Positive electrode and non-aqueous electrolyte secondary battery

Abstract

This invention relates to a positive electrode and a non-aqueous electrolyte secondary battery. The positive electrode is used in a non-aqueous electrolyte secondary battery. The positive electrode comprises a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer is disposed on the surface of the positive electrode substrate. The positive electrode active material layer comprises a first layer and a second layer. The second layer is disposed between the positive electrode substrate and the first layer. The first layer comprises a first positive electrode active material. The first positive electrode active material comprises first aggregated particles. The second layer comprises a second positive electrode active material. The second positive electrode active material comprises second aggregated particles and single particles. The first aggregated particles and the second aggregated particles are each formed by the aggregation of more than 50 primary particles. The single particles have an arithmetic mean diameter larger than that of the primary particles.

Description

Technical Field

[0001] This technology relates to positive electrode and non-aqueous electrolyte secondary batteries. Background Technology

[0002] Japanese Patent Application Publication No. 2020-087879 discloses a lithium metal composite oxide powder composed of secondary particles formed by the aggregation of primary particles and single particles. Summary of the Invention

[0003] Generally, the positive electrode of a non-aqueous electrolyte secondary battery (hereinafter referred to as "battery") comprises a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer is formed on the surface of the positive electrode substrate.

[0004] The positive electrode active material layer contains the positive electrode active material. In most cases, the positive electrode active material is condensed particles. Condensed particles are secondary particles formed by the aggregation of multiple primary particles.

[0005] One approach proposed is to mix single particles into aggregated particles. Single particles are relatively large primary particles. Single particles can exist independently of aggregated particles. Single particles offer good filling properties. By mixing single particles into aggregated particles, the filling properties of the positive electrode active material layer can be improved. This improved filling properties of the positive electrode active material layer can thus increase the energy density of the battery.

[0006] However, single particles tend to have higher resistivity than condensed particles. By mixing single particles into condensed particles, the resistivity of the positive electrode active material layer tends to increase. This increase in resistivity of the positive electrode active material layer may, for example, reduce the input-output characteristics of the battery.

[0007] The purpose of this technology is to balance the filling capacity and resistivity of the positive electrode active material layer.

[0008] The following describes the structure and effects of this technology. However, the mechanism of action in this specification is speculative. The mechanism of action does not limit the scope of this technology.

[0009] [1] The positive electrode is used in a non-aqueous electrolyte secondary battery. The positive electrode comprises a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer is disposed on the surface of the positive electrode substrate. The positive electrode active material layer comprises a first layer and a second layer. The second layer is disposed between the positive electrode substrate and the first layer. The first layer comprises a first positive electrode active material. The first positive electrode active material comprises a first aggregated particle. The second layer comprises a second positive electrode active material. The second positive electrode active material comprises a second aggregated particle and a single particle. The first aggregated particle and the second aggregated particle are each formed by the aggregation of more than 50 primary particles. The single particle has an arithmetic mean diameter larger than that of the primary particles.

[0010] In this specification, the first condensed particle and the second condensed particle will be collectively referred to as "condensed particles". Furthermore, the second condensed particle may be the same as or different from the first condensed particle.

[0011] The positive electrode active material layer of this technology has a multi-layer structure. That is, the positive electrode active material layer includes a first layer (upper layer) and a second layer (lower layer). Compared with the second layer (lower layer), the first layer (upper layer) is disposed on the surface side of the positive electrode active material layer. According to the new understanding of this technology, the overall resistivity of the positive electrode active material layer tends to be strongly influenced by the resistivity near the surface of the positive electrode active material layer. The first layer (upper layer) is mainly composed of aggregated particles. Aggregated particles can have relatively low resistivity. By making the upper layer mainly composed of aggregated particles, the increase in resistivity associated with mixing with single particles can be mitigated.

[0012] The second layer (lower layer) consists of a mixture of aggregated particles and single particles. By mixing single particles into the lower layer, the increase in resistivity is mitigated, while the filling capacity of the positive electrode active material layer is improved.

[0013] [2] For example, the first condensed particle and the second condensed particle may each have an arithmetic mean diameter larger than that of a single particle.

[0014] By condensing particles into larger particles than single particles, improvements in filling capacity can be expected, for example.

