Non-aqueous electrolyte secondary battery
By forming positive electrode composite material layers with different phthalate oil absorption capacities on both sides of the positive electrode current collector, the permeation of non-aqueous electrolyte is homogenized, solving the problem of reduced charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries and achieving high capacity retention.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PANASONIC ENERGY CO LTD
- Filing Date
- 2021-11-17
- Publication Date
- 2026-06-16
Smart Images
Figure CN116529903B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a non-aqueous electrolyte secondary battery. Background Technology
[0002] In recent years, non-aqueous electrolyte secondary batteries, which have high output power and high energy density, have been widely used as secondary batteries. They have a positive electrode, a negative electrode, and a non-aqueous electrolyte, and allow lithium ions to move between the positive and negative electrodes for charging and discharging.
[0003] For example, in Patent Document 1, in order to provide a non-aqueous electrolyte secondary battery with both excellent output characteristics and good charge-discharge cycle characteristics, a positive electrode is proposed to use a positive electrode having a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer consists of two layers separated in the thickness direction, including an upper layer relatively close to the surface and a lower layer relatively close to the positive electrode current collector. The oil absorption of dibutyl phthalate per unit mass of the lower layer is greater than that of the upper layer per unit mass. When the overall thickness of the positive electrode active material layer is set to 100%, the thickness of the lower layer is 40% or less.
[0004] In addition, for example, Patent Document 2 proposed a positive electrode active material containing a lithium-containing composite oxide powder with an oil absorption capacity of 20 mL / 100 g to 40 mL / 100 g of dibutyl phthalate.
[0005] Existing technical documents
[0006] Patent documents
[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-100241
[0008] Patent Document 2: Japanese Patent Application Publication No. 2005-515465 Summary of the Invention
[0009] The problem that the invention aims to solve
[0010] The purpose of this invention is to provide a non-aqueous electrolyte secondary battery that can suppress the degradation of charge-discharge cycle characteristics.
[0011] Methods for solving problems
[0012] The non-aqueous electrolyte secondary battery of the present invention is characterized by having a wound electrode body formed by winding a positive electrode and a negative electrode with a spacer between them. The positive electrode has a positive current collector, a first positive electrode composite material layer formed on a first surface of the positive current collector facing the outside of the electrode body, and a second positive electrode composite material layer formed on a second surface of the positive current collector facing the inside of the electrode body. The first positive electrode composite material layer and the second positive electrode composite material layer contain a positive electrode active material. The phthalate oil absorption of the positive electrode active material contained in the first positive electrode composite material layer is less than the phthalate oil absorption of the positive electrode active material contained in the second positive electrode composite material layer.
[0013] Invention Effects
[0014] According to one aspect of the present invention, it is possible to suppress the degradation of charge-discharge cycle characteristics. Attached Figure Description
[0015] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method.
[0016] Figure 2 This is a cross-sectional view of the positive electrode as an example of an implementation method. Detailed Implementation
[0017] One embodiment will be described with reference to the accompanying drawings. It should be noted that the non-aqueous electrolyte secondary battery of the present invention is not limited to the embodiment described below. Furthermore, the drawings referenced in the description of the embodiment are schematic illustrations.
[0018] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method. Figure 1 The non-aqueous electrolyte secondary battery 10 shown includes a wound electrode body 14 formed by winding a positive electrode 11 and a negative electrode 12 with a spacer 13 between them, a non-aqueous electrolyte, insulating plates 18 and 19 respectively disposed above and below the electrode body 14, and a battery casing 15 that houses the above and below the components. The battery casing 15 includes a bottomed cylindrical casing body 16 and a sealing body 17 that blocks the opening of the casing body 16. In addition, examples of battery casing 15 include bottomed cylindrical cans such as cylindrical or square cans, and soft packaging formed by laminating resin sheets and metal sheets.
[0019] The outer casing 16 is, for example, a bottomed cylindrical metal outer packaging can. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure the airtightness of the battery interior. The outer casing 16 has, for example, a bulge 22 that bulges inward from a portion of its side surface and supports the sealing body 17. The bulge 22 is preferably formed in a ring shape along the circumference of the outer casing 16, with its upper surface supporting the sealing body 17.
