Lithium ion battery and manufacturing method for lithium ion battery

Abstract

To inhibit resistance of a battery from increasing when tha battery is configured using cathode active material having an O2 type structure of a Li deficiency type.SOLUTION: A battery includes a cathode active material layer, an electrolyte layer, and an anode active material layer. The cathode active material layer contains cathode active material having an O2 type structure of a Li deficiency type and sulfide solid electrolyte. And a Raman spectrum of the cathode active material layer satisfies a relation IR1 / IR2≤0.20 and IR3 / IR2≤0.20 (IR1: peak intensity derived from P2S64- in the Raman spectrum, IR2: peak intensity derived from PS43- in the Raman spectrum, IR3: peak intensity derived from S-S in the Raman spectrum).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] This application discloses a lithium ion battery and a method for manufacturing a lithium ion battery. [Background technology]

[0002] Patent Document 1 discloses a positive electrode active material for an all-solid-state battery having an O2 type structure (O: Octahedral). The positive electrode active material having the O2 type structure is obtained by ion-exchanging at least a part of Na in a Na-containing oxide having a P2 type structure with Li. The positive electrode active material thus obtained has a Li-deficient O2 type structure. That is, the composition ratio Li / O of Li and O constituting the O2 type structure is usually less than 0.5. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-085829 Summary of the Invention [Problem to be solved by the invention]

[0004] Lithium-ion batteries using positive electrode active materials with a Li-deficient O2-type structure have room for improvement in terms of resistance. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> 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 is A positive electrode active material having a Li-deficient O2 type structure; Sulfide solid electrolyte and The Raman spectrum of the positive electrode active material layer satisfies the following relationships (1) and (2): I R1 / I R2 ≦0.20 (1) I R3 / I R2 ≦0.20 (2) I R1 : P in the Raman spectrum 2 S 6 4- Peak intensity derived from I R2 : PS in the Raman spectrum 4 3- Peak intensity derived from I R3 : Peak intensity due to SS in the Raman spectrum Fulfilling Lithium-ion battery. <Aspect 2> 2. The lithium ion battery of embodiment 1, The XPS spectrum of the positive electrode active material layer satisfies the following relationships (3) and (4): I X1 / I X2 ≦1.20 (3) I X3 / I X4 ≦1.60 (4) I X1 : Peak intensity due to PSP in the XPS spectrum of S2p I X2 :PS in the XPS spectrum for S2p 4 3- Peak intensity derived from I X3 PO in the XPS spectrum for P2p x S 4-x 3- Peak intensity derived from I X4 :PS in the XPS spectrum for P2p 4 3- Peak intensity derived from Fulfilling Lithium-ion battery. <Aspect 3> A lithium-ion battery according to Aspect 1 or 2, assuming that the total solid content contained in the positive electrode active material layer is 100% by mass, the content of the positive electrode active material is 40% by mass or more and less than 100% by mass, and the content of the sulfide solid electrolyte is more than 0% by mass and 60% by mass or less, A lithium-ion battery. <Aspect 4> A lithium-ion battery according to any one of Aspects 1 to 3, wherein the positive electrode active material is Li a Na b Mn x-p Ni y-q Co z-r M p+q+r O 2 (where 0 < a < 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W), A lithium-ion battery. <Aspect 5> A lithium-ion battery according to any one of Aspects 1 to 4, wherein the electrolyte layer contains a solid electrolyte, A lithium-ion battery. <Aspect 6> A method for manufacturing a lithium-ion battery, comprising: mixing a positive electrode active material having an O2-type structure with Li deficiency and a sulfide solid electrolyte to obtain a positive electrode mixture, and pressing the positive electrode mixture at a temperature lower than 165°C to obtain a positive electrode active material layer, A method for manufacturing a lithium-ion battery.

Advantages of the Invention

[0006] The lithium-ion battery of the present disclosure has low resistance.

Brief Description of the Drawings

[0007] [Figure 1] 1 illustrates a schematic diagram of an example of the configuration of a lithium ion battery. [Diagram 2] 1 shows an example of a flow of a manufacturing method for a lithium-ion battery. [Diagram 3] 1 shows Raman spectra of the positive electrode active material layers of Examples 1 and 2, Comparative Examples 1 to 3, and a Reference Example. [Figure 4] 1 shows XPS spectra (P2p) of the positive electrode active material layers of Examples 1 and 2, Comparative Examples 1 to 3, and a reference example. [Diagram 5] 1 shows XPS spectra (S2p) of the positive electrode active material layers of Examples 1 and 2, Comparative Examples 1 to 3, and a reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, one embodiment of the lithium ion battery and the manufacturing method thereof according to the present disclosure will be described, however, the lithium ion battery and the manufacturing method thereof according to the present disclosure are not limited to the embodiment described below.

[0009] 1. Lithium-ion battery As shown in Fig. 1, a lithium ion battery 100 according to one embodiment includes a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30. The positive electrode active material layer 10 includes a positive electrode active material having a Li-deficient O2 type structure, and a sulfide solid electrolyte. The Raman spectrum of the positive electrode active material layer 10 satisfies the following relationships (1) and (2): I R1 / I R2 ≦0.20 (1) I R3 / I R2 ≦0.20 (2) I R1 : P in the Raman spectrum 2 S 6 4- Peak intensity derived from I R2 : PS in the Raman spectrum 4 3-Peak intensity derived from I R3 : Peak intensity due to SS in the Raman spectrum The lithium ion battery 100 that satisfies the relationships (1) and (2) has a low resistance.

[0010] 1.1 Cathode active material layer The positive electrode active material layer 10 includes a positive electrode active material having a Li-deficient O2 type structure and a sulfide solid electrolyte. The positive electrode active material layer 10 may optionally include other positive electrode active materials, other electrolytes, conductive assistants, binders, and the like. The positive electrode active material layer 10 may also include various other additives. The contents of the positive electrode active material, electrolyte, conductive assistant, binder, and the like in the positive electrode active material layer 10 may be appropriately determined according to the intended battery performance. For example, the content of the positive electrode active material having a Li-deficient O2 type structure may be 40% by mass or more and less than 100% by mass, and the content of the sulfide solid electrolyte may be more than 0% by mass and 60% by mass or less, based on the entire solid content included in the positive electrode active material layer 10 being 100% by mass. The content of the positive electrode active material having a Li-deficient O2 type structure may be 50 mass% or more, 60 mass% or more, 70 mass% or more, or 80 mass% or more, or 90 mass% or less, and the content of the sulfide solid electrolyte may be 10 mass% or more, and 50 mass% or less, 40 mass% or less, 30 mass% or less, or 20 mass% or less. These lower and upper limits may be combined arbitrarily.

[0011] 1.1.1 Positive electrode active material with Li-deficient O2 structure The positive electrode active material layer 10 includes a positive electrode active material having a Li-deficient O2-type structure (belonging to the space group P63mc). In other words, the positive electrode active material layer 10 includes a Li-containing oxide having a Li-deficient O2-type structure as a positive electrode active material. The term "Li-deficient" refers to a positive electrode active material whose chemical composition has a composition ratio Li / O of Li and O of less than 0.5 (for example, "a" in the composition formula described below is less than 1.0).

[0012] 1.1.1.1 Crystal structure The positive electrode active material according to an embodiment may have an O2 type structure and may have a crystal structure other than the O2 type structure. Examples of the crystal structure other than the O2 type structure include a T♯2 type structure (belonging to the space group Cmca) formed when Li is deintercalated 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 or more and 3.5 nm or less, typically 2.9 nm or more and 3.0 nm or less, which is different from the O3 type structure also belonging to the space group R-3m). Any of the crystal structures may be Li-deficient crystal structures. The positive electrode active material according to an embodiment may have an O2 type structure as a main phase, or may have a crystal structure other than the O2 type structure (for example, an O6 type structure) as a main phase. The positive electrode active material according to an embodiment may have a crystal structure as a main phase that changes depending on its charge / discharge state.

[0013] 1.1.1.2 Crystallites The positive electrode active material having a Li-deficient O2 type structure may be a single crystal consisting of one crystallite, or may be a polycrystal having a plurality of crystallites. For example, the surface of the positive electrode active material according to one embodiment may be composed of a plurality of crystallites. In other words, the positive electrode active material may have a structure in which a plurality of crystallites are connected to each other on its surface. When the surface of the positive electrode active material is composed of a plurality of crystallites, a crystal grain boundary is present on the surface. Here, the crystal grain boundary may be an inlet and an outlet of intercalation. That is, when the positive electrode active material is a polycrystal having a plurality of crystallites, the effect of increasing the number of inlets and outlets of intercalation and decreasing the reaction resistance, the effect of shortening the movement distance of lithium ions and decreasing the diffusion resistance, the effect of reducing the absolute amount of expansion and contraction during charging and discharging, and the effect of making it difficult for cracks to occur, etc. can be expected. The size of the crystallite may be large or small, but it is considered that the smaller the size of the crystallite, the more the crystal grain boundaries will be, and the more likely the above-mentioned advantageous effects will be exhibited. For example, if the diameter of the crystallite constituting the positive electrode active material is less than 1 μm, higher performance is likely to be obtained. The "crystallite" and "diameter of crystallite" can be obtained by observing the surface of the positive electrode active material with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). That is, when the surface of the positive electrode active material is observed and a closed region surrounded by a grain boundary is observed, the region is regarded as a "crystallite". The maximum Feret diameter of the crystallite is obtained and regarded as the "diameter of the crystallite". If the positive electrode active material is composed of a single crystal particle, the particle itself can be said to be a single crystallite, and the maximum Feret diameter of the particle is the "diameter of the crystallite". If the diameter of the crystallite of the positive electrode active material is less than 1 μm, higher performance is likely to be exhibited. The crystallite constituting the positive electrode active material may have a first surface exposed on the surface of the oxide, and the first surface may be planar. That is, the surface of the positive electrode active material may have a structure in which a plurality of planes are connected. As described later, when producing a Na-containing oxide that is a raw material for a Li-containing oxide that is a positive electrode active material, crystallites having a planar first surface can be easily obtained by growing the crystallites on the surface of the particles until one crystallite and another crystallite are connected to each other.