[0015] [3] For example, the following relationship (I) can be satisfied:

[0016] 0.2≦T1 / (T1+T2)≦0.5…(I)

[0017] In the above formula (I), "T1" represents the thickness of the first layer and "T2" represents the thickness of the second layer.

[0018] By satisfying the relationship in equation (I) above, an improvement in the balance between filling properties and resistivity is expected, for example. Hereinafter, "T1 / (T1+T2)" will also be denoted as "thickness ratio" in this specification.

[0019] [4] The non-aqueous electrolyte secondary battery includes the positive electrode described in any one of [1] to [3] above.

[0020] In batteries using this technology, a balance between energy density and input / output characteristics is expected.

[0021] The above and other objects, features, aspects and advantages of this technology will become more apparent from the following detailed description of the technology as understood in conjunction with the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating an example of the configuration of a non-aqueous electrolyte secondary battery in this embodiment.

[0023] Figure 2 This is a schematic diagram illustrating an example of the configuration of the electrode body in this embodiment.

[0024] Figure 3 This is a schematic cross-sectional view illustrating an example of the configuration of the positive electrode in this embodiment.

[0025] Figure 4 Conceptual diagrams for condensed particles and single particles. Detailed Implementation

[0026] The following describes embodiments of this technology (also referred to as "this embodiment" in this specification). However, the following description does not limit the scope of this technology. For example, descriptions related to the effects described in this specification are not limited to the scope of this technology as long as all such effects are achieved.

[0027] <Definitions of terms, etc.>

[0028] In this specification, expressions such as "comprise," "include," "have," and variations thereof [e.g., "be composed of," "encompass," "involve," "contain," "carry," "support," "hold," etc.] are open forms. Open forms may include additional elements beyond the essential elements, or they may not contain any. The expression "consist of" is a closed form. The expression "consist essentially of" is a semi-closed form. A semi-closed form indicates that additional elements may be included beyond the essential elements without hindering the purpose of this technology. For example, elements commonly conceived in the art (e.g., unavoidable impurities) may be included as additional elements.

[0029] In this specification, the expressions “may…” and “can…” are used not in the mandatory sense of “must…” but in the permissible sense of “there is a possibility of…”.

[0030] In this specification, unless otherwise specified, elements represented in the singular form (a, an, the) include elements represented in the plural form. For example, "particle" can mean not only "a single particle" but also "an aggregate of particles (powder, powder, particle swarm)".

[0031] In this specification, numerical ranges such as "10μm to 20μm" and "10~20μm" include both upper and lower limits unless otherwise specified. That is, "10μm to 20μm" and "10~20μm" both represent a numerical range of "above 10μm and below 20μm". Furthermore, any value selected from the numerical range can be set as a new upper and lower limit. For example, a new numerical range can be set by arbitrarily combining values ​​within the numerical range with values ​​described in other parts of this specification, tables, figures, etc.

[0032] In this specification, all numerical values ​​are described using the term "approximately". "Approximately" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​are approximate values ​​that may vary depending on the application of this technology. All numerical values ​​are expressed in significant figures. To account for the number of significant figures, all measured values ​​may be rounded. All numerical values ​​may include errors associated with, for example, detection limits.

[0033] In this specification, when a compound is represented by a stoichiometric formula such as "LiCoO2", the stoichiometric formula is merely a representative example. The composition ratio may be non-stoichiometric. For example, when lithium cobalt oxide is represented as "LiCoO2", unless otherwise specified, lithium cobalt oxide is not limited to a composition ratio of "Li / Co / O = 1 / 1 / 2", and can contain Li, Co, and O in any composition ratio. Furthermore, doping or substitution of trace elements is also permissible.

[0034] The geometric terms used in this specification (such as "parallel," "perpendicular," etc.) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." The geometric terms used in this specification may include tolerances and errors, such as those related to design, operation, and manufacturing. The dimensional relationships in the drawings may sometimes differ from the actual dimensional relationships. To aid in understanding this technology, the dimensional relationships (length, width, thickness, etc.) in the drawings may sometimes be altered. Furthermore, some components may sometimes be omitted.

