Lithium ion secondary battery

Abstract

To provide a lithium ion secondary battery excellent in adhesion between an electrode mixture layer and an electron insulating layer provided thereon.SOLUTION: A lithium-ion secondary battery of the present disclosure includes a cathode including a cathode current collector, a cathode mixture layer provided on the cathode current collector, and a cathode electron insulating layer provided on the cathode mixture layer, and an anode including an anode current collector, an anode mixture layer provided on the anode current collector, and an anode electron insulating layer provided on the anode mixture layer. The unevenness height of the interface between the positive electrode mixture layer and the positive electrode electron-insulating layer is 2 μm or more. An unevenness height of an interface between the negative electrode mixture layer and the negative electrode electronic insulating layer is 2 μm or more, a thickness of the positive electrode electronic insulating layer is smaller than that of the positive electrode mixture layer, and a thickness of the negative electrode electronic insulating layer is smaller than that of the negative electrode mixture layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a lithium ion secondary battery. [Background technology]

[0002] Fuel economy and environmental regulations are becoming increasingly stringent in the automotive industry. To comply with these regulations, attention is being paid to the development of electric vehicles, which are battery-powered and emit no carbon dioxide, and fuel cell vehicles, which use hydrogen as a fuel source. However, electric vehicles and fuel cell vehicles have various problems, such as insufficient infrastructure. For this reason, plug-in hybrid electric vehicles (PHEVs) and hybrid electric vehicles (HEVs), which are powered by both an internal combustion engine and batteries and emit less carbon dioxide, are becoming leading candidates for complying with fuel economy and environmental regulations.

[0003] Lithium-ion secondary batteries are used in PHEVs or HEVs. Patent Document 1 describes a lithium-ion secondary battery including an electrode having an electrode foil, a mixture layer provided on the surface of the electrode foil, and an insulating layer containing ceramic particles provided on the surface of the mixture layer, in which a plurality of pores with a diameter of 2.5 μm or more are provided on the surface of the mixture layer facing the interface between the insulating layer and the mixture layer.

[0004] Patent Document 2 describes a method for manufacturing a lithium-ion secondary battery that includes a ceramic separator layer instead of a conventional porous polymer separator such as a stretched film. The manufactured lithium-ion secondary battery includes a battery element including a positive electrode, a negative electrode, a ceramic separator layer disposed between the positive electrode and the negative electrode, and a lithium ion conductive nonaqueous electrolyte, and an exterior body that houses the battery element. The ceramic separator layer is formed by applying a ceramic slurry containing insulating inorganic fine particles to the surface of at least one of the positive electrode and the negative electrode, and drying the applied slurry. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2019 / 244401 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-191710 Summary of the Invention [Problem to be solved by the invention]

[0006] The electrode mixture layer expands and contracts due to charging and discharging of a lithium ion secondary battery. The inventors have found through extensive studies that this expansion and contraction may cause separation between the electrode mixture layer and a layer provided thereon.

[0007] Therefore, the present invention provides a lithium ion secondary battery having excellent adhesion between an electrode mixture layer and an electronic insulating layer formed thereon. [Means for solving the problem]

[0008] According to one aspect of the present invention, a positive electrode including a positive electrode current collector, a positive electrode mixture layer provided on the positive electrode current collector, and a positive electrode electronic insulating layer provided on the positive electrode mixture layer; a negative electrode including a negative electrode current collector, a negative electrode mixture layer provided on the negative electrode current collector, and a negative electrode electronic insulating layer provided on the negative electrode mixture layer; Equipped with the height of the unevenness at the interface between the positive electrode mixture layer and the positive electrode electronic insulating layer is 2 μm or more, the height of the unevenness at the interface between the negative electrode mixture layer and the negative electrode electronic insulating layer is 2 μm or more, the positive electrode electronic insulating layer has a thickness smaller than that of the positive electrode mixture layer, A lithium ion secondary battery is provided in which the negative electrode electronic insulating layer has a thickness smaller than that of the negative electrode mixture layer. [Effects of the Invention]

[0009] In the lithium ion secondary battery of the present disclosure, the adhesion between the mixture layer and the structure provided thereon is good. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of the appearance of a lithium ion secondary battery according to one embodiment. [Figure 2] FIG. 2 is an exploded perspective view of a lithium ion secondary battery according to one embodiment. [Figure 3] FIG. 3 is a perspective view showing a part of the wound group in development. [Figure 4] FIG. 4 is a schematic diagram of a positive electrode and a negative electrode of a lithium ion secondary battery according to one embodiment. [Figure 5] FIG. 5 is a schematic enlarged cross-sectional view of the interface between the positive electrode material mixture layer and the positive electrode electronic insulating layer and its vicinity in a lithium ion secondary battery according to one embodiment. [Figure 6] FIG. 6 is an enlarged view of a die head and a back roller used in manufacturing a positive electrode. [Figure 7] FIG. 7 is an example of a cross-sectional SEM image of the interface between the negative electrode mixture layer and the negative electrode electronic insulating layer and its vicinity. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, identical components or components having similar functions are denoted by the same reference numerals, and repeated description may be omitted. Furthermore, the dimensional ratios in the drawings may differ from the actual ratios for the sake of convenience, and some components may be omitted from the drawings. Furthermore, in this application, a numerical range expressed using the symbol "to" includes the numerical values ​​before and after the symbol "to" as the lower and upper limits, respectively.

