². 2 More than 0.32J / mm 2 A method for manufacturing an active material layer for a battery, comprising an irradiation step performed under the following conditions. <2> The irradiation step is a step of irradiating with a femtosecond laser under the conditions of an output of 10W or more and 150W or less, and an overlap rate of 0% or more and 37.5% or less. <1> A method for manufacturing an active material layer for batteries as described above. <3> A battery active material layer comprising a binder and an active material, A battery active material layer wherein the brightness in the surface image obtained by EPMA mapping after staining the binder is lower than the brightness in the image of a cross-section with a depth of 20 μm obtained by EPMA mapping. <4> A battery active material layer comprising a binder and an active material, A battery active material layer wherein the average particle size of the binder in the surface image obtained by EPMA mapping after staining the binder is 10.0 μm or less. <5> <3> or <4> A battery having the battery active material layer described in [reference] as at least one of the positive electrode active material layer and the negative electrode active material layer.

Advantages of the Invention

[0009] According to the present disclosure, there are provided a method for manufacturing an active material layer for a battery, the active material layer for a battery, and a battery having the active material layer for a battery, which can reduce the resistance of the battery while suppressing a reduction in the battery capacity in the battery.

Brief Description of the Drawings

[0010] [Figure 1] It is a graph showing the results of measuring the change in the mass (mass loss (%)) of the active material layer before and after femtosecond laser irradiation in the examples and comparative examples. [Figure 2] It is a graph showing the results of measuring the battery resistance in the examples and reference examples.

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments which are an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerically described range. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0012] Each component may contain a plurality of corresponding substances. When referring to the amount of each component 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 the plurality of substances present in the composition. The term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended action of the step is achieved.

[0013] <Method for Manufacturing Active Material Layer for Battery> A method for manufacturing an active material layer for a battery according to the embodiments of this disclosure comprises the steps of preparing an active material layer including a binder and an active material, and feeding a femtosecond laser into the active material layer with a heat energy of 0.04 J / mm². 2 More than 0.32J / mm 2 The process includes an irradiation step performed under the following conditions.

[0014] In the method for manufacturing an active material layer for a battery according to the embodiments of this disclosure, a femtosecond laser is locally irradiated onto the surface of the active material layer, and at that time, 0.04 J / mm 2 The above amount of heat is applied. As a result, the binder on the surface of the active material layer is sublimated, and the particle size of the binder can be reduced. This ensures a reaction surface on the surface of the active material layer, and ensures a penetration path for the electrolyte into the interior of the active material layer, and as a result, the resistance of the battery equipped with this active material layer can be reduced.

[0015] Furthermore, a femtosecond laser is used as the laser irradiated onto the surface of the active material layer, and the heat input when irradiating with the femtosecond laser is 0.32 J / mm². 2 The following suppression is achieved: In other words, the femtosecond laser is irradiated locally onto the surface of the active material layer, and the total amount of heat is suppressed. As a result, the removal of active material from the active material layer by laser irradiation is suppressed, and the mass loss of the active material is suppressed, thus preventing a reduction in the battery capacity of a battery equipped with this active material layer.

[0016] The method for manufacturing the battery active material layer according to the embodiment of this disclosure will be described below for each step.

[0017] -Process for preparing the active material layer- A method for manufacturing an active material layer for a battery according to the embodiments of this disclosure includes a step of preparing an active material layer containing a binder and an active material. Furthermore, either a negative electrode active material layer or a positive electrode active material layer can be used as the active material layer. The negative electrode active material layer and the positive electrode active material layer can be formed by conventionally known methods. For example, they can be formed by coating a solution containing the raw materials for the active material layer and drying it.

[0018] Hereinafter, the active materials, binders, etc. will be described separately for the negative electrode active material layer and the positive electrode active material layer.

[0019] · 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 thickener. Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC).

[0020] · 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, z are 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1). LNCM may contain other additive elements in addition to Li, Ni, Co, and Mn, 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, occupy 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, etc.

[0021] 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 conductive materials. Examples of conductive materials include poorly graphitizable carbon, easily graphitizable carbon such as carbon black, and graphite.

