Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) is characterized by comprising an electrode body (14) in which a positive electrode (11) and a negative electrode (12) face each other with a separator (13) therebetween, and a battery case (15) that accommodates the electrode body (14), wherein: the positive electrode (11) has a positive electrode mixture layer containing a positive electrode active material; and when the non-aqueous electrolyte secondary battery (10) is used in a fixed state, and the electrode body (14) in the fixed state is bisected in the vertical direction, a dibutyl phthalate oil absorption amount of the positive electrode active material contained in the positive electrode mixture layer disposed in the top half region is higher than a dibutyl phthalate oil absorption amount of the positive electrode active material contained in the positive electrode mixture layer disposed in the bottom half region.

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries, which consist of a positive electrode, a negative electrode, and a non-aqueous electrolyte, and perform charging and discharging by moving lithium ions and other elements between the positive and negative electrodes, have been widely used as high-power, high-energy-density secondary batteries.

[0003] For example, Patent Document 1 describes a non-aqueous electrolyte secondary battery comprising a wound electrode body including a positive electrode sheet and a negative electrode sheet, and a non-aqueous electrolyte, wherein the positive electrode sheet comprises a long positive electrode current collector and a positive electrode composite layer formed on the surface of the positive electrode current collector, the portions of the positive electrode composite layer in the winding axis direction of the wound electrode body are mainly composed of a first positive electrode active material, and the central portion of the positive electrode composite layer in the winding axis direction, including at least the center, is mainly composed of a second positive electrode active material, and between the first positive electrode active material and the second positive electrode active material, JIS A non-aqueous electrolyte secondary battery is disclosed, characterized in that the DBP absorption amounts [mL / 100g] based on K6217-4 are different from each other, and the DBP absorption amount A [mL / 100g] of the first positive electrode active material is smaller than the DBP absorption amount B [mL / 100g] of the second positive electrode active material.

[0004] Furthermore, for example, Patent Document 2 proposes a positive electrode active material consisting of a lithium-containing composite oxide powder in which the dibutyl phthalate oil absorption capacity is 20 mL / 100 g to 40 mL / 100 g. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-131322 [Patent Document 2] Japanese Patent Publication No. 2005-285606 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] This disclosure aims to provide a non-aqueous electrolyte secondary battery that enables improved charge-discharge cycle characteristics. [Means for solving the problem]

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are opposed to each other via a separator, and a battery case housing the electrode body, wherein the positive electrode has a positive electrode composite layer containing a positive electrode active material, and the non-aqueous electrolyte secondary battery is used in a fixed state, and when the electrode body in the fixed state is divided vertically into two equal parts, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the upper half of the region is higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the lower half of the region.

[0008] Furthermore, a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are opposed to each other via a separator, a bottomed cylindrical outer can containing the electrode body, and a sealing body that closes the opening of the outer can, wherein the positive electrode has a positive electrode composite layer containing a positive electrode active material, and when the electrode body is divided into two equal parts in the direction of insertion into the outer can, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the area of ​​the sealing body side is higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the area of ​​the bottom half of the outer can.

[0009] In addition, a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode body in which a positive electrode and a negative electrode face each other through a separator, a bottomed cylindrical exterior can that houses the electrode body, and a sealing body that closes an opening of the exterior can. The positive electrode has a positive electrode composite material layer containing a positive electrode active material. When the electrode body is divided into two equal parts with respect to the insertion direction into the exterior can, the dibutyl phthalate oil absorption amount of the positive electrode active material contained in the positive electrode composite material layer disposed in the region on the bottom side half of the exterior can is higher than the dibutyl phthalate oil absorption amount of the positive electrode active material contained in the positive electrode composite material layer disposed in the region on the sealing body side half.

Advantages of the Invention

[0010] According to one aspect of the present disclosure, it becomes possible to improve charge-discharge cycle characteristics.

