Power storage element

Abstract

This power storage element comprises: a first conductor having a first surface and a second surface facing opposite the first surface; a first active material layer provided on the first surface of the first conductor and containing a plurality of first negative electrode active material particles; and a first layer that contains an inorganic material, that has a first section provided across two or more first negative electrode active material particles exposed on a side opposite the first conductor in the first active material layer, and that has a second section which intrudes, from the first section, into the gap between the first negative electrode active material particles of the first active material layer.

Description

Energy storage element

[0001] The present disclosure relates to an energy storage element.

[0002] Lithium-ion secondary batteries are widely used as a power source for mobile devices such as mobile phones and laptops, as well as hybrid cars, etc. In recent years, there has been an increasing demand for larger batteries, such as those used in stationary energy storage devices and electric vehicles, and higher performance batteries that combine high capacity with safety are required.

[0003] Cited Document 1 (WO2018-168075A1) discloses that forming an intermediate layer containing at least one of a fluororesin and particles between a positive electrode and a separator and using a specific fluorine-based binder in the positive electrode suppresses gas generation and improves safety.

[0004] Cited Document 2 (JP2008-506244T) discloses an electrochemical element that can ensure high capacity, long life, and safety by forming a multi-component oxide coating layer on the surface of an electrode active material.

[0005] WO2018 / 168075 Publication Special Publication No. 2008-506244

[0006] However, there is room for improvement in the cycle characteristics of the energy storage element when used at high temperatures.

[0007] [1] An energy storage element comprising a negative electrode having: a first conductor having a first surface and a second surface facing an opposite side to the first surface; a first active material layer provided on the first surface of the first conductor and containing a plurality of first negative electrode active material particles; and a first layer containing an inorganic material, the first layer having a first portion provided across two or more first negative electrode active material particles exposed on the side of the first active material layer opposite the first conductor, and a second portion extending from the first portion and penetrating between the first negative electrode active material particles of the first active material layer.

[0008] [2] The energy storage element described in [1], in a cross-sectional image along a first direction in which the first active material layer and the first conductor are aligned, the length of the surface of the first layer on the first conductor side is greater than the length of the surface of the first layer opposite the first conductor.

[0009] [3] The energy storage element according to [1] or [2], wherein the second portion of the first layer extends from the first portion to a position exceeding half the particle diameter of at least one of the first negative electrode active material particles exposed on the side opposite to the first conductor in a first direction in which the first active material layer and the first conductor are aligned.

[0010] [4] The energy storage element according to any one of [1] to [3], wherein the second portion of the first layer extends from the first portion to a position covering a portion of at least one of the first negative electrode active material particles that is exposed on the opposite side from the first conductor in a first direction in which the first active material layer and the first conductor are aligned.

[0011] [5] The energy storage element according to any one of [1] to [4], wherein, when Hav is an average thickness of a second portion of the first layer in a cross-sectional image taken along a first direction in which the first active material layer and the first conductor are aligned, and Rav is an average particle size of a plurality of first negative electrode active material particles contained in the first active material layer, 0.3≦Hav / Rav≦3.0 is satisfied.

[0012] [6] The energy storage element according to [5], wherein 0.3≦Hav / Rav≦3.0 is satisfied in the multiple cross-sectional images.

[0013] [7] The energy storage element according to [5] or [6], wherein 0.5≦Hav / Rav≦2.0 is satisfied.

[0014] [8] The energy storage element according to any one of [1] to [7], wherein the inorganic material is an inorganic compound.

[0015] [9] The energy storage element according to [8], wherein the inorganic compound contains aluminum oxide.

[0016]

[10] The energy storage element according to any one of [1] to [9], wherein the first layer further contains an organic compound.

[0017]

[11] The energy storage element according to

[10] , wherein the organic compound includes a polymer compound containing fluorine.

[0018]

[12] The energy storage element according to

[11] , wherein the polymer compound is polyvinylidene fluoride.

[0019]

[13] The energy storage element according to any one of

[10] to

[12] , wherein a mass ratio of the inorganic material to the organic compound is 1:1 to 100:1.

[0020]

[14] The energy storage element according to any one of [1] to

[13] , wherein the negative electrode active material particles of the first active material layer contain at least one of a carbon material, a metal, a metal oxide, a semi-metal, and a semi-metal oxide.

[0021]

[15] The energy storage element according to any one of [1] to

[14] , wherein the negative electrode further includes: a second active material layer provided on a second surface of the first conductor and containing a plurality of second negative electrode active material particles; and a second layer containing an inorganic material, the second layer having a third portion provided across two or more of the second negative electrode active material particles exposed on the side of the second active material layer opposite to the first conductor, and a fourth portion extending from the third portion and penetrating between the second negative electrode active material particles of the second active material layer.

[0022]

[16] The energy storage element according to

[15] , wherein the third portion of the second layer extends from the third portion to a position exceeding half the particle diameter of at least one of the second negative electrode active material particles exposed on the opposite side from the first electric conductor in the second direction in which the second active material layer and the first electric conductor are aligned.

[17] The energy storage element according to

[15] , wherein the third portion of the second layer extends from the third portion to a position covering a portion of at least one of the second negative electrode active material particles exposed on the opposite side from the first electric conductor in the second direction in which the second active material layer and the first electric conductor are aligned, the portion being closest to the first electric conductor.

[0023]

[18] The energy storage element according to any one of

[15] to

[17] , wherein the thickness of the first part of the first layer in a first direction in which the first active material layer and the first conductor are aligned is different from the thickness of the third part of the second layer in a second direction in which the second active material layer and the first conductor are aligned.

[0024]

[19] A storage element according to any one of

[15] to

[18] , wherein the thickness of the first part of the first layer in a first direction in which the first active material layer and the first conductor are aligned is greater than the thickness of the third part of the second layer in a second direction in which the second active material layer and the first conductor are aligned.

[0025]

[20] The energy storage element according to any one of [1] to

[19] , further comprising a positive electrode and a separator disposed between the negative electrode and the positive electrode.

[0026]

[21] The energy storage element according to any one of

[15] to

[19] , further comprising a positive electrode and a separator disposed between the negative electrode and the positive electrode, wherein a laminate having the negative electrode, the separator, and the positive electrode is wound.

[0027]

[22] The energy storage element according to

[21] , wherein the laminate is wound so that the second layer is located inside the first layer.

[0028]

[23] The energy storage element according to

[22] , wherein the thickness of the second layer is smaller than the thickness of the first layer.

[0029]

[24] The laminate is wound so as to have alternating flat portions and curved portions, and the thickness of the first layer of the curved portions is thinner than the thickness of the first layer of the flat portions.

[21] A storage element as described in

[21] .

[0030] According to the present disclosure, an energy storage device such as a lithium ion secondary battery having excellent cycle characteristics when used at high temperatures is provided.

[0031] FIG. 1 is a perspective view of a lithium ion secondary battery 100 according to an embodiment; FIG. 2 is a cross-sectional view of a laminate 90 according to an embodiment; FIG. 3 is an enlarged cross-sectional view of a laminate 90 according to an embodiment; FIG. 4 is an enlarged cross-sectional view of a negative electrode according to an embodiment; FIG. 5 is an enlarged cross-sectional view of a negative electrode according to another embodiment; FIG. 6 is an enlarged cross-sectional view of a negative electrode according to another embodiment; FIG. 7 is an enlarged cross-sectional view of a negative electrode according to another embodiment; FIG. 8 is an enlarged cross-sectional view of a negative electrode according to another embodiment; FIG. 9 is an enlarged cross-sectional view of a laminate according to another embodiment; FIG. 10 is an enlarged cross-sectional view of a curved portion of a laminate according to another embodiment; FIG. 11 is a cross-sectional view of a lithium ion secondary battery according to another embodiment; FIG. 12 is a cross-sectional view of a lithium ion secondary battery according to another embodiment.

[0032] The following provides a clear and detailed description of the technical solutions in the embodiments of the present disclosure, but it is clear that the described embodiments are only a part of the embodiments of the present disclosure, and are not all of them. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. The terms used in the present specification are used only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0033] DETAILED DESCRIPTION OF THE INVENTION The present disclosure may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein.

[0034] Furthermore, in the accompanying figures, the dimensions or thicknesses of various components, layers may be exaggerated for simplicity and clarity. Like numbers refer to like elements throughout the text. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0035] Furthermore, when element A is said to "connect" element B, it should be understood that element A may be directly connected to element B, or there may be an intermediate element C such that elements A and B are indirectly connected to each other.

[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0037] As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0038] As used herein, the term "comprising" means the presence of mentioned features, values, steps, operations, elements and / or components, but it is further understood that it does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0039] Spatially relative terms, such as "above," may be used herein for ease of description to describe the relationship of an element or feature to another element(s) or feature(s) as illustrated in the figures. It should be understood that spatially relative terms are intended to encompass different orientations of a device or apparatus in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures were turned over, elements described as being "above" or "on" the other elements or features would then be oriented "below" or "below" the other elements or features. Thus, the exemplary term "above" can encompass both an orientation of above and below.

