Non-aqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery (10) is characterized by including an electrode body (14) in which a positive electrode (11) and a negative electrode (12) face each other with a separator (13) interposed therebetween, and a battery case (15) that houses the electrode body (14), the negative electrode (12) having a negative electrode mixture layer containing first carbon particles and second carbon particles having a smaller internal porosity than the first carbon particles, and in a case where the electrode body (14) in a fixed state of the nonaqueous electrolyte secondary battery (10) is divided into an upper half region and a lower half region in a vertical direction, the second carbon particles are more contained in the upper half region than 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 are high-output, high-energy-density rechargeable batteries, have been widely used. They have a positive electrode, a negative electrode, and a non-aqueous electrolyte, and charge and discharge by moving lithium ions between the positive and negative electrodes.

[0003] For example, Patent Document 1 discloses a cylindrical battery with high interparticle porosity in the compound layer on the positive electrode lead side (sealing body side), Patent Document 2 discloses a cylindrical battery with high interparticle porosity in the compound layer on the negative electrode lead side (bottom side), Patent Document 3 discloses a secondary battery in which the electrode density in the two end regions of the negative electrode in the width direction is higher than the electrode density in the central region of the negative electrode in the width direction, and Patent Document 4 discloses a secondary battery in which the porosity per unit area of ​​the positive electrode in the positive electrode compound layer existing between adjacent positive electrode current collectors and negative electrode current collectors is greater in the central region than in the end regions of the positive electrode in the width direction.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-172881

[0007] Patent Document 2: Japanese Patent Application Publication No. 2007-172878

[0008] Patent Document 3: Japanese Patent Application Publication No. 2005-209411

[0009] Patent Document 4: Japanese Patent Application Publication No. 2007-329077 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] The purpose of this invention is to provide a non-aqueous electrolyte secondary battery that can improve charge-discharge cycle characteristics.

[0012] Methods for solving problems

[0013] 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 negative electrode has a negative electrode compound layer containing a first carbon particle and a second carbon particle with an internal porosity less than the first carbon particle. When the non-aqueous electrolyte secondary battery is used in a fixed state, and the electrode body in the fixed state is divided into an upper half region and a lower half region in the vertical direction, the second carbon particle is more abundant in the upper half region than in the lower half region.

[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 sealing the opening of the outer packaging can. The negative electrode has a negative electrode mixture layer containing a first carbon particle and a second carbon particle with an internal porosity less than the first carbon particle. When the electrode body is divided into a region on the side half of the sealing body and a region on the bottom half of the outer packaging can in the insertion direction toward the outer packaging can, the second carbon particle is more abundant in the region on the side half of the sealing body compared to the region on the bottom half of the outer packaging can.

[0015] 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 sealing the opening of the outer packaging can. The negative electrode has a negative electrode mixture layer containing a first carbon particle and a second carbon particle with an internal porosity less than the first carbon particle. When the electrode body is divided into a region on the side half of the sealing body and a region on the bottom half of the outer packaging can in the insertion direction toward the outer packaging can, the second carbon particle is more abundant in the region on the bottom half of the outer packaging can compared to the region on the side half of the sealing body.

[0016] Invention Effects

[0017] According to one aspect of the present invention, it is possible to improve charge-discharge cycle characteristics. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method.

[0019] Figure 2 This is a cross-sectional view showing an example of carbon particles used as a negative electrode active material.

[0020] Figure 3 It means Figure 1The side view shown is of a non-aqueous electrolyte secondary battery in a fixed state.

[0021] Figure 4 yes Figure 3 A three-dimensional view of the wound electrode body used in a non-aqueous electrolyte secondary battery.

[0022] Figure 5 It means Figure 1 A side view of another example of a non-aqueous electrolyte secondary battery in a fixed state.

[0023] Figure 6 yes Figure 5 A three-dimensional view of the wound electrode body used in a non-aqueous electrolyte secondary battery. Detailed Implementation

[0024] 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.

