Electrode active material, electrode mixture material, and battery

Abstract

To provide a technique of improving the cycle characteristics of a battery in a case where a battery is formed by using an electrode active material with an O2-type structure.SOLUTION: The electrode active material according to the present disclosure includes an O2-type Li-containing oxide and lithium hydroxide. The O1s spectrum of the electrode active material as obtained by XPS satisfies the condition 0.20≤S1 / (S1+S2)≤0.73, in which S1 represents the peak area at 531.4 eV attributed to the lithium hydroxide, and S2 represents the peak area at 529.4 eV attributed to the O2-type lithium-containing oxide.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present application discloses an electrode active material, an electrode mixture, and a battery. [Background technology]

[0002] Active materials for batteries having an O2 type structure are known. As disclosed in Patent Document 1, an electrode active material having an 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-092824 A Summary of the Invention [Problem to be solved by the invention]

[0004] Batteries using electrode active materials with an O2 structure have room for improvement in terms of cycle characteristics. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> An electrode active material, O2-type Li-containing oxide; Lithium hydroxide, Including, The O1s spectrum of the electrode active material obtained by XPS has the following relationship (1): 0.20≦S1 / (S1+S2)≦0.73 (1) S1: Area of ​​the peak due to lithium hydroxide at 531.4 eV S2: Area of ​​the peak at 529.4 eV originating from O2-type Li-containing oxide Fulfilling Electrode active material. <Aspect 2> The electrode active material of embodiment 1, The O1s spectrum satisfies the following relationship (1A): 0.39≦S1 / (S1+S2)≦0.68 (1A) Fulfilling Electrode active material. <Aspect 3> The electrode active material according to embodiment 1 or 2 is included. Electrode composite material. <Aspect 4> A battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer comprises the electrode active material of embodiment 1 or 2. battery. Effect of the Invention

[0006] When a battery is constructed using the electrode active material of the present disclosure, the cycle characteristics of the battery are likely to be improved. [Brief description of the drawings]

[0007] [Figure 1] 2 shows a schematic diagram of an example of a cross-sectional configuration of an electrode active material. [Diagram 2] 1 shows an example of a flow of a method for producing an electrode active material. [Diagram 3] 1 shows a schematic diagram of an example of a battery configuration. [Figure 4] 1 shows XPS-O1s spectra of the electrode active materials according to Examples 2 and 4 and Comparative Examples 1 and 3. [Diagram 5] The relationship between S1 / (S1+S2) and the capacity retention rate is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, one embodiment of the electrode active material, electrode mixture, and battery according to the present disclosure will be described, but the electrode active material, electrode mixture, and battery according to the present disclosure are not limited to the embodiment described below.

[0009] 1. Electrode active material 1, an electrode active material 1 according to an embodiment includes an O2-type Li-containing oxide 1a and lithium hydroxide 1b. Here, the O1s spectrum of the electrode active material 1 obtained by XPS satisfies the following relationship (1): 0.20≦S1 / (S1+S2)≦0.73 (1) S1: Area of ​​the peak due to lithium hydroxide at 531.4 eV S2: Area of ​​the peak at 529.4 eV originating from O2-type Li-containing oxide Meet the following.

[0010] 1.1 O2 type Li-containing oxide 1.1.1 Crystal structure The O2-type Li-containing oxide 1a has an O2-type structure as a crystal structure. The O2-type Li-containing oxide 1a may have a crystal structure other than the O2-type structure in addition to the O2-type structure. Examples of crystal structures 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 to 3.5 nm, typically 2.9 nm to 3.0 nm, and different from the O3-type structure also belonging to the space group R-3m). The O2-type Li-containing oxide 1a 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 O2-type Li-containing oxide 1a may have a crystal structure as a main phase that changes depending on its charge / discharge state.

[0011] 1.1.2 Chemical composition The O2-type Li-containing oxide 1a may contain, for example, at least one element selected from Mn, Ni, and Co, Li, and O as constituent elements. In particular, when the O2-type Li-containing oxide 1a contains, as constituent elements, at least Li, Mn, one or both of Ni and Co, and O, and particularly when the O2-type Li-containing oxide 1a contains, as constituent elements, at least Li, Mn, Ni, Co, and O, higher performance is likely to be obtained. The O2-type Li-containing oxide 1a contains Li aSo b Mr x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2 (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). When the O2-type Li-containing oxide 1a 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 is at most 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 is at most 0.20, 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 is at most 1.00, 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 is at most 1.00, 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 is at most 1.00, 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, when 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 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.

