Negative electrode plate, lithium ion secondary battery, and method for manufacturing negative electrode plate

Abstract

The present application relates to a negative electrode plate, a lithium ion secondary battery provided with the negative electrode plate, and a manufacturing method of the negative electrode plate. The negative electrode plate (1) is provided with a current collector foil (3) and an active material layer (5, 6) formed on the current collector foil (3), the active material layer (5, 6) contains flaky graphite particles (11) and a binder resin (13), the flaky graphite particles (11) are bonded to each other and to the current collector foil (3) by the binder resin (13) which is hot melted, and the peak intensity ratio (Rp) of XRD analysis of the active material layer (5, 6) is 130 or less.

Description

Technical Field

[0001] This disclosure relates to a negative electrode plate having an active material layer comprising flake-like graphite particles and a binder resin on a current collector foil, a lithium-ion secondary battery having the negative electrode plate, and a method for manufacturing the negative electrode plate. Background Technology

[0002] As a negative electrode plate used in lithium-ion secondary batteries (hereinafter, also simply referred to as "battery"), a negative electrode plate is known to have an active material layer containing flake-shaped graphite particles (negative electrode active material particles) and binder resin formed on a current collector foil. Such a negative electrode plate is manufactured, for example, by the following method: flake-shaped graphite particles, binder particles composed of binder resin, and a dispersion medium are mixed to obtain an active material paste in advance, in which the flake-shaped graphite particles are dispersed in the dispersion medium and the binder particles are dissolved in the dispersion medium. Next, the active material paste is coated onto the current collector foil to form an undried active material layer on the current collector foil. Then, hot air is blown onto the undried active material layer to heat and dry it, forming the active material layer. As a result, the binder resin dissolved in the dispersion medium precipitates out, and the flake-shaped graphite particles bond to each other and to the current collector foil through the precipitated binder resin. Hereinafter, this method of manufacturing the negative electrode plate will also be referred to as the "conventional manufacturing method". It should be noted that, as a prior art related to this prior method, Japanese Patent Application Publication No. 2020-087569 can be cited as an example. Summary of the Invention

[0003] However, the aforementioned conventional manufacturing method uses an active material paste containing a dispersion medium. Therefore, in order to remove the dispersion medium, a heating and drying process is required to remove the undried active material layer. Consequently, the production rate of the negative electrode plate is low, and the negative electrode plate becomes expensive.

[0004] However, flake-shaped graphite particles typically have a flattened morphology comprising a pair of principal faces (basal faces) and end faces connecting the basal faces and being approximately orthogonal to them. In a battery, lithium ions primarily enter the particle from the outside through the end faces of the flake-shaped graphite particles, or are released from the particle from the inside out. Therefore, the more flake-shaped graphite particles are arranged upright within the active material layer with their end faces facing the surface of the active material layer, and the fewer flake-shaped graphite particles are arranged horizontally with their basal faces facing the surface of the active material layer, the easier it is for lithium ions to smoothly enter the active material layer from the outside, or to smoothly be released from the active material layer from the inside out. Therefore, if a negative electrode plate with such an active material layer is used to manufacture a battery, the battery resistance can be reduced.

[0005] However, in the aforementioned conventional manufacturing method, a large number of flake-shaped graphite particles are arranged in a so-called "flat" position within the active material layer, with their base surfaces facing the surface of the active material layer. When the active material paste is coated onto the current collector foil, the flake-shaped graphite particles tend to be arranged in a flat position with a pair of base surfaces parallel to the main surface of the current collector foil. Furthermore, considering that even flake-shaped graphite particles arranged in an upright position may fall over due to subsequent hot air blowing during the coating of the active material paste, they are prone to becoming flat. In such an active material layer, lithium ions are difficult to embed within and release from the active material layer, thus increasing the battery resistance when using this negative electrode plate to manufacture the battery.

[0006] Thus, the negative electrode plates manufactured by the aforementioned conventional methods are expensive and have high battery resistance.

[0007] This disclosure is made in view of the above-mentioned situation, and provides a low-cost negative electrode plate that can reduce battery resistance, a lithium-ion secondary battery having the negative electrode plate, and a method for manufacturing the negative electrode plate.

[0008] One aspect of the present disclosure for solving the above-mentioned problem is a negative electrode plate having a current collector foil and an active material layer formed on the current collector foil, the active material layer comprising flake-shaped graphite particles and a binder resin, wherein the flake-shaped graphite particles are bonded to each other and to the current collector foil by thermally molten binder resin, and the peak intensity ratio of XRD analysis is 130 or less.

[0009] In the aforementioned negative electrode plate, the flake-shaped graphite particles forming the active material layer are bonded together with each other and with the current collector foil via a hot-melted binder resin. Unlike conventional methods that use an active material paste containing a dispersion medium, this active material layer is formed by dry-melting binder particles composed of binder resin. Therefore, a heating and drying process to remove the dispersion medium is unnecessary, resulting in higher productivity and lower prices compared to conventional methods.

[0010] Furthermore, the peak intensity ratio of the XRD analysis of the active material layer of the aforementioned negative electrode plate is below 130. It should be noted that "peak intensity ratio" refers to the value obtained by the following method: X-ray diffraction (XRD) of CuKα rays is performed on the active material layer of the negative electrode plate. The peak indicating the presence of the (004) plane appears near a diffraction angle of 2θ = 54.6°, and the peak indicating the presence of the (110) plane appears near a diffraction angle of 2θ = 77.5°. The peak intensity ratio (= P(004) / P(110)) is calculated by dividing the peak intensity (count) P(004) of the (004) plane by the peak intensity (count) P(110) of the (110) plane.