[0025] 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 includes an outer packaging can 16 and a sealing body 17 that seals the opening of the outer packaging can 16. It should be noted that, instead of the wound electrode body 14, other forms of electrode bodies, such as a stacked electrode body in which the positive and negative electrodes are alternately stacked with a spacer between them, can also be used. In addition, examples of battery case 15 include cylindrical, square, coin-shaped, button-shaped, and other bottomed cylindrical outer packaging cans, and soft outer packaging bodies formed by laminating resin sheets and metal sheets.

[0026] 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 bulge 22 on a portion of its side that bulges inward and supports the sealing body 17. The bulge 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.

[0027] 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 has, for example, a circular or ring shape, 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 generated 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, 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, allowing gas to escape from the opening of the cap 27.

[0028] 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 to the sealing body 17 side, and the negative electrode lead 21, mounted on the negative electrode 12, extends through the outside of the insulating plate 19 to the bottom side 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.

[0029] In this embodiment, the sealing body 17 is used as the upper surface of the battery box 15, the surface of the outer packaging can 16 opposite to the sealing body 17 is used as the bottom surface of the battery box 15, and the side connecting the upper surface and the bottom surface is used as the side surface of the battery box 15. Furthermore, the direction from the bottom surface of the battery box 15 towards the upper surface is used as the height direction of the non-aqueous electrolyte secondary battery 10.

[0030] The following is a detailed description of each component of the non-aqueous electrolyte secondary battery 10.

[0031] [positive electrode]

[0032] 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 can be a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, or a film on which such metal is disposed on the surface. The positive electrode flux layer contains a positive electrode active material and, if necessary, includes additives such as binder materials and conductive materials.

[0033] For example, after coating a positive electrode mixture slurry containing positive electrode active material, binder material, conductive material, etc. onto a positive electrode current collector and drying it to form a positive electrode mixture layer, the positive electrode mixture layer is calendered using a calendering roller or the like to produce a positive electrode 11.

[0034] 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, and Li2MPO4F (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and 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.

[0035] The binder materials may include, for example, fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. These can be used alone or in combination of two or more. The content of the binder material in the positive electrode binder layer is preferably, for example, 0.5% to 10% by mass, more preferably 1% to 5% by mass.

[0036] 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.

[0037] [negative electrode]

[0038] 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. The negative electrode flux layer contains a negative electrode active material and, if necessary, includes additives such as binder materials and conductive materials.

[0039] Examples of binder materials include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). These can be used alone or in combination of two or more. The content of the binder material in the negative electrode binder layer is preferably, for example, 0.5% to 10% by mass, more preferably 1% to 5% by mass.

[0040] Conductive materials include, for example, carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNTs), and carbon-based particles such as graphite. They can be used alone or in combination of two or more.

[0041] In this embodiment, the negative electrode active material contained in the negative electrode mixture layer includes various carbon particles with different internal porosities. The following is a detailed description using the accompanying drawings.

[0042] Figure 2 This is a cross-sectional view showing an example of carbon particles used as a negative electrode active material. For example... Figure 2 As shown, carbon particle 30 has, in cross-section, a closed void 34 (hereinafter referred to as internal void 34) that does not connect from the inside of the particle to the surface of the particle, and a void 36 (hereinafter referred to as external void 36) that connects from the inside of the particle to the surface of the particle.

[0043] The carbon particles 30 used as the negative electrode active material in this embodiment include a first carbon particle and a second carbon particle with an internal porosity lower than that of the first carbon particle. Here, the internal porosity of the carbon particle is a two-dimensional value calculated based on the ratio of the area of ​​the internal voids 34 of the carbon particle to the cross-sectional area of ​​the carbon particle. Moreover, the internal porosity of the carbon particle can be calculated using the following steps.

[0044] <Methods for determining internal porosity>

[0045] (1) Exposing the cross-section of the carbon particles. One method for exposing the cross-section is to cut a portion of the negative electrode and expose the cross-section of the negative electrode binder layer using a particle milling device (e.g., Hitachi High-Tech IM4000PLUS). This cross-section is perpendicular to the thickness direction of the negative electrode active material layer. Alternatively, carbon particles can be embedded in resin, and the cross-section of the resin block containing the embedded carbon particles can be exposed using a particle milling device (e.g., Hitachi High-Tech IM4000PLUS).