[0012] 1.2 Lithium hydroxide The electrode active material 1 contains lithium hydroxide 1b together with an O2-type Li-containing oxide 1a. As shown in Fig. 1, the electrode active material 1 may have an O2-type Li-containing oxide 1a and lithium hydroxide 1b that covers at least a part of the surface of the O2-type Li-containing oxide 1a. The amount of lithium hydroxide 1b contained in the electrode active material 1 may be any amount that satisfies the relationship (1) described later.

[0013] 1.3 O1s spectrum of electrode active material obtained by XPS The amount of lithium hydroxide 1b in the electrode active material 1 can be measured by X-ray photoelectron spectroscopy (XPS). XPS is a method for analyzing the constituent elements and their electronic states on the surface of a sample by irradiating the surface of the sample with X-rays and measuring the emitted photoelectron energy. The spectrum obtained by XPS shows a peak area proportional to the substance's specific pattern and the amount of substance, so that the substance can be analyzed qualitatively and quantitatively. When the O1s spectrum of the electrode active material 1 obtained by XPS satisfies the above relationship (1), it can be said that lithium hydroxide 1b is appropriately precipitated on the surface of the O2-type Li-containing oxide 1a. When lithium hydroxide 1b is appropriately precipitated on the surface of the O2-type Li-containing oxide 1a, when a battery is formed using the electrode active material 1 and the battery is charged to a high potential region, the lithium hydroxide 1b prevents contact between the O2-type Li-containing oxide 1a and the electrolyte while securing a Li conduction path between the active material and the electrolyte, and deterioration and decomposition of the electrolyte during charging are easily suppressed. That is, by forming a battery using the electrode active material 1, a battery with excellent cycle characteristics can be obtained.

[0014] In particular, when the O1s spectrum of the electrode active material 1 obtained by XPS satisfies the following relationship (1A), the effect of improving the cycle characteristics becomes more remarkable. 0.39≦S1 / (S1+S2)≦0.68 (1A)

[0015] In the O1s spectrum, the peak at 531.4 eV derived from lithium hydroxide and the peak at 529.4 eV derived from O2-type Li-containing oxide may overlap. Therefore, when identifying the peak areas S1 and S2, waveform separation is performed by curve fitting (typically, fitting based on the nonlinear least squares method). This allows the peak at the position of binding energy 531.4 eV and the peak at the position of 529.4 eV to be separated, and each peak area can be identified. The waveform separation can be performed, for example, by using the software "MultiPak" manufactured by ULVAC PHI. In addition, the "peak at the position of 531.4 eV" and the "peak at the position of 529.4 eV" allow for a deviation (±0.1 eV) in the position of the peak top that may occur due to measurement conditions, etc.

[0016] 1.4 Other As described later, the electrode active material 1 can be obtained by substituting Na of a Na-containing oxide having a P2 type structure with Li to obtain an O2 type Li-containing oxide 1a, and then precipitating lithium hydroxide 1b. Here, the P2 type structure is a hexagonal crystal system, has a large diffusion coefficient of Na ions, and is likely to grow crystals 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 crystals tend to grow in a plate-like shape in a specific direction. Therefore, the Na-containing oxide having the P2 type structure usually becomes a plate-like particle with a large aspect ratio in which the crystal growth direction is biased in a specific direction. The electrode active material 1 may be obtained based on such plate-like Na-containing oxide particles, or may be obtained based on spherical Na-containing oxide particles. That is, the shape of the electrode active material 1 may be a plate-like particle or a spherical particle. When the electrode active material 1 is a spherical particle, the reaction resistance decreases due to the reduction in the crystallite size, and the diffusion resistance inside the particle tends 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 electrode active material 1 may be, for example, a solid particle, a hollow particle, or a particle having a void. The size of the particles of the electrode active material 1 is not particularly limited, but it is considered that a smaller size is more advantageous. For example, the average particle diameter (D50) of the particles of the electrode active material 1 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 a volume-based particle size distribution by a laser diffraction / scattering method.