[0011] The greater the peak intensity P(004) of the (004) plane, the more flake-like graphite particles lie flat on the surface of the active material layer with their base facing the surface. Conversely, the greater the peak intensity P(110) of the (110) plane, the more flake-like graphite particles stand upright on the surface of the active material layer with their end faces facing the surface. In the active material layer of the negative electrode plate manufactured by the conventional method described above, as described later, the peak intensity ratio exceeds, for example, 180.

[0012] In contrast, the peak intensity ratio of the active material layer in the aforementioned negative electrode plate is below 130. Therefore, compared to the active material layer of the negative electrode plate obtained by conventional methods, there are fewer flat, scaly graphite particles with their base facing the surface of the active material layer, and more flat, scaly graphite particles with their end faces facing the surface of the active material layer. In such an active material layer, lithium ions are easily embedded within and released from the active material layer. If a battery is manufactured using a negative electrode plate with this active material layer, the battery resistance can be reduced. Thus, the aforementioned negative electrode plate is an inexpensive negative electrode plate that can reduce battery resistance.

[0013] It should be noted that "flake-like graphite particles" refers to graphite particles whose aspect ratio (d / t) is greater than 5, meaning the ratio of the maximum diameter d of the flake-like graphite particle to its thickness t (the particle thickness in the direction orthogonal to the basal plane). This aspect ratio (d / t) is determined by magnifying and measuring each graphite particle individually using a scanning electron microscope, and then calculating the average aspect ratio (d / t) of multiple graphite particles.

[0014] Alternatively, another approach is to use a lithium-ion secondary battery with the aforementioned negative electrode plate.

[0015] The aforementioned lithium-ion secondary battery has the aforementioned negative electrode plate, which enables the battery to be inexpensive and reduces battery resistance.

[0016] Another method is a manufacturing method for a negative electrode plate, wherein the negative electrode plate comprises a current collector foil and an active material layer formed on the current collector foil. The active material layer comprises flake-shaped graphite particles and a binder resin. The flake-shaped graphite particles are bonded to each other and to the current collector foil by thermally molten binder resin. The peak intensity ratio of the XRD analysis is 130 or less. The manufacturing method of the negative electrode plate comprises the following steps: an uncompressed layer forming step, wherein composite active material particles formed by binder particles composed of the binder resin being attached to the flake-shaped graphite particles are deposited on the current collector foil to form an uncompressed active material layer; and a pressurizing step, wherein the uncompressed active material layer and the current collector foil are heated and pressurized to form the active material layer in which the flake-shaped graphite particles are bonded to each other and to the current collector foil by thermally molten binder resin, and the flake-shaped graphite particles are configured to have a peak intensity ratio of 130 or less.

[0017] The above-described method for manufacturing a negative electrode plate includes the aforementioned uncompressed layer formation step and pressurization step, enabling the active material layer to be formed dry without using an active material paste. Therefore, a heating and drying step to remove the dispersion medium is unnecessary. Compared to the conventional method described above, this method offers higher productivity for negative electrode plates and allows for their manufacture at a lower cost.

[0018] Furthermore, in the above-described manufacturing method, an active material layer with a peak intensity ratio of 130 or less in XRD analysis is formed. As described above, compared to the active material layer of a negative electrode plate obtained by conventional methods, lithium ions are more easily embedded in and released from the active material layer. Therefore, if a battery is manufactured using a negative electrode plate with this active material layer, the battery resistance can be reduced. Thus, according to the above-described manufacturing method, a low-cost negative electrode plate that reduces battery resistance can be manufactured.

[0019] Furthermore, the above-mentioned method for manufacturing the negative electrode plate can be the following method for manufacturing the negative electrode plate, wherein the above-mentioned uncompressed layer forming process includes: a supply process, in which the above-mentioned composite active material particles are supplied to the film forming region; and an electrostatic deposition process, in the above-mentioned film forming region, the above-mentioned composite active material particles are caused to fly toward the above-mentioned current collector foil by electrostatic force, so that the above-mentioned composite active material particles are deposited on the above-mentioned current collector foil to form the above-mentioned uncompressed active material layer.

[0020] In the above-described method for manufacturing the negative electrode plate, during the uncompressed layer formation process, composite active material particles are supplied to the film-forming area (supply process), and electrostatic force is used to deposit the composite active material particles onto the current collector foil to form an uncompressed active material layer (electrostatic deposition process). This allows for the easy formation of an uncompressed active material layer.

[0021] In the supply process, one method for supplying composite active material particles to the film-forming region is, for example, to electrostatically adsorb the composite active material particles onto magnetic carrier particles to form composite carrier particles, and then supply these composite carrier particles to the film-forming region, thereby supplying the composite active material particles to the film-forming region. Alternatively, a method can be used where composite active material particles are layered on rollers or belts, and the particles are supplied to the film-forming region by the movement of the rollers or belts.

[0022] Furthermore, the manufacturing method of the aforementioned negative electrode plate is preferably the following method, wherein the uncompressed layer forming step further includes a magnetic adsorption step, in which the composite carrier particles on which the composite active material particles are electrostatically adsorbed are magnetically adsorbed onto the surface of the magnetic roller; the supply step is a carrier supply step in which the composite carrier particles magnetically adsorbed onto the surface of the roller are supplied to the film-forming area by rotating the magnetic roller; and the electrostatic deposition step is a process in which the composite active material particles in the composite carrier particles fly toward the current collector foil in the film-forming area.