[0046] (2) Using a scanning electron microscope, take a cross-sectional image of the exposed negative electrode active material layer. The magnification of the reflected electron image is 3,000 to 5,000 times.

[0047] (3) Import the cross-sectional image obtained through the above operation into the computer and perform binarization processing using image analysis software (such as ImageJ, manufactured by the National Institutes of Health, USA) to obtain a binarized image in which the particle cross-sections in the cross-sectional image are transformed into black and the gaps existing in the particle cross-sections are transformed into white.

[0048] (4) Select carbon particles with a diameter of 5μm to 50μm from the binarized image and calculate the area of ​​the cross-section of the carbon particle and the area of ​​the internal voids within the cross-section. Here, the area of ​​the carbon particle cross-section refers to the area of ​​the region surrounded by the outer periphery of the carbon particle, that is, the area of ​​the entire cross-section of the carbon particle. In addition, for voids with a width of less than 3μm within the cross-section of the carbon particle, it is sometimes difficult to distinguish whether they are internal or external voids in image analysis. Therefore, voids with a width of less than 3μm can be defined as internal voids. Subsequently, based on the calculated area of ​​the carbon particle cross-section and the area of ​​the internal voids within the carbon particle cross-section, calculate the internal porosity of the carbon particle (area of ​​internal voids in the carbon particle cross-section × 100 / area of ​​the carbon particle cross-section). The internal porosity of the carbon particle is the average value of 10 carbon particles.

[0049] Regarding the internal porosity of the first carbon particle, from the perspective of improving charge-discharge cycle characteristics, it is preferably 8% or more and 20% or less, more preferably 10% or more and 18% or less, and even more preferably 12% or more and 16% or less. Regarding the internal porosity of the second carbon particle, from the perspective of improving charge-discharge cycle characteristics, it is acceptable as long as it is less than the internal porosity of the first carbon particle; however, it is preferably 5% or less, more preferably 1% or more and 5% or less, and even more preferably 3% or more and 5% or less.

[0050] The first carbon particle and the second carbon particle are manufactured, for example, as shown below.

[0051] <The first carbon particle with an internal porosity of 8%–20%>

[0052] For example, coke (precursor), which will become the main raw material, is pulverized to a given size, agglomerated with a binder material, and then further pressed into a block shape. This block is then fired at a temperature above 2600°C to graphitize it. The graphitized block is then pulverized and sieved to obtain carbon particles of the desired size. Here, the internal porosity can be adjusted to 8%–20% by adjusting the amount of volatile components added to the block. If a portion of the binder material added to the coke (precursor) volatilizes during firing, the binder material can be used as the volatile component. Pitch pitch can be cited as an example of such a binder material.

[0053] <Second carbon particle with an internal porosity of less than 5%>

[0054] For example, coke (precursor), which will become the main raw material, is pulverized to a given size, and while it is agglomerated with a binder, it is calcined at a temperature of 2600°C or higher to graphitize it. After sieving, carbon particles of the desired size are obtained. Here, the internal porosity can be adjusted to 5% or less by utilizing the particle size of the pulverized precursor and the particle size of the agglomerated precursor. For example, the average particle size (median particle size D50) of the pulverized precursor is preferably in the range of 12 μm to 20 μm. Furthermore, when reducing the internal porosity within the range of 5% or less, it is preferable to increase the particle size of the pulverized precursor.

[0055] In this embodiment, the first and second carbon particles are preferably graphite, such as natural graphite or artificial graphite; however, they can also be carbon materials other than graphite. If graphite is used, artificial graphite is preferred considering the ease of adjusting the internal porosity. The interplanar spacing (d) of the (002) plane of the first and second carbon particles used in this embodiment, based on X-ray large-angle diffraction, is... 002 For example, the preferred size is 0.3354 nm or more, more preferably 0.3357 nm or more, and preferably less than 0.340 nm, more preferably 0.338 nm or less. Furthermore, the crystallite size (Lc(002)) of the first and second carbon particles used in this embodiment, determined by X-ray diffraction, is preferably 5 nm or more, more preferably 10 nm or more, and preferably 300 nm or less, more preferably 200 nm or less. In the interplanar spacing (d... 002 When the crystallite size (Lc(002)) meets the above range, there is a trend for the capacity of non-aqueous electrolyte secondary batteries to increase compared with the case where the above range is not met.