[0018] 2. Manufacturing method of electrode active material The electrode active material 1 can be produced, for example, by the following method. That is, as shown in FIG. 2, the method for producing the electrode active material 1 according to one embodiment includes the following steps: Obtaining a sodium-containing transition metal oxide having an S1:P2 type structure; S2: replacing at least a portion of the Na in the Na-containing oxide with Li by ion exchange to obtain a Li-containing oxide having an O2 type structure; S3: further doping the Li-containing oxide with Li in a step separate from the ion exchange; and S4: Precipitating lithium hydroxide on the surface of the Li-doped Li-containing oxide. It may include.

[0019] 2.1 S1 In S1, the Na-containing transition metal oxide having a P2 type structure is, for example, S11: Obtaining a precursor (e.g., a precursor including at least one element of Mn, Ni, and Co); S12: Coating the surface of the precursor with a Na source to obtain a composite; and S13: Firing the composite. Here, the S13 can be produced through the following steps: S13-1: Pre-firing the composite at a temperature of 300°C or higher and lower than 700°C for 2 hours or higher and 10 hours or lower; S13-2: 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 S13-3: Following the main sintering, the composite may be rapidly cooled from a temperature T1 of 200° C. or higher to a temperature T2 of 100° C. or lower.

[0020] 2.1.1 Preparation of precursor The precursor may contain at least Mn and 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.

[0021] In S11, 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 of 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 of Mn, Ni, and Co. Specifically, in S11, 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.

[0022] In S11, 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 obtaining a precursor by coprecipitation in S11, 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 S11, and element M may be doped when Na-doping baking is performed in S2 and S3 described later.

[0023] 2.1.2 Preparation of the complex In S12, the surface of the precursor obtained in S11 is coated with a Na source to obtain a composite. The Na source may be a salt containing Na, such as carbonate or nitrate, or a compound other than salt, such as sodium oxide or sodium hydroxide. In S12, 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 firing. In S12, the coverage rate of the Na source on the surface of the precursor is not particularly limited. In S12, the method of coating the surface of the precursor with the Na source is not particularly limited. For example, the precursor and the Na source may be mixed in a mortar or a mixer, or the precursor may be contacted with a solution containing a Na source using a tumbling fluidized coating method or a spray drying method, and then dried.

[0024] In S12, the precursor may be coated with an M source together with a Na source. For example, in S12, the precursor obtained in S11, 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.

[0025] 2.1.3 Firing of the composite In S13, the composite obtained in S12 is fired to obtain a Na-containing oxide having a P2 type structure. S13 may include the above S13-1, S13-2, and S13-3. By adjusting the conditions in S13-1, S13-2, and S13-3, the crystallinity and shape (plate-like particles or spherical particles) of the P2 type Na-containing oxide obtained in S13 can be adjusted.

[0026] In S13-1, 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 S13-1, the composite may be optionally 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 S13-1 is insufficient, the P2 phase may not be sufficiently generated in the finally obtained Na-containing oxide. In S13-1, 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 improved, and the Na-containing oxide obtained through S13-2 and S13-3 described later is likely to be appropriate. The pre-firing 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 less than 8 hours, 3 hours or more and less than 8 hours, 4 hours or more and less than 8 hours, 5 hours or more and less than 8 hours, or 5 hours or more and less than 7 hours. The pre-firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere.

[0027] In S13-2, 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 48 hours. In S13-2, the main firing temperature of the composite may be 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. In S13-2, the shape of the Na-containing oxide can be controlled by the main firing time. If the main firing time is too short, the generation of the P2 phase is insufficient. On the other hand, if the main firing time is too long, the P2 phase grows excessively, and the particles are likely to become coarse and plate-like.