[0035] The "arithmetic mean diameter" in this specification is measured in a cross-sectional SEM (scanning electron microscope) image of the positive electrode active material layer. The cross-sectional SEM image is obtained at a section parallel to the thickness direction of the positive electrode active material layer. The measurement object can be aggregated particles, primary particles, or single particles. The observation magnification can be adjusted appropriately depending on the measurement object. For example, when primary particles are the measurement object, the observation magnification can be 10,000 to 30,000 times. For example, when aggregated particles or single particles are the measurement object, the observation magnification can be 100 to 5,000 times. The diameter of each measurement object represents the distance between the two farthest points on the outline of the measurement object. The arithmetic mean diameter is considered the arithmetic mean diameter of more than 100 diameters.

[0036] <Non-aqueous electrolyte secondary battery>

[0037] Figure 1 This is a schematic diagram illustrating an example of the configuration of a non-aqueous electrolyte secondary battery in this embodiment.

[0038] Battery 100 can be used in any application. For example, it can be used as a main power source or auxiliary power source in electric vehicles. Multiple batteries 100 can be connected to form a battery module or battery pack. Battery 100 can have a rated capacity of, for example, 1 to 200 Ah.

[0039] The battery 100 includes an outer casing 90. The outer casing 90 is square (flat rectangular). However, square is just one example. The outer casing 90 can have any shape. The outer casing 90 can be, for example, cylindrical or pouch-shaped. The outer casing 90 can be made of, for example, aluminum (Al) alloy. The outer casing 90 houses the electrode body 50 and electrolyte (not shown). The outer casing 90 may include, for example, a sealing plate 91 and an outer can 92. The sealing plate 91 plugs the opening of the outer can 92. The sealing plate 91 and the outer can 92 can be joined by, for example, laser welding.

[0040] A positive terminal 81 and a negative terminal 82 are provided on the sealing plate 91. An injection port (not shown) and a gas vent valve (not shown) may be further provided on the sealing plate 91. Electrolyte can be injected into the interior of the outer casing 90 through the injection port. A positive current collector 71 connects the electrode body 50 to the positive terminal 81. The positive current collector 71 may be, for example, an Al plate. A negative current collector 72 connects the electrode body 50 to the negative terminal 82. The negative current collector 72 may be, for example, a copper (Cu) plate.

[0041] Figure 2 This is a schematic diagram illustrating an example of the configuration of the electrode body in this embodiment.

[0042] The electrode body 50 is a wound type. The electrode body 50 includes a positive electrode 10, a separator 30, and a negative electrode 20. That is, the battery 100 includes a positive electrode 10, a negative electrode 20, and an electrolyte. The positive electrode 10, the separator 30, and the negative electrode 20 are all strip-shaped sheets. The electrode body 50 may include multiple separators 30. The electrode body 50 is formed by sequentially stacking and winding the positive electrode 10, the separator 30, and the negative electrode 20 into a vortex shape. One of the positive electrode 10 or the negative electrode 20 can be held by the separator 30. Both the positive electrode 10 and the negative electrode 20 can be held by the separator 30. The electrode body 50 can be formed into a flat shape after winding. Furthermore, the wound type is one example. The electrode body 50 can also be, for example, a stacked type.

[0043] "positive electrode"

[0044] The positive electrode 10 includes a positive electrode substrate 11 and a positive electrode active material layer 12. The positive electrode substrate 11 is a conductive sheet. The positive electrode substrate 11 can be, for example, an Al alloy foil. The positive electrode substrate 11 can have a thickness of, for example, 10 to 30 μm. The positive electrode active material layer 12 is disposed on the surface of the positive electrode substrate 11. The positive electrode active material layer 12 can be disposed on only one side of the positive electrode substrate 11, for example. The positive electrode active material layer 12 can be disposed on both the front and back sides of the positive electrode substrate 11, for example. In the width direction of the positive electrode 10 ( Figure 2 In the X-axis direction, the positive electrode substrate 11 may be exposed at one end. The positive electrode current collector 71 may be joined to the exposed portion of the positive electrode substrate 11.