[0056] In addition to carbon particles, negative electrode active materials may also include metals that are alloyed with lithium, such as silicon (Si) and tin (Sn), or alloys or composite oxides containing metal elements such as Si and Sn, which can reversibly absorb and release lithium ions.

[0057] Figure 3 It means Figure 1 The side view shown illustrates a non-aqueous electrolyte secondary battery in a fixed state. The non-aqueous electrolyte secondary battery of this embodiment is preferably used as a power source for indoor or outdoor placement or stationary applications, or as a power source for mobile devices such as electric vehicles. The non-aqueous electrolyte secondary battery 10 used as such a power source is as follows: Figure 3 As shown, the non-aqueous electrolyte secondary battery 10 is mounted on the fixing part 38 of a platform, box, etc., and used in a fixed state. "Used in a fixed state" means that when the non-aqueous electrolyte secondary battery 10 is mounted on the fixing part 38, its orientation will not change drastically after use. For example, a non-aqueous electrolyte secondary battery used as a power source for a mobile phone is placed in any orientation during mobile phone use and is therefore not included in the case of being used in a fixed state.

[0058] Figure 3 In the diagram, arrow Z points in the vertical direction (the direction of gravity). That is, Figure 3 The non-aqueous electrolyte secondary battery 10 shown is erected vertically. Furthermore, Figure 3 The non-aqueous electrolyte secondary battery 10 shown is configured such that the bottom of the battery case 15 contacts the fixing part 38 and the height direction of the non-aqueous electrolyte secondary battery 10 is along the vertical direction.

[0059] Figure 4 yes Figure 3 A perspective view of a wound electrode body used in a non-aqueous electrolyte secondary battery. Here, Figure 4 Region A of the electrode body 14 shown is equivalent to the area to which it is housed Figure 3 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 4 Region B of the electrode body 14 shown is equivalent to the area to which it is housed Figure 3 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.

[0060] Moreover, in this embodiment, with Figure 4 The area shown is B (i.e. Figure 3 Compared to the lower half of region 10b shown, the negative electrode mixture layer contains more second carbon particles. Figure 4 The area A shown is (i.e. Figure 3In the upper half of region 10a) shown. It should be noted that, due to Figure 3 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 an upper half and a lower half in the height direction of the non-aqueous electrolyte secondary battery 10, the second carbon particles contained in the negative electrode mixture layer are more concentrated in the upper half than in the lower half.

[0061] Figure 5 It means Figure 1 A side view of another example of a non-aqueous electrolyte secondary battery in a fixed state. Figure 5 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 5 The non-aqueous electrolyte secondary battery 10 shown is configured such that the side of the battery case 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).

[0062] Figure 6 yes Figure 5 A perspective view of a wound electrode body used in a non-aqueous electrolyte secondary battery. Here, Figure 6 Region A of the electrode body 14 shown is equivalent to the area to which it is housed Figure 5 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 6 Region B of the electrode body 14 shown is equivalent to the area to which it is housed Figure 5 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.

[0063] Moreover, in this embodiment, with Figure 6 The area shown is B (i.e. Figure 5 Compared to the lower half of region 10b shown, the negative electrode mixture layer contains more second carbon particles. Figure 6 The area A shown is (i.e. Figure 5 In the upper half of region 10a) shown.

[0064] 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 characteristics. However, since the carbon particles with small internal porosity are hard and not easily crushed, a large number of large voids are easily formed between the carbon particles in the negative electrode compound layer during the manufacture of the negative electrode 12. Therefore, by distributing more second carbon particles with a smaller internal porosity than the first carbon particles in the upper half of the region 10a compared to the lower half of the region 10b, as in the non-aqueous electrolyte secondary battery 10 of this embodiment, the non-aqueous electrolyte can be retained in the large interparticle voids formed in the negative electrode compound layer in the upper half of the region 10a, thus improving the retention of the non-aqueous electrolyte in the vertical direction. As a result, the bias of the non-aqueous electrolyte downwards in the vertical direction is suppressed, and thus the charge-discharge cycle characteristics 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.