[0028] In step S13-3, following the main firing, the composite is rapidly cooled (cooled at a temperature drop rate of 20°C / min or more) from a temperature T1 of 200°C or more to a temperature T2 of 100°C or less. The preliminary firing and main firing are performed, for example, in a heating furnace. In step S13-3, for example, after the main firing of the composite is performed in a heating furnace, it is cooled to an arbitrary temperature T1 of 200°C or more in the heating furnace, and after the temperature T1 is reached, the fired product is removed from the heating furnace and rapidly cooled outside the furnace to an arbitrary temperature T2 of 100°C or less. The temperature T1 may be an arbitrary temperature of 200°C or more, or an arbitrary temperature of 250°C or more. The temperature T2 may be an arbitrary temperature of 100°C or less, or an arbitrary temperature of 50°C or less, or may be the cooling end temperature. In a certain temperature range between the temperature T1 and the temperature T2, moisture is likely to penetrate between the layers of the P2 type structure due to atomic vibration, molecular motion, etc. 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 is reduced by shortening the time in which the temperature range in which moisture easily penetrates (i.e., by cooling quickly). In this regard, when cooling the composite after the main firing in step S13-3, for example, by cooling in a dry atmosphere outside the furnace from an arbitrary temperature T1 of 200°C or higher to an arbitrary temperature T2 of 100°C or lower, the cooling rate from temperature T1 to temperature T2 is high (for example, 20°C / min or higher), making it difficult for moisture to penetrate between the layers of the P2 type structure, and the collapse of the P2 type structure can be suppressed. As a result, Na can be efficiently ion-exchanged with Li in S2.

[0029] By S13, a Na-containing oxide having a P2 type structure and a predetermined chemical composition can be produced. 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 Mnx-p Ni y-q Co z-r M p+q+r It may have a chemical composition represented by O2. 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 contribution of element M to charge and discharge is small. In this regard, in the above chemical composition, when 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 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 it is not necessarily exactly 2.0 and is indeterminate.

[0030] 2.2 S2 In S2, at least a part of Na in the Na-containing oxide obtained in S1 is ion-exchanged with Li to obtain a Li-containing oxide having an 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 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 the molten salt, the melting point becomes lower than when lithium halide or other lithium salt is used alone, and ion exchange can be performed at a lower temperature. 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.

[0031] 2.3 S3 In S3, the Li-containing oxide obtained by S2 is further doped with Li in a process separate from the ion exchange, thereby increasing the molar ratio of Li in the Li-containing oxide (a above). In S3, for example, the Li-containing oxide may be further doped with Li in a process separate from the ion exchange, without applying a driving force by voltage. For example, the Li-containing oxide may be doped with Li by contacting the Li-containing oxide with a Li-doping source. Specifically, in S3, it is preferable to contact the Li-containing oxide with a reducing solution containing Li ions, thereby further doping the Li-containing oxide with Li in a process separate from the ion exchange. The "reducing solution" means a solution having reducing properties, and may be, for example, a solution containing an electrophile. The reducing solution may be obtained, for example, by dissolving an electrophile and a Li source in a solvent. As the solvent, various organic solvents capable of dissolving the electrophile and the Li source may be adopted. As the solvent, for example, an ether-based solvent such as tetrahydrofuran or dimethoxyethane is preferable. As the electrophile, various substances that dissolve in the above-mentioned solvent may be adopted. The electrophile is preferably an aromatic organic compound such as biphenyl. The Li source may be any of various substances that dissolve in the above-mentioned solvent to generate Li ions. The Li source may be metallic lithium or a Li compound. The concentration of the electrophile and Li ions contained in the reduction solution may be appropriately determined according to the desired doping amount. In S3, for example, the Li-containing oxide can be doped with Li by simply contacting the Li-containing oxide with the above-mentioned reduction solution. The contact form between the reduction solution and the Li-containing oxide is not particularly limited. For example, the Li-containing transition metal oxide may be immersed in the reduction solution, or the reduction solution may be sprayed onto the Li-containing transition metal oxide. There is no particular limit to the temperature during contact, and the mixture may or may not be heated. The Li-containing oxide may be immersed in the reduction solution and then stirred. There is no particular limit to the time for which the Li-containing oxide is contacted with the reduction solution, and the time may be appropriately determined according to the desired doping amount.

[0032] 2.4 S4 In S4, for example, the Li-containing oxide doped with Li by the above S3 is exposed to an arbitrary dew point environment to precipitate lithium hydroxide on the surface of the Li-containing oxide. That is, a part of Li contained in the Li-containing oxide is reacted with moisture or the like to precipitate lithium hydroxide on the surface of the Li-containing oxide, thereby obtaining the above electrode active material 1. Here, the amount of lithium hydroxide precipitated on the surface of the Li-containing oxide can be adjusted by adjusting the dew point environment, exposure time, etc. In S4, the dew point environment, exposure time, etc. may be adjusted so that the electrode active material 1 obtained after exposure satisfies the above relationship (1).