Brief Description of the Drawings

[0011] [Figure 1] It is a cross-sectional view of a non-aqueous electrolyte secondary battery which is an example of an embodiment. [Figure 2] It is a side view showing a state in which the non-aqueous electrolyte secondary battery shown in FIG. 1 is fixed. [Figure 3] It is a perspective view of a wound electrode body used for the non-aqueous electrolyte secondary battery of FIG. 2. [Figure 4] It is a side view showing another example of a state in which the non-aqueous electrolyte secondary battery shown in FIG. 1 is fixed. [Figure 5] It is a perspective view of a wound electrode body used for the non-aqueous electrolyte secondary battery of FIG. 4.

Modes for Carrying Out the Invention

[0012] An example of an embodiment will be described while referring to the drawings. Note that the non-aqueous electrolyte secondary battery of the present disclosure is not limited to the embodiments described below. Also, the drawings referred to in the description of the embodiments are schematically drawn.

[0013] Figure 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. The non-aqueous electrolyte secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, a non-aqueous electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, respectively, and a battery case 15 that houses the above components. The battery case 15 is composed of an outer casing 16 and a sealing body 17 that closes the opening of the outer casing 16. In addition, other forms of electrode bodies may be used instead of the wound electrode body 14, such as a laminated electrode body in which the positive electrode and negative electrode are alternately stacked with a separator. Examples of battery cases 15 include cylindrical, square, coin-shaped, button-shaped, and other bottomed cylindrical outer casings, and pouch outer casings formed by laminating a resin sheet and a metal sheet.

[0014] The outer casing 16 is, for example, a metal case in the shape of a bottomed cylinder. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has, for example, a protruding portion 22 that supports the sealing body 17, which is a part of the side surface that protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17.

[0015] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the non-aqueous electrolyte secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0016] In the non-aqueous electrolyte secondary battery 10 shown in Figure 1, the positive electrode lead 20 attached to the positive electrode 11 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 attached to the negative electrode 12 extends outside the insulating plate 19 towards the bottom of the outer casing 16. The positive electrode lead 20 is connected by welding or the like to the lower surface of the filter 23, which is the bottom plate of the sealing body 17, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner surface of the bottom of the outer casing 16, and the outer casing 16 becomes the negative electrode terminal.

[0017] In this embodiment, the sealing body 17 is the top surface of the battery case 15, the surface of the outer casing 16 facing the sealing body 17 is the bottom surface of the battery case 15, and the side surface connecting the top surface and the bottom surface is the side surface of the battery case 15. Furthermore, the direction from the bottom surface to the top surface of the battery case 15 is the height direction of the non-aqueous electrolyte secondary battery 10.

[0018] The following provides a detailed explanation of each component of the non-aqueous electrolyte secondary battery 10.

[0019] [Positive electrode] The positive electrode 11 comprises a positive electrode current collector and a positive electrode composite material layer provided on the positive electrode current collector. The positive electrode current collector can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, or a film with the metal arranged on its surface. The positive electrode composite material layer contains a positive electrode active material and preferably also contains a binder and a conductive material.

[0020] The positive electrode 11 is manufactured, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a binder, a conductive material, etc., onto a positive electrode current collector, drying it to form a positive electrode composite layer, and then rolling the positive electrode composite layer with a rolling roller or the like. Details of the method for manufacturing the positive electrode composite layer will be described later.

[0021] In this embodiment, the positive electrode active material contained in the positive electrode composite layer includes multiple positive electrode active materials with different dibutyl phthalate oil absorption amounts. This will be explained in detail below with reference to the drawings.

[0022] Figure 2 is a side view showing the non-aqueous electrolyte secondary battery shown in Figure 1 in a fixed state. The non-aqueous electrolyte secondary battery of this embodiment is preferably used as a stationary or fixed power source installed indoors or outdoors, or as a power source installed in a mobile device such as an electric vehicle. The non-aqueous electrolyte secondary battery 10 used as such a power source is installed on a fixing part 38 such as a mounting base or case, as shown in Figure 2, and is used in a fixed state. Used in a fixed state means that after the non-aqueous electrolyte secondary battery 10 is installed on the fixing part 38 and use begins, the orientation of the non-aqueous electrolyte secondary battery 10 does not change significantly. For example, a non-aqueous electrolyte secondary battery used as a power source for a mobile phone is placed in any orientation as the mobile phone is used, so it is not included in the case of being used in a fixed state.