[0065] Furthermore, in this embodiment, it is preferable that, compared to the upper region 10a, more first carbon particles with a higher internal porosity than the second carbon particles are disposed in the lower region 10b. Since carbon particles with a high internal porosity are soft and easily crushed, the gaps between carbon particles within the negative electrode mixture layer are reduced during the fabrication of the negative electrode 12, thus decreasing the number of larger gaps. Therefore, by distributing more first carbon particles with a higher internal porosity than the second carbon particles in the lower region 10b compared to the upper region 10a, excessive retention of non-aqueous electrolyte in the negative electrode mixture layer of the lower region 10b is less likely. As a result, the tendency of non-aqueous electrolyte to be biased downwards in the vertical direction is further suppressed, thereby further improving charge-discharge cycle characteristics.

[0066] In this embodiment, it is sufficient that the second carbon particles are contained in the upper region 10a in greater quantities than in the lower region 10b. However, for example, from the perspective of further improving charge-discharge cycle characteristics, the ratio of the second carbon particles contained in the upper region 10a to the second carbon particles contained in the lower region 10b is preferably 60:40 to 100:0 by mass. Furthermore, from the perspective of further improving charge-discharge cycle characteristics, the ratio of the first carbon particles to the second carbon particles in the upper region 10a is preferably 70:30 to 0:100 by mass. Furthermore, from the perspective of further improving charge-discharge cycle characteristics, the ratio of the first carbon particles to the second carbon particles in the lower region 10b is further preferably 80:20 to 100:0 by mass.

[0067] Figure 3 The non-aqueous electrolyte secondary battery 10 shown is fixed to the bottom of the outer packaging can 16 by contacting the fixing part 38. In this case, when the electrode body 14 is divided into a region of the sealing body 17 side half and a region of the bottom side half of the outer packaging can 16 in the insertion direction toward the outer packaging can 16, the region of the sealing body 17 side half contains more second carbon particles with a lower internal porosity than the region of the bottom side half of the outer packaging can 16 compared to the region of the bottom side half of the outer packaging can 16. In addition, in this case, it is preferable that the region of the bottom side half of the outer packaging can 16 contains more first carbon particles with a higher internal porosity than the region of the sealing body 17 compared to the region of the side half of the sealing body 17. In addition, when the battery box 15 includes a bottom 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 of 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 a region on the side half of the sealing body 17 and a region on the bottom half of the outer packaging can 16 in the insertion direction toward the outer packaging can 16, compared to the region on the side half of the sealing body 17, the region on the bottom half of the outer packaging can 16 contains more second carbon particles with an internal porosity lower than that of the first carbon particles. Furthermore, in this case, it is preferable that the region on the side half of the sealing body 17 contains more first carbon particles with an internal porosity greater than that of the second carbon particles compared to the region on the bottom half of the outer packaging can 16. This improves the charge-discharge cycle characteristics of the non-aqueous electrolyte secondary battery 10. It should be noted that the internal porosity and content ratio of each carbon particle are also the same as described above.

[0068] An example of the method for manufacturing the negative electrode 12 will be described. For example, firstly, a negative electrode active material containing a first carbon particle (and a second carbon particle if necessary), a binder material, and a solvent are mixed together to prepare slurry B for the lower region 10b. Then, a negative electrode active material containing a second carbon particle (and a first carbon particle if necessary), a binder material, and a solvent are mixed together to prepare slurry A for the upper region 10a. For example, in… Figure 3 In the case of a non-aqueous electrolyte secondary battery used in the state shown, slurries A and B are applied adjacently along the length direction of the negative 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, slurries A and B are applied adjacently along the length direction of the negative electrode current collector and in the width direction orthogonal to the length direction. Figure 5 In the case of a non-aqueous electrolyte secondary battery used in the state shown, slurry A and B are alternately coated along the length of the negative electrode current collector at a given length. The coated slurry is then dried and calendered to form a coating (negative electrode mixture layer), thereby forming the negative electrode of this embodiment. By using the electrode formed as described, when the non-aqueous electrolyte secondary battery is fixed, and the electrode body is divided into two equal parts in the vertical direction, the second carbon particles can be disposed in more of the upper half of the electrode body compared to the lower half. Alternatively, when the electrode body is divided into two equal parts in the insertion direction toward the outer packaging can, the second carbon particles can be disposed in more of the sealing body side half of the outer packaging can compared to the bottom side half, or more of the bottom side half of the outer packaging can compared to the sealing body side half.

