Electrode and lithium ion secondary battery

Abstract

The electrodes (20, 30) are provided with current collectors (22, 32) and active material layers (24, 34) in contact with one surfaces of the current collectors (22, 32). The active material layers (24, 34) have main parts (25, 35) and auxiliary parts (26, 36) when viewed from the lamination direction. The sub-sections (26, 36) are separated from the main sections (25, 35) and are located at the outer peripheral end sections of the active material layers (24, 34). The area of the main parts (25, 35) is larger than the area of the auxiliary parts (26, 36).

Description

Technical Field

[0001] This invention relates to electrodes and lithium-ion secondary batteries.

[0002] This application claims priority based on Japan Patent Application No. 2023-180185, filed on October 19, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Lithium-ion secondary batteries are also widely used as power sources for mobile devices such as mobile phones and laptops, or hybrid vehicles.

[0004] Lithium-ion secondary batteries consist of a power generation element and an outer casing that houses the element. If an impact is applied to a lithium-ion secondary battery, the power generation element comes into contact with the casing, and sometimes the positive or negative active material may detach from the element. This detached positive and negative active material does not participate in the battery reaction. Therefore, the detachment of the positive and negative active materials leads to a decrease in the performance of the lithium-ion secondary battery.

[0005] For example, Patent Document 1 discloses a lithium-ion secondary battery in which the corners of the electrodes are chamfered. By chamfering the corners of the electrodes, the shedding of the positive and negative active materials can be suppressed.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2022 / 176492 Summary of the Invention

[0009] The technical problem the invention aims to solve

[0010] As described in Patent Document 1, if the corners of the electrodes are chamfered, the capacity of the lithium-ion secondary battery will be reduced accordingly.

[0011] This disclosure was made in view of the above-mentioned technical problems, and its purpose is to provide an electrode and a lithium-ion secondary battery that prevent the active material layer from falling off due to stress concentration and have a large capacity.

[0012] Means for solving technical problems

[0013] To address the above problems, the present invention provides the following means.

[0014] (1) The electrode involved in the first embodiment has a current collector and an active material layer in contact with one side of the current collector. When viewed from the stacking direction, the active material layer has a main portion and a secondary portion. The secondary portion is separate from the main portion and is located at the outer peripheral end of the active material layer. The area of ​​the main portion is larger than the area of ​​the secondary portion.

[0015] (2) In the electrode involved in the above method (1), the sub-part may also be located at the outer corner of the active material layer.

[0016] (3) In the electrodes involved in the above methods (1) or (2), the active material layer may also have a plurality of said sub-parts.

[0017] (4) In any of the above methods (1) to (3), the area of ​​the main part may be more than 55% and less than 88% of the total area of ​​the active material layer.

[0018] (5) In any of the above methods (1) to (4), the electrode may also have a concave-convex edge on the side of the main part opposite to the sub-part when viewed from the stacking direction.

[0019] (6) In any of the above methods (1) to (5), the active material contained in the active material layer may be lithium titanate.

[0020] (7) In any of the above methods (1) to (5), the active material contained in the active material layer may be lithium cobalt oxide.

[0021] (8) The lithium-ion secondary battery involved in the second aspect includes the electrode and electrolyte involved in any of the above methods (1) to (7).

[0022] Invention Effects

[0023] The electrodes and lithium-ion secondary batteries involved in the above methods prevent the active material layer from falling off due to stress concentration, and have a large capacity. Attached Figure Description

[0024] Figure 1 This is a cross-sectional schematic diagram of the lithium-ion secondary battery according to the first embodiment.

[0025] Figure 2 This is a top view of the positive electrode according to the first embodiment.

[0026] Figure 3 This is a top view of the negative electrode according to the first embodiment.

[0027] Figure 4 This is a top view of the positive electrode involved in the first variation.