[0014] 1.1.1.3 Chemical composition The positive electrode active material having a Li-deficient O2 type structure may contain, for example, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. In particular, when the positive electrode active material contains, as constituent elements, at least Li, Mn, one or both of Ni and Co, and O, and particularly when the positive electrode active material contains, as constituent elements, at least Li, Mn, Ni, Co, and O, higher performance is likely to be obtained.

[0015] The positive electrode active material with a Li-deficient O2 structure is a Na b Mn x-p Ni y-q Co z-r M p+q+r O 2(Here, 0 < a < 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). It may have a chemical composition represented by this. When the positive electrode active material has such a chemical composition, the O2-type structure is likely to be maintained. In the above chemical composition, a is greater than 0, and may be 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 less than 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b is 0 or more, and may be 0.01 or more, 0.02 or more, or 0.03 or more, and 0.20 or less, and may be 0.15 or less, or 0.10 or less. Also, x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, and may be 0.10 or more, or 0.20 or more, and 1.00 or less, and may be 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. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, or 0.30 or more, and 1.00 or less, and may be 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. The element M has a small contribution to charge and discharge. In this regard, in the above chemical composition, since p + q + r is less than 0.17, a high charge and discharge capacity is likely to be ensured. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is included, the O2-type structure is likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more.)The composition of O is approximately 2, but is not necessarily exactly 2.0 and is variable.

[0016] 1.1.1.4 Shape A positive electrode active material having a Li-deficient O2 type structure can be obtained by substituting Li for Na in a Na-containing oxide having a P2 type structure, as described later. Here, the P2 type structure is a hexagonal crystal system, has a large diffusion coefficient of Na ions, and is prone to crystal growth in a specific direction. In particular, when at least one of Mn, Ni, and Co is included as a transition metal element constituting the P2 type structure, the crystal is prone to grow in a plate-like shape in a specific direction. Therefore, the Na-containing oxide having the P2 type structure is usually a plate-like particle with a large aspect ratio in which the crystal growth direction is biased in a specific direction. The positive electrode active material according to one embodiment may be obtained based on such plate-like Na-containing oxide particles, or may be obtained based on spherical Na-containing oxide particles, as described later. That is, the shape of the positive electrode active material may be plate-like particles or spherical particles. When the positive electrode active material is a spherical particle, the reaction resistance decreases due to the reduction in crystallite size, and the diffusion resistance inside the particle is likely to decrease. Furthermore, when applied to a battery, it is believed that the degree of curvature is reduced by the spheroidization, and the lithium ion conduction resistance is reduced. This, for example, improves the rate characteristics and tends to increase the reversible capacity. In this application, the term "spherical particles" refers to particles having a circularity of 0.80 or more. The circularity of the particles 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 particles is 4πS / L 2 Here, 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 a particle can be determined by observing the appearance of the particle using a scanning electron microscope (SEM), transmission electron microscope (TEM), or optical microscope.

[0017] The positive electrode active material having a Li-deficient O2 type structure may be, for example, a solid particle, a hollow particle, or a particle having a void. The size of the positive electrode active material particles is not particularly limited, but it is considered that a smaller size is more advantageous. For example, the average particle diameter (D50) of the positive electrode active material particles may be 0.1 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 average particle diameter (D50) is the particle diameter (D50, median diameter) at an integrated value of 50% in the volume-based particle size distribution by a laser diffraction / scattering method.

[0018] 1.1.1.5 Manufacturing method for a positive electrode active material having a Li-deficient O2-type structure The positive electrode active material having a Li-deficient O2 type structure can be produced, for example, by the following method. That is, the method for producing the positive electrode active material according to one embodiment is as follows: S1: Obtaining a precursor (e.g., a precursor containing at least one element of Mn, Ni, and Co); S2: Coating the surface of the precursor with a Na source to obtain a composite; S3: Calcining the composite to obtain a Na-containing oxide having a P2 type structure; and S4: At least a part of the Na in the Na-containing oxide is ion-exchanged with Li to obtain a Li-containing oxide having an O2 type structure. Here, S3 is S3-1: Pre-firing the composite at a temperature of 300° C. or more and less than 700° C. for 2 hours or more and 10 hours or less; S3-2: Following the preliminary firing, the composite is subjected to a main firing at a temperature of 700° C. or more and 1100° C. or less for a period of 30 minutes to 48 hours or less; and S3-3: Following the main sintering, the composite is heated to a temperature T 1 Temperature T below 100°C 2 and rapidly cooling until the temperature reaches a temperature of 100.degree.

[0019] In S1, a precursor containing at least one element of Mn, Ni, and Co is obtained. The precursor may contain at least Mn, one or both of Ni and Co, or may contain at least Mn, Ni, and Co. The precursor may be a salt containing at least one element of Mn, Ni, and Co. For example, the precursor may be at least one of carbonate, sulfate, nitrate, and acetate. Alternatively, the precursor may be a compound other than a salt. For example, the precursor may be a hydroxide. The precursor may be a hydrate. The precursor may be a combination of multiple types of compounds. The precursor may have various shapes. For example, the precursor may be particulate, or may be spherical particles as described later. The particle size of the particles made of the precursor is not particularly limited.

[0020] In S1, a precipitate as the precursor may be obtained by a coprecipitation method using an ion source capable of forming a precipitate in an aqueous solution with transition metal ions and a transition metal compound containing at least one element selected from Mn, Ni, and Co. This makes it easier to obtain spherical particles as the precursor. The "ion source capable of forming a precipitate in an aqueous solution with transition metal ions" may be at least one selected from, for example, sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. The transition metal compound may be the above salt or hydroxide containing at least one element selected from Mn, Ni, and Co. Specifically, in S1, the ion source and the transition metal compound may be prepared as solutions, and the solutions may be dropped and mixed to obtain a precipitate as the precursor. In this case, for example, water is used as the solvent. In this case, various sodium compounds may be used as the base, and an aqueous ammonia solution or the like may be added to adjust the basicity. In the case of the coprecipitation method, for example, an aqueous solution of a transition metal compound and an aqueous solution of sodium carbonate are prepared, and the aqueous solutions are dropped and mixed to obtain a precipitate as the precursor. Alternatively, the precursor can be obtained by a sol-gel method, and in particular, by a coprecipitation method, spherical particles can be easily obtained as the precursor.

[0021] In S1, the precursor may contain element M. Element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. These elements M have a function of stabilizing, for example, a P2 type structure or an O2 type structure. The method of obtaining a precursor containing element M is not particularly limited. When the precursor is obtained by coprecipitation in S1, for example, an aqueous solution of a transition metal compound containing at least one of Mn, Ni, and Co, an aqueous solution of sodium carbonate, and an aqueous solution of a compound of element M are prepared, and each aqueous solution is dropped and mixed to obtain a precursor containing element M together with at least one element of Mn, Ni, and Co. Alternatively, in the manufacturing method of the present disclosure, element M may not be added in S1, and element M may be doped when Na-doping baking is performed in S2 and S3 described later.

[0022] In S2, the surface of the precursor obtained in S1 is coated with a Na source to obtain a composite. The Na source may be a salt containing Na, such as a carbonate or a nitrate, or may be a compound other than a salt, such as sodium oxide or sodium hydroxide. In S2, the amount of the Na source coated on the surface of the precursor may be determined taking into account the amount of Na lost during the subsequent calcination.

[0023] In S2, the coverage of the Na source on the surface of the precursor is not particularly limited. For example, in S2, the above-mentioned composite may be obtained by covering 40 area% or more, 50 area% or more, 60 area% or more, or 70 area% or more of the surface of the above-mentioned precursor with the Na source. Here, when the precursor obtained by S1 is a spherical particle, and the composite obtained by S2 is obtained by covering 40 area% or more of the surface of the precursor with the Na source, the Na-containing oxide having the P2 type structure is likely to become a spherical particle in S3 described later. If the coverage of the Na source is small, when the composite is fired, P2 type crystals are likely to grow on the surface of the composite, and the Na-containing oxide is likely to become a plate-like. If the coverage of the Na source is large, when the composite is fired, the crystallites of the P2 type crystals are likely to become small, and the Na-containing oxide is likely to become a spherical particle corresponding to the shape of the precursor.

