Composite cathode active material

Abstract

The present disclosure is a composite positive electrode active material. A composite positive electrode active material capable of reducing the rate of increase in resistance accompanying charging and discharging of a battery is provided. The composite positive electrode active material includes a positive electrode active material, a compound A including La, Ni, and O, and a compound B including Li, W, and O, the positive electrode active material is a crystalline primary particle containing Li, a transition metal, and O, the positive electrode active material is a single crystal system active material composed of the primary particle, the compound B is present in a film shape on at least a part of the surface of the primary particle, and the compound A is independently present as an isolated particle.

Description

Technical Field

[0001] This disclosure relates to composite positive electrode active materials. Background Technology

[0002] Various technologies have been proposed for positive electrode active materials as disclosed in Patent Documents 1-2.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2022-542774

[0006] Patent Document 2: Japanese Patent Publication No. 2024-511223 Summary of the Invention

[0007] In the past, various positive electrode active materials have been proposed in order to obtain positive electrodes with high battery characteristics such as high cycle performance and high output performance.

[0008] In conventional positive electrode active materials, there is room for improvement regarding the rate of increase in resistance that occurs during battery charging and discharging.

[0009] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide a composite positive electrode active material capable of reducing the rate of increase in resistance that occurs during the charging and discharging of a battery.

[0010] That is, the following schemes are included in this disclosure.

[0011] <1> A composite positive electrode active material,

[0012] The composite positive electrode active material comprises a positive electrode active material, compound A, and compound B. Compound A comprises La, Ni, and O, and compound B comprises Li, W, and O.

[0013] The positive electrode active material is a crystalline primary particle containing Li, transition metals, and O.

[0014] The positive electrode active material is a single-crystal active material composed of the primary particles.

[0015] Compound B exists in a film-like form on at least a portion of the surface of the primary particles.

[0016] Compound A exists independently as an isolated particle.

[0017] <2> Based on the composite positive electrode active material described in <1>,

[0018] The composite positive electrode active material contains La, which is more than 0.005 mol and less than 2.000 mol per mol of Ni, Co and Mn contained in the positive electrode active material.

[0019] <3> Based on the composite positive electrode active material described in <1> or <2>,

[0020] The composite positive electrode active material contains W in an amount of more than 0.010 mol and less than 1.000 mol per mol of the total amount of Ni, Co and Mn contained in the positive electrode active material.

[0021] <4> The composite positive electrode active material according to any one of <1> to <3>,

[0022] The primary particles of the positive electrode active material have a particle size of 0.5 μm or more.

[0023] <5> The composite positive electrode active material according to any one of <1> to <4>,

[0024] The average particle size of the isolated particles of compound A is greater than 0.1 μm and less than 20 μm.

[0025] <6> The composite positive electrode active material according to any one of <1> to <5>,

[0026] Compound A is La4LiNiO8.

[0027] <7> The composite positive electrode active material according to any one of <1> to <6>,

[0028] The compound B is at least one of Li2WO4 and Li6WO6.

[0029] <8> A positive electrode layer comprising the composite positive electrode active material described in any one of <1> to <7>.

[0030] <9> A battery comprising a positive electrode layer comprising the composite positive electrode active material described in any one of <1> to <7>.

[0031] <10> A method for manufacturing a composite positive electrode active material, comprising the method for manufacturing the composite positive electrode active material described in any one of <1> to <7>, and having the following characteristics:

[0032] The first firing process involves firing a first mixture of a transition metal hydroxide and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material, wherein the transition metal hydroxide is a precursor of the positive electrode active material.

[0033] The second firing process involves firing the positive electrode active material and the second mixture of W source at 500°C to 700°C to obtain a fired body. The W source is a raw material for compound B. The fired body comprises the positive electrode active material and compound B, and at least a portion of compound B exists in a film-like form on the surface of the primary particles of the positive electrode active material.

[0034] The third firing process involves firing the fired body and the third mixture of the La source at 800°C to 1100°C to obtain the composite positive electrode active material, wherein the La source is the raw material of compound A.

[0035] According to this disclosure, a composite positive electrode active material is provided that can reduce the rate of increase in resistance that occurs during the charging and discharging of a battery. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating a structural example of the composite positive electrode active material disclosed herein.

[0037] [Explanation of reference numerals in the attached figures]

[0038] 10… Primary particles of the positive electrode active material

[0039] 20…Compound B

[0040] 30…Compound A

[0041] 100… Composite positive electrode active material Detailed Implementation

[0042] The embodiments of this disclosure will be described below. Furthermore, matters necessary for implementing this disclosure other than those specifically mentioned in this specification (e.g., the general composition and manufacturing process of the composite positive electrode active material not characterized by this disclosure) can be grasped as design matters by those skilled in the art. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

[0043] In addition, the dimensional relationships (length, width, thickness, etc.) in the diagram do not reflect the actual dimensional relationships.

[0044] Elements described in the "singular form" may also include plural forms unless otherwise specified. For example, "particle" may sometimes represent multiple particles (a swarm of particles).

[0045] In this disclosure, an example of a method for calculating the average particle size is described below. First, for a single particle, the particle size is calculated as if the particle were considered spherical, based on a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image at an appropriate magnification (e.g., 50,000 to 1,000,000 times). For 2 to 300 particles of the same type, the particle size is calculated based on such TEM or SEM observations, and the average value of these particles is taken as the average particle size.

[0046] 1. Composite positive electrode active material

[0047] This disclosure provides a composite positive electrode active material, which comprises a positive electrode active material, compound A, and compound B, wherein compound A comprises La, Ni, and O, and compound B comprises Li, W, and O.

[0048] The positive electrode active material is a crystalline primary particle containing Li, transition metals, and O.

[0049] The positive electrode active material is a single-crystal active material composed of the primary particles.

[0050] Compound B exists in a film-like form on at least a portion of the surface of the primary particles.

[0051] Compound A exists independently as an isolated particle.

[0052] In conventional sintered bodies containing positive electrode active materials such as Li, Ni, Co, and Mn, structural changes occur during sintering accompanied by oxygen desorption from Ni. This, along with rock saltation in the single crystal grains formed during sintering, increases the reaction resistance when used in batteries. If the particle size of the single crystal particles decreases, the contact area with the conductive material contained in the positive electrode layer decreases, resulting in reduced electronic conductivity.

[0053] To improve electronic conductivity, compound A, containing La and exhibiting excellent electronic conductivity, can be added to the positive electrode active material. To reduce reaction resistance, compound B, containing W and exhibiting excellent Li conductivity, can be added to the positive electrode active material. However, if the La and W sources are mixed with transition metal hydroxides used as precursors for the positive electrode active material and then calcined, a layer containing both La and W compounds (compound A and compound B) will form on the surface of the resulting positive electrode active material, making it difficult to achieve the desired effects of improving Li conductivity and electronic conductivity.

[0054] In this disclosure, a positive electrode active material is generated, and then a mixture of the positive electrode active material and a W source is calcined at a medium temperature of 500°C to 700°C, causing a W-containing compound B to adhere to the surface of the primary particles of the positive electrode active material. A La source is then added, and the mixture is calcined at a high temperature of 800°C to 1000°C to obtain the composite positive electrode active material of this disclosure. According to this disclosure, a composite positive electrode active material with an excellent balance between the improved Li conductivity effect of the W-containing compound B and the improved electronic conductivity effect of the La-containing compound A can be produced.

[0055] Figure 1 This is a schematic diagram illustrating an example of the structure of the composite positive electrode active material of this disclosure. For example... Figure 1 As shown, the composite positive electrode active material 100 of this disclosure has a film-like coating of compound B20 on the surface of the primary particles 10 of the plurality of positive electrode active materials, and compound A30 exists independently as an isolated particle on the surface of compound B20.

[0056] The composite positive electrode active material includes a positive electrode active material, compound A, and compound B.

[0057] The composite positive electrode active material is used in batteries. Details about the battery will be described later.

[0058] Composite positive electrode active materials can be particles. The particles of composite positive electrode active materials can be secondary particles.

[0059] The average particle size of the composite positive electrode active material can be, for example, 0.5 μm or more. The average particle size of the composite positive electrode active material can be, for example, 30 μm or less.

[0060] The positive electrode active material is a lithium transition metal composite oxide containing Li, a transition metal (TM), and O. This lithium transition metal composite oxide can contain one, two, three, or more transition metals. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, and Nb.