[0012] 1 and 2, a lithium-ion secondary battery 100 according to an embodiment includes a battery can 1 and a battery lid 6. The battery can 1 has a rectangular bottom surface 1d, side surfaces including a pair of opposing wide side surfaces 1b with relatively large areas and a pair of opposing narrow side surfaces 1c with relatively small areas, rising from the bottom surface 1d, and an opening 1a that opens upward at the upper ends of the wide side surfaces 1b and the narrow side surfaces 1c. Here, upward refers to the Z direction in FIGS. 1 and 2.

[0013] The opening 1a of the battery can 1 is sealed by a battery lid 6. The battery lid 6 has a substantially rectangular flat plate shape, and is welded to close the opening 1a of the battery can 1, thereby sealing the battery can 1.

[0014] A gas release valve 10 is integrally provided on the battery lid 6. When the pressure inside the battery can 1 increases, the gas release valve 10 opens, allowing gas to be released from inside the battery can 1, thereby reducing the pressure inside the battery can 1. This ensures the safety of the lithium-ion secondary battery 100.

[0015] A liquid filling port 9 is formed in the battery lid 6 for filling the electrolyte into the battery can 1. The liquid filling port 9 is sealed by a liquid filling plug 11 after the electrolyte has been filled into the battery can 1. The liquid filling plug 11 is joined to the battery lid 6 by laser welding to seal the liquid filling port 9 and hermetically seal the lithium ion secondary battery 100.

[0016] The battery lid 6 is further provided with a positive electrode side through-hole 46 and a negative electrode side through-hole 26 .

[0017] A positive electrode external terminal 14 and a negative electrode external terminal 12 are provided above the battery lid 6. A positive electrode current collector plate 44 and a negative electrode current collector plate 24 are provided below the battery lid 6 and inside the battery can 1.

[0018] The positive external terminal 14 and the positive current collector plate 44 may be made of, for example, an aluminum alloy, and the negative external terminal 12 and the negative current collector plate 24 may be made of, for example, a copper alloy.

[0019] The positive electrode external terminal 14 and the negative electrode external terminal 12 each have a welded joint to which a bus bar or the like is welded. The welded joint has a rectangular block shape that protrudes upward from the battery lid 6. The lower surface of the welded joint faces the surface of the battery lid 6, and the upper surface of the welded joint is located at a predetermined height and is approximately parallel to the battery lid 6.

[0020] The positive current collector 44 has a rectangular plate-shaped positive current collector base 41 facing the underside of the battery lid 6, and a positive electrode side connection end 42 extending from a side end of the positive current collector base 41 along the wide side surface 1b of the battery can 1 toward the bottom surface 1d. Similarly, the negative current collector 24 has a rectangular plate-shaped negative current collector base 21 facing the underside of the battery lid 6, and a negative electrode side connection end 22 extending from a side end of the negative current collector base 21 along the wide side surface 1b of the battery can 1 toward the bottom surface 1d. A positive electrode side opening hole 43 and a negative electrode side opening hole 23 are formed in the positive current collector base 41 and the negative current collector base 21, respectively.

[0021] A positive electrode connecting portion 14a and a negative electrode connecting portion 12a are provided so as to protrude from the lower surfaces of the positive electrode external terminal 14 and the negative electrode external terminal 12, respectively. The positive electrode connecting portion 14a and the negative electrode connecting portion 12a are formed integrally with the positive electrode external terminal 14 and the negative electrode external terminal 12, respectively.

[0022] The positive electrode connection portion 14a has a cylindrical shape that can be inserted into the positive electrode side through-hole 46 of the battery lid 6 and the positive electrode side opening hole 43 of the positive electrode current collector base 41. Similarly, the negative electrode connection portion 12a has a cylindrical shape that can be inserted into the negative electrode side through-hole 26 of the battery lid 6 and the negative electrode side opening hole 23 of the negative electrode current collector base 21. The positive electrode connection portion 14a passes through the positive electrode side through-hole 46 of the battery lid 6 and the positive electrode side opening hole 43 of the positive electrode current collector base 41, penetrating the battery lid 6 and the positive electrode current collector base 41. The positive electrode external terminal 14 and the positive electrode current collector 44 are electrically connected and fixed to the battery lid 6 via the positive electrode connection portion 14a. Similarly, the negative electrode connection portion 12a passes through the negative electrode side through-hole 26 of the battery lid 6 and the negative electrode side opening hole 23 of the negative electrode current collector base 21, penetrating the battery lid 6 and the negative electrode current collector base 21. The negative electrode external terminal 12 and the negative electrode current collector plate 24 are electrically connected via a negative electrode connecting portion 12 a and are fixed to the battery lid 6 .