[0023] In Figure 2, arrow Z points in the vertical direction (direction of gravity). That is, the non-aqueous electrolyte secondary battery 10 shown in Figure 2 is erected along the vertical direction. More specifically, in the non-aqueous electrolyte secondary battery 10 shown in Figure 2, the bottom of the battery case 15 is in contact with the fixing part 38, and the non-aqueous electrolyte secondary battery 10 is installed so that its height direction is aligned with the vertical direction.

[0024] Figure 3 is a perspective view of the wound electrode body used in the non-aqueous electrolyte secondary battery shown in Figure 2. However, in Figure 3, in order to facilitate the explanation of the configuration of the positive electrode 11, a part of the positive electrode 11 to be wound around the electrode body 14 (the winding end) is shown in its pre-winding state. Here, region A of the electrode body 14 shown in Figure 3 corresponds to the upper half region 10a when the electrode body 14 housed in the non-aqueous electrolyte secondary battery 10 shown in Figure 2 is divided into two equal parts in the vertical direction, and region B of the electrode body 14 shown in Figure 3 corresponds to the lower half region 10b when the electrode body 14 housed in the non-aqueous electrolyte secondary battery 10 shown in Figure 2 is divided into two equal parts in the vertical direction.

[0025] In this embodiment, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer 11a located in region A shown in Figure 3 (i.e., the upper half region 10a shown in Figure 2) is higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer 11b located in region B shown in Figure 3 (i.e., the lower half region 10b shown in Figure 2). Note that the height direction of the non-aqueous electrolyte secondary battery 10 shown in Figure 2 is aligned with the vertical direction, so the vertical direction can also be rephrased as the height direction of the non-aqueous electrolyte secondary battery 10. That is, if the electrode body 14 is divided into two equal parts with respect to the height direction of the non-aqueous electrolyte secondary battery 10, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the upper half region is higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the lower half region.

[0026] Figure 4 is a side view showing another example of the non-aqueous electrolyte secondary battery shown in Figure 1 in a fixed state. In Figure 4, arrow Z points in the vertical direction (direction of gravity), and arrow Y points in the direction perpendicular to the vertical direction (horizontal direction). In the non-aqueous electrolyte secondary battery 10 shown in Figure 4, the side of the battery case 15 is in contact with the fixing part 38, and the height direction of the non-aqueous electrolyte secondary battery 10 is aligned with the direction perpendicular to the vertical direction (horizontal direction).

[0027] Figure 5 is a perspective view of the wound electrode body used in the non-aqueous electrolyte secondary battery shown in Figure 4. Here, region A of the electrode body 14 shown in Figure 5 corresponds to the upper half region 10a when the electrode body 14 housed in the non-aqueous electrolyte secondary battery 10 shown in Figure 4 is divided vertically into two equal parts, and region B of the electrode body 14 shown in Figure 5 corresponds to the lower half region 10b when the electrode body 14 housed in the non-aqueous electrolyte secondary battery 10 shown in Figure 4 is divided vertically into two equal parts.

[0028] In this embodiment, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in region A shown in Figure 5 (i.e., the upper half of region 10a shown in Figure 4) is higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in region B shown in Figure 5 (i.e., the lower half of region 10b shown in Figure 4).