[0040] Terms such as first, second, and third may be used herein to describe various elements, components, regions, layers, and / or sections, but it should be understood that these elements, components, regions, layers, and / or sections are not limited by these terms. These terms are used to distinguish one element, component, region, layer, or section from another. Thus, a first element, component, region, layer, or section described below could be referred to as a second element, component, region, layer, or section without departing from the teachings of the exemplary embodiments.

[0041] 1 is a perspective view of an energy storage element according to an embodiment of the present disclosure. The energy storage element 100 includes a case 80 and a laminate 90 housed in the case 80. Leads 101 and 102 are connected to the laminate 90 and extend from the inside to the outside of the case 80. There are no particular limitations on the material of the case 80, and it may be a resin sheet, a resin-coated metal sheet, or the like.

[0042] In this specification, the axial direction of the winding of the laminate 90 is defined as the Y direction, the thickness direction of the laminate 90 (the direction perpendicular to the Y direction and in which the thickness of the laminate 90 is thinnest) is defined as the Z' direction (first direction), and the direction perpendicular to the Y direction and the Z' direction is defined as the X' direction.

[0043] FIG. 2 is a cross-section of a laminate 90 according to an embodiment of the present disclosure taken along an X'Z' plane perpendicular to the Y axis, and is an enlarged view of cross-section CS of the laminate 90 in FIG. 1 . This laminate 90 includes a negative electrode 10, a positive electrode 30, and a separator 20. The negative electrode 10, the positive electrode 30, and the separator 20 are wound together with the separator 20 interposed between the negative electrode 10 and the positive electrode 30. The wound ends of the laminate 90 are fixed with tape 13. The negative electrode 10, the positive electrode 30, and the separator 20 are each sheet-shaped. The laminate 90 has a flat portion 90M where the laminate of the positive electrode 30, the separator 20, and the negative electrode 10 is flat, and curved portions 90C located at both ends of the flat portion 90M where the laminate of the positive electrode 30, the separator 20, and the negative electrode 10 is curved. The laminate 90 is wound so as to have alternating flat portions 90M and curved portions 90C. The positive electrode 30 has a second conductor 32 and a positive electrode active material layer 34, and the negative electrode 10 mainly has a first conductor 12 and a first active material layer 14.

[0044] (Negative electrode 10) Figure 3 shows an example of an enlarged cross-section of a flat portion 90M of the laminate 90 of Figure 2. The negative electrode 10 has a first conductor 12, a first active material layer 14α provided on a first surface 12a of the first conductor 12, a first layer 16α sandwiching the first active material layer 14α together with the first conductor 12, a second active material layer 14β provided on a second surface 12b of the first conductor 12, and a second layer 16β sandwiching the second active material layer 14β together with the first conductor 12. A major surface of the first layer 16α of the negative electrode 10 contacts a major surface of the separator 20. A major surface of the second layer 16β of the negative electrode 10 contacts a major surface of the separator 20.

[0045] 3 to 10, the Y direction is the direction parallel to the winding axis of the laminate 90, as in FIGS.

[0046] 3 to 10 , the Z direction is the direction (first direction) in which the first active material layer 14α and the first conductor 12 are aligned, and can also be considered to be the direction perpendicular to the first surface 12a of the first conductor 12. The Z direction is also the direction (second direction) in which the second active material layer 14β and the first conductor 12 are aligned, and can also be considered to be the direction perpendicular to the second surface 12b of the first conductor 12.

[0047] 3 to 10, the X direction is perpendicular to the Y and Z directions. In this specification, a cross section is a cross section along the Z direction unless otherwise defined. In Figures 3 to 10, the vertical direction is the Z direction, and the horizontal direction is the X direction.

[0048] (First conductor 12) The first conductor 12 is, for example, a thin metal plate (metal foil) made of copper, nickel, stainless steel, or an alloy thereof, and is a conductive plate material. The thickness of the first conductor 12 can be, for example, 5 to 20 μm.

[0049] (First Active Material Layer 14α, Second Active Material Layer 14β) The first active material layer 14α includes a plurality of negative electrode active material particles (first negative electrode active material particles) 14P, and the second active material layer 14β includes a plurality of negative electrode active material particles (second negative electrode active material particles) 14P. The negative electrode active material may be any material capable of absorbing and releasing (intercalating and deintercalating, or doping and dedoping) lithium ions. Examples of the negative electrode active material particles 14P may include at least one of a carbon material, a metal, a metal oxide, a semi-metal, and a semi-metal oxide. The negative electrode active material particles (first negative electrode active material particles) 14P of the first active material layer 14α and the negative electrode active material particles (second negative electrode active material particles) 14P of the second active material layer 14β may be the same or different.

[0050] Examples of the carbon material used for the negative electrode active material particles 14P include graphite, non-graphitizable carbon, easily graphitizable carbon, and low-temperature fired carbon.

[0051] Examples of metals used for the negative electrode active material particles 14P include metals that can combine with lithium, such as Al and Sn.

[0052] An example of a semimetal used for the negative electrode active material particles 14P is Si.

[0053] Examples of metal oxides used for the negative electrode active material particles 14P include TiO ２ , SnO ２ , lithium titanate (Li ４ Ti ５ O １２ )

[0054] Examples of semi-metal oxides used for the negative electrode active material particles 14P include SiOｘ (0<x<2).

[0055] In the first active material layer 14α and the second active material layer 14β in FIG. 3, the negative electrode active material particles 14P may be arranged randomly.

[0056] The particle size of the negative electrode active material particles 14P may be 2 to 20 μm in terms of D50 of the number-based distribution of the diameter of circles equivalent to the area of ​​cross-sectional images of the first active material layer 14α and the second active material layer 14β.

[0057] (Organic Compound) The first active material layer 14α and the second active material layer 14β may contain an organic compound 14B such as a polymer. The organic compound can bond the negative electrode active material particles 14P together and / or the negative electrode active material particles 14P to the first conductor 12. In Figures 3, 6, and 9 to 11, the hatched area extending from the upper left to the lower right and having the narrowest spacing corresponds to the organic compound 14B.

[0058] Examples of the organic compound 14B include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Other examples of the organic compound include cellulose, styrene-butadiene rubber, ethylene-propylene rubber, acrylic resin, polyimide resin, and polyamide-imide resin.

[0059] The organic compound may be an electron-conductive conductive polymer or an ion-conductive conductive polymer. An example of an electron-conductive conductive polymer is polyacetylene. In this case, the organic compound also functions as a conductive additive particle, so there is no need to add a conductive additive. An ion-conductive conductive polymer may be, for example, one having ion conductivity such as lithium ions, and examples thereof include a polymer compound (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide, polyphosphazene, etc.) and a monomer of LiClO ４ , LiBF ４ , LiPF ６Examples of the polymerization initiator used for the complex include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-mentioned monomers.

[0060] When added, the amount of the organic compound added may be 2 to 20% by mass relative to the mass of the negative electrode active material particles.

[0061] (Negative Electrode Conductive Aid) The first active material layer 14α and the second active material layer 14β may further contain a negative electrode conductive aid 14F. Known conductive aids can be used as the negative electrode conductive aid. Examples include carbon-based materials such as graphite, carbon black, and acetylene black; metal fine powders such as copper, nickel, stainless steel, and iron; mixtures of carbon materials and metal fine powders; and conductive oxides such as ITO. The amount of the negative electrode conductive aid added may be 0.5 to 5 mass% relative to the mass of the negative electrode active material particles. In Figures 3, 6, and 9 to 11, the hatched area with the narrowest spacing extending from the upper right to the lower left corresponds to the negative electrode conductive aid 14F.

[0062] (Thickness of First Active Material Layer 14α and Second Active Material Layer 14β) The thicknesses of the first active material layer 14α and the second active material layer 14β can be 5 to 300 μm and may be the same or different. FIG. 4A shows an example of an enlarged cross-sectional view of the negative electrode 10 at the flat portion 90M of the laminate 90 in FIG. 2. The thickness of the first active material layer 14α is defined as the arithmetic average of the distance DPP1 from the point PP1 farthest from the first conductor 12 in the Z direction to the first conductor 12 among each negative electrode active material particle 14Pout exposed on the side opposite the first conductor 12 included in the first active material layer 14α in the cross-sectional image along the Z direction of the negative electrode illustrated in FIG. 4A.

[0063] The thickness of the second active material layer 14β is defined as the arithmetic mean of the distance DPP1 from a point PP1 farthest from the first conductor 12 in the Z direction to the first conductor 12 among the negative electrode active material particles 14Pout exposed on the side opposite the first conductor 12 contained in the second active material layer 14β in the cross-sectional image along the Z direction of the negative electrode illustrated in Figures 4A and 4B, for all negative electrode active material particles 14Pout exposed on the side opposite the first conductor 12 contained in the second active material layer 14β in the cross-sectional image.