[0020] The sealing body 17 has a structure in which a filter sheet 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 is, for example, circular or annular, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. If the internal pressure of the non-aqueous electrolyte secondary battery 10 increases due to heat release caused by internal short circuits, for example, the lower valve body 24 deforms and breaks by pushing the upper valve body 26 towards the cap 27, thus blocking the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure increases further, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.
[0021] Figure 1 In the non-aqueous electrolyte secondary battery 10 shown, the positive electrode lead 20, installed on the positive electrode 11, extends towards the sealing body 17 after passing through the through hole in the insulating plate 18, and the negative electrode lead 21, installed on the negative electrode 12, extends towards the bottom of the outer casing 16 after passing through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the filter 23, which serves as the bottom plate of the sealing body 17, by welding or the like, and the cap 27, which serves as the top plate of the sealing body 17 and is electrically connected to the filter 23, becomes the positive terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative terminal.
[0022] The following is a detailed description of each component of the non-aqueous electrolyte secondary battery 10.
[0023] [positive electrode]
[0024] Figure 2 This is a cross-sectional view of the positive electrode as an example of an embodiment. The positive electrode 11 includes a positive electrode current collector 40, a first positive electrode composite material layer 41 formed on a first surface 40a of the positive electrode current collector 40 facing the outer side of the electrode body 14, and a second positive electrode composite material layer 42 formed on a second surface 40b of the positive electrode current collector 40 facing the inner side of the electrode body 14. The positive electrode current collector 40 can be a foil of a metal such as aluminum that is stable in the potential range of the positive electrode 11, or a film of the metal disposed on its surface. The first positive electrode composite material layer 41 and the second positive electrode composite material layer 42 contain a positive electrode active material, and preferably also contain a binder material, a conductive material, etc.
[0025] The positive electrode 11 is obtained, for example, by coating a first positive electrode composite material slurry containing a positive electrode active material, a binder material, a conductive material, etc., onto the first surface 40a of the positive electrode current collector 40 and drying it to form a first positive electrode composite material layer 41. Furthermore, a second positive electrode composite material slurry containing a second positive electrode active material, a binder material, a conductive material, etc., is coated onto the second surface 40b of the positive electrode current collector 40 and dried to form a second positive electrode composite material layer 42. Then, the first positive electrode composite material layer 41 and the second positive electrode composite material layer 42 are calendered using calendering rolls or the like, thereby obtaining the positive electrode 11.
[0026] like Figure 2 As shown, the positive electrode 11 constituting the wound electrode body 14 is bent along its entire length. The positive electrode 11 is manufactured in a flat plate state and is wound together with the negative electrode 12 and the spacer 13 during the manufacturing of the electrode body 14, thereby causing the bending. It should be noted that the positive electrode 11 generally has a radius of curvature of about 1 mm to 100 mm, and the radius of curvature is different on the beginning and end sides of the winding of the electrode body 14.
[0027] Because the positive electrode 11 is manufactured in a flat plate state, its convex side is stretched and its concave side is compressed when bent. That is, as... Figure 2 As shown, the first positive electrode composite material layer 41, formed on the first surface 40a of the positive electrode current collector 40 facing the outer side of the electrode body 14, mainly elongates along the direction of arrow A, while the second positive electrode composite material layer 42, formed on the second surface 40b of the positive electrode current collector 40 facing the inner side of the electrode body 14, mainly compresses along the direction of arrow B. As a result, voids are created in the first positive electrode composite material layer 41 due to elongation, making it easier for the amount of non-aqueous electrolyte to permeate. Conversely, the voids in the second positive electrode composite material layer 42 decrease due to compression, making it easier for the amount of non-aqueous electrolyte to permeate. Furthermore, if there is a difference in the amount of non-aqueous electrolyte permeation between the first positive electrode composite material layer 41 and the second positive electrode composite material layer 42, the reaction between the two layers becomes uneven, thus causing a decrease in charge-discharge cycle performance.