[0023] The positive electrode external terminal 14 is electrically connected to the wound pack 3, which will be described later, via the positive electrode connection portion 14a and the positive electrode current collector plate 44. Similarly, the negative electrode external terminal 12 is electrically connected to the wound pack 3 via the negative electrode connection portion 12a and the negative electrode current collector plate 24. When the lithium ion secondary battery 100 is being charged, electricity is supplied from an external power source to the wound pack 3 via the positive electrode external terminal 14, the positive electrode connection portion 14a, and the positive electrode current collector plate 44, as well as the negative electrode external terminal 12, the negative electrode connection portion 12a, and the negative electrode current collector plate 24. When the lithium ion secondary battery 100 is being discharged, electricity is supplied from the wound pack 3 to an external load via the positive electrode external terminal 14, the positive electrode connection portion 14a, and the positive electrode current collector plate 44, as well as the negative electrode external terminal 12, the negative electrode connection portion 12a, and the negative electrode current collector plate 24.

[0024] In order to electrically insulate the positive electrode current collector 44, the negative electrode current collector 24, the positive electrode external terminal 14, and the negative electrode external terminal 12 from the battery lid 6, a gasket 5 is provided between each of the positive electrode external terminal 14 and the negative electrode external terminal 12 and the battery lid 6, and an insulating plate 7 is provided between each of the positive electrode current collector 44 and the negative electrode current collector 24 and the battery lid 6. Examples of materials for the insulating plate 7 and the gasket 5 include insulating resin materials such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy fluororesin.

[0025] The battery can 1 contains an electrolyte and a wound group 3 .

[0026] The electrolyte is poured into the battery can 1 through a pouring hole 9. As the electrolyte, for example, a non-aqueous electrolyte in which a lithium salt such as lithium hexafluorophosphate (LiPF6) is dissolved in a carbonate ester organic solvent such as ethylene carbonate can be used.

[0027] 3, the wound group 3 has a negative electrode 32 and a positive electrode 34. The negative electrode 32 and the positive electrode 34 are stacked and wound in a flat shape.

[0028] The wound group 3 has a pair of opposing end faces 3a, 3b perpendicular to the winding axis and a side face 3c between the pair of end faces 3a, 3b. The side face 3c has a pair of curved portions with a semicircular cross section that face each other and a flat portion formed continuously between the pair of curved portions. The wound group 3 is placed inside the battery can 1 so that the flat portion of the side face 3c and the wide side face 1b of the battery can 1 are approximately parallel.

[0029] If necessary, a core may be disposed on the innermost periphery of the wound group 3. The core may be formed by winding a resin sheet having higher bending rigidity than both the positive electrode current collector 34a and the negative electrode current collector 32a, which will be described later.

[0030] As shown in FIGS. 3 and 4 , the positive electrode 34 includes a positive electrode current collector 34a, a positive electrode mixture layer 34b provided on the positive electrode current collector 34a, and a positive electrode electronic insulating layer 34d provided on the positive electrode mixture layer 34b. The positive electrode mixture layer 34b is provided on both sides of the positive electrode current collector 34a. The positive electrode electronic insulating layer 34d is provided on each of the positive electrode mixture layers 34b. The negative electrode 32 includes a negative electrode current collector 32a, a negative electrode mixture layer 32b provided on the negative electrode current collector 32a, and a negative electrode electronic insulating layer 32d provided on the negative electrode mixture layer 32b. The negative electrode mixture layer 32b is provided on both sides of the negative electrode current collector 32a. The negative electrode electronic insulating layer 32d is provided on each of the negative electrode mixture layers 32b. In the present application, the positive electrode current collector 34a and the negative electrode current collector 32a may be collectively referred to as current collectors 34a and 32a, the positive electrode mixture layer 34b and the negative electrode mixture layer 32b may be collectively referred to as electrode mixture layers 34b and 32b, and the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may be collectively referred to as electronic insulating layers 34d and 32d.

[0031] The current collectors 34a, 32a are formed from any material that is highly conductive and does not alloy with lithium ions. The current collectors 34a, 32a may be plate-like (sheet-like). The positive electrode current collector 34a may be, for example, aluminum foil. The negative electrode current collector 32a may be, for example, copper foil. One end of the positive electrode current collector 34a is provided with a portion 34c (hereinafter referred to as the "positive electrode current collector exposed portion") that is not covered by either the positive electrode mixture layer 34b or the positive electrode electronic insulating layer 34d. The positive electrode current collector exposed portion 34c is provided on and in the vicinity of the end face 3a of the winding group 3. The positive electrode current collector exposed portion 34c faces the positive electrode side connection end 42 of the positive electrode current collector plate 44 and is electrically connected thereto. Similarly, one end of the negative electrode current collector 32a is provided with a portion 32c (hereinafter referred to as the "negative electrode current collector exposed portion") that is not covered by either the negative electrode mixture layer 32b or the negative electrode electronic insulating layer 32d. The negative electrode current collector exposed portion 32c is provided on the end face 3b of the wound group 3 and in its vicinity. The negative electrode current collector exposed portion 32c faces the negative electrode side connection end 22 of the negative electrode current collector plate 24 and is electrically connected thereto.