[0064] The magnification of the cross-sectional image can be set so that the number of negative electrode active material particles 14Pout exposed on the side opposite to first conductor 12 contained in each active material layer is approximately 5 to 100.

[0065] (First layer 16α and second layer 16β) The first layer 16α has a first portion 16αA that is provided across two or more negative electrode active material particles 14Pout (first negative electrode active material particles) exposed on the side of the first active material layer 14α opposite to the first conductor 12, and a second portion 16αB that penetrates from the first portion 16αA into the spaces between adjacent negative electrode active material particles (first negative electrode active material particles) 14P of the first active material layer 14α.

[0066] The second layer 16β has a third portion 16βA that is provided across two or more negative electrode active material particles 14Pout (second negative electrode active material particles) exposed on the side of the second active material layer 14β opposite to the first conductor 12, and a fourth portion 16βB that penetrates from the third portion 16βA into the spaces between adjacent negative electrode active material particles (second negative electrode active material particles) 14P of the second active material layer 14β.

[0067] In this specification, the space between the anode active material particles (first anode active material particles) 14P where the second portions 16αB are arranged refers to an aggregate V of regions sandwiched between any two anode active material particles 14P (first anode active material particles) that may be adjacent in any direction in the first active material layer 14α. The second portions 16αB can extend until they come into contact with the first conductor 12.

[0068] The first portion 16αA is a region of the first layer 16α that is separated from the aggregate V of the above-mentioned regions.

[0069] The space between the negative electrode active material particles (first negative electrode active material particles) 14P where the fourth portion 16βB is arranged refers to an aggregate V of the region sandwiched between any two negative electrode active material particles 14P (second negative electrode active material particles) that may be adjacent in any direction in the second active material layer 14β.

[0070] The third portion 16βA is a region of the second layer 16β that is separated from the aggregate V of the above-mentioned regions.

[0071] The boundary between the first portion 16αA and the second portion 16αB is formed by a common circumferential line W of the negative electrode active material particles 14Pout that are exposed on the side opposite to the first conductor 12 and that are adjacent to each other in a direction perpendicular to the Z direction (e.g., the X direction in FIGS. 3 and 4A ) (see FIG. 4A ). The boundary between the third portion 16βA and the fourth portion 16βB is formed by a common circumferential line W of the negative electrode active material particles 14Pout that are exposed on the side opposite to the first conductor 12 and that are adjacent to each other in a direction perpendicular to the Z direction (e.g., the X direction in FIGS. 3 and 4A ) (see FIG. 4A ).

[0072] 4B , for example, in the cross section, when a common circumferential line W1 between the negative electrode active material particles 14Pout1 and 14Pout2 that are adjacent in a direction perpendicular to the Z direction and a common circumferential line W2 between the negative electrode active material particles 14Pout2 and 14Pout3 that are adjacent in a direction perpendicular to the Z direction intersect, the side closer to the first conductor 12 than each common circumferential line W is defined as the second part 16αB rather than the first part 16αA. Therefore, in FIG. 4B , the boundary between the first part 16αA and the second part 16αB of the first layer 16α has a shape (V-shaped in the drawing) formed by the parts of the common circumferential lines W1 and W2 that are farthest from the first conductor 12. Although not shown in the figure, in the above cross section, when the common circumferential tangents intersect with each other at the boundary between the third part 16βA and the fourth part 16βB, the side closer to the first conductor 12 than each common circumferential tangent is defined as the fourth part 16βB rather than the third part 16βA, as described above.

[0073] (Thickness U and average thickness Uav of first portion 16αA, and thickness U' and average thickness U'av of third portion 16βA) The thickness U of first portion 16αA is the distance of first portion 16αA along the Z direction. The thickness U' of third portion 16βA is the distance of third portion 16βA along the Z direction.

[0074] The average thickness Uav of the first portion 16αA and the average thickness U'av of the third portion 16βA may be 0.1 to 5.0 μm. Uav and U'av may be 0.5 μm or more, 0.7 μm or more, or 1.0 μm or more. Uav and U'av may be 4.0 μm or less, or 3.0 μm or less.

[0075] The average thickness Uav of the first portion 16αA is defined as the area of ​​the first portion 16αA that does not penetrate between the negative electrode active material particles 14P of the first active material layer 14α, of the first layer 16α extracted by image processing in a cross-sectional image of the negative electrode along the Z direction, divided by the length of the first portion 16αA in a direction perpendicular to the Z direction in the image (for example, the Z direction in FIG. 3, but it may be the Y direction depending on the cross section). The magnification of the cross-sectional image can be set so that the length of the first portion 16αA in the direction perpendicular to the Z direction is, for example, 50 to 500 μm.

[0076] The average thickness U'av of the third portions 16βA is defined as the area of ​​the third portions 16βA that do not penetrate between the negative electrode active material particles 14P of the second active material layer 14β, of the second layer 16β extracted by image processing in a cross-sectional image of the negative electrode along the Z direction, divided by the length of the third portions 16βA in a direction perpendicular to the Z direction in the image. The magnification of the cross-sectional image can be set so that the length of the third portions 16βA in the direction perpendicular to the Z direction is, for example, 50 to 500 μm.

[0077] (Thickness H, average thickness Hav, and average particle size Rav of negative electrode active material particles contained in first active material layer 14α of second portion 16αB, and thickness H', average thickness H'av, and average particle size R'av of negative electrode active material particles contained in second active material layer 14β of fourth portion 16βB)

[0078] The thickness H of the second portion 16αB is the distance of the second portion 16αB along the Z direction. The thickness H′ of the fourth portion 16βB is the distance of the fourth portion 16βB along the Z direction.

[0079] The average thickness Hav of the second portions 16αB is defined as the area of ​​the second portions 16αB that penetrate between the negative electrode active material particles 14P of the first active material layer 14α, of the first layer 16α extracted by image processing in a cross-sectional image of one negative electrode, divided by the length in the X direction of the second portions 16αB. The magnification of the cross-sectional image can be set so that the length in the X direction of the second portions 16αB is, for example, 50 to 500 μm.

[0080] The average thickness H'av of the fourth portions 16βB is defined as the area of ​​the fourth portions 16βB that penetrate between the negative electrode active material particles 14P of the second active material layer 14β, of the second layer 16β extracted by image processing in a cross-sectional image of one negative electrode, divided by the length in the X direction of the fourth portions 16βB. The magnification of the cross-sectional image can be set so that the length in the X direction of the fourth portions 16βB is, for example, 50 to 500 μm.

[0081] In another embodiment of the present disclosure, as shown in FIG. 4A , when the average thickness of second portion 16αB in one cross-sectional image along the first direction (Z direction) is Hav and the average particle size of multiple negative electrode active material particles 14P contained in first active material layer 14α in the image is Rav, the relationship 0.3≦Hav / Rav≦3.0 is satisfied.

[0082] In another embodiment of the present disclosure, when the average thickness of the fourth portion 16βB in one cross-sectional image along the second direction (Z direction) is H'av and the average particle size of the multiple negative electrode active material particles 14P contained in the second active material layer 14β in the image is R'av, the relationship 0.3≦H'av / R'av≦3.0 is satisfied.

[0083] Rav is the particle size obtained by D50 based on the number of equivalent-area circle diameters of all negative electrode active material particles contained in first active material layer 14α in one cross-sectional image. R'av is the particle size obtained by D50 based on the number of equivalent-area circle diameters of all negative electrode active material particles contained in second active material layer 14β in one cross-sectional image. The number of active material particles measured in one cross-sectional image can be 10 to 1,000.

[0084] In other embodiments of the present disclosure, from the viewpoint of improving cycle characteristics, 0.5≦Hav / Rav≦2.0 may be satisfied, Hav / Rav≦1.5 may be satisfied, Hav / Rav≦1.3 may be satisfied, 0.5≦H'av / R'av≦2.0 may be satisfied, H'av / R'av≦1.5 may be satisfied, and H'av / R'av≦1.3 may be satisfied.

[0085] At least one of Hav / Rav and H'av / R'av may be satisfied in one cross-sectional image, or may be satisfied in multiple cross-sectional images, specifically, in two cross-sectional images, three cross-sectional images, or five cross-sectional images.

[0086] (Thickness T and average thickness Tav of first layer 16α, and thickness T' and average thickness T'av of second layer 16β) The thickness T of the first layer 16α is the distance of the first layer 16α along the Z direction. The thickness T' of the second layer 16β is the distance of the second layer 16β along the Z direction.

[0087] Specifically, the thickness T of the first layer 16α is the distance in the Z direction from the surface 16αAS of the first layer 16α opposite the first conductor 12 to the surface of the second part 16αB located on the first conductor 12 side in the Z direction.

[0088] The thickness T' of the second layer 16β is the distance in the Z direction from the surface 16βAS of the second layer 16β opposite the first conductor 12 to the surface of the fourth portion 16βB located on the first conductor 12 side in the Z direction.