[0028] Symbol Explanation

[0029] 10...diaphragm

[0030] 20……Positive electrode

[0031] 22……Positive current collector

[0032] 24……Positive electrode active material layer

[0033] 25, 35...main part

[0034] 26, 36... Deputy Minister

[0035] 30……Negative electrode

[0036] 32……Negative current collector

[0037] 34……Negative electrode active material layer

[0038] 40……Power generation components

[0039] 50…outer body

[0040] 52…metal foil

[0041] 54……Resin layer

[0042] 60, 62... terminals

[0043] 100… Lithium-ion secondary battery Detailed Implementation

[0044] The embodiments will now be described in detail with appropriate reference to the accompanying drawings. In the drawings used in the following description, for ease of understanding, some features are sometimes shown enlarged for convenience, and the dimensions and proportions of each component may differ from the actual dimensions. The materials, dimensions, etc., illustrated in the following description are merely examples, and the present invention is not limited thereto; it can be implemented with appropriate modifications without altering its spirit.

[0045] Lithium-ion rechargeable batteries

[0046] Figure 1 This is a schematic diagram of a lithium-ion secondary battery according to the first embodiment. Figure 1 The lithium-ion secondary battery 100 shown includes a power generation element 40, an outer casing 50, and an electrolyte (e.g., a non-aqueous electrolyte). The outer casing 50 surrounds the power generation element 40. The power generation element 40 is connected to the outside via a pair of terminals 60, 62 connected to the power generation element 40. The non-aqueous electrolyte is contained within the outer casing 50. Figure 1 The example shown illustrates a case where there is one power generation element 40 within the outer casing 50, but multiple power generation elements 40 may also be stacked.

[0047] (Power generation components)

[0048] The power generation element 40 includes a diaphragm 10, a positive electrode 20, and a negative electrode 30.

[0049] <Positive electrode>

[0050] Figure 2 This is a top view of the positive electrode according to the first embodiment. The positive electrode 20, for example, has a positive current collector 22 and a positive active material layer 24. Hereinafter, one direction of the extended surface of the positive current collector 22 is defined as the x-direction, and the direction orthogonal to the x-direction in the extended surface of the positive current collector 22 is defined as the y-direction. In addition, the direction orthogonal to both the x-direction and the y-direction is defined as the z-direction. The z-direction is an example of the stacking direction.

[0051] [Positive current collector]

[0052] The positive current collector 22 is, for example, a conductive sheet. The positive current collector 22 extends continuously in the xy plane. The positive current collector 22 is, for example, a thin sheet of metal such as aluminum, copper, nickel, titanium, or stainless steel. Alternatively, the surface of the thin metal sheet may be coated with a conductive layer. For example, a layer containing a conductive material, an adhesive, and a thickener as needed, in a prescribed proportion can be considered. Examples of conductive materials include conductive carbon materials such as carbon black, acetylene black, graphite, carbon fiber, and carbon nanotubes. Examples of adhesives include acrylic adhesives and styrene-butadiene rubber adhesives. Examples of thickeners include carboxymethyl cellulose. Lightweight aluminum is suitable for the positive current collector 22. The average thickness of the positive current collector 22 is, for example, 10 μm or more and 30 μm or less.

[0053] Alternatively, a laminate in which a metal layer is formed on the surface of the resin layer can be used in the positive current collector 22. The metal layer can be, for example, aluminum, copper, nickel, titanium, stainless steel, etc., with lightweight aluminum being preferred. The resin layer can be, for example, polyethylene terephthalate (PET), polyimide (PI), polyamide-imide (PAI), polypropylene (PP), polyethylene (PE), etc.

[0054] [Positive electrode active material layer]

[0055] The positive electrode active material layer 24 is in contact with at least one side of the positive electrode current collector 22. Viewed from the z-direction, the positive electrode active material layer 24 has a main portion 25 and a secondary portion 26. The main portion 25 and the secondary portion 26 are respectively connected to the same positive electrode current collector 22. The main portion 25 and the secondary portion 26 are electrically connected in parallel with the positive electrode current collector 22.

[0056] The main portion 25 forms the main body of the positive electrode active material layer 24. The area of ​​the main portion 25 is larger than the area of ​​the secondary portion 26. For example, the area of ​​the main portion 25 is more than 55% and less than 88% of the total area of ​​the positive electrode active material layer 24.

