Positive electrode composite, lithium ion battery, and method for manufacturing lithium ion battery

Abstract

To provide a positive electrode active material having an O2 type structure capable of improving the capacity when applied to a positive electrode active material layer of a lithium-ion battery.SOLUTION: A disclosed positive electrode composite includes a first active material and a second active material. The first active material has an O2-type structure and has a plate-like shape. The second active material has an O2-type structure and has a spherical shape. The ratio D1L / D2 of the major axis of the first active material D1L to the diameter of the second active material D2 is equal to or more than 0.1 and equal to or less than 1.5. The ratio of the first active material to the total of the first active material and the second active material is 10% by mass or more and 90% by mass or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application discloses a cathode composite, a lithium-ion battery, and a method for manufacturing a lithium-ion battery. [Background technology]

[0002] Positive electrode active materials for lithium ion batteries are known to have an O2-type structure. As disclosed in Patent Document 1, a positive electrode active material having an O2-type structure is obtained by ion-exchanging at least a portion of Na in a sodium-containing transition metal oxide having a P2-type structure with Li. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-169365 Summary of the Invention [Problem to be solved by the invention]

[0004] There is room for improvement in the capacity of a positive electrode active material having an O2 type structure when it is applied to the positive electrode active material layer of a lithium ion battery. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> a positive electrode composite comprising a first active material and a second active material; the first active material has an O2 type structure and is plate-shaped; the second active material has an O2 type structure and is spherical; The major axis D of the first active material 1L and the diameter D2 of the second active material 1L / D2 is 0.1 or more and 1.5 or less, a ratio of the first active material to the total of the first active material and the second active material is 10% by mass or more and 90% by mass or less; Positive electrode mixture. <Aspect 2> The positive electrode composite of Aspect 1, the surface of the second active material has a plurality of crystallites; Positive electrode mixture. <Aspect 3> The positive electrode composite of Aspect 1 or 2, including a solid electrolyte, Positive electrode mixture. <Aspect 4> The positive electrode composite of any one of Aspects 1 to 3, The conductive material may include one or both of a conductive additive and a binder. Positive electrode mixture. <Aspect 5> A lithium ion battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer includes the positive electrode mixture according to any one of embodiments 1 to 4. Lithium-ion battery. <Aspect 6> 6. The lithium ion battery of embodiment 5, one or both of the electrolyte layer and the negative electrode active material layer contains a solid electrolyte; Lithium-ion battery. <Aspect 7> A method for manufacturing a lithium ion battery, comprising: Obtaining a positive electrode active material layer using the positive electrode mixture of any one of Aspects 1 to 4; and obtaining a lithium ion battery using the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer; A manufacturing method comprising: [Effects of the Invention]

[0006] By using the positive electrode mixture of the present disclosure to form a positive electrode active material layer of a lithium ion battery, the capacity of the lithium ion battery is likely to be improved. [Brief explanation of the drawings]

[0007] [Figure 1] 1 shows a schematic diagram of a first active material and a second active material contained in a positive electrode mixture of the present disclosure. [Figure 2] FIG. 3 is a schematic diagram illustrating the major axis and minor axis of a first active material. [Figure 3] FIG. 1 is a schematic diagram for explaining the problems of a plate-shaped O2-type active material. [Figure 4] 1 shows an example of a flow of a method for producing a first active material and a second active material. [Figure 5] 1 shows a schematic diagram of an example of the configuration of a lithium ion battery. [Figure 6] 1 shows an example of a manufacturing method for a lithium-ion battery. [Figure 7] An example of the calcination conditions for obtaining a P2 type compound is shown below. [Figure 8A] FIG. 1 is an SEM photograph of a plate-shaped O2-type positive electrode active material particle. [Figure 8B] FIG. 1 is an SEM photograph of spherical O2-type positive electrode active material particles. [Figure 9] The graph shows the relationship between the plate-like particle ratio and the discharge capacity. [Figure 10A] 2 is a cross-sectional SEM photograph of a positive electrode active material layer of the evaluation cell according to Example 1. FIG. [Figure 10B] 10 is a cross-sectional SEM photograph of a positive electrode active material layer of an evaluation cell according to Example 2. FIG. [Figure 10C] 1 is a cross-sectional SEM photograph of a positive electrode active material layer of an evaluation cell according to Comparative Example 1. FIG. [Figure 10D] 10 is a cross-sectional SEM photograph of a positive electrode active material layer of an evaluation cell according to Comparative Example 2. FIG. [Figure 10E] 10 is a cross-sectional SEM photograph of a positive electrode active material layer of an evaluation cell according to Comparative Example 3. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1. Cathode mixture FIG. 1 shows a positive electrode composite 1 according to one embodiment. The positive electrode composite 1 includes a first active material 1a and a second active material 1b. The first active material 1a has an O2-type structure and is plate-shaped. The second active material 1b has an O2-type structure and is spherical. The major axis D of the first active material 1a is 1L and the diameter D2 of the second active material 1b. 1L / D2 is equal to or greater than 0.1 and equal to or less than 1.5. The proportion of the first active material 1a to the total of the first active material 1a and the second active material 1b is equal to or greater than 10 mass % and equal to or less than 90 mass %.

[0009] 1.1 First active material The first active material 1a has an O2 type structure and is plate-shaped.

[0010] 1.1.1 Crystal structure of the first active material The first active material 1a has at least an O2-type structure (belonging to the space group P63mc) as a crystalline structure. The first active material 1a has the O2-type structure, but may also have a crystalline structure other than the O2-type structure. Examples of crystalline structures other than the O2-type structure include a T#2-type structure (belonging to the space group Cmca) formed when Li is inserted and removed from the O2-type structure, and an O6-type structure (belonging to the space group R-3m, with a c-axis length of 2.5 nm to 3.5 nm, typically 2.9 nm to 3.0 nm, and different from the O3-type structure also belonging to the space group R-3m). The first active material 1a may have an O2-type structure as a main phase, or may have a crystalline structure other than the O2-type structure as a main phase. The crystalline structure of the main phase of the first active material 1a can change depending on its charge / discharge state.

[0011] The first active material 1a may be a single crystal consisting of one crystallite, or may be a polycrystal having a plurality of crystallites.

[0012] 1.1.2 Chemical composition of the first active material The chemical composition of the first active material 1a is not particularly limited as long as the O2-type structure is maintained. The first active material 1a may contain, as constituent elements, at least one transition metal element of at least one of Mn, Ni, and Co, Li, and O. In particular, when the constituent elements include at least Li, Mn, at least one of Ni and Co, and O, among others, especially when the constituent elements include at least Li, Mn, Ni, Co, and O, higher performance is more likely to be obtained. However, for the first active material 1a, for example, Li may be released upon charging, and the abundance of Li may become close to 0.

[0013] The first active material 1a is Li a Na b Mn x-p Ni y-q Co z-r M p+q+r It may have a chemical composition represented by O2. Here, 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r ≤ 0.15. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the first active material 1a has such a chemical composition, the O2-type structure is more likely to be maintained.

[0014] In the above chemical composition, a may be greater than 0, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, 0.50 or greater, or 0.60 or greater, and may be 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b may be 0 or greater, 0.01 or greater, 0.02 or greater, or 0.03 or greater, and may be 0.20 or less, 0.15 or less, or 0.10 or less. In the above chemical composition, x may be 0 or greater, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, or 0.50 or greater, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. In the above chemical composition, y may be 0 or more, 0.10 or more, or 0.20 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. In the above chemical composition, z may be 0 or more, 0.10 or more, 0.20 or more, or 0.30 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. M often does not contribute to charge and discharge. In this regard, a high charge and discharge capacity is easily ensured by having p + q + r be 0.15 or less. p + q + r may be 0.10 or less, or may be 0. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0015] 1.1.3 Shape of the first active material As shown in Fig. 1, the first active material 1a is plate-shaped. Whether the active material contained in the positive electrode composite 1 is "plate-shaped" or not can be determined by forming a positive electrode active material layer 20 (described later) using the positive electrode composite 1, and observing a cross section of the positive electrode active material layer 20 along the thickness direction with a scanning electron microscope (SEM), a transmission electron microscope (TEM), an optical microscope, or the like. In the cross section, the active material has a major diameter D 1L and minor axis D 1S and the aspect ratio of the major axis to the minor axis (major axis D 1L / minor diameter D 1S) is 2 or more, the active material is considered to be plate-shaped. 1L refers to the maximum length from one point to another point on the surface of the first active material 1a in the cross section of the first active material 1a, and the minor axis D 1S In the cross-sectional shape of the first active material 1a, the major axis D 1L The maximum length of the line extending from one point to another on the surface of the first active material 1a is a line perpendicular to the line 1a. The plate-like first active material 1a is not limited to one having a constant thickness, and the thickness may vary from part to part. Furthermore, the plate-like first active material 1a is not limited to one having a flat plate shape, and may be one having a curve or distortion.

