Non-aqueous electrolyte secondary battery

Abstract

The present invention provides a non-aqueous electrolyte secondary battery (10), characterized in that it comprises an electrode body (14) with a positive electrode (11) and a negative electrode (12) separated by a spacer (13) and a battery case (15) for housing the electrode body (14). The positive electrode (11) has a positive electrode compound layer containing a positive electrode active material. When the non-aqueous electrolyte secondary battery (10) is used in a fixed state and the electrode body (14) in the fixed state is divided into two equal parts in the vertical direction, the phthalic acid oil absorption of the positive electrode active material contained in the positive electrode compound layer disposed in the upper half region is higher than that of the positive electrode active material contained in the positive electrode compound layer disposed in the lower half region.

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 a positive electrode, a negative electrode, and a non-aqueous electrolyte, and which allow lithium ions to move between the positive and negative electrodes for charging and discharging, have been widely used as high-output power and high-energy-density secondary batteries.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery, characterized by having a wound electrode body including a positive electrode and a negative electrode and a non-aqueous electrolyte. The positive electrode has an elongated positive current collector and a positive electrode mixture layer containing at least a positive active material formed on the surface of the positive current collector. The two ends of the positive electrode mixture layer in the winding axis direction of the wound electrode body are mainly composed of a first positive active material, and the central portion of the positive electrode mixture layer in the winding axis direction, including at least the center, is mainly composed of a second positive active material. The DBP absorption amount [mL / 100g] of the first positive active material and the second positive active material is different from each other based on JIS K6217-4. The DBP absorption amount A [mL / 100g] of the first positive active material is less than the DBP absorption amount B [mL / 100g] of the second positive active material.

[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. 2013-131322

[0008] Patent Document 2: Japanese Patent Application Publication No. 2005-285606 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 improve charge-discharge cycle characteristics.

[0011] Methods for solving problems

[0012] A non-aqueous electrolyte secondary battery, as an embodiment of the present invention, is characterized by comprising an electrode body with a positive electrode and a negative electrode facing each other separated by a spacer, and a battery case for housing the electrode body. The positive electrode has a positive electrode compound layer containing a positive electrode active material. When the non-aqueous electrolyte secondary battery is used in a fixed state and the electrode body in the fixed state is divided into two equal parts in the vertical direction, the phthalic acid oil absorption of the positive electrode active material contained in the positive electrode compound layer disposed in the upper half of the region is higher than that of the positive electrode active material contained in the positive electrode compound layer disposed in the lower half of the region.

[0013] Furthermore, a non-aqueous electrolyte secondary battery, as an embodiment of the present invention, is characterized by comprising an electrode body with a positive electrode and a negative electrode facing each other separated by a spacer, a bottomed cylindrical outer packaging can containing the electrode body, and a sealing body that closes the opening of the outer packaging can. The positive electrode has a positive electrode mixture layer containing a positive electrode active material. When the electrode body is divided into two equal parts in the insertion direction toward the outer packaging can, the phthalate oil absorption of the positive electrode active material contained in the positive electrode mixture layer disposed in the side half of the sealing body is higher than the phthalate oil absorption of the positive electrode active material contained in the positive electrode mixture layer disposed in the bottom half of the outer packaging can.

[0014] Furthermore, a non-aqueous electrolyte secondary battery, as an embodiment of the present invention, is characterized by comprising an electrode body with a positive electrode and a negative electrode facing each other separated by a spacer, a bottomed cylindrical outer packaging can containing the electrode body, and a sealing body that closes the opening of the outer packaging can. The positive electrode has a positive electrode mixture layer containing a positive electrode active material. When the electrode body is divided into two equal parts in the insertion direction toward the outer packaging can, the phthalate oil absorption of the positive electrode active material contained in the positive electrode mixture layer disposed in the bottom half of the outer packaging can is higher than the phthalate oil absorption of the positive electrode active material contained in the positive electrode mixture layer disposed in the side half of the sealing body.

[0015] Invention Effects

[0016] According to one aspect of the present invention, it is possible to improve the charge-discharge cycle characteristics. Attached Figure Description

[0017] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method.

[0018] Figure 2 It means Figure 1 The side view shown is of a non-aqueous electrolyte secondary battery in a fixed state.