[0061] Lithium transition metal composite oxides may contain at least Ni as a transition metal, and may further contain, for example, Co and Mn as transition metals.

[0062] Lithium transition metal composite oxides can also contain metals other than Li and transition metals, such as M. 1 (Including semi-metals). As other metals M 1 Examples include Al, Si, Ga, Ge, In, and Sn.

[0063] Lithium transition metal composite oxides can be composite oxides containing Li, Ni, Co, Mn and O, or composite oxides containing Li, Ni, Co, Al and O.

[0064] Compared to the total of 1 mol of all metals other than Li contained in the lithium transition metal composite oxide, the total proportion of Ni, Co, and Mn contained in the lithium transition metal composite oxide is, for example, 0.80 mol or more, 0.90 mol or more, or 0.95 mol or more. Furthermore, "total of Ni, Co, and Mn" also includes the case where the proportion of one or two of Ni, Co, and Mn is 0.

[0065] Lithium transition metal composite oxides can possess the properties of the general formula Li x Ni a Co b Mn c O y The composition represented by (0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 1.5≤y≤2.1).

[0066] In the general formula, the Li composition ratio "x" only needs to satisfy the relationship "0.1≤x≤1.5". For example, the Li composition ratio "x" can be 0.4 or higher, 0.6 or higher, 0.8 or higher, 1.0 or higher, or 1.05 or higher. For example, the Li composition ratio "x" can be 1.4 or lower, or 1.2 or lower.

[0067] In the above general formula, the ratio "y" of component O only needs to satisfy the relationship "1.5≤y≤2.1". For example, the ratio "y" of component O can be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher. For example, the ratio "y" of component O can be 2.0 or lower.

[0068] In the above general formula, the Ni composition ratio "a", the Co composition ratio "b", and the Mn composition ratio "c" satisfy the relationship "a+b+c=1.0".

[0069] In the above general formula, the Ni composition ratio "a" only needs to satisfy the relationship "0.5≤a≤1.0". For example, the Ni composition ratio "a" can be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher. For example, the Ni composition ratio "a" can be 0.9 or lower.

[0070] In the above general formula, the Co composition ratio "b" only needs to satisfy the relationship "0 ≤ b ≤ 0.3". For example, the Co composition ratio "b" can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. For example, the Co composition ratio "b" can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0071] In the above general formula, the composition ratio "c" of Mn only needs to satisfy the relationship "0 ≤ c ≤ 0.3". For example, the composition ratio "c" of Mn can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. For example, the composition ratio "c" of Mn can be less than 0.25, less than 0.20, less than 0.15, less than 0.10, less than 0.09, or less than 0.08.

[0072] Any dopant can be added to the lithium transition metal composite oxide. Dopant refers to an element other than Li, Ni, Co, Mn, and O. For example, the dopant may contain at least one element selected from Zr, Mo, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, and Ag. The composition ratio of the dopant may be, for example, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. Alternatively, the composition ratio of the dopant may be, for example, less than 0.05, less than 0.04, less than 0.03, less than 0.02, or less than 0.01.

[0073] The positive electrode active material is a crystalline primary particle.

[0074] The positive electrode active material is a single-crystal active material composed of the aforementioned primary particles. A single-crystal active material is not a polycrystalline active material (an active material in which multiple primary particles are aggregated without gaps). That is, a single-crystal active material can be a single crystal particle. Compared with polycrystalline active materials, single-crystal active materials have the advantage of less degradation over time.

[0075] In SEM images, single-crystal active materials appear as unaggregated, independent, single particles (primary particles). Single-crystal active materials do not exhibit grain boundaries in SEM images. The magnification of SEM images can range from, for example, 10,000x to 30,000x.

[0076] The crystal structure of the positive electrode active material can be a layered rock salt structure. Alternatively, the positive electrode active material can have a crystal structure belonging to space group R-3m.

[0077] The particle size of the primary particles in the positive electrode active material can be 0.5 μm or larger, 0.6 μm or larger, 0.8 μm or larger, or 1.0 μm or larger. If the particle size of the primary particles is too small, the particles may not grow sufficiently and it may be difficult to fabricate them as single crystals. On the other hand, the particle size of the primary particles can be, for example, 10 μm or smaller, or 5 μm or smaller. The particle size of the primary particles can be determined, for example, by using the longest diameter in TEM or SEM images. Furthermore, for example, when the positive electrode layer contains primary particles (positive electrode active material), the particle size of the primary particles can be determined from the longest diameter of the primary particles in the SEM cross-sectional image of the positive electrode layer.

[0078] The "particle size of primary particles" mentioned here is not the average particle size. That is, when the positive electrode active material contains multiple primary particles, the "particle size of primary particles" refers to the "particle size of each individual primary particle".

[0079] The primary particles of lithium transition metal composite oxides used as positive electrode active materials do not contain La and W, or may contain a total of less than 0.005 mol of La and W.

[0080] Compound A contains La, Ni, and O. Compound A may consist solely of La, Ni, and O, or it may contain other elements. For example, Li could be considered as another element. That is, compound A may or may not contain Li. As an example of the composition of compound A, La could be included. a Ni b O c (0.8≤a≤1.2, 0.8≤b≤1.2, 2.8≤c≤3.2). For example, LaNiO3 is a typical perovskite composition with good electronic conductivity. Other examples of the composition of compound A include La. a Li b Ni c O d (3.5≤a≤4.5, 0.5≤b≤1.5, 0.5≤c≤0.8, 7.5≤d≤8.5).

[0081] Compound A could be La4LiNiO8, etc. La4LiNiO8 is known to have good electronic conductivity and is envisioned to have a crystalline phase similar to that of perovskite.

[0082] Compound A can have a perovskite-type crystalline phase or a crystalline phase similar to perovskite. Compound A can have at least one of LaNiO3 and La4LiNiO8 as the crystalline phase. This is because it provides good electronic conductivity. Furthermore, the aforementioned crystalline phases can contain crystalline phases that lack a portion of the constituent atoms (e.g., a portion of O atoms) or crystalline phases that have a portion of the constituent atoms (e.g., a portion of La atoms).

[0083] Compound A exists independently as an isolated particle. Compound A can exist on the surface of compound B.

[0084] In SEM images, isolated particles appear to be independent particles. These isolated particles can be primary or secondary particles. Regarding compound A, in a cross-sectional image of compound A, if the length of compound A in the direction normal to the surface of compound A is denoted as L1, and the length of compound A in the direction perpendicular to the normal direction is denoted as L2, then the ratio of L2 to L1 (L2 / L1) can be 3.0 or less. A cross-sectional image of compound A is, for example, an SEM cross-sectional image.

[0085] The average particle size of isolated particles of compound A can be greater than 0.1 μm and less than 20 μm.

[0086] For example, the proportion of La in compound A of the composite positive electrode active material can be between 0.005 mol and 2.000 mol, relative to the total amount of Ni, Co, and Mn in the positive electrode active material per 1 mol. Similarly, the proportion of La in compound A of the composite positive electrode active material can be between 0.005 mol and 2.000 mol, relative to the total amount of Ni, Co, and Mn in the positive electrode active material per 1 mol. If the amount of La in the composite positive electrode active material is too low, the electron conductivity will not be improved; if the amount of La in the composite positive electrode active material is too high, it will hinder Li conduction.

[0087] The volume proportion of compound A, which is an isolated particle contained in the composite positive electrode active material, can be 0.005 vol% to 75 vol%.

[0088] Compound B contains Li, W, and O. Compound B may consist solely of Li, W, and O, or it may contain other elements. As an example of the composition of compound B, Li can be included. a W b O c (5.5≤a≤6.5, 0.5≤b≤1.5, 5.5≤c≤6.5). Compound B having the above composition is typically Li6WO6. Other examples of the composition of compound B include Li... a Wb O c (1.5≤a≤2.5, 0.5≤b≤1.5, 3.5≤c≤4.5). Compound B with the above composition is typically Li2WO4.

[0089] Compound B can be at least one of Li2WO4 and Li6WO6.

[0090] Compound B may exist as a film on at least a portion of the surface of the primary particles of the positive electrode active material, or it may exist as a film on the entire surface of the primary particles of the positive electrode active material. Regarding the film-like compound B, in a cross-sectional image of the composite positive electrode active material, if the length of compound B in the direction normal to the surface of the composite positive electrode active material is denoted as L3, and the length of compound B in the direction perpendicular to the normal direction is denoted as L4, the ratio of L4 to L3 (L4 / L3) may be greater than 3.0. A cross-sectional image of the composite positive electrode active material may be, for example, a TEM cross-sectional image.