[0032] The positive electrode mixture layer 34b is formed of a material represented by the following formula (1): Li 1+X M A O2(1) (In the formula, X satisfies -0.15≦X≦0.15, M A represents an element group including at least one selected from the group consisting of Mn and Al, Ni, and Co. The positive electrode active material is represented by the formula:

[0033] When −0.15≦X≦0.15, the positive electrode active material has high true density and high reversibility.

[0034] M A However, by including at least one selected from the group consisting of Mn and Al in addition to Ni and Co, the positive electrode active material has high thermal stability and high stability in a high potential state, and thus the lithium-ion secondary battery 100 has high safety.

[0035] M A may further include at least one selected from the group consisting of Zr, Ti, Cr, Fe, Cu, Zn, Ge, Sn, Mg, Ag, Ta, Nb, B, P, Ca, Sr, and Ba. A When Zr is contained, the internal resistance of the lithium ion secondary battery 100 at low temperatures is reduced. The content of Zr may be 0.1 to 2.0 mol %, particularly 0.2 to 1.0 mol %, based on the total amount of Ni, Co, Mn, and Al. A The proportion of elements other than Ni, Co, Mn, and Al in all elements constituting the lithium ion secondary battery 100 may be 10 mol % or less, and particularly 3 mol % or less, thereby allowing the lithium ion secondary battery 100 to have a sufficient discharge capacity.

[0036] The amount of each element in the positive electrode active material can be measured by an ICP (Inductive Coupled Plasma) method.

[0037] The positive electrode active material may be in a particulate form. The shape of the particulate positive electrode active material (hereinafter referred to as "positive electrode active material particles") is not particularly limited. For example, the positive electrode active material particles may have a spherical shape and an average particle diameter in the range of 4.5 to 5.5 μm. In the present application, the spherical shape is not limited to a perfect sphere, but also includes approximately spherical shapes such as oblate spheroids, elongated spheroids, and shapes with slight surface irregularities. The average particle diameter of the positive electrode active material particles can be determined by calculating the arithmetic mean of the diameters of circles equivalent to the projected area of ​​100 or more randomly selected positive electrode active material particles based on a microscope image of the positive electrode mixture layer 34b.

[0038] The positive electrode mixture layer 34b may further include a binder, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, polyacrylonitrile, polyvinyl fluoride, polypropylene fluoride, polychloroprene fluoride, butyl rubber, nitrile rubber, styrene butadiene rubber (SBR), polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylic resins, or mixtures thereof.

[0039] The positive electrode mixture layer 34b may further include a conductive agent. A carbon-based material can be used as the conductive agent. The carbon-based material can be crystalline carbon, amorphous carbon, or a mixture thereof. Examples of crystalline carbon include artificial graphite, natural graphite (e.g., flake graphite), or a mixture thereof. Examples of amorphous carbon include carbon black (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, or a mixture thereof).

[0040] The negative electrode mixture layer 32b includes a negative electrode active material. The negative electrode active material includes a carbon-based material capable of inserting and extracting lithium ions, or is essentially made of a carbon-based material. Examples of such carbon-based materials include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon (hard carbon), and easily graphitizable carbon (soft carbon), graphite coated with amorphous carbon, a mixture of graphite and carbon black (e.g., acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black) as a conductive additive, a composite obtained by coating such a mixture with amorphous carbon, a mixture of graphite and non-graphitizable carbon or easily graphitizable carbon, and mixtures thereof. The negative electrode active material may be particulate. The shape of the particulate negative electrode active material (hereinafter referred to as "negative electrode active material particles") is not particularly limited and may be, for example, spherical, flaky, fibrous, or a pulverized form of any of these. In particular, the negative electrode active material particles may have a scale-like shape (which may also be referred to as a flake-like, plate-like, or thin-plate-like shape) and an average particle diameter in the range of 9 to 11 μm. The average particle diameter of the negative electrode active material particles can be determined by calculating the arithmetic mean of the projected area equivalent circle diameters of 100 or more randomly selected negative electrode active material particles based on a microscope observation image of the negative electrode mixture layer 32b.

[0041] The negative electrode mixture layer 32b may further contain a binder. The binder for the negative electrode mixture layer 32b may be the same as the materials exemplified as the binder for the positive electrode mixture layer 34b.

[0042] The negative electrode mixture layer 32b may further contain a dispersant, such as carboxymethyl cellulose (CMC).

[0043] The electronic insulating layers 34d, 32d have the function of preventing a short circuit between the positive electrode mixture layer 34b and the negative electrode mixture layer 32b and the function of conducting ions between the positive electrode mixture layer 34b and the negative electrode mixture layer 32b. The electronic insulating layers 34d, 32d may be porous layers made of an electrically insulating (i.e., electronically insulating and ionically insulating) material. The porous layer can retain an electrolyte in its pores, and ions can be conducted between the positive electrode mixture layer 34b and the negative electrode mixture layer 32b via this electrolyte.