[0019] Figure 3 yes Figure 2 A three-dimensional view of the wound electrode body used in a non-aqueous electrolyte secondary battery.

[0020] Figure 4 It means Figure 1 A side view of another example of a non-aqueous electrolyte secondary battery in a fixed state.

[0021] Figure 5 yes Figure 4 A three-dimensional view of the wound electrode body used in a non-aqueous electrolyte secondary battery. Detailed Implementation

[0022] 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.

[0023] 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 case 15 that houses the above and below the components. The battery case 15 consists of an outer packaging can 16 and a sealing body 17 that closes the opening of the outer packaging can 16. It should be noted that other forms of electrode bodies, such as a stacked electrode body formed by alternating layers of positive and negative electrodes with spacers between them, can also be used instead of the wound electrode body 14. In addition, examples of battery cases 15 include cylindrical, square, coin-shaped, button-shaped, and other bottomed cylindrical outer packaging cans, as well as pouch-type outer packaging bodies formed by laminating resin sheets and metal sheets.

[0024] The outer packaging can 16 is, for example, a bottomed cylindrical metal box. A gasket 28 is provided between the outer packaging can 16 and the sealing body 17 to ensure the airtightness of the battery interior. The outer packaging can 16 has, for example, a protrusion 22 extending inward from a portion of its side surface to support the sealing body 17. The protrusion 22 is preferably formed in a ring shape along the circumference of the outer packaging can 16, with its upper surface supporting the sealing body 17.

[0025] 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.

[0026] Figure 1 In the non-aqueous electrolyte secondary battery 10 shown, the positive electrode lead 20, mounted on the positive electrode 11, extends through the through hole of the insulating plate 18 toward the sealing body 17, and the negative electrode lead 21, mounted on the negative electrode 12, extends through the outside of the insulating plate 19 toward the bottom of the outer packaging can 16. 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 packaging can 16 by welding or the like, and the outer packaging can 16 becomes the negative terminal.

[0027] In this embodiment, the sealing body 17 is positioned on the top of the battery box 15, the surface of the outer packaging can 16 facing the sealing body 17 is positioned on the bottom of the battery box 15, and the side connecting the top and bottom surfaces is positioned on the side of the battery box 15. Furthermore, the direction from the bottom surface of the battery box 15 upwards is defined as the height direction of the non-aqueous electrolyte secondary battery 10.

[0028] The following is a detailed description of each component of the non-aqueous electrolyte secondary battery 10.

[0029] [positive electrode]

[0030] The positive electrode 11 includes a positive current collector and a positive electrode flux layer disposed on the positive current collector. The positive current collector may be a foil of a metal such as aluminum that is stable within the potential range of the positive electrode 11, or a film of the metal disposed on its surface. The positive electrode flux layer contains a positive electrode active material, and preferably also contains a binder material, a conductive material, etc.

[0031] For example, a positive electrode slurry containing positive electrode active material, binder, and conductive material is coated onto the positive electrode current collector and dried to form a positive electrode slurry layer. This layer is then calendered using calendering rollers, thereby producing the positive electrode 11. It should be noted that details of the method for producing the positive electrode slurry layer will be described later.

[0032] In this embodiment, the positive electrode active material contained in the positive electrode mixture layer includes various positive electrode active materials with different oil absorption capacities of dibutyl phthalate. The following is a detailed description using the accompanying drawings.

[0033] Figure 2 It means Figure 1 The image shows a side view of the non-aqueous electrolyte secondary battery in a fixed position. The non-aqueous electrolyte secondary battery of this embodiment is preferably used as a fixed or stationary power source for indoor or outdoor installations, or as a power source for mobile devices such as electric vehicles. Figure 2 As shown, the non-aqueous electrolyte secondary battery 10 used as this type of power source is mounted on the fixing part 38 of the mounting platform, box, etc., and is used in a fixed state. "Used in a fixed state" means that after the non-aqueous electrolyte secondary battery 10 is mounted on the fixing part 38 and used, 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 during the use of the mobile phone, and therefore is not included in the case of being used in a fixed state.