[0024] In S2, the method for coating the surface of the precursor with the Na source is not particularly limited. As described above, when 40% or more of the area of ​​the surface of the precursor is coated with the Na source, various methods can be used. For example, a tumbling fluidized coating method or a spray drying method can be used. That is, a coating solution in which a Na source is dissolved is prepared, and the coating solution is brought into contact with the surface of the precursor, and dried at the same time or after the contact. By adjusting the coating conditions (temperature, time, number of times, etc.), 40% or more of the area of ​​the surface of the precursor can be coated with the Na source.

[0025] In S2, the precursor may be coated with an M source together with a Na source. For example, in S2, the precursor obtained in S1, a Na source, and an M source containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W may be mixed to obtain a composite. The M source may be, for example, a salt containing the element M, such as a carbonate or sulfate, or a compound other than a salt, such as an oxide or hydroxide. The amount of the M source relative to the precursor may be determined depending on the chemical composition of the Na-containing oxide after firing.

[0026] In S3, the composite obtained in S2 is calcined to obtain a Na-containing oxide having a P2 type structure. S3 includes the above S3-1, S3-2, and S3-3.

[0027] In S3-1, the composite is pre-fired at a temperature of 300°C or more and less than 700°C for 2 hours or more and 10 hours or less. In S3-1, the composite may be arbitrarily molded and then pre-fired. The pre-fire is performed at a temperature lower than that of the main firing. If the pre-fire in S3-1 is insufficient, the P2 phase may not be sufficiently generated in the finally obtained Na-containing oxide. In S3-1, the pre-fire temperature is 300°C or more and less than 700°C, and the pre-fire time is 2 hours or more and 10 hours or less, so that the composite can be sufficiently pre-fired, the heat uniformity is increased, and the Na-containing oxide obtained through S3-2 and S3-3 described later is likely to be appropriate. The pre-fire temperature may be 400°C or more and less than 700°C, 450°C or more and less than 700°C, 500°C or more and less than 700°C, 550°C or more and less than 700°C, or 550°C or more and less than 650°C. The pre-firing time may be 2 hours or more and 8 hours or less, 3 hours or more and 8 hours or less, 4 hours or more and 8 hours or less, 5 hours or more and 8 hours or less, or 5 hours or more and 7 hours or less. The pre-firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere.

[0028] In S3-2, following the above pre-firing, the composite is subjected to main firing at a temperature of 700°C to 1100°C for 30 minutes to 10 hours. In S3-2, the main firing temperature of the composite is 700°C to 1100°C, preferably 800°C to 1000°C. If the main firing temperature is too low, the P2 phase is not generated, and if the main firing temperature is too high, the O3 phase and the like are likely to be generated instead of the P2 phase. The temperature rise condition from the pre-firing temperature to the main firing temperature is not particularly limited. The main firing time is not particularly limited, and may be, for example, 30 minutes to 48 hours. However, the shape of the Na-containing oxide can be controlled by the main firing time. As described above, in the method of the present disclosure, when the coverage of the Na source in the composite is 40 area % or more, when the composite is fired, P2 type crystals with small crystallites are likely to be formed on the surface. In the method of the present disclosure, the P2 type crystals are grown along the surface of the particles so as to connect one P2 type crystallite with another P2 type crystallite, so that the shape of the Na-containing oxide corresponds to the shape of the precursor. For example, when the precursor is a spherical particle, the Na-containing oxide can also be a spherical particle. If the firing time is too short, the generation of the P2 phase is insufficient. On the other hand, if the firing time is too long, the P2 phase grows excessively, resulting in plate-like particles rather than spherical ones. As far as the present inventors have confirmed, spherical particles of the Na-containing oxide are easily obtained when the firing time is 30 minutes or more and 3 hours or less. The Na-containing oxide obtained after firing may have a structure in which a plurality of crystallites are present on the surface and the crystallites are connected to each other.

[0029] In S3-3, following the main sintering, the composite is heated to a temperature T 1 Temperature T below 100°C 2 The above pre-baking and main baking are performed, for example, in a heating furnace. In step S3-3, for example, after the main baking of the composite is performed in the heating furnace, the composite is heated to an arbitrary temperature T 1 Cool to the temperature T 1 After this, the baked product is removed from the furnace and heated to any temperature T below 100°C. 2Rapid cooling is performed outside the furnace until the temperature T 1 is any temperature above 200° C., and may be any temperature above 250° C. 2 is any temperature below 100°C, may be any temperature below 50°C, or may be the cooling end temperature. 1 from temperature T 2 In a certain temperature range between the temperatures, moisture easily penetrates between the layers of the P2 type structure due to atomic vibrations and molecular motions. When cooling the composite (Na-containing oxide having a P2 type structure) after the main firing, it is considered that the amount of moisture that penetrates between the layers of the P2 type structure can be reduced by shortening the time during which the composite is in the temperature range in which moisture easily penetrates (i.e., by cooling quickly). In this regard, in step S3-3, when cooling the composite after the main firing, an arbitrary temperature T 1 Any temperature T below 100°C 2 For example, by cooling in a dry atmosphere outside the furnace, the temperature T 1 from temperature T 2 The cooling rate during the cooling process is high (for example, 20°C / min or more) until the temperature reaches 100°C, which makes it difficult for moisture to penetrate between the layers of the P2 type structure, thereby preventing the collapse of the P2 type structure, etc. As a result, Na can be efficiently ion-exchanged with Li in S4.

[0030] By using S3, it is possible to produce a Na-containing oxide having a P2 type structure and a predetermined chemical composition. The Na-containing oxide contains at least one transition metal element selected from Mn, Ni, and Co, Na, and O as constituent elements. 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 is more likely to be improved. The Na-containing oxide contains Na c Mn x-p Ni y-q Co z-r M p+q+r O 2It may have a chemical composition represented by the following. Here, 0 < c < 1.00, x + y + z = 1, and 0 ≤ p + q + r < 0.17. 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 oxide has such a chemical composition, the P2-type structure is more likely to be maintained. In the above chemical composition, c is greater than 0, and may be 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 less than 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, and may be 0.10 or more or 0.20 or more, and 1.00 or less, and may be 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. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, or 0.30 or more, and 1.00 or less, and may be 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. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, since p + q + r is less than 0.17, it is easy to ensure a high charge and discharge capacity. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is included, the P2-type structure and the O2-type structure are likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0031] In S4, at least a part of Na in the Na-containing oxide obtained in S3 is ion-exchanged with Li to obtain a Li-containing oxide having a Li-deficient O2-type structure. For example, there are a method using an aqueous solution containing lithium halide and a method using a mixture of lithium halide and other lithium salts (for example, molten salt) for ion exchange. From the viewpoint that the P2-type structure is easily broken by the intrusion of water and from the viewpoint of crystallinity, the method using a molten salt is preferable among the above two methods. That is, by mixing the Na-containing oxide having the above-mentioned P2-type structure with the molten salt and heating it to a temperature equal to or higher than the melting point of the molten salt, at least a part of Na in the Na-containing oxide can be replaced with Li by ion exchange. 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 a molten salt, the melting point becomes lower than when lithium halide or other lithium salts are used alone, and ion exchange can be performed at a lower temperature. The temperature in the ion exchange may be, for example, above the melting point of the molten salt and below 600°C, below 500°C, below 400°C, or below 300°C. If the temperature in the ion exchange is too high, the stable O3 structure is likely to be formed instead of the O2 structure. On the other hand, from the viewpoint of shortening the time required for the ion exchange, it is preferable that the temperature in the ion exchange is as high as possible.

[0032] 1.1.1.6 Protection layer An ion-conductive protective layer may be formed on the surface of the positive electrode active material having a Li-deficient O2 type structure. That is, the positive electrode active material layer 10 may include a complex of the positive electrode active material and a protective layer, and at least a part of the surface of the positive electrode active material in the complex may be covered with a protective layer. According to the knowledge of the present inventor, even if a protective layer is formed on the surface of a positive electrode active material having a Li-deficient O2 type structure, the reaction between the positive electrode active material and the sulfide solid electrolyte may not be suppressed. As described later, in the present disclosure, the reaction between the positive electrode active material and the sulfide solid electrolyte is suppressed by controlling the pressing temperature of the positive electrode active material layer.

[0033] The ion-conductive protective layer may contain various ion-conductive compounds, which may be, for example, at least one selected from ion-conductive oxides and ion-conductive halides.

[0034] 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 be an oxynitride containing N. More specifically, the ion conductive oxide may contain Li 3 BO 3 , LiBO 2 , Li 2 CO 3 , LiAlO 2 , Li 4 SiO 4 , Li 2 SiO 3 , Li 3 PO 4 , Li 2 SO 4 , Li 2 TiO 3 , Li 4 Ti 5 O 12 , Li 2 Ti 2 O 5 , Li 2 ZrO 3 , LiNbO 3 , Li 2 MoO 4 , Li 2 WO 4 , LiPON, Li 2 O-LaO 2 , Li 2 O-ZnO 2 etc. The ion conductive oxide may be one in which some elements are substituted with various doping elements.