[0091] That is, the composite positive electrode active material may have a coating composed of compound B on at least a portion of the surface of the primary particles of the positive electrode active material. This coating may cover more than 50% of the surface area of ​​the primary particles of the positive electrode active material, or it may cover the entire surface of the primary particles of the positive electrode active material. The coverage rate achieved by the coating composed of compound B can be determined, for example, by TEM observation.

[0092] The coating composed of compound B can be confirmed, for example, by compositional analysis (elemental analysis) of TEM images obtained through TEM observation using energy dispersive X-ray spectroscopy (EDX). Compositional analysis can be performed using known methods, such as SEM-EDX and X-ray photoelectron spectroscopy (XPS), in addition to TEM-EDX.

[0093] The thickness of the coating composed of compound B is not particularly limited, for example, it can be 0.5 nm or more and 20 nm or less, or it can be 1 nm or more and 15 nm or less. Here, the thickness of the coating composed of compound B is calculated as the average value obtained by measuring the thickness at at least 5 locations in the observation of primary particles of the positive electrode active material using TEM.

[0094] Compound B can be either crystalline or amorphous. "Crystalline" means that X-ray diffraction using CuKα rays confirms a peak originating from the target compound. Conversely, "amorphous" means that X-ray diffraction using CuKα rays does not confirm a peak originating from the target compound. Furthermore, in the case of an amorphous compound, there are instances where no peak is observed but a halo pattern is observed.

[0095] For example, the proportion of W in compound B of the composite positive electrode active material can be 0.010 mol or more and 1.000 mol or less, relative to the total amount of metals other than Li contained in 1 mol of the positive electrode active material. Furthermore, for example, the proportion of W in compound B of the composite positive electrode active material can be 0.010 mol or more and 1.000 mol or less, relative to the total amount of Ni, Co, and Mn contained in 1 mol of the positive electrode active material.

[0096] If the amount of W in the composite positive electrode active material is too small, the conductivity of Li will not be improved; if the amount of W in the composite positive electrode active material is too large, it will hinder electron conduction.

[0097] The volume proportion of film-like compound B contained in the composite positive electrode active material can be 0.010 vol% to 50 vol%.

[0098] 2. Method for manufacturing composite positive electrode active material

[0099] This disclosure provides a method for manufacturing a composite positive electrode active material, which is a method for manufacturing the aforementioned composite positive electrode active material, comprising:

[0100] The first firing process involves firing a first mixture of a transition metal hydroxide and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material, wherein the transition metal hydroxide is a precursor of the positive electrode active material.

[0101] The second firing process involves firing the positive electrode active material and the second mixture of W source at 500°C to 700°C to obtain a fired body. The W source is a raw material for compound B. The fired body comprises the positive electrode active material and compound B, and at least a portion of compound B exists in a film-like form on the surface of the primary particles of the positive electrode active material.

[0102] The third firing process involves firing the fired body and the third mixture of the La source at 800°C to 1100°C to obtain the composite positive electrode active material, wherein the La source is the raw material of compound A.

[0103] The method for manufacturing the composite positive electrode active material disclosed herein includes (1) a first firing step, (2) a second firing step and (3) a third firing step.

[0104] (1) First firing process

[0105] The first firing process involves firing a first mixture of a transition metal hydroxide and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material, wherein the transition metal hydroxide is a precursor of the positive electrode active material.

[0106] The method for manufacturing the precursor of the positive electrode active material disclosed herein is not particularly limited, and the following methods can be cited as examples. First, an aqueous solution of a transition metal hydroxide is prepared. For example, a method for preparing the aqueous solution can be used to dissolve a water-soluble transition metal compound in water. For example, metal salts such as sulfates and nitrates can be used as transition metal compounds. For example, NiSO4 and Ni(NO3)2 can be used as Ni sources. For example, CoSO4, Co(NO3)2, and Co(NO3)3 can be used as Co sources. For example, MnSO4 and Mn(NO3)2 can be used as Mn sources. The composition of the aqueous solution is appropriately adjusted according to the target positive electrode active material.

[0107] Next, a certain amount of NH3 aqueous solution is added to the reaction vessel, and while stirring with a stirrer or similar device, nitrogen is used to purge the atmosphere and create a non-oxidizing atmosphere. The nitrogen flow rate for purging is not particularly limited; for example, it can be set to 2–6 L / min.

[0108] Next, an aqueous sodium hydroxide solution is added to the reaction vessel to maintain an alkaline pH (e.g., pH 11.3–12.0), and the above-mentioned raw material aqueous solution and NH3 aqueous solution are added dropwise to the reaction vessel over 5–15 hours. The reaction temperature is not particularly limited; for example, it can be set above 50°C and below 65°C.

[0109] After the reaction is complete, pre-firing is carried out. Pre-firing can be carried out, for example, at 120°C to 220°C, for 4 to 10 hours, and at 0.2 to 1.0 MPa.

[0110] After pre-firing, the mixture is washed with water, then filtered to remove the transition metal hydroxide, and then dried. The drying process can be carried out, for example, at 110°C for 10–12 hours.

[0111] In this disclosure, the transition metal hydroxide contains a transition metal. The transition metal hydroxide can be a nickel-cobalt-manganese composite hydroxide containing nickel (Ni), cobalt (Co), and manganese (Mn). In the nickel-cobalt-manganese composite hydroxide, the molar ratio of each metal relative to the total stoichiometry of nickel, cobalt, and manganese is the same as the composition ratio expressed by the above general formula in the positive electrode active material.

[0112] Examples of lithium compounds (Li sources) include at least one selected from lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, and lithium chloride. The lithium compound may be lithium hydroxide. The molar ratio of Li in the Li source to the amount of TM contained in the transition metal hydroxide may be, for example, 0.4 or more, 0.6 or more, 0.8 or more, 1.0 or more, or 1.05 or more, or 1.4 or less, or 1.2 or less.

[0113] Regarding the ratio of lithium compounds and precursors in the mixture, typically, the molar ratio (of lithium and other metals in the target positive electrode active material) relative to the total stoichiometry of lithium and the metals contained in the precursor is equal to the molar ratio (of lithium and other metals) in the first mixture. The mixing method is not particularly limited, and known methods can be used.

[0114] The first mixture may contain a molten salt. The molten salt acts as a flux, enabling sufficient particle growth of the primary particles. The molten salt may contain Li. Examples of molten salts include lithium hydroxide. The molar ratio (Li / TM) of Li in the molten salt relative to the amount of TM contained in the transition metal hydroxide is, for example, 0.01 or more, 0.05 or more, 0.10 or more, or 0.15 or more. On the other hand, the Li / TM ratio is, for example, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

[0115] The first mixture may contain lithium hydroxide as a Li source and a molten salt. The total molar ratio of Li contained in the Li source and the molten salt to the TM contained in the transition metal hydroxide (Li´ / TM) is, for example, 1.01 or more, 1.05 or more, 1.10 or more, or 1.15 or more. On the other hand, Li´ / TM is, for example, 1.60 or less, 1.50 or less, 1.40 or less, or 1.30 or less.

[0116] A positive electrode active material, which is a lithium transition metal composite oxide, can be obtained by calcining the first mixture at, for example, 800°C to 1000°C for 8 to 15 hours. A known calcining furnace, such as a muffle furnace, can be used during the calcination process.

[0117] The firing temperature in the first firing process can be above 850℃, above 900℃, or above 950℃.

[0118] The firing time in the first firing process can be more than 9 hours or more than 10 hours.

[0119] The firing time in the first firing process can be less than 13 hours or less than 11 hours.

[0120] The positive electrode active material obtained by sintering the precursor of this disclosure is usually a single-crystal active material composed of primary particles.

[0121] (2) Second firing process

[0122] The second firing process involves firing the positive electrode active material and the second mixture of W source at 500°C to 700°C to obtain a fired body containing the positive electrode active material and the compound B. The W source is the raw material of the compound B, and at least a portion of the compound B exists in a film-like form on the surface of the primary particles of the positive electrode active material.

[0123] Examples of raw materials (W source) for compound B include H2WO4. The amount of W source added is adjusted appropriately based on the target composite positive electrode active material.

[0124] In the second firing process, by firing the second mixture at 500°C to 700°C, the isolated particle formation of compound B can be suppressed, and compound B can preferentially form as a film on the surface of the primary particles of the positive electrode active material compared with compound A.