[0089] The average thickness Tav of the first layer 16α is defined as the area of ​​the first layer 16α extracted by image processing in a cross-sectional image of one negative electrode, divided by the length of the first layer 16α in the first direction (X direction). The magnification of the cross-sectional image can be set so that the length of the first layer 16α in the X direction is, for example, 50 to 500 μm.

[0090] The average thickness T'av of the second layer 16β is defined as the area of ​​the second layer 16β extracted by image processing in a cross-sectional image of one negative electrode, divided by the length of the second layer 16β in the second direction (X direction). The magnification of the cross-sectional image can be set so that the length of the second layer 16β in the X direction is, for example, 50 to 500 μm.

[0091] The average thickness Tav of the first layer 16α and the average thickness T'av of the second layer 16β may be 0.1 to 300 μm.

[0092] In this specification, Tav, Uav, Hav, and Hav / Rav, as well as T'av, U'av, H'av, and H'av / R'av, may each be a numerical value obtained from one cross-sectional image, or may be the arithmetic mean of the numerical values ​​obtained from, for example, three or five cross-sectional images.

[0093] (Relationship between Roughness on Both Surfaces of First Layer 16α and Roughness on Both Surfaces of Second Layer 16β) In another embodiment of the present disclosure, in a cross-sectional image of the negative electrode along the Z direction, the length LαBS of the surface 16αBS of the first layer 16α on the first conductor 12 side is greater than the length LαAS of the surface 16αAS of the first layer 16α on the opposite side from the first conductor 12. LαBS / LαAS may be 1.1 or greater, or may be 1.2 or greater.

[0094] In another embodiment of the present disclosure, in a cross-sectional image of the negative electrode along the Z direction, the length LβBS of the surface 16βBS of the second layer 16β on the side of the first conductor 12 is greater than the length LβAS of the surface 16βAS of the second layer 16β on the side opposite to the first conductor 12. LβBS / LβAS may be 1.1 or greater, or may be 1.2 or greater.

[0095] Here, the surface 16αBS of the first layer 16α facing the first conductor 12 also includes the contact interface between the first layer 16α and the negative electrode active material particles 14P. The surface 16βBS of the second layer 16β facing the first conductor 12 also includes the contact interface between the second layer 16β and the negative electrode active material particles 14P.

[0096] 4A, the isolated portion ISO of the second portion 16αB of the first layer 16α that is not connected to the first portion 16αA is excluded from the calculation of the length LαAS of the surface 16αBS. Similarly, the isolated portion ISO of the fourth portion 16βB of the second layer 16β that is not connected to the third portion 16βA is excluded from the calculation of the length LβBS of the surface 16βBS.

[0097] The magnification of the cross-sectional image for obtaining the length of each surface can be set so that the number of negative electrode active material particles 14Pout exposed on the side opposite to the first conductor 12 in the cross-sectional image is approximately 5 to 100. The length of each surface can be obtained based on the number and size of pixels constituting each curve after extracting curves on both surfaces of the first and second layers from the SEM-EDX cross-sectional image based on the difference in composition between the first and second layers and the negative electrode active material particles.

[0098] In one embodiment, in a cross-sectional image of the negative electrode along the Z direction, the length LαAS of the surface 16αAS of the first layer 16α opposite the first conductor 12 may be less than 1.1 or less than 1.05 relative to the length of the first layer 16α in a direction perpendicular to the Z direction (X direction in Figure 3).

[0099] In one embodiment, in a cross-sectional image of the negative electrode along the Z direction, the length LβAS of the surface 16βAS of the second layer 16β opposite the first conductor 12 may be less than 1.1 or less than 1.05 relative to the length of the second layer 16β in a direction perpendicular to the Z direction (the X direction in Figure 3).

[0100] 5, the ratio of the length of the surface 16αAS of the first layer 16α to the length of the first layer 16α in a direction perpendicular to the Z direction (X direction in FIG. 3) may be less than 1.1 or less than 1.05, while the ratio of the length of the surface 16βAS of the second layer 16β to the length of the second layer 16β in a direction perpendicular to the Z direction (X direction in FIG. 3) may be 1.1 or more or 1.2 or more. Conversely, the ratio of the length of the surface 16αAS of the first layer 16α to the length of the first layer 16α in a direction perpendicular to the Z direction (X direction in FIG. 3) may be 1.1 or more or 1.2 or more, while the ratio of the length of the surface 16βAS of the second layer 16β to the length of the second layer 16β in a direction perpendicular to the Z direction (X direction in FIG. 3) may be less than 1.1 or less than 1.05.

[0101] In this case, a gap VV may be formed between the separator 20 and the surface 16αAS of the first layer 16α or the surface 16βAS of the second layer 16β, whichever has a larger ratio to the above length. The surface 16βAs of the first layer 16α or the surface 16βAs of the second layer 16β, whichever has a larger ratio to the above length, may be on the inside or outside of the winding. The inside of the winding refers to the side closer to the winding axis, and the outside of the winding refers to the side farther from the winding axis.

[0102] (Form of second portion 16αB and fourth portion 16βB) In another embodiment of the present disclosure, as shown in the schematic diagram of the cross-sectional image of Figure 4A, the second portion 16αB of the first layer 16α includes a portion extending from the first portion 16αA to a position exceeding dp / 2, which is half the length of the particle diameter dp of at least one negative electrode active material particle 14P1 (first negative electrode active material particle) exposed on the side opposite to the first conductor 12 in the Z direction.

[0103] Here, the particle diameter dp of the negative electrode active material particle is the distance along the first direction (Z direction) between a point PP1 of the negative electrode active material particle 14P1 that is farthest from the first conductor 12 and a point PP2 of the negative electrode active material particle 14P that is closest to the first conductor 12 in a cross-sectional image of the negative electrode 10 taken along the first direction (Z direction). Furthermore, in the first active material layer 14α, the distance DPP1 in the first direction (Z direction) between the first surface 12a of the first conductor 12 and the point PP1 of the negative electrode active material particle 14P that is farthest from the first conductor 12 may be different for each negative electrode active material particle 14P. In the second active material layer 14β, the distance DPP1 in the first direction (Z direction) between the second surface 12b of the first conductor 12 and the point PP1 of the negative electrode active material particle 14P that is farthest from the first conductor 12 may be different for each negative electrode active material particle 14P.

[0104] The second portion 16αB extending to a position exceeding a length dp / 2 that is half the particle diameter dp means that the second portion 16αB extends beyond a line A in the Z direction, which passes through a point that is half the particle diameter (dp / 2) of the negative electrode active material particle 14P1 and extends in the X direction perpendicular to the Z direction, on at least one side of the negative electrode active material particle P1 in the X direction. The second portion 16αB extends in the Z direction from the first portion 16αA across the line A.

[0105] Similarly, the fourth portion 16βB of the second layer 16β includes a portion extending from the third portion 16βA in the Z direction to a position exceeding dp / 2, which is half the length of the particle diameter dp of at least one negative electrode active material particle 14P1 (second negative electrode active material particle) exposed on the side opposite to the first conductor 12.

[0106] The fourth portion 16βB of the second layer 16β extending to a position exceeding a length dp / 2 that is half the particle diameter dp means that the fourth portion 16βB extends beyond a line A in the Z direction, which passes through a point that is half the particle diameter (dp / 2) of the negative electrode active material particle 14P1 and extends in the X direction perpendicular to the Z direction, on at least one side of the negative electrode active material particle P1 in the X direction. The fourth portion 16βB extends in the Z direction from the third portion 16βA across the line A.

[0107] In another embodiment of the present disclosure, the thicknesses and average thicknesses of the first conductor 12, first active material layer 14α, second active material layer 14β, first layer 16α, second layer 16β constituting the negative electrode 10, and the second conductor 32 and positive electrode active material layer 34 constituting the positive electrode 30 are the same in the flat portion 90M shown in FIG. 2 and the curved portion 90C.

[0108] In another embodiment of the present disclosure, as shown in FIG. 6 , the second portion 16αB of the first layer 16α extends from the first portion 16αA in the first direction (Z direction) to a position covering a point PP2 closest to the first conductor 12 of at least one negative electrode active material particle 14P1 exposed on the side opposite the first conductor, and extends beyond point PP2 in the Z direction.

[0109] In another embodiment of the present disclosure, as shown in FIG. 6 , the fourth portion 16βB of the second layer 16β extends from the third portion 16βA in the second direction (Z direction) to a position covering a point PP2 closest to the first conductor 12 of at least one negative electrode active material particle 14P2 exposed on the side opposite to the first conductor, and extends beyond the point PP2 in the Z direction.

[0110] 2 to 6, the first layer 16α is provided for the first active material layer 14α, and the second layer 16β is provided for the second active material layer 14β, as shown in Fig. 3 etc. However, in other embodiments of the present disclosure, even if the negative electrode 10 has the first active material layer 14α and the second active material layer 14β on both sides of the first conductor 12, the negative electrode 10 may have only either the first layer 16α or the second layer 16β.