[0023] In the above-described method for manufacturing the negative electrode plate, the uncompressed layer formation process includes the aforementioned magnetic adsorption process and carrier supply process, where magnetic carrier particles and a magnetic roller are used to supply composite active material particles to the film-forming area. This process facilitates the formation of an uncompressed active material layer. Attached Figure Description

[0024] Figure 1 This is a perspective view of the battery according to the implementation method.

[0025] Figure 2 This is a perspective view of the negative electrode plate in the implementation method.

[0026] Figure 3 This is a cross-sectional schematic diagram of the first active material layer in the negative electrode plate of the embodiment.

[0027] Figure 4 This is a flowchart of the manufacturing method of the negative electrode plate in the implementation method.

[0028] Figure 5 This is an explanatory diagram of the active substance layer forming apparatus according to the embodiment.

[0029] Figure 6 This is an illustration showing a state in which composite carrier particles are magnetically adsorbed onto the surface of a magnetic roller below the roller, and the composite carrier particles on the roller surface move upward by rotating the magnetic roller.

[0030] Figure 7 This is an explanatory diagram schematically illustrating the state in which composite active material particles in the composite carrier particles fly toward the current collector foil in the film-forming region, and the composite active material particles are deposited on the current collector foil.

[0031] Figure 8 This is a graph showing the battery resistance ratio of the batteries in Examples 1-4 and the comparative examples.

[0032] Symbol Explanation

[0033] 1 Negative electrode plate

[0034] 3. Current collector foil

[0035] 5 First active substance layer

[0036] 5X First Uncompressed Active Material Layer

[0037] 6 Second active substance layer

[0038] 6X Second Uncompressed Active Material Layer

[0039] 11. Flake-like graphite particles

[0040] 11E end face

[0041] 11B base plane

[0042] 13 Adhesive Resin

[0043] 13P binder particles

[0044] 21 Composite active substance particles

[0045] 51 Magnetic carrier particles

[0046] 61 Composite carrier particles

[0047] 100 Battery (Lithium-ion Rechargeable Battery)

[0048] 120 Electrode Body

[0049] 200 Active Material Layer Forming Device

[0050] 220 magnetic roller

[0051] 220m roller surface

[0052] 230 support roller

[0053] 240V DC power supply

[0054] MR film formation area

[0055] Vd DC voltage

[0056] Fg magnetic force

[0057] Fs electrostatic force

[0058] S1 Composite Active Material Powder Manufacturing Process

[0059] S2 Electrostatic Adsorption Process

[0060] S3 First Uncompressed Layer Formation Process

[0061] S31 First Magnetic Adsorption Process

[0062] S32 First carrier supply process (first supply process)

[0063] S33 First Electrostatic Deposition Process

[0064] S4 First Pressurization Process

[0065] S5 Second Uncompressed Layer Formation Process

[0066] S51 Second Magnetic Adsorption Process

[0067] S52 Second Carrier Supply Process (Second Supply Process)

[0068] S53 Second Electrostatic Deposition Process

[0069] S6 Second Pressurization Process Detailed Implementation

[0070] (Implementation Method)

[0071] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Figure 1 The diagram shows a perspective view of the battery (lithium-ion secondary battery) 100 according to this embodiment. This battery 100 is a square, enclosed lithium-ion secondary battery used in vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and electric vehicles. The battery 100 comprises a battery casing 110, electrodes 120 and electrolyte 115 housed within it, and a positive terminal component 130 and a negative terminal component 140 supported by the battery casing 110.

[0072] The battery casing 110 is a cubic box made of aluminum, consisting of a bottomed cylindrical casing body 111 with an opening only on the top and a rectangular plate-shaped casing cover 113 welded to close the opening of the casing body 111. The positive terminal component 130 and the negative terminal component 140 are fixed to the casing cover 113 in a state of electrical insulation from the casing cover 113.

[0073] The electrode body 120 is flat and is stored in the battery casing 110 in a horizontal position. The electrode body 120 is a component formed by overlapping and winding a strip-shaped positive electrode plate 121 and a strip-shaped negative electrode plate 1 around an axis via a pair of strip-shaped separators 125.

[0074] The positive electrode plate 121 has a strip-shaped current collector foil made of aluminum foil and active material layers formed on two main surfaces of the current collector foil. These active material layers are respectively composed of positive electrode active material particles capable of absorbing and releasing lithium ions, conductive particles, and binder resin. In this embodiment, the positive electrode active material particles are lithium nickel cobalt manganese composite oxide particles, the conductive particles are acetylene black (AB) particles, and the binder resin is polyvinylidene fluoride (PVDF).

[0075] Next, the negative electrode plate 1 of this embodiment will be described. Figure 2 A three-dimensional view of negative electrode plate 1 is shown. Figure 3 A cross-sectional schematic diagram of the first active material layer 5 in the negative electrode plate 1 is shown. It should be noted that, hereinafter, the length direction EH, width direction FH, and thickness direction GH of the negative electrode plate 1 are defined as... Figure 2 and Figure 3 The direction shown is explained. The negative electrode 1 has a strip-shaped current collector foil 3 extending along the length direction EH, composed of copper foil with a thickness of 8 μm. In the first main surface 3a of this current collector foil 3, on one side of the width direction FH ( Figure 2 A first active material layer 5 (hereinafter also simply referred to as "active material layer 5") with a thickness of 60 μm is formed in a strip on the region extending in the length direction EH (in the middle, diagonally upward to the left). Additionally, on the second main surface 3b opposite to the current collector foil 3, a second active material layer 6 (hereinafter also simply referred to as "active material layer 6") with a thickness of 60 μm is also formed in a strip on the side in the width direction FH and extending in the length direction EH. On the other side of the negative electrode plate 1 in the width direction FH (… Figure 2 In the middle, diagonally below the right), there are no active material layers 5 and 6 in the thickness direction of GH, which become the exposed part 1r of the current collector foil 3 in the thickness direction of GH.