[0057] The secondary portion 26 and the primary portion 25 exist on the same plane. The secondary portion 26 is separate from the primary portion 25. The secondary portion 26 is located at the outer peripheral end of the positive electrode active material layer 24. The secondary portion 26 is preferably located at the outer peripheral corner of the positive electrode active material layer 24. When viewed from the z-direction, the outer periphery of the positive electrode active material layer 24 is the outer periphery of the outer region enclosing the primary portion 25 and the secondary portion 26. The secondary portion 26 is located on the outer side of the positive electrode active material layer 24 compared to the primary portion 25.

[0058] The edge L1 of the main portion 25 opposite to the sub-portion 26 preferably has an irregularity or irregularity. Similarly, the edge L2 of the sub-portion 26 opposite to the main portion 25 also preferably has an irregularity or irregularity. Here, "irregularity or irregularity" means that the edge L1 or edge L2 is curved or bent relative to the straight line connecting the two ends of the edge L1 or edge L2. If edge L1 has an irregularity or irregularity, the contact area between the main portion 25 and the electrolyte can be increased. Likewise, if edge L2 has an irregularity or irregularity, the contact area between the sub-portion 26 and the electrolyte can be increased.

[0059] Both the main portion 25 and the secondary portion 26 contain positive electrode active material. In addition to the positive electrode active material, the main portion 25 and the secondary portion 26 may also contain conductive additives and binders. The main portion 25 and the secondary portion 26 can be made of different materials or the same material. When the main portion 25 and the secondary portion 26 are made of the same material, the manufacture of the lithium-ion secondary battery 100 becomes easier.

[0060] Regarding positive electrode active materials, those capable of ion absorption and release, ion deintercalation and insertion (intercalation), or ion-counteracting anions (e.g., PF6) can be used. - The doping and dedoping of active materials can be reversibly carried out. Lithium, magnesium, etc. can be used as ions.

[0061] Positive electrode active materials include, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), lithium manganese spinel (LiMn2O4), and those derived from the general formula: LiNi x Co y Mn z M a O2 (x+y+z+a=1, 0≤x<1, 0≤y<1, 0≤z<1, 0≤a<1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr) represents composite metal oxides, lithium vanadium compounds (LiV2O5), olivine-type LiMPO4 (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr or VO), lithium titanate (Li4Ti5O) 12 LiNi x Co y Al zO2 (0.9 < x + y + z < 1.1), polyacetylene, polyaniline, polypyrrole, polythiophene, poly(benzo[]benzene]. Lithium cobalt oxide is particularly preferred as the positive electrode active material.

[0062] The conductive additives in the positive electrode active material layer 24 improve the electronic conductivity between the positive electrode active materials. Examples of conductive additives include carbon powder, carbon nanotubes, carbon materials, fine metal powders, mixtures of carbon materials and fine metal powders, and conductive oxides. Examples of carbon powders include carbon black, acetylene black, and Ketzen black. Examples of fine metal powders include powders of copper, nickel, stainless steel, and iron.

[0063] An adhesive in the positive electrode active material layer 24 bonds the positive electrode active materials together. Known adhesives can be used. Examples of adhesives include fluoropolymers. Other adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamide-imide (PAI), polybenzimidazole (PBI), polyethersulfone (PES), polyacrylic acid and its copolymers, metal ion crosslinkers of polyacrylic acid and its copolymers, polypropylene (PP) or polyethylene (PE) grafted with maleic anhydride, and mixtures thereof. PVDF is particularly preferred as the adhesive for the positive electrode active material layer.

[0064] Alternatively, the positive electrode active material layer 24 can also be a sintered plate or pressed powder. When using a sintered plate or pressed powder, it may not contain conductive additives or binders.

[0065] <Negative electrode>

[0066] Figure 3 This is a top view of the negative electrode 30 according to the first embodiment. The negative electrode 30 has, for example, a negative electrode current collector 32 and a negative electrode active material layer 34.

[0067] [Negative current collector]

[0068] The negative current collector 32 is, for example, a conductive plate. The negative current collector 32 extends continuously in the xy plane. The negative current collector 32 can be made of the same material as the positive current collector 22.

[0069] [Negative electrode active material layer]

[0070] The negative electrode active material layer 34 is in contact with at least one side of the negative electrode current collector 32. When viewed from the z-direction, the negative electrode active material layer 34 has a main portion 35 and a secondary portion 36. The main portion 35 and the secondary portion 36 are respectively connected to the same negative electrode current collector 32. The main portion 35 and the secondary portion 36 are electrically connected in parallel with the negative electrode current collector 32.