[0033] 3. Electrode composite material The electrode mixture according to an embodiment includes the electrode active material 1 of the present disclosure. The components other than the electrode active material 1 contained in the electrode mixture are not particularly limited and can be appropriately determined according to the target performance. The electrode mixture according to an embodiment may include the electrode active material 1 of the present disclosure and at least one of an electrolyte, a conductive assistant, and a binder. The electrode mixture 5 according to an embodiment may optionally include other additives. The contents of the active material, electrolyte, conductive assistant, binder, and the like in the electrode mixture may be appropriately determined according to the target battery performance. For example, the content of the electrode active material may be 40% by mass or more and less than 100% by mass, with the entire solid content contained in the electrode mixture being 100% by mass.

[0034] 3.1 Active material The active material contained in the electrode mixture may consist only of the electrode active material 1 of the present disclosure, or may contain other active materials (other active materials) in addition to the electrode active material 1. From the viewpoint of further enhancing the effect of the technology of the present disclosure, the ratio of other active materials in the entire active materials contained in the electrode mixture may be small. For example, the content of the electrode active material 1 of the present disclosure 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 active materials contained in the electrode mixture being 100% by mass. Any other active materials known as active materials can be used as the other active materials that can be contained in the electrode mixture.

[0035] 3.2 Electrolytes The electrode mixture may contain an electrolyte together with the electrode active material 1. The electrolyte that may be contained in the electrode mixture may be a solid electrolyte, a liquid electrolyte, or a combination thereof. As the solid electrolyte, a known solid electrolyte for 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 the inorganic solid electrolyte include an oxide solid electrolyte, a sulfide solid electrolyte, and an ion-bonded inorganic solid electrolyte. In particular, when the electrode mixture 5 contains a sulfide solid electrolyte as a solid electrolyte, higher performance is likely to be ensured. The sulfide solid electrolyte may contain at least Li, S, and P as constituent elements, for example. Alternatively, the electrode mixture 5 may contain an ion-bonded solid electrolyte as a solid electrolyte, and may contain, for example, a solid electrolyte containing at least Li, Y, and a halogen (at least one of Cl, Br, I, and F) as constituent elements. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be particulate. The solid electrolyte may have an average particle diameter (D50) of, 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. The liquid electrolyte (electrolytic solution) is a liquid containing lithium ions as carrier ions. The electrolytic solution may be an aqueous electrolytic solution or a non-aqueous electrolytic solution. The composition of the electrolytic solution may be the same as that of the electrolytic solution of a lithium ion battery known in the art. The electrolytic solution may be a solution in which a lithium salt is 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 LiPF6.

[0036] 3.3 Conductive additives Examples of the conductive assistant that may be included in the electrode mixture 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 is not particularly limited. Only one type of conductive assistant may be used alone, or two or more types may be used in combination.

[0037] 3.4 Binder Examples of binders that can be included in the electrode mixture 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.

[0038] 3.5 Other The electrode mixture may contain various additives in addition to the above components, such as a dispersant and a lubricant.

[0039] 4.Battery The electrode active material 1 can be employed, for example, as a positive electrode active material of a battery. As shown in Fig. 3, a battery 100 according to one embodiment has 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 contains the electrode active material 1 of the present disclosure.

[0040] 4.1 Cathode active material layer The positive electrode active material layer 10 includes at least the electrode active material 1 of the present disclosure, and may further include an electrolyte, a conductive assistant, a binder, and the like. Furthermore, the positive electrode active material layer 10 may include various other additives. In other words, the positive electrode active material layer 10 may be composed of the above-mentioned electrode mixture. In particular, when the positive electrode active material layer 10 includes a liquid electrolyte (electrolytic solution), a higher effect can be expected. The shape of the positive electrode active material layer 10 is not particularly limited, and may be, for example, a sheet-like positive electrode active material layer 10 having a substantially flat surface. 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.

[0041] 4.2 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 a liquid electrolyte, and may further include a binder or the like. 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 liquid electrolyte 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.

[0042] 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 (electrode mixture) (solid electrolytes and / or liquid electrolytes). In particular, when the electrolyte layer 20 contains a liquid electrolyte (electrolytic solution), a higher effect can be expected. 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 electrolyte and the binder may be used alone or in combination of two or more kinds. The separator may be any separator that is commonly used in 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 structure 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.