[0125] The firing temperature in the second firing process can be above 550℃, above 600℃, or above 650℃.

[0126] The firing time in the second firing stage can be more than 1 hour, more than 9 hours, or more than 10 hours. On the other hand, the firing time in the second firing stage can be less than 15 hours, less than 13 hours, or less than 11 hours.

[0127] (3) The third firing process

[0128] The third firing process involves firing the sintered body and the third mixture of La source at 800°C to 1100°C to obtain the composite positive electrode active material, wherein the La source is the raw material of compound A.

[0129] Examples of raw materials (La sources) for compound A include La(OH)3, LaSO4, and La(NO3)3. The amount of La source added is adjusted appropriately based on the target composite positive electrode active material.

[0130] In the third firing process, by firing the third mixture at 800℃~1100℃, the isolated particle formation of compound A can be promoted.

[0131] The firing temperature in the third firing process can be above 850℃, above 900℃, above 950℃, above 1000℃, or above 1050℃.

[0132] The firing time in the third firing stage can be more than 1 hour, more than 9 hours, or more than 10 hours. On the other hand, the firing time in the third firing stage can be less than 15 hours, less than 13 hours, or less than 11 hours.

[0133] 3. Battery

[0134] The composite positive electrode active material provided by this disclosure can be used, for example, as a positive electrode active material constituting the positive electrode of a battery (such as a lithium-ion battery). That is, this disclosure can provide a battery in which a positive electrode, an electrolyte layer, and a negative electrode are stacked in sequence, and the positive electrode contains the composite positive electrode active material of this disclosure.

[0135] According to this disclosure, by using the above-mentioned composite positive electrode active material in a battery, the rate of increase in resistance that occurs during the charging and discharging of the battery can be reduced.

[0136] The following is an explanation of the battery.

[0137] [positive electrode]

[0138] The positive electrode has a positive electrode layer, and may further have a positive electrode current collector if needed.

[0139] The positive electrode layer is a layer that contains at least the composite positive electrode active material disclosed herein as the positive electrode active material.

[0140] The positive electrode layer can be disposed on one or both surfaces of the positive electrode current collector. The positive electrode can have two or more positive electrode layers formed on at least one surface of the positive electrode current collector, thus creating a multilayer structure. Furthermore, when two or more positive electrode layers are formed, the types of positive electrode active materials contained in each positive electrode layer can be the same or different.

[0141] The positive electrode active material used in the positive electrode layer may contain only the composite positive electrode active material disclosed herein, or it may further contain other active materials. Additionally, the positive electrode layer may, as needed, contain at least one of an electrolyte, a conductive material, and a binder.

[0142] The mixing ratio (mass ratio) of the composite positive electrode active material with other active materials can be, for example, "composite positive electrode active material / other active material = 9.5 / 0.5~0.5 / 9.5", "composite positive electrode active material / other active material = 9 / 1~1 / 9", "composite positive electrode active material / other active material = 8 / 2~2 / 8", "composite positive electrode active material / other active material = 7 / 3~3 / 7", or "composite positive electrode active material / other active material = 6 / 4~4 / 6". Other active materials can be polycrystalline active materials (polycrystalline particles) composed of secondary particles of the aforementioned lithium transition metal composite oxides. Additionally, other active materials can be, for example, lithium iron phosphate (olivine structure), lithium manganese phosphate (olivine structure), lithium manganese iron phosphate (olivine structure), LiMnO2 (rock salt structure), Li(NiMn)2O4 (spinel structure), and LiCoO2 (layered structure), etc.

[0143] The proportion of positive electrode active material in the positive electrode layer is, for example, 20% by mass or more, 30% by mass or more, or 40% by mass or more. If the proportion of positive electrode active material is too low, there is a possibility that sufficient energy density cannot be obtained. On the other hand, the proportion of positive electrode active material in the positive electrode layer is, for example, 95% by mass or less, 70% by mass or less, or 60% by mass or less. If the proportion of positive electrode active material is too high, there is a possibility that the ionic conductivity and electronic conductivity in the positive electrode layer will be relatively reduced.

[0144] As an electrolyte, examples include solid electrolytes. Solid electrolytes can be inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complex hydride solid electrolytes, or organic solid electrolytes such as gel electrolytes.

[0145] Sulfide solid electrolytes are electrolytes containing sulfur (S). They typically contain at least lithium (Li) and sulfur (S). Sulfide solid electrolytes may also further contain nitrogen (M) (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). Additionally, sulfide solid electrolytes may also contain halogens such as sulfur (F), chlorine (Cl), br, and iron (I).

[0146] Sulfide solid electrolytes can be glass-based (amorphous), glass-ceramic, or crystalline. They can also possess a crystalline phase. Examples of such crystalline phases include the Thio-LISICON type, the argyrocerium sulfide type, and the LGPS type.

[0147] The composition of sulfide solid electrolytes is not particularly limited; examples include xLi₂S・(1-x)P₂S₅ (0.5 ≤ x < 1) and yLiI・zLiBr・(100-yz)(xLi₂S・(1-x)P₂S₅) (0.5 ≤ x < 1, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30). In these compositions, x can also satisfy 0.7 ≤ x ≤ 0.8. Other examples of sulfide solid electrolyte compositions include Li 7-x PS 6-x X x X is at least one of F, Cl, Br, and I, and x satisfies 0 ≤ x < 2. Other examples of sulfide solid electrolytes include Li. 4-x Me 1-x P x S4 (0 < x < 1). Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi. Examples of sulfide solid electrolytes include LiI-LiBr-Li2S-P2S5, LiI-Li2S-P2S5, LiI-Li2S-P2O5, and LiI-Li3PO4-P2S5.

[0148] Examples of oxide solid electrolytes include substances having the elements Li, La, A (where A is at least one of Zr, Nb, Ta, and Al), and O, and possessing a garnet-type crystal structure. Examples of oxide solid electrolytes include Li₂O-B₂O₃-P₂O₅, Li₂O-SiO₂, Li₂O-B₂O₃, and Li₂O-B₂O₃. 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4 and Li 3+x PO 4-x N x (1≤x≤3), etc.

[0149] As a halide solid electrolyte, it can be, for example, a solid electrolyte containing Li, D, and X (D represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br).

[0150] Gel electrolytes may comprise an electrolyte and a polymeric material. The polymeric material may form a polymeric matrix. The polymeric material may, for example, comprise at least one selected from polyvinylidene fluoride (PVdF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polyacrylonitrile (PAN), PVdF-PAN, polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives thereof.

[0151] From a practical standpoint, solid electrolytes can be in the form of particles.

[0152] In addition, the average particle size of the solid electrolyte is not particularly limited and can be from 1 nm to 100 μm.

[0153] The proportion of solid electrolyte in the positive electrode layer can be, for example, 1% by mass or more. If the proportion of solid electrolyte is too low, there is a possibility that the ion conduction pathway in the positive electrode layer is insufficient. On the other hand, the proportion of solid electrolyte in the positive electrode layer can be, for example, 60% by mass or less. If the proportion of solid electrolyte is too high, there is a possibility that the proportion of positive electrode active material will be relatively low and the energy density will be low.

[0154] The positive electrode layer can contain conductive materials. By adding conductive materials, the electronic conductivity of the positive electrode layer is improved. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include particulate materials such as acetylene black (AB) and Ketjen black (KB), and fibrous materials such as vapor-phase carbon fiber (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0155] The proportion of conductive material in the positive electrode layer can be, for example, 0.1% by mass or more. If the proportion of conductive material is too low, there is a possibility that the electron conduction pathway in the positive electrode layer is insufficient. On the other hand, the proportion of conductive material in the positive electrode layer can be, for example, 5% by mass or less. If the proportion of conductive material is too high, there is a possibility that the proportion of positive electrode active material will be relatively low, and the energy density will be low.

[0156] The positive electrode layer may contain an adhesive. Examples of adhesives include styrene-butadiene rubber (SBR), polyimide (PI), polyacrylic acid (PAA), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-isoprene-styrene block copolymer (SIS), and ethylene-propylene-diene copolymer (EPDM).

[0157] The proportion of binder in the positive electrode layer can be, for example, 0.5% by mass or more. If the proportion of binder is too small, there is a possibility that the increase in resistance caused by charging and discharging may not be sufficiently reduced. On the other hand, the proportion of binder in the positive electrode layer can be, for example, 15% by mass or less. If the proportion of binder is too large, there is a possibility that the proportion of positive electrode active material will be relatively small and the energy density will be low.