[0022] -Irradiation process- Next, in the irradiation process, a femtosecond laser is injected into the active material layer at a heat output of 0.04 J / mm². 2 More than 0.32J / mm 2 Irradiation will be carried out under the following conditions. A femtosecond laser refers to a pulsed laser with a pulse width of 1 fs or more and 500 fs or less. Preferably, the pulse width of a femtosecond laser is between 1 fs and 100 fs.

[0023] ·Input heat amount The femtosecond laser used to irradiate the active material layer during the irradiation process has a heat input of 0.04 J / mm². 2 More than 0.32J / mm 2 The following applies: The heat input is 0.04 J / mm². 2 As a result, the binder on the surface of the active material layer can be sublimated, reducing the particle size of the binder. Therefore, a penetration path for the electrolyte into the active material layer is secured, which reduces the resistance in batteries equipped with an active material layer. On the other hand, the heat input is 0.32 J / mm². 2 The following conditions suppress the removal of active material from the active material layer by laser irradiation, thereby suppressing a reduction in battery capacity in a battery equipped with an active material layer. The lower limit of the heat input is further reduced to 0.07 J / mm². 2 Preferably, it is 0.10 J / mm 2 It is more preferable that the values ​​are as described above. On the other hand, the upper limit of the heat input is further set to 0.25 J / mm². 2 Preferably, it is 0.20 J / mm 2 The following is more preferable:

[0024] The amount of heat input to a femtosecond laser can be controlled, for example, by adjusting the power output and overlap rate.

[0025] ·output From the viewpoint of reducing the battery resistance while suppressing a reduction in battery capacity, the output of the femtosecond laser is preferably 10W to 150W, more preferably 20W to 150W, and even more preferably 30W to 100W.

[0026] • Wrap rate When irradiating with a femtosecond laser, the overlap rate is preferably 0% to 37.5%, more preferably 0% to 30%, and even more preferably 0% to 15%, from the viewpoint of reducing the battery resistance while suppressing a reduction in battery capacity.

[0027] Here, the overlap rate refers to the ratio of the area of ​​regions that are irradiated by overlapping femtosecond lasers, and is expressed by the following formula. Formula: (Areas irradiated by overlapping laser beams) / ((Areas irradiated by overlapping laser beams) + (Areas not irradiated by overlapping laser beams)) A femtosecond laser is a pulsed laser with a pulse width of femtoseconds. By repeatedly irradiating an area for a short time while slightly moving the laser's irradiation position, the entire area to be irradiated is covered. An overlapping irradiated area refers to an area that is irradiated by the laser in the repeated irradiations while moving the irradiation position, but the movement of the irradiation position is small enough that it overlaps with the area irradiated in the previous irradiation. For example, if the irradiation is repeated without moving the irradiation position at all, the overlap rate will be 100%, and if the irradiation position is moved so as to be outside the area irradiated by a single laser pulse, the overlap rate will be 0%. The overlap rate can be controlled by adjusting, for example, the distance moved during repeated laser irradiations.

[0028] • Frequency, pulse energy When irradiating with a femtosecond laser, it is preferable to further adjust the frequency, pulse energy, etc. The frequency used when irradiating with a femtosecond laser is preferably 100 kHz to 3 MHz, more preferably 300 kHz to 2.5 MHz, and even more preferably 500 kHz to 2 MHz, from the viewpoint of reducing the battery resistance while suppressing a reduction in battery capacity. The pulse energy when irradiating with a femtosecond laser is preferably 0.01 mJ or more and 0.4 mJ or less, more preferably 0.03 mJ or more and 0.3 mJ or less, and even more preferably 0.05 mJ or more and 0.2 mJ or less, from the viewpoint of reducing the battery resistance while suppressing a reduction in the battery capacity of the battery.

[0029] <Battery active material layer> -First active material layer- In this disclosure, the battery active material layer according to the first embodiment (simply referred to as the "first active material layer") comprises a binder and an active material, wherein the brightness in the surface image obtained by EPMA mapping by staining the binder is lower than the brightness in the image of a cross-section with a depth of 20 μm obtained by EPMA mapping.