[0044] The porous electronic insulating layers 34d, 32d may also have the function of buffering the expansion and contraction of the electrode mixture layers 34b, 32b that accompany the charge and discharge of the lithium-ion secondary battery 100. The expansion and contraction of the negative electrode mixture layer 32b that accompanies the charge and discharge of the lithium-ion secondary battery 100 is generally greater than that of the positive electrode mixture layer 34b. Therefore, in order to buffer the expansion and contraction of the larger negative electrode mixture layer 32b, the negative electrode electronic insulating layer 32d may have an average pore diameter that is larger than that of the positive electrode electronic insulating layer 34d. In this application, the average pore diameter of the electronic insulating layers 34d, 32d refers to the average value of the volumetric pore diameters measured by mercury intrusion porosimetry.

[0045] The total content of Na and Fe in the electronic insulating layers 34d, 32d may be 300 ppm or less based on the weight of the electronic insulating layers 34d, 32d. The amount of each element contained in the electronic insulating layers 34d, 32d can be measured by an ICP (Inductive Coupled Plasma) method.

[0046] The positive electrode electronic insulating layer 34d may contain positive electrode electronic insulating particles, and the negative electrode electronic insulating layer 32d may contain negative electrode electronic insulating particles. Hereinafter, the positive electrode electronic insulating particles and the negative electrode electronic insulating particles will be collectively referred to as electronic insulating particles. The electronic insulating particles may be electrically insulating particles. Examples of electrically insulating particles include ceramic particles. The ceramic particles may contain at least one selected from the group consisting of alumina (Al2O3), boehmite (Al2O3 hydrate), magnesia (MgO), zirconia (ZrO2), titania (TiO2), iron oxide, silica (SiO2), and barium titanate (BaTiO2), and preferably contain at least one selected from the group consisting of alumina, boehmite, magnesia, zirconia, and titania. The electronic insulating particles may have an average particle diameter in the range of 0.7 to 1.1 μm. The average particle diameter of the electronic insulating particles can be determined by calculating the arithmetic mean of the projected area circle equivalent diameters of 100 or more randomly selected electronic insulating particles based on a microscopic image of the electronic insulating layers 34d and 32d. The electronic insulating particles may contain at least one of 100 to 200 ppm of Na, 50 to 100 ppm of Fe, or 50 to 100 ppm of Ca, based on the weight of the electronic insulating particles.

[0047] The electronic insulating layers 34d and 32d may further include a binder. The binder may be dispersed or dissolved in an aqueous solvent or a non-aqueous solvent (e.g., N-methyl-2-pyrrolidone (NMP)), and may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC).

[0048] The electronic insulating layers 34d, 32d may further contain a dispersant. The dispersant may contain at least one selected from the group consisting of carboxylic acid compounds and phosphoric acid compounds. The carboxylic acid compound or phosphoric acid compound generates anions in the solvent, which can improve the dispersibility of the electronic insulating particles in the solvent due to electrostatic repulsion with the electronic insulating particles. In this application, a carboxylic acid compound refers to a compound having at least one carboxy group or a salt thereof. In this application, a phosphoric acid compound refers to a compound having at least one polar functional group represented by the formula: *-OP(=O)(OR')(OR'') (where * represents a bond to another structural moiety, and R' and R'' each independently represent a hydrogen atom or a monovalent organic group), or a salt thereof.

[0049] The interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode mixture layer 34b has an uneven shape, and the unevenness height is 2 μm or more, preferably in the range of 2 to 4 μm. The interface 32e between the negative electrode electronic insulating layer 32d and the negative electrode mixture layer 32b has an uneven shape, and the unevenness height is 2 μm or more, preferably in the range of 2 to 4 μm. Since the unevenness heights of the interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode mixture layer 34b and the interface 32e between the negative electrode electronic insulating layer 32d and the negative electrode mixture layer 32b are 2 μm or more, the adhesion between the positive electrode electronic insulating layer 34d and the positive electrode mixture layer 34b and the adhesion between the negative electrode electronic insulating layer 32d and the negative electrode mixture layer 32b can be improved. This makes it possible to prevent or reduce peeling of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d from the positive electrode mixture layer 34b and the negative electrode mixture layer 32b, respectively, thereby improving the reliability of the lithium ion secondary battery 100.

[0050] The height of the irregularities at the interface 34e between the positive electrode mixture layer 34b and the positive electrode electronic insulating layer 34d can be controlled, for example, by the particle sizes of the positive electrode active material particles and the positive electrode electronic insulating particles. As shown in FIG. 5, when the average particle size of the positive electrode active material particles 34bp is larger than the average particle size of the positive electrode electronic insulating particles 34dp, the positive electrode electronic insulating particles 34dp penetrate into the gaps between the positive electrode active material particles 34bp, resulting in an irregular shape at the interface 34e between the positive electrode mixture layer 34b and the positive electrode electronic insulating layer 34d. For example, by using spherical positive electrode active material particles 34bp with an average particle size in the range of 4.5 to 5.5 μm and positive electrode electronic insulating particles 34dp with an average particle size in the range of 0.7 to 1.1 μm, the height of the irregularities at the interface 34e between the positive electrode mixture layer 34b and the positive electrode electronic insulating layer 34d can be set to 2 μm or more, preferably in the range of 2 to 4 μm.