[0071] The main portion 35 is the main body of the negative electrode active material layer 34. The area of ​​the main portion 35 is larger than the area of ​​the secondary portion 36. For example, the area of ​​the main portion 35 is more than 55% and less than 88% of the total area of ​​the negative electrode active material layer 34.

[0072] The secondary portion 36 and the primary portion 35 exist on the same plane. The secondary portion 36 is separate from the primary portion 35. The secondary portion 36 is located at the outer peripheral end of the negative electrode active material layer 34. The secondary portion 36 is preferably located at the outer peripheral corner of the negative electrode active material layer 34. Viewed from the z-direction, the outer periphery of the negative electrode active material layer 34 is the outer periphery of the outer region enclosing the primary portion 35 and the secondary portion 36. The secondary portion 36 is located on the outer side of the negative electrode active material layer 34 compared to the primary portion 35.

[0073] The positional relationship between the sub-part 26 of the positive electrode active material layer 24 and the sub-part 36 of the negative electrode active material layer 34 is arbitrary. Sub-part 26 and sub-part 36 can also be located at different positions in the xy plane. Additionally, for example, as... Figure 2 and Figure 3 As shown, sub-parts 26 and 36 can also be in a relative position. For example, depending on the intended use of the lithium-ion secondary battery 100, stress may sometimes concentrate at specific locations. In this case, sub-parts 26 and 36 are provided at the locations where stress is prone to concentrate. Thus, if sub-parts 26 and 36 are in a relative position, it may be possible to further suppress the shedding of active material from the lithium-ion secondary battery 100.

[0074] The edge L3 of the main portion 35 opposite to the sub-portion 36 preferably has an unevenness. Similarly, the edge L4 of the sub-portion 36 opposite to the main portion 35 also preferably has an unevenness. Here, "unevenness" means that the edge L3 or edge L4 is curved or bent relative to the straight line connecting the two ends of the edge L3 or edge L4. If the edge L3 has an unevenness, the contact area between the main portion 35 and the electrolyte can be increased. Likewise, if the edge L4 has an unevenness, the contact area between the sub-portion 36 and the electrolyte can be increased.

[0075] Both the main portion 35 and the secondary portion 36 contain negative electrode active material. In addition to the negative electrode active material, the main portion 35 and the secondary portion 36 may also contain conductive additives and binders. The main portion 35 and the secondary portion 36 can be made of different materials or the same material. When the main portion 35 and the secondary portion 36 are made of the same material, the manufacture of the lithium-ion secondary battery 100 becomes easier.

[0076] Regarding the negative electrode active material, any compound that can absorb and release ions is acceptable, and active materials used in known lithium-ion secondary batteries can be used. Negative electrode active materials include carbon materials, metals or alloys that can combine with lithium, composites of these metals or alloys and carbon materials, oxides, sulfur-modified polyacrylonitrile, and metallic lithium. Examples of carbon materials include natural graphite, artificial graphite, mesophase carbon microspheres, mesophase carbon fibers (MCF), coke, glassy carbon, and sintered organic compounds. Metals or alloys that can combine with lithium include Si and SiO2. x Sn, aluminum, etc. The oxide is lithium titanate (Li₄Ti₅O₂). 12 SnO2, etc. The preferred negative electrode active material is natural graphite or lithium titanate (Li4Ti5O3). 12 ).

[0077] The conductive additive in the negative electrode active material layer 34 improves the electronic conductivity between the negative electrode active materials. The conductive additive in the negative electrode active material layer 34 can be the same material as the conductive additive in the positive electrode active material layer 24.

[0078] The adhesive in the negative electrode active material layer 34 bonds the negative electrode active materials together. The adhesive in the negative electrode active material layer 34 can be made of the same material as the adhesive in the positive electrode active material layer 24.

[0079] <Septum>

[0080] The separator 10 is sandwiched between the positive electrode 20 and the negative electrode 30. The separator 10 isolates the positive electrode 20 and the negative electrode 30, preventing short circuits between them. The separator 10 extends inward along the positive electrode 20 and the negative electrode 30. Lithium ions can pass through the separator 10.