[0076] The active material layers 5 and 6 are respectively composed of negative electrode active material particles, namely flake graphite particles 11, capable of absorbing and releasing lithium ions, and binder resin 13. In this embodiment, the binder resin 13 is PVDF. The weight ratio of flake graphite particles 11 to binder resin 13 is active material particles: binder resin = 95:5. The flake graphite particles 11 constituting the active material layers 5 and 6 are bonded to each other and to the current collector foil 3 by the thermally molten binder resin 13.

[0077] Furthermore, the peak intensity ratio Rp of the XRD analysis of these active material layers 5 and 6 is below 130, specifically, Rp = 23. It should be noted that the peak intensity ratio Rp was determined using the Ultima IV sample-level multi-purpose X-ray diffractometer from Rigaku Corporation, obtained through the method described above.

[0078] The flake-shaped graphite particles 11 constituting the active material layers 5 and 6 are arranged in a generally random orientation. That is, the active material layers 5 and 6 randomly include: flake-shaped graphite particles 11 with their end face 11E facing the thickness direction GH of the active material layers 5 and 6 and their base face 11B facing the planar direction MH (orthogonal to the thickness direction GH) along the surfaces 5m and 6m of the active material layers 5 and 6; flake-shaped graphite particles 11 with their base face 11B facing the thickness direction GH of the active material layers 5 and 6 and their end face 11E facing the planar direction MH; and flake-shaped graphite particles 11 with their end face 11E and base face 11B inclined towards the thickness direction GH and the planar direction MH, respectively.

[0079] In the aforementioned negative electrode plate 1, the flake-shaped graphite particles 11 forming the active material layers 5 and 6 are bonded to each other and to the current collector foil 3 by thermally molten binder resin 13. Unlike conventional methods that use an active material paste containing a dispersion medium, these active material layers 5 and 6 are formed by thermally melting the binder particles 13P composed of binder resin 13 in a dry process, as described later. Therefore, a heating and drying process for removing the dispersion medium is unnecessary, resulting in higher productivity of the negative electrode plate 1 compared to conventional methods, and thus lower cost. Furthermore, the battery 100 using this negative electrode plate 1 can be made inexpensive.

[0080] Furthermore, the peak intensity ratio Rp of the active material layers 5 and 6 of the negative electrode plate 1 is less than 130. Therefore, compared with the active material layers of the negative electrode plate obtained by conventional manufacturing methods, there are fewer flat, flaky graphite particles 11 with the base surface 11B facing the surfaces 5m and 6m of the active material layers 5 and 6, and more upright, flaky graphite particles 11 with the end face 11E facing the surfaces 5m and 6m of the active material layers 5 and 6. In such active material layers 5 and 6, lithium ions are easily embedded within and released from the active material layers 5 and 6. Therefore, for the battery 100 using the negative electrode plate 1 having these active material layers 5 and 6, as described later, the battery resistance R can be reduced.

[0081] Next, the manufacturing method of the negative electrode plate 1 described above will be explained (see reference). Figures 4-7 First, the "composite active substance powder preparation process S1" (refer to...) Figure 4In this process, a composite active material powder 22 is prepared, which is an aggregate of composite active material particles 21 formed by binder particles 13P composed of binder resin 13 attached to flake graphite particles 11. Specifically, a binder powder 14 is prepared, which is an aggregate of graphite powder 12 composed of flake graphite particles 11 and binder particles 13P (PVDF particles in this embodiment). Next, the graphite powder 12 and the binder powder 14 are added into a mixer (MP Mixer of NIPPON COKE & ENGINEERING Co., Ltd.) at a weight ratio of graphite powder: binder powder = 95:5 and stirred and mixed at 4500 rpm for 2 minutes. As a result, a composite active material particle 21 composed of multiple binder particles 13P attached to each flake graphite particle 11 with a particle size D is obtained. 50 The composite active material powder 22 has a median particle size of approximately 10 μm. This composite active material powder 22 does not contain a dispersion medium (solid content NV is 100 wt%).

[0082] Next, "electrostatic adsorption process S2" (refer to...) Figure 4 In this process, the aforementioned composite active material powder 22 is mixed with magnetic carrier powder 52 formed by the aggregation of magnetic carrier particles 51, resulting in composite carrier powder 62 composed of composite carrier particles 61 formed by the electrostatic adsorption of composite active material particles 21 onto magnetic carrier particles 51. In this embodiment, Powdertech Co., Ltd.'s MF96-100 (particle size D) is used as the magnetic carrier powder 52. 50 (Median particle size: approximately 100 μm). In this electrostatic adsorption process S2, the composite active material powder 22 and the magnetic carrier powder 52 are added to a polyethylene container at a volume ratio VR (composite active material powder / magnetic carrier powder) = 0.4. The plastic container is then placed on a pot-mill rotary table and mixed at 105 rpm for 90 minutes. As a result, a composite carrier powder 62 is obtained, which is composed of composite carrier particles 61 formed by the electrostatic adsorption of multiple composite active material particles 21 onto individual magnetic carrier particles 51.