[0029] In a non-aqueous electrolyte secondary battery 10 used in a fixed state, the non-aqueous electrolyte in the battery case 15 tends to be unevenly distributed vertically downward due to gravity, and the non-aqueous electrolyte is easily depleted vertically upward. This uneven distribution of the non-aqueous electrolyte leads to a decrease in charge-discharge cycle characteristics. However, in the non-aqueous electrolyte secondary battery 10 of this embodiment, by making the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the upper half region 10a higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the lower half region 10b, the retention of the non-aqueous electrolyte in the vertically upward direction is improved. Therefore, uneven distribution of the non-aqueous electrolyte vertically downward is suppressed, making it possible to improve charge-discharge cycle characteristics. The above explanation used a non-aqueous electrolyte secondary battery having a cylindrical, bottomed battery case and a wound electrode body as an example. However, similar effects can be obtained in the case of a rectangular, bottomed cylindrical battery case or a non-aqueous electrolyte secondary battery having a stacked electrode body.

[0030] In this embodiment, in terms of improving charge-discharge cycle characteristics, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the upper half region 10a 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 more preferably 17 mL / 100g or more and 21 mL / 100g or less. Also in this embodiment, in terms of improving charge-discharge cycle characteristics, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the lower half region 10b 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 more preferably 13 mL / 100g or more and 17 mL / 100g or less.

[0031] The values ​​for the amount of dibutyl phthalate oil absorbed by the positive electrode contained in the positive electrode mixture layer located in the upper half region 10a and the lower half region 10b are average values. That is, the positive electrode mixture layer located in the upper half region 10a and the positive electrode mixture layer located in the lower half region 10b may each contain multiple positive electrode active materials with different amounts of dibutyl phthalate oil absorbed. For example, if the positive electrode mixture layer located in the upper half region 10a contains three types of positive electrode active materials (P1, P2, P3) with different amounts of dibutyl phthalate oil absorbed, the amount of dibutyl phthalate oil absorbed by the positive electrode active materials contained in that positive electrode mixture layer will be the amount of dibutyl phthalate oil absorbed by the mixture consisting of positive electrode active materials P1, P2, and P3. The same applies to the positive electrode mixture layer located in the lower half region 10b.

[0032] If the amount of oil absorbed by the mixture of multiple positive electrode active materials in the positive electrode composite layer located in the upper half region 10a is 15 mL / 100g or more and 23 mL / 100g or less, it is desirable that the amount of dibutyl phthalate absorbed by all positive electrode active materials is 15 mL / 100g or more and 23 mL / 100g or less. However, if the amount of dibutyl phthalate absorbed by the mixture of multiple positive electrode active materials contained in the positive electrode composite layer located in the upper half region 10a is 15 mL / 100g or more and 23 mL / 100g or less, the amount of dibutyl phthalate absorbed by each positive electrode active material does not need to meet the above range. For example, if the positive electrode composite layer located in the upper half region 10a contains two types of positive electrode active materials (P1, P2) with different dibutyl phthalate oil absorption amounts, the amount of dibutyl phthalate oil absorbed by the mixture of positive electrode active materials P1 and P2 may be less than 15 mL / 100 g, or the amount of dibutyl phthalate oil absorbed by positive electrode active material P2 may be more than 23 mL / 100 g, as long as the total dibutyl phthalate oil absorbed by the mixture of positive electrode active materials P1 and P2 is between 15 mL / 100 g and 23 mL / 100 g. In this case, it is necessary to adjust the content of positive electrode active materials P1 and P2 so that the total dibutyl phthalate oil absorbed by the mixture of positive electrode active materials P1 and P2 is between 15 mL / 100 g and 23 mL / 100 g.