[0051] The height of the irregularities at the interface 32e between the negative electrode mixture layer 32b and the negative electrode electronic insulating layer 32d can also be controlled by the particle sizes of the negative electrode active material particles and the negative electrode electronic insulating particles. For example, by using scale-like negative electrode active material particles having an average particle size in the range of 9 to 11 μm and negative electrode electronic insulating particles having an average particle size in the range of 0.7 to 1.1 μm, the height of the irregularities at the interface 32e between the negative electrode mixture layer 32b and the negative electrode electronic insulating layer 32d can be set to 2 μm or more, preferably in the range of 2 to 4 μm.

[0052] In the present application, the height of the unevenness at the interface 34e, 32e between the electronic insulating layer 34d, 32d and the electrode mixture layer 34b, 32b is measured as follows: Cross-sectional SEM images of three arbitrary locations on the positive electrode 34 or the negative electrode 32 are obtained using a scanning electron microscope (SEM), and in each cross-sectional SEM image, the distances from any 10 or more points on the interface 34e, 32e between the electronic insulating layer 34d, 32d and the electrode mixture layer 34b, 32b to a predetermined reference plane are measured (for example, the distances from any 10 or more points on the interface 34e, 32e between the electronic insulating layer 34d, 32d and the electrode mixture layer 34b, 32b to the surface 34f, 32f of the electronic insulating layer 34d, 32d, i.e., the thickness of any 10 or more points on the electronic insulating layer 34d, 32d). The standard deviation of the obtained distance values ​​is defined as the unevenness height of the interfaces 34e, 32e between the electronic insulating layers 34d, 32d and the electrode mixture layers 34b, 32b. Note that the surface 34f of the positive electrode electronic insulating layer 34d and the surface 32f of the negative electrode electronic insulating layer 32d are surfaces facing each other and may be sufficiently flat compared to the interfaces 34e, 32e. For example, the unevenness height of the surfaces 34f, 32f of the electronic insulating layers 34d, 32d may be one-tenth or less of the unevenness height of the interfaces 34e, 32e, respectively.

[0053] The phrase "the interface 34e between the positive electrode electronic insulating layer 34d and the positive electrode mixture layer 34b has an uneven shape" can also be rephrased as "a positive electrode mixed layer containing a positive electrode active material and an electronic insulating material is present between the positive electrode electronic insulating layer 34d and the positive electrode mixture layer 34b." Similarly, the phrase "the interface 32e between the negative electrode electronic insulating layer 32d and the negative electrode mixture layer 32b has an uneven shape" can also be rephrased as "a negative electrode mixed layer containing a negative electrode active material and an electronic insulating material is present between the negative electrode electronic insulating layer 32d and the negative electrode mixture layer 32b." The thickness of the positive electrode mixed layer is 2 μm or more, preferably in the range of 2 to 4 μm. The thickness of the negative electrode mixed layer is 2 μm or more, preferably in the range of 2 to 4 μm. The thicknesses of the positive electrode mixed layer and the negative electrode mixed layer can be measured in the same manner as the unevenness height of the interfaces 34e, 32e between the electronic insulating layers 34d, 32d and the electrode mixture layers 34b, 32b described above.

[0054] The positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may be in contact with each other. Preferably, the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may be in contact without being fixed to each other. By not fixing the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d to each other, stress caused by expansion and contraction of the negative electrode mixture layer 32b and the positive electrode mixture layer 34b due to charging and discharging of the lithium-ion secondary battery 100 can be alleviated, and dendrites that could cause a short circuit between the positive electrode mixture layer 34b and the negative electrode mixture layer 32b can be prevented or reduced from growing through the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d.

[0055] The peel strength of the positive electrode electronic insulating layer 34d from the positive electrode mixture layer 34b and the peel strength of the negative electrode electronic insulating layer 32d from the negative electrode mixture layer 32b may be greater than the peel strength of the positive electrode electronic insulating layer 34d from the negative electrode electronic insulating layer 32d. The peel strengths can be measured, for example, by a 180° tape peel test in accordance with JIS C 0806-3 1999.