[0083] It should be noted that, omitting detailed explanations of the investigation results, the volume ratio VR is preferably within the range of 0.2 to 0.6. If the volume ratio VR is less than 0.2, the composite active material powder 22 is too small relative to the magnetic carrier powder 52, resulting in a smaller amount of composite active material particles 21 flying towards the current collector foil 3 in the first uncompressed layer forming step S3 and the second uncompressed layer forming step S5 described later, and a smaller unit area weight of the first uncompressed active material layer 5X and the second uncompressed active material layer 6X. On the other hand, if the volume ratio VR is greater than 0.6, the composite active material powder 22 is too large relative to the magnetic carrier powder 52, therefore, the composite active material powder 22 and the magnetic carrier powder 52 cannot be properly mixed, and the composite carrier powder 62 cannot be properly produced. Therefore, it is difficult to form a uniform first uncompressed active material layer 5X and second uncompressed active material layer 6X in the first uncompressed layer forming step S3 and the second uncompressed layer forming step S5 described later.

[0084] Next, "first uncompressed layer formation process S3" (see...) Figure 4 In this process, an uncompressed first uncompressed active material layer 5X (hereinafter also simply referred to as "uncompressed active material layer 5X") is formed on the first main surface 3a of the current collector foil 3 by deposition of composite active material particles 21. This first uncompressed layer formation step S3 and the first pressurization step S4 described later use an active material layer formation apparatus 200 (see reference 200). Figures 5-7 The process is carried out continuously. The active material layer forming apparatus 200 includes a layer forming section 203 for forming an uncompressed active material layer 5X on a current collector foil 3, and a pressurizing section 205 for heating and pressurizing the uncompressed active material layer 5X and the current collector foil 3 to form the active material layer 5X from the uncompressed active material layer 5X.

[0085] The layer forming section 203 includes: a supply section 210 that supplies the composite carrier powder 62 obtained in the electrostatic adsorption process S2 to the magnetic roller 220; a magnetic roller 220 disposed above the supply section 210; a support roller 230 disposed parallel to the magnetic roller 220 and conveying the current collector foil 3 in the longitudinal direction EH; a DC power supply 240 electrically connected to the magnetic roller 220 and the support roller 230; and a recovery section 250 that recovers the magnetic carrier particles 51.

[0086] The supply unit 210 includes a container 211 for holding composite carrier powder 62 and three stirring blades 213, 214, and 215 disposed within the container 211, configured to convey the composite carrier powder 62 fed into the container 211 to an upward magnetic roller 220. Furthermore, within the container 211 of the supply unit 210, Figure 5 In the middle, a scraper 217 protruding towards the roller surface 220m of the magnetic roller 220 is provided in the upper right part. The scraper 217 smooths the composite carrier powder 62 that is magnetically adsorbed on the roller surface 220m.

[0087] The magnetic roller 220 can attract composite carrier particles 61 to its surface 220m by the magnetic force Fg generated on its roller surface 220m. Furthermore, by rotating the magnetic roller 220, the composite carrier particles 61 magnetically attracted to the roller surface 220m are transported to the gap KB (film-forming region MR) between the magnetic roller 220 and the current collector foil 3. Specifically, the magnetic roller 220 has: a cylindrical metal cylinder 221 made of a soft magnetic metal (aluminum in this embodiment), and a cylindrical inner magnetic part 223 with a 5-pole structure arranged coaxially with the metal cylinder 221 inside the metal cylinder 221.

[0088] The outer circumferential surface 221m of the metal cylinder 221 forms the roller surface 220m of the magnetic roller 220. This metal cylinder 221 is driven by a motor (not shown) connected to it. Figure 5 Rotate counterclockwise.

[0089] On the other hand, the inner magnetic part 223 is fixed and does not rotate. The inner magnetic part 223 has multiple magnets (first magnet 223N1 and fourth magnet 223N2) with N poles on the outer periphery and multiple magnets (second magnet 223S1, third magnet 223S2, and fifth magnet 223S3) with S poles on the outer periphery arranged circumferentially SH. The first magnet 223N1 is positioned at the top, and the second magnet 223S1, third magnet 223S2, fourth magnet 223N2, and fifth magnet 223S3 are arranged counterclockwise from the first magnet 223N1.

[0090] The support roller 230 is positioned parallel to the magnetic roller 220, with a gap KA above it. A gap KB (film-forming region MR) is formed between the current collector foil 3 wound around the support roller 230 and the magnetic roller 220. The support roller 230 is driven by a motor (not shown) connected to it in the opposite direction to the magnetic roller 220. Figure 5 Rotate clockwise (in the middle). Figure 5 In the middle, the current collector foil 3 is in contact with the second main surface 3b of the current collector foil 3 supplied from the right obliquely downward to the layer forming section 203 of the active material layer forming apparatus 200, and the wound current collector foil 3 is conveyed along the length direction EH toward the pressure section 205 described later.

[0091] In the DC power supply 240, its positive terminal is electrically connected to the support roller 230, and its negative terminal is electrically connected to the magnetic roller 220. The support roller 230 is grounded. In this embodiment, a DC voltage Vd = -800V is applied between the magnetic roller 220 and the support roller 230 via the DC power supply 240. Specifically, with the support roller 230 as a reference (0V), the potential of the magnetic roller 220 is set to -800V. As a result, an electrostatic force Fs is applied to the composite active material particles 21 that form the composite carrier particles 61 on the magnetic roller 220, causing the composite active material particles 21 to fly from the roller surface 220m towards the current collector foil 3.