[0016] 1.1.4 Size of the first active material Major axis D of the first active material 1a 1L The minor axis D of the first active material 1a may be, for example, 0.3 μm or more and 8.0 μm or less, 0.5 μm or more and 6.0 μm or less, or 1.0 μm or more and 4.0 μm or less. 1S The major axis D of the first active material 1a in the case where the positive electrode composite 1 includes a plurality of first active materials 1a may be, for example, 0.1 μm or more and 4.0 μm or less, 0.3 μm or more and 3.0 μm or less, or 0.5 μm or more and 2.0 μm or less. 1L is the number average value of the major axis of each of the first active materials 1a contained in the positive electrode composite 1, and 1S is the number average value of the minor axis of each of the first active materials 1 a contained in the positive electrode mixture 1 .

[0017] 1.2 Second active material The second active material 1b has an O2 type structure and is spherical.

[0018] 1.2.1 Crystal structure of the second active material The second active material 1b has at least an O2-type structure (belonging to the space group P63mc) as a crystalline structure. The second active material 1b has the O2-type structure, but may also have a crystalline structure other than the O2-type structure. Examples of crystalline structures other than the O2-type structure include a T#2-type structure (belonging to the space group Cmca) formed when Li is inserted or removed from the O2-type structure, and an O6-type structure (belonging to the space group R-3m, with a c-axis length of 2.5 nm to 3.5 nm, typically 2.9 nm to 3.0 nm, and different from the O3-type structure also belonging to the space group R-3m). The second active material 1b may have an O2-type structure as a main phase, or may have a crystalline structure other than the O2-type structure as a main phase. The crystalline structure of the main phase of the second active material 1b can change depending on the charge / discharge state.

[0019] The second active material 1b may be a single crystal consisting of a single crystallite, or a polycrystal having multiple crystallites. The surface of the second active material 1b may have multiple crystallites. When the surface of the second active material 1b has multiple crystallites, crystal grain boundaries exist on the surface of the second active material 1b. Here, the crystal grain boundaries may serve as inlets and outlets for intercalation. That is, when the second active material 1b has multiple crystallites on its surface, it is expected to have the following effects: an increased number of inlets and outlets for intercalation reduces reaction resistance; a shorter migration distance of lithium ions reduces diffusion resistance; and a smaller absolute amount of expansion and contraction during charge and discharge, making cracks less likely to occur.

[0020] The size of the crystallites constituting the second active material 1b may be large or small. However, smaller crystallite sizes result in more grain boundaries, making it easier to achieve the above-mentioned advantageous effects. For example, if the diameter of the crystallites constituting the second active material 1b is less than 1 μm, higher performance is likely to be obtained. The "crystallite" and "crystallite diameter" can be determined by observing the surface of the positive electrode active material particles using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). That is, when observing the surface of the second active material 1b, if a single closed region surrounded by grain boundaries is observed, that region is considered to be a "crystallite." The maximum Feret diameter of the crystallite is determined and considered to be the "crystallite diameter." If a particle is composed of a single crystal, the particle itself can be considered a single crystallite, and the maximum Feret diameter of the particle is the "crystallite diameter." Alternatively, the crystallite diameter can be determined using EBSD or XRD. For example, the crystallite diameter can be determined from the half-width of the diffraction line in the XRD pattern using the Scherrer equation. If the crystallite diameter of the second active material 1b determined by any of these methods is less than 1 μm, higher performance is likely to be obtained.

[0021] The crystallites of the second active material 1b may have a first surface exposed on the particle surface, and the first surface may be planar. The surface of the second active material 1b may have a structure in which multiple planes are connected. When producing the second active material 1b, crystallites having planar first surfaces can be easily obtained by growing the crystallites on the particle surface until one crystallite and another crystallite are connected to each other.

[0022] 1.2.2 Chemical composition of the second active material The chemical composition of the second active material 1b is not particularly limited as long as the O2-type structure is maintained. The chemical composition of the second active material 1b may be the same as or different from the chemical composition of the first active material 1a. The second active material 1b may contain, as constituent elements, at least one transition metal element among at least Mn, Ni, and Co, Li, and O. In particular, when it contains, as constituent elements, at least Li, Mn, at least one of Ni and Co, and O, especially when it contains, as constituent elements, at least Li, Mn, Ni, Co, and O, higher performance is more likely to be obtained. However, for the second active material 1b, for example, Li may be released upon charging and the abundance of Li may approach 0.

[0023] The second active material 1b is Li a Na b Mn x-p Ni y-q Co z-r M p+q+r It may have a chemical composition represented by O2. Here, 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r ≤ 0.15. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the second active material 1b has such a chemical composition, the O2-type structure is more likely to be maintained.

[0024] In the above chemical composition, a may be greater than 0, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, 0.50 or greater, or 0.60 or greater, and may be 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b may be 0 or greater, 0.01 or greater, 0.02 or greater, or 0.03 or greater, and may be 0.20 or less, 0.15 or less, or 0.10 or less. In the above chemical composition, x may be 0 or greater, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, or 0.50 or greater, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. In the above chemical composition, y may be 0 or more, 0.10 or more, or 0.20 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. In the above chemical composition, z may be 0 or more, 0.10 or more, 0.20 or more, or 0.30 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. M often does not contribute to charge and discharge. In this regard, a high charge and discharge capacity is easily ensured by having p + q + r be 0.15 or less. p + q + r may be 0.10 or less, or may be 0. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0025] 1.2.3 Shape of the second active material The second active material 1b is spherical. "Spherical" means that the circularity is 0.80 or more. The circularity of the active material may be 0.81 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, or 0.90 or more. The circularity of the active material is 4πS / L 2 where S is the orthogonal projected area of ​​the particle, and L is the perimeter of the orthogonal projected image of the particle. The circularity of the active material can be determined by observing the appearance or the cross-sectional shape of the particles using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an optical microscope.

[0026] The second active material 1b may be solid particles, hollow particles, or particles with voids. When the second active material 1b is hollow particles or particles with voids, it is possible to fill the hollows or voids with a liquid. For example, the electrolyte may penetrate not only the outer surface of the active material but also the interior, increasing the contact area between the particles and the electrolyte.

[0027] 1.2.4 Size of the second active material The size of the second active material 1b is the above D 1L / D2) is not particularly limited as long as the relationship is satisfied. For example, the diameter D2 of the second active material 1b may be 0.5 μm or more and 10 μm or less, 1.0 μm or more and 8.0 μm or less, or 2.0 μm or more and 6.0 μm or less. The diameter D2 of the second active material 1b refers to the circle-equivalent diameter when the external appearance or cross-sectional shape of the second active material 1b is observed using an SEM or the like. When the positive electrode composite 1 contains multiple second active materials 1b, the diameter D2 of the second active material 1b is the number-average value of the circle-equivalent diameter of each of the second active materials 1b contained in the positive electrode composite 1.

[0028] 1.3 Ratio of the major axis of the first active material to the diameter of the second active material In the positive electrode composite 1, the major axis D of the first active material 1a 1L and the diameter D2 of the second active material 1b. 1L / D2 is 0.1 or more and 1.5 or less. 1L / D2 may be 0.2 to 1.5, 0.3 to 1.5, 0.4 to 1.5, 0.5 to 1.5, 0.6 to 1.5, 0.7 to 1.5, 0.8 to 1.5, 0.9 to 1.5, 1.0 to 1.5, or 1.1 to 1.5. Alternatively, it may be 0.1 to 1.5, 0.1 to 1.4, or 0.1 to 1.3. As described below, when the second active material 1b has a predetermined size relative to the first active material 1a, the second active material 1b causes the first active material 1a to stand up, increasing the amount of first active material 1a intersecting the plane direction of the positive electrode active material layer 20, reducing the degree of bending, and increasing the utilization rate of the first active material 1a. Furthermore, the second active material 1b itself can contribute to improving the capacity. As a result, the capacity of the positive electrode is likely to increase.

[0029] 1.3 Ratio of first active material to second active material In the positive electrode composite 1, the ratio of the first active material 1a to the total of the first active material 1a and the second active material 1b is 10% by mass or more and 90% by mass or less. If the amount of the first active material 1a is too small or too large, the capacity tends to decrease. The mass ratio of the first active material 1a to the total of the first active material 1a and the second active material 1b may be lower or higher than the mass ratio of the second active material 1b. When combined with a solid electrolyte, better performance is likely to be exhibited when the mass ratio of the first active material 1a to the total of the first active material 1a and the second active material 1b is higher than the mass ratio of the second active material 1b. On the other hand, when combined with a liquid electrolyte, better performance is likely to be exhibited when the mass ratio of the first active material 1a to the total of the first active material 1a and the second active material 1b is lower than the mass ratio of the second active material 1b. The proportion of the first active material 1a may be 15% by mass or more and 85% by mass or less, and the lower limit may be 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, or 70% by mass or more, and the upper limit may be 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less.