[0035] The ion conductive halide may be, for example, at least one of various compounds exemplified as the halide solid electrolyte described later. The ion conductive halide may include, 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 include 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 include 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.

[0036] 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 or 1 nm or more, and may be 100 nm or less, or 20 nm or less.

[0037] 1.1.2 Sulfide solid electrolyte The positive electrode active material layer 10 includes a sulfide solid electrolyte together with the above-mentioned positive electrode active material having a Li-deficient O2 type structure. A method for producing a sulfide solid electrolyte is publicly known. That is, a desired sulfide solid electrolyte can be produced by selecting and weighing raw materials according to a desired chemical composition, and then mixing the raw materials.

[0038] 1.1.2.1 Crystallinity 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). In addition, when the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON type crystalline phase, a LGPS type crystalline phase, and an Argyrodite type crystalline phase.

[0039] 1.1.2.2 Chemical composition The sulfide solid electrolyte may contain, for example, Li, P, and S elements. The sulfide solid electrolyte may further contain an X element (X is at least one of As, Sb, Si, Ge, Sn, B, Al, Ga, and In). The sulfide solid electrolyte may further contain at least one of an O element and a halogen element. The sulfide solid electrolyte may contain an S element as a main component of an anion element. The sulfide solid electrolyte may contain, for example, Li 2 SP 2 S 5 , Li 2 SP 2 S 5 - LiI, Li 2 SP 2 S 5 -GeS 2 , Li 2 SP 2 S 5 -Li 2 O, Li 2 SP 2 S 5 -Li 2 O-LiI, Li 2 SP 2 S 5 -LiI-LiBr, Li 2 S-SiS 2 -P 2 S 5 - LiI, Li 2 SP 2 S 5 -ZmSn (where m and n are positive numbers. Z is Ge, Zn, or Ga), Li 2 S-SiS2 -Li 3 PO 4 、Li 2 S - SiS 2 -Li x MO y (However, x and y are positive numbers. M may be at least one selected from P and optionally any one of Si, Ge, B, Al, Ga, In.) Or, the sulfide solid electrolyte is not particularly limited. For example, xLi 2 S·(100 - x)P 2 S 5 (70 ≦ x ≦ 80), yLiI·zLiBr·(100 - y - z)(xLi 2 S·(1 - x)P 2 S 5 )(0.7 ≦ x ≦ 0.8, 0 ≦ y ≦ 30, 0 ≦ z ≦ 30), etc. may have at least one chemical composition selected therefrom. Or, the sulfide solid electrolyte may have a chemical composition represented by the general formula: Li 4-x Ge 1-x P x S 4 (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, 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). Or, the sulfide solid electrolyte may have a chemical composition represented by Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number from 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, and may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less.

[0040] 1.1.2.3 Shape The sulfide solid electrolyte may be in the form of particles. The average particle size (D50) of the sulfide solid electrolyte may be, for example, 10 nm or more and 100 μm or less.

[0041] 1.1.3 Other ingredients The positive electrode active material layer 10 may optionally contain other positive electrode active materials, other electrolytes, conductive assistants, binders, and the like.

[0042] 1.1.3.1 Other positive electrode active materials The positive electrode active material contained in the positive electrode active material layer 10 may be composed of only the positive electrode active material having the Li-deficient O2 type structure, or may contain other positive electrode active materials (other positive electrode active materials) together with the positive electrode active material. From the viewpoint of further enhancing the effect of the technology of the present disclosure, the proportion of other positive electrode active materials in the entire positive electrode active material may be small. For example, the content of the positive electrode active material having the Li-deficient O2 type structure may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less, based on the entire positive electrode active material being 100% by mass.

[0043] Other cathode active materials that can be included in the cathode active material layer 10 can adopt any of those known as cathode active materials for lithium ion batteries. The other cathode active materials may be, for example, at least one selected from various lithium compounds other than the above-mentioned Li-containing oxides having the Li-deficient O2-type structure, elemental sulfur, sulfur compounds, etc. The lithium compound as the other cathode active material may be a Li-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 may be at least one selected from the group consisting of Mn, Ni, Co, Al, Fe, and Ti. More specifically, the Li-containing oxide as the other cathode active material is lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel cobaltate, 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 O 4 (M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), such as hetero-element substituted Li-Mn spinel with the composition represented thereby), lithium nickel cobalt aluminum oxide (for example, Li 1±α Ni p Co q Al r O 2±δ (for example, p + q + r = 1)), lithium titanate, lithium metal phosphate (LiMPO 4and the like, M may be at least one selected from Fe, Mn, Co, and Ni). In particular, when the other positive electrode active material contains at least one of Ni, Co, and Mn as a constituent element, and a Li-containing oxide containing Li and O, the performance of the lithium ion battery is more likely to be improved. Alternatively, when the other positive electrode active material contains at least one of Ni, Co, and Al as a constituent element, and a Li-containing oxide containing Li and O, the performance of the lithium ion battery is more likely to be improved. Only one type of the other positive electrode active material may be used alone, or two or more types may be used in combination. The shape of the other positive electrode active material may be a general shape as a positive electrode active material for a lithium ion battery. The other positive electrode active material may be, for example, particulate. The other positive electrode active material may be solid or may have voids, for example, may be porous or may be hollow. The other positive electrode active material may be primary particles, or may be secondary particles in which a plurality of primary particles are aggregated. The average particle diameter D50 of other positive electrode active materials may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0044] 1.1.3.2 Other electrolytes The electrolyte contained in the positive electrode active material layer 10 may be composed of only the sulfide solid electrolyte, or may contain other electrolytes (other electrolytes) in addition to the sulfide solid electrolyte. From the viewpoint of further enhancing the effect of the technology of the present disclosure, the proportion of other electrolytes in the entire electrolyte contained in the positive electrode active material layer 10 may be small. For example, the content of the sulfide solid electrolyte may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less, based on the entire electrolyte contained in the positive electrode active material layer 10 being 100% by mass.

[0045] The other electrolytes that may be included in the positive electrode active material layer 10 may be solid electrolytes, liquid electrolytes, or combinations thereof. As the solid electrolyte, any known solid electrolyte for lithium ion batteries may be used. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, the inorganic solid electrolyte is excellent in ion conductivity and heat resistance. Examples of inorganic solid electrolytes other than the sulfide solid electrolyte include oxide solid electrolytes and ion-bonded inorganic solid electrolytes. Among the ion-bonded solid electrolytes, the performance of a solid electrolyte containing at least Li, Y, and a halogen (at least one of Cl, Br, I, and F) as constituent elements is high. The other solid electrolytes may be amorphous or crystalline. The other solid electrolytes may be particulate. The average particle diameter (D50) of the other solid electrolytes may be, for example, 10 nm or more and 10 μm or less. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0046] The oxide solid electrolyte is lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X (PO 4 ) 3 , Li-SiO-based glass, Li-Al-SO-based glass, etc. In addition, when an oxide solid electrolyte is combined with a liquid electrolyte, ion conductivity can be improved.

[0047] The ion-bonded solid electrolyte may contain at least one element selected from the group consisting of, for example, Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb and Sm. These elements may generate cations in water. The ion-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 may generate anions in water. The ion-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 ion-bonded solid electrolyte may contain Li and Y, and at least one element selected from the group consisting of Cl, Br, I and F. More specifically, the ionically bonded 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. 3 YBr 2 Cl 4 , Li 2.8 Ca 0.1 Y 0.5 Gd 0.5 Br 2 Cl 4 , and Li 2.5 Y 0.5 Zr 0.5 Cl 6 It may be at least one of the above.

[0048] 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 those represented by the formula (A): 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 contained in Groups 1 to 12 of the periodic table (excluding hydrogen) and (ii) all elements contained in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se). The metal element can form an inorganic compound with a halide ion and become a cation.

[0049] In formula (A), M may contain Y (i.e., yttrium). The halide solid electrolyte containing Y is Li a Me b Y c X 6 (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) may have a composition represented by the following. Me may be at least one selected from the group consisting of, for example, Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0050] The halide solid electrolyte may have a composition represented by formula (A1): Li 6-3d Y d X 6 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 may be 1. The halide solid electrolyte may have a composition represented by formula (A2): Li 3-3δ Y 1+δ Cl 6It may have a composition represented by. In formula (A2), 0 < δ ≦ 0.15 may be satisfied. The halide solid electrolyte has the formula (A3): Li 3-3δ Y 1+δ Br 6 It may have a composition represented by. 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 It 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, 0 ≦ 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 It 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 It 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 Brx I y In 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。

[0051] The ionically bonded 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 ion containing H may have, for example, an element M containing at least one of a nonmetallic element, a semimetallic element, and a metallic element, and H bonded to the element M. In addition, the complex ion 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 ion containing H may be (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 a nonmetallic element or a 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. Also, 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 contains C and B, higher ionic conductivity is likely to be ensured. Specific examples of complex ions containing H include (CB 9 H 10 ) - , (C.B. 11 H 12 ) - , (B 10 H 10 ) 2- , (B 12 H 12 ) 2- , (BH 4 ) - , (NH 2 ) - , (AlH 4 ) -, and combinations thereof. In particular, (CB 9 H 10 ) - , (C.B. 11 H 12 ) - In other words, the complex hydride solid electrolyte may contain Li, C, B, and H.