[0033] Similarly, in the positive electrode composite layer located in the lower half of region 10b, if the oil absorption amount of the mixture of multiple positive electrode active materials is 11 mL / 100g or more and 19 mL / 100g or less, it is desirable that the dibutyl phthalate oil absorption amount of all positive electrode active materials be 11 mL / 100g or more and 19 mL / 100g or less. However, if the dibutyl phthalate oil absorption amount of the mixture of multiple positive electrode active materials contained in the positive electrode composite layer located in the lower half of region 10b is 11 mL / 100g or more and 19 mL / 100g or less, the dibutyl phthalate oil absorption amount of each positive electrode active material does not need to meet the above range. For example, if the positive electrode composite layer located in the lower half region 10b contains two types of positive electrode active materials (P1, P2) with different dibutyl phthalate oil absorption amounts, the amount of dibutyl phthalate oil absorbed by the mixture of positive electrode active materials P1 and P2 may be less than, for example, 11 mL / 100 g, or more than, and 19 mL / 100 g, as long as the total dibutyl phthalate oil absorbed by the mixture is 11 mL / 100 g or more and 19 mL / 100 g or less. In this case, it is necessary to adjust the content of positive electrode active materials P1 and P2 so that the total dibutyl phthalate oil absorbed by the mixture of positive electrode active materials P1 and P2 is 11 mL / 100 g or more and 19 mL / 100 g or less.

[0034] In the non-aqueous electrolyte secondary battery 10 shown in Figure 2, the bottom of the outer casing 16 is fixed in contact with the fixing part 38. In this case, when the electrode body 14 is divided in half with respect to the insertion direction into the outer casing 16, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the region on the sealing body 17 side is made higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the region on the bottom side of the outer casing 16. If the battery case 15 is composed of a bottomed cylindrical outer casing 16 and a sealing body 17, the non-aqueous electrolyte secondary battery 10 can also be fixed so that the sealing body 17, rather than the bottom of the outer casing 16, is in contact with the fixing part 38. In this case, when the electrode body 14 is divided into two equal parts with respect to the insertion direction into the outer casing 16, the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the bottom half of the outer casing 16 is made higher than the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode composite layer located in the sealing body 17 side half. This improves the charge-discharge cycle characteristics of the non-aqueous electrolyte secondary battery 10.

[0035] The amount of dibutyl phthalate absorbed by the positive electrode active material is measured according to the DBP (dibutyl phthalate) 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 tester (manufactured by Asahi Research Institute Co., Ltd., model name "S-500"), DBP is added at a constant speed to a sample (positive electrode active material) being stirred by two blades. The change in viscosity characteristics at this time is detected by a torque detector, and the output is converted to torque using a microcomputer. The amount of dibutyl phthalate absorbed is then calculated by converting the DBP corresponding to the torque at 100% of the maximum torque generated to per 100g of the sample (positive electrode active material).

[0036] Examples of positive electrode active materials include lithium metal composite oxides containing transition metal elements such as Co, Mn, and Ni. Lithium metal composite oxides include, for example, Li x CoO2, Li x KiO2, Li x MnO2, Li x Co y Ni 1-yO2, Li x Co y M 1-y O z , Li x Ni 1-y M y O z , Li x , LiMn2O4, Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M is 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). These may be used alone or in combination of multiple kinds. In terms of achieving high capacity of the non-aqueous electrolyte secondary battery, the cathode active material is Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (M is 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), etc., and preferably contains lithium nickel composite oxides.

[0037] The cathode active material can be obtained, for example, by mixing a precursor and a lithium compound and firing the mixture. The precursor can be obtained, for example, by dropping an alkaline solution such as sodium hydroxide while stirring a solution containing one or more metal salts of transition metals, etc., and adjusting the pH to the alkaline side (for example, 8.5 - 11.5) to precipitate (co-precipitate) metal hydroxides and then heat-treating them. By adjusting the heat treatment temperature, heat treatment time, etc. during this heat treatment, precursors with different dibutyl phthalate oil absorption amounts can be obtained, and thus cathode active materials with different dibutyl phthalate oil absorption amounts can be obtained.

[0038] Examples of conductive materials include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), and carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0039] Examples of binders include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used individually or in combination of two or more types.