[0034] Figure 2 In the diagram, arrow Z points in the vertical direction (the direction of gravity). That is, Figure 2 The non-aqueous electrolyte secondary battery 10 shown is erected vertically. Furthermore, Figure 2 The non-aqueous electrolyte secondary battery 10 shown is configured such that the bottom of the battery box 15 contacts the fixing part 38, and the height direction of the non-aqueous electrolyte secondary battery 10 is along the vertical direction.

[0035] Figure 3 yes Figure 2 A three-dimensional diagram of the wound electrode body used in a non-aqueous electrolyte secondary battery. However, Figure 3 In order to facilitate the explanation of the structure of the positive electrode 11, a portion (the winding end) of the positive electrode 11 that should be wound around the electrode body 14 is shown in its unwound state. Here, Figure 3 Region A of the electrode body 14 shown is equivalent to the area to which it is housed Figure 2 The region 10a of the upper half of the electrode body 14 in the non-aqueous electrolyte secondary battery 10 shown is divided into two equal parts in the vertical direction. Figure 3 Region B of the electrode body 14 shown is equivalent to the area to which it is housed Figure 2 The region 10b of the lower half of the electrode body 14 in the non-aqueous electrolyte secondary battery 10 shown is divided into two equal parts in the vertical direction.

[0036] Moreover, in this embodiment, it is configured in Figure 3 The area A shown is (i.e. Figure 2The upper region 10a) shown above contains a higher oil absorption rate of dibutyl phthalate (DBP) in the positive electrode mixture layer 11a than the material disposed in the upper region 10a). Figure 3 The area shown is B (i.e. Figure 2 The lower half of the region 10b) shows the oil absorption capacity of dibutyl phthalate, a positive electrode active material, contained in the positive electrode mixture layer 11b. It should be noted that, due to... Figure 2 The height direction of the non-aqueous electrolyte secondary battery 10 shown is along the vertical direction, so the vertical direction can also be referred to as the height direction of the non-aqueous electrolyte secondary battery 10. That is, when the electrode body 14 is divided into two equal parts along 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 mixture layer 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 mixture layer in the lower half region.

[0037] Figure 4 It means Figure 1 A side view of another example of a non-aqueous electrolyte secondary battery in a fixed state. Figure 4 In the diagram, arrow Z points in the vertical direction (the direction of gravity), and arrow Y points in the direction orthogonal to the vertical direction (the horizontal direction). Figure 4 The non-aqueous electrolyte secondary battery 10 shown is configured such that the side of the battery box 15 contacts the fixing part 38, and the height direction of the non-aqueous electrolyte secondary battery 10 is along a direction orthogonal to the vertical direction (horizontal direction).

[0038] Figure 5 yes Figure 4 A perspective view of a wound electrode body used in a non-aqueous electrolyte secondary battery. Here, Figure 5 Region A of the electrode body 14 shown is equivalent to the area to which it is housed Figure 4 The region 10a of the upper half of the electrode body 14 in the non-aqueous electrolyte secondary battery 10 shown is divided into two equal parts in the vertical direction. Figure 5 Region B of the electrode body 14 shown is equivalent to the area to which it is housed Figure 4 The region 10b of the lower half of the electrode body 14 in the non-aqueous electrolyte secondary battery 10 shown is divided into two equal parts in the vertical direction.

[0039] Moreover, in this embodiment, it is configured in Figure 5 The area A shown is (i.e. Figure 4 The upper region 10a) shown in the diagram contains a higher oil absorption rate of dibutyl phthalate, the positive active material, in the positive electrode mixture layer than the material prepared in the [other region]. Figure 5 The area shown is B (i.e. Figure 4The lower half of the region 10b) shows the amount of dibutyl phthalate oil absorbed by the positive electrode active material contained in the positive electrode mixture layer.