[0092] The recovery section 250 is in the magnetic roller 220 Figure 5 The recovery unit 250 is located on the left. It has a recovery scraper 251 protruding onto the roller surface 220m of the magnetic roller 220. The recovery scraper 251 scrapes off the magnetic carrier particles 51 that are magnetically adsorbed onto the roller surface 220m for recovery.

[0093] The pressurizing section 205 of the active material layer forming apparatus 200 has a pair of pressurizing rollers 271 and 272 arranged in parallel with the empty roller gap KC. These pressurizing rollers 271 and 272 are configured to heat and pressurize the current collector foil 3 and the uncompressed active material layer 5X conveyed from the layer forming section 203 through the roller gap KC.

[0094] Next, the first uncompressed layer formation step S3 and the first pressurization step S4 (refer to the above description) performed using the active material layer forming apparatus 200 will be discussed. Figure 4 (Refer to) Figures 5-7 The first uncompressed layer formation process S3 sequentially includes a first magnetic adsorption process S31, a first carrier supply process (first supply process) S32, and a first electrostatic deposition process S33.

[0095] First, in the "first magnetic adsorption process S31", the composite carrier particles 61 that form the composite carrier powder 62 obtained in the electrostatic adsorption process S2 are magnetically adsorbed onto the roller surface 220m of the magnetic roller 220. Specifically, the composite carrier powder 62 is fed into the container 211 of the supply unit 210, and the composite carrier powder 62 is conveyed upward onto the magnetic roller 220 by the stirring blades 213, 214, and 215. Next, below the magnetic roller 220, the composite carrier particles 61 that form the composite carrier powder 62 are magnetically adsorbed onto the roller surface 220m by the magnetic force Fg generated on the roller surface 220m.

[0096] Next, in the "first carrier supply process S32", the composite carrier particles 61 magnetically adsorbed on the roller surface 220m below are moved upward by the rotation of the magnetic roller 220 (metal cylinder 221) and supplied to the film-forming region MR. Specifically, the composite carrier particles 61 on the roller surface 220m form a carrier group 71 of multiple composite carrier particles 61 arranged in a beaded pattern. This carrier group 71 is positioned upright on the roller surface 220m at the right-sloping downwards, through the N pole of the fourth magnet 223N2. Then, as the carrier group 71 passes near the boundary between the fourth magnet 223N2 and the fifth magnet 223S3, it becomes horizontally tilted along the roller surface 220m. Next, the carrier group 71 is positioned upright again from the roller surface 220m through the S pole of the fifth magnet 223S3. Then, as the carrier group 71 passes near the boundary between the fifth magnet 223S3 and the first magnet 223N1, it again assumes a horizontal position along the roller surface 220m. Next, the carrier group 71 is supplied to the film-forming region MR.

[0097] Next, in the "first electrostatic deposition process S33", in the film-forming region MR, by applying a DC voltage Vd between the magnetic roller 220 and the current collector foil 3, the composite active material particles 21 in the composite carrier particles 61 are propelled towards the current collector foil 3, causing the composite active material particles 21 to deposit on the current collector foil 3 to form an uncompressed active material layer 5X. Specifically, the carrier group 71 on the roller surface 220m is near the film-forming region MR, and by the N pole of the first magnet 223N1, it is once again brought into an upright position from the roller surface 220m. On the other hand, the current collector foil 3 is transported to the film-forming region MR by the support roller 230. In the film-forming region MR, by applying a DC voltage Vd between the magnetic roller 220 and the current collector foil 3, the composite active material particles 21 in the composite carrier particles 61 are propelled from the roller surface 220m towards the current collector foil 3, causing the composite active material particles 21 to deposit on the current collector foil 3 to continuously form an uncompressed active material layer 5X. It should be noted that, then, by rotating the magnetic roller 220, the magnetic carrier particles 51 remaining on the roller surface 220m are moved downwards and scraped off by the recycling scraper 251 of the recycling section 250 for recycling.

[0098] Next, in the "first pressurization process S4", the uncompressed active material layer 5X and the current collector foil 3 are heated and pressurized to form an active material layer 5 in which the flake graphite particles 11 of the uncompressed active material layer 5X are bonded to each other and to the current collector foil 3 by hot-melt adhesive resin 13, and the flake graphite particles 11 are configured such that the peak intensity ratio Rp obtained by XRD analysis is less than 130 (Rp≤130).

[0099] Specifically, the current collector foil 3, to which the uncompressed active material layer 5X is formed, is conveyed from the layer forming section 203 to the pressurizing section 205, where it is heated and pressurized by a pair of pressurizing rollers 271 and 272. The pressurizing conditions (heating temperature, pressurizing pressure, etc.) are pre-tested to set appropriate pressurizing conditions. As a result, the binder particles 13P contained in the uncompressed active material layer 5X are temporarily melted, and the flake-shaped graphite particles 11 are bonded to each other and to the current collector foil 3 via the binder resin 13. Simultaneously, the flake-shaped graphite particles 11 are arranged with a peak intensity ratio Rp of 130 or less (Rp≤130). Thus, the active material layer 5, composed of flake-shaped graphite particles 11 and the hot-molten binder resin 13, is continuously formed on the current collector foil 3. It should be noted that the negative electrode plate having the active material layer 5 on this current collector foil 3 is also referred to as the "single-sided negative electrode plate 1Y".

[0100] Next, the single-sided negative electrode plate 1Y is subjected to a second uncompressed layer formation process S5, which is the same as the first uncompressed layer formation process S3, to form a second uncompressed active material layer 6X (hereinafter also simply referred to as "uncompressed active material layer 6X") on the second main surface 3b of the current collector foil 3. Then, a second pressurization process S6, which is the same as the first pressurization process S4, is performed to form the active material layer 6 from the uncompressed active material layer 6X.