[0081] The diaphragm 10 may have a porous structure with electrical insulation properties. The diaphragm 10 may be a single layer or laminate of a polyolefin membrane. The diaphragm 10 may also be an extended membrane of a mixture of polyethylene or polypropylene. The diaphragm 10 may also be a nonwoven fabric made of fibers selected from at least one constituent material chosen from cellulose, polyester, polyacrylonitrile, polyamide, polyethylene, and polypropylene. The diaphragm 10 may also be a solid electrolyte. Solid electrolytes may include, for example, polymeric solid electrolytes, oxide solid electrolytes, sulfide solid electrolytes, and chloride solid electrolytes. The diaphragm 10 may also be an inorganic coated diaphragm. An inorganic coated diaphragm is formed by coating the surface of the above-mentioned membrane with resins such as PVDF or CMC and alumina or silica or Li7La3Zr2O. 12 It is formed from a mixture of inorganic substances. Inorganic coating membranes have excellent heat resistance and inhibit the deposition of transition metals eluted from the positive electrode onto the negative electrode surface.

[0082] Electrolyte

[0083] The electrolyte is encapsulated within the outer casing 50 and immersed in the power generation element 40. The electrolyte is not limited to a liquid electrolyte; it can also be a solid electrolyte. Non-aqueous electrolytes may include, for example, a non-aqueous solvent and an electrolytic salt. The electrolytic salt is dissolved in the non-aqueous solvent.

[0084] The solvent is not particularly limited as long as it is a solvent commonly used in lithium-ion secondary batteries. The solvent may include, for example, any of the following: cyclic carbonate compounds, chain carbonate compounds, cyclic ester compounds, and chain ester compounds. These compounds may also be mixed in any proportion. Examples of cyclic carbonate compounds include ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate, and vinylene carbonate. Examples of chain carbonate compounds include diethyl carbonate (DEC) and methyl ethyl carbonate (EMC). Examples of cyclic ester compounds include γ-butyrolactone. Examples of chain ester compounds include propyl propionate, ethyl propionate, and ethyl acetate.

[0085] Electrolyte salts, for example, are lithium salts. Electrolytes, for example, are LiPF6, LiClO4, LiBF4, LiCF3SO3, LiCF3CF2SO3, LiC(CF3SO2)3, LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(CF3CF2CO)2, LiBOB, LiN(FSO2)2, etc. A single lithium salt or two or more can be used. From the viewpoint of degree of ionization, the electrolyte preferably contains LiPF6. The degree of dissociation of the electrolyte salt in a carbonate solvent at room temperature is preferably 10% or more.

[0086] The electrolyte is preferably a solution formed by dissolving LiPF6 in a carbonate solvent. The concentration of LiPF6 is, for example, 1 mol / L. When the polyimide resin contains a large amount of aromatics, it sometimes exhibits charging behavior similar to soft carbon. When the electrolyte is a carbonate electrolyte solvent containing cyclic carbonates, lithium can react uniformly with the polyimide. In this case, the cyclic carbonate is preferably ethylene carbonate, fluoroethylene carbonate, or vinylene carbonate.

[0087] <Exterior body>

[0088] The outer casing 50 seals the power generation element 40 and the non-aqueous electrolyte inside. The outer casing 50 prevents the non-aqueous electrolyte from leaking to the outside or moisture from entering the lithium-ion secondary battery 100 from the outside.

[0089] For example, such as Figure 1 As shown, the outer casing 50 has a metal foil 52 and resin layers 54 laminated on each side of the metal foil 52. The outer casing 50 is a metal laminate obtained by coating the metal foil 52 with a polymer film (resin layer 54) from both sides.

[0090] For example, aluminum foil can be used as the metal foil 52. The resin layer 54 can be a polymer film such as polypropylene. The materials constituting the resin layer 54 can also be different on the inner and outer sides. For example, as the material on the outer side, a high-melting-point polymer such as polyethylene terephthalate (PET) or polyamide (PA) can be used, while as the material on the inner side of the polymer film, polyethylene (PE) or polypropylene (PP) can be used.