[0040] In the non-aqueous electrolyte secondary battery 10 used in a fixed state, the non-aqueous electrolyte in the battery case 15 tends to be biased downwards in the vertical direction due to gravity, and the non-aqueous electrolyte in the vertical direction is prone to depletion. If the non-aqueous electrolyte is biased in this way, it will lead to a decrease in charge-discharge cycle performance. However, by making the oil absorption capacity of dibutyl phthalate, the positive active material contained in the positive electrode mixture layer in the upper region 10a, as in the non-aqueous electrolyte secondary battery 10 of this embodiment, higher than that of dibutyl phthalate, the positive active material contained in the positive electrode mixture layer in the lower region 10b, the retention of the non-aqueous electrolyte in the vertical direction is improved. Therefore, since the situation of the non-aqueous electrolyte being biased downwards in the vertical direction is suppressed, the charge-discharge cycle performance can be improved. The above description uses a non-aqueous electrolyte secondary battery with a cylindrical bottomed battery box and a wound electrode as an example. However, the same effect can be obtained in the case of a non-aqueous electrolyte secondary battery with a square bottomed battery box and a stacked electrode.

[0041] In this embodiment, considering the improvement of charge-discharge cycle performance, the oil absorption capacity of dibutyl phthalate, the positive active material contained in the positive electrode mixture layer in the upper 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 even more preferably 17 mL / 100g or more and 21 mL / 100g or less. Furthermore, in this embodiment, considering the improvement of charge-discharge cycle performance, the oil absorption capacity of dibutyl phthalate, the positive active material contained in the positive electrode mixture layer in the lower 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 even more preferably 13 mL / 100g or more and 17 mL / 100g or less.

[0042] The value of the dibutyl phthalate oil absorption capacity of the positive electrode contained in the positive electrode mixture layer in the upper region 10a and the lower region 10b is an average value. That is, the positive electrode mixture layer in the upper region 10a and the positive electrode mixture layer in the lower region 10b can each contain multiple positive electrode active materials with different dibutyl phthalate oil absorption capacities. For example, if the positive electrode mixture layer in the upper region 10a contains three positive electrode active materials (P1, P2, P3) with different dibutyl phthalate oil absorption capacities, the dibutyl phthalate oil absorption capacity of the positive electrode active materials contained in this positive electrode mixture layer becomes the dibutyl phthalate oil absorption capacity of the mixture containing positive electrode active materials P1, P2, and P3. The same applies to the positive electrode mixture layer in the lower region 10b.

[0043] When the oil absorption capacity of the mixture of various positive electrode active materials contained in the positive electrode mixture layer in the upper region 10a is 15 mL / 100g or more and 23 mL / 100g or less, it is preferable that the oil absorption capacity 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 capacity of the mixture of various positive electrode active materials contained in the positive electrode mixture layer in the upper region 10a meets the requirement of 15 mL / 100g or more and 23 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 positive electrode mixture layer in the upper region 10a contains two positive electrode active materials (P1 and P2) with different dibutyl phthalate (DBP) oil absorption capacities, then 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, 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.

[0044] Similarly, for the positive electrode mixture layer disposed in the lower half of region 10b, when the oil absorption capacity of the mixture containing multiple positive electrode active materials 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 positive electrode mixture layer disposed in the lower half of region 10b satisfies 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 positive electrode mixture layer in the lower half of region 10b contains two positive electrode active materials (P1 and P2) with different dibutyl phthalate (DBP) oil absorption capacities, then as long as the DBP 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, the DBP oil absorption capacity of positive electrode active material P1 can, for example, be less than 11 mL / 100g, while the DBP 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 DBP 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.

[0045] Figure 2 The non-aqueous electrolyte secondary battery 10 shown is fixed by contacting the fixing part 38 at the bottom of the outer packaging can 16. In this case, when the electrode body 14 is divided into two equal parts in the insertion direction toward the outer packaging can 16, the oil absorption of dibutyl phthalate, the positive active material contained in the positive electrode mixture layer disposed in the side half of the sealing body 17, is higher than the oil absorption of dibutyl phthalate, the positive active material contained in the positive electrode mixture layer disposed in the bottom side half of the outer packaging can 16. When the battery box 15 is composed of a bottomed cylindrical outer packaging can 16 and a sealing body 17, the non-aqueous electrolyte secondary battery 10 can also be fixed by contacting the fixing part 38 with the sealing body 17 instead of the bottom of the outer packaging can 16. In this case, when the electrode body 14 is divided into two equal parts in the insertion direction toward the outer packaging can 16, the amount of dibutyl phthalate (DBP) in the positive electrode active material contained in the positive electrode mixture layer disposed in the bottom half of the outer packaging can 16 is higher than the amount of DBP in the positive electrode active material contained in the positive electrode mixture layer disposed in the side half of the sealing body 17. As a result, the charge-discharge cycle characteristics of the non-aqueous electrolyte secondary battery 10 are improved.