[0040] An example of a method for preparing a positive electrode composite layer is described below. For example, a positive electrode active material having a dibutyl phthalate oil absorption capacity of 11 mL / 100g or more and 19 mL / 100g or less, along with a binder, conductive material, etc., is mixed with a solvent to prepare a positive electrode composite slurry B for the lower half of region 10b. Separately from this slurry, a positive electrode active material having a dibutyl phthalate oil absorption capacity of 15 mL / 100g or more and 23 mL / 100g or less, along with a binder, conductive material, etc., is mixed with a solvent to prepare a positive electrode composite slurry A for the upper half of region 10a. Then, in the case of a non-aqueous electrolyte secondary battery used in the state shown in Figure 2, positive electrode composite slurry A and B are applied along the longitudinal direction of the positive electrode current collector and adjacent to each other in the width direction perpendicular to the longitudinal direction. In the case of a non-aqueous electrolyte secondary battery used in the state shown in Figure 4, positive electrode composite slurry A and B are applied alternately along the longitudinal direction of the positive electrode current collector at a predetermined length. Then, by drying the applied slurry and rolling the coating film, a positive electrode composite layer can be formed.

[0041] [Negative electrode] The negative electrode 12 comprises a negative electrode current collector and a negative electrode composite layer provided on the negative electrode current collector. The negative electrode current collector can be, for example, a foil of a metal that is stable in the negative electrode potential range, such as copper, or a film with the metal arranged on its surface.

[0042] The negative electrode composite layer preferably contains a negative electrode active material and further contains a binder, a conductive material, etc. The negative electrode 12 can be manufactured, for example, by preparing a negative electrode composite slurry containing a negative electrode active material, a binder, etc., applying this negative electrode composite slurry onto a negative electrode current collector, drying it to form a negative electrode composite layer, and rolling this negative electrode composite layer.

[0043] The negative electrode active material is, for example, a material that can reversibly intercept and release lithium ions, and includes carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as silicon (Si) and tin (Sn), or alloys and composite oxides containing metallic elements such as Si and Sn.

[0044] Examples of binders include fluororesins, PAN, polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0045] Examples of conductive materials include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), and carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0046] [Separator] For the separator 13, for example, a porous sheet having ion permeability and insulating properties can be used. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator include polyethylene, olefin resins such as polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it may be a multilayer separator containing a polyethylene layer and a polypropylene layer, or a separator with a material such as aramid resin or ceramic coated on its surface may be used.

[0047] [Non-aqueous electrolytes] Non-aqueous electrolytes comprise a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may also contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine.

[0048] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters 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 linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.

[0049] Examples of the above ethers include cyclic ethers such as 1,3 - dioxolane, 4 - methyl - 1,3 - dioxolane, tetrahydrofuran, 2 - methyltetrahydrofuran, propylene oxide, 1,2 - butylene oxide, 1,3 - dioxane, 1,4 - dioxane, 1,3,5 - trioxane, furan, 2 - methylfuran, 1,8 - cineole, crown ether, etc., and chain - like ethers such as 1,2 - dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, 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, etc.

[0050] As the above - mentioned halogen - substituted compounds, it is preferable to use fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain - like carbonates, fluorinated chain - like carboxylic acid esters such as methyl fluoropropionate (FMP), etc.

[0051] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 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, lithium lower aliphatic carboxylate, borates such as Li2B4O7, Li(B(C2O4)F2), LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 Examples include imide salts such as SO2){l,m are integers of 1 or more}. Lithium salts may be used individually or in mixtures of multiple types. Of these, LiPF6 is preferred from the viewpoint of ionic conductivity and electrochemical stability. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per liter of solvent. [Examples]

[0052] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0053] (Preparation of lithium metal composite oxide A) A nickel-cobalt-aluminum composite hydroxide was obtained by coprecipitation, and the resulting precursor was heated and mixed with lithium hydroxide monohydrate (LiOH·H2O) so that the atomic ratio of lithium, nickel, cobalt, and aluminum was Li:Ni:Co:Al = 1.00:0.82:0.15:0.03. This mixed powder was calcined in an electric furnace under an oxygen atmosphere at 750°C for 15 hours to obtain lithium metal composite oxide A.