[0030] 1.4 Other ingredients The positive electrode composite 1 includes at least the first active material 1a and the second active material 1b as positive electrode active materials. The positive electrode composite 1 may also include an electrolyte. The electrolyte may be a solid electrolyte, a liquid electrolyte, or a combination of a solid electrolyte and a liquid electrolyte. When the positive electrode composite 1 includes a solid electrolyte, excellent effects are likely to be exhibited. The positive electrode composite 1 may also include one or both of a conductive additive and a binder. The positive electrode composite 1 may also include an electrolyte and one or both of a conductive additive and a binder. The positive electrode composite 1 may also include an electrolyte, a conductive additive, and a binder. The positive electrode composite 1 may also include various additives. The contents of the first active material 1a, the second active material 1b, the electrolyte, the conductive additive, the binder, and the like in the positive electrode composite 1 may be appropriately determined depending on the desired performance. For example, assuming that the entire positive electrode composite 1 (total solid content) is 100% by mass, the content of the positive electrode active material (the total of the first active material 1a, the second active material 1b, and other positive electrode active materials) may be 40% by mass or more and 100% by mass or less, with a lower limit of 50% by mass or more or 60% by mass or more, and an upper limit of 90% by mass or less.

[0031] 1.4.1 Other positive electrode active materials The positive electrode mixture 1 may contain only the first active material 1a and the second active material 1b as the positive electrode active material. Alternatively, the positive electrode mixture 1 may contain, in addition to the first active material 1a and the second active material 1b, a different type of positive electrode active material (another positive electrode active material). From the viewpoint of further enhancing the effects of the technology of the present disclosure, the content of the other positive electrode active material in the positive electrode mixture 1 may be small. For example, when the total positive electrode active material contained in the positive electrode mixture 1 is taken as 100% by mass, the content of the positive electrode active material derived from the first active material 1a and the second active material 1b may be 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 99% by mass to 100% by mass.

[0032] Any other positive electrode active material can be any of those known as positive electrode active materials for secondary batteries. Among the known active materials, a material with a relatively high potential (charge-discharge potential) for occluding and releasing a predetermined carrier ion can be used as the positive electrode active material, and a material with a relatively low potential can be used as the negative electrode active material. The other positive electrode active materials may be, for example, at least one selected from various lithium-containing compounds, elemental sulfur, sulfur compounds, etc. The lithium-containing compound as the positive electrode active material may be a lithium-containing oxide containing at least one element M, Li, and O. The element M may be, for example, at least one selected from Mn, Ni, Co, Al, Mg, Ca, Sc, V, Cr, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, Bi, Fe, and Ti, or at least one selected from the group consisting of Mn, Ni, Co, Al, Fe, and Ti. More specifically, the lithium-containing oxide is lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium nickel cobalt oxide, lithium nickel manganate, lithium cobalt manganate, lithium nickel cobalt manganate (Li 1±α Ni x Co y Mn z O 2±δ (for example, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1)), spinel-type lithium compounds (Li 1+x Mn 2-x-y M y O4 (M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), such as hetero-element-substituted Li-Mn spinel with a composition represented by this formula), lithium nickel cobalt aluminum oxide (for example, Li 1±α Ni p Co q Al r O 2±δThe other positive electrode active material may be at least one selected from lithium phosphate (e.g., LiMPO4, where M is one or more selected from Fe, Mn, Co, and Ni), etc. The other positive electrode active material may include, as constituent elements, a lithium-containing oxide containing at least one of Ni, Co, and Mn, Li, and O. Alternatively, the other positive electrode active material may include, as constituent elements, a lithium-containing oxide containing at least one of Ni, Co, and Al, Li, and O. Only one of the other positive electrode active materials may be used alone, or two or more of them may be used in combination.

[0033] The shape of the other positive electrode active material may be any shape commonly used for positive electrode active materials in secondary batteries. The other positive electrode active material may be, for example, particulate. The other positive electrode active material may have voids, for example, be porous or hollow. The other positive electrode active material may be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle diameter D50 of the other positive electrode active material may be, for example, 1 nm or more and 500 μm or less, with a lower limit of 5 nm or more or 10 nm or more and an upper limit of 100 μm or less, 50 μm or less, or 30 μm or less. The average particle diameter D50 is the particle diameter (median diameter) at 50% of the cumulative value in a volume-based particle size distribution determined by a laser diffraction / scattering method.

[0034] 1.4.2 Protective layer An ion-conductive protective layer may be formed on the surface of the positive electrode active material (first active material 1a, second active material 1b, other positive electrode active materials). That is, the positive electrode composite 1 may include a composite of the positive electrode active material and a protective layer, and in the composite, at least a portion of the surface of the positive electrode active material may be covered with a protective layer. This makes it easier to suppress, for example, reactions between the positive electrode active material and other battery materials (such as the sulfide solid electrolyte described below). The ion-conductive protective layer may include various ion-conductive compounds. The ion-conductive compound may be, for example, at least one selected from ion-conductive oxides and ion-conductive halides.

[0035] The ion-conductive oxide may contain, for example, at least one element selected from B, C, Al, Si, P, S, Ti, La, Zr, Nb, Mo, Zn, and W, Li, and O. The ion-conductive oxide may also be an oxynitride containing N. More specifically, the ion-conductive oxide may be Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, or Li4Ti5O. 12 , Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4, LiPON, Li2O-LaO2, Li2O-ZnO2, etc. The ion-conductive oxide may be one in which some elements are substituted with various doping elements.

[0036] The ion-conductive halide may be, for example, at least one of the various compounds exemplified as halide solid electrolytes described below. The ion-conductive halide may contain, for example, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm, at least one halogen element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conductive halide may contain at least one element selected from the group consisting of Ti, Al, Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conductive halide may also contain at least one element selected from the group consisting of Ti and Al, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conductive halide may also be, for example, a complex halide of Li, Ti, Al, and F.

[0037] The coverage (area ratio) of the protective layer with respect to the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more and 100 nm or less, with a lower limit of 1 nm or more and an upper limit of 20 nm or less.

[0038] 1.4.3 Electrolytes The positive electrode composite 1 may contain an electrolyte. The electrolyte that may be contained in the positive electrode composite 1 may be a solid electrolyte, a liquid electrolyte, or a combination of a solid electrolyte and a liquid electrolyte. As described above, when the positive electrode composite 1 contains a solid electrolyte, excellent effects are likely to be exhibited.

[0039] 1.4.3.1 Solid electrolyte The solid electrolyte may be any known solid electrolyte for lithium-ion batteries. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have excellent ionic conductivity and heat resistance. Examples of inorganic solid electrolytes include oxide solid electrolytes, sulfide solid electrolytes, and ionically bonded inorganic solid electrolytes. Among inorganic solid electrolytes, sulfide solid electrolytes, especially sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have high performance. Among inorganic solid electrolytes, ionically bonded solid electrolytes, especially solid electrolytes containing at least Li, Y, and a halogen (at least one of Cl, Br, I, and F) as constituent elements, have high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be particulate. The average particle diameter (D50) of the solid electrolyte may be, for example, 10 nm or more and 10 μm or less. The average particle diameter D50 referred to in this application is the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution determined by a laser diffraction / scattering method. The ionic conductivity of the solid electrolyte at 25°C is, for example, 1×10 -5 S / cm or more, 1×10 -4 S / cm or more, or 1×10 -3 The solid electrolyte may be used singly or in combination of two or more kinds.

[0040] Oxide solid electrolytes include lithium lanthanum zirconate, LiPON, and Li 1+X Al X Ge 2-X It may be one or more selected from (PO4)3, Li-SiO-based glass, Li-Al-SO-based glass, etc. Furthermore, when an oxide solid electrolyte is combined with a liquid electrolyte, ionic conductivity can be improved.

[0041] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte (sulfide glass), a glass-ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide glass is amorphous. The sulfide glass may have a glass transition temperature (Tg). When the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON-type crystalline phase, an LGPS-type crystalline phase, and an Argyrodite-type crystalline phase.

[0042] The sulfide solid electrolyte may contain, for example, Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element. The sulfide solid electrolyte may also contain S as a main anion element.

[0043] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In).

[0044] The composition of the sulfide solid electrolyte is not particularly limited. For example, xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30), etc. may be mentioned. Alternatively, the sulfide solid electrolyte has a composition represented by the general formula: Li 4-x Ge 1-x P x S4 (0 < x < 1). In the above general formula, at least a part of Ge may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, at least a part of P may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the above general formula, a part of S may be substituted with a halogen (at least one of F, Cl, Br, and I). Alternatively, the sulfide solid electrolyte is Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number of 0 or more and 2 or less). a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, or may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less.