[0046] 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.

[0047] 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 1-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.

[0048] 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 resulting 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.

[0049] Conductive materials include, for example, carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), and carbon-based particles such as graphite. They can be used alone or in combination of two or more.

[0050] 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.

[0051] An example of a method for preparing the positive electrode mixture layer will be described. For example, a positive electrode active material having an oil absorption capacity of 11 mL / 100g or more and 19 mL / 100g or less of dibutyl phthalate, along with a binder material, a conductive material, etc., are mixed with a solvent to prepare a positive electrode mixture slurry B for the lower region 10b. In addition to this slurry, a positive electrode active material having an oil absorption capacity of 15 mL / 100g or more and 23 mL / 100g or less of dibutyl phthalate, along with a binder material, a conductive material, etc., are mixed with a solvent to prepare a positive electrode mixture slurry A for the upper region 10a. Furthermore, in addition to this slurry... Figure 2 In the case of a non-aqueous electrolyte secondary battery used in the state shown, positive electrode slurry A and B are coated adjacently along the length direction of the positive electrode current collector and in the width direction orthogonal to the length direction. Furthermore, in the case of a non-aqueous electrolyte secondary battery used in the state shown, positive electrode slurry A and B are coated adjacently along the length direction of the positive electrode current collector and in the width direction orthogonal to the length direction. Figure 4 In the case of a non-aqueous electrolyte secondary battery as shown, positive electrode slurry A and B are alternately coated with a given length along the length of the positive electrode current collector. The coated slurry is then dried and calendered to form a positive electrode slurry layer.

[0052] [negative electrode]

[0053] The negative electrode 12 has a negative electrode current collector and a negative electrode flux 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.

[0054] The negative electrode mixture layer contains a negative electrode active material, and preferably also contains a binder material, a conductive material, etc. For example, a negative electrode mixture slurry containing a negative electrode active material, a binder material, etc. is prepared, the negative electrode mixture slurry is coated on a negative electrode current collector and dried to form a negative electrode mixture layer, and the negative electrode mixture layer is calendered, thereby producing a negative electrode 12.

[0055] 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.

[0056] 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.

[0057] Conductive materials include, for example, carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), and carbon-based particles such as graphite. They can be used alone or in combination of two or more.

[0058] [Spacer]

[0059] 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.

[0060] [Non-aqueous electrolytes]

[0061] 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.

[0062] 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.

[0063] Examples of the aforementioned ethers include cyclic ethers such as 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, and crown ethers; as well as cyclic ethers such as 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.

[0064] 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.

[0065] 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 10LiCl, 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 Imine salts such as SO2 (where m is an integer greater than or equal to 1) can be used as lithium salts. A single one of these substances can be used, or a mixture of several can be used. Among them, LiPF6 is preferred from the viewpoints of ionic conductivity and electrochemical stability. The concentration of the lithium salt is preferably set at 0.8–1.8 mol per 1 L of solvent.

[0066] Example

[0067] The present invention will be further illustrated below with reference to embodiments; however, the present invention is not limited to these embodiments.

[0068] (Preparation of lithium metal composite oxide A)

[0069] 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.

[0070] (Preparation of lithium metal composite oxides B-D)

[0071] In lithium metal composite oxides B to D, except that the heating temperature and heating time of the above-mentioned nickel-cobalt-aluminum composite hydroxide are changed, they are prepared under the same conditions as lithium metal composite oxide A.

[0072] Table 1 summarizes the oil absorption of dibutyl phthalate for lithium metal composite oxides A through D. The method for determining the oil absorption of dibutyl phthalate is as described above.

[0073] [Table 1]

[0074]

[0075] <Example 1>

[0076] [The production of the positive electrode]

[0077] 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 at a mass ratio of 98:1:1. This slurry was designated as the positive electrode slurry for the lower half of the region.

[0078] In addition, a slurry with a solid content of 70% by mass was prepared by mixing 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 in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 98:1:1. This slurry was designated as the positive electrode slurry for the upper region.