[0069] [Spacer]

[0070] Spacer 13 may be made of porous sheets, for example, that have ion permeability and insulation properties. 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.

[0071] [Non-aqueous electrolyte]

[0072] 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 solvents. The non-aqueous solvent 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.

[0073] 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.

[0074] Examples of the aforementioned ethers include 1,3-dioxane, 4-methyl-1,3-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, crown ethers and other cyclic ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and dihexyl ether. Ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and other chain ethers.

[0075] 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.

[0076] The preferred electrolyte salt is a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), and LiPF6. 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 LiCl, LiBr, LiI, lithium chloroborane, lower aliphatic carboxylic acids, Li₂B₄O₇, Li(B(C₂O₄)F₂) and other borates, LiN(SO₂CF₃)₂, LiN(C₁F₂) 21+1 SO2)(C m F 2m+1Imidamine salts such as SO2 (where l and m are integers greater than or equal to 1) are used. Lithium salts can be used alone or in combination. Among these, LiPF6 is preferred from the viewpoint of ionic conductivity and electrochemical stability. The preferred concentration of the lithium salt is 0.8–1.8 mol per 1 L of solvent.

[0077] Example

[0078] The present invention will be further illustrated below with reference to embodiments; however, the present invention is not limited to these embodiments.

[0079] <Example 1>

[0080] [The production of the positive electrode]

[0081] 95 parts by weight of LiNi 0.8 Co 0.15 Al 0.05 O2, 2.5 parts by mass of acetylene black (AB), and 2.5 parts by mass of polyvinylidene fluoride (PVDF) with an average molecular weight of 1.1 million were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry with a solid content of 70% by mass. This positive electrode slurry was then coated onto both sides of a strip-shaped positive electrode current collector made of 15 μm thick aluminum foil, and the coating was dried at 100°C–150°C. After compressing the dried coating using rollers, it was cut to a given electrode size to create a positive electrode with a positive electrode slurry layer formed on both sides of the positive electrode current collector. Approximately at the center of the positive electrode's length, a positive electrode exposure portion was formed, where no positive electrode slurry layer was present on the surface of the positive electrode current collector, and an aluminum positive electrode lead was soldered to the positive electrode exposure portion.

[0082] [The Production of Carbon Particle A]

[0083] The coke was pulverized until the average particle size (median particle size D50) was 15 μm. Pitch was added to the pulverized coke as a binder, causing the coke to agglomerate until the average particle size (median particle size D50) was 17 μm. This agglomerate was then graphitized by firing at 2800 °C and sieved using a 250-mesh sieve to obtain carbon particles A with an average particle size (median particle size D50) of 23 μm and an internal porosity of 1%.

[0084] [The Production of Carbon Particle B]

[0085] Coke was pulverized until the average particle size (median particle size D50) was 15 μm. Pitch, used as a binder, was added to the pulverized coke to cause it to coagulate. Then, isotropic pressure was applied to produce a product with a particle size of 1.6 g / cm³. 3 ~1.9g / cm 3A block-shaped molded body with a certain density was formed. The block-shaped molded body was graphitized by firing at a temperature of 2800°C. Then, the graphitized block-shaped molded body was crushed and sieved using a 250-mesh sieve to obtain carbon particles B with an average particle size (median particle size D50) of 23 μm and an internal porosity of 8%.