[0045] The positive electrode active material layer 12 may have a thickness of, for example, 10–200 μm, 50–150 μm, or 50–100 μm. The positive electrode active material layer 12 may have a thickness of, for example, 3.5–3.8 g / cm³. 3 Its apparent density can be 3.5–3.7 g / cm³. 3 The apparent density of the positive electrode active material layer 12 is obtained by dividing the mass of the positive electrode active material layer 12 by the apparent volume of the positive electrode active material layer 12.

[0046] For example, an intermediate layer (not shown) may exist between the positive electrode active material layer 12 and the positive electrode substrate 11. The intermediate layer does not contain positive electrode active material. In this embodiment, even with an intermediate layer present, the positive electrode active material layer 12 is considered to be disposed on the surface of the positive electrode substrate 11. The intermediate layer may be thinner than both the positive electrode active material layer 12 and the positive electrode substrate 11. The intermediate layer may have a thickness of, for example, 0.1 to 10 μm. The intermediate layer may contain, for example, a conductive material, an insulating material, etc.

[0047] (Multi-layer structure)

[0048] Figure 3 This is a schematic cross-sectional view illustrating an example of the configuration of the positive electrode in this embodiment.

[0049] The positive electrode active material layer 12 has a multilayer structure. That is, the positive electrode active material layer 12 includes a first layer 1 and a second layer 2. The second layer 2 is disposed between the positive electrode substrate 11 and the first layer 1.

[0050] The positive electrode active material layer 12 may include additional layers (not shown) provided that it includes a first layer 1 and a second layer 2. These additional layers may have a different composition than the first layer 1 and the second layer 2. For example, an additional layer may be formed between the first layer 1 and the second layer 2. For example, an additional layer may be formed between the surface of the positive electrode active material layer 12 and the first layer 1. For example, an additional layer may be formed between the second layer 2 and the positive electrode substrate 11.

[0051] (Level 1)

[0052] The first layer 1 is the upper layer. Compared with the second layer 2, the first layer 1 is disposed on the surface side of the positive electrode active material layer 12. The first layer 1 can be exposed on the surface of the positive electrode active material layer 12. The first layer 1 can form the surface of the positive electrode active material layer 12.

[0053] The first layer 1 contains a first positive electrode active material. For example, the first layer 1 may be essentially composed of the first positive electrode active material. For example, in addition to the first positive electrode active material, the first layer 1 may further contain a conductive material and a binder. For example, the first layer 1, expressed as a mass fraction, may consist of 0.1 to 10% conductive material, 0.1 to 10% binder, and the balance being the first positive electrode active material.

[0054] The first positive electrode active material includes first aggregated particles mc1. By disposing the first aggregated particles mc1 on the upper layer, it is expected to reduce the increase in resistivity associated with mixing with single particles sc2. The first positive electrode active material may be substantially composed of the first aggregated particles mc1. In addition to the first aggregated particles mc1, the first positive electrode active material may further contain single particles. However, the first aggregated particles mc1 may be the main component of the first positive electrode active material. In this embodiment, "main component" refers to the component with the highest mass fraction among multiple components. In the first positive electrode active material, the mass fraction of the first aggregated particles mc1 may be, for example, 50% or more, 70% or more, or 90% or more.

[0055] Figure 4 Conceptual diagrams for condensed particles and single particles.

[0056] The first aggregated particle, mc1, is a secondary particle. The first aggregated particle, mc1, can also be called "multiple crystal." The first aggregated particle, mc1, is formed by the aggregation of more than 50 primary particles. For example, the first aggregated particle, mc1, can contain more than 100 primary particles. There is no upper limit to the number of primary particles. For example, the first aggregated particle, mc1, can contain less than 10,000 primary particles. Furthermore, "number of particles" refers to the number of particles appearing in the cross-sectional SEM image.

[0057] In this embodiment, "primary particles" refer to particles whose grain boundaries cannot be visually identified in cross-sectional SEM images. Primary particles can have any shape. They can be, for example, spherical, columnar, or blocky. Primary particles can have, for example, an arithmetic mean diameter of less than 0.5 μm, or an arithmetic mean diameter of 0.05 to 0.2 μm.