[0101] That is, in the "second magnetic adsorption step S51" of the "second uncompressed layer formation step S5", the composite carrier particles 61 obtained in the electrostatic adsorption step S2 are magnetically adsorbed onto the roller surface 220m of the magnetic roller 220. In the "second carrier supply step (second supply step) S52", the composite carrier particles 61 are supplied to the film-forming region MR through the magnetic roller 220. Next, in the "second electrostatic deposition step S53", in the film-forming region MR, the composite active material particles 21 in the composite carrier particles 61 are made to fly towards the second main surface 3b of the current collector foil 3, so that the composite active material particles 21 are deposited on the second main surface 3b to continuously form the second uncompressed active material layer 6X.

[0102] Then, in the "second pressurization step S6", the second uncompressed active material layer 6X, the current collector foil 3, and the first active material layer 5 are heated and pressurized to form the second active material layer 6 from the second uncompressed active material layer 6X, thus producing the pre-cut negative electrode plate 1Z before cutting. In this "second pressurization step S6", the second uncompressed active material layer 6X and the current collector foil 3 are also heated and pressurized to form the active material layer 6 from the second uncompressed active material layer 6X, in which the flake graphite particles 11 are bonded to each other and to the current collector foil 3 by a hot-melted adhesive resin 13, and the flake graphite particles 11 are configured to have a peak intensity ratio Rp of 130 or less (Rp≤130) in XRD analysis.

[0103] Next, in the "cutting process S7", the aforementioned negative electrode plate 1Z before cutting is cut (divided into two) at the center of the width direction FH along the length direction EH, resulting in... Figure 2 The negative electrode plate 1 is shown.

[0104] As explained above, the manufacturing method of the negative electrode plate 1 includes uncompressed layer formation steps S3 and S5, and pressurization steps S4 and S6. Therefore, unlike conventional manufacturing methods that use an active material paste containing a dispersion medium, the active material layers 5 and 6 can be formed by dry forming. Thus, a heating and drying step to remove the dispersion medium is unnecessary. Compared to conventional manufacturing methods, the negative electrode plate 1 has higher productivity and can be manufactured at a lower cost.

[0105] Furthermore, in the manufacturing method of the negative electrode plate 1, active material layers 5 and 6 are formed with a peak intensity ratio Rp of 130 or less according to XRD analysis. Compared with the active material layers of negative electrode plates obtained by conventional manufacturing methods, lithium ions are more easily embedded in and released from the active material layers 5 and 6. Therefore, if a battery 100 is manufactured using a negative electrode plate 1 having these active material layers 5 and 6, the battery resistance R can be reduced as described later.

[0106] Thus, according to the manufacturing method of negative electrode plate 1, it is possible to manufacture a low-cost negative electrode plate 1 that can reduce the battery resistance R.

[0107] Furthermore, in this embodiment, during the uncompressed layer formation processes S3 and S5, the composite active material particles 21 are supplied to the film-forming region MR using magnetic carrier particles 51 and a magnetic roller 220. In the film-forming region MR, the composite active material particles 21 are deposited onto the current collector foil 3 by electrostatic force Fs to form uncompressed active material layers 5X and 6X. This process allows for the easy formation of uncompressed active material layers 5X and 6X.

[0108] (Experimental Results)

[0109] Next, the results of the tests conducted to verify the effectiveness of this disclosure will be explained.

[0110] As Example 1, an active material layer 5 (electrode density 0.91 g / cm³) was prepared on the current collector foil 3, similar to that in the embodiment. 3 The single-sided negative plate 1Z (hereinafter also referred to as "negative plate 1Z").

[0111] As in Example 2, the negative electrode plate 1Z of the embodiment was subjected to roller pressing with a pair of pressure rollers with a roller gap of 40 μm to form a negative electrode plate with further compaction of the active material layer 5 (electrode density 1.19 g / cm³). 3 ).

[0112] As in Example 3, the negative electrode plate 1Z of the embodiment was subjected to roller pressing with a pair of pressure rollers with a roller gap of 35 μm to form a negative electrode plate with further compaction of the active material layer 5 (electrode density 1.21 g / cm³). 3 ).

[0113] As in Example 4, the negative electrode plate 1Z of the embodiment was subjected to roller pressing with a pair of pressure rollers with a roller gap of 30 μm to form a negative electrode plate with the active material layer 5 further compacted (electrode density 1.41 g / cm³). 3 ).

[0114] On the other hand, as a comparative example, the negative electrode plate 1Z was manufactured using the conventional method described above. Specifically, flake-shaped graphite particles 11, binder particles 13P, and a dispersion medium (water) were mixed to pre-obtain an active material paste in which the flake-shaped graphite particles 11 were dispersed in the dispersion medium and the binder particles 13P were dissolved in the dispersion medium. Next, this active material paste was coated onto a current collector foil 3, forming an undried active material layer on the current collector foil 3. Then, hot air was blown onto the undried active material layer to heat and dry it, forming an active material layer 5, thus obtaining the comparative example negative electrode plate 1Z (electrode density 0.86 g / cm³). 3 ).

[0115] Next, the active material layer 5 of the negative electrode plate 1Z in Examples 1-4 and the Comparative Example were subjected to the above-described XRD analysis to determine the peak intensity ratio Rp. The results showed that the peak intensity ratio Rp was 184 in the Comparative Example, 23 in Example 1, 76 in Example 2, 117 in Example 3, and 126 in Example 4 (see also...). Figure 8 ).