[0028] Therefore, in this embodiment, the amount of dibutyl phthalate (DBP) in the first positive electrode composite material layer 41, which is formed on the first surface 40a of the positive electrode current collector 40 facing the outer side of the electrode body 14, is less than the amount of DBP in the second positive electrode composite material layer 42, which is formed on the second surface 40b of the positive electrode current collector 40 facing the inner side of the electrode body 14. As a result, since the first positive electrode composite material layer 41, which is prone to increasing non-aqueous electrolyte permeation, contains a positive electrode active material with low oil absorption, the permeation of non-aqueous electrolyte is suppressed. Furthermore, since the second positive electrode composite material layer 42, which is prone to decreasing non-aqueous electrolyte permeation, contains a positive electrode active material with high oil absorption, the permeation of non-aqueous electrolyte is increased. It is speculated that the difference in the amount of non-aqueous electrolyte permeation between the first positive electrode composite layer 41 and the second positive electrode composite layer 42 becomes smaller, and the reaction between the first positive electrode composite layer 41 and the second positive electrode composite layer 42 becomes more uniform, thus suppressing the reduction in charge-discharge cycle characteristics.
[0029] In this embodiment, considering factors such as suppressing the reduction in charge-discharge cycle performance, the oil absorption capacity of dibutyl phthalate in the positive electrode active material contained in the first positive electrode composite material layer 41 is preferably 11 mL / 100g or more and 19 mL / 100g or less, more preferably 12 mL / 100g or more and 18 mL / 100g or less, and even more preferably 13 mL / 100g or more and 17 mL / 100g or less. Furthermore, in this embodiment, considering factors such as suppressing the reduction in charge-discharge cycle performance, the oil absorption capacity of dibutyl phthalate in the positive electrode active material contained in the second positive electrode composite material layer 42 is preferably 15 mL / 100g or more and 23 mL / 100g or less, more preferably 16 mL / 100g or more and 22 mL / 100g or less, and even more preferably 17 mL / 100g or more and 21 mL / 100g or less.
[0030] In this embodiment, the dibutyl phthalate oil absorption values of the positive electrode active materials contained in each of the first positive electrode composite material layer 41 and the second positive electrode composite material layer 42 are average values. That is, each of the first positive electrode composite material layer 41 and the second positive electrode composite material layer 42 may contain multiple positive electrode active materials with different dibutyl phthalate oil absorption values. For example, if the first positive electrode composite material layer 41 contains three positive electrode active materials (P1, P2, P3) with different dibutyl phthalate oil absorption values, the dibutyl phthalate oil absorption value of the positive electrode active materials contained in the first positive electrode composite material layer 41 is the dibutyl phthalate oil absorption value of the mixture containing positive electrode active materials P1, P2, and P3. The same applies to the second positive electrode composite material layer 42.
[0031] When the oil absorption capacity of the mixture of multiple positive electrode active materials contained in the first positive electrode composite layer 41 is 11 mL / 100g or more and 19 mL / 100g or less, it is preferable that the oil absorption capacity of dibutyl phthalate of all positive electrode active materials is 11 mL / 100g or more and 19 mL / 100g or less. However, as long as the oil absorption capacity of dibutyl phthalate of the mixture containing multiple positive electrode active materials contained in the first positive electrode composite layer 41 meets the requirement of 11 mL / 100g or more and 19 mL / 100g or less, the oil absorption capacity of dibutyl phthalate of each positive electrode active material does not need to meet the above range. For example, if the first positive electrode composite layer 41 contains two positive electrode active materials (P1 and P2) with different dibutyl phthalate oil absorption capacities, as long as the dibutyl phthalate oil absorption capacity of the mixture containing positive electrode active materials P1 and P2 is 11 mL / 100g or more and 19 mL / 100g or less, then the dibutyl phthalate oil absorption capacity of positive electrode active material P1 can, for example, be less than 11 mL / 100g, and the dibutyl phthalate oil absorption capacity of positive electrode active material P2 can, for example, be greater than 19 mL / 100g. In this case, it is necessary to adjust the content of positive electrode active materials P1 and P2 so that the dibutyl phthalate oil absorption capacity of the mixture containing positive electrode active materials P1 and P2 is 11 mL / 100g or more and 19 mL / 100g or less.