[0158] The thickness of the positive electrode layer can be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 30 μm or more and 100 μm or less.

[0159] The manufacturing method of the positive electrode layer is not particularly limited. For example, the following method can be used: mixing the above-mentioned composite positive electrode active material, the above-mentioned conductive material, and a solvent to obtain a positive electrode slurry; applying the above-mentioned positive electrode slurry to a positive electrode current collector and drying it to form a positive electrode layer. During the formation of the positive electrode layer, a pressing process can be performed to press the positive electrode layer in the thickness direction. Examples of pressing processes include roll pressing and flat pressing.

[0160] Examples of solvents include N-methylpyrrolidone (NMP), tetrahydronaphthalene, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene, and may contain two or more of these components.

[0161] Materials used for the positive current collector include, for example, stainless steel (SUS), Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive current collector can be foil-like, plate-like, etc. The top view shape of the positive current collector is not particularly limited; for example, it can be circular, elliptical, rectangular, or any polygonal shape. The positive current collector can also be composed of a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0162] [negative electrode]

[0163] The negative electrode has a negative electrode layer, and may further have a negative electrode current collector if needed.

[0164] The negative electrode layer is a layer containing at least a negative electrode active material. Additionally, the negative electrode layer may, as needed, contain at least one of an electrolyte, a conductive material, and a binder. The negative electrode layer can have a larger area than the positive electrode layer.

[0165] The negative electrode active material can be in particle or sheet form. The average particle size of the negative electrode active material can be, for example, 1 μm or more. Alternatively, the average particle size of the negative electrode active material can be, for example, 30 μm or less.

[0166] The negative electrode active material may include at least one selected from carbon-based active materials, Li-based active materials, Si-based active materials, Si-C composite materials, and lithium titanate.

[0167] Carbon-based active materials may include at least one selected from graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite may also be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) of natural graphite and artificial graphite may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1" or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0168] Examples of Li-based active materials include Li, lithium silicate, and Li alloys.

[0169] Examples of Si-based active materials include Si, SiO, and Si alloys.

[0170] Si-C composite materials refer to composite materials composed of carbon-based active materials (such as graphite) and Si-based active materials (such as Si). For example, Si microparticles can be dispersed within carbon particles. For example, Si microparticles can be dispersed within graphite particles. For example, lithium silicate particles can be coated with carbon materials (such as amorphous carbon).

[0171] Regarding the electrolyte, conductive material, and adhesive used in the negative electrode layer, the same electrolyte, conductive material, and adhesive described in the above description of the positive electrode layer can be cited.

[0172] Materials used as negative current collectors include, for example, stainless steel (SUS), aluminum, copper, nickel, iron, titanium, and carbon. Furthermore, the thickness of the negative current collector varies depending on its shape, ranging from 1 μm to 50 μm. The shape of the negative current collector can be foil-like, plate-like, etc. The top-view shape of the negative current collector is not particularly limited; examples include circular, elliptical, rectangular, and arbitrary polygonal shapes. The negative current collector can also be composed of a buffer layer, elastic layer, or PTC thermistor layer disposed on its surface.

[0173] [Electrolyte layer]

[0174] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least an electrolyte. The electrolyte can be a solid electrolyte or a liquid electrolyte (electrolyte).

[0175] The electrolyte layer can contain solid electrolytes and electrolyte solutions, etc.

[0176] Solid electrolytes can be the same as those described in the section on the positive electrode layer.

[0177] As an electrolyte, aqueous electrolytes and non-aqueous electrolytes can be used. They can be used alone or in combination of two or more.

[0178] The solvent of an aqueous electrolyte contains water as its main component. That is, based on the total amount of solvent (liquid component) constituting the electrolyte (100 mol%), water can account for more than 50 mol%, particularly more than 70 mol%, and even more than 90 mol%. On the other hand, there is no particular upper limit to the proportion of water in the solvent.

[0179] The solvent is a solvent containing water as its main component, but it may also contain solvents other than water. Examples of solvents other than water include one or more selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. Based on the total amount (100 mol%) of the solvent (liquid component) constituting the electrolyte, the solvent other than water may be 50 mol% or less, particularly 30 mol% or less, and further, 10 mol% or less.

[0180] The aqueous electrolyte used in this disclosure contains an electrolyte. The electrolyte used in the aqueous electrolyte can be a conventionally known electrolyte. Examples of electrolytes include lithium salts, nitrates, acetates, and sulfates of imide compounds. Specific examples of electrolytes include lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(nonafluorobutanesulfonyl)imide, lithium nonafluoro-N-[(trifluoromethane)sulfonyl]butanesulfonamide, lithium N,N-hexafluoro-1,3-disulfonylimide, CH3COOLi, LiPF6, LiBF4, Li2SO4, and LiNO3.

[0181] The concentration of the electrolyte in an aqueous electrolyte solution can be appropriately set according to the required battery characteristics, within a range that does not exceed the saturation concentration of the electrolyte relative to the solvent. This is because if solid electrolyte residues remain in the aqueous electrolyte solution, these solids may hinder the battery reaction.

[0182] For example, when LiTFSI is used as an electrolyte, the aqueous electrolyte may contain 1 mol or more of LiTFSI relative to 1 kg of the aforementioned water, particularly 5 mol or more, and further, 7.5 mol or more. There is no particular upper limit; for example, it may be 25 mol or less.

[0183] As a non-aqueous electrolyte, a non-aqueous electrolyte containing lithium salt and non-aqueous solvent is usually used.

[0184] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2 (Li-TFSI), LiN(SO2C2F5)2, and LiC(SO2CF3)3.

[0185] Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), γ-butyrolactone, sulfolane, acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), and mixtures thereof. From the viewpoint of ensuring high dielectric constant and low viscosity, it can be a mixture of cyclic carbonate compounds such as EC, PC, and BC with high dielectric constant and high viscosity and chain carbonate compounds such as DMC, DEC, and EMC with low dielectric constant and low viscosity, or a mixture of EC and DEC.

[0186] The concentration of lithium salt in non-aqueous electrolytes can be, for example, 0.3–5 M.

[0187] Non-aqueous electrolytes may contain ionic liquids. Ionic liquids may, for example, contain at least one selected from sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidineium salts, morpholinium salts, phosphonium salts, imidazolium salts, and their derivatives.

[0188] A membrane that can be impregnated with the electrolyte and prevents the positive electrode layer from contacting the negative electrode layer can be used in the electrolyte layer.

[0189] The material used for the membrane is not particularly limited as long as it is a porous membrane. Examples include resins such as polyethylene (PE), polypropylene (PP), polyester, polyvinyl alcohol, cellulose, and polyamide, with polyethylene and polypropylene being particularly suitable. Furthermore, the membrane can be a single-layer or multi-layer structure. Examples of multi-layer membranes include two-layer PE / PP membranes, or three-layer PP / PE / PP or PE / PP / PE membranes.

[0190] The diaphragm can be made of resin nonwoven fabric, glass fiber nonwoven fabric, or other nonwoven fabrics.

[0191] [Solid electrolyte layer]

[0192] The electrolyte layer can be a solid electrolyte layer composed of solids.

[0193] In the case where the electrolyte layer is a solid electrolyte layer, the solid electrolyte layer contains a solid electrolyte and, if necessary, an adhesive, etc.

[0194] Solid electrolytes can be the same as those described in the section on the positive electrode layer.

[0195] Solid electrolytes can be used alone or in combination of two or more. In addition, when using two or more solid electrolytes, two or more solid electrolytes can be mixed, or two or more solid electrolyte layers can be formed to create a multilayer structure.

[0196] The proportion of solid electrolyte in the solid electrolyte layer is not particularly limited; for example, it can be 50% or more by mass, or it can be in the range of 60% or more and less than 100% by mass, or it can be in the range of 70% or more and less than 100% by mass, or it can be 100% by mass. The solid electrolyte layer may contain less than 1% by mass of electrolyte relative to the total amount of solid electrolyte layer.

[0197] Examples of adhesives that can be incorporated into the aforementioned positive electrode layer can be cited as examples.

[0198] The content of the binder in the solid electrolyte layer can be 0% to 10% by mass relative to the total amount of the solid electrolyte layer.