[0045] The ionically bonded solid electrolyte may contain, for example, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm. These elements can generate cations in water. The ionically bonded solid electrolyte material may further contain, for example, at least one halogen element selected from the group consisting of Cl, Br, I, and F. These elements can generate anions in water. The ionically bonded solid electrolyte may contain at least one element selected from the group consisting of Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. The ionically bonded solid electrolyte may also contain Li and Y, and at least one element selected from the group consisting of Cl, Br, I, and F. More specifically, the ionic solid electrolyte may contain Li, Y, Cl, and Br, or may contain Li, Ca, Y, Gd, Cl, and Br, or may contain Li, Zr, Y, and Cl. Even more specifically, the ionic solid electrolyte may be Li3YBr2Cl4, Li 2.8 Ca 0.1 Y 0.5 Gd 0.5 Br2Cl4 and Li 2.5 Y 0.5 Zr 0.5 It may be at least one of Cl6.

[0046] The ionically bonded solid electrolyte may be a halide solid electrolyte. The halide solid electrolyte has excellent ion conductivity. Examples of the halide solid electrolyte include a halide solid electrolyte represented by the formula (1): Li α M β X γ (A) It may have a composition represented by the following. Here, α, β, and γ are each independently a value greater than 0, M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, and X is at least one selected from the group consisting of Cl, Br, and I. Note that the "metalloid element" may be at least one selected from the group consisting of B, Si, Ge, As, Sb, and Te. Further, the "metal element" may include (i) all elements (excluding hydrogen) contained in Groups 1 to 12 of the periodic table and (ii) all elements (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se) contained in Groups 13 to 16 of the periodic table. The metal element can form an inorganic compound with a halide ion and become a cation.

[0047] In formula (A), M may contain Y (i.e., yttrium). The halide solid electrolyte containing Y is Li a Me b Y c It may have a composition represented by X6 (where a + mb + 3c = 6, c > 0, Me is at least one selected from the group consisting of metal elements and metalloid elements other than Li and Y, and m is the valence of Me). Me may be, for example, at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0048] The halide solid electrolyte may have a composition represented by formula (A1): Li 6-3d Y d X6. In formula (A1), X is one or more elements selected from the group consisting of Cl, Br, and I. d may satisfy 0 < d < 2, or d = 1. The halide solid electrolyte may have a composition represented by formula (A2): Li 3-3δ Y 1+δ Cl6. In formula (A2), 0 < δ ≦ 0.15 may hold. The halide solid electrolyte may have a composition represented by formula (A3): Li 3-3δ Y 1+δIt may have a composition represented by Br6. In formula (A3), 0 < δ ≦ 0.25 may be satisfied. The halide solid electrolyte has the formula (A4): Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y and may have a composition represented by. In formula (A4), Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In formula (A4), for example, -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, �≦ y ≦ 6, and (x + y) ≦ 6 are satisfied. The halide solid electrolyte has the formula (A5): Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y and may have a composition represented by. In formula (A5), Me may be at least one selected from the group consisting of Al, Sc, Ga, and Bi. In formula (A5), -1 < δ < 1, 0 < a < 2, 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 may be satisfied. The halide solid electrolyte has the formula (A6): Li 3-3δ-a Y 1+δ-a Me a Cl 6-x-y Br x I y and may have a composition represented by. In formula (A6), Me may be at least one selected from the group consisting of Zr, Hf, and Ti. In formula (A6), -1 < δ < 1, 0 < a < 1.5, 0 < (3 - 3δ - a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 may be satisfied. The halide solid electrolyte has the formula (A7): Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I yIn formula (A7), Me may be at least one selected from the group consisting of Ta and Nb. In formula (A7), -1<δ<1, 0 <a<1.2、0<(3-3δ-2a)、0<(1+δ-a)、0≦x≦6、0≦y≦6、かつ、(x+y)≦6であってもよい。

[0049] The ionic solid electrolyte may be a complex hydride solid electrolyte. The complex hydride solid electrolyte may be composed of Li ions and complex ions containing H. The complex ions containing H may have, for example, an element M containing at least one of a nonmetal element, a semimetal element, and a metal element, and H bonded to the element M. In addition, the complex ions containing H may have the element M as a central element and H surrounding the element M bonded to each other via a covalent bond. In addition, the complex ions containing H may be composed of (M m H n ) α- In this case, m is any positive number, and n and α can be any positive number depending on m and the valence of element M. Element M may be any nonmetallic element or metallic element capable of forming a complex ion. For example, element M may contain at least one of B, C, and N as a nonmetallic element, or may contain B. Furthermore, for example, element M may contain at least one of Al, Ni, and Fe as a metallic element. In particular, when the complex ion contains B or when it contains C and B, higher ionic conductivity is likely to be ensured. Specific examples of complex ions containing H include (CBH 10 ) - , (CB 11 H 12 ) - , (B 10 H 10 ) 2- , (B 12 H 12 ) 2- , (BH4) - , (NH2) - , (AlH4) - , and combinations thereof. In particular, (CB9H 10 ) - , (CB 11H 12 ) - In other words, the complex hydride solid electrolyte may contain Li, C, B, and H.

[0050] 1.4.3.2 Liquid electrolyte A liquid electrolyte (electrolytic solution) is a liquid containing carrier ions. In the case of a positive electrode composite for a lithium ion battery, the electrolytic solution contains lithium ions. The electrolytic solution may be an aqueous electrolytic solution or a non-aqueous electrolytic solution. The composition of the electrolytic solution may be the same as that of known electrolytic solutions for lithium ion secondary batteries. The electrolytic solution may be one in which a lithium salt is dissolved in water or a non-aqueous solvent. Examples of non-aqueous solvents include carbonate-based solvents. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of lithium salts include LiPF6, LiTFSI, and LiFSI.

[0051] 1.4.4 Conductive additives Examples of conductive additives that can be contained in the positive electrode composite 1 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials such as nickel, titanium, aluminum, and stainless steel. The conductive additive may be, for example, particulate or fibrous, and its size is not particularly limited. Only one type of conductive additive may be used alone, or two or more types may be used in combination.

[0052] 1.4.5 Binder Examples of binders that can be contained in the positive electrode mixture 1 include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0053] 1.4.6 Other In addition to the above components, the positive electrode mixture 1 may contain various additives, such as a dispersant and a lubricant.

[0054] 1.5 Effect of positive electrode mixture As described above, the positive electrode composite 1 includes a predetermined first active material 1a and a predetermined second active material 1b. Here, the plate-shaped O2-type active material (first active material 1a) has an intercalation port at its edge. Therefore, when a positive electrode active material layer is formed using a plate-shaped O2-type active material, it is preferable that the plate surface of the plate-shaped O2-type active material intersects (preferably orthogonal to) the surface direction of the positive electrode active material layer. However, when a positive electrode active material layer is formed using only a plate-shaped O2-type active material as the positive electrode active material, the plate surface of the plate-shaped O2-type active material is aligned with the surface direction of the positive electrode active material layer (FIG. 3). Therefore, the capacity is likely to decrease due to an increase in the degree of bending and a decrease in the utilization rate of the plate-shaped O2-type active material. In contrast, with the positive electrode composite 1, by mixing a spherical O2-type active material (second active material 1b) with a plate-shaped O2-type active material, the spherical O2-type active material can raise the plate-shaped O2-type active material, making it easier to randomize the orientation of the plate surfaces of the plate-shaped O2-type active material (Figure 1). That is, the amount of plate-shaped O2-type active material intersecting the surface direction of the positive electrode active material layer 20 increases, which tends to increase capacity due to reduced bending and increased utilization of the plate-shaped O2-type active material. Furthermore, the spherical O2-type active material itself can contribute to improving capacity, which can further increase capacity.

[0055] 2. Manufacturing method of cathode composite The positive electrode composite 1 is obtained by mixing at least a first active material 1a and a second active material 1b. Here, the first active material 1a and the second active material 1b can be produced, for example, as follows.

[0056] 2.1 Method for producing the first and second active materials As shown in FIG. 4, the first active material 1a and the second active material 1b are each produced by the following method: Obtaining precursor particles (step S1), Coating the surface of the precursor particles with a Na salt to obtain coated particles (step S2); The coated particles are calcined to obtain Na-containing transition metal oxide particles having a P2 type structure (step S3); and At least a portion of the Na in the Na-containing transition metal oxide particles is replaced with Li by ion exchange to obtain positive electrode active material particles having an O2-type structure (step S4); It may include:

[0057] 2.1.1 Process S1 In step S1, precursor particles are obtained. The precursor particles may be a salt or compound containing at least one transition metal element selected from Mn, Ni, and Co. The precursor particles may be, for example, at least one of carbonate, sulfate, nitrate, acetate, and hydroxide. Specifically, the precursor particles may be a salt represented by MeCO3 (where Me is at least one transition metal element selected from Mn, Ni, and Co), a salt represented by MeSO4, a salt represented by Me(NO3)2, a salt represented by Me(CH3COO)2, or a compound represented by Me(OH)2. These may also be hydrates. Furthermore, the precursor particles may contain, in addition to the transition metal element Me, at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W.