[0091] <Terminal>

[0092] Terminals 60 and 62 are connected to the negative terminal 30 and the positive terminal 20, respectively. Terminal 62, connected to the positive terminal 20, is the positive terminal, and terminal 60, connected to the negative terminal 30, is the negative terminal. Terminals 60 and 62 are responsible for the electrical connection between the power generation element and the external environment. Terminals 60 and 62 are made of conductive materials such as aluminum, nickel, and copper. The connection method can be welding or screw connection. To prevent short circuits, terminals 60 and 62 are preferably protected with insulating tape.

[0093] The lithium-ion secondary battery 100 is manufactured by separately preparing the negative electrode 30, the positive electrode 20, the separator 10, the electrolyte, and the outer casing 50, and assembling them. An example of the manufacturing method of the lithium-ion secondary battery 100 will be described below.

[0094] The positive electrode 20 is manufactured by sequentially performing a slurry preparation process, an electrode coating process, a drying process, a calendering process, and a separation process.

[0095] The slurry preparation process involves mixing the positive electrode active material, conductive additives, and binder with a solvent to create the slurry. Solvents may include, for example, water or N-methyl-2-pyrrolidone.

[0096] The electrode coating process involves applying a slurry to the surface of the positive current collector 22. There are no particular limitations on the slurry application method. For example, slot die coating or blade coating can be used. The slurry is applied, for example, at room temperature.

[0097] The drying process is the process of removing solvent from the slurry. For example, the positive current collector 22 coated with slurry is dried in an atmosphere of 80°C to 350°C.

[0098] A calendering process is performed as needed. The calendering process is a process in which pressure is applied to the positive electrode active material layer 24 and the density of the positive electrode active material layer 24 is adjusted. For example, the calendering process is performed by a rolling mill or the like.

[0099] In the separation process, the similarly expanded positive electrode active material layer 24 is divided into a main portion 25 and a secondary portion 26. For example, the main portion 25 and the secondary portion 26 can be separated by bending the corners of the positive electrode active material layer 24.

[0100] This example shows a manufacturing example where the main portion 25 and the secondary portion 26 are separated after calendering. However, the main portion 25 and the secondary portion 26 can also be coated separately during the electrode coating process. For example, the slurry can be coated with a mask provided at the boundary between the main portion 25 and the secondary portion 26. After drying and calendering, the mask is removed, and the main portion 25 and the secondary portion 26 are separated. Alternatively, for example, the main portion 25 and the secondary portion 26 can be formed by pattern printing without providing a mask.

[0101] Except for the different materials used to form the slurry, the negative electrode 30 can be manufactured using the same steps as the positive electrode 20. The separator 10 and the outer casing 50 can be commercially available products.

[0102] Next, the positive electrode 20 and negative electrode 30 are stacked with the separator 10 between them to create a power generation element 40.

[0103] Finally, the power generation element 40 is sealed within the outer casing 50. A non-aqueous electrolyte is injected into the outer casing 50. By applying pressure reduction or heating after injection, the non-aqueous electrolyte is made to immerse the power generation element 40. Heat is applied to seal the outer casing 50, thereby obtaining a lithium-ion secondary battery 100. Alternatively, the power generation element 40 may be immersed in the electrolyte without injecting it into the outer casing 50. After injecting the electrolyte into the power generation element, it is preferable to allow it to stand for 24 hours.

[0104] In the lithium-ion secondary battery 100 of the first embodiment, the positive electrode active material layer 24 and the negative electrode active material layer 34 each have secondary portions 26 and 36, respectively. The spaces between the main portion 25 and the secondary portion 26, and between the main portion 35 and the secondary portion 36, function as buffer areas when stress is applied to the lithium-ion secondary battery 100, preventing the active material from detaching from the lithium-ion secondary battery 100. Furthermore, the secondary portion 26 is electrically connected in parallel with the main portion 25, and the secondary portion 26 also functions as a battery. Similarly, the secondary portion 36 is electrically connected in parallel with the main portion 35, and the secondary portion 36 also functions as a battery. Therefore, unlike the case where the corners of the active material layers are cut off, the battery capacity is not significantly reduced. Therefore, the lithium-ion secondary battery 100 according to the first embodiment has a large capacity while preventing the active material layers from detaching due to stress concentration.