[0058] The first aggregated particle mc1 can have any shape. The first aggregated particle mc1 can be, for example, spherical, columnar, or blocky. The first aggregated particle mc1 can have, for example, an arithmetic mean diameter larger than that of a single particle sc2. Therefore, a decrease in resistivity is expected, for example. The arithmetic mean diameter of the first aggregated particle mc1 can be, for example, 5–20 μm, or 15–19 μm.

[0059] (Level 2)

[0060] The second layer 2 is the lower layer. Compared with the first layer 1, the second layer 2 is disposed on the side of the positive electrode substrate 11. The second layer 2 can be in direct contact with the positive electrode substrate 11. The second layer 2 can be formed on the surface of the positive electrode substrate 11.

[0061] The second layer 2 contains a second positive electrode active material. For example, the second layer 2 may be essentially composed of the second positive electrode active material. For example, in addition to the second positive electrode active material, the second layer 2 may further contain a conductive material and a binder. For example, the second layer 2, expressed as a mass fraction, may consist of 0.1 to 10% conductive material, 0.1 to 10% binder, and the balance being the second positive electrode active material.

[0062] The second layer 2 contains second aggregated particles mc2 and single particles sc2. By configuring a mixture of second aggregated particles mc2 and single particles sc2 in the lower layer, improved filling performance is expected. The mixing ratio of second aggregated particles mc2 to single particles sc2 is arbitrary. For example, it can satisfy the relationship of "second aggregated particles / single particles = 9 / 1 to 5 / 5 (mass ratio)" or "second aggregated particles / single particles = 9 / 1 to 7 / 3 (mass ratio)".

[0063] The second condensed particle mc2 is formed by the aggregation of more than 50 primary particles. Details of the primary particles are as described above. The second condensed particle mc2 may have, for example, substantially the same structure, shape, and size as the first condensed particle mc1, or it may have a different structure, shape, and size. The second condensed particle m2 may have a larger arithmetic mean diameter than the single particle sc2. This results in, for example, improved filling capacity. The arithmetic mean diameter of the second condensed particle mc2 may be, for example, 5–20 μm, or 15–19 μm.

[0064] Single-particle sc2 exists independently of the second aggregated particle mc2. In this embodiment, "single particle" refers to a particle whose grain boundary cannot be visually identified in a cross-sectional SEM image. Single-particle sc2 can also be called a "single crystal." A single-particle sc2 can exist individually. Two to ten single-particle sc2 can form an aggregate (see reference). Figure 4 ).

[0065] Single-particle sc2 can have any shape. Single-particle sc2 can be, for example, spherical, columnar, or blocky. Single-particle sc2 is a relatively large primary particle. That is, single-particle sc2 has an arithmetic mean diameter larger than the primary particles contained in the first condensate mc1 and the second condensate mc2. The arithmetic mean diameter of single-particle sc2 can be, for example, 0.5–10 μm, or 3.5–4.5 μm.

[0066] (Thickness ratio)

[0067] Layer 1 and Layer 2 can satisfy, for example, the relationship shown in equation (I).

[0068] 0.2≦T1 / (T1+T2)≦0.5…(I)

[0069] In equation (I) above, "T1" represents the thickness of the first layer 1, and "T2" represents the thickness of the second layer 2. By satisfying the relationship in equation (I) above, an improvement in the balance between fillability and resistivity is expected, for example. "T1 / (T1+T2)" can be, for example, 0.3 or less.

[0070] Layer 1 and Layer 2 can satisfy, for example, the relationship shown in equation (II).

[0071] 0.5≦T2 / (T1+T2)≦0.8…(II)

[0072] By satisfying the relationship in equation (II) above, an improvement in the balance between filling properties and resistivity can be expected, for example. "T2 / (T1+T2)" can be, for example, 0.7 or higher.

[0073] The thickness of each layer was determined in cross-sectional SEM images of the positive electrode active material layer 12. The cross-sectional SEM images are taken in the direction corresponding to the thickness of the positive electrode active material layer 12. Figure 3 The thickness was obtained at a cross-section parallel to the Z-axis direction. For each layer, the thickness was measured at at least five locations. The arithmetic mean of the thicknesses at these five locations was taken as the thickness of each layer.