[0058] The precursor particles may also be spherical. The definition of "spherical" is as described above. If the precursor particles are spherical, the shape of the final active material can also be spherical. In other words, the second active material 1b can be easily obtained. The size of the spherical precursor particles is not particularly limited. Spherical precursor particles can be obtained by a solution method such as a coprecipitation method or a sol-gel method. Specifically, in the case of the coprecipitation method, an aqueous solution of MeSO4 and an aqueous solution of Na2CO3 are prepared, and each aqueous solution is dropped and mixed to obtain a precipitate. The precipitate is a spherical precursor particle represented by MeCO3. A carbonate containing Me and M may be obtained as the precursor particle by dissolving a sulfate or the like of M in the aqueous solution of MeSO4.

[0059] 2.1.2 Process S2 In step S2, the surfaces of the precursor particles are coated with a Na salt to obtain coated particles. When a spherical O2-type positive electrode active material (second active material 1b) is obtained, the coated particles may be obtained by coating 40 area % or more of the surface of the precursor particles with a Na salt. The coated particles may be obtained by coating 50 area % or more, 60 area % or more, or 70 area % of the surface of the precursor particles with a Na salt. Examples of Na salts include carbonates and nitrates.

[0060] Various methods can be used to coat the surface of precursor particles with Na salt. To finally obtain a spherical O2-type positive electrode active material (second active material 1b), for example, a tumbling fluidized bed coating method or a spray drying method may be employed. That is, a coating solution containing dissolved Na salt is prepared, and the coating solution is brought into contact with the entire surface of the precursor particles, and then dried simultaneously or after the contact. By adjusting the coating conditions (temperature, time, number of times, etc.), for example, 40% or more of the surface area of ​​the precursor particles can be coated with Na salt. According to the findings of the present inventors, if the coverage rate of Na salt is low, abnormal growth of P2-type crystals is likely to occur on the surface of the coated particles when the coated particles are fired, resulting in plate-shaped Na-containing transition metal oxide particles, while spherical Na-containing transition metal oxide particles are difficult to obtain. If the coverage rate of Na salt is high, the crystallites of the P2-type crystals can be made small when the coated particles are fired, and the shape of the coated particles is likely to become spherical, corresponding to the shape of the precursor particles. The amount of Na salt coated on the coated particles may be sufficient to obtain a P2 type structure (amount that allows a sufficient amount of Na to be doped).

[0061] 2.1.3 Process S3 In step S3, the coated particles are calcined to obtain Na-containing transition metal oxide particles having a P2-type structure. Here, the Na-containing transition metal oxide particles may be plate-shaped or spherical. When the Na-containing transition metal oxide particles are plate-shaped, the O2-type positive electrode active material obtained thereafter will also be plate-shaped. That is, a first active material 1a is obtained. On the other hand, when the Na-containing transition metal oxide particles are spherical, the O2-type positive electrode active material obtained thereafter will also be spherical. That is, a second active material 1b is obtained.

[0062] The Na-containing transition metal oxide particles may contain, as constituent elements, at least one transition metal element selected from Mn, Ni, and Co, Na, and O. In particular, when the constituent elements contain at least Na, Mn, at least one of Ni and Co, and O, and especially when the constituent elements contain at least Na, Mn, Ni, Co, and O, the performance of the positive electrode active material particles is likely to be further improved. The Na-containing transition metal oxide particles may contain Na c Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2. Here, 0 < c ≤ 1.00, x + y + z = 1, and 0 ≤ p + q + r ≤ 0.15. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the Na-containing transition metal oxide particles have such a chemical composition, the P2-type structure is more likely to be maintained. In the above chemical composition, c may be greater than 0, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and may also be 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, x may be 0 or more, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and may also be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. In the above chemical composition, y may be 0 or more, 0.10 or more, or 0.20 or more, and may also be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. In the above chemical composition, z may be 0 or more, 0.10 or more, 0.20 or more, or 0.30 or more, and may also be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. Many of M do not contribute to charge and discharge. In this regard, when p + q + r is 0.15 or less, it is easy to ensure a high charge-discharge capacity. p + q + r may be 0.10 or less, or may be 0. The composition of O is approximately 2, but it is not necessarily exactly 2.0 and is indeterminate.

[0063] The firing temperature may be any temperature at which the P2-type structure is formed. If the firing temperature is too low, Na doping will not occur and it is difficult to obtain the P2-type structure. On the other hand, if the firing temperature is too high, an O3-type structure is likely to be formed instead of the P2-type structure. The firing temperature may be, for example, 700 °C or higher and 1100 °C or lower, or may be 800 °C or higher and 1000 °C or lower.

[0064] The calcination time may be adjusted appropriately depending on the shape of the desired Na-containing transition metal oxide particles. As described above, if the coverage rate of the Na salt on the coated particles is low, abnormal growth of P2-type crystals is likely to occur on the surface of the coated particles when the coated particles are calcined, and plate-shaped Na-containing transition metal oxide particles are likely to be obtained. On the other hand, if the coverage rate of the Na salt on the coated particles is high, small P2-type crystallites are likely to form on the surface of the particles when the coated particles are calcined. By growing P2-type crystallites along the surface of the particles so as to connect one P2-type crystallite to another, spherical Na-containing transition metal oxide particles can be obtained. If the calcination time is too short, Na doping will not occur, and the desired P2-type structure will not be obtained. On the other hand, if the calcination time is too long, excessive growth of the P2-type structure will result in plate-shaped particles. As far as the inventors have confirmed, spherical Na-containing transition metal oxide particles are likely to be obtained when the firing time is 30 minutes or more and 3 hours or less, and plate-shaped Na-containing transition metal oxide particles are likely to be obtained when the firing time is longer than this.

[0065] The firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere such as air atmosphere or an inert gas atmosphere.

[0066] 2.1.4 Process S4 In step S4, at least a portion of the Na in the Na-containing transition metal oxide particles is replaced with Li by ion exchange to obtain positive electrode active material particles having an O2-type structure. Here, by ion-exchanging a portion of the Na in the plate-shaped P2-type particles with Li, a plate-shaped O2-type active material (first active material 1a) is obtained. On the other hand, by ion-exchanging a portion of the Na in the spherical P2-type particles with Li, a spherical O2-type active material (second active material 1b) is obtained.

[0067] Ion exchange can be performed, for example, using an aqueous solution containing lithium halide or using a mixture of lithium halide and other lithium salts (e.g., molten salt). Of the two methods, the method using molten salt is preferred because the P2 structure is easily broken by water penetration and from the viewpoint of crystallinity. That is, by mixing the Na-containing transition metal oxide particles having the P2 structure with the molten salt and heating the mixture to a temperature equal to or higher than the melting point of the molten salt, at least a portion of the Na in the Na-containing transition metal oxide particles can be replaced with Li by ion exchange.

[0068] The lithium halide constituting the molten salt is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. The other lithium salt constituting the molten salt is preferably lithium nitrate. By using the molten salt, the melting point becomes lower than when lithium halide or other lithium salt is used alone, and ion exchange can be performed at a lower temperature.

[0069] The temperature for ion exchange may be, for example, equal to or higher than the melting point of the molten salt and equal to or lower than 600°C, 500°C, 400°C, or 300°C. If the temperature for ion exchange is too high, the stable O3 structure is likely to be formed rather than the O2 structure. On the other hand, from the viewpoint of shortening the time required for ion exchange, it is preferable that the temperature for ion exchange be as high as possible.

[0070] 2.2 Mixing with other ingredients The first active material 1a and second active material 1b produced as described above are mixed with the above-mentioned solid electrolyte or the like to obtain the positive electrode composite 1. The mixing means is not particularly limited, and the mixing may be carried out using a known mixing device.

[0071] 3. Lithium-ion battery The cathode composite 1 of the present disclosure can be used as a cathode material for lithium-ion batteries. FIG. 5 schematically illustrates the configuration of a lithium-ion battery 100 according to one embodiment. As illustrated in FIG. 5, the lithium-ion battery 100 includes a cathode active material layer 20, an electrolyte layer 30, and an anode active material layer 40. The cathode active material layer 20 includes the cathode composite 1 of the present disclosure. In the lithium-ion battery 100, one or both of the electrolyte layer 30 and the anode active material layer 40 may contain a solid electrolyte. Alternatively, the lithium-ion battery 100 may include all of the cathode active material layer 20, the electrolyte layer 30, and the anode active material layer 40. Furthermore, the lithium-ion battery 100 may be a solid-state battery. A solid-state battery is one in which the electrolyte having carrier ion conductivity is primarily composed of a solid electrolyte. However, a liquid component may be included in part. Alternatively, the lithium-ion battery 100 may be an all-solid-state battery substantially free of liquid components. 4, the lithium-ion battery 100 may include a positive electrode current collector 10 in contact with the positive electrode active material layer 20. The lithium-ion battery 100 may also include a negative electrode current collector 50 in contact with the negative electrode active material layer 40.