[0056] An example of a method for manufacturing a positive electrode 34 will be described. Positive electrode active material particles, and optionally a conductive agent and a binder, are dispersed in a solvent to prepare a positive electrode mixture slurry. Positive electrode electronic insulating particles, and optionally a binder and a dispersant, are dispersed in a solvent to prepare a positive electrode electronic insulating material slurry. The positive electrode mixture slurry and the positive electrode electronic insulating material slurry are simultaneously applied to a positive electrode current collector 34a. For example, a die head 50 as shown in FIG. 6 is used to simultaneously apply the positive electrode mixture slurry and the positive electrode electronic insulating material slurry to a positive electrode current collector 34a. The die head 50 includes an outlet block 47, a three-dimensional shim 48, and an inlet block 49. A manifold 52 for a positive electrode electronic insulating material slurry and a manifold 51 for a positive electrode mixture layer slurry are provided inside the die head 50. The positive electrode mixture slurry and the positive electrode electronic insulating material slurry are simultaneously discharged from the manifolds 52 and 51 toward the positive electrode current collector 34a being conveyed along the back rollers 56. This forms a positive electrode mixture slurry layer 33b and a positive electrode electronic insulating material slurry layer 33d. Next, the solvent contained in the positive electrode mixture slurry layer 33b and the positive electrode electronic insulating material slurry layer 33d is evaporated in a drying oven or the like, thereby drying the positive electrode mixture slurry layer 33b and the positive electrode electronic insulating material slurry layer 33d. This forms a positive electrode mixture layer 34b and a positive electrode electronic insulating layer 34d on one surface of the positive electrode current collector 34a. The positive electrode mixture layer 34b and the positive electrode electronic insulating layer 34d are similarly formed on the other surface of the positive electrode current collector 34a. Next, the current collector 34a, the positive electrode mixture layer 34b, and the positive electrode electronic insulating layer 34d are press-formed. Specifically, a laminate including the current collector 34a, the positive electrode mixture layer 34b, and the positive electrode electronic insulating layer 34d is sandwiched between rollers heated to 60 to 120° C. and pressure is applied. The laminate is then slit to a predetermined width, thereby obtaining the positive electrode 34.

[0057] The negative electrode 32 can be manufactured in the same manner as the positive electrode 34. Additionally, the positive electrode 34 and the negative electrode 32 may be manufactured in a continuous process using an unwinding roller and a winding roller.

[0058] The height of the unevenness at the interface 34e between the positive electrode mixture layer 34b and the positive electrode electronic insulating layer 34d can be controlled by the particle sizes of the positive electrode active material particles and the positive electrode electronic insulating particles, as well as by the type and viscosity of the solvent for the positive electrode mixture slurry and the positive electrode electronic insulating material slurry. Similarly, the height of the unevenness at the interface 32e between the negative electrode mixture layer 32b and the negative electrode electronic insulating layer 32d can be controlled by the type and viscosity of the solvent for the negative electrode mixture slurry and the negative electrode electronic insulating material slurry.

[0059] The average pore size of the electronic insulating layers 34d, 32d can be controlled by the particle size of the electronic insulating particles, the pressing pressure during pressing, etc. Specifically, the higher the pressing pressure, the smaller the average pore size, and the smaller the particle size of the electronic insulating particles, the smaller the average pore size.

[0060] FIG. 7 shows an example of a cross-sectional SEM image of the interface 32e between the negative electrode mixture layer 32b and the negative electrode electronic insulating layer 32d and its vicinity. In this example, the negative electrode mixture layer 32b and the negative electrode electronic insulating layer 32d were formed by simultaneously applying a negative electrode mixture slurry and a negative electrode electronic insulating material slurry to a negative electrode current collector. The cross-sectional SEM image was used to determine the standard deviation of the thickness of the negative electrode electronic insulating layer 32d, thereby determining the unevenness height of the interface 32e between the negative electrode mixture layer 32b and the negative electrode electronic insulating layer 32d. As a result, the unevenness height of the interface 32e was 2.4 μm. On the other hand, when the negative electrode mixture layer and the negative electrode electronic insulating layer were formed by applying and drying the negative electrode mixture slurry on the negative electrode current collector and then applying and drying the negative electrode electronic insulating material slurry thereon, the unevenness height of the interface between the negative electrode mixture layer and the negative electrode electronic insulating layer, determined in the same manner as above, was 0.9 μm.

[0061] The present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as defined in the claims. Examples of modified embodiments that fall within the scope of the present invention are given below.

[0062] In one variant of the present invention, the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d are each a layer containing a solid electrolyte (i.e., an electronically insulating and ionically conductive material). A lithium-ion secondary battery according to this variant does not need to contain an electrolyte solution, and therefore can have high safety. In this variant, the electronically insulating particles contained in the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may be solid electrolyte particles. A solid electrolyte can be easily formed by press molding. Therefore, it is not essential that the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d contain a binder and a dispersant.

[0063] Examples of solid electrolytes include sulfide-based solid electrolytes, such as Li 10 GeP2S 12 , Li6PS5Cl, Li2S-P2S5-based glass, Li2S-SiS2-based glass, Li2S-P2S5-GeS2-based glass, Li2S-B2S3-based glass, oxide-based solid electrolytes, for example, Li7La3Zr2O 12 , LiLaTiO3, LiTi(PO4)3, LiGe(PO4)3, and complex hydride-based solid electrolytes such as LiBH4-LiI, LiBH4-LiNH2, and mixtures of two or more thereof.

[0064] In this modified embodiment, at least one of the electrode mixture layers 34b, 32b may further contain a solid electrolyte in addition to the electrode active material and optional binders, conductive agents, and dispersants, thereby improving the ionic conductivity of the electrode mixture layers 34b, 32b.