[0032] Similarly, for the second positive electrode composite layer 42, when the oil absorption of the mixture containing multiple positive electrode active materials is 15 mL / 100g or more and 23 mL / 100g or less, it is preferable that the oil absorption of dibutyl phthalate of all positive electrode active materials is 15 mL / 100g or more and 23 mL / 100g or less. However, as long as the oil absorption of dibutyl phthalate in the mixture containing multiple positive electrode active materials in the second positive electrode composite layer 42 meets the requirement of 15 mL / 100g or more and 23 mL / 100g or less, the oil absorption of dibutyl phthalate of each positive electrode active material does not need to meet the above range. For example, if the second positive electrode composite layer 42 contains two positive electrode active materials (P1 and P2) with different dibutyl phthalate (DBP) oil absorption capacities, as long as the DBP oil absorption capacity of the mixture containing positive electrode active materials P1 and P2 is 15 mL / 100g or more and 23 mL / 100g or less, then the DBP oil absorption capacity of positive electrode active material P1 can, for example, be less than 15 mL / 100g, while the DBP oil absorption capacity of positive electrode active material P2 can, for example, be greater than 23 mL / 100g. In this case, it is necessary to adjust the content of positive electrode active materials P1 and P2 so that the DBP oil absorption capacity of the mixture containing positive electrode active materials P1 and P2 is 15 mL / 100g or more and 23 mL / 100g or less.
[0033] The oil absorption of dibutyl phthalate (DBP) in the positive electrode active material is determined according to the DBP absorption method A (mechanical method) specified in JIS K-6217-4 "Carbon black for rubber - basic properties - Part 4: method for determining DBP absorption". Specifically, using an absorption testing machine (manufactured by ASAHI SOKEN Co., Ltd., model "S-500"), DBP is added to the sample (positive electrode active material) stirred by two blades at a certain speed. The change in viscosity characteristics at this time is detected by a torque detector, and the output is converted into torque by a microcomputer. The DBP corresponding to the torque at 100% of the maximum torque is converted into the oil absorption of DBP per 100g of sample (positive electrode active material) to obtain the oil absorption of DBP.
[0034] In this embodiment, when the first positive electrode composite material layer 41 is divided into two equal parts in the thickness direction, the amount of dibutyl phthalate (DBP) oil absorbed by the positive electrode active material in the upper half region 41b is preferably less than the amount of DBP oil absorbed by the positive electrode active material in the lower half region 41a. This more effectively suppresses the permeation of non-aqueous electrolyte into the first positive electrode composite material layer 41. Here, "dividing the first positive electrode composite material layer 41 into two equal parts in the thickness direction" means that when the stacking direction of the positive electrode current collector 40 and the first positive electrode composite material layer 41 is set to the thickness direction of the first positive electrode composite material layer 41, the layer is divided in two at the middle Z1 of the thickness of the first positive electrode composite material layer 41. Furthermore, after dividing the first positive electrode composite material layer 41 into two equal parts in the thickness direction, the region 41a of the first positive electrode composite material layer 41 located close to the positive electrode current collector 40 is designated as the lower half region, and the region 41b of the first positive electrode composite material layer 41 located far from the positive electrode current collector 40 is designated as the upper half region.
[0035] In this embodiment, when the second positive electrode composite material layer 42 is divided into two equal parts in the thickness direction, the amount of dibutyl phthalate (DBP) of the positive electrode active material contained in the upper half region 42b is preferably greater than the amount of DBP of the positive electrode active material contained in the lower half region 42a. This further increases the amount of non-aqueous electrolyte permeating into the second positive electrode composite material layer 42. Here, "dividing the second positive electrode composite material layer 42 into two equal parts in the thickness direction" means that when the stacking direction of the positive electrode current collector 40 and the second positive electrode composite material layer 42 is set as the thickness direction of the second positive electrode composite material layer 42, the layer is divided in two at the middle Z2 of the thickness of the second positive electrode composite material layer 42. Furthermore, after dividing the second positive electrode composite material layer 42 into two equal parts in the thickness direction, the second positive electrode composite material layer 42 located near the positive electrode current collector 40 is designated as the lower half region 42a, and the second positive electrode composite material layer 42 located far from the positive electrode current collector 40 is designated as the upper half region 42b.
[0036] Positive electrode active materials can include lithium metal composite oxides containing transition metal elements such as Co, Mn, and Ni. Examples of lithium metal composite oxides include Li. x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M l-y O z Li x Ni 1- y M y O z Li x Mn2O4, Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). They can be used individually or in combination. From the perspective of achieving high capacity in non-aqueous electrolyte secondary batteries, the positive electrode active material preferably contains Li. x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z(M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3) and other lithium nickel composite oxides.