[0054] (Preparation of lithium metal composite oxides B-D) Lithium metal composite oxides B to D were prepared under the same conditions as lithium metal composite oxide A, except that the heat treatment temperature and heating time were changed when heat-treating the nickel-cobalt-aluminum composite hydroxide.

[0055] Table 1 summarizes the dibutyl phthalate oil absorption amounts of lithium metal composite oxides A to D. The method for measuring dibutyl phthalate oil absorption is as described above.

[0056] [Table 1]

[0057] <Example 1> [Fabrication of the positive electrode] A slurry with a solid content of 70% by mass was prepared by mixing lithium metal composite oxide A 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 in a mass ratio of 98:1:1. This slurry was used as the positive electrode composite material slurry for the lower half of the region.

[0058] Furthermore, lithium metal composite oxide D 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 were mixed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 98:1:1 to prepare a slurry with a solid content of 70% by mass. This slurry was used as the positive electrode composite material slurry for the upper half of the region.

[0059] A cathode composite slurry for the lower half region and a cathode composite slurry for the upper half region were applied in stripes to both sides of a 15 μm thick aluminum foil, along the longitudinal direction of the aluminum foil and adjacent to each other in the width direction perpendicular to the longitudinal direction. After drying, the cathode was fabricated by rolling with a rolling roller.

[0060] [Fabrication of the negative electrode] 95 parts by mass of graphite powder, 5 parts by mass of Si oxide, and 1 part by mass of carboxymethylcellulose (CMC) were mixed with an appropriate amount of water. A negative electrode slurry was prepared by adding 1.2 parts by mass of styrene-butadiene rubber (SBR) and an appropriate amount of water to this mixture. This negative electrode slurry was applied to both sides of an 8 μm thick copper foil, and after the coating film was dried, it was rolled with a rolling roller to produce a negative electrode in which negative electrode slurry layers were formed on both sides of the negative electrode current collector.

[0061] [Preparation of non-aqueous electrolytes] 100 parts by mass of a mixed solvent consisting of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio: EC:DMC = 1:3) was mixed with 5 parts by mass of vinylene carbonate (VC), and LiPF6 was dissolved at a concentration of 1 mol / L. This was used as a non-aqueous electrolyte.

[0062] [Manufacturing of secondary batteries] (1) After attaching leads to the positive and negative electrodes, a wound electrode body was fabricated by winding the leads around a 20 μm thick polyethylene separator between the positive and negative electrodes. (2) The electrode body was inserted into the outer casing, the negative electrode lead was welded to the bottom of the outer casing, and the positive electrode lead was welded to the sealing body. The electrode body was inserted into the outer casing such that, when the non-aqueous electrolyte secondary battery is divided in the height direction into two equal parts, the positive electrode material layer located in the upper half region is derived from the positive electrode material slurry for the upper half region, and the positive electrode material layer located in the lower half region is derived from the positive electrode material slurry for the lower half region. (3) After injecting a non-aqueous electrolyte into the outer casing, the open end of the outer casing was crimped to a sealing body via a gasket. This was then subjected to non-aqueous electrolysis to form a secondary battery.

[0063] <Example 2> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that lithium metal composite oxide C was used as the positive electrode active material for the positive electrode slurry for the lower half of the region.

[0064] <Example 3> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that lithium metal composite oxide B was used as the positive electrode active material for the positive electrode slurry for the upper half region.

[0065] <Comparative Example 1> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that lithium metal composite oxide D was used as the positive electrode active material for the positive electrode slurry for the lower half region, and lithium metal composite oxide A was used as the positive electrode active material for the positive electrode slurry for the upper half region.

[0066] <Comparative Example 2> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that lithium metal composite oxide A was used as the positive electrode active material for the positive electrode slurry for the upper half region.

[0067] <Comparative Example 3> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that lithium metal composite oxide D was used as the positive electrode active material for the positive electrode slurry for the lower half of the region.