[0072] 3.1 Positive electrode current collector The positive electrode current collector 10 can be any of those commonly used as positive electrode current collectors for lithium-ion batteries. The positive electrode current collector 10 may have at least one shape selected from foil, plate, mesh, punched metal, and foam. The positive electrode current collector 10 may be made of metal foil or metal mesh. Metal foil is particularly easy to handle. The positive electrode current collector 10 may be made of multiple foils. Examples of metals constituting the positive electrode current collector 10 include at least one selected from Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, V, Mg, Pb, Ge, In, Sn, Zr, and stainless steel. In particular, the positive electrode current collector 10 may contain Al to ensure oxidation resistance. The positive electrode current collector 10 may have a coating layer on its surface for purposes such as adjusting resistance. For example, the positive electrode current collector 10 may have a carbon coating layer. The positive electrode current collector 10 may also be a metal foil or a substrate plated or vapor-deposited with the above-mentioned metal. When the positive electrode current collector 10 is made of multiple metal foils, some layer may be present between the multiple metal foils. The thickness of the positive electrode current collector 10 is not particularly limited. For example, it may be 0.1 μm or more and 1 mm or less, with a lower limit of 1 μm or more and an upper limit of 100 μm or less.

[0073] 3.2 Cathode active material layer The positive electrode active material layer 20 includes the above-described positive electrode composite 1. The shape of the positive electrode active material layer 20 is not particularly limited, and may be, for example, a substantially flat sheet-like positive electrode active material layer 20. The thickness of the positive electrode active material layer 20 is not particularly limited, and may be, for example, 0.1 μm or more or 1 μm or more, and may be 2 mm or less or 1 mm or less.

[0074] The positive electrode active material layer 20 can be manufactured by applying a known method. For example, the positive electrode active material layer 20 can be easily formed by dry or wet molding the positive electrode composite 1. The positive electrode active material layer 20 may be molded together with the positive electrode current collector 10, or may be molded separately from the positive electrode current collector 10.

[0075] 3.3 Electrolyte layer The electrolyte layer 30 is disposed between the positive electrode active material layer 20 and the negative electrode active material layer 40. The electrolyte layer 30 contains at least an electrolyte. The electrolyte layer 30 may contain one or both of a solid electrolyte and a liquid electrolyte (electrolytic solution), and may further contain a binder and various additives. The contents of the electrolyte and binder in the electrolyte layer 30 are not particularly limited. Alternatively, the electrolyte layer 30 may include a separator or the like for retaining the electrolytic solution and preventing contact between the positive electrode active material layer 20 and the negative electrode active material layer 40. The thickness of the electrolyte layer 30 is not particularly limited and may be, for example, 0.1 μm or more and 2 mm or less, with a lower limit of 1 μm or more and an upper limit of 1 mm or less.

[0076] The electrolyte layer 30 may consist of one layer or multiple layers. For example, the electrolyte layer 30 may include a first layer disposed on the positive electrode active material layer 20 side and a second layer disposed on the negative electrode active material layer 40 side, where the first layer may contain a first electrolyte and the second layer may contain a second electrolyte. The first electrolyte and the second electrolyte may be different from each other. The first electrolyte and the second electrolyte may each be at least one selected from the oxide solid electrolyte, sulfide solid electrolyte, and ionic solid electrolyte described above. For example, the first layer may contain an ionic solid electrolyte, and the second layer may contain at least one of an ionic solid electrolyte and a sulfide solid electrolyte.

[0077] The electrolyte contained in the electrolyte layer 30 may be appropriately selected from the examples (solid electrolytes and / or liquid electrolytes) of the electrolytes that can be contained in the positive electrode active material layer 20 described above. The binder that can be contained in the electrolyte layer 30 may also be appropriately selected from the examples of the binders that can be contained in the positive electrode active material layer 20 described above. Each of the electrolytes and binders may be used alone or in combination of two or more. The separator may be any separator commonly used in secondary batteries, such as those made of resins such as polyethylene (PE), polypropylene (PP), polyester, and polyamide. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a two-layer structure of PE / PP, or a three-layer structure of PP / PE / PP or PE / PP / PE. The separator may be made of a nonwoven fabric such as a cellulose nonwoven fabric, a resin nonwoven fabric, or a glass fiber nonwoven fabric.

[0078] 3.4 Negative electrode active material layer The negative electrode active material layer 40 includes at least a negative electrode active material. The negative electrode active material layer 40 may also optionally include an electrolyte, a conductive additive, a binder, various additives, and the like. The content of each component in the negative electrode active material layer 40 may be appropriately determined depending on the desired battery performance. For example, the total solid content of the negative electrode active material layer 40 is taken as 100% by mass, and the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or may be 100% by mass or less, less than 100% by mass, 95% by mass or less, or 90% by mass or less. Alternatively, the total content of the negative electrode active material layer 40, taken as 100% by volume, may be 85% by volume or more, 90% by volume or more, or 95% by volume or more, and the remainder may be voids or other components. The shape of the negative electrode active material layer 40 is not particularly limited and may be, for example, a substantially flat sheet. The thickness of the negative electrode active material layer 40 is not particularly limited and may be, for example, 0.1 μm to 2 mm, with a lower limit of 1 μm, 10 μm, or 30 μm, and an upper limit of 1 mm, 500 μm, or 100 μm.

[0079] 3.4.1 Negative electrode active material The negative electrode active material contained in the negative electrode active material layer 40 may be any of those known as negative electrode active materials for lithium ion batteries. Among known active materials, various materials may be used that have a potential (charge / discharge potential) at which they absorb and release predetermined carrier ions that is lower than that of the positive electrode active material. The negative electrode active material may be at least one selected from, for example, silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloys, and the like. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination. The negative electrode active material may have any shape commonly used for negative electrode active materials for lithium ion batteries. For example, the negative electrode active material may be in the form of particles. The negative electrode active material particles may be primary particles or secondary particles formed by agglomeration of multiple primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more and 500 μm or less, with a lower limit of 5 nm or more or 10 nm or more and an upper limit of 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material layer 40 may be made of a sheet-like (foil-like, film-like) active material such as lithium foil.

[0080] 3.4.2 Other The electrolyte that can be contained in the anode active material layer 40 may be appropriately selected from the examples (solid electrolytes and / or liquid electrolytes) of the electrolytes that can be contained in the cathode active material layer 20 described above. The conductive additive that can be contained in the anode active material layer 40 may be appropriately selected from the examples of the conductive additive that can be contained in the cathode active material layer 20 described above. The binder that can be contained in the anode active material layer 40 may be appropriately selected from the examples of the binders that can be contained in the cathode active material layer 20 described above. Each of the electrolyte, conductive additive, and binder may be used alone or in combination of two or more.

[0081] The negative electrode active material layer 40 may contain various additives in addition to the above components, such as a dispersant and a lubricant.

[0082] The negative electrode active material layer 40 can be manufactured by applying a known method. For example, the negative electrode active material layer 40 can be easily formed by dry or wet molding a negative electrode composite containing the above-mentioned various components. The negative electrode active material layer 40 may be molded together with the negative electrode current collector 50, or may be molded separately from the negative electrode current collector 50.

[0083] 3.5 Negative electrode current collector The negative electrode current collector 50 can be any of those commonly used as negative electrode current collectors for lithium-ion batteries. The negative electrode current collector 50 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The negative electrode current collector 50 may be a metal foil or metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of ease of handling. The negative electrode current collector 50 may be composed of multiple foils or sheets. Examples of metals constituting the negative electrode current collector 50 include at least one selected from Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, V, Mg, Pb, Ge, In, Sn, Zr, and stainless steel. In particular, from the viewpoints of ensuring reduction resistance and being less likely to alloy with lithium, the negative electrode current collector 50 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 50 may have some kind of coating layer on its surface for the purpose of adjusting the resistance, etc. For example, the negative electrode current collector 50 may have a carbon coating layer. The negative electrode current collector 50 may be an aluminum foil having a carbon coating layer. The negative electrode current collector 50 may also be a metal foil or a substrate on which the above metal is plated or vapor-deposited. When the negative electrode current collector 50 is made of multiple sheets of metal foil, some kind of layer may be present between the multiple sheets of metal foil. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more and 1 mm or less, with a lower limit of 1 μm or more and an upper limit of 100 μm or less.