[0111] In the above-described embodiment shown using Figures 2 to 6, the negative electrode 10 has a first active material layer 14α and a second active material layer 14β on both sides of the first conductor 12, respectively. However, when the negative electrode 10 has only one of the first active material layer 14α or the second active material layer 14β, the negative electrode 10 may have either the first layer 16α or the second layer 16β.

[0112] The first layer 16α and the second layer 16β contain an inorganic material. Examples of the inorganic material are inorganic compounds. Examples of the inorganic compounds are metal oxides and metal hydroxides. Examples of the metal oxides are particles of one or more metal oxides selected from aluminum oxide, magnesia, titania, silica, zirconia, zinc oxide, iron oxide, ceria, yttria, etc. Examples of the metal hydroxides are magnesium hydroxide. Examples of aluminum oxides are alumina (Al ２ O ３ ), anodized aluminum (Al ２ O ３ ・3H ２ O), boehmite (Al ２ O ３ ・5H ２ O). Preferred inorganic materials are alumina, boehmite, magnesia, and magnesium hydroxide. The inorganic material may be in the form of a plurality of particles. The particles of the inorganic material may have an average particle size of 10 to 1,000 nm, as defined by D50 in the particle size distribution on a volume basis by laser diffraction.

[0113] The first layer 16α and the second layer 16β may further include an organic compound. An example of the organic compound is a fluorine-containing polymer compound, such as polyvinylidene fluoride (PVdF). The organic compound can function as a binder that binds inorganic material particles together and between the inorganic material particles and the negative electrode active material particles.

[0114] The mass ratio of the inorganic compound to the organic compound in the first layer 16α and the second layer 16β may be 1:1 to 100:1.

[0115] (Positive Electrode) The positive electrode 30 has a plate-shaped second conductor 32 and a positive electrode active material layer 34 provided on one or both surfaces of the second conductor 32 .

[0116] (Second Electrical Conductor) The second electrical conductor 32 may be, for example, a thin metal plate (metal foil) made of aluminum, copper, nickel, or an alloy thereof.

[0117] (Positive Electrode Active Material Layer) The positive electrode active material layer 34 may mainly include positive electrode active material particles, a positive electrode binder, and an appropriate amount of a conductive additive.

[0118] (Positive Electrode Active Material) The positive electrode active material is a material that absorbs and releases lithium ions, desorbs and inserts lithium ions (intercalates), or converts lithium ions into counter anions (e.g., ClO ４ － There are no particular limitations on the active material as long as it is possible to reversibly dope and undope it with lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese spinel (LiMn ２ O ４ ), and the general formula: LiNi ｘ Co ｙ Mn ｚ M ａ O ２ (x+y+z+a=1, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr), a composite metal oxide represented by the formula (x+y+z+a=1, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr), a lithium vanadium compound (LiV ２ O ５ ), olivine-type LiMPO ４ (wherein M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr, or VO), lithium titanate (Li ４ Ti ５ O １２ ), LiNi ｘ Co ｙ Al ｚ O ２ (0.9<x+y+z<1.1) and the like.

[0119] (Positive Electrode Binder) The positive electrode active material layer 34 may contain an organic compound. The organic compound may function as a binder that binds the active materials together and also binds the active materials and the second conductor 32 together. The organic compound may be any compound that can form the above-described bonds, and examples of such organic compounds include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In addition to the above, other binders may also be used, such as cellulose, styrene-butadiene rubber, ethylene-propylene rubber, acrylic resin, polyimide resin, and polyamide-imide resin.

[0120] The content of the organic compound in the positive electrode active material layer 34 is not particularly limited, but when added, it is preferably 0.5 to 5 mass % relative to the mass of the active material.

[0121] (Positive Electrode Conductive Aid) The positive electrode active material layer 34 may contain a conductive aid. The conductive aid is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 34, and the conductive aids listed above for the negative electrode conductive aid can be used.

[0122] The content of the conductive additive in the positive electrode active material layer 34 is not particularly limited, but when added, it may be 0.5 to 5 mass % relative to the mass of the active material.

[0123] (Separator 20) There are no particular limitations on the material of the separator 20. An example of a separator has a main layer 22 that is generally a porous sheet of polyolefin such as polyethylene or polypropylene, or a nonwoven fabric. The thickness of the main layer 22 may be 3.0 to 30 μm.

[0124] The separator 20 may have an inorganic compound-containing layer 21 on the side of the main layer 22 that contacts the positive electrode active material layer 34. Examples of the inorganic compound of the inorganic compound-containing layer 21 are the same as those exemplified for the first layer 16α, and may be, for example, alumina particles. The inorganic compound-containing layer 21 may have an organic compound that functions as a binder. Examples of the organic compound are the same as those exemplified for the first layer 16α. The thickness of the main layer 22 may be 3.0 to 30 μm.

[0125] (Stacking Configuration) As shown in FIG. 2, a stack 90 having a separator / positive electrode 30 / separator / negative electrode 10 structure is wound so that the separator 20 is interposed between the positive electrode 30 and the negative electrode 10.

[0126] One main surface of each positive electrode active material layer 34 of the positive electrode 30 is in contact with the second conductor 32, and the other main surface of each positive electrode active material layer 34 is in contact with a main surface of the separator 20. The main surface of the first active material layer 14α of the negative electrode 10 opposite the first layer 16α is in contact with a main surface of the first conductor 12. The surface of the first layer 16α of the negative electrode 10 opposite the first active material layer 14α is in contact with a main surface of the separator 20. The surface of the second active material layer 14β of the negative electrode 10 opposite the second layer 16β is in contact with the first conductor 12. The surface of the second layer 16β of the negative electrode 10 opposite the second active material layer 14β is in contact with the separator 20. For example, in the flat portion 90M of the laminate 90, the layers are stacked in the Z direction.

[0127] 1 is connected to a portion of the second conductor 32 that is exposed from the positive electrode active material layer 34. A lead 102 is connected to a portion of the first conductor 12 that is exposed from the first active material layer 14α or the second active material layer 14β. The leads 101 and 102 extend from the inside to the outside of the case 80.

[0128] 3 , in another embodiment of the present disclosure, the first layer 16α of the negative electrode 10 and the main layer 22 of the separator 20 are in contact with each other. In one embodiment, the positive electrode active material layer 34 of the positive electrode 30 and the inorganic compound-containing layer 21 of the separator 20 are in contact with each other.

[0129] (Method of Producing the First and Second Layers of the Negative Electrode) First, a laminate having a first active material layer 14α and a second active material layer 14β formed on both sides of a first conductor 12 is prepared by a conventionally known method.

[0130] Next, inorganic particles, a binder, and a solvent are mixed to prepare a first layer-forming slurry. The first layer-forming slurry is then applied to at least one of the first active material layer 14α and the second active material layer 14β, followed by drying at high temperature for a predetermined period of time. When the first layer and the second layer have different compositions, a second layer-forming slurry may be applied separately from the first layer-forming slurry. In particular, vacuum drying facilitates penetration of the first layer 16α and / or the second layer 16β between the negative electrode active material particles. Furthermore, extending the vacuum drying time facilitates penetration of the first layer 16α and / or the second layer 16β between the negative electrode active material particles. After the formation of the first layer 16α and / or the second layer 16β, pressing the negative electrode facilitates penetration of the first layer 16α and / or the second layer 16β between the negative electrode active material particles.

[0131] (Another embodiment) FIG. 7 is a cross-sectional view of a negative electrode 10 according to another embodiment. In this embodiment, only the structure on one side of the first conductor 12 is illustrated, and the structure on the other side is omitted. In this embodiment, in the first active material layer 14α, a portion 14P1S of each surface of the negative electrode active material particles 14P1 exposed on the side opposite the first conductor 12 is flattened. This configuration is easily obtained by pressing each surface of the negative electrode active material particles 14P1 before forming the first layer 16. This configuration has the effect of reducing the likelihood of negative electrode active material particles 14P not being covered by the first layer 16α. If there are protrusions on the surface of the negative electrode active material particles 14P1, the protrusions may protrude from the first layer 16α. If there are areas of the negative electrode active material particles that are not covered, the difference in resistance between the first layer 16α and the first active material layer 14α will cause current to concentrate in areas of the first active material layer 14α where the first layer 16α is not present, increasing the utilization rate in only those areas, resulting in variations in deterioration within the first active material layer 14α and possibly reducing the cycle characteristics.

[0132] 8 is a cross-sectional view of a negative electrode according to another embodiment, in which negative electrode active material particles 14P are aligned in the in-plane direction in a first active material layer 14α.