[0052] The liquid electrolyte is a liquid containing lithium ions as carrier ions. The electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. The composition of the electrolyte may be the same as that of the electrolyte of a lithium ion battery. The electrolyte may be a solution of a lithium salt dissolved in water or a non-aqueous solvent. Examples of the non-aqueous solvent include various carbonate-based solvents. Examples of the lithium salt include lithium amide salt and LiPF 6 etc.

[0053] 1.1.3.3 Conductive additives Examples of the conductive assistant that may be included in the positive electrode active material layer 10 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 assistant may be, for example, particulate or fibrous, and the size thereof is not particularly limited. Only one type of conductive assistant may be used alone, or two or more types may be used in combination.

[0054] 1.1.3.4 Binders Examples of binders that can be included in the positive electrode active material layer 10 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.

[0055] 1.1.3.5 Other The positive electrode active material layer 10 may contain various additives in addition to the above components, such as a dispersant and a lubricant.

[0056] 1.1.4 Raman spectrum of the positive electrode active material layer The Raman spectrum of the positive electrode active material layer 10 satisfies the following relationships (1) and (2).

[0057] I R1 / I R2 ≦0.20 (1) I R3 / I R2 ≦0.20 (2) I R1 : P in the Raman spectrum 2 S 6 4- Peak intensity derived from I R2 : PS in the Raman spectrum 4 3- Peak intensity derived from I R3 : Peak intensity due to SS in the Raman spectrum

[0058] where the peak intensity I R1 is the 385 cm -1 It corresponds to the peak intensity at R2 is the 420 cm -1 It corresponds to the peak intensity atR3 is the 475 cm -1 The Raman spectrum corresponds to the peak intensity at 300 cm -1 The peak intensity at is normalized to 0 (background processing).

[0059] Conventionally, when a positive electrode active material layer is obtained, pressing is performed at as high a temperature as possible to improve the density of the positive electrode active material layer, thereby reducing the resistance of the positive electrode active material layer. However, according to the new findings of the present inventors, when the positive electrode active material layer contains a positive electrode active material having a Li-deficient O2 type structure and a sulfide solid electrolyte, pressing the positive electrode active material layer at a high temperature causes a reaction between the positive electrode active material having a Li-deficient O2 type structure and the sulfide solid electrolyte, resulting in the PS of the sulfide solid electrolyte being generated. 4 The skeleton collapses, and resistance increases instead. This problem occurs specifically when a positive electrode active material having a Li-deficient O2-type structure is combined with a sulfide solid electrolyte in the positive electrode active material layer. This problem does not occur when a Li-non-deficient positive electrode active material (for example, a positive electrode active material having an O2-type structure doped with Li, or a positive electrode active material having an O3-type structure) is combined with a sulfide solid electrolyte.

[0060] According to the inventor's new findings, the PS of the sulfide solid electrolyte contained in the positive electrode active material layer 4 When the skeleton is broken, the Raman spectrum of the positive electrode active material layer shows that P 2 S 6 4- The smaller the Raman peaks due to such reaction products, the more likely it is that the PS and SS of the sulfide solid electrolyte contained in the positive electrode active material layer are. 4 It can be said that the skeleton is maintained, and the reaction between the positive electrode active material having a Li-deficient O2-type structure and the sulfide solid electrolyte is suppressed.

[0061] According to the new findings of the present inventors, when the Raman spectrum of the positive electrode active material layer 10 is obtained, the peak intensity ratio I R1 / I R2is 0.20 or less, and the peak intensity ratio I R3 / I R2 If the ratio is 0.20 or less, the PS of the sulfide solid electrolyte in the positive electrode active material layer 10 is 4 It can be said that the skeleton is properly maintained, and low resistance can be maintained. Peak intensity ratio I R1 / I R2 may be 0.15 or less, 0.10 or less, or 0.05 or less. In addition, the peak intensity ratio I R3 / I R2 may be 0.15 or less, 0.10 or less, or 0.05 or less. In particular, the peak intensity ratio I R1 / I R2 is 0.10 or less, and the peak intensity ratio I R3 / I R2 When the peak intensity ratio I is 0.10 or less, a more significant drag reduction effect is likely to be obtained. R1 / I R2 and peak intensity ratio I R3 / I R2 The lower limit of each of these is not particularly limited, and each may be 0 or more, and may be 0.01 or more.

[0062] 1.1.5 XPS spectrum of the positive electrode active material layer The XPS spectrum of the positive electrode active material layer 10 may satisfy the following relationships (3) and (4).

[0063] I X1 / I X2 ≦1.20 (3) I X3 / I X4 ≦1.60 (4) I X1 : Peak intensity due to PSP in the XPS spectrum of S2p I X2 :PS in the XPS spectrum for S2p 4 3- Peak intensity derived from I X3 PO in the XPS spectrum for P2p x S 4-x 3- Peak intensity derived from I X4 :PS in the XPS spectrum for P2p 4 3- Peak intensity derived from

[0064] Here, the peak intensity ratio I X1 / I X2 is the peak intensity I at 162.9 eV in the XPS spectrum for S2p X1 and the peak intensity I at 161.6 eV in the XPS spectrum for S2p X2 Comparison with I X1 / I X2 In addition, the peak intensity ratio I X3 / I X4 is the peak intensity I at 133.6 eV in the XPS spectrum for P2p X3 and the peak intensity I at 132.2 eV in the XPS spectrum for P2p X4 Comparison with I X3 / I X4 The XPS spectrum is normalized (background processing) by setting the peak intensities at 138 eV and 170 eV to 0.

[0065] According to the inventor's new findings, the above-mentioned mechanism is responsible for the PS of the sulfide solid electrolyte in the positive electrode active material layer. 4 When the skeleton is broken, the XPS spectrum of the positive electrode active material layer shows that PSP and PO x S 4-x 3- The smaller the XPS peaks derived from such reaction products, the more the PS of the sulfide solid electrolyte contained in the positive electrode active material layer is. 4 It can be said that the skeleton is maintained, and the reaction between the positive electrode active material having a Li-deficient O2-type structure and the sulfide solid electrolyte is suppressed.

[0066] According to the new findings of the present inventors, when the XPS spectrum of the positive electrode active material layer 10 is obtained, the peak intensity ratio I X1 / I X2 is 1.20 or less, and the peak intensity ratio IX3 / I X4 If the value is 1.60 or less, the PS of the sulfide solid electrolyte in the positive electrode active material layer 10 is 4 It can be said that the skeleton is more properly maintained, and a lower resistance can be maintained. Peak Intensity Ratio I X1 / I X2 may be 1.10 or less, 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less. X3 / I X4 may be 1.40 or less, 1.20 or less, 1.00 or less, 0.80 or less, 0.60 or less, or 0.40 or less. In particular, the peak intensity ratio I X1 / I X2 is 0.70 or less, and the peak intensity ratio I X3 / I X4 When the peak intensity ratio I is 0.50 or less, a more significant drag reduction effect is likely to be obtained. X1 / I X2 and peak intensity ratio I X3 / I X4 The lower limit of each of the peak intensity ratios I is not particularly limited, and each of the peak intensity ratios I is 0 or more. X1 / I X2 may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more. X3 / I X4 may be 0.10 or more, 0.20 or more, or 0.30 or more.

[0067] 1.1.6 Shape of the positive electrode active material layer The shape of the positive electrode active material layer 10 is not particularly limited, and may be, for example, a substantially flat sheet-like positive electrode active material layer 10. The thickness of the positive electrode active material layer 10 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.

[0068] 1.2 Electrolyte layer The electrolyte layer 20 is disposed between the positive electrode active material layer 10 and the negative electrode active material layer 30. The electrolyte layer 20 includes at least an electrolyte. The electrolyte layer 20 may include at least one of a solid electrolyte and an electrolytic solution, and may further include a binder or the like. In particular, when the electrolyte layer 20 includes a solid electrolyte, higher performance is likely to be ensured. The content of the electrolyte and the binder or the like in the electrolyte layer 20 is not particularly limited. Alternatively, the electrolyte layer 20 may have a separator or the like for holding the electrolytic solution and preventing contact between the positive electrode active material layer 10 and the negative electrode active material layer 30. The thickness of the electrolyte 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.

[0069] The electrolyte layer 20 may be composed of one layer or may be composed of multiple layers. For example, the electrolyte layer 20 may include a first layer disposed on the positive electrode active material layer 10 side and a second layer disposed on the negative electrode active material layer 30 side, and the first layer may include the first electrolyte, and the second layer may include the 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 above-mentioned oxide solid electrolyte, sulfide solid electrolyte, and ionic solid electrolyte. For example, the first layer may include an ionic solid electrolyte, and the second layer may include at least one of an ionic solid electrolyte and a sulfide solid electrolyte.