[0086] [Making the negative electrode]

[0087] A first negative electrode slurry was prepared by mixing 100 parts by weight of carbon particles A, 1 part by weight of carboxymethyl cellulose (CMC), 1 part by weight of styrene-butadiene rubber (SBR), and an appropriate amount of water. A second negative electrode slurry was prepared by mixing 100 parts by weight of carbon particles B, 1 part by weight of carboxymethyl cellulose (CMC), 1 part by weight of styrene-butadiene rubber (SBR), and an appropriate amount of water.

[0088] On both sides of a strip-shaped negative electrode current collector made of copper foil, a first negative electrode slurry and a second negative electrode slurry are applied in a strip pattern, adjacent to each other along the length of the copper foil and in a width direction orthogonal to the length direction. The coating is then dried, compressed using rollers, and cut to a given electrode size to create a negative electrode with negative electrode slurry layers formed on both sides of the negative electrode current collector. A negative electrode exposure portion, where no negative electrode slurry layer is present and the surface of the negative electrode current collector is exposed, is provided at the beginning end. A nickel / copper negative electrode lead is soldered to the negative electrode exposure portion.

[0089] [Preparation of non-aqueous electrolytes]

[0090] A non-aqueous electrolyte was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0091] [Construction of a non-aqueous electrolyte secondary battery]

[0092] (1) A wound electrode body is made by winding a polyethylene spacer with a thickness of 20μm between the positive and negative electrodes.

[0093] (2) Insert the electrode body into the outer packaging can, solder the negative electrode lead to the bottom of the outer packaging can, and solder the positive electrode lead to the sealing body. For the electrode body, insert it into the outer packaging can such that, when the electrode body is divided into two equal parts in the height direction of the non-aqueous electrolyte secondary battery, the negative electrode mixture layer in the upper half is a layer from the first negative electrode mixture slurry mentioned above, and the negative electrode mixture layer in the lower half is a layer from the second negative electrode mixture slurry mentioned above.

[0094] (3) After injecting 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 used as a non-aqueous electrolyte secondary battery.

[0095] <Example 2>

[0096] [The Production of Carbon Particles (C)]

[0097] Except for increasing the amount of asphalt added and setting the internal porosity to 5%, carbon particles C are obtained by operating in the same manner as carbon particles A.

[0098] Except that carbon material C was used as the carbon material in the first negative electrode slurry, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

[0099] <Example 3>

[0100] [The Making of Carbon Particle D]

[0101] Except for increasing the amount of asphalt added and setting the internal porosity to 15%, carbon particles D are obtained by operating in the same manner as carbon particles B.

[0102] Except for using carbon material C as the carbon material used in the first negative electrode slurry and carbon material D as the carbon material used in the second negative electrode slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0103] <Example 4>

[0104] [The Production of Carbon Particle E]

[0105] Except for increasing the amount of asphalt added and setting the internal porosity to 20%, carbon particles E are obtained by operating in the same manner as carbon particles B.

[0106] Except for using carbon material C as the carbon material used in the first negative electrode slurry and carbon material E as the carbon material used in the second negative electrode slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0107] <Comparative Example 1>

[0108] Except for using carbon material B as the carbon material used in the first negative electrode slurry and carbon material A as the carbon material used in the second negative electrode slurry, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0109] <Comparative Example 2>

[0110] Except for forming the negative electrode layer using only the first negative electrode slurry of Example 2, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0111] <Comparative Example 3>

[0112] Except for forming the negative electrode layer using only the second negative electrode slurry of Example 1, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1.

[0113] <Comparative Example 4>

[0114] Except that a mixture of carbon material B and carbon material C (mass ratio 1:1) was used instead of carbon material C, a non-aqueous electrolyte secondary battery was fabricated in the same manner as in Comparative Example 2.

[0115] [Evaluation of charge-discharge cycle characteristics]

[0116] The non-aqueous electrolyte secondary batteries of Examples 1-4 and Comparative Examples 1-4 were placed on the mounting stage with their bottoms in contact with the stage and their height direction aligned vertically. Each non-aqueous electrolyte secondary battery was then 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. Subsequently, they were 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.