[0037] Positive electrode active materials can be obtained, for example, by mixing a precursor with a lithium compound and calcining the mixture. The precursor can be obtained, for example, by stirring a solution containing one or more metal salts such as transition metals while adding an alkaline solution such as sodium hydroxide dropwise, adjusting the pH to the alkaline side (e.g., 8.5–11.5), and then heat-treating the precipitated (co-precipitated) metal hydroxide. Furthermore, by adjusting the heat treatment temperature and time, precursors with different dibutyl phthalate oil absorption rates can be obtained, thereby yielding positive electrode active materials with different dibutyl phthalate oil absorption rates.
[0038] Conductive materials include, for example, carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNTs), and carbon-based particles such as graphite. They can be used alone or in combination of two or more.
[0039] Examples of adhesive materials include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. They can be used alone or in combination of two or more.
[0040] [negative electrode]
[0041] The negative electrode 12 has a negative electrode current collector and a negative electrode composite material layer disposed on the negative electrode current collector. The negative electrode current collector may be, for example, a foil of a metal such as copper that is stable in the potential range of the negative electrode, or a film of the metal disposed on the surface.
[0042] The negative electrode composite material layer contains a negative electrode active material, and preferably also contains a binder and a conductive material. For example, a negative electrode composite material slurry containing a negative electrode active material and a binder is prepared, the negative electrode composite material slurry is coated onto a negative electrode current collector and dried to form a negative electrode composite material layer, and the negative electrode composite material layer is calendered, thereby producing a negative electrode 12.
[0043] Negative electrode active materials can be substances that can reversibly absorb and release lithium ions, such as carbon materials like natural graphite and artificial graphite, metals alloyed with lithium such as silicon (Si) and tin (Sn), or alloys and composite oxides containing metal elements such as Si and Sn.
[0044] Examples of adhesive materials include fluorinated resins, PAN, polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and also partially neutralized salts), and polyvinyl alcohol (PVA). They can be used alone or in combination of two or more.
[0045] Conductive materials include, for example, carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNTs), and carbon-based particles such as graphite. They can be used alone or in combination of two or more.
[0046] [Spacer]
[0047] Spacer 13 may be made of porous sheets, for example, that are ion-permeable and insulating. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Suitable materials for spacers include olefin resins such as polyethylene and polypropylene, and cellulose. Spacer 13 may be a laminate containing a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it may be a multilayer spacer containing a polyethylene layer and a polypropylene layer, or a spacer with an aromatic polyamide resin, ceramic, or other material coated on its surface may be used.
[0048] [Non-aqueous electrolytes]
[0049] Non-aqueous electrolytes comprise a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents may include, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these solvents. Non-aqueous solvents may also contain halogen substitutes in which at least a portion of the hydrogen atoms of these solvents have been replaced by halogen atoms such as fluorine.
[0050] Examples of the aforementioned esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.
[0051] Examples of the aforementioned ethers include 1,3-dioxane, 4-methyl-1,3-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, crown ethers and other cyclic ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and dihexyl ether. Ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and other chain ethers.
[0052] As the halogen substitutes mentioned above, fluorocyclic carbonates such as fluoroethylene carbonate (FEC), fluorochain carbonates, and fluorochain carboxylic acid esters such as methyl fluoropropionate (FMP) are preferred.
[0053] The preferred electrolyte salt is a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), and LiPF6. 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 LiCl, LiBr, LiI, lithium chloroborane, lower aliphatic carboxylic acids, Li₂B₄O₇, Li(B(C₂O₄)F₂) and other borates, LiN(SO₂CF₃)₂, LiN(C₁F₂) 21+1 SO2)(C m F 2m+1 Imidamine salts such as SO2 (where m is an integer greater than or equal to 1) are used. Lithium salts can be used alone or in combination. Among these, LiPF6 is preferred from the viewpoints of ionic conductivity and electrochemical stability. The preferred concentration of the lithium salt is 0.8–1.8 mol per 1 L of solvent.
[0054] Example
[0055] The present invention will be further illustrated below with reference to embodiments; however, the present invention is not limited to these embodiments.
[0056] (Preparation of lithium metal composite oxide A)
[0057] After obtaining a nickel-cobalt-aluminum composite hydroxide via co-precipitation, the precursor was subjected to heat treatment and mixed with lithium hydroxide monohydrate (LiOH·H2O) to achieve an atomic ratio of lithium to nickel to cobalt to aluminum of Li:Ni:Co:Al = 1.00:0.82:0.15:0.03. This mixed powder was then calcined in an electric furnace under an oxygen atmosphere at 750°C for 15 hours to obtain lithium metal composite oxide A.