[0084] 3.6 Other Configurations In addition to the above components, the lithium-ion battery 100 may also include typical battery components. For example, tabs and terminals. The lithium-ion battery 100 may have the above components housed inside an exterior body. Any known battery exterior body can be used as the exterior body. Furthermore, multiple lithium-ion batteries 100 may be electrically connected and stacked in any desired manner to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case. The lithium-ion battery 100 may also include other obvious components, such as necessary terminals. The lithium-ion battery 100 may have, for example, a coin type, a laminate type, a cylindrical type, or a rectangular type. The lithium-ion battery 100 may also be a secondary battery.

[0085] 4. Lithium-ion battery manufacturing method The lithium ion battery 100 can be manufactured by applying a known method. As shown in Fig. 6, the manufacturing method of the lithium ion battery 100 may include, for example, obtaining a positive electrode active material layer 20 using the positive electrode composite 1 of the present disclosure (step S11), and obtaining the lithium ion battery 100 using the positive electrode active material layer 20, an electrolyte layer 30, and a negative electrode active material layer 40 (step S12). More specifically, for example, the lithium ion battery 100 may be manufactured as follows. However, the manufacturing method of the lithium ion battery 100 is not limited to the following method, and each layer may be formed by, for example, dry molding or the like. (1) A positive electrode mixture constituting a positive electrode active material layer is dispersed in a solvent to obtain a positive electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The positive electrode slurry is then applied to the surface of a positive electrode current collector or an electrolyte layer (described later) using a doctor blade or the like, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector or the electrolyte layer, thereby forming a positive electrode. Here, the positive electrode active material layer may be press-molded. (2) The negative electrode mixture constituting the negative electrode active material layer is dispersed in a solvent to obtain a negative electrode slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The negative electrode slurry is then applied to the surface of the negative electrode current collector or the electrolyte layer described below using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector or the electrolyte layer, thereby forming a negative electrode. Here, the negative electrode active material layer may be press-molded. (3) The layers are stacked so that the electrolyte layer is sandwiched between the negative electrode and the positive electrode, thereby obtaining a laminate having a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. The electrolyte layer may be obtained, for example, by molding an electrolyte mixture containing an electrolyte and a binder, or by press molding. Here, the laminate may be further press-molded. Other members such as terminals may be attached to the laminate as necessary. When an electrolytic solution is used, a separator may be used in the electrolyte layer. (4) The laminate is housed in a battery case and sealed to obtain a lithium ion battery.

[0086] 5. How to increase the capacity of a lithium-ion battery The technology of the present disclosure also has an aspect as a method for increasing the capacity of a lithium ion battery. That is, the method for increasing the capacity of a lithium ion battery of the present disclosure is characterized by using the positive electrode composite of the present disclosure as a material constituting the positive electrode active material layer of the lithium ion battery.

[0087] 6. Vehicles equipped with lithium-ion secondary batteries As described above, when a positive electrode active material layer of a lithium-ion battery is formed using the positive electrode mixture of the present disclosure, an increase in the capacity of the lithium-ion battery can be expected. Such a lithium-ion battery can be suitably used in at least one type of vehicle selected from, for example, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and an electric vehicle (BEV). That is, the technology of the present disclosure also has an aspect of a vehicle having a lithium-ion battery, in which the lithium-ion battery has a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and the positive electrode active material layer has the positive electrode mixture of the present disclosure. [Example]

[0088] As described above, one embodiment of the positive electrode composite, lithium ion secondary battery, and manufacturing method thereof according to the present disclosure has been described, but the technology of the present disclosure can be modified in various ways other than the above embodiment without departing from the gist thereof. Below, the technology of the present disclosure will be described in more detail with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0089] 1. Preparation of Precursor Particles MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed to achieve the desired composition ratio and dissolved in distilled water to a concentration of 1.2 mol / L to obtain the first solution. In a separate container, Na2CO3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain the second solution. Next, 500 mL of each of the first and second solutions was added dropwise at a rate of approximately 4 mL / min to a reaction vessel containing 1000 mL of pure water. After the addition, the mixture was stirred at room temperature for 1 hour at a stirring rate of 150 rpm. The precipitate was washed with pure water and subjected to solid-liquid separation using a centrifuge. The resulting precipitate was dried overnight at 120°C, crushed in a mortar, and then air-classified to remove fine particles, yielding mixed salt particles (precursor particles) containing Mn, Ni, and Co. The precursor particles were spherical with a circularity of 0.98.

[0090] 2. Preparation of Na-containing transition metal oxide particles with P2-type structure 2.1 First P2-type plate-like particles Na2CO3 and the above precursor particles were mixed 0.7 Mn 0.5 Ni 0.2 Co 0.3 The materials were weighed in a dry atmosphere to have a composition of 02, and mixed in a mortar to obtain a mixture. The mixture was fired in an electric furnace using an alumina crucible in an air atmosphere. Specifically, the mixture was subjected to the "first heating step," "pre-firing step," "second heating step," "main firing step," "in-furnace cooling step," and "out-furnace cooling step" as shown in Table 1 below. The "in-furnace cooling step" refers to a cooling step in an electric furnace, and the "out-furnace cooling step" refers to a step of cooling in the air outside the electric furnace. Thereafter, the mixture was pulverized in a mortar in a dry atmosphere to obtain a Na-containing transition metal oxide (Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 The Na-containing transition metal oxide was a plate-like particle having an aspect ratio (major axis / minor axis) of 2.0 or more in a cross section along the thickness direction.

[0091] [Table 1]

[0092] 2.2 Second P2-type plate-like particles The mixture was fired under the same conditions as the first plate-like particles, except that the temperature rise time in the second temperature rise step was 70 minutes, the end temperature was 950°C, the start and end temperatures in the main firing step were 950°C, and the start temperature in the furnace cooling step was 950°C and the cooling time was 140 minutes. Thereafter, the mixture was pulverized in a mortar in a dry atmosphere to obtain a Na-containing transition metal oxide (Na) having a P2 structure. 0.7 Mn 0.5 Ni 0.2 Co 0.3 The Na-containing transition metal oxide was a plate-like particle having an aspect ratio (major axis / minor axis) of 2.0 or more in a cross section along the thickness direction.

[0093] 2.3 Spherical P2-type particles After weighing out Na2CO3 and distilled water so that the total concentration was 1150 g / L, the mixture was stirred using a stirrer until completely dissolved to prepare an aqueous Na2CO3 solution. The precursor particles were mixed into the aqueous Na2CO3 solution to form a slurry. The Na2CO3 and the precursor particles were dried and then mixed to form a Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 The resulting slurry was dried by spray drying. Specifically, a spray drying apparatus DL410 was used, with a slurry delivery rate of 30 mL / min, an inlet temperature of 200°C, and a circulating air volume of 0.8 m 3 / min and a spray air pressure of 0.3 MPa, 77 area % of the surface of the precursor particles was coated with Na2CO3 to obtain coated particles.

[0094] The coated particles were fired in an electric furnace using an alumina crucible in an air atmosphere. Specifically, the coated particles were subjected to the "first heating step," "pre-firing step," "second heating step," "main firing step," "in-furnace cooling step," and "out-furnace cooling step" as shown in Table 2 below and FIG. 7. Thereafter, the particles were pulverized in a mortar in a dry atmosphere to obtain a Na-containing transition metal oxide (Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 O2) was obtained. The Na-containing transition metal oxide was in the form of spherical particles.

[0095] [Table 2]

[0096] 3. Preparation of active materials with O2-type structures LiNO3 and LiCl were weighed out to a molar ratio of 50:50 and mixed with P2-type plate-shaped particles or P2-type spherical particles in a molar ratio 10 times the minimum Li amount required for ion exchange to obtain a mixture. The mixture was fired in an alumina crucible at 280°C for 1 hour in an air atmosphere to obtain a fired product. The salt remaining in the fired product was washed with pure water, and solid-liquid separation was performed by vacuum filtration to obtain a second precipitate. The second precipitate was dried overnight at 120°C to obtain positive electrode active material particles with an O2 structure.

[0097] When the first P2 type plate-like particles are used, the cathode active material particles have an O2 type structure, and in the cross section along the thickness direction thereof, the aspect ratio of the major axis to the minor axis (major axis / minor axis) is 3.1, and the major axis D 1L First O2 type plate-like particles having a particle size of 2.9 μm were obtained.

[0098] When the second P2 type plate-like particles are used, the cathode active material particles have an O2 type structure, and in the cross section along the thickness direction thereof, the aspect ratio of the major axis to the minor axis (major axis / minor axis) is 3.2, and the major axis D 1L Second O2 type plate-like particles were obtained with a particle size of 4.1 μm.

[0099] When spherical P2 type particles were used, spherical O2 type particles having a circularity of 0.85 and a diameter D2 of 2.3 μm were obtained as positive electrode active material particles having an O2 type structure.