[0105] As described above, embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, each structure and combination thereof in each embodiment is only one example. Without departing from the spirit of the present invention, structures can be added, omitted, replaced, and other changes can be made.

[0106] For example, it is disclosed that both the positive electrode active material layer 24 and the negative electrode active material layer 34 have secondary parts 26 and 36, but it is also possible that only one of the positive electrode active material layer 24 and the negative electrode active material layer 34 has a secondary part.

[0107] Additionally, for example, such as Figure 4 As shown, the number of sub-parts 26 is not limited to one; there can be multiple sub-parts 26. Even in this case, the area of ​​the main part 25 is larger than the total area of ​​the multiple sub-parts 26. Furthermore, in Figure 4 The diagram shows an example where there are multiple sub-parts 26 in the positive electrode active material layer 24, but there can also be multiple sub-parts 36 in the negative electrode active material layer 34.

[0108] Example

[0109] Example 1

[0110] First, the positive electrode active material, conductive additive, binder, and solvent were mixed to prepare the positive electrode slurry. LiCoO2 was used as the positive electrode active material. Acetylene black was used as the conductive additive. Polyvinylidene fluoride (PVDF) was used as the binder. N-methyl-2-pyrrolidone was used as the solvent. The mass ratio of the positive electrode active material, conductive additive, and binder was set at 90wt%:5wt%:5wt%.

[0111] Next, the positive electrode slurry was coated onto one side of a 15 μm thick aluminum foil. During the coating process, pattern printing was performed to form the main and secondary portions. The solvent in the positive electrode slurry was removed in a drying oven to create the positive electrode active material layer. The positive electrode active material layer was then pressed using a roller press to fabricate the positive electrode. The loading of the positive electrode active material in the dried positive electrode active material layer was set to 22 mg / cm³. 2 The secondary portion is located at one corner of the positive electrode active material layer. The area of ​​the secondary portion is set to 10% of the total area of ​​the positive electrode active material layer.

[0112] Similarly, a negative electrode slurry was prepared by mixing the negative electrode active material, conductive additives, binder, and solvent. The negative electrode active material used was Li4Ti5O. 12 Acetylene black was used as the conductive additive. Polyvinylidene fluoride (PVDF) was used as the binder. N-methyl-2-pyrrolidone was used as the solvent. The mass ratio of the negative electrode active material, conductive additive, and binder was set at 90wt%:5wt%:5wt%.

[0113] Next, the negative electrode paste was coated onto one side of a 10 μm thick copper foil. During the coating process, pattern printing was performed to form the main and secondary layers. The solvent in the negative electrode paste was removed in a drying oven, creating the negative electrode active material layer. The negative electrode active material layer was then pressurized using a roller press to fabricate the negative electrode. The loading of the negative electrode active material in the dried negative electrode active material layer was set to 24 mg / cm³. 2 The secondary part is located at one corner of the negative electrode active material layer. The area of ​​the secondary part is set to 10% of the total area of ​​the negative electrode active material layer.

[0114] Next, the electrolyte was prepared. The solvent for the electrolyte was set as ethylene carbonate (EC): methyl ethyl carbonate (EMC): diethyl carbonate (DEC) = 30 vol%: 50 vol%: 20 vol%. Additionally, LiPF6 was added to the electrolyte as an electrolytic salt. The concentration of LiPF6 was set to 1.5 mol / L.

[0115] (Evaluation of the fabrication of lithium-ion secondary batteries)

[0116] The prepared negative and positive electrodes were stacked with positive and negative active material layers facing each other via a separator (porous polyethylene sheet) to obtain a laminate. This laminate was inserted into an aluminum laminate outer casing, and the surrounding area was heat-sealed except for one area, thus forming a closed section. Then, the electrolyte was injected into the outer casing, and the remaining section was sealed using a vacuum sealing machine while under reduced pressure via heat sealing, thereby producing a lithium-ion secondary battery. The manufactured lithium-ion secondary battery was then left to stand for 24 hours.