[0030] The fact that the brightness on the surface of the active material layer is lower than the brightness in the cross-section at a depth of 20 μm from the surface indicates that the particle size of the binder on the surface of the active material layer is smaller. As a result, a reaction surface is secured on the surface of the active material layer, ensuring a penetration path for the electrolyte into the interior of the active material layer, and consequently, the resistance of the battery equipped with this active material layer can be reduced.

[0031] The first active material layer can be obtained, for example, by the method for manufacturing an active material layer for a battery according to the embodiment of this disclosure described above.

[0032] -Second Active Material Layer- In this disclosure, the battery active material layer according to the second embodiment (simply referred to as the "second active material layer") comprises a binder and an active material, wherein the average particle size of the binder in the surface image obtained by EPMA mapping after staining the binder is 10.0 μm or less.

[0033] Because the average particle size of the binder on the surface of the active material layer is small, less than 10.0 μm, a reaction surface is secured on the surface of the active material layer, ensuring a penetration path for the electrolyte into the interior of the active material layer. As a result, the resistance of a battery equipped with this active material layer can be reduced.

[0034] In the second active material layer, the average particle size of the binder on the surface is 10.0 μm or less, preferably 7.0 μm or less, and more preferably 6.0 μm or less. The lower limit of the average particle size of the binder is preferably 2.0 μm or more, and more preferably 4.0 μm or more.

[0035] The second active material layer can be obtained, for example, by the method for manufacturing an active material layer for a battery according to the embodiment of this disclosure described above.

[0036] Here, we will explain the method for measuring the brightness on the surface of the active material layer and the average particle size of the binder. First, the active material layer is stained according to the binder it contains (e.g., osmium (Os) staining). Next, an EPMA (Electron Probe Micro Analysis) mapping image is obtained from the surface of the stained active material layer. Brightness is measured from the obtained mapping image. Furthermore, the brightness data of the top 10% is calculated, and this brightness data is set as a threshold for binarization processing. From the binarized image, the particle size of the binder particles (meaning the length of the longest part of the target binder particle in the image) is measured. This measurement is performed for 20 binder particles, and the arithmetic mean is taken as the average particle size. Furthermore, the brightness of the binder at a cross-section 20 μm deep from the surface is measured by exposing the cross-section 20 μm deep from the surface using a method such as cutting, and then determining the brightness in the same manner as the brightness measurement method for the surface of the active material layer described above.

[0037] <Battery> The battery according to the embodiment of this disclosure has the aforementioned first active material layer or second active material layer as at least one of the positive electrode active material layer and the negative electrode active material layer. A battery has, for example, a negative electrode, a positive electrode, a separator, and an electrolyte.

[0038] (electrolyte) ·solvent The electrolyte solution contains a solvent (non-aqueous solvent) and an electrolyte. Examples of solvents (non-aqueous solvents) include N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI), and 1-ethyl-2,3-dimethylimidazolium bis(fluorosulfonyl)imide (DEMI-FSI).

[0039] ·Electrolyte Examples of electrolytes in electrolyte solutions include lithium salts. Examples of lithium salts include lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluoride phosphate), lithium tetrafluoroborate (LiBF4), and Li[N(CF3SO2)2]. The amount of electrolyte may be, for example, 1.0 to 2.0 ml / L, and preferably 1.0 to 1.5 ml / L.

[0040] The electrolyte may contain various additives in addition to the solvent and electrolyte, such as thickeners, film-forming agents, and gas-generating agents. The electrolyte is typically a non-aqueous electrolyte that is liquid at room temperature (e.g., 25±10°C). The electrolyte is typically liquid under the battery's operating environment (e.g., a temperature environment of -20 to +60°C).

[0041] (Negative electrode) The negative electrode comprises, for example, a negative electrode current collector and a negative electrode active material layer fixed on the negative electrode current collector. A conductive member made of a metal with good conductivity (e.g., copper) is preferred as the negative electrode current collector. For example, the first active material layer or the second active material layer described above may be used as the negative electrode active material layer.

[0042] (positive electrode) The positive electrode comprises, for example, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector. A conductive member made of a metal with good conductivity (e.g., aluminum) is preferred as the positive electrode current collector. For example, the first active material layer or the second active material layer described above may be used as the positive electrode active material layer.