[0199] The thickness of the electrolyte layer can be, for example, 0.1 μm or more and 1000 μm or less, or 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0200] The battery of this disclosure may further include a restraint clamp that applies restraint pressure to the positive electrode layer, electrolyte layer, and negative electrode layer in the thickness direction. Particularly when the electrolyte layer is a solid electrolyte layer, restraint pressure can be applied to form good ion conduction and electron conduction pathways. The restraint pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the restraint pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0201] [Battery]

[0202] The type of battery disclosed herein is not particularly limited, but lithium-ion batteries are typically used. Furthermore, the battery in this disclosure can be a liquid battery with an electrolyte layer containing an electrolyte solution, or a solid battery with an electrolyte layer containing a solid electrolyte. Solid batteries can be semi-solid batteries or all-solid batteries. In this disclosure, a semi-solid battery is a battery whose electrolyte layer contains both solid components such as inorganic solid electrolytes and liquid components (e.g., solvents and electrolyte solutions). In this disclosure, an all-solid battery is a battery whose electrolyte layer contains only solid components such as inorganic solid electrolytes as the electrolyte. Additionally, the battery in this disclosure can be a primary battery or a secondary battery, but is particularly suitable for secondary batteries. This is because it can be repeatedly charged and discharged, making it useful, for example, as a battery for automotive applications.

[0203] The shape of the battery is not particularly limited; for example, it can be coin-shaped, cylindrical, square, sheet-shaped, button-shaped, flat, or stacked.

[0204] In the case of a battery stack obtained by stacking multiple batteries, the battery stack can be either unipolar or bipolar.

[0205] Batteries are used in various applications, including as power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, they can be used as a power source for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, batteries can be used as a power source for mobile bodies other than vehicles (such as trains, ships, and airplanes), and also as a power source for electrical appliances such as information processing devices.

[0206] Furthermore, this disclosure is not limited to the above-described embodiments. The above embodiments are illustrative examples, and technical solutions having substantially the same structure as the technical concept described in the claims of this disclosure and achieving the same effect are included within the technical scope of this disclosure.

[0207] Example

[0208] (Example 1)

[0209] Synthesis of precursors (transition metal hydroxides) for positive electrode active materials

[0210] NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to prepare a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was set as Ni:Co:Mn = 85:7.5:7.5. The concentration of the raw material aqueous solution (the ratio of all raw materials to the raw material aqueous solution) was 0.2 mol%.

[0211] <Hydrothermal Synthesis (Crystallization)>

[0212] A certain amount of NH3 aqueous solution was added to the reaction vessel, and nitrogen gas was purged while stirring. NaOH aqueous solution was then added to maintain an alkaline pH (pH=12). The temperature was controlled, and the above-mentioned raw material aqueous solution and NH3 aqueous solution were added dropwise to precipitate the transition metal hydroxide. The reaction temperature was set at 60℃, and the reaction time was set at 10 hours.

[0213] <Pre-firing>

[0214] After the precipitation reaction was completed, the transition metal hydroxide was dehydrated and pre-calcined under the following temperature and pressure conditions.

[0215] Temperature: 120℃~220℃

[0216] Time: 4 to 10 hours

[0217] Pressure: 0.2MPa~1.0MPa

[0218] <Filtering>

[0219] After pre-firing, the transition metal hydroxides were dispersed by ion-exchange water and then washed. The washed transition metal hydroxides were then filtered and removed.

[0220] <Drying>

[0221] The transition metal hydroxide was dried at 110°C for 12 hours to evaporate the moisture.

[0222] Synthesis of positive electrode active materials

[0223]

[0224] The dried transition metal hydroxide and LiOH, which serves as a lithium source and is a lithium compound, are mixed in an agate mortar to obtain a mixture.

[0225] The mixture is prepared in such a manner that the molar ratio (Li / NCM ratio) of Li in the lithium compound relative to the total (NCM) of Ni, Co, and Mn in the transition metal hydroxide is 1.05.

[0226] <Firing of Section 1>

[0227] The resulting mixture was calcined in a furnace at 900°C under an oxygen atmosphere for 10 hours, thereby synthesizing the positive electrode active material (Li). 1.05 Ni 0.85 Co 0.075 Mn 0.075 O2).

[0228] [Preparation of composite positive electrode active material]

[0229] <Firing in Section 2>

[0230] The obtained positive electrode active material and H2WO4, which was previously classified using a 40μm sieve and used as a W source, were mixed in an agate mortar. The resulting mixture was then calcined in a calcining furnace at 600°C in an oxygen atmosphere for 10 hours to obtain the second calcined material.

[0231] The W source is mixed with the positive electrode active material in such a way that the molar ratio of W to 1 mol of the total amount of Ni, Co and Mn (NCM) contained in the positive electrode active material (W / NCM ratio) is 0.01.

[0232] <Firing in Section 3>

[0233] The obtained second calcined product was mixed with La(OH)3, which was obtained in advance by sieving with a 40 μm sieve as the La source, in an agate mortar. The resulting mixture was calcined in a calcining furnace at 1000 °C in an oxygen atmosphere for 10 hours to obtain the third calcined product.

[0234] The La source is mixed with the positive electrode active material in such a way that the molar ratio of La to the total amount of Ni, Co and Mn (NCM) contained in the positive electrode active material is 0.01 (La / NCM ratio).

[0235] <Washing and Filtration>

[0236] The calcined material from section 3 above was pulverized to a particle size of less than 0.2 mm using an agate mortar and pestle to obtain a pulverized material. Then, the pulverized material was dispersed in 500 mL of pure water and stirred vigorously for 1 minute to obtain a slurry.

[0237] Then, the slurry was filtered using a Buchner funnel and filter paper. The resulting filter material was rinsed with 500 mL of pure water, and the resulting filter cake was vacuum dried at 90 °C to obtain the dried material.

[0238] <Broken>

[0239] The dried material was crushed to the specified particle size using an agate mortar and pestle to obtain particles of the composite positive electrode active material.

[0240] (Example 2)

[0241] In the above-mentioned <third stage firing>, the La source was mixed with the positive electrode active material in such a way that the molar ratio (La / NCM ratio) of La relative to the total amount of Ni, Co and Mn contained in the positive electrode active material (NCM) was 1 mol was 0.005. The resulting mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the third stage fired product. Otherwise, the same procedure as in Example 1 was performed to produce a composite positive electrode active material.

[0242] (Example 3)

[0243] In the above-mentioned <third stage firing>, the obtained mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the third stage fired product. Otherwise, the same procedure as in Example 1 was carried out to produce a composite positive electrode active material.

[0244] (Example 4)

[0245] In the above-mentioned <third stage firing>, the La source was mixed with the positive electrode active material in such a way that the molar ratio (La / NCM ratio) of La relative to the total amount of Ni, Co and Mn contained in the positive electrode active material (NCM) was 1.0. The resulting mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the third stage fired product. Otherwise, the same procedure as in Example 1 was performed to produce a composite positive electrode active material.

[0246] (Example 5)

[0247] In the above-mentioned <third stage firing>, the La source was mixed with the positive electrode active material in such a way that the molar ratio (La / NCM ratio) of La relative to the total amount of Ni, Co and Mn contained in the positive electrode active material (NCM) was 2.0. The resulting mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the third stage fired product. Otherwise, the same procedure as in Example 1 was performed to produce a composite positive electrode active material.

[0248] (Example 6)

[0249] In the above-mentioned <second firing stage>, the W source is mixed with the positive electrode active material in such a way that the molar ratio of W to the total (NCM) of Ni, Co, and Mn contained in the positive electrode active material is 0.5 (W / NCM ratio).

[0250] In the above-mentioned <third stage firing>, the La source was mixed with the positive electrode active material in such a way that the molar ratio (La / NCM ratio) of La relative to the total amount of Ni, Co and Mn contained in the positive electrode active material (NCM) was 1.0. The resulting mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the third stage fired product. Otherwise, the same procedure as in Example 1 was performed to produce a composite positive electrode active material.

[0251] (Example 7)

[0252] In the above-mentioned <second firing stage>, the W source is mixed with the positive electrode active material in such a way that the molar ratio (W / NCM ratio) of W to 1 mol of the total amount of Ni, Co and Mn (NCM) contained in the positive electrode active material is 1.0.

[0253] In the above-mentioned <third stage firing>, the La source was mixed with the positive electrode active material in such a way that the molar ratio (La / NCM ratio) of La relative to the total amount of Ni, Co and Mn contained in the positive electrode active material (NCM) was 1.0. The resulting mixture was fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the third stage fired product. Otherwise, the same procedure as in Example 1 was performed to produce a composite positive electrode active material.