[0079] The positive electrode slurry for the lower half and the positive electrode slurry for the upper half are applied in stripes along the length of the aluminum foil and in a width direction orthogonal to the length direction on both sides of a 15μm thick aluminum foil. After drying, the foil is calendered using calendering rolls to produce the positive electrode.

[0080] [Making the negative electrode]

[0081] 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 slurry. This negative electrode 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 slurry layers formed on both sides of the negative electrode current collector.

[0082] [Preparation of non-aqueous electrolytes]

[0083] Add 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = 1:3 by volume) to dissolve LiPF6 at a concentration of 1 mol / L. Set it as a non-aqueous electrolyte.

[0084] [Making a Secondary Battery]

[0085] (1) After installing leads on the positive and negative electrodes respectively, a polyethylene spacer with a thickness of 20μm is sandwiched between the positive and negative electrodes and wound to produce a wound electrode body.

[0086] (2) Insert the electrode body into the outer packaging can, solder the lead on the negative electrode side to the bottom of the outer packaging can, and solder the lead on the positive electrode side to the sealing body. Insert the electrode body into the outer packaging can as shown below, that is, when the non-aqueous electrolyte secondary battery is divided into two equal parts in the height direction, the positive electrode mixture layer disposed in the upper half region is derived from the positive electrode mixture slurry layer used in the upper half region, and the positive electrode mixture layer disposed in the lower half region is derived from the positive electrode mixture slurry layer used in the lower half region.

[0087] (3) After injecting the non-aqueous electrolyte into the outer packaging can, the open end of the outer packaging can is clamped and riveted to the sealing body through the gasket. It is set as a non-aqueous electrolyte secondary battery.

[0088] <Example 2>

[0089] Except for the use of lithium metal composite oxide C as the positive electrode active material in the positive electrode slurry for the lower half region, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0090] <Example 3>

[0091] Except for the use of lithium metal composite oxide B as the positive electrode active material in the positive electrode slurry for the upper part, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0092] <Comparative Example 1>

[0093] Except for the positive electrode active material used in the positive electrode slurry for the lower half region using lithium metal composite oxide D, and the positive electrode active material used in the positive electrode slurry for the upper half region using lithium metal composite oxide A, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0094] <Comparative Example 2>

[0095] Except for using lithium metal composite oxide A as the positive electrode active material in the positive electrode slurry used in the upper part of the region, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0096] <Comparative Example 3>

[0097] Except for the use of lithium metal composite oxide D as the positive electrode active material in the positive electrode slurry for the lower half region, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0098] [Evaluation of charge-discharge cycle characteristics]

[0099] The non-aqueous electrolyte secondary batteries of each embodiment and comparative example were placed on the mounting stage with their bottoms in contact with the stage and their height direction aligned vertically. Then, each non-aqueous electrolyte secondary battery was charged at a constant current of 0.7 It at 25°C until the voltage reached 4.2V, followed by constant voltage charging at 4.2V until the current reached 0.05 It. Then, it was discharged at a constant current of 0.7 It until the voltage reached 2.5V. This charge-discharge cycle was defined as one cycle, and 1000 cycles were performed. The capacity retention rate was calculated using the following formula.

[0100] Capacity retention (%) = (Discharge capacity in the 1000th cycle / Discharge capacity in the 1st cycle) × 100

[0101] Table 2 summarizes the results of charge-discharge cycle characteristics for each embodiment and comparative example.

[0102] [Table 2]

[0103]

[0104] Compared to Comparative Examples 1-3, Examples 1-3 all showed high capacity retention rates during charge-discharge cycles. Based on these results, as shown in Examples 1-3, when a non-aqueous electrolyte secondary battery is used in a fixed state, and the electrode body in this fixed state is divided into two equal parts in the vertical direction, the charge-discharge cycle characteristics can be improved by making the oil absorption capacity of dibutyl phthalate of the positive active material contained in the positive electrode mixture layer disposed in the upper half region higher than that of dibutyl phthalate of the positive active material contained in the same positive electrode mixture layer disposed in the lower half region.