[0065] At least one of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may have a multilayer structure including two or more electronic insulating layers. For example, at least one of the positive electrode electronic insulating layer 34d and the negative electrode electronic insulating layer 32d may include a porous layer made of an electrically insulating material provided on an electrode mixture layer, and a layer containing a solid electrolyte provided on this porous layer. Such a multilayer structure can improve electronic insulation.

[0066] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety. [Explanation of symbols]

[0067] 32 Negative electrode 32a Negative electrode current collector 32b Negative electrode mixture layer 32d Negative electrode electronic insulating layer 32e Interface between the negative electrode mixture layer and the negative electrode electronic insulating layer 34 Positive electrode 34a Positive electrode current collector 34b Positive electrode mixture layer 34d Positive electrode electronic insulating layer 34e Interface between the positive electrode mixture layer and the positive electrode electronic insulating layer 100 Lithium-ion secondary battery

Claims

1. a positive electrode including a positive electrode current collector, a positive electrode mixture layer provided on the positive electrode current collector, and a positive electrode electronic insulating layer provided on the positive electrode mixture layer; a negative electrode including a negative electrode current collector, a negative electrode mixture layer provided on the negative electrode current collector, and a negative electrode electronic insulating layer provided on the negative electrode mixture layer; Equipped with the height of irregularities at the interface between the positive electrode mixture layer and the positive electrode electronic insulating layer is 2 μm or more; the height of irregularities at the interface between the negative electrode mixture layer and the negative electrode electronic insulating layer is 2 μm or more; the positive electrode electronic insulating layer has a thickness smaller than that of the positive electrode mixture layer, the negative electrode electronic insulating layer has a thickness smaller than that of the negative electrode mixture layer.

2. the positive electrode electronic insulating layer has a surface in contact with the negative electrode electronic insulating layer and an interface in contact with the positive electrode mixture layer, the negative electrode electronic insulating layer has a surface in contact with the positive electrode electronic insulating layer and an interface in contact with the negative electrode mixture layer, the height of the irregularities on the surface of the positive electrode electronic insulating layer is one-tenth or less of the height of the irregularities on the interface of the positive electrode electronic insulating layer, 2. The lithium ion secondary battery according to claim 1, wherein the height of the irregularities on the surface of the negative electrode electronic insulating layer is not more than one-tenth of the height of the irregularities on the interface of the negative electrode electronic insulating layer.

3. 3. The lithium ion secondary battery according to claim 1, wherein the positive electrode electronic insulating layer and the negative electrode electronic insulating layer are in contact with each other without being fixed to each other.

4. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the negative electrode electronic insulating layer has an average pore diameter larger than the average pore diameter of the positive electrode electronic insulating layer.

5. the total content of Na and Fe in the positive electrode electronic insulating layer is 300 ppm or less based on the weight of the positive electrode electronic insulating layer, The lithium ion secondary battery according to any one of claims 1 to 4, wherein the total content of Na and Fe in the negative electrode electronic insulating layer is 300 ppm or less based on the weight of the negative electrode electronic insulating layer.

6. the positive electrode electronic insulating layer contains positive electrode electronic insulating particles, The lithium ion secondary battery according to any one of claims 1 to 5, wherein the negative electrode electronic insulating layer contains negative electrode electronic insulating particles.

7. the positive electrode mixture layer contains positive electrode active material particles, The lithium ion secondary battery according to claim 6 , wherein the average particle size of the positive electrode active material particles is larger than the average particle size of the positive electrode electronic insulating particles.

8. 8. The lithium ion secondary battery according to claim 7, wherein the positive electrode active material particles have a spherical shape and an average particle diameter in the range of 4.5 to 5.5 μm.

9. the negative electrode mixture layer contains negative electrode active material particles, The lithium ion secondary battery according to any one of claims 6 to 8, wherein the average particle size of the negative electrode active material particles is larger than the average particle size of the negative electrode electronic insulating particles.

10. 10. The lithium ion secondary battery according to claim 9, wherein the negative electrode active material particles have a scale-like shape and an average particle diameter in the range of 9 to 11 μm.

11. The lithium ion secondary battery according to any one of claims 6 to 10, wherein the positive electrode electronically insulating particles and the negative electrode electronically insulating particles are both electrically insulating particles.

12. The lithium ion secondary battery according to claim 11, wherein the negative electrode electronically insulating particles are ceramic particles having an average particle size in the range of 0.7 to 1.1 μm.

13. The negative electrode electronic insulating particles contain at least one of 100 to 200 ppm of Na, 50 to 100 ppm of Fe, or 50 to 100 ppm of Ca, based on the weight of the negative electrode electronic insulating particles. The lithium ion secondary battery according to claim 11 or 12.

14. The lithium ion secondary battery according to any one of claims 1 to 10, wherein each of the positive electrode electronic insulating layer and the negative electrode electronic insulating layer contains a solid electrolyte.

15. The lithium ion secondary battery according to any one of claims 6 to 10, wherein the positive electrode electronically insulating particles and the negative electrode electronically insulating particles are both solid electrolyte particles.

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