[0074] (Chemical composition)

[0075] The first condensed particle mc1, the second condensed particle mc2, and the single particle sc2 can have arbitrary chemical compositions. The first condensed particle mc1, the second condensed particle mc2, and the single particle sc2 can have different chemical compositions from each other, or they can have substantially the same chemical composition.

[0076] For example, the first aggregated particle mc1, the second aggregated particle mc2, and the single particle sc2 can each independently contain at least one element selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. In formulas such as "Li(NiCoMn)O2", the sum of the composition ratios within parentheses is 1 (Ni + Co + Mn = 1). As long as the sum of the composition ratios is 1, the composition ratios of each element (Ni, Co, Mn) are arbitrary.

[0077] For example, the first aggregate particle mc1, the second aggregate particle mc2, and the single particle sc2 may each have a chemical composition, for example, represented by the following formula (III).

[0078] Li 1-a Ni x Me 1-x O2…(III)

[0079] In equation (III) above, "a" satisfies the relationship "-0.3≦a≦0.3". "x" satisfies the relationship "0.3≦x≦1.0". "Me" represents at least one of the following: cobalt (Co), manganese (Mn), aluminum (Al), zirconium (Zr), boron (B), magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), titanium (Ti), silicon (Si), vanadium (V), chromium (Cr), and germanium (Ge).

[0080] For example, the first aggregate particle mc1, the second aggregate particle mc2, and the single particle sc2 may each independently have a chemical composition, for example, represented by the following formula (IV).

[0081] Li 1-a Nix Co y Mn 1-x-y O2…(IV)

[0082] In equation (IV) above, "a" satisfies the relationship "-0.3≦a≦0.3". "x" satisfies the relationship "0.5≦x≦0.8". "y" satisfies the relationship "0.2≦y≦0.5".

[0083] (Conductive materials)

[0084] Layer 1 and Layer 2 may each independently contain any conductive material. For example, Layer 1 and Layer 2 may each independently contain at least one material selected from acetylene black, carbon nanotubes, graphite flakes, and graphite.

[0085] (Adhesive)

[0086] Layer 1 and Layer 2 may each independently contain any adhesive. For example, Layer 1 and Layer 2 may each independently contain at least one selected from polyvinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA).

[0087] "negative electrode"

[0088] The negative electrode 20 may include, for example, a negative electrode substrate 21 and a negative electrode active material layer 22. The negative electrode substrate 21 is a conductive sheet. The negative electrode substrate 21 may be, for example, a Cu alloy foil. The negative electrode substrate 21 may have a thickness of, for example, 5 to 30 μm. The negative electrode active material layer 22 may be disposed on the surface of the negative electrode substrate 21. The negative electrode active material layer 22 may be disposed only on, for example, one side of the negative electrode substrate 21. The negative electrode active material layer 22 may be disposed on, for example, both the front and back sides of the negative electrode substrate 21. In the width direction of the negative electrode 20 ( Figure 2 In the X-axis direction, the negative electrode substrate 21 may be exposed at one end. The negative electrode current collector 72 can be joined at the exposed portion of the negative electrode substrate 21.

[0089] The negative electrode active material layer 22 may have a thickness of, for example, 10 to 200 μm. The negative electrode active material layer 22 contains a negative electrode active material. The negative electrode active material may contain any composition. The negative electrode active material may contain, for example, materials selected from graphite, soft carbon, hard carbon, SiO, Si-based alloys, Si, SnO, Sn-based alloys, Sn, and Li4Ti5O. 12 At least one of them.

[0090] In addition to the negative electrode active material, the negative electrode active material layer 22 may further include, for example, a binder. For instance, the negative electrode active material layer 22, expressed as a mass fraction, may consist essentially of 0.1 to 10% binder and the balance being the negative electrode active material. The binder may contain any components. The binder may contain, for example, at least one selected from carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR).

[0091] Separator

[0092] At least a portion of the separator 30 is located between the positive electrode 10 and the negative electrode 20. The separator 30 separates the positive electrode 10 and the negative electrode 20. The separator 30 may have a thickness of, for example, 10 to 30 μm.

[0093] The separator 30 is a porous sheet. The separator 30 allows electrolyte to pass through. The separator 30 may have an air permeability of, for example, 100–400 s / 100 mL. In this specification, “air permeability” refers to “air resistance” as specified in “JIS P 8117:2009”. Air permeability is determined using the Glee test method.