[0058] (Preparation of lithium metal composite oxides B-F)
[0059] In lithium metal composite oxides B to F, except for changing the heating temperature and heating time when heating the above-mentioned nickel-cobalt-aluminum composite hydroxide, they are prepared under the same conditions as lithium metal composite oxide A.
[0060] Table 1 summarizes the oil absorption of dibutyl phthalate for lithium metal composite oxides A through F. The method for determining the oil absorption of dibutyl phthalate is as described above.
[0061] [Table 1]
[0062]
[0063] <Example 1>
[0064] [The production of the positive electrode]
[0065] A slurry with a solid content of 70% by mass was prepared by mixing lithium metal composite oxide B (as the positive electrode active material), acetylene black (as the conductive material), and polyvinylidene fluoride (PVDF) with an average molecular weight of 1.1 million as the binder in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 98:1:1. This slurry was designated as the first positive electrode composite material slurry.
[0066] In addition, a slurry with a solid content of 70% by mass was prepared by mixing lithium metal composite oxide E as the positive electrode active material, acetylene black as the conductive material, and polyvinylidene fluoride (PVDF) with an average molecular weight of 1.1 million as the binder in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 98:1:1. This slurry was designated as the second positive electrode composite material slurry.
[0067] A first positive electrode composite material slurry is coated on one side of an aluminum foil with a thickness of 15 μm, and a second positive electrode composite material slurry is coated on the other side of the aluminum foil. After drying, the foil is calendered using calendering rollers to produce a positive electrode with a first positive electrode composite material layer formed on one side of the positive electrode current collector and a second positive electrode composite material layer formed on the other side of the positive electrode current collector.
[0068] [Making the negative electrode]
[0069] 95 parts by weight of graphite powder, 5 parts by weight of Si oxide, and 1 part by weight of carboxymethyl cellulose (CMC) were mixed with an appropriate amount of water. 1.2 parts by weight of styrene-butadiene rubber (SBR) and an appropriate amount of water were added to this mixture to prepare a negative electrode composite slurry. This negative electrode composite slurry was coated onto both sides of an 8 μm thick copper foil. After drying the coating, it was calendered using calendering rollers to produce a negative electrode with negative electrode composite layers formed on both sides of the negative electrode current collector.
[0070] [Preparation of non-aqueous electrolytes]
[0071] Add 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent containing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC:MEC = 1:3 by volume) to dissolve LiPF6 at a concentration of 1 mol / L. Set it as a non-aqueous electrolyte.
[0072] [Making a Second-hand Battery]
[0073] (1) After installing leads on the positive and negative electrodes respectively, a polyethylene spacer with a thickness of 20 μm is placed between the positive and negative electrodes, and they are wound up so that the first positive electrode composite material layer of the positive electrode is on the outer periphery and the second positive electrode composite material layer is on the inner periphery to create a wound electrode body.
[0074] (2) Insert the electrode into the outer shell body, weld the negative electrode lead to the bottom of the outer shell body, and weld the positive electrode lead to the sealing body.
[0075] (3) After injecting non-aqueous electrolyte into the outer casing, the open end of the outer casing is clamped and riveted to the sealing body through the gasket. It is then set as a non-aqueous electrolyte secondary battery.
[0076] <Example 2>
[0077] Except for using lithium metal composite oxide D as the positive electrode active material in the first positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0078] <Example 3>
[0079] Except for using lithium metal composite oxide C as the positive electrode active material in the second positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0080] <Example 4>
[0081] Except for using lithium metal composite oxide A as the positive electrode active material in the first positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0082] <Example 5>
[0083] Except for using lithium metal composite oxide B as the positive electrode active material in the first positive electrode composite slurry and lithium metal composite oxide F as the positive electrode active material in the second positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0084] <Comparative Example 1>
[0085] Except for using lithium metal composite oxide E as the positive electrode active material in the first positive electrode composite slurry and using lithium metal composite oxide B as the positive electrode active material in the second positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0086] <Comparative Example 2>
[0087] Except that the same lithium metal composite oxide B as the first positive electrode composite slurry was used as the positive electrode active material in the second positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0088] <Comparative Example 3>
[0089] Except that the same lithium metal composite oxide E as the second positive electrode composite slurry was used as the positive electrode active material in the first positive electrode composite slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.