[0068] [Evaluation of charge-discharge cycle characteristics] The non-aqueous electrolyte secondary batteries of each example and comparative example were placed on the mounting platform with their bottoms in contact with the platform, so that the height of the batteries was aligned with the vertical direction. Then, each non-aqueous electrolyte secondary battery was charged with a constant current of 0.7It at a temperature of 25°C until the voltage reached 4.2V, and then charged with a constant voltage of 4.2V until the current reached 0.05It. Finally, a constant current discharge was performed with a current of 0.7It until the voltage reached 2.5V. This charge-discharge cycle was considered one cycle, and 1000 cycles were performed. The capacity retention rate was then calculated using the following formula. Capacity retention rate (%) = (Discharge capacity at 1000th cycle / Discharge capacity at 1st cycle) × 100

[0069] Table 2 summarizes the charge-discharge cycle characteristics of each example and comparative example.

[0070] [Table 2]

[0071] Examples 1 to 3 all showed higher capacity retention rates during charge-discharge cycles compared to Comparative Examples 1 to 3. Therefore, as in Examples 1 to 3, when a non-aqueous electrolyte secondary battery is used in a fixed state, and the electrode body in this fixed state is divided vertically into two equal parts, the charge-discharge cycle characteristics can be improved by making the amount of dibutyl phthalate absorbed by the positive electrode active material in the positive electrode composite layer located in the upper half of the region higher than the amount of dibutyl phthalate absorbed by the positive electrode active material in the positive electrode composite layer located in the lower half of the region. [Explanation of Symbols]

[0072] 10 Non-aqueous electrolyte secondary battery, 10a Upper half region, 10b Lower half region, 11 Positive electrode, 11a, 11b Positive electrode composite layer, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 38 Fixing part.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are opposed to each other via a separator, and a battery case housing the electrode body, The positive electrode has a positive electrode composite layer containing a positive electrode active material, and the positive electrode active material contains a lithium metal composite oxide. A non-aqueous electrolyte secondary battery in which the non-aqueous electrolyte secondary battery is used in a fixed state, and when the electrode body in the fixed state is divided vertically into two equal parts, the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the upper half is higher than the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the lower half.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode composite layer located in the upper half region is 15 mL / 100 g or more and 23 mL / 100 g or less, and the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode composite layer located in the lower half region is 11 mL / 100 g or more and 19 mL / 100 g or less.

3. A non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are opposed to each other via a separator, a bottomed cylindrical outer container housing the electrode body, and a sealing body that closes the opening of the outer container, The positive electrode has a positive electrode composite layer containing a positive electrode active material, and the positive electrode active material contains a lithium metal composite oxide. When the electrode body is divided into two equal parts with respect to the insertion direction into the outer can, the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the sealing body side half is higher than the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the bottom side half of the outer can. A non-aqueous electrolyte secondary battery, wherein the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the half-side region of the sealing body is 15 mL / 100 g or more and 23 mL / 100 g or less, and the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the bottom half-side region of the outer casing is 11 mL / 100 g or more and 19 mL / 100 g or less.

4. A non-aqueous electrolyte secondary battery comprising an electrode body in which a positive electrode and a negative electrode are opposed to each other via a separator, a bottomed cylindrical outer container housing the electrode body, and a sealing body that closes the opening of the outer container, The positive electrode has a positive electrode composite layer containing a positive electrode active material, and the positive electrode active material contains a lithium metal composite oxide. When the electrode body is divided into two equal parts with respect to the insertion direction into the outer can, the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the bottom half of the outer can is higher than the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the sealing body side half. A non-aqueous electrolyte secondary battery, wherein the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the bottom half of the outer casing is 15 mL / 100 g or more and 23 mL / 100 g or less, and the amount of dibutyl phthalate absorbed by the lithium metal composite oxide contained in the positive electrode material layer located in the sealing half is 11 mL / 100 g or more and 19 mL / 100 g or less.

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