[0070] The electrolyte contained in the electrolyte layer 20 may be appropriately selected from those exemplified as electrolytes that may be contained in the above-mentioned positive electrode active material layer 10 (solid electrolytes and / or liquid electrolytes). The binder that may be contained in the electrolyte layer 20 may also be appropriately selected from those exemplified as binders that may be contained in the above-mentioned positive electrode active material layer. Each of the electrolytes and binders may be used alone or in combination of two or more. The separator may be any separator that is commonly used in lithium ion batteries, and examples of the separator include those made of resins such as polyethylene (PE), polypropylene (PP), polyester, and polyamide. The separator may have a single layer structure or a multilayer structure. Examples of the multilayer separator include a separator with a two-layer structure of PE / PP, or a separator with 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.

[0071] 1.3 Negative electrode active material layer The negative electrode active material layer 30 includes at least a negative electrode active material. The negative electrode active material layer 30 may also include an electrolyte, a conductive assistant, a binder, various additives, and the like. The content of each component in the negative electrode active material layer 30 may be appropriately determined according to the intended battery performance. For example, 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 100% by mass or less, less than 100% by mass, 95% by mass or less, or 90% by mass or less, based on the entire solid content of the negative electrode active material layer 30 being 100% by volume. Alternatively, the negative electrode active material and optionally the electrolyte, the conductive assistant, and the binder may be included in a total amount of 85% by volume or more, 90% by volume or more, or 95% by volume or more, based on the entire negative electrode active material layer 30 being 100% by volume, and the remainder may be voids or other components. The shape of the negative electrode active material layer 30 is not particularly limited, and may be, for example, a sheet having a substantially flat surface. The thickness of the negative electrode active material layer 30 is not particularly limited, and may be, for example, 0.1 μm or more, 1 μm or more, 10 μm or more, or 30 μm or more, and may be 2 mm or less, 1 mm or less, 500 μm or less, or 100 μm or less.

[0072] 1.3.1 Negative electrode active material The negative electrode active material may be any of those known as negative electrode active materials for lithium ion batteries. Of the known active materials, various materials may be used that have a potential (charge / discharge potential) for absorbing and releasing lithium ions that is lower than the above-mentioned positive electrode active material. 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 may be used. Among them, when the negative electrode active material layer 30 contains Si as the negative electrode active material, the performance of the lithium ion battery 100 is likely to be improved. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination. The shape of the negative electrode active material may be any shape that is common as a negative electrode active material 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 may be secondary particles formed by agglomeration of a plurality of primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material may be in the form of a sheet (foil or film) such as a lithium foil. That is, the negative electrode active material layer 30 may be made of a sheet of the negative electrode active material.

[0073] 1.3.2 Other Examples of the electrolyte that can be contained in the negative electrode active material layer 30 include the above-mentioned solid electrolyte, electrolytic solution, or a combination thereof. The conductive assistant that can be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, those exemplified as the conductive assistant that can be contained in the above-mentioned positive electrode active material layer. The binder that can be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, those exemplified as the binder that can be contained in the above-mentioned positive electrode active material layer. Each of the electrolyte, conductive assistant, and binder may be used alone or in combination of two or more kinds.

[0074] 1.4 Positive electrode current collector As shown in FIG. 1, the lithium ion battery 100 may include a positive electrode current collector 40 in contact with the positive electrode active material layer 10. The positive electrode current collector 40 may be any of those commonly used as positive electrode current collectors for lithium ion batteries. The positive electrode current collector 40 may have at least one shape selected from a foil shape, a plate shape, a mesh shape, a punched metal shape, and a foam. The positive electrode current collector 40 may be made of a metal foil or a metal mesh. In particular, a metal foil is excellent in terms of handling and the like. The positive electrode current collector 40 may be made of a plurality of foils. Examples of metals constituting the positive electrode current collector 40 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 viewpoint of ensuring oxidation resistance, the positive electrode current collector 40 may contain Al. The positive electrode collector 40 may have some kind of coating layer on its surface for the purpose of adjusting the resistance or the like. For example, the positive electrode collector 40 may have a carbon coating layer. The positive electrode collector 40 may be a metal foil or a substrate on which the above-mentioned metal is plated or vapor-deposited. When the positive electrode collector 40 is made of a plurality of metal foils, some kind of layer may be present between the plurality of metal foils. The thickness of the positive electrode collector 40 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0075] 1.5 Negative electrode current collector As shown in FIG. 1, the lithium ion battery 100 may include a negative electrode current collector 50 in contact with the negative electrode active material layer 30. The negative electrode current collector 50 may 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, a plate, a mesh, a punched metal, a foam, or the like. The negative electrode current collector 50 may be a metal foil or a metal mesh, or may be a carbon sheet. In particular, a metal foil is excellent in terms of ease of handling. The negative electrode current collector 50 may be made of a plurality of 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 viewpoint of ensuring reduction resistance and being difficult 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 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 base material on which the above metal is plated or vapor-deposited. In addition, when the negative electrode current collector 50 is made of a plurality of metal foils, some kind of layer may be present between the plurality of metal foils. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less.

[0076] 1.6 Other configurations The lithium ion battery 100 may have a general configuration for a battery in addition to the above configuration. For example, a tab, a terminal, etc. The lithium ion battery 100 may have each of the above configurations housed inside an exterior body. Any known exterior body for a battery can be adopted as the exterior body. In addition, a plurality of batteries 100 may be electrically connected in any way and stacked in any way to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case. Examples of the shape of the lithium ion battery 100 include a coin type, a laminate type, a cylindrical type, and a square type. The lithium ion battery 100 may be a secondary battery.

[0077] 2. Manufacturing method of lithium-ion batteries The above-mentioned lithium ion battery 100 can be manufactured, for example, by the following method. That is, as shown in FIG. 2, the manufacturing method of the lithium ion battery 100 according to the embodiment includes the following steps: Mixing a positive electrode active material 11 having a Li-deficient O2 type structure with a sulfide solid electrolyte 12 to obtain a positive electrode mixture 15; and and pressing the positive electrode mixture 15 at a temperature of less than 165° C. to obtain a positive electrode active material layer 10.

[0078] 2.1 Mixing The method of mixing the positive electrode active material 11 and the sulfide solid electrolyte 12 is not particularly limited. The positive electrode active material 11 and the sulfide solid electrolyte 12 may be mixed in a dry manner or in a wet manner using a solvent. The mixing means is also not particularly limited. For example, various mechanical mixing means such as a ball mill may be adopted. As described above, the positive electrode active material layer 10 may contain an optional component in addition to the positive electrode active material 11 and the sulfide solid electrolyte 12. That is, the positive electrode mixture 15 may be obtained by mixing the optional component with the positive electrode active material 11 and the sulfide solid electrolyte 12. The positive electrode mixture 15 may be dispersed in a solvent to form a slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. As shown in FIG. 2, the slurry is applied to the surface of the positive electrode current collector 40 using a doctor blade or the like, and then dried, so that the positive electrode mixture 15 can be laminated on the surface of the positive electrode current collector 40.

[0079] 2.2 Press The positive electrode mixture 15 is pressed at a temperature of less than 165° C. As a result, the positive electrode active material layer 10 is obtained. As shown in FIG. 2, the positive electrode mixture 15 may be laminated on the surface of the positive electrode collector 40, and then the positive electrode mixture 15 may be pressed together with the positive electrode collector 40 in the lamination direction to form the positive electrode active material layer 10 on the surface of the positive electrode collector 40. The pressing temperature must be less than 165° C. If the pressing temperature is 165° C. or higher, the positive electrode active material 11 and the sulfide solid electrolyte 12 react with each other to form the PS of the sulfide solid electrolyte 12. 4The skeleton collapses, and the above-mentioned relationships (1) to (4) are no longer satisfied. The pressing temperature may be 160°C or lower, 155°C or lower, or 150°C or lower. Meanwhile, the lower limit of the pressing temperature is not particularly limited. The pressing temperature may be room temperature (25°C) or higher, 50°C or higher, 75°C or higher, 100°C or higher, or 125°C or higher. The pressure during pressing is not particularly limited, and may be a pressure that can densify the positive electrode mixture 15 and form the positive electrode active material layer 10. The pressing means may be any means that can appropriately press the positive electrode mixture 15. For example, various pressing means such as a roll press may be adopted. The pressing of the positive electrode mixture 15 may be performed together with the electrolyte layer 20 and the negative electrode active material layer 30 described later. That is, in one embodiment, a laminate having the positive electrode current collector 40, the positive electrode composite 15, the electrolyte layer 20, the negative electrode active material layer 30, and the negative electrode current collector 50 in this order may be obtained, and then the laminate may be pressed in the stacking direction.