[0254] (Comparative Example 1)

[0255] In the above-mentioned [Preparation of composite positive electrode active material], the <second stage firing> and <third stage firing> are not performed. In the <first stage firing> of [synthesis of positive electrode active material], the W source is mixed with the mixture of transition metal hydroxide and lithium compound in such a way that the molar ratio of W to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 1 mol (W / NCM ratio) is 0.01. The mixture is then fired in a firing furnace at 1000°C in an oxygen atmosphere for 10 hours to obtain the fired product. Otherwise, the same procedure as in Example 1 is followed to prepare the composite positive electrode active material.

[0256] (Comparative Example 2)

[0257] In the above-mentioned [Preparation of composite positive electrode active material], the <second stage firing> and <third stage firing> are not performed. In the <first stage firing> of [synthesis of positive electrode active material], the W source is mixed with a mixture of transition metal hydroxide and lithium compound in such a way that the molar ratio of W to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 0.01 (W / NCM ratio) of 1 mol. In addition, the La source is mixed in such a way that the molar ratio of La to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 0.01 (La / NCM ratio) of 1 mol. The mixture is then fired in a firing furnace at 1000°C in an oxygen atmosphere for 10 hours to obtain the calcined product. Otherwise, the same procedure as in Example 1 is followed to prepare the composite positive electrode active material.

[0258] (Comparative Example 3)

[0259] In the above-mentioned [Preparation of composite positive electrode active material], the <second stage firing> and <third stage firing> are not performed. In the <first stage firing> of [synthesis of positive electrode active material], the W source is mixed with a mixture of transition metal hydroxide and lithium compound in such a way that the molar ratio of W to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 0.01 (W / NCM ratio) and the La source is mixed in such a way that the molar ratio of La to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 0.005 (La / NCM ratio) and the mixture is fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the calcined product. Otherwise, the same procedure as in Example 1 is followed to prepare the composite positive electrode active material.

[0260] (Comparative Example 4)

[0261] In the above-mentioned [Preparation of composite positive electrode active material], the <second stage firing> and <third stage firing> are not performed. In the <first stage firing> of [synthesis of positive electrode active material], the W source is mixed with a mixture of transition metal hydroxide and lithium compound in such a way that the molar ratio of W to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 1 mol (W / NCM ratio) is 0.01. In addition, the La source is mixed in such a way that the molar ratio of La to the total (NCM) of Ni, Co and Mn contained in the transition metal hydroxide is 1 mol (La / NCM ratio) is 0.01. The mixture is then fired in a firing furnace at 850°C in an oxygen atmosphere for 10 hours to obtain the fired product. Otherwise, the same procedure as in Example 1 is followed to prepare the composite positive electrode active material.

[0262] [SEM-EDX Analysis]

[0263] The composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4 were subjected to cross-sectional observation and elemental analysis using SEM-EDX, and the following results were obtained. The results are shown in Table 2.

[0264] It was confirmed that the positive electrode active materials contained in the composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4 contain Ni, Co and Mn.

[0265] In addition, in Examples 1-7 and Comparative Examples 2-4, compound A containing La, Ni and O was identified based on the mapping images.

[0266] In addition, in Examples 1-7 and Comparative Examples 3-4, particulate compounds were identified, and the particulate compounds were identified as compound A containing La, Ni and O based on the mapping images.

[0267] It was confirmed that compound A, contained in the composite positive electrode active materials of Examples 1-7 and Comparative Examples 3-4, exists independently as an isolated particle. It is speculated that by having compound A exist independently as an isolated particle, the effect of improved electron conductivity brought about by compound A becomes easier to obtain.

[0268] It was confirmed that compound A contained in the composite positive electrode active material of Comparative Example 2 exists as a film on the surface of the primary particles of the positive electrode active material. It is speculated that by calcining at a high temperature of 1000°C, compound B is isolated into particles, and through this isolation, compound A forms a film on the surface of the primary particles of the positive electrode active material. It is speculated that if compound A forms a film on the surface of the primary particles of the positive electrode active material, it is difficult to ensure the contact between compound B and the primary particles of the positive electrode active material, thus reducing the Li conductivity effect brought by compound B.

[0269] Cross-sectional image analysis using SEM-EDX confirmed that the average particle size of isolated particles of compound A in Examples 1-7 was 0.1 μm. Cross-sectional image analysis using SEM-EDX confirmed that the average particle size of isolated particles of compound A in Comparative Examples 3-4 was 5 μm. Furthermore, cross-sectional image analysis using SEM-EDX confirmed that the particle size of primary particles of the positive electrode active material contained in the composite positive electrode active material of Examples 1-7 and Comparative Examples 1-4 was 0.5 μm.

[0270] [TEM-EDX Analysis]

[0271] The composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4 were subjected to cross-sectional image analysis and elemental analysis using TEM-EDX, and the following results were obtained. The results are shown in Table 2.

[0272] In the composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4, compound B containing Li, W and O was identified based on the mapping images.

[0273] Compound B, contained in the composite positive electrode active materials of Examples 1-7, was confirmed to exist in a film-like form because TEM-EDX revealed a W concentration region on the surface of the primary particles of the positive electrode active material. It is speculated that sintering the W source at 600°C failed to promote the sintering of compound B, resulting in compound B forming a film-like form on the surface of the primary particles of the positive electrode active material. It is further speculated that if compound B forms a film-like form on the surface of the primary particles, it can ensure the contact point between the compound B and the primary particles of the positive electrode active material, thereby improving the Li conductivity.

[0274] Compound B, contained in the composite positive electrode active materials of Comparative Examples 1-4, was confirmed to exist independently as isolated particles based on mapping images. It is speculated that by performing a single-stage sintering process at a high temperature above 850°C, compound B was accelerated to form isolated particles. It is further speculated that if compound B is isolated, it is difficult to ensure contact with the primary particles of the positive electrode active material, thus reducing the Li conductivity effect brought by compound B.

[0275] By analyzing cross-sectional images using TEM-EDX, it was confirmed that compound B contained in the composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4 was Li6WO6.

[0276] [XRD Measurement]

[0277] XRD patterns of the composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4 were obtained using Rigaku Smart-Lab. The samples were loaded onto glass sample plates for measurement. The measurement conditions are as follows.

[0278] • 2θ measurement range: 10°~120°

[0279] • X-rays: Cu-Kα (λ = 1.5418 angstroms)

[0280] • Scanning speed: 2.0° / minute

[0281] • Temperature: Room temperature

[0282] The results of XRD analysis confirmed that the positive electrode active materials contained in the composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4 all have layered rock salt type crystalline phases belonging to space group R-3m.

[0283] The diffraction data obtained from XRD measurements were used to identify the compounds using Rigaku Smart-Lab Studio II. Peaks originating from the LaNiO-based crystalline phase (La4LiNiO8) were identified in the composite positive electrode active materials of Examples 1-7 and Comparative Examples 2-4.

[0284] In the composite positive electrode active materials of Comparative Examples 1-4, peaks originating from the LiWO-based crystalline phase (Li6WO6) were identified. On the other hand, in the composite positive electrode active materials of Examples 1-7, no peaks originating from the LiWO-based crystalline phase were identified. Therefore, it is presumed that compound B present on the surface of the composite positive electrode active materials of Examples 1-7 is amorphous.

[0285] [Battery (Miniature Laminated Battery) Construction]

[0286] Small laminated batteries of Examples 1-7 and Comparative Examples 1-4 were fabricated using the composite positive electrode active materials of Examples 1-7 and Comparative Examples 1-4.

[0287] Specifically, firstly, using a film applicator (manufactured by Allgood Co., Ltd.) with film thickness adjustment function, a positive electrode paste containing a composite positive electrode active material and acetylene black as a conductive material is applied to the surface of a metal foil serving as the positive electrode current collector. Then, the paste is dried at 80°C for 5 minutes using a dryer to create a positive electrode with a positive electrode layer on the positive electrode current collector.

[0288] On the other hand, using a film applicator (manufactured by Allgood Co., Ltd.) with film thickness adjustment function, a negative electrode paste containing natural graphite as the negative electrode active material was applied to the surface of a metal foil serving as the negative electrode current collector. Then, the negative electrode with a negative electrode layer on the negative electrode current collector was produced by drying at 80°C for 5 minutes using a dryer.