[0043] 4.3 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.

[0044] The negative electrode active material may be any of those known as negative electrode active materials for batteries. Of the known active materials, various materials may be used that have a potential (charge / discharge potential) for absorbing and releasing carrier 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 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 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.

[0045] Examples of the electrolyte that may be contained in the negative electrode active material layer 30 include the above-mentioned solid electrolyte, liquid electrolyte, or a combination thereof. In particular, when the negative electrode active material layer 30 contains a liquid electrolyte (electrolytic solution), a higher effect can be expected. The conductive assistant that may be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, those exemplified as the conductive assistant that may be contained in the above-mentioned positive electrode active material layer 10 (electrode mixture 5). The binder that may be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, those exemplified as the binder that may be contained in the above-mentioned positive electrode active material layer 10 (electrode mixture 5). Each of the electrolyte, conductive assistant, and binder may be used alone or in combination of two or more kinds.

[0046] 4.4 Positive electrode current collector As shown in FIG. 3, the 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 a positive electrode current collector for a battery. 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.

[0047] 4.5 Negative electrode current collector As shown in FIG. 3, the 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 a negative electrode current collector for a battery. 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.

[0048] 4.6 Other configurations In addition to the above configuration, the battery 100 may have a general configuration for a battery. For example, a tab, a terminal, etc. The battery 100 may have each of the above configurations housed inside an exterior body. Any known exterior body for a battery can be used 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 battery 100 include a coin type, a laminate type, a cylindrical type, and a square type. The battery 100 may be a secondary battery.

[0049] The battery 100 can be manufactured by applying a known method, except for using the above-mentioned specific electrode active material 1. For example, it can be manufactured as follows. However, the manufacturing method of the battery 100 is not limited to the following method, and each layer may be formed by, for example, dry molding or the like. (1) The electrode active material 1 constituting the positive electrode active material layer is dispersed in a solvent to obtain a positive electrode layer slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The positive electrode layer slurry is applied to the surface of a positive electrode current collector using a doctor blade or the like, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector, forming a positive electrode. (2) The negative electrode active material constituting the negative electrode active material layer is dispersed in a solvent to obtain a negative electrode layer slurry. 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 using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector, thereby forming a negative electrode. (3) The layers are laminated so that the electrolyte layer (solid electrolyte layer or separator) is sandwiched between the negative electrode and the positive electrode to obtain a laminate having the negative electrode current collector, the negative electrode active material layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector in this order. Other members such as terminals are attached to the laminate as necessary. (4) The laminate is housed in a battery case, and in the case of an electrolyte battery, the battery case is filled with electrolyte, and the laminate is immersed in the electrolyte and sealed in the battery case to form a secondary battery. In the case of an electrolyte battery, the electrolyte may be impregnated in the negative electrode active material layer, the separator, and the positive electrode active material layer at the above step (3).

[0050] 5. Vehicles The battery of the present disclosure has excellent cycle characteristics due to the use of the electrode active material 1. Such a battery can be suitably used in at least one type of vehicle selected from, for example, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and an electric vehicle (BEV). That is, the technology of the present disclosure also has an aspect of a vehicle having a battery, the battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and the positive electrode active material layer contains the electrode active material 1 of the present disclosure. EXAMPLES

[0051] As described above, one embodiment of the electrode active material 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.

[0052] 1. Preparation of Electrode Active Material 1.1 Preparation of P2-type Na-containing oxide 1.1.1 Preparation of precursor (1) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed out to achieve the desired composition ratio (Mn:Ni:Co=5:2:3) and dissolved in distilled water to a concentration of 1.2 mol / L to obtain a first solution. In a separate container, Na2CO3 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 150 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. The fine particles were removed to obtain coarse particles as precursor particles.

[0053] 1.1.2 Preparation of the complex (1) Na2CO3 and distilled water were weighed out so that the total concentration was 1,150 g / L, and then the mixture was stirred using a stirrer until it was completely dissolved, thereby preparing an aqueous Na2CO3 solution. (2) The above-mentioned Na2CO3 aqueous solution and the above-mentioned precursor particles are mixed together to obtain a composition after calcination, which will be described later. 0.8 Mn 0.5 Ni 0.2 Co 0.3 The components were weighed and mixed to obtain a slurry of O2. (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 at a spray rate of 0.3 MPa and a flow rate of 100 / min, to coat the surfaces of the precursor particles with Na2CO3, thereby obtaining a composite.