[0080] Through the above mixing and pressing, the positive electrode active material layer 10 is obtained. The positive electrode active material layer 10 thus obtained is combined with the electrolyte layer 20 and the negative electrode active material layer 30 to manufacture the lithium ion battery 100. For example, the process is as follows. (1) The negative electrode active material constituting the negative electrode active material layer is dispersed in a solvent to obtain a slurry for the negative electrode layer. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The negative electrode layer slurry is applied to the surface of the negative electrode current collector 50 using a doctor blade or the like, and then dried and optionally pressed, to form the negative electrode active material layer 30 on the surface of the negative electrode current collector 50. (2) The layers are laminated so that the electrolyte layer 20 (solid electrolyte layer or separator) is sandwiched between the positive electrode active material layer 10 and the negative electrode active material layer 30, to obtain a laminate having the positive electrode current collector 40, the positive electrode active material layer 10, the electrolyte layer 20, the negative electrode active material layer 30, and the negative electrode current collector 50 in this order. When a solid electrolyte layer is used as the electrolyte layer 20, the solid electrolyte layer may be formed on a peelable substrate, and then the solid electrolyte layer may be transferred to the positive electrode active material layer 10 or the negative electrode active material layer 30 to obtain the laminate. Other members such as terminals are attached to the laminate as necessary. (3) The laminate is housed in a battery case. When an electrolyte is to be contained, the battery case is filled with the electrolyte, and the laminate is immersed in the electrolyte and sealed in the battery case. In this way, the lithium ion battery 100 is obtained.

[0081] 3. Vehicles with lithium-ion batteries As described above, the lithium ion battery of the present disclosure has low resistance. Such a lithium ion battery can be suitably used in at least one vehicle selected from, for example, a hybrid vehicle (HEV), a plug-in hybrid 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, the 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 including a positive electrode active material having a Li-deficient O2 type structure and a sulfide solid electrolyte, and the Raman spectrum of the positive electrode active material layer satisfies the above relationships (1) and (2). EXAMPLES

[0082] As described above, one embodiment of the lithium ion secondary battery and the like 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 of the technology. The technology of the present disclosure will be described in more detail below while showing examples, but the technology of the present disclosure is not limited to the following examples.

[0083] 1. Preparation of a cathode active material with a Li-deficient O2 structure 1.1 Preparation of precursor (1) MnSO 4 5H 2 O, NiSO 4 6H 2 O, CoSO 4 7H 2 The first solution was obtained by weighing out the desired composition ratio of O and dissolving it in distilled water to a concentration of 1.2 mol / L. 2 CO 3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain a second solution. (2) 1000 mL of pure water was placed in a reaction vessel (with a baffle plate), and 500 mL of the first solution and 500 mL of the second solution were each added dropwise at a rate of about 4 mL / min. (3) After the dropwise addition was completed, the mixture was stirred at room temperature at a stirring speed of 100 rpm for 1 hour to obtain a product. (4) The product was washed with pure water, subjected to solid-liquid separation using a centrifuge, and the precipitate was collected. (5) The obtained precipitate was dried overnight at 120°C, crushed in a mortar, and then separated into coarse particles and fine particles by air classification. Here, both the coarse particles and the fine particles are composite salts containing Mn, Ni, and Co. In this embodiment, the coarse particles were used as precursor particles out of the coarse particles and the fine particles. The coarse particles were spherical particles having an average particle diameter D50 of 3.5 μm.

[0084] 1.2 Preparation of the complex (1) Na to 1150g / L 2 CO 3 After weighing out and distilled water, stir using a stirrer until completely dissolved. 2 CO 3 An aqueous solution was prepared. (2) The above Na 2 CO 3 The aqueous solution and the above-mentioned precursor particles are mixed together to obtain a mixture having a composition of Na 0.8 Mn 0.5 Ni 0.2 Co 0.3 O 2 The components were weighed and mixed so as to obtain a slurry. (3) The above slurry was air-dried by spray drying to obtain a composite. Specifically, a DL410 spray dryer 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 The above slurry was dried by air flow under the conditions of 0.3 MPa spray pressure at 1000 rpm, and the surface of the precursor particles was coated with Na. 2 CO 3 In the composite, 70% or more of the surface area of ​​the precursor particles was covered with Na. 2 CO 3 It was covered with.

[0085] 1.3 Firing of the composite The composite was placed in an alumina crucible and sintered in an air atmosphere to obtain a Na-containing oxide having a P2 structure under the following sintering conditions (1) to (5). (1) An alumina crucible containing the above composite is placed in a heating furnace in an air atmosphere. (2) The temperature inside the heating furnace is raised from room temperature (25°C) to 600°C in 115 minutes. (3) The temperature in the heating furnace is kept at 600°C for 360 minutes to perform pre-baking. (4) After the preliminary firing, the temperature inside the heating furnace is raised to 900°C and then held at 900°C for 60 minutes for main firing. (5) After the main firing, the temperature inside the heating furnace is lowered from 900°C to 250°C, and the alumina crucible is removed from the heating furnace at 250°C and allowed to cool outside the furnace in a dry atmosphere until it reaches 25°C in 10 minutes.

[0086] The fired product after cooling was pulverized in a mortar in a dry atmosphere to obtain Na-containing oxide particles having a P2 type structure (P2 type particles).

[0087] 1.4 Ion exchange (1) LiNO 3 and LiCl were weighed out to have a molar ratio of 50:50, and mixed with the above P2 type particles in a molar ratio that was 10 times the minimum Li amount required for ion exchange to obtain a mixture. (2) Using an alumina crucible, ion exchange was carried out in air at 280°C for 1 hour to obtain a product containing Li-containing oxide. (3) The salt remaining in the product was washed with pure water, and solid-liquid separation was performed by vacuum filtration to obtain a precipitate. (4) The obtained precipitate was dried overnight at 120°C to obtain a positive electrode active material. The chemical composition of the positive electrode active material was Li 0.7 Mn 0.5 Ni 0.2 Co 0.3 O 2In addition, when the crystal phase contained in the positive electrode active material was confirmed by XRD, it was found that the positive electrode active material had an O2 type structure. In other words, the positive electrode active material had a Li-deficient O2 type structure.

[0088] 2. Preparation of Li-free (Li-doped) positive electrode active material A Li-non-deficient positive electrode active material was prepared by doping Li into the above-mentioned Li-deficient O2-type positive electrode active material. Specifically, 9-fluorenone was mixed and dissolved in tetrahydrofuran (THF) in a glove box (Ar atmosphere) to obtain a fluorenone solution at 1 mol / L. Li foil was further added to the fluorenone solution in the same mole amount as the fluorenone, and the solution was stirred for 2 hours to obtain a reduced solution containing 1 mol / L Li ions. The above-mentioned positive electrode active material was added to the reduced solution, immersed, and stirred for 24 hours. After stirring, the positive electrode active material was washed with THF and subjected to solid-liquid separation by vacuum filtration. The obtained precipitate was dried overnight at 120°C to obtain a Li-non-deficient positive electrode active material. The chemical composition of the positive electrode active material was Li 1.0 Mn 0.5 Ni 0.2 Co 0.3 O 2 In addition, when the crystal phase contained in the positive electrode active material was confirmed by XRD, the positive electrode active material had an O2 type structure.

[0089] 3. Preparation of positive electrode active material with O3 structure A commercially available NCA-based positive electrode active material was prepared as a positive electrode active material having a Li-non-deficient O3-type structure.

[0090] 4. Preparation of Evaluation Cell Using each of the above positive electrode active materials, an evaluation cell was produced according to the following procedure. (1) Positive electrode active material and sulfide solid electrolyte (Li 2 SP 2 S 5A positive electrode mixture was obtained by weighing and mixing the positive electrode active material:sulfide solid electrolyte:PVDF:VGCF=81.1:15.9:0.6:2.4 (mass ratio). The obtained positive electrode mixture was dispersed in a solvent (butyl butyrate) to obtain a positive electrode slurry. The obtained positive electrode slurry was applied to a positive electrode current collector (Al foil) and dried. Thereafter, the positive electrode active material layer was formed on the surface of the positive electrode current collector by pressing with a roll press at a line pressure of 100 kN at the pressing temperature shown in Table 1 below. (2) Negative electrode active material (lithium titanate) and sulfide solid electrolyte (Li 2 SP 2 S 5 A negative electrode mixture was obtained by weighing and mixing 100% 1,0 ... (3) Sulfide solid electrolyte (Li 2 SP 2 S 5 The sulfide solid electrolyte (LiI-LiBr) and acrylate butadiene rubber (ABR) were weighed and mixed in a ratio of sulfide solid electrolyte:ABR=99.4:0.6 (mass ratio) to obtain an electrolyte mixture. (4) An electrolyte mixture was sandwiched between the positive electrode active material layer and the negative electrode active material layer to obtain a laminate having a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector in this order. The obtained laminate was pressed at room temperature (25° C.) with a surface pressure of 50 kN to obtain an evaluation cell (solid-state battery).

[0091] 4. Raman and XPS measurements In a glove box, the positive electrode current collector (Al foil) was peeled off and removed from the above evaluation cell to expose the positive electrode active material layer, and then Raman and XPS measurements were performed on the outermost surface of the positive electrode active material layer to obtain Raman and XPS spectra (S2p, P2p). As a reference example, a positive electrode composite was laminated on the surface of the positive electrode current collector, and the Raman and XPS spectra of the positive electrode composite were obtained as is without pressing. In addition, in the Raman measurement, a 300 cm -1 The intensity at 138 eV and 170 eV was normalized to 0 (background processing). In the XPS measurement, the peak intensities at 138 eV and 170 eV were normalized to 0 (background processing).