[0289] As an electrolyte, a 1M LiPF6 solution was prepared, containing LiPF6 as the electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents in a ratio of EC / DMC / EMC = 3 / 4 / 3 vol%.

[0290] The above-mentioned positive electrode, separator and negative electrode were stacked, and the separator was impregnated with the above-mentioned electrolyte to produce small laminated batteries of Examples 1 to 7 and Comparative Examples 1 to 4.

[0291] [Battery Review]

[0292] For each small laminated cell fabricated, the IV resistance was measured before and after a 100-cycle cycle test. The cycle test was conducted under the following conditions for 100 cycles.

[0293] <Loop Condition>

[0294] • Voltage range: 3.0V to 4.3V

[0295] • C-ratio: 0.3C

[0296] • Mode: CC charge / discharge

[0297] • Temperature: 50℃

[0298] [IV Resistance Measurement]

[0299] The voltage is adjusted within a range of 3.0V to 4.3V, and the voltage is adjusted to become SOC 50% when the upper limit voltage of 4.3V is set to SOC 100%.

[0300] The voltage drop (V) during 10 seconds of discharge at various C rates of 0.1C, 0.3C, 0.5C, 0.7C, and 1.0C was measured at 0°C.

[0301] Plot the voltage drop (V) against the current value, and use the slope of the line drawn as a linear function as the IV resistance.

[0302] [Calculation of the increase rate of IV resistance after 100 cycles]

[0303] The above measurements were performed before and after a 100-cycle test, and the ratio of the IV resistance after the cyclic test to the IV resistance before the cyclic test was calculated and treated as the resistance increase rate.

[0304] The increase in IV resistance after 100 cycles (%) = (IV resistance after cycle test) / (IV resistance before cycle test) × 100

[0305] In this disclosure, the increase rate of resistance IV, standardized based on Comparative Example 1, was calculated. The results are shown in Table 2.

[0306]

[0307]

[0308] The following comparative analysis was conducted based on the results shown in Tables 1 and 2.

[0309] (Comparison between Comparative Example 1 and Comparative Example 2)

[0310] As shown in Table 2, the battery using the composite positive electrode active material of Comparative Example 2 exhibits a smaller rate of resistance increase after 100 cycles compared to the battery using the composite positive electrode active material of Comparative Example 1. Therefore, it can be concluded that by including a predetermined amount of compound A in the composite positive electrode active material, the rate of resistance increase during battery charging and discharging can be reduced.

[0311] (Comparison between Example 1 and Comparative Example 2)

[0312] It can be seen that the battery using the composite positive electrode active material of Example 1 has a smaller resistance increase rate after 100 cycles compared to the battery using the composite positive electrode active material of Comparative Example 2. Therefore, it can be seen that when the La / NCM ratio in the composite positive electrode active material is 0.01, compound A exists as an isolated particle, thereby reducing the resistance increase rate that occurs during battery charging and discharging.

[0313] (Comparison between Example 2 and Comparative Example 3)

[0314] It can be seen that the battery using the composite positive electrode active material of Example 2 has a smaller resistance increase rate after 100 cycles compared to the battery using the composite positive electrode active material of Comparative Example 3. Therefore, it can be seen that when the La / NCM ratio in the composite positive electrode active material is 0.005, compound B exists in a film-like form on the surface of the primary particles of the positive electrode active material, thereby reducing the resistance increase rate that occurs during battery charging and discharging.

[0315] (Comparison between Example 3 and Comparative Example 4)

[0316] It can be seen that the battery using the composite positive electrode active material of Example 3 has a smaller resistance increase rate after 100 cycles compared to the battery using the composite positive electrode active material of Comparative Example 4. Therefore, it can be seen that when the firing temperature is set to 850°C to obtain compound A and the La / NCM ratio in the composite positive electrode active material is 0.01, the resistance increase rate that occurs during battery charging and discharging can be reduced.

[0317] (Comparison between Example 4 and Example 3)

[0318] The battery using the composite positive electrode active material of Example 4, with a La / NCM ratio of 1.000, exhibited a smaller rate of resistance increase after 100 cycles compared to the battery using the composite positive electrode active material of Example 3, with a La / NCM ratio of 0.01. Therefore, it can be concluded that when compound A is obtained by setting the firing temperature to 850°C, a La / NCM ratio of 1.000 in the composite positive electrode active material reduces the rate of resistance increase during battery charging and discharging compared to a La / NCM ratio of 0.01.

[0319] (Comparison between Example 5 and Example 2)

[0320] It can be seen that the battery using the composite positive electrode active material of Example 5, with a La / NCM ratio of 2.000, exhibits a greater rate of resistance increase after 100 cycles compared to the battery using the composite positive electrode active material of Example 2, with a La / NCM ratio of 0.005. Therefore, it can be concluded that when compound A is obtained by setting the firing temperature to 850°C, a La / NCM ratio of 0.005 in the composite positive electrode active material reduces the rate of resistance increase during battery charging and discharging compared to a La / NCM ratio of 2.000. It is speculated that the higher La content in the composite positive electrode active material of Example 5 compared to Example 2 hinders lithium conduction.

[0321] (Comparison of Examples 6, 7 and 4)

[0322] It can be seen that the battery using the composite positive electrode active material of Example 6, which has a W / NCM ratio of 0.500, has a greater resistance increase rate after 100 cycles compared to the battery using the composite positive electrode active material of Example 4, which has a W / NCM ratio of 0.010, and the battery using the composite positive electrode active material of Example 7, which has a W / NCM ratio of 1.000. Therefore, it can be seen that when compound A is obtained by setting the firing temperature to 850°C and the La / NCM ratio in the composite positive electrode active material is 1.000, the W / NCM ratio in the composite positive electrode active material is 0.010, which reduces the rate of resistance increase during battery charging and discharging compared to the W / NCM ratio of 1.000. Similarly, the W / NCM ratio in the composite positive electrode active material is 0.500, which also reduces the rate of resistance increase during battery charging and discharging compared to the W / NCM ratio of 0.010. It is speculated that because Example 7 contains a higher amount of W compared to Examples 4 and 6, it hinders electron conduction.

Claims

1. A composite positive electrode active material, The composite positive electrode active material comprises a positive electrode active material, compound A, and compound B. Compound A comprises La, Ni, and O, and compound B comprises Li, W, and O. The positive electrode active material is a crystalline primary particle containing Li, transition metals, and O. The positive electrode active material is a single-crystal active material composed of the primary particles. Compound B exists in a film-like form on at least a portion of the surface of the primary particles. Compound A exists independently as an isolated particle.

2. The composite positive electrode active material according to claim 1, The composite positive electrode active material contains La, which is more than 0.005 mol and less than 2.000 mol per mol of Ni, Co and Mn contained in the positive electrode active material.

3. The composite positive electrode active material according to claim 1, The composite positive electrode active material contains W in an amount of more than 0.010 mol and less than 1.000 mol per mol of the total amount of Ni, Co and Mn contained in the positive electrode active material.

4. The composite positive electrode active material according to claim 1, The primary particles of the positive electrode active material have a particle size of 0.5 μm or more.

5. The composite positive electrode active material according to claim 1, The average particle size of the isolated particles of compound A is greater than 0.1 μm and less than 20 μm.

6. The composite positive electrode active material according to claim 1, Compound A is La4LiNiO8.

7. The composite positive electrode active material according to claim 1, The compound B is at least one of Li2WO4 and Li6WO6.

8. A positive electrode layer comprising the composite positive electrode active material as described in claim 1.

9. A battery comprising a positive electrode layer including the composite positive electrode active material as described in claim 1.

10. A method for manufacturing a composite positive electrode active material, comprising the method for manufacturing the composite positive electrode active material according to claim 1, wherein: The first firing process involves firing a first mixture of a transition metal hydroxide and a lithium compound at 800°C to 1000°C to obtain the positive electrode active material, wherein the transition metal hydroxide is a precursor of the positive electrode active material. The second firing process involves firing the positive electrode active material and the second mixture of W source at 500°C to 700°C to obtain a fired body. The W source is a raw material for compound B. The fired body comprises the positive electrode active material and compound B, and at least a portion of compound B exists in a film-like form on the surface of the primary particles of the positive electrode active material. The third firing process involves firing the fired body and the third mixture of the La source at 800°C to 1100°C to obtain the composite positive electrode active material, wherein the La source is the raw material of compound A.

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