[0094] The separator 30 is electrically insulating. The separator 30 may contain, for example, a polyolefin resin. The separator 30 may be substantially composed of a polyolefin resin, for example, at least one selected from polyethylene (PE) and polypropylene (PP). The separator 30 may have, for example, a single-layer structure. The separator 30 may be substantially composed of a PE layer, for example. The separator 30 may have, for example, a multi-layer structure. The separator 30 can be formed by sequentially stacking, for example, a PP layer, a PE layer, and another PP layer. A heat-resistant layer (ceramic particle layer), for example, may be formed on the surface of the separator 30.

[0095] Electrolyte

[0096] The electrolyte is a liquid electrolyte. The electrolyte comprises a solvent and a supporting electrolyte. The solvent is aprotic. The solvent may contain any components. The solvent may contain at least one of, for example, ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL).

[0097] The supporting electrolyte is soluble in a solvent. The supporting electrolyte may, for example, comprise at least one selected from LiPF6, LiBF4, and LiN(FSO2)2. The supporting electrolyte may have a molar concentration of, for example, 0.5–2.0 mol / L, or 0.8–1.2 mol / L.

[0098] In addition to the solvent and supporting electrolyte, the electrolyte may further contain any additives. For example, the electrolyte may contain 0.01% to 5% additives by mass fraction. The additives may include, for example, at least one selected from vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (FSO3Li), and lithium bis(oxalato)borate (LiBOB).

[0099] Furthermore, gel electrolytes or solid electrolytes can be used instead of liquid electrolytes. Solid electrolytes can also function as separators; that is, a solid electrolyte layer can separate the positive and negative electrodes.

[0100] Example

[0101] The following describes embodiments of the present technology (also referred to as "the present embodiments" in this specification). However, the following description does not limit the scope of the present technology.

[0102] <The Manufacturing of the Positive Electrode>

[0103] No.1

[0104] Prepare the following materials.

[0105] Aggregated particles: Li(NiCoMn)O2

[0106] Single particle: Li(NiCoMn)O2

[0107] Conductive material: Acetylene black

[0108] Adhesive: PVdF

[0109] Dispersion medium: N-methyl-2-pyrrolidone

[0110] Positive electrode substrate: Al foil

[0111] Agglomerated particles are treated as the first positive electrode active material. That is, the first positive electrode active material is composed of agglomerated particles. The first slurry is prepared by mixing 97.5 parts by mass of the first positive electrode active material, 1 part by mass of conductive material, 1.5 parts by mass of binder, and a specified amount of dispersion medium.

[0112] The second positive electrode active material is prepared by mixing aggregated particles and single particles. The mixing ratio is "aggregated particles / single particles = 5 / 5 (mass ratio)". The second slurry is prepared by mixing 97.5 parts by mass of the second positive electrode active material, 1 part by mass of conductive material, 1.5 parts by mass of binder, and a specified amount of dispersion medium.

[0113] A simultaneous multilayer coating apparatus was prepared. A coating film was formed by substantially simultaneously coating a first slurry and a second slurry on the surface (one side) of the cathode substrate. The second slurry was discharged between the cathode substrate and the first slurry. By drying the coating film, a cathode active material layer was formed. The cathode active material layer consists of a first layer and a second layer. The first layer is formed from the first slurry. The second layer is formed from the second slurry. The second layer is positioned between the cathode substrate and the first layer. Similarly, a cathode active material layer was also formed on the back side of the cathode substrate. That is, cathode active material layers were formed on both the front and back sides of the cathode substrate. The cathode active material layers were compressed using a calender. Through the above operations, the cathode described in No. 1 was manufactured.

[0114] No. 2

[0115] A third slurry was prepared in the same manner as the first slurry, by treating single particles as the first positive electrode active material. The positive electrode described in No. 2 was manufactured in the same manner as the positive electrode described in No. 1, except that the third slurry was used instead of the first slurry.

[0116] No. 3

[0117] In addition to using the first slurry to form a single-layer positive electrode active material layer, the positive electrode described in No.3 was manufactured in the same manner as the positive electrode described in No.1.