[0092] Fig. 3 shows Raman spectra for each of the Examples, Comparative Examples, and Reference Examples. Fig. 4 shows XPS spectra (P2p) for each of the Examples, Comparative Examples, and Reference Examples. Fig. 5 shows XPS spectra (S2p) for each of the Examples, Comparative Examples, and Reference Examples.

[0093] P in the Raman spectrum 2 S 6 4- Peak intensity I due to R1 As, 385cm -1 The peak intensity in the Raman spectrum was also identified. 4 3- Peak intensity I due to R2 As, 420cm -1 In addition, the peak intensity I R3 As shown in the Raman spectrum at 475 cm -1 The peak intensity ratio I R1 / I R2 and I R3 / I R2 The calculation results for each are shown below.

[0094] The peak intensity I due to PSP in the XPS spectrum of S2p X1The peak intensity at 162.9 eV was determined as the peak intensity at 162.9 eV. In addition, the PS 4 3- Peak intensity I due to X2 The peak intensity at 161.6 eV was determined as the peak intensity ratio I X1 / I X2 The calculation results are shown below.

[0095] PO in the XPS spectrum for P2p x S 4-x 3- Peak intensity I due to X3 The peak intensity at 133.6 eV was identified as the peak intensity at 133.6 eV. 4 3- Peak intensity I due to X4 The peak intensity at 132.2 eV was determined as the peak intensity ratio I X3 / I X4 The calculation results are shown below.

[0096] 5.Charge / Discharge Characteristics Evaluation For each evaluation cell, a two-cycle charge-discharge test was performed at 0.1C (1C=220mA / g) in a voltage range of 1.8-4.6V in a thermostatic chamber maintained at 25°C. Then, a current equivalent to 3C was applied for 10 seconds in a thermostatic chamber maintained at 25°C at SOC50% (2.35V vs. LTO) to measure the DCIR resistance. The measurement results are shown in Table 1 below.

[0097] 6. Evaluation Results For each of Examples 1 and 2, Comparative Example 1 (when a positive electrode active material having a Li-deficient O2 type structure was used), Comparative Example 2 (when a positive electrode active material having a Li-non-deficient (Li-doped) O2 type structure was used), Comparative Example 3 (when a positive electrode active material having a Li-non-deficient O3 type structure was used), and the reference example (positive electrode composite), the type of positive electrode active material, the presence or absence of pressing of the positive electrode composite and the pressing temperature, the peak intensity ratio I in the Raman spectrum, R1 / I R2 and I R3 / I R2 , peak intensity ratio in the XPS spectrum I X1 / I X2 and I X3 / I X4 , as well as the resistance measurement results.

[0098] [Table 1]

[0099] The results shown in Table 1 and FIGS.

[0100] I R1 / I R2 is less than 0.20, and I R3 / I R2 is less than 0.20, and I X1 / I X2 is less than 1.20, and I X3 / I X4 The evaluation cells according to Examples 1 and 2, in which I is 1.60 or less, R1 / I R2 is over 0.20, and I R3 / I R2 is over 0.20, and I X1 / I X2 is over 1.20, I X3 / I X4 The cell had a lower resistance than the evaluation cell according to Comparative Example 1, in which the resistance was more than 1.60. From the comparison between Examples 1 and 2 and Comparative Example 1, it was found that when a cathode active material having a Li-deficient O2 type structure and a sulfide solid electrolyte were combined in a cathode mixture and the cathode mixture was pressed at a temperature of 165°C or higher, the cathode active material reacted with the sulfide solid electrolyte, and the PS 4 It can be seen that the skeleton collapses and by-products are generated. In Comparative Example 1, it is believed that the by-products increased the resistance of the evaluation cell.

[0101] On the other hand, in Comparative Examples 2 and 3, in which a Li-free positive electrode active material was used, no by-products were observed even when the positive electrode mixture was pressed at 165°C, and the PS of the sulfide solid electrolyte was 4In other words, it can be understood that the issue of increased resistance due to the reaction between the positive electrode active material and the sulfide solid electrolyte is unique to the combination of a positive electrode active material having a Li-deficient O2-type structure with a sulfide solid electrolyte in the positive electrode active material layer.

[0102] 7. Supplementary Information In the above examples, a specific chemical composition is exemplified as a positive electrode active material having a Li-deficient O2 type structure, but the chemical composition of the positive electrode active material is not limited to this. The chemical composition of the sulfide solid electrolyte is also not limited to the above. When a positive electrode active material layer is formed using a positive electrode active material having a Li-deficient O2 type structure and a sulfide solid electrolyte, it is considered that the same effect can be achieved regardless of the chemical composition of the positive electrode active material and the sulfide solid electrolyte.

[0103] 8. Summary As described above, in a lithium ion battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, if the following requirements (A) and (B) are satisfied, the lithium ion battery can be said to have low resistance. (A) The positive electrode active material layer includes a positive electrode active material having a Li-deficient O2 type structure and a sulfide solid electrolyte. (B) The Raman spectrum of the positive electrode active material layer satisfies the following relationships (1) and (2): I R1 / I R2 ≦0.20 (1) I R3 / I R2 ≦0.20 (2) I R1 : P in the Raman spectrum 2 S 6 4- Peak intensity derived from I R2 : PS in the Raman spectrum 4 3- Peak intensity derived from I R3 : Peak intensity due to SS in the Raman spectrum Meet the following.

[0104] Furthermore, when the following requirement (C) is satisfied in addition to the above requirements (A) and (B), it can be said that the lithium-ion battery has a lower resistance. (C) The XPS spectrum of the positive electrode active material layer satisfies the following relationships (3) and (4): I X1 / I X2 ≦1.20 (3) I X3 / I X4 ≦1.60 (4) I X1 : Peak intensity due to PSP in the XPS spectrum of S2p I X2 :PS in the XPS spectrum for S2p 4 3- Peak intensity derived from I X3 PO in the XPS spectrum for P2p x S 4-x 3- Peak intensity derived from I X4 :PS in the XPS spectrum for P2p 4 3- Peak intensity derived from Meet the following. [Explanation of symbols]

[0105] 100 Lithium-ion batteries 10 Cathode active material layer 11 Positive electrode active material with Li-deficient O2 structure 12 Sulfide solid electrolyte 15 Positive electrode mixture 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector

Claims

1. 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 is A positive electrode active material having a Li-deficient O2 type structure; Sulfide solid electrolyte and The Raman spectrum of the positive electrode active material layer satisfies the following relationships (1) and (2): I Ｒ１ / I Ｒ２ ≦0.20 ・・・(1) I Ｒ３ / I Ｒ２ ≦0.20 ・・・(2) I Ｒ１ : P in the Raman spectrum ２ S ６ ４－ Peak intensity derived from I Ｒ２ : PS in the Raman spectrum ４ ３－ Peak intensity derived from I Ｒ３ : Peak intensity due to S-S in the Raman spectrum Fulfilling Lithium-ion battery.

2. 2. The lithium ion battery of claim 1, The XPS spectrum of the positive electrode active material layer satisfies the following relationships (3) and (4): I Ｘ１ / I Ｘ２ ≦1.20 ・・・(3) I Ｘ３ / I Ｘ４ ≦1.60 ・・・(4) I Ｘ１ : Peak intensity derived from P-S-P in the XPS spectrum of S2p I Ｘ２ : PS in the XPS spectrum for S2p ４ ３－ Peak intensity derived from I Ｘ３ : PO in the XPS spectrum for P2p ｘ S ４－ｘ ３－ Peak intensity derived from I Ｘ４ : PS in the XPS spectrum for P2p ４ ３－ Peak intensity derived from Fulfilling Lithium-ion battery.

3. 3. The lithium ion battery according to claim 1, The total solid content contained in the positive electrode active material layer is taken as 100 mass %, The content of the positive electrode active material is 40% by mass or more and less than 100% by mass, and The content of the sulfide solid electrolyte is more than 0 mass% and not more than 60 mass%. Lithium-ion battery.

4. 3. The lithium ion battery according to claim 1, The positive electrode active material is Li ａ Na ｂ Mn ｘ－ｐ Ni ｙ－ｑ Co ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (wherein 0<a<1.00, 0≦b≦0.20, x+y+z=1, and 0≦p+q+r<0.17; and element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). Lithium-ion battery.

5. 3. The lithium ion battery according to claim 1, The electrolyte layer includes a solid electrolyte. Lithium-ion battery.

6. A method for manufacturing a lithium ion battery, comprising: Mixing a positive electrode active material having a Li-deficient O2 type structure with a sulfide solid electrolyte to obtain a positive electrode mixture; and pressing the positive electrode mixture at a temperature of less than 165° C. to obtain a positive electrode active material layer; A method for producing a lithium ion battery, comprising:

Images