[0043] (Separator) The separator is an electrically insulating porous membrane. The separator electrically isolates the positive electrode and the negative electrode. The separator may have a thickness of, for example, 5 to 30 μm. The separator may be made of, for example, a porous polyethylene (PE) membrane, a porous polypropylene (PP) membrane, etc. The separator may have a multilayer structure. For example, the separator may be made by laminating a porous PP membrane, a porous PE membrane, and a porous PP membrane in this order. The separator may have a heat-resistant layer on its surface. The heat-resistant layer contains a heat-resistant material. Examples of heat-resistant materials include metal oxide particles such as alumina and high-melting-point resins such as polyimide.

[0044] (Application) Applications of batteries include, for example, power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). [Examples]

[0045] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" all refer to mass.

[0046] <Examples 1-3, Comparative Example 1> In each example and comparative example, the active material layer having the following composition was irradiated onto the surface of the active material layer by adjusting the output and overlap rate of the femtosecond laser used for irradiation, as shown in Table 1, thereby changing the amount of heat input. (Irradiation conditions) Laser pulse width: 500 fs (0.0005 ns), output: 100 W, frequency: 500 kHz ~ 2 MHz, pulse energy: 0.05 mJ ~ 0.2 mJ, overlap rate: 0% ~ 62.5% • Active material layer composition: Negative electrode active material = graphite, binder = styrene-butadiene copolymer (SBR), thickener = carboxymethylcellulose (CMC), conductive material: carbon nanotube (CNT)

[0047] [Table 1]

[0048] <Rating> (1) Mass loss In each example and comparative example, the change in mass of the active material layer (mass loss (%)) was measured before and after femtosecond laser irradiation. The results are shown in graph form in Figure 1.

[0049] As shown in the graph in Figure 1, Example 1 (heat input 0.04 J / mm²) 2 ), Example 2 (0.11 J / mm 2 ), and Example 3 (0.32 J / mm 2 In comparative example 1 (heat input 0.53 J / mm³), the mass loss of the active material layer was kept to 6% or less, whereas in comparative example 1 (heat input 0.53 J / mm³), the mass loss of the active material layer was kept to 6% or less. 2 In this study, the mass loss of the active material layer exceeded 6%.

[0050] (2) Battery resistance Batteries were fabricated using the active material layers from Examples 1 and 2, which exhibited low mass loss, and their battery resistance was tested. As a reference example (Ref), the same battery resistance test was also performed on an active material layer whose surface was not irradiated with a femtosecond laser. The evaluation results are shown in Figure 2 as a graph of the ratio (%) compared to the reference example (Ref). For the battery resistance test, the battery configuration was a laminated type (positive electrode 45mm x 47mm, negative electrode 47mm x 49mm).

[0051] As shown in the graph in Figure 2, it can be seen that the battery resistance has been reduced in Examples 1 and 2 compared to the reference example (Ref).

[0052] (3) Average particle size of the binder For Example 1 and the Reference Example (Reference: Ref), the average particle size of the binder was measured in the surface image obtained by EPMA mapping after staining the binder. Osmium (Os) staining was performed on the active material layers of Example 1 and Reference Example, and EPMA (Electron Probe Micro Analysis) mapping images were obtained for the surface of the stained active material layers. The top 10% of brightness data was calculated from the mapping images, and this brightness data was set as a threshold for binarization processing. The particle size (longest part length) of 20 binder (SBR) particles was measured from the binarized images, and the arithmetic mean was taken as the average particle size. The results are shown below. -Average particle size- Example 1: 7.7 μm Reference example (Ref): 17μm

Claims

1. A battery active material layer comprising a binder and an active material, A battery active material layer wherein the brightness in the surface image obtained by EPMA mapping after staining the binder is lower than the brightness in the image of a cross-section at a depth of 20 μm obtained by EPMA mapping.

2. A battery active material layer comprising a binder and an active material, A battery active material layer wherein the average particle size of the binder in the surface image obtained by EPMA mapping after staining the binder is 10.0 μm or less.

3. A battery having the battery active material layer described in claim 1 or claim 2 as at least one of the positive electrode active material layer and the negative electrode active material layer.

Images