[0105] Explanation of reference numerals in the attached figures

[0106] 10 Non-aqueous electrolyte secondary battery, 10a Upper half region, 10b Lower half region, 11 Positive electrode, 11a, 11b Positive electrode compound layer, 12 Negative electrode, 13 Spacer, 14 Electrode body, 15 Battery box, 16 Outer packaging can, 17 Sealing body, 18, 19 Insulating plates, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protrusion, 23 Filter, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cap, 28 Gasket, 38 Fixing part.

Claims

1. A non-aqueous electrolyte secondary battery, It has electrodes with positive and negative electrodes facing each other separated by a spacer and a battery case that houses the electrodes. The positive electrode has a positive electrode mixture layer containing positive electrode active material. When the non-aqueous electrolyte secondary battery is used in a fixed state, and the electrode body in the fixed state is divided into two equal parts in the vertical direction, the dibutyl phthalate oil absorption capacity of the positive electrode active material contained in the positive electrode mixture layer disposed in the upper half region is higher than that of the dibutyl phthalate oil absorption capacity of the positive electrode active material contained in the positive electrode mixture layer disposed in the lower half region. The vertical direction is the direction of gravity.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The dibutyl phthalate of the positive electrode active material contained in the positive electrode mixture layer disposed in the upper half region has an oil absorption capacity of more than 15 mL / 100g and less than 23 mL / 100g, and the dibutyl phthalate of the positive electrode active material contained in the positive electrode mixture layer disposed in the lower half region has an oil absorption capacity of more than 11 mL / 100g and less than 19 mL / 100g.

3. A non-aqueous electrolyte secondary battery, It comprises electrode bodies with positive and negative electrodes facing each other separated by a spacer, a bottomed cylindrical outer packaging can containing the electrode bodies, and a sealing body that closes the opening of the outer packaging can. The positive electrode has a positive electrode mixture layer containing positive electrode active material. The non-aqueous electrolyte secondary battery is fixed to the bottom of the outer packaging can by contact with the fixing part. In this fixed state, when the electrode body is divided into two equal parts in the insertion direction into the outer packaging can, the phthalic acid (DAB) oil absorption of the positive electrode active material contained in the positive electrode mixture layer disposed in the region of the sealing body side half is higher than the DAB oil absorption of the positive electrode active material contained in the positive electrode mixture layer disposed in the region of the bottom side half of the outer packaging can. The sealing body is located above the direction of gravity, and the bottom of the outer packaging can is located below the direction of gravity.

4. The non-aqueous electrolyte secondary battery according to claim 3, wherein, The positive electrode active material contained in the positive electrode mixture layer in the region of the side half of the sealing body has an oil absorption capacity of more than 15 mL / 100g and less than 23 mL / 100g of dibutyl phthalate. The positive electrode active material contained in the positive electrode mixture layer in the region of the bottom half of the outer packaging can has an oil absorption capacity of more than 11 mL / 100g and less than 19 mL / 100g of dibutyl phthalate.

5. A non-aqueous electrolyte secondary battery, It comprises electrode bodies with positive and negative electrodes facing each other separated by a spacer, a bottomed cylindrical outer packaging can containing the electrode bodies, and a sealing body that closes the opening of the outer packaging can. The positive electrode has a positive electrode mixture layer containing positive electrode active material. When the non-aqueous electrolyte secondary battery is fixed by contacting the sealing body with the fixing part, and in the fixed state, when the electrode body is divided into two equal parts in the insertion direction into the outer packaging can, the oil absorption capacity of the dibutyl phthalate of the positive electrode active material contained in the positive electrode mixture layer disposed in the bottom half of the outer packaging can is higher than the oil absorption capacity of the dibutyl phthalate of the positive electrode active material contained in the positive electrode mixture layer disposed in the side half of the sealing body. The bottom of the outer packaging can is located above the direction of gravity, and the sealing body is located below the direction of gravity.

6. The non-aqueous electrolyte secondary battery according to claim 5, wherein, The dibutyl phthalate of the positive electrode active material contained in the positive electrode mixture layer disposed in the bottom half of the outer packaging can has an oil absorption capacity of more than 15 mL / 100g and less than 23 mL / 100g, and the dibutyl phthalate of the positive electrode active material contained in the positive electrode mixture layer disposed in the side half of the sealing body has an oil absorption capacity of more than 11 mL / 100g and less than 19 mL / 100g.

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