[0133] 9 is an enlarged view of a laminate 90 according to another embodiment. In the above embodiment, the average thickness Uav of the first portion 16αA of the first layer 16α and the average thickness U'av of the third portion 16βA of the second layer 16β are the same as in FIG. 4A . However, in this embodiment, the average thickness U'av of the third portion 16βA of the second layer 16β is smaller than the average thickness Uav of the first portion 16αA of the first layer 16α. The average thickness U'av of the third portion 16βA of the second layer 16β, which is closer to the positive electrode 30, of the first layer 16α and the second layer 16β, is smaller than the average thickness Uav of the first portion 16αA of the first layer 16α which is farther from the positive electrode 30.

[0134] In this embodiment, the negative electrode 10 may be wound so that the second layer 16β is disposed on the outer side of the winding than the first layer 16α, or may be wound so that the second layer 16β is disposed on the inner side of the winding than the first layer 16α. The inner side of the winding refers to the side closer to the winding axis, and the outer side of the winding refers to the side farther from the winding axis. When the second layer 16β is wound so that it is disposed on the inner side of the winding than the first layer 16α, the third portion 16βA of the second layer 16β on the inner side of the winding, which has a relatively smaller radius of curvature, can be made thinner, and the adhesion with the opposing positive electrode is improved, thereby improving the high-temperature cycle characteristics.

[0135] The difference between the average thickness Uav and U'av of the first portion 16αA and the third portion 16βA may be 0 to 2.0 μm.

[0136] 10 is an enlarged view of a laminate 90 according to another embodiment. In this embodiment, the average thickness T'av of the second layer 16β is smaller than the average thickness Tav of the first layer 16α on the outer side of the winding.

[0137] The negative electrode 10 may be wound so that the second layer 16β is positioned on the outer side of the winding than the first layer 16α, or may be wound so that the second layer 16β is positioned on the inner side of the winding than the first layer 16α. The inner side of the winding refers to the side closer to the winding axis, and the outer side of the winding refers to the side farther from the winding axis. When the second layer 16β is wound so that it is positioned on the inner side of the winding than the first layer 16α, the average thickness T'av of the second layer 16β on the inner side of the winding, where the radius of curvature is relatively small, can be reduced, and the adhesion with the opposing positive electrode is improved, thereby improving the high-temperature cycle characteristics.

[0138] The difference between the average thicknesses Tav and T'av of the first layer 16α and the second layer 16β may be 0 to 2.0 μm.

[0139] In this case, in one embodiment, the average thickness U'av of the third portion 16βA is smaller than the average thickness Uav of the first portion 16αA, and the average thickness H'av of the fourth portion 16βB is smaller than the average thickness Hav of the second portion 16αB. In one embodiment, the average thickness U'av of the third portion 16βA is smaller than the average thickness Uav of the first portion 16αA, and the average thickness H'av of the fourth portion 16βB is the same as the average thickness Hav of the second portion 16αB. In one embodiment, the average thickness T'av of the third portion 16βA is the same as the average thickness Tav of the first portion 16αA, and the average thickness H'av of the fourth portion 16βB is smaller than the average thickness Hav of the second portion 16αB.

[0140] The difference between the average thickness Hav of the second portion 16αB and the average thickness H'av of the fourth portion 16βB may be 0 to 2.0 μm. The difference between the average thickness Uav of the first portion 16αA and the average thickness U'av of the third portion 16βA may be 0 to 4.0 μm.

[0141] 11 is an enlarged cross-sectional view of a curved portion 90C of a laminate 90 according to another embodiment. Unlike in FIGS. 3 to 10, the Z direction, which is the direction (first direction) in which the first active material layer 14α and the first conductor 12 are aligned, is the radial direction of the curved portion 90C. The X, Y, and Z directions shown in FIG. 11 are the directions at the center of the laminate 90 in the vertical direction, i.e., when the radial direction of the curved portion is horizontal.

[0142] In the embodiment described above with reference to Figures 2 to 8, there was no difference in the average thickness Tav of the first layer 16α and the average thickness T'av of the second layer 16β of the negative electrode 10 shown in Figure 4A between the flat portion 90M in Figure 2 and the curved portion 90C.

[0143] In contrast, in this embodiment, the average thickness Tav-c of the first layer 16α of the curved curved portion 90C shown in Figure 11 is smaller than the average thickness Tav (see Figure 4A) of the first layer 16α of the flat flat portion 90M shown in Figure 3.

[0144] In another embodiment, the average thickness T'av-c of the second layer 16β of the curved curved portion 90C of FIG. 11 is smaller than the average thickness T'av of the second layer 16β of the flattened flat portion 90M of FIG. 3 (see FIG. 4A).

[0145] 11 is smaller than the average thickness Tav of the first layer 16α of the curved portion 90C of the flat portion 90M, and the average thickness T'av-c of the second layer 16β of the curved portion 90C of the flat portion 90M of the second layer 16β of the curved portion 90C of the second layer 16β of the flat portion 90M of the second layer 16β of the flat portion 90M of the second layer 16β of the flat portion 90M of the second layer 16β of the flat portion 90M of the second layer 16β of the flat portion 90M of the second layer 16α ...

[0146] The difference between the average thickness Tav and the average thickness Tav-c, and the difference between the average thickness T'av and the average thickness T'av-c may each be 0 to 2.0 μm. The average thickness Tav-c of the first layer 16α and the average thickness T'av-c of the second layer 16β in the cross-sectional image of the curved portion are obtained by dividing the area of ​​the first layer 16α by the length of the first layer 16α along the surface of the separator 20 facing the first layer 16α, and by dividing the area of ​​the second layer 16β by the length of the second layer 16β along the surface of the separator 20 facing the second layer 16β, respectively.

[0147] 12 is a cross-sectional view showing an example in which a laminate 90 having a negative electrode 10, a separator 20, and a positive electrode 30 is wound into a cylindrical shape and housed in a case 80. The case 80 includes a metal can 81, a gasket 83, and an electrode lead 82. In FIG. 12, the axis of winding is the Y direction, the horizontal direction is the Z direction in which the first active material layer 14α and the first conductor 12 are aligned, and the X direction is the direction perpendicular to the Y and X directions.

[0148] 13 shows a stacked energy storage element in which a plurality of negative electrodes 10 and a plurality of positive electrodes 30 are stacked with a separator 20 interposed between each positive electrode 30 and negative electrode 10. In Fig. 13, the direction in which the first active material layer 14α and the first conductor 12 are aligned is the Z direction, and the X direction and Y direction are directions perpendicular to the Z direction.

[0149] (Effect) The inventors have found that, as in this embodiment, by allowing a portion of the first layer 16α and the second layer 16β containing an inorganic compound provided on the surface of the first active material layer 14α and the second active material layer 14β to penetrate between the negative electrode active material particles 14P of the first active material layer 14α and / or the second active material layer 14β, the cycle characteristics during high-temperature use are improved.

[0150] The gaps between the negative electrode active material particles are covered by a portion of the first layer 16α and the second layer 16β, which contain an inorganic material, thereby reducing the surface roughness on the outer surface of the negative electrode 10 and reducing the resistance at the interface between the negative electrode 10 and the separator 20. Furthermore, by filling in the groove-like portions formed between the negative electrode active material particles 14P, current concentration during charging is alleviated and the generation of dendrites can be suppressed, enabling stable cycling even at high temperatures.

[0151] (Method of producing lithium-ion secondary batteries for evaluation: Examples 1 to 22, Comparative Example 1)

[0152] (Example 1: Example in which the first layer is present only in the first active material layer 14α) (Preparation of Positive Electrode) Positive electrode active material particles, a conductive material, and a binder were mixed to prepare a positive electrode mixture. The positive electrode active material was lithium cobalt oxide (LiCoO ２ (hereinafter, abbreviated as LCO when specified) The conductive material was carbon black, and the binder was polyvinylidene fluoride (PVDF). The positive electrode active material particles, conductive material, and binder were in a mass ratio of 96:2:2. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. Then, a 15 μm-thick aluminum foil was applied as a second conductor to one side thereof, with a weight per unit area of ​​approximately 20.0 mg / cm after drying. ２ After coating, the positive electrode slurry was dried at 100°C to remove the solvent, and a positive electrode active material layer was formed on one side of the aluminum foil. After drying, a positive electrode active material layer was applied to the other side of the aluminum foil so that the weight per unit area after drying was about 10.0 mg / cm. ２ After coating, the positive electrode slurry was dried at 100°C to remove the solvent, thereby forming positive electrode active material layers on both sides of the aluminum foil. After forming the positive electrode active material layers on both sides of the second conductor, the positive electrode was obtained by pressing at 1000 kgf / cm.