[0054] 1.1.3 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 (7). (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 the main firing temperature 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.

[0055] 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).

[0056] 1.2 Ion exchange (1) LiNO3 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 intermediate particles A. Intermediate particles A are Li 0.6 Mn 0.5 Ni 0.2 Co 0.3 The intermediate particle A was a Li-containing oxide represented by O2. When the crystal phase contained in the intermediate particle A was confirmed by XRD, the intermediate particle A had an O2 type structure.

[0057] 1.3 Li doping (1) In a glove box (Ar atmosphere), biphenyl was mixed and dissolved in tetrahydrofuran (THF) to give a concentration of 1 mol / L to obtain a biphenyl solution. (2) Li foil was added to the biphenyl solution in the same mole as biphenyl, and the solution was stirred for 2 hours to obtain a reduced solution containing 1 mol / L Li ions. (3) The intermediate particles A were added to the obtained reduction solution, immersed, and stirred for 24 hours. The amount of intermediate particles A added was adjusted so that the ratio of the number of moles of dissolved Li ions to the number of moles of intermediate particles A (Li / O2) was 0.4. (4) After stirring, intermediate particles A were washed with THF and subjected to solid-liquid separation by vacuum filtration. The obtained precipitate was dried overnight at 120°C to obtain intermediate particles B. Intermediate particles B are Li 0.98 Mn 0.5 Ni 0.2 Co 0.3 The intermediate particles B were Li-containing oxides represented by O2. When the crystal phase contained in the intermediate particles B was confirmed by XRD, the intermediate particles B had an O2 type structure.

[0058] 1.4 Precipitation of lithium hydroxide (1) The obtained intermediate particles B were sealed in a screw bottle under an Ar environment and then carried out of the glove box. (2) An electrode active material for evaluation was obtained by exposing intermediate particles B to an arbitrary dew point environment and precipitating lithium hydroxide on the surface of intermediate particles B. By adjusting the dew point environment and exposure time, several types of electrode active materials with different amounts of lithium hydroxide precipitated were obtained. (3) Each of the obtained types of electrode active materials was again sealed in a screw bottle, and the bottle was transported to and stored in a glove box.

[0059] 2. Evaluation of the amount of lithium hydroxide precipitated in the electrode active material For each of the above-mentioned multiple types of electrode active materials, an O1s spectrum was obtained by X-ray photoelectron spectroscopy (XPS). The measurement conditions for XPS are as follows. In the XPS measurement, the measurement point of 527.5 eV was set as the starting point and the measurement point of 534 eV as the end point, and background processing was performed by the Shirley method. Measurement equipment: Scanning X-ray photoelectron spectrometer (u-XPS) Quantera II (manufactured by ULVAC PHI Inc.) X-ray source used: mono-AlKa ray (1486.6V) Photoelectron take-off angle: 35° X-ray beam diameter: approx. 100 μm Neutralization gun conditions: 1.0V, 20μA

[0060] For each of the acquired O1s spectra, waveform separation was performed by curve fitting (fitting based on the nonlinear least squares method), and the peaks at binding energies of 531.4 eV and 529.4 eV were separated, and the peak areas S1 and S2 were determined. The waveform separation was performed using the software "MultiPak" manufactured by ULVAC PHI.

[0061] 3. Coin Cell Fabrication A coin cell (CR2032) was prepared using each electrode active material. The procedure for preparing the coin cell is as follows. (1) The above electrode active material, acetylene black (AB) as a conductive assistant, and polyvinylidene fluoride (PVdF) as a binder were weighed out so that the mass ratio of electrode active material:AB:PVdF=85:10:5, and dispersed and mixed in N-methyl-2-pyrrolidone to obtain a positive electrode mixture slurry. The positive electrode mixture slurry was applied onto an aluminum foil and vacuum dried overnight at 120°C to obtain a positive electrode, which is a laminate of a positive electrode active material layer and a positive electrode current collector. (2) LiPF6 was dissolved at a concentration of 1 M in a mixed solvent of trifluoropropylene carbonate (TFPC) and trifluoroethyl methyl carbonate (TFEMC) in a ratio of TFPC:TFEMC = 30 vol%:70 vol% to obtain an electrolyte solution. (3) Metallic lithium foil was prepared as the negative electrode. (4) A coin cell (CR2032) was prepared using the positive electrode, electrolyte, and negative electrode.