[0100] The plate-shaped O2-type positive electrode active material particles were substantially composed of one crystallite. On the other hand, the surface of the spherical O2-type positive electrode active material particles was composed of multiple crystallites, and the diameter of the crystallites was less than 1 μm. The crystallites had a first surface exposed on the particle surface, and the first surface was planar. Furthermore, elemental analysis revealed that both the plate-shaped O2-type positive electrode active material particles and the spherical O2-type positive electrode active material particles contained Li 0.63 Mn 0.5 Ni 0.2 Co 0.3It was confirmed that the positive electrode active material particles had a chemical composition represented by O2. Figures 8A and 8B show SEM photographs of the appearance of the positive electrode active material particles. Figure 8A shows plate-shaped O2-type positive electrode active material particles, and Figure 8B shows spherical O2-type positive electrode active material particles.

[0101] 4. Preparation of Evaluation Cell The above O2 type positive electrode active material particles, sulfide solid electrolyte A (Argyrodite type sulfide solid electrolyte), PVDF, and VGCF were weighed and mixed in a mass ratio of O2 type positive electrode active material particles: sulfide solid electrolyte A: PVDF: VGCF = 82.1: 14.9: 0.6: 2.4 to obtain a positive electrode composite. 15 Si4 and Si element), sulfide solid electrolyte B (Li2S-P2S5-LiI-LiBr), PVDF, and VGCF, 15 A negative electrode composite was obtained by weighing and mixing S4:Si:sulfide solid electrolyte B:PVDF:VGCF = 30.5:50.7:15.5:0.9:2.4 (mass ratio). Furthermore, sulfide solid electrolyte B and acrylate butadiene rubber (ABR) were weighed and mixed to a sulfide solid electrolyte B:ABR = 99.4:0.6 (mass ratio). The electrolyte composite was placed in a McCorm cylinder and pressed at 9.8 kN for 1 minute to form an electrolyte layer. The positive electrode composite was then placed on one side of the electrolyte layer and pressed at 19.6 kN for 1 minute to form a positive electrode active material layer. The negative electrode composite was then placed on the other side of the electrolyte layer and pressed at 58 kN for 3 minutes to form a negative electrode active material layer. Finally, current collectors were placed on both ends of each layer in the stacking direction to obtain an evaluation cell.

[0102] 2.1 Example 1 The O2-type positive electrode active material was a mixture of first O2-type plate-like particles and spherical O2-type particles in a mass ratio of plate-like to spherical particles of 80:20. 1L and the diameter D2 of the spherical O2-type particle 1L / D2 was 1.26.

[0103] 2.2 Example 2 The O2-type positive electrode active material was a mixture of first O2-type plate-like particles and spherical O2-type particles in a mass ratio of plate-like to spherical particles of 20:80. The major axis D of the first O2-type plate-like particles was 1L and the diameter D2 of the spherical O2-type particle 1L / D2 was 1.26.

[0104] 2.3 Comparative Example 1 The O2-type positive electrode active material was a mixture of second O2-type plate-like particles and spherical O2-type particles in a mass ratio of plate-like to spherical particles of 80:20. The major axis D of the second O2-type plate-like particles was 1L and the diameter D2 of the spherical O2-type particle 1L / D2 was 1.78.

[0105] 2.4 Comparative Example 2 Only spherical O2-type particles were used as the O2-type positive electrode active material.

[0106] 2.5 Comparative Example 3 As the O2-type positive electrode active material, only the first O2-type plate-like particles were used.

[0107] 3. Evaluation conditions The above evaluation cell was charged and discharged in a thermostatic chamber maintained at 25° C. at a voltage range of 1.8-4.6 V and a 0.1 C rate (1 C = 220 mA / g), and the discharge capacity was measured. The results are shown in Table 3 below and FIG. 9.

[0108] [Table 3]

[0109] 4. Cross-section observation A cross section of the positive electrode active material layer of the evaluation cell taken along the thickness direction of the layer was observed using an SEM, and the results are shown in Figures 10A to 10E.

[0110] 5. Evaluation Results As shown in Table 2 and FIG. 9, the cells according to Examples 1 and 2 exhibited high discharge capacities. In particular, the cell according to Example 1 exhibited a significantly high discharge capacity. This is believed to be due to the following mechanism. First, the plate-shaped O2-type active material (first active material) has an intercalation entrance / exit at its edge. Therefore, when a positive electrode active material layer is formed using a plate-shaped O2-type active material, it is preferable that the plate surface of the plate-shaped O2-type active material intersects (preferably orthogonal to) the surface direction of the positive electrode active material layer. However, when a positive electrode active material layer is formed using only a plate-shaped O2-type active material as the positive electrode active material, the plate surface of the plate-shaped O2-type active material is aligned with the surface direction of the positive electrode (FIG. 10E, Comparative Example 3). Therefore, the capacity is likely to decrease due to an increase in the degree of bending and a decrease in the utilization rate of the plate-shaped O2-type active material. Even when a spherical O2-type active material is used together with a plate-shaped O2-type active material, the spherical O2-type active material has a small size (D 1L When the ratio of D / D2 exceeds 1.5, this problem is not resolved (FIG. 10C, Comparative Example 1). In contrast, when a spherical O2 type active material is used together with a plate-like O2 type active material and the size of the spherical O2 type active material is large (D 1L By using a positive electrode active material having a diameter of 1.5 or less (where / D2 is 1.5 or less), the spherical O2-type active material can raise the plate-shaped O2-type active material, making it easier to randomize the orientation of the plate surfaces of the plate-shaped O2-type active material (Figures 10A and 10B, Examples 1 and 2). That is, it is thought that the amount of plate-shaped O2-type active material intersecting the surface direction of the positive electrode active material layer increases, reducing the degree of bending and increasing the utilization rate of the plate-shaped O2-type active material, thereby increasing the capacity. It is also thought that the spherical O2-type active material itself can contribute to improving the capacity, resulting in a further increase in capacity.

[0111] 6. Supplementary Information In the above examples, positive electrode active material particles having a specific chemical composition are exemplified, but the chemical composition of the positive electrode active material particles of the present disclosure is not limited thereto. However, according to the findings of the present inventors, when the transition metal contains at least one of Mn, Ni, and Co, the P2 type structure undergoes crystal growth in a specific direction to form a plate-like shape, and the final O2 type particles also tend to be plate-like. The problem solved by the technology of the present disclosure is particularly pronounced when the transition metal contains at least one of Mn, Ni, and Co.

[0112] 7. Summary From the above examples, when a positive electrode active material layer of a lithium ion battery is formed using a positive electrode mixture having the following configurations (1) to (5), the capacity of the lithium ion battery is likely to be improved. (1) A positive electrode mixture, comprising a first active material and a second active material. (2) The first active material has an O2 type structure and is plate-shaped. (3) The second active material has an O2 type structure and is spherical. (4) The major axis D of the first active material 1L and the diameter D2 of the second active material 1L / D2 is 0.1 or more and 1.5 or less. (5) The proportion of the first active material to the total of the first active material and the second active material is 10% by mass or more and 90% by mass or less. [Explanation of symbols]

[0113] 1. Positive electrode mixture 1a First active material 1b Second active material 100 Lithium-ion batteries 10 Positive electrode current collector 20 Cathode active material layer 30 Electrolyte layer 40 Negative electrode active material layer 50 Negative electrode current collector

Claims

1. a positive electrode composite including a first active material and a second active material; the first active material contains, as constituent elements, at least one transition metal element selected from Mn, Ni, and Co, Li, and O, has an O2-type structure, and is plate-shaped; the second active material contains, as constituent elements, at least one transition metal element selected from Mn, Ni, and Co, Li, and O, has an O2-type structure, and is spherical; The major axis D of the first active material １Ｌ and the diameter D of the second active material ２ Relative to D １Ｌ / D ２ is equal to or greater than 0.1 and equal to or less than 1.5, a ratio of the first active material to the total of the first active material and the second active material is 10% by mass or more and 90% by mass or less; Positive electrode mixture.

2. The positive electrode mixture according to claim 1, the surface of the second active material has a plurality of crystallites; Positive electrode mixture.

3. The positive electrode mixture according to claim 1, including a solid electrolyte, Positive electrode mixture.

4. The positive electrode mixture according to claim 1, The conductive material may include one or both of a conductive additive and a binder. Positive electrode mixture.

5. The positive electrode composite according to claim 1, a ratio D 1L / D 2 of a major axis D 1L of the first active material to a diameter D 2 of the second active material is 0.8 or more and 1.5 or less; Positive electrode mixture.

6. A lithium ion battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer comprises the positive electrode mixture according to any one of claims 1 to 5. Lithium-ion battery.

7. 7. The lithium ion battery of claim 6, one or both of the electrolyte layer and the negative electrode active material layer contains a solid electrolyte; Lithium-ion battery.

8. A method for manufacturing a lithium ion battery, comprising: Obtaining a positive electrode active material layer using the positive electrode mixture according to any one of claims 1 to 5; and obtaining a lithium ion battery using the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer; A manufacturing method comprising:

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