[0117] (Output characteristic evaluation)

[0118] The initial discharge capacity of the manufactured lithium-ion secondary battery was determined using a secondary battery charge-discharge test apparatus (manufactured by Hokuto Electric Co., Ltd.). The battery was charged at a constant current rate of 0.5C (the current value at which charging ends within 2 hours during constant current charging at 25°C) until the battery voltage reached 2.8V, and then discharged at a constant current rate of 1.0C until the battery voltage reached 1.3V. The discharge capacity was measured after the charge-discharge cycle to determine the battery capacity.

[0119] Examples 2 and 3

[0120] In Examples 2 and 3, the number of sub-elements in the positive and negative active material layers was changed, which differs from Example 1. Other conditions were the same as in Example 1, and the battery capacity of the lithium-ion secondary battery was measured.

[0121] Examples 4 and 5

[0122] In Examples 4 and 5, the areas of the secondary portions in the positive and negative active material layers were changed, which differs from Example 1. Other conditions were the same as in Example 1, and the battery capacity of the lithium-ion secondary battery was measured.

[0123] Comparative Example 1

[0124] In Comparative Example 1, the main and secondary portions were not separately coated during the fabrication of the positive and negative active material layers, which differs from Example 1. That is, the positive and negative active material layers in Comparative Example 1 do not have secondary portions, which also differs from Example 1. Other conditions were the same as in Example 1, and the battery capacity of the lithium-ion secondary battery was measured.

[0125] Comparative Example 2

[0126] In Comparative Example 2, the slurry was not applied to the portions corresponding to the secondary parts during the fabrication of the positive and negative active material layers, which differs from Example 1. That is, the positive and negative active material layers in Comparative Example 2 do not have secondary parts, and lack portions corresponding to secondary parts, which differs from Example 1. Other conditions were the same as in Example 1, and the battery capacity of the lithium-ion secondary battery was measured.

[0127] Comparative Example 3

[0128] In Comparative Example 3, the sub-parts in the positive and negative active material layers were positioned at the center of each layer, which differs from Example 1. Other conditions were the same as in Example 1, and the battery capacity of the lithium-ion secondary battery was measured.

[0129] The results of Examples 1-5 and Comparative Examples 1-3 are summarized in Table 1.

[0130] [Table 1]

[0131]

[0132] In Table 1, the total area of ​​the secondary portion is the area ratio when the area of ​​the active material layer of Comparative Example 1 is set to 100%. Similarly, in Table 1, the area of ​​the main portion is the area ratio when the area of ​​the active material layer of Comparative Example 1 is set to 100%. Furthermore, the capacity in Table 1 is the capacity ratio when the capacity of the lithium-ion secondary battery of Comparative Example 1 is set to 100%. Additionally, the bending resistance is determined according to ISO 14443-1, after a bending and torsion test, confirming whether the active material layer is damaged. "○" indicates no damage was detected, and "×" indicates damage exists.

[0133] As shown in Table 1, no breakage was detected in Examples 1-5 during the bending resistance test. Furthermore, Examples 1-5 all exhibited larger battery capacities compared to Comparative Example 2.

[0134] Industrial availability

[0135] The electrode of this embodiment is suitable for use in lithium-ion secondary batteries.

Claims

1. An electrode, wherein, It comprises: a current collector and an active material layer in contact with one side of the current collector. When viewed from the stacking direction, the active material layer has a main part and a secondary part. The secondary portion is separate from the main portion and is located at the outer peripheral end of the active material layer. The area of ​​the main part is larger than the area of ​​the secondary part.

2. The electrode according to claim 1, wherein, The sub-part is located at the outer peripheral corner of the active material layer.

3. The electrode according to claim 1, wherein, The active material layer has a plurality of said sub-parts.

4. The electrode according to claim 1, wherein, The area of ​​the main part is more than 55% and less than 88% of the total area of ​​the active material layer.

5. The electrode according to claim 1, wherein, When viewed from the stacking direction, the edge of the main part opposite to the sub-part has concavity and convexity.

6. The electrode according to claim 1, wherein, The active material contained in the active material layer is lithium titanate.

7. The electrode according to claim 1, wherein, The active material contained in the active material layer is lithium cobalt oxide.

8. A lithium-ion secondary battery, wherein, It includes the electrode and electrolyte as described in any one of claims 1 to 7.

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