[0062] 4. Evaluation of charge / discharge characteristics of coin cells Each coin cell was charged and discharged 30 times at a voltage range of 2.0 to 4.8 V and a rate of 0.1 C (1 C = 240 mA / g) in a thermostatic chamber maintained at 25°C, and the ratio of the discharge capacity after 30 cycles to the initial discharge capacity (capacity retention rate (%)) was calculated.

[0063] 5. Evaluation Results Table 1 below shows the area S1 of the peak at 531.4 eV derived from lithium hydroxide, the area S2 of the peak at 529.4 eV derived from O2-type Li-containing oxide, and the ratio of S1 to the sum of S1 and S2 (S1 / (S1+S2)) of the O1s spectrum obtained by XPS for each electrode active material. Table 1 also shows the initial discharge capacity, discharge capacity after 30 cycles, and capacity retention rate of each coin cell.

[0064] [Table 1]

[0065] Fig. 4 shows the XPS-O1s spectrum of each of the electrode active materials according to Examples 2 and 4 and Comparative Examples 1 and 3. Fig. 5 shows the relationship between S1 / (S1+S2) and the capacity retention rate.

[0066] From the results shown in Table 1, Figures 4 and 5, it can be seen that the capacity retention rate of the battery is high when S1 / (S1+S2) in the XPS-O1s spectrum of the electrode active material is 0.20 or more and 0.73 or less. In particular, the capacity retention rate is significantly improved when S1 / (S1+S2) is 0.39 or more and 0.68 or less. This is thought to be because an appropriate amount of lithium hydroxide is precipitated on the surface of the electrode active material, preventing contact between the active material and the electrolyte in the high potential region during charging, and suppressing decomposition of the electrolyte. On the other hand, when S1 / (S1+S2) exceeds 0.70, the capacity retention rate of the battery is reduced. This is thought to be because excessive lithium hydroxide is precipitated on the surface of the electrode active material, locally inhibiting Li conduction between the active material and the electrolyte, and the active material in the active material-electrolyte where Li conduction is not inhibited is overworked.

[0067] In addition, the electrolyte (LiPF6) commonly used in liquid batteries generates hydrogen fluoride due to trace amounts of moisture in the battery. It is believed that the lithium hydroxide precipitated on the surface of the electrode active material reacts with hydrogen fluoride in the battery to become lithium fluoride. That is, in the coin cell, it is believed that a lithium fluoride layer is formed on the surface of the electrode active material, which is believed to further improve the potential stability.

[0068] 6. Summary From the above results, it can be said that the cycle characteristics of a battery can be improved by constructing a battery using an electrode active material that satisfies the following (1) and (2).

[0069] (1) The electrode active material contains an O2-type Li-containing oxide and lithium hydroxide. (2) The O1s spectrum of the electrode active material obtained by XPS satisfies the following relationship (1). 0.20≦S1 / (S1+S2)≦0.73 (1) S1: Area of ​​the peak due to lithium hydroxide at 531.4 eV S2: Area of ​​the peak at 529.4 eV originating from O2-type Li-containing oxide [Explanation of symbols]

[0070] 1 Electrode active material 1a O2 type Li-containing oxide 1b Lithium hydroxide 100 batteries 10 Cathode active material layer 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector

Claims

1. An electrode active material, O2 type Li-containing oxide; Lithium hydroxide, Including, The O1s spectrum of the electrode active material obtained by XPS has the following relationship (1): 0.20≦S1 / (S1+S2)≦0.73...(1) S1: Peak area due to lithium hydroxide at 531.4 eV S2: Peak area at 529.4 eV due to O2-type Li-containing oxide Fulfilling Electrode active material.

2. The electrode active material according to claim 1 , The O1s spectrum satisfies the following relationship (1A): 0.39≦S1 / (S1+S2)≦0.68 (1A) Fulfilling Electrode active material.

3. The electrode active material according to claim 1 or 2 is included. Electrode composite material.

4. A battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer comprises the electrode active material according to claim 1 or 2. battery.

Images