[0153] (Preparation of Negative Electrode) Negative electrode active material particles, a conductive material, and a binder were mixed to prepare a negative electrode mixture. The negative electrode active material was graphite, and the binder was polyvinylidene fluoride (PVDF). The mass ratio of the negative electrode active material particles to the binder was 95:5. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode slurry. Then, a copper foil with a thickness of 10 μm was applied as a first conductor to one side thereof, with a weight per unit area of ​​approximately 6.0 mg / cm after drying. ２ After coating, the negative electrode slurry was dried at 100°C to remove the solvent, forming a first active material layer on one side of the copper foil. After drying, the other side of the copper foil was coated with a first active material layer having a weight per unit area of ​​about 10.0 mg / cm after drying. ２ The negative electrode slurry was applied so that the thickness of the first active material layer was approximately 50 μm. After application, the negative electrode slurry was dried at 100° C. to remove the solvent, and a first active material layer was formed on both sides of the copper foil and on both sides of the first conductor.

[0154] (Preparation of Slurry for First Layer) Inorganic particles and a binder were mixed to prepare a composite material for the first layer. The inorganic particles were alumina (Al ２ O ３ The inorganic particles and the binder were mixed in a mass ratio of 95:5. This first layer composite was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a first layer slurry.

[0155] The obtained first layer slurry was applied to one surface of the first active material layer formed on the first conductor using an applicator to a thickness of 30 μm. After application, the coating was dried under reduced pressure at 90° C. for 12 hours. After drying under reduced pressure, the coating was pressed at 300 kgf / cm to obtain the negative electrode of Example 1.

[0156] (Cross-sectional SEM Observation of Negative Electrode) Cross-sectional observation of the negative electrode was performed using a cross-sectional SEM image of the obtained negative electrode. Cross-sectional SEM observation was performed on five fields of the obtained negative electrode, and the average thickness Tav of the first layer and the second layer, the average thickness Uav of the first portion, the average thickness Hav of the second portion, the average particle diameter Rav and Hav / Rav of the active material, and the state of the first layer and second layer regions in the negative electrode were observed.

[0157] As a result of cross-sectional SEM observation, it was observed in one cross-sectional image that the first layer 16α had penetrated into the first active material layer 14α to form the second portion 16αB. In the negative electrode of Example 1, the first layer 16α had penetrated in a manner that covered the portion of the outermost particle closest to the first conductor (wound up to the back).

[0158] Similarly, cross-sectional SEM observation was performed on four different fields of view from the negative electrode, and Tav, Uav, Hav, and Hav / Rav were calculated for each of the five images, and the average value of the five fields of view was calculated.

[0159] The results of cross-sectional SEM observations of the following examples and comparative examples are also shown in the table. In Example 10, the average thickness of the second part was almost zero, but some second parts were present. In Example 9, the average thickness of the second part was almost zero, but at least one part where the second part extended to a position exceeding half the particle diameter was confirmed.

[0160] (Preparation of Lithium-ion Secondary Battery for Evaluation) The prepared negative and positive electrodes were punched into predetermined rectangular shapes (negative electrode: 19 mm x 23 mm, positive electrode: 18 mm x 22 mm), and alternately stacked with 25 μm thick polypropylene separators interposed therebetween. Five negative electrodes and four positive electrodes were stacked to prepare a laminate. In order to connect the terminal electrodes to both the positive and negative electrodes, a 1 mm wide uncoated portion was provided at the end where the positive electrode active material layer and the first active material layer were not formed, and a nickel negative electrode lead was attached to the uncoated portion of the negative electrode where the first active material layer was not provided. Meanwhile, for the positive electrode, an aluminum positive electrode lead was attached to the uncoated portion of the positive electrode where the positive electrode active material layer was not provided using an ultrasonic fusion machine.

[0161] The laminate was inserted into an exterior case made of aluminum laminate film and heat-sealed except for one peripheral opening to form an opening. A nonaqueous electrolyte solution was poured into the exterior case. The nonaqueous electrolyte solution was prepared by dissolving 1.5 mol / L of lithium hexafluorophosphate (LiPF6) in a solvent containing equal amounts of ethylene carbonate (EC) and propylene carbonate (PC). The remaining opening was then heat-sealed while reducing the pressure using a vacuum sealer, producing a lithium-ion secondary battery for evaluation according to the example.

[0162] (Battery Evaluation: 85°C Cycle Characteristics) The cycle characteristics of the fabricated lithium ion secondary battery for evaluation were evaluated in an environment of 85°C using a secondary battery charge / discharge tester (manufactured by Hokuto Denko Corporation). The cycle characteristics were evaluated by repeating 500 charge / discharge cycles of constant current / constant voltage charging at 0.5 C to 4.35 V and constant current discharging at 1 C to 2.8 V. The ratio of the discharge capacity after 500 cycles to the discharge capacity of the first cycle was defined as the capacity retention rate. The capacity retention rate relative to the initial capacity is the discharge capacity at the 500th cycle when the discharge capacity at the initial (first) cycle is defined as 100%.

[0163] (Production of Negative Electrodes According to Examples 2 to 9) Negative electrodes of Examples 2 to 9 were produced under the same conditions as in Example 1, except that the time for drying under reduced pressure after applying the first layer slurry was changed.

[0164] The reduced pressure drying time was 10 hours in Example 2, 8 hours in Example 3, 5 hours in Example 4, 3 hours in Example 5, 1 hour in Example 6, 30 minutes in Example 7, 10 minutes in Example 8, and 5 minutes in Example 9.

[0165] In Examples 4 to 9, in order to completely remove the solvent component in the first layer, additional drying was carried out in the air at 100° C. after drying under reduced pressure.

[0166] (Production of Negative Electrode of Example 10) The negative electrode of Example 10 was produced under the same conditions as in Example 1, except that after applying the first layer slurry, drying was not performed under reduced pressure but was performed in the air at 100°C.

[0167] (Production of Negative Electrode According to Comparative Example 1) The negative electrode of Comparative Example 1 was produced under the same conditions as in Example 10, except that the first layer slurry was not applied.

[0168] (Production of negative electrode according to comparative example 2: first layer present but not penetrated due to application after pressing) The slurry for the first layer was applied to one surface of the first active material layer of the negative electrode (after pressing) produced in comparative example 1, and dried under reduced pressure at 90°C for 12 hours to produce the negative electrode of comparative example 2.

[0169] (Production of Negative Electrode of Example 11: Example in which the First Layer Exists on the First Active Material Layer and the Second Layer Exists on the Second Active Material Layer) The slurry for the first layer was applied to one surface of the first active material layer formed on the first conductor using an applicator, with the thickness adjusted to 20 μm. After application, the slurry was dried under reduced pressure at 90° C. for 3 hours. After drying under reduced pressure, additional drying was performed in the air at 100° C. to remove the solvent component in the first layer. In other words, the drying conditions for the first layer were the same as those in Example 5.

[0170] The first layer slurry was applied to the second active material layer (the back surface of the current collector) using an applicator to a thickness of 20 μm. After application, the slurry was dried under reduced pressure at 90° C. for 12 hours. The negative electrode of Example 11 was then obtained by pressing at 300 kgf / cm, which included a second layer in addition to the first layer.

[0171] (Production of Negative Electrodes According to Examples 12 to 19) Negative electrodes according to Examples 12 to 20 were produced under the same conditions as in Example 11, except that the time for vacuum drying was changed when the second layer was produced on the second active material layer.

[0172] The reduced pressure drying time was 10 hours in Example 12, 8 hours in Example 13, 5 hours in Example 14, 3 hours in Example 15, 1 hour in Example 16, 30 minutes in Example 17, 10 minutes in Example 18, and 5 minutes in Example 19.

[0173] In Examples 14 to 19, in order to completely remove the solvent component in the second layer, additional drying was carried out in the air at 100° C. after drying under reduced pressure.

[0174] (Production of Negative Electrode of Example 20) The negative electrode of Example 20 was produced under the same conditions as in Example 11, except that drying under reduced pressure was not performed when producing the second layer, but drying was performed in the air at 100°C.

[0175] (Production of Negative Electrode of Example 22) The slurry for the first layer was applied onto the second active material layer of the negative electrode (after pressing) produced in Example 21, and the slurry was dried under reduced pressure at 90°C for 12 hours to produce a second layer, thereby producing the negative electrode of Example 22.

[0176] Examples 23 to 32: Examples Related to Wound Body (Basic Method for Producing Lithium-Ion Secondary Batteries for Evaluation: Examples 23 to 32) The prepared negative electrode and positive electrode were punched into predetermined long shapes (negative electrode: 19 mm x 160 mm, positive electrode: 18 mm x 200 mm), and two 25 μm thick polypropylene separators were placed on both sides of the negative electrode. The positive electrode was laminated on one side of the separator. At this time, an uncoated portion without an active material layer was formed at the end of the negative electrode, and a nickel negative electrode lead was attached to the uncoated portion of the negative electrode without the negative electrode active material layer. Meanwhile, for the positive electrode, an uncoated portion without a positive electrode active material layer was formed at both ends of the positive electrode, and an aluminum positive electrode lead was attached to one end of the uncoated portion of the positive electrode using an ultrasonic fusion machine. A wound body was produced by winding the laminate with the surface of the negative electrode without the positive electrode facing inward. At this time, the stacking was carried out so that the end with the negative electrode lead was on the inner side of the winding and the end with the positive electrode lead was on the outer side of the winding.