[0090] [Evaluation of charge-discharge cycle characteristics]
[0091] For the non-aqueous electrolyte secondary batteries of each embodiment and comparative example, constant current charging was performed at 0.7 It at a temperature of 25°C until the voltage reached 4.2V. Then, constant voltage charging was performed at 4.2V until the current reached 0.05 It. Next, constant current discharging was performed at 0.7 It until the voltage reached 2.5V. This charge-discharge cycle was defined as one cycle, and 300 cycles were performed. The capacity retention rate was calculated using the following formula.
[0092] Capacity retention (%) = (Discharge capacity at 300th cycle / Discharge capacity at 1st cycle) × 100
[0093] Table 2 summarizes the results of charge-discharge cycle characteristics for each embodiment and comparative example.
[0094] [Table 2]
[0095]
[0096] Examples 1-5 all exhibited high capacity retention compared to Comparative Examples 1-3. Based on these results, by using a positive electrode, as shown in Examples 1-5, in which the oil absorption of dibutyl phthalate, the positive active material contained in the first positive electrode composite material layer formed on the first surface of the positive electrode current collector facing the outer side of the electrode body, is less than the oil absorption of the positive active material contained in the second positive electrode composite material layer formed on the second surface of the positive electrode current collector facing the inner side of the electrode body, the reduction in charge-discharge cycle characteristics can be suppressed. Furthermore, in Examples 1 to 5, since Examples 1 to 3 showed a capacity retention rate of 85% or more, from the perspective of further suppressing charge-discharge cycle characteristics, it is preferable that the oil absorption of dibutyl phthalate in the positive electrode active material contained in the first positive electrode composite material layer is 11 mL / 100g or more and 19 mL / 100g or less, and the oil absorption of dibutyl phthalate in the positive electrode active material contained in the second positive electrode composite material layer is 15 mL / 100g or more and 23 mL / 100g or less.
[0097] Explanation of reference numerals in the attached figures
[0098] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Spacer, 14 Electrode body, 15 Battery casing, 16 Casing body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Bulging part, 23 Filter, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cap, 28 Gasket, 40 Positive electrode current collector, 41 First positive electrode composite material layer, 41a, 42a lower half area, 41b, 42b upper half area, 42 Second positive electrode composite material layer.
Claims
1. A non-aqueous electrolyte secondary battery, It has a wound electrode body formed by winding the positive and negative electrodes together with a spacer between them. The positive electrode has a positive current collector, a first positive electrode composite material layer formed on a first surface of the positive current collector facing the outer side of the electrode body, and a second positive electrode composite material layer formed on a second surface of the positive current collector facing the inner side of the electrode body. The first positive electrode composite material layer and the second positive electrode composite material layer contain positive electrode active materials. The oil absorption capacity of dibutyl phthalate in the positive electrode active material contained in the first positive electrode composite material layer is less than that of dibutyl phthalate in the positive electrode active material contained in the second positive electrode composite material layer. The first positive electrode composite material layer contains a dibutyl phthalate oil absorption capacity of 11 mL / 100g or more and 19 mL / 100g or less for the positive electrode active material. The second positive electrode composite material layer contains a dibutyl phthalate oil absorption capacity of 15 mL / 100g or more and 23 mL / 100g or less for the positive electrode active material. When the first positive electrode composite material layer is divided into two equal parts in the thickness direction, the upper half region of the positive electrode active material, as observed from the positive electrode current collector, contains a dibutyl phthalate oil absorption capacity of 11 mL / 100g or more and 23 mL / 100g or less for the positive electrode active material. The oil absorption of butyl phthalate is less than that of dibutyl phthalate in the lower half region of the positive electrode active material when viewed from the positive electrode current collector. Furthermore, when the second positive electrode composite layer is divided into two equal parts in the thickness direction, the oil absorption of dibutyl phthalate in the upper half region of the positive electrode active material when viewed from the positive electrode current collector is greater than that of dibutyl phthalate in the lower half region of the positive electrode active material when viewed from the positive electrode current collector. The positive electrode active material is a lithium metal composite oxide.