[0117] Capacity retention (%) = (Discharge capacity in the 1000th cycle / Discharge capacity in the 1st cycle) × 100

[0118] Table 1 summarizes the results of charge-discharge cycle characteristics of Examples 1-4 and Comparative Examples 1-4.

[0119] [Table 1]

[0120]

[0121] Compared to Comparative Examples 1-4, Examples 1-4 all showed higher capacity retention rates during charge-discharge cycles. Therefore, by using the non-aqueous electrolyte secondary battery in a fixed state, as shown in Examples 1-4, and dividing the electrode body in this fixed state into an upper and lower half in the vertical direction, the charge-discharge cycle characteristics can be improved by distributing more carbon particles with lower internal porosity in the upper half compared to the lower half.

[0122] Explanation of reference numerals in the attached figures

[0123] 10 Non-aqueous electrolyte secondary battery, 10a Upper half region, 10b Lower half region, 11 Positive electrode, 12 Negative electrode, 13 Spacer, 14 Electrode body, 15 Battery box, 16 Outer packaging can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Bulging part, 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, comprising electrode bodies with a positive electrode and a negative electrode separated by a spacer, and a battery case for housing the electrode bodies. The negative electrode has a negative electrode mixture layer comprising a first carbon particle and a second carbon particle with an internal porosity smaller than that of the first carbon particle. When the non-aqueous electrolyte secondary battery is used in a fixed state, and the electrode body in this fixed state is divided into an upper half and a lower half in the vertical direction, the second carbon particles are more concentrated in the upper half than in the lower half. The vertical direction refers to the direction of gravity.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, Compared to the upper region, the first carbon particle is more concentrated in the lower region.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The internal porosity of the first carbon particle is 8% or more and 20% or less, and the internal porosity of the second carbon particle is 5% or less.

4. A non-aqueous electrolyte secondary battery, comprising electrode bodies with a positive electrode and a negative electrode facing each other separated by a spacer, a bottomed cylindrical outer packaging can containing the electrode bodies, and a sealing body sealing the opening of the outer packaging can, wherein the non-aqueous electrolyte secondary battery is fixed such that the bottom of the outer packaging can contacts a fixing part. The negative electrode has a negative electrode mixture layer comprising a first carbon particle and a second carbon particle with an internal porosity smaller than that of the first carbon particle. When the electrode body is divided into a region of the sealing body side half and a region of the bottom side half of the outer packaging can in the insertion direction toward the outer packaging can, the second carbon particles are more concentrated in the region of the sealing body side half compared to the region of the bottom side half of the outer packaging can.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein, Compared to the area of ​​the side half of the sealing body, the first carbon particles are more concentrated in the area of ​​the bottom side half of the outer packaging can.

6. The non-aqueous electrolyte secondary battery according to claim 4 or 5, wherein, The internal porosity of the first carbon particle is 8% or more and 20% or less, and the internal porosity of the second carbon particle is 5% or less.

7. A non-aqueous electrolyte secondary battery comprising electrode bodies with a positive electrode and a negative electrode facing each other separated by a spacer, a bottomed cylindrical outer packaging can housing the electrode bodies, and a sealing body sealing the opening of the outer packaging can, wherein the non-aqueous electrolyte secondary battery is fixed such that the sealing body contacts the fixing part. The negative electrode has a negative electrode mixture layer comprising a first carbon particle and a second carbon particle with an internal porosity smaller than that of the first carbon particle. When the electrode body is divided into a region of the sealing body side half and a region of the bottom side half of the outer packaging can in the insertion direction toward the outer packaging can, the second carbon particles are more concentrated in the region of the bottom side half of the outer packaging can compared to the region of the sealing body side half.

8. The non-aqueous electrolyte secondary battery according to claim 7, wherein, Compared to the area of ​​the bottom half of the outer packaging can, the first carbon particles are more concentrated in the area of ​​the side half of the sealing body.

9. The non-aqueous electrolyte secondary battery according to claim 7 or 8, wherein, The internal porosity of the first carbon particle is 8% or more and 20% or less, and the internal porosity of the second carbon particle is 5% or less.

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