[0177] (Production of Negative Electrode of Example 23) A negative electrode produced under the same conditions as in Example 16 was used, and the wound body of Example 23 was produced by winding the negative electrode so that the first layer of the negative electrode was on the inner side of the winding and the second layer was on the outer side of the winding.

[0178] (Production of Negative Electrode According to Example 24) A wound body of Example 24 was produced under the same conditions as in Example 23, except that the second layer of the negative electrode was wound so as to be on the inner side of the winding and the first layer was wound so as to be on the outer side of the winding.

[0179] (Production of Negative Electrode of Example 25) A negative electrode produced under the same conditions as in Example 15, except that the thickness of the applied first layer slurry was adjusted to 10 μm using an applicator when forming the first and second layers, was used, and the negative electrode was wound so that the first layer of the negative electrode was on the inner side of the winding and the second layer was on the outer side of the winding, to produce a wound body of Example 25.

[0180] (Production of Negative Electrode of Example 26) The wound body of Example 24 was produced under the same conditions as in Example 25, except that the second layer of the negative electrode was wound so as to be on the inner side of the winding and the first layer was wound so as to be on the outer side of the winding.

[0181] (Production of Negative Electrode of Example 27) A negative electrode produced under the same conditions as in Example 15, except that the thickness of the applied first layer slurry was adjusted to 5 μm using an applicator when forming the first and second layers, was used, and the negative electrode was wound so that the first layer of the negative electrode was on the inner side of the winding and the second layer was on the outer side of the winding, to produce a wound body of Example 27.

[0182] (Production of Negative Electrode of Example 28) The wound body of Example 27 was produced under the same conditions as in Example 27, except that the second layer of the negative electrode was wound so as to face the inner side of the winding and the first layer was wound so as to face the outer side of the winding.

[0183] (Production of Negative Electrode of Example 29) A negative electrode produced under the same conditions as in Example 15, except that when forming the first layer, the thickness of the slurry for the first layer to be applied was adjusted to a thickness of 10 μm using an applicator, and when forming the second layer, the thickness of the slurry for the first layer to be applied was adjusted to a thickness of 5 μm using an applicator, was used, and the negative electrode was wound so that the first layer of the negative electrode was on the inner side of the winding and the second layer was on the outer side of the winding, to produce a wound body of Example 29.

[0184] (Production of negative electrode according to example 30) A wound body of example 30 was produced under the same conditions as in example 29, except that the second layer of the negative electrode was wound so as to be on the inner side of the winding and the first layer was wound so as to be on the outer side of the winding.

[0185] (Production of Negative Electrode According to Example 31) A negative electrode produced under the same conditions as in Example 15, except that when forming the first layer, the thickness of the slurry for the first layer to be applied was adjusted to a thickness of 5 μm using an applicator, and when forming the second layer, the thickness of the slurry for the first layer to be applied was adjusted to a thickness of 8 μm using an applicator, was used, and the negative electrode was wound so that the first layer of the negative electrode was on the inner side of the winding and the second layer was on the outer side of the winding, to produce a wound body of Example 31.

[0186] (Production of Negative Electrode According to Example 32) A wound body of Example 32 was produced under the same conditions as in Example 31, except that the second layer of the negative electrode was wound so that it was on the inner side of the winding and the first layer was wound so that it was on the outer side of the winding. The conditions and results are shown in Tables 1 to 3.

[0187]

[0188]

[0189]

[0190] 10...negative electrode, 12...first conductor, 12a...first surface, 12b...second surface, 14α...first active material layer, 14β...second active material layer, 14P1 (14P)...negative electrode active material particle (first negative electrode active material particle), 14P2 (14P)...negative electrode active material particle (second negative electrode active material particle), 16α...first layer, 16αA...first part, 16αB...second part, 16β...second layer, 16βA...third part, 16βB...fourth part, 16αAS, 16αBS, 16αBS, 16βBS...surface, 20...separator, 30...positive electrode, 90...laminated body, 90C...curved portion, 90M...flat portion, 100...storage element, dp...particle size, VV...gap.

Claims

1. An energy storage element comprising: a negative electrode having: a first conductor having a first surface and a second surface facing a side opposite to the first surface; a first active material layer provided on the first surface of the first conductor and containing a plurality of first negative electrode active material particles; and a first layer containing an inorganic material, the first layer having a first portion provided across two or more first negative electrode active material particles exposed on the side of the first active material layer opposite the first conductor, and a second portion extending from the first portion between the first negative electrode active material particles of the first active material layer.

2. The energy storage element described in claim 1, wherein in a cross-sectional image taken along a first direction in which the first active material layer and the first conductor are aligned, the length of the surface of the first layer facing the first conductor is greater than the length of the surface of the first layer facing away from the first conductor.

3. A storage element as described in claim 1 or 2, wherein the second portion of the first layer extends from the first portion to a position exceeding half the particle size of at least one of the first negative electrode active material particles exposed on the side opposite the first conductor in a first direction in which the first active material layer and the first conductor are aligned.

4. A storage element as described in claim 1 or 2, wherein the second portion of the first layer extends from the first portion to a position covering a portion of at least one of the first negative electrode active material particles exposed on the side opposite to the first conductor in a first direction in which the first active material layer and the first conductor are aligned, the portion being closest to the first conductor.

5. The energy storage element according to claim 1 or 2, wherein 0.3≦Hav / Rav≦3.0 is satisfied, where Hav is the average thickness of the second portion of the first layer in a cross-sectional image taken along a first direction in which the first active material layer and the first conductor are aligned, and Rav is the average particle size of a plurality of first negative electrode active material particles contained in the first active material layer.

6. The energy storage element according to claim 5, wherein the relationship 0.3≦Hav / Rav≦3.0 is satisfied in the multiple cross-sectional images.

7. The energy storage element according to claim 5, wherein 0.5≦Hav / Rav≦2.0 is satisfied.

8. The energy storage element according to claim 1 or 2, wherein the inorganic material is an inorganic compound.

9. The energy storage element according to claim 8, wherein the inorganic compound includes aluminum oxide.

10. The energy storage element according to claim 1 or 2, wherein the first layer further contains an organic compound.

11. The energy storage element according to claim 10, wherein the organic compound includes a polymer compound containing fluorine.

12. The electric storage element according to claim 11, wherein the polymer compound is polyvinylidene fluoride.

13. The energy storage element according to claim 10, wherein a mass ratio of the inorganic material to the organic compound is 1:1 to 100:

1.

14. The energy storage element according to claim 1 or 2, wherein the negative electrode active material particles of the first active material layer contain at least one of a carbon material, a metal, a metal oxide, a semi-metal, and a semi-metal oxide.

15. The energy storage element according to claim 1 or 2, wherein the negative electrode further comprises: a second active material layer provided on the second surface of the first conductor and containing a plurality of second negative electrode active material particles; and a second layer containing an inorganic material, the second layer having a third portion provided across two or more of the second negative electrode active material particles exposed on the side of the second active material layer opposite the first conductor, and a fourth portion penetrating from the third portion between the second negative electrode active material particles of the second active material layer.

16. The energy storage element described in claim 15, wherein the third portion of the second layer extends from the third portion to a position that exceeds half the particle size of at least one of the second negative electrode active material particles exposed on the side opposite the first conductor in a second direction in which the second active material layer and the first conductor are aligned.

17. The energy storage element described in claim 15, wherein the third portion of the second layer extends from the third portion to a position covering a portion of at least one of the second negative electrode active material particles exposed on the side opposite to the first conductor in a second direction in which the second active material layer and the first conductor are aligned, the portion being closest to the first conductor.

18. An energy storage element as described in claim 15, wherein a thickness of a first portion of the first layer in a first direction in which the first active material layer and the first conductor are aligned is different from a thickness of a third portion of the second layer in a second direction in which the second active material layer and the first conductor are aligned.

19. An energy storage element as described in claim 15, wherein the thickness of a first portion of the first layer in a first direction in which the first active material layer and the first conductor are aligned is greater than the thickness of a third portion of the second layer in a second direction in which the second active material layer and the first conductor are aligned.

20. The energy storage element according to claim 1 or 2, further comprising a positive electrode and a separator disposed between the negative electrode and the positive electrode.

21. The energy storage element according to claim 15, further comprising a positive electrode and a separator disposed between the negative electrode and the positive electrode, wherein a laminate having the negative electrode, the separator, and the positive electrode is wound.

22. The energy storage element according to claim 21, wherein the laminate is wound so that the second layer is located on the inner side than the first layer.

23. The energy storage element according to claim 22, wherein the thickness of the second layer is smaller than the thickness of the first layer.

24. The energy storage element described in claim 21, wherein the laminate is wound so as to have alternating flat portions and curved portions, and the thickness of a first layer of the curved portions is thinner than the thickness of the first layer of the flat portions.