[0116] Next, laminated battery-type lithium-ion batteries (not shown) were fabricated using the negative electrode plates 1Z of Examples 1-4 and Comparative Examples. That is, each negative electrode plate 1Z and positive electrode plate were placed opposite each other via a separator and housed together with the electrolyte in an outer casing made of a laminated film to fabricate test batteries.

[0117] Next, the battery resistance R of each battery was measured. Specifically, the SOC of the battery was adjusted to 56% (battery voltage 3.70V) at an ambient temperature of -10°C. Then, the battery was discharged for 10 seconds with a constant current I of 1C, and the battery voltage V before and after discharge was measured. The change in battery voltage V, ΔV, was calculated. Furthermore, the battery resistance (IV resistance) R of each battery was calculated using R = ΔV / I. Next, using the battery resistance R of the comparative example battery as a reference (=1.00), the "battery resistance ratio" of the battery resistance R of Examples 1 to 4 was calculated. The results are shown below. Figure 8 .

[0118] Depend on Figure 8As can be seen from the graphs, compared to the comparative example batteries where the peak intensity ratio Rp of the active material layer 5 exceeds 130, the battery resistance ratio (battery resistance R) is smaller in all of the batteries of Examples 1 to 4 where the peak intensity ratio Rp of the active material layer 5 is below 130. Furthermore, comparing the batteries of Examples 1 to 4 with each other, it can be seen that the smaller the value of the peak intensity ratio Rp, the smaller the battery resistance ratio (battery resistance R).

[0119] The smaller the peak intensity of the active material layer 5 compared to Rp, the fewer the flat, flaky graphite particles 11 on the surface 5m of the active material layer 5 (base surface 11B facing the surface 5m of the active material layer 5), and the more upright, flaky graphite particles 11 on the end face 11E facing the surface 5m of the active material layer 5. Lithium ions in such an active material layer 5 are more easily embedded within and released from it. Therefore, it is believed that the battery using a negative electrode plate 1 with an active material layer 5 having a peak intensity lower than Rp has a lower battery resistivity (battery resistance R).

[0120] The present disclosure has been described above based on the embodiments, but the present disclosure is not limited to the embodiments, and needless to say, appropriate changes can be made and applied without departing from its spirit.

Claims

1. A negative electrode plate provided with a current collector foil and an active material layer formed on the current collector foil, the active material layer containing flaky graphite particles and a binder resin, an aspect ratio of a maximum diameter d to a thickness t of the flaky graphite particles, that is, d / t is 5 or greater, the flaky graphite particles being bonded to each other and to the current collector foil by the binder resin that is thermally fused, a peak intensity ratio of XRD analysis of the active material layer is 23 to 130; the peak intensity ratio refers to a value obtained by dividing a peak intensity (counts) P(004) of a peak indicating the presence of a (004) plane that appears near a diffraction angle 2θ = 54.6° by a peak intensity (counts) P(110) of a peak indicating the presence of a (110) plane that appears near a diffraction angle 2θ = 77.5°, that is, P(004) / P(110), in X-ray diffraction measurement, that is, XRD measurement, using CuKα rays on the active material layer of the negative electrode plate.

2. A lithium ion secondary battery provided with the negative electrode plate according to claim 1.

3. A method of manufacturing a negative electrode plate provided with a current collector foil and an active material layer formed on the current collector foil, the active material layer containing flaky graphite particles and a binder resin, an aspect ratio of a maximum diameter d to a thickness t of the flaky graphite particles, that is, d / t is 5 or greater, the flaky graphite particles being bonded to each other and to the current collector foil by the binder resin that is thermally fused, a peak intensity ratio of XRD analysis of the active material layer is 23 to 130, the peak intensity ratio refers to a value obtained by dividing a peak intensity (counts) P(004) of a peak indicating the presence of a (004) plane that appears near a diffraction angle 2θ = 54.6° by a peak intensity (counts) P(110) of a peak indicating the presence of a (110) plane that appears near a diffraction angle 2θ = 77.5°, that is, P(004) / P(110), in X-ray diffraction measurement, that is, XRD measurement, using CuKα rays on the active material layer of the negative electrode plate; the method of manufacturing the negative electrode plate is provided with the following steps: an uncompressed layer forming step in which composite active material particles in which binder particles composed of the binder resin are attached to the flaky graphite particles are deposited on the current collector foil to form an uncompressed active material layer that is not compressed; a pressurizing step of heating and pressurizing the uncompressed active material layer and the current collector foil to form the active material layer in which the flaky graphite particles are bonded to each other and to the current collector foil by the binder resin that is thermally fused and in which the flaky graphite particles are arranged so that the peak intensity ratio is 23 to 130.

4. The method of manufacturing the negative electrode plate according to claim 3, wherein the uncompressed layer forming step is provided with the following steps: a supply step of supplying the composite active material particles to a film forming region; An electrostatic deposition process deposits the composite active material particles on the current collector by flying the composite active material particles toward the current collector by electrostatic force in the film formation region to form the uncompressed active material layer.

5. The method of manufacturing a negative plate according to claim 4, wherein The uncompressed layer formation process further has a magnetic adsorption process of magnetically adsorbing the composite carrier particles on which the composite active material particles are electrostatically adsorbed to a roller surface of a magnetic roller, The supply process is a carrier supply process of supplying the composite carrier particles magnetically adsorbed to the roller surface to the film formation region by rotation of the magnetic roller, The electrostatic deposition process flies the composite active material particles in the composite carrier particles toward the current collector in the film formation region.

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