[0118] No. 4

[0119] In addition to using the third slurry to form a single-layer positive electrode active material layer, the positive electrode described in No.4 was manufactured in the same manner as the positive electrode described in No.1.

[0120] No. 5

[0121] In addition to using the second slurry to form a single-layer positive electrode active material layer, the positive electrode described in No. 5 was manufactured in the same manner as the positive electrode described in No. 1.

[0122] <Evaluation>

[0123] Fill Rate

[0124] A sample of a specified size is cut from the positive electrode. The apparent density of the positive electrode active material layer is determined from the thickness and mass of the sample. In this embodiment, the apparent density is considered as the fill power.

[0125] Resistivity

[0126] The resistivity of the positive electrode active material layer was measured using an electrode resistance measuring machine.

[0127] The results of the filling ratio and resistivity measurements are shown in Table 1 below. In this example, the filling ratio is 3.56 g / cm³. 3When the values ​​are above 28 Ω·cm and the resistivity is below 28 Ω·cm, it is considered that both fill factor and resistivity are taken into account.

[0128] "other"

[0129] The thickness ratio "T1 / (T1+T2)" was also measured in the cross-sectional SEM images. The arithmetic mean diameters of aggregated particles and single particles were also measured in the cross-sectional SEM images. Aggregated particles have a larger arithmetic mean diameter than single particles.

[0130] Table 1

[0131]

[0132] <Results>

[0133] In the cathode described in No.1, both fill rate and resistivity are considered. In the cathode described in No.1, agglomerated particles are arranged in the first layer 1 (upper layer), and a mixture of agglomerated particles and single particles is arranged in the second layer (lower layer).

[0134] The positive electrode involved in No. 2 has high resistivity. In the positive electrode involved in No. 2, single particles are disposed in the first layer 1 (upper layer).

[0135] The positive electrode described in No. 3 has a high resistivity. In the positive electrode described in No. 3, the active material layer has a monolayer structure. This monolayer structure is composed of aggregated particles. It is believed that due to the poor filling properties of the active material layer, the contact resistance increases, leading to an increase in resistivity.

[0136] The cathode described in No. 4 has a high resistivity. In the cathode described in No. 4, the active material layer has a monolayer structure. The monolayer structure consists of single particles. It is assumed that because single particles have high resistivity, the resistivity of the active material layer increases.

[0137] The cathode described in No. 5 has high resistivity. In the cathode described in No. 5, the active material layer has a monolayer structure. The monolayer structure consists of a mixture of aggregated particles and single particles (homogeneous phase).

[0138] This embodiment and example are illustrative in all respects. This embodiment and example are not restrictive. The scope of this technology includes all changes within the meaning and scope equivalent to the claims. For example, it was contemplated from the outset that any components could be extracted from this embodiment and example and combined arbitrarily.

Claims

1. Positive electrode: This is the positive electrode used in non-aqueous electrolyte secondary batteries. It includes a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer is disposed on the surface of the positive electrode substrate. The positive electrode active material layer comprises a first layer and a second layer. The second layer is disposed between the positive electrode substrate and the first layer. The first layer contains a first positive electrode active material. The first positive electrode active material contains first aggregated particles. The second layer contains a second positive electrode active material. The second positive electrode active material comprises second aggregated particles and single particles. The first condensed particle and the second condensed particle are each formed by the aggregation of more than 50 primary particles. The arithmetic mean diameter of the first condensed particle is 5–20 μm. The arithmetic mean diameter of the second condensed particle is 5–20 μm. The primary particles have an arithmetic mean diameter of 0.05–0.2 μm. The single particle has a larger arithmetic mean diameter than the primary particle. The second condensed particle is the same as the first condensed particle.

2. The positive electrode according to claim 1, wherein, The first condensed particle and the second condensed particle each have an arithmetic mean diameter larger than that of the single particle.

3. The positive electrode according to claim 1 or claim 2, wherein, The relationship satisfying equation (I) is as follows: 0.2≦T1 / (T1+T2)≦0.5…(I) In the formula (I), T1 represents the thickness of the first layer and T2 represents the thickness of the second layer.

4. A non-aqueous electrolyte secondary battery comprising a positive electrode according to any one of claims 1 to 3.

Images