Non-aqueous electrolyte secondary batteries

Abstract

A nonaqueous electrolyte secondary battery comprises: a separator having an adhesive on at least one surface; and an electrode having a core and an electrode composite material layer, wherein the electrode composite material layer is in contact with the adhesive. The electrode composite material layer is configured such that the concentration of porous material increases from the core toward the adhesive in the thickness direction.

Description

Technical Field

[0001] The present disclosure relates to a nonaqueous electrolyte secondary battery. Background Art

[0002] In recent years, the demand for secondary batteries in various occasions has increased. Among them, lithium-ion secondary batteries, which are non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, can achieve high energy density and therefore have attracted much attention. In this type of secondary battery, a flat electrode body formed by stacking a plurality of layers of positive plates and negative plates with a separator between them is inserted into an outer shell. In the positive plate, the positive electrode composite material layer is arranged on both sides of the positive electrode core, and in the negative plate, the negative electrode composite material layer is arranged on both sides of the negative electrode core. The positive electrode active material and the negative electrode active material are structures that can insert / deinsert lithium ions respectively. The separator is a porous material that can pass lithium ions and, on the other hand, prevents short circuits caused by electrical contact between the positive plate and the negative plate.

[0003] The positive and negative plates are electrically connected to the current collector plates and inserted into the outer shell. After the electrolyte is injected, the outer shell is sealed. In this secondary battery, to prevent the electrode body from collapsing due to the load during transportation, an adhesive layer is provided on the surface of the separator and then thermally pressed to bond the positive plate to the separator and the negative plate to the separator.

[0004] The subject of patent document 1 is: when a separator with an adhesive layer and an electrode are hot-pressed to manufacture an electrode / separator stack, the separator is bonded to the electrode with sufficient bonding force, and the following scheme is disclosed: a separator with an adhesive layer formed by a porous polyolefin film having an adhesive layer on at least one side and an electrode having an electrode active material layer containing an electrode active material and an electrode binder are stacked in such a way that the adhesive layer is in contact with the electrode active material layer. In the manufacturing method of the electrode / separator stack including the process of hot-pressing, the adhesive layer contains a granular polymer A with a glass transition temperature of -50 to 5°C and a granular polymer B with a glass transition temperature of 50 to 120°C, the average thickness of the adhesive layer is 0.2 to 1.0 μm, and hot-pressing is performed at 50 to 100°C.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2014 / 081035 Summary of the Invention

[0008] In order to improve the adhesion between the separator and the electrode, the cost of using multiple particulate polymers with different glass transition temperatures will increase accordingly.

[0009] The non-aqueous electrolyte secondary battery disclosed herein comprises: a separator having an adhesive on at least one side; and an electrode having a core and an electrode composite material layer, wherein the electrode composite material layer is in contact with the adhesive, wherein the concentration of the porous body in the thickness direction of the electrode composite material layer increases from the core toward the adhesive.

[0010] In the non-aqueous electrolyte secondary battery disclosed herein, the concentration of the porous material within the electrode composite material layer is controlled so that it is non-uniform across the thickness direction and increases from the core toward the adhesive. Specifically, the concentration of the porous material is relatively high near the surface of the separator electrode composite material layer that contacts the adhesive. Therefore, during the thermocompression bonding process, the adhesive is bonded to the porous material, allowing more of the adhesive to penetrate into the pores of the porous material, thereby preferentially exhibiting an anchoring effect.

[0011] In one embodiment of the present disclosure, in the electrode composite material layer, the ratio of the porous body within a range of 5 μm from the surface on the binder side is 50% or more.

[0012] In another embodiment of the present disclosure, the electrode composite material layer is a positive electrode composite material layer containing a positive electrode active material, and the porous body is a conductive material.

[0013] According to the present disclosure, the adhesion between the separator and the electrode can be improved without changing the material composition of an adhesive composed of multiple polymers or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. 1 is a diagram showing the configuration of a nonaqueous electrolyte secondary battery according to an embodiment.

[0015] Figure 2A It is an explanatory diagram of bonding of the nonaqueous electrolyte secondary battery according to the embodiment.

[0016] Figure 2B This is a diagram illustrating bonding of a conventional non-aqueous electrolyte secondary battery.

[0017] Figure 3 This is a diagram showing the structure of a method for evaluating the adhesive strength of a non-aqueous electrolyte secondary battery according to an embodiment.

[0018] Figure 4A This is an explanatory diagram (Part 1) of a method for evaluating the adhesive strength of a non-aqueous electrolyte secondary battery according to an embodiment.

[0019] Figure 4B This is an explanatory diagram (part 2) of a method for evaluating the adhesive strength of a non-aqueous electrolyte secondary battery according to an embodiment.

[0020] Figure 5A This is an explanatory diagram of a binary image of a non-aqueous electrolyte secondary battery of an example (Part 1).

[0021] Figure 5B This is an explanatory diagram of a binary image of the non-aqueous electrolyte secondary battery of the example (part 2).

[0022] Figure 6 This is a diagram illustrating a method for evaluating the concentration of porous bodies in a non-aqueous electrolyte secondary battery of an example.

[0023] Figure 7 This is an explanatory diagram of a method for evaluating the porous body concentration in a non-aqueous electrolyte secondary battery of a comparative example. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the present disclosure will be described based on the drawings.

[0025] First, the outline of the square secondary battery is described. The square secondary battery of one embodiment of the present disclosure (hereinafter also referred to as the secondary battery) comprises: an electrode body; an electrolyte; an outer shell for accommodating the electrode body and the electrolyte; and a sealing plate on which the positive terminal and the negative terminal are installed and for sealing the opening of the outer shell. The electrode body has a structure in which the positive electrode and the negative electrode are alternately stacked with a separator. The outer shell is, for example, a flat, roughly rectangular metal container with one end open in the height direction. The outer shell and the sealing plate are, for example, composed of a metal material with aluminum as the main component.

[0026] The electrolyte is preferably a non-aqueous electrolyte, for example, comprising a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may also contain a halogen-substituted product in which at least a portion of the hydrogen atoms in these solvents are replaced by a halogen atom such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF6.

[0027] The sealing plate is mounted with a positive terminal and a negative terminal. The sealing plate has an elongated rectangular shape, with a positive terminal at one end and a negative terminal at the other. The positive and negative terminals are external connection terminals for electrical connection to other secondary batteries and loads, and are mounted to the sealing plate via an insulating member.

[0028] The positive electrode includes a positive tab electrically connected to the positive terminal, and the negative electrode includes a negative tab electrically connected to the negative terminal. The positive terminal is electrically connected to a stack of positive tabs, formed by stacking multiple positive tabs, via a positive current collector plate. The negative terminal is electrically connected to a stack of negative tabs, formed by stacking multiple negative tabs, via a negative current collector plate. The sealing plate also features an injection port for injecting non-aqueous electrolyte and a vent valve that opens to release gas in the event of a battery anomaly.

[0029] The electrode body is divided into, for example, a first electrode group and a second electrode group. These electrode groups have the same stacking structure and dimensions and are stacked along the thickness direction of the electrode body. The upper ends of each electrode group form a positive electrode tab group consisting of multiple positive electrode tabs and a negative electrode tab group consisting of multiple negative electrode tabs, which are respectively connected to the current collector plates of the sealing plate. The outer peripheral surfaces of these electrode groups are covered by separators, and the battery reaction is independently carried out in these electrode groups.

[0030] The electrode body includes a plurality of positive electrodes and a plurality of negative electrodes. In the electrode group constituting the electrode body, for example, one more negative electrode is included than the positive electrode, and the negative electrodes are arranged on both sides of the thickness direction of the electrode group. Separators are arranged one by one between the positive electrode and the negative electrode, but the separators included in the electrode group may also be separate sheets. The electrode groups each include an adhesive layer and are manufactured using a hot pressing process. In more detail, the electrode groups are respectively manufactured by using a pair of hot plates to press a stack formed by alternately stacking a plurality of positive electrodes and a plurality of negative electrodes one by one with separators therebetween in the stacking direction, thereby applying heat and pressure to the stack to make it a state in which at least a portion of the adhesive layer exhibits adhesive force.

[0031] The positive electrode has a positive electrode core and a positive electrode composite material layer provided on the surface of the positive electrode core. The positive electrode core can be made of a foil of a metal such as aluminum or aluminum alloy that is stable within the potential range of the positive electrode, or a film in which the metal is arranged on the surface. The positive electrode composite material layer preferably comprises a positive electrode active material, a conductive material, and a binding material, and is provided on both sides of the positive electrode core. The positive electrode can be produced, for example, by coating a positive electrode composite material slurry comprising a positive electrode active material, a conductive material, and a binding material on the positive electrode core, drying the coating, and then compressing it to form the positive electrode composite material layer on both sides of the positive electrode core.

[0032] The positive electrode has a structure in which a positive electrode composite material layer composed of a positive electrode composite material is arranged on the entire area of the surface of the positive electrode core except for the positive electrode tab (hereinafter referred to as the "base"). The thickness of the positive electrode core is, for example, 5μm to 20μm, preferably 8μm to 15μm. The base of the positive electrode core is square in front view, and the positive electrode tab protrudes from one side of the square. Usually, a single metal foil is processed to obtain a positive electrode core in which the base and the positive electrode tab are integrally formed.

[0033] A lithium transition metal composite oxide can be used as the positive electrode active material. Examples of the metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. It is preferred that at least one of Ni, Co, and Mn be contained. As an example of an ideal composite oxide, a lithium transition metal composite oxide containing Ni, Co, and Mn and a lithium transition metal composite oxide containing Ni, Co, and Al can be cited.

[0034] As the conductive material included in the positive electrode composite material layer, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be exemplified. As the binding material included in the positive electrode composite material layer, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. can be exemplified. In addition, these resins can also be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0035] The negative electrode comprises: a negative electrode core; and a negative electrode composite material layer disposed on the surface of the negative electrode core and composed of a negative electrode composite material. The negative electrode core may be made of a foil of a metal such as copper that is stable within the potential range of the negative electrode, or a thin film having the metal disposed on the surface. The negative electrode composite material layer preferably comprises a negative electrode active material and a binding material, and is disposed on both sides of the negative electrode core. The negative electrode can be manufactured, for example, by coating a negative electrode composite material slurry comprising a negative electrode active material and a binding material on the surface of the negative electrode core, drying the coating, and then compressing the coating to form the negative electrode composite material layers on both sides of the negative electrode core.

[0036] The negative electrode has a structure in which a negative electrode composite material layer is formed on the surface of the negative electrode core, excluding the negative electrode tab, i.e., the entire base area. The thickness of the negative electrode core is, for example, 3 μm to 15 μm, preferably 5 μm to 10 μm. As with the positive electrode, the base of the negative electrode core is square in front view, with the negative electrode tab protruding from one side of the square. Typically, a single sheet of metal foil is processed to obtain a negative electrode core with the base and negative electrode tab integrally formed.

[0037] As the negative electrode active material, for example, a carbon-based active material that reversibly stores and releases lithium ions can be used. Ideal carbon-based active materials include natural graphites such as flaky graphite, bulk graphite, and earthy graphite, as well as graphites such as bulk artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB). Furthermore, the negative electrode active material can be a Si-based active material composed of at least one of Si and a Si-containing compound, or a combination of a carbon-based active material and a Si-based active material.

[0038] The binding material included in the negative electrode composite material layer is the same as that in the positive electrode, and fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can be used, preferably styrene-butadiene rubber (SBR). In addition, the negative electrode composite material layer preferably further includes CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. Among them, it is ideal to use SBR in combination with CMC or its salt, PAA or its salt.

[0039] The above is an overview of the prismatic secondary battery. Next, the structure of the electrode group and the separator in this embodiment will be further described.

[0040] Figure 1 This is an enlarged schematic cross-sectional view when the electrode group is cut along a plane substantially perpendicular to the height direction in the stacking direction, and includes a portion of the separator, a portion of the positive electrode, and an adhesive layer.

[0041] like Figure 1 As shown, the separator 20 comprises: a substrate; and an adhesive 18 on at least one side, preferably on both sides (for ease of explanation, the figure shows the case where it is present on only one side). The substrate is composed of a porous sheet having ion permeability and insulating properties. For example, the separator 20 can be composed of a porous substrate mainly composed of at least one selected from polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aramid. It is preferably composed of polyolefin, and particularly preferably composed of polyethylene and polypropylene.

[0042] The adhesive 18 is formed by disposing a plurality of adhesive dots (dot-shaped portions) on at least one of the entire surface of one side and the entire surface of the other side of the separator 20 by coating or other processing so that the area density is substantially constant.

[0043] It should be noted that the adhesive 18 can be applied to the entire surface of the separator, rather than in a dotted pattern. Specifically, the adhesive 18 can be applied to at least one of one side surface and the other side surface of the separator at a substantially constant area density, forming an adhesive layer on at least one side surface of the separator. Adhesive 18 can be made from known materials, such as acrylic resin adhesives, polyurethane resin adhesives, ethylene-vinyl acetate resin adhesives, or epoxy resin adhesives.

[0044] In a manner such that one side of the separator 20 provided with the adhesive 18 is opposite to the positive electrode, the positive electrode and the negative electrode are alternately stacked across the separator 20 to form a laminate, and then pressure and heat are applied to the laminate from both sides of the stacking direction using hot plates arranged on one side and the other side of the stacking direction, thereby softening a portion of the adhesive. In this way, the separator 20 is bonded to the positive electrode with an adhesive, and the separator 20 is bonded to the negative electrode with an adhesive, thereby preventing the positive electrode, the negative electrode, and the separator 20 from shifting in position and preventing a short circuit. It should be noted that a heat-resistant layer can be configured in any of the positive electrode, the negative electrode, and the separator for the purpose of preventing a short circuit between the positive electrode and the negative electrode. The heat-resistant layer comprises inorganic particles such as aluminum oxide, and is, for example, composed of a ceramic heat-resistant layer.

[0045] like Figure 1 As shown, the positive electrode has a positive electrode core 10 and a positive electrode composite material layer 12 provided on the surface of the positive electrode core 10. The positive electrode composite material layer 12 contains a positive electrode active material, a conductive material, and a binding material. For example, it can be prepared by coating a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binding material on the positive electrode core 10, drying the coating film, and then compressing it to form the positive electrode composite material layer 12 on the surface of the positive electrode core 10. The positive electrode composite material layer 12 of this embodiment is composed of a layer 14 with a relatively low porous body concentration and a layer 16 with a relatively high porous body concentration. In other words, the porous body concentration of the positive electrode composite material layer 12 is not uniform in the thickness direction, but is non-uniform, and is configured such that the porous body concentration increases from the positive electrode core 10 toward the binder 18, and conversely, the porous body concentration decreases from the binder 18 toward the positive electrode core 10. Figure 1 In the figure, the non-porous body 13 is schematically represented by a black circle, and the porous body 15 is represented by a shaded circle. It can be said that in the positive electrode composite material layer 12, the concentration of the porous body 15 is relatively higher on the binder 18 side, and the concentration of the non-porous body 13 is relatively higher on the positive electrode core 10 side. Alternatively, it can be said that in the positive electrode composite material layer 12, the porous body is biased toward the binder 18 side.

[0046] As described above, the positive electrode composite material layer 12 includes a positive electrode active material, a conductive material, and a binding material. The positive electrode active material can use a lithium transition metal composite oxide. As a conductive material, carbon black, acetylene black, Ketjen black, graphite and other carbon materials can be exemplified. As a binding material, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) and other fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins and the like can be exemplified. Among these, acetylene black is a typical example of a porous body. Therefore, as an example, it can be: by making the concentration of acetylene black as a conductive material included in the positive electrode composite material layer 12 non-uniform in the thickness direction, the concentration of acetylene black is increased from the positive electrode core 10 to the adhesive 18, thereby constituting the porous body concentration to increase from the positive electrode core 10 to the adhesive 18.

[0047] Figure 2A The bonding state between the positive electrode and the separator 20 in this embodiment is schematically shown. The positive electrode composite material layer 12 is in contact with the adhesive 18. When pressure and heat are applied to the laminate from both sides in the stacking direction in this state, the adhesive 18 softens. The softened adhesive 18 enters the pores of the porous body 15, preferentially exhibiting an anchoring effect, thereby improving the bonding strength between the positive electrode and the separator 20.

[0048] on the other hand, Figure 2B This diagram schematically illustrates the bonding state of a conventional positive electrode and separator 20, where the porous material concentration of the positive electrode composite material layer 12 is uniform throughout the thickness. The positive electrode composite material layer 12 is in contact with the adhesive 18. When pressure and heat are applied to the laminate from both sides in the stacking direction, the adhesive 18 softens. However, the softened adhesive 18 has difficulty entering the pores of the porous material 15 (in other words, the non-porous material 13 inhibits the anchoring effect of the porous material 15), and thus does not preferentially exhibit an anchoring effect. The bonding strength is positively correlated with the porous material concentration on the side of the positive electrode composite material layer 12 in contact with the adhesive 18; a higher porous material concentration results in greater bonding strength.

[0049] It should be noted that the above is an explanation of the bonding force between the positive electrode and the separator 20, and the same applies to the bonding force between the negative electrode and the separator 20. That is, the concentration of the porous body contained in the negative electrode composite material layer is made non-uniform in the thickness direction, so that the concentration of the porous body increases from the negative electrode core toward the adhesive 18. When pressure and heat are applied to the stack from both sides of the stacking direction in this state, the adhesive 18 softens, and the softened adhesive 18 enters the pores of the porous body, preferentially exhibiting an anchoring effect, and the bonding force between the negative electrode and the separator 20 is improved. Therefore, in at least any one of the positive and negative electrodes, it is sufficient to be configured in such a way that the concentration of the porous body in the thickness direction of the electrode composite material layer increases from the electrode core toward the adhesive.

[0050] Hereinafter, examples will be described.

[0051] <Example>

[0052] Figure 3 The adhesive strength evaluation method in this example is described.

[0053] First, prepare the separator 20 and the positive electrode 30. The separator 20 has a heat-resistant layer 32 and further has an adhesive 18. The adhesive 18 is formed by arranging a plurality of dot-shaped adhesives 18 on the entire area of one side of the separator 20 provided with the heat-resistant layer 32 using a coating or other process in such a manner that the area density becomes approximately constant. The positive electrode 30 has a positive electrode composite material layer. The adhesive 18 of the separator 20 is brought into contact with the positive electrode composite material layer of the positive electrode 30, and a pair of hot plates are used to press the separator 20 and the positive electrode 30 under specified conditions, thereby applying heat and pressure to the adhesive 18 so that it exhibits adhesive force. After cooling, if the separator 20 is peeled off, the heat-resistant layer 32 is transferred to the positive electrode composite material layer of the positive electrode 30. The adhesive force between the heat-resistant layer 32 of the separator 20 and the substrate is weaker than the adhesive force between the positive electrode 30 and the adhesive. Therefore, when the separator 20 is peeled from the positive electrode 30 , the bonded portion of the adhesive 18 is not peeled from the positive electrode 30 and the heat-resistant layer 32 , but the heat-resistant layer 32 is peeled from the substrate.

[0054] Figure 4A This diagram schematically illustrates the state in which the heat-resistant layer 32 is transferred onto the positive electrode composite material layer of the positive electrode 30. The adhesive 18 and the heat-resistant layer 32 are transferred onto the positive electrode composite material layer of the positive electrode 30 in a dotted pattern. When the adhesive 18 has a relatively strong adhesive force, the heat-resistant layer 32 is transferred, but when the adhesive 18 has a relatively weak adhesive force, the heat-resistant layer 32 is not transferred. Therefore, by evaluating the amount of transferred heat-resistant layer 32 or the concentration of transferred heat-resistant layer 32, the adhesive force can be quantitatively evaluated.

[0055] Figure 4B The image schematically shows an image obtained by peeling the separator 20 from the positive electrode 30 , photographing the surface of the positive electrode 30 on the side where the separator 20 is peeled off using a camera, a scanner, or the like, and binarizing the obtained photographed image. Figure 4B In the figure, the black color represents the positive electrode composite material layer, and the dotted white circles represent the transferred heat-resistant layer 32, i.e., the transfer traces.

[0056] Transfer mark density = (white area) / (black area)

[0057] The transfer mark density was calculated to quantitatively evaluate the adhesive strength between the separator 20 and the positive electrode 30. It should be noted that when the separator 20 and the positive electrode 30 are pressed using a pair of hot plates under prescribed conditions, if the prescribed conditions are the same, the adhesive strength between the heat-resistant layer 32 and the adhesive 18 is considered to be the same.

[0058] Hereinafter, this embodiment will be described in more detail.

[0059] <Production of positive electrode>

[0060] A positive electrode composite material layer is formed on both sides of an aluminum foil having a thickness of 13 μm. The thickness of the positive electrode composite material layer is 60 μm per side after compression treatment. The length of the positive electrode plate in the width direction is 80 mm. The width (length in the width direction) of the collector ear portion exposed by the positive electrode core is 20 mm. The length of the positive electrode plate in the longitudinal direction is 140 mm. The positive electrode composite material layer contains lithium nickel cobalt manganese composite oxide as a positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride (PVDF) as a binding material in a mass ratio of 97:2:1.

[0061] At this time, the positive electrode can be coated on the positive electrode core body with a positive electrode composite material slurry including a positive active material, a conductive material, and a binding material, and the like, so that the coating is dried and then compressed, and the positive electrode composite material layer is formed on the positive electrode core body, thereby making, but by changing the drying speed when the coating is dried, the distribution of acetylene black as a conductive material can be changed in the thickness direction and the concentration of the porous body can be changed in the thickness direction. Specifically, a positive electrode in which the porous body concentration is roughly uniform in the past is made by drying at the same drying speed as in the past, and a positive electrode in which the drying speed is greater than that in the past so that the porous body concentration is uneven in the thickness direction and the acetylene black as a conductive material on the positive electrode surface is relatively biased in many places. By controlling the drying speed (water evaporation rate) when the positive active material layer slurry is dried, the concentration distribution of the conductive material in the positive electrode composite material layer will change, and the faster the drying speed, the more the amount of conductive material contained in the region close to the surface of the positive electrode composite material layer will increase.

[0062] More specifically, as the drying conditions for applying a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binder, the cumulative temperature is calculated by multiplying the temperature difference between the furnace temperature during the drying process and the time (in minutes) required for the plate to pass through the furnace, using a reference temperature of 25°C. Drying is performed under conditions such that the cumulative temperature to which the plate is subjected during the entire drying process reaches approximately 265°C / minute, thereby producing the positive electrode plate of the embodiment. As described later, the proportion of porous bodies within the 5μm range of the surface layer of this positive electrode plate is 63.7%, which is greater than 50%.

[0063] Similarly, as the drying conditions for applying a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binding material, the cumulative temperature is calculated by multiplying the temperature difference between the temperature in the furnace during the drying process and the time (minutes) required for the plate to pass through the furnace, with a reference temperature of 25°C. The plate is dried under conditions such that the cumulative temperature to which it is subjected during the entire drying process reaches approximately 170°C / minute, thereby producing a conventional positive electrode plate as a comparative example. As described later, the proportion of porous bodies within the 5μm range of the surface layer of this positive electrode plate is 10.8%, which is less than 50%.

[0064] In summary, the materials of the electrode composite material layers of the embodiment and the comparative example are the same, and the drying speed of the positive electrode composite material slurry is changed to

[0065] Example: about 265°C / min

[0066] Comparative Example: approximately 170°C / min.

[0067] <Separator>

[0068] The separator used was a polyethylene monolayer substrate coated on one side with a ceramic heat-resistant layer and dot-coated with an acrylic resin adhesive layer on both sides. The separator had a substrate thickness of 12 μm, a heat-resistant layer thickness of 4 μm, and a width of 80 mm. The amount of adhesive applied to each dot was kept roughly the same. Furthermore, the number density of the adhesive dots was maintained at a roughly constant level on one side of the separator.

[0069] <Thermocompression bonding process>

[0070] For samples using the positive electrode of the example and samples using the conventional positive electrode, the processing conditions for thermocompression bonding the separator 20 and the positive electrode 30 were changed as follows.

[0071] (1) 74 degrees, 20 kN, 25 seconds

[0072] (2) 74 degrees, 25 kN, 15 seconds

[0073] (3) 74 degrees, 25 kN, 20 seconds

[0074] (4) 74 degrees, 25 kN, 25 seconds

[0075] (5) 74 degrees, 30 kN, 15 seconds

[0076] <Adhesion Evaluation>

[0077] For the examples and the conventional samples that were thermocompression bonded under the thermocompression bonding conditions (1) to (5) above, after sufficient cooling after thermocompression bonding, the separator 20 was peeled off from the positive electrode 30, and the surface of the positive electrode 30 was photographed with a scanner to obtain an image, which was binarized to obtain a binary image.

[0078] Transfer mark density = (white area) / (black area)

[0079] The transfer mark concentration in the binary image is calculated in the form of and used as an indicator of adhesion. The white area is the heat-resistant layer transfer area, and the black area is the total area of the electrode plate. Therefore, the above formula can be expressed as

[0080] Transfer mark concentration = (heat-resistant layer transfer area) / (total plate area).

[0081] Figure 5A is an example of a binary image of a sample of the embodiment. Figure 5B This is an example of a binary image of a conventional sample. In the sample of the embodiment, the concentration of the conductive material on the surface of the positive electrode 30 is relatively high, and the concentration of the porous body is also high, so the white area is larger than that of the conventional sample.

[0082] Table 1 shows the adhesive strength evaluation results when thermocompression bonding was performed on the examples and conventional samples under five conditions (1) to (5).

[0083] [Table 1]

[0084]

[0085] In Table 1, when thermocompression bonding was performed at 74°C, 20 kN, and 25 seconds, the transfer mark concentration of the sample of the example was 4962 ppm, or 0.4962%, while the transfer mark concentration of the conventional sample was 3037 ppm, or 0.3037%. Therefore, the ratio of the adhesive strength of the sample of the example to that of the conventional sample was 163%.

[0086] Similarly, when hot pressing was performed at 74 degrees Celsius, 25 kN, and 15 seconds, the transfer mark concentration of the sample of the embodiment was 2662 ppm, or 0.2662%, while the transfer mark concentration of the conventional sample was 1415 ppm, or 0.1415%. Therefore, the ratio of the adhesion strength of the sample of the embodiment to the conventional sample was 188%. Furthermore, when hot pressing was performed at 74 degrees Celsius, 25 kN, and 20 seconds, the transfer mark concentration of the sample of the embodiment was 5629 ppm, or 0.5629%, while the transfer mark concentration of the conventional sample was 5381 ppm, or 0.5381%. Therefore, the ratio of the adhesion strength of the sample of the embodiment to the conventional sample was 105%. Furthermore, when hot pressing was performed at 74 degrees Celsius, 25 kN, and 25 seconds, the transfer mark concentration of the sample of the embodiment was 20014 ppm, or 2.014%, while the transfer mark concentration of the conventional sample was 12596 ppm, or 1.2596%. Therefore, the ratio of the adhesion strength of the sample in the example to that of the conventional sample was 159%. Furthermore, when thermocompression bonding was performed at 74°C, 30 kN, and 15 seconds, the transfer mark concentration of the sample in the example was 12010 ppm, or 1.2010%, while the transfer mark concentration of the conventional sample was 3430 ppm, or 0.3430%. Therefore, the ratio of the adhesion strength of the sample in the example to that of the conventional sample was 350%.

[0087] These results confirm that the adhesive strength of the samples of the examples is greater than that of conventional samples regardless of the thermocompression bonding conditions. In particular, it was confirmed that the adhesive strength of the samples of the examples is significantly increased by more than three times under the thermocompression bonding conditions of 74°C, 30 kN, and 15 seconds.

[0088] Next, EDX (energy dispersive X-ray spectroscopy) mapping of the positive electrode cross-section was performed on the samples of the examples and conventional samples. The electrode plates, manufactured using an ion milling device or the like, were cut along the thickness direction of the electrode plates and captured using a SEM at an accelerating voltage of 3 kV to obtain cross-sectional SEM images. EDX was then used to perform carbon mapping to obtain the thickness distribution of the porous body.

[0089] Figure 6 In the EDX mapping image 304 of the example sample shown, the porous object and non-porous material are separated into two colors and then binarized. The concentration of acetylene black, the conductive material, is uneven in the thickness direction, with a relatively high concentration on the positive electrode surface.

[0090] in addition, Figure 7 In the EDX mapping image 314 of the conventional sample shown, Figure 6Similarly, the porous object and the non-porous substance were separated into two colors and then binarized. The concentration of acetylene black as a conductive material was approximately uniform in the thickness direction, and the concentration on the positive electrode surface was relatively lower than that of the sample of the embodiment.

[0091] Furthermore, to quantitatively evaluate the concentration of the conductive material on the positive electrode surface of the two samples, that is, the concentration of the porous body, the proportion of the conductive material on the positive electrode surface, more specifically within 5 μm from the positive electrode composite material layer surface, was counted.

[0092] The conductive material concentration within 5 μm from the surface of the positive electrode composite material layer, that is, the porous body concentration, is calculated as the ratio of the white area to the black area in the binary image, similarly to the transfer mark concentration described above.

[0093] Porous body concentration = (white area) / (black area).

[0094] as a result,

[0095] Sample of Example = 63.7%

[0096] Conventional sample = 10.8%.

[0097] In addition, it should be noted that the transfer mark concentration in Table 1 is the concentration in the plane image of the positive electrode composite material layer. Figure 6 and Figure 7 The conductive material concentration in is the concentration in the image in the thickness direction of the positive electrode composite material layer.

[0098] In order for the porous material to adhere to the binder and for the binder to enter the pores of the porous material, thereby preferentially exhibiting an anchoring effect, it is desirable to have as much porous material as possible within a thickness range of approximately 5 μm, where the binder particles are assumed to enter. It is believed that a porous material concentration of 50% or more, compared to other materials in the positive electrode composite material layer, can fully exert the anchoring effect. Therefore, focusing on the range of 5 μm from the surface of the positive electrode composite material layer, the conductive material concentration, i.e., the porous material concentration, is preferably 50% or more, and more preferably 60% or more.

[0099] Description of Reference Numerals

[0100] 10. Positive electrode core

[0101] 12. Positive electrode composite material layer

[0102] 14 Layer with relatively low concentration of porous bodies

[0103] 16 Layer with relatively high concentration of porous bodies

[0104] 18 Adhesive

[0105] 20 dividers

Claims

1. A non-aqueous electrolyte secondary battery comprising: a separator having an adhesive on at least one side; and An electrode having a core and an electrode composite material layer, wherein the electrode composite material layer is in contact with the adhesive, In the electrode composite material layer, the concentration of the porous body in the thickness direction increases from the core toward the binder. In the electrode composite material layer, the proportion of the porous body within a range of 5 μm from the surface on the adhesive side is 50% or more. The electrode composite material layer is a positive electrode composite material layer containing a positive electrode active material, The porous body is a conductive material, The method for measuring the ratio of the porous body within a range of 5 μm from the surface on the adhesive side includes: The electrode plate produced by the ion thinning device was cut along the thickness direction of the electrode plate, and a cross-sectional image was taken using an SEM device at an accelerating voltage of 3kV to obtain a cross-sectional SEM image. After that, carbon mapping was performed using an energy dispersive X-ray spectrometer to obtain the thickness direction distribution of the porous body. In the obtained energy dispersive X-ray spectrometer mapping image, porous objects and non-porous materials are divided into two colors and then binarized. Furthermore, the proportion of the conductive material within a range of 5 μm from the surface on the adhesive side was counted and calculated as: porous body proportion